Manteca City Council
April 15, 2025

GROUNDWATER

SUSTAINABILITY PLAN

AMENDED
November 2024
Eastern San Joaquin
Groundwater Subbasin
ATTACHMENT 2
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ATTACHMENT 2
Eastern San Joaquin Groundwater
Subbasin
Groundwater
Sustainability Plan
Prepared by:

November 2024
ATTACHMENT 2
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ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan i
Table of Contents November 2024
EXECUTIVE SUMMARY ......................................................................................................................................... ES-1

1. AGENCY INFORMATION, PLAN AREA, AND COMMUNICATION............................................................... 1-1

1.1 Introduction and Agency Information..................................................................................................... 1-1

1.1.1 Purpose of the Groundwater Sustainability Plan ................................................................. 1-1

1.1.2 Sustainability Goal............................................................................................................... 1-2

1.1.3 Contact Information ............................................................................................................. 1-2

1.1.4 Agency Information.............................................................................................................. 1-3

1.1.5 GSP Organization..............................................................................................................1-10

1.2 Plan Area............................................................................................................................................. 1-10

1.2.1 Description of Plan Area.................................................................................................... 1-11

1.2.2 Water Resources Monitoring and Management Programs................................................ 1-23

1.2.3 Land Use Elements or Topic Categories of Applicable General Plans .............................. 1-35

1.2.4 Additional GSP Elements .................................................................................................. 1-35

1.3 Notice and Communication.................................................................................................................. 1-44

1.3.1 Beneficial Uses and Users in the Basin............................................................................. 1-44

1.3.2 List of Public Meetings Where the 2024 GSP was Discussed........................................... 1-45

1.3.3 Decision-Making Process .................................................................................................. 1-46

1.3.4 Opportunities for Public Engagement and How Public Input was Used............................. 1-46

1.3.5 Inter-basin Coordination .................................................................................................... 1-57

1.3.6 Notice of Intent to Adopt the GSP...................................................................................... 1-57

2. BASIN SETTING ........................................................................................................................................... 2-10

2.1 Hydrogeologic Conceptual Model ........................................................................................................ 2-10

2.1.1 Data Compilation ............................................................................................................... 2-10

2.1.2 Regional Geologic and Structural Setting .......................................................................... 2-19

2.1.3 Geologic History ................................................................................................................ 2-20

2.1.4 Near-Surface Conditions ................................................................................................... 2-20

2.1.5 Geologic Formations and Stratigraphy .............................................................................. 2-36

2.1.6 Faults and Structural Features........................................................................................... 2-44

2.1.7 Geologic Cross-Sections ................................................................................................... 2-47

2.1.8 Basin Boundaries ............................................................................................................... 2-58

2.1.9 Principal Aquifer ................................................................................................................. 2-59

2.1.10 HCM Data Gaps ................................................................................................................ 2-80

2.2 Historical Groundwater Conditions ...................................................................................................... 2-81

2.2.1 Groundwater Elevation ...................................................................................................... 2-81

2.2.2 Groundwater Storage ...................................................................................................... 2-100

2.2.3 Seawater Intrusion ........................................................................................................... 2-102

2.2.4 Conditions as of 2019: Groundwater Quality ................................................................... 2-102

2.2.5 Conditions in 2019: Land Subsidence ............................................................................. 2-123

2.2.6 Conditions in 2019: Interconnected Surface Water Systems ........................................... 2-124

2.2.7 Conditions in 2019: Groundwater-Dependent Ecosystems ............................................. 2-127

2.3 Current Groundwater Conditions ....................................................................................................... 2-135

2.3.1 Groundwater Elevation .................................................................................................... 2-135

2.3.2 Groundwater Storage ...................................................................................................... 2-140

2.3.3 Seawater Intrusion ........................................................................................................... 2-141

2.3.4 Groundwater Quality ........................................................................................................ 2-145

2.3.5 Land Subsidence ............................................................................................................. 2-148

2.3.6 Interconnected Surface Water Systems .......................................................................... 2-156 ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan ii
Table of Contents November 2024

2.3.7 Groundwater-Dependent Ecosystems ............................................................................. 2-162

2.4 Water Budgets ................................................................................................................................... 2-164

2.4.1 Water Budget Background Information ............................................................................ 2-164

2.4.2 Identification of Hydrologic Periods.................................................................................. 2-166

2.4.3 Use of the ESJWRM and Associated Data in Water Budget Development ..................... 2-167

2.4.4 Water Budget Definitions and Assumptions ..................................................................... 2-168

2.4.5 Water Budget Estimates .................................................................................................. 2-174

2.4.6 Projected Water Budget with Demand Reduction Estimates (ESJWRM PCBL-DR Version

3.0) .................................................................................................................................. 2-197

2.4.7 Projected Water Budget with Climate Change and Demand Reduction Estimates (ESJWRM PCBL-CC-DR Version 3.0) .............................................................................................. 2-203

2.4.8 Projected Water Budget with PMAs Estimates (ESJWRM PCBL-PMA Version 3.0) ....... 2-208

2.4.9 Projected Water Budget with Climate Change and PMAs Estimates (ESJWRM PCBL-CCPMA Version 3.0) ............................................................................................................. 2-215

3. SUSTAINABLE MANAGEMENT CRITERIA................................................................................................... 3-1

3.1 Sustainability Goal................................................................................................................................. 3-1

3.2 Updates to Sustainability INdicators...................................................................................................... 3-3

3.3 Revised Sustainability Indicators........................................................................................................... 3-3

3.3.1 Chronic Lowering of Groundwater Levels............................................................................ 3-3

3.3.2 Reduction in Groundwater Storage.................................................................................... 3-13

3.3.3 Degraded Water Quality .................................................................................................... 3-15

3.3.4 Seawater Intrusion............................................................................................................. 3-23

3.3.5 Land Subsidence............................................................................................................... 3-23

3.3.6 Depletions of Interconnected Surface Water ..................................................................... 3-28

4. MONITORING NETWORKS ................................................................................................................. 4-1

4.1 Monitoring Network for Chronic Lowering of Groundwater Levels ......................................................... 4-1

4.1.1 Representative Monitoring Network for Groundwater Levels............................................... 4-1

4.1.2 Monitoring Protocols for Groundwater Level Data Collection and Monitoring ...................... 4-5

4.1.3 Frequency and Timing of Groundwater Level Monitoring .................................................... 4-6

4.1.4 Spatial Density of Groundwater Level Monitoring Network .................................................. 4-6

4.2 Monitoring Network for Reduction in Groundwater Storage .................................................................. 4-7

4.3 Monitoring Networks for Degraded Water Quality ................................................................................. 4-7

4.3.1 Representative Monitoring Network for Groundwater Quality .............................................. 4-8

4.3.2 Monitoring Protocols for Groundwater Quality Data Collection and Monitoring ................. 4-10

4.3.3 Frequency and Timing of Groundwater Quality Monitoring................................................ 4-11

4.3.4 Spatial Density of Groundwater Quality Monitoring Wells .................................................. 4-11

4.4 Monitoring Network for Seawater Intrusion .......................................................................................... 4-11

4.5 Monitoring Network for Land Subsidence ............................................................................................ 4-12

4.5.1 Representative Monitoring Network for Subsidence .......................................................... 4-12

4.5.2 Monitoring Protocols for Subsidence Data Collection and Monitoring ............................... 4-14

4.5.3 Frequency and Timing of Subsidence Monitoring .............................................................. 4-14

4.5.4 Spatial Density of Subsidence Monitoring Stations ........................................................... 4-14

4.6 Monitoring Network for Depletions of Interconnected Surface Waters ................................................ 4-15

4.6.1 Representative Monitoring Network for Interconnected Surface Water ............................. 4-15

4.6.2 Monitoring Protocols for Interconnected Surface Water Data Collection and Monitoring .. 4-18

4.6.3 Frequency and Timing of Interconnected Surface Water Monitoring ................................. 4-18

4.6.4 Spatial Density of Interconnected Surface Water Monitoring Network .............................. 4-18

4.7 Data Gaps ........................................................................................................................................... 4-18

4.7.1 Groundwater Level Data Gaps .......................................................................................... 4-18

4.7.2 Groundwater Quality Data Gaps ........................................................................................ 4-18 ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan iii
Table of Contents November 2024

4.7.3 Interconnected Surface Water System Data Gaps ............................................................ 4-19

4.7.4 Groundwater-Dependent Ecosystem Data Gaps ............................................................... 4-19

4.7.5 Plan to Fill Data Gaps ........................................................................................................ 4-19

5. DATA MANAGEMENT SYSTEM .................................................................................................................... 5-1

5.1 Overview of the Eastern San Joaquin Subbasin Data Management System........................................ 5-1

5.2 Functionality of the Data Management System..................................................................................... 5-1

5.2.1 User and Data Access Permissions..................................................................................... 5-2

5.2.2 Data Entry and Validation.................................................................................................... 5-3

5.2.3 Visualization and Analysis ................................................................................................... 5-5

5.2.4 Query and Reporting ........................................................................................................... 5-7

5.3 Data Included in the Data Management System................................................................................... 5-7

6. PROJECTS AND MANAGEMENT ACTIONS................................................................................................. 6-1

6.1 Projects, Management Actions, and Adaptive Management Strategies ................................................ 6-1

6.2 Projects.................................................................................................................................................. 6-1

6.2.1 Project Identification ............................................................................................................ 6-1

6.2.2 Project Implementation........................................................................................................ 6-2

6.2.3 List of Projects ..................................................................................................................... 6-2

6.2.4 Category A Projects........................................................................................................... 6-13

6.2.5 Category B Projects........................................................................................................... 6-28

6.2.6 Mokelumne River Loss Study ............................................................................................ 6-54

6.2.7 Notification Process ........................................................................................................... 6-54

6.3 Management Actions........................................................................................................................... 6-54

6.4 Adaptive Management Strategies........................................................................................................ 6-56

6.5 Simulation of Projects and Management Actions in Projected Water Budget ..................................... 6-58

6.6 Potential Available Funding Mechanisms ............................................................................................ 6-58

6.7 References .......................................................................................................................................... 6-60

7. PLAN IMPLEMENTATION.............................................................................................................................. 7-1

7.1 Implementation Schedule ...................................................................................................................... 7-1

7.2 Implementation Costs............................................................................................................................ 7-6

7.3 Monitoring and Reporting ...................................................................................................................... 7-8

7.3.1 Monitoring............................................................................................................................ 7-9

7.3.2 Developing Annual Reports ................................................................................................. 7-9

7.3.3 Data Management System Updates.................................................................................. 7-10

7.4 Data Collection and Analysis............................................................................................................... 7-10

7.4.1 Model Refinements............................................................................................................ 7-10

7.4.2 Construction of Additional Wells ........................................................................................7-11

7.4.3 Data Gaps and Uncertainties............................................................................................. 7-11

7.5 Administrative Actions ......................................................................................................................... 7-11

7.6 Developing 5-Year Periodic Evaluation Reports.................................................................................. 7-11

7.6.1 New Information................................................................................................................. 7-11

7.6.2 Sustainability Evaluation.................................................................................................... 7-12

7.6.3 Status of Projects and Management Actions ..................................................................... 7-12

7.6.4 Basin Setting Based on New Information or Changes in Water Use ................................. 7-12

7.6.5 Monitoring Network Description......................................................................................... 7-12

7.6.6 Legal or Enforcement Actions............................................................................................ 7-12

7.6.7 Coordination ...................................................................................................................... 7-12 ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan iv
Table of Contents November 2024

7.6.8 Other Information............................................................................................................... 7-12

7.7 Outreach.............................................................................................................................................. 7-13

7.8 Implementing GSP-Related Projects and Management Actions ......................................................... 7-13

7.9 GSP Implementation Funding.............................................................................................................. 7-18

8. REFERENCES ................................................................................................................................................. 8-1 ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan v
Table of Contents November 2024
Appendices
Appendix 1-A Eastern San Joaquin Groundwater Authority JPA Agreement and Bylaws Appendix 1-B Legal Authority of Eastern San Joaquin GSAs Appendix 1-C Agency Resolutions to Become GSAs
Appendix 1-D DWR Preparation Checklist
Appendix 1-E Community Water Systems
Appendix 1-F Relevant General Plan Goals and Policies
Appendix 1-G Freshwater Species in the Eastern San Joaquin Subbasin Appendix 1-H 2024 Eastern San Joaquin Subbasin Communication and Engagement Plan Update Appendix 1-I Public Comments Received
Appendix 1-J Response to Public Comments
Appendix 1-K Notice of Intent to Adopt the 2024 GSP Amendment Appendix 2-A Eastern San Joaquin Water Resources Model (ESJWRM) Report Appendix 2-B Eastern San Joaquin Water Resources Model (ESJWRM) Report Version 2.0 Update (2022) Appendix 2-C Eastern San Joaquin Water Resources Model (ESJWRM) Report Version 3.0 Update (2024) Appendix 3-A Consultation Initiation Letter from the California Department of Water Resources to the Eastern San Joaquin Plan Administrator entitled “Eastern San Joaquin Subbasin – 2020 Groundwater Sustainability Plan”, dated November 18, 2021
Appendix 3-B Determination Letter from DWR to ESJ Entitled “Approved Determination of the Revised Groundwater Sustainability Plan Submitted for the San Joaquin Valley – Eastern San Joaquin Subbasin” Dated July 6, 2023
Appendix 3-C Technical Memorandum No. 1 – Groundwater Levels Appendix 3-D Technical Memorandum No. 2 – Subsidence
Appendix 3-E Technical Memorandum No. 4 – Water Budgets and Groundwater Storage Appendix 3-F Technical Memorandum No. 3 – Groundwater Quality Appendix 3-G Technical Memorandum No. 5 – Interconnected Surface Water Appendix 3-H Supplemental Data for Groundwater Level Minimum Thresholds Appendix 3-I Hydrographs Showing Groundwater Level Minimum Thresholds and Measurable Objectives Appendix 3-J Domestic Well Mitigation Program
Appendix 5-A List of DMS Data Types
Appendix 6-A Additional Projects Added to GSP
Appendix 6-B Technical Memorandum No. 6 – Demand Management Program ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan vi
Table of Contents November 2024
Tables
Table 1 1: Minimum Depth of Seal Below Ground Surface for Wells in San Joaquin County ................................... 1-39 Table 1 2: Minimum Depth of Seal Below Ground Surface for Wells in Calaveras County ....................................... 1-40 Table 1 3: Minimum Depth of Seal Below Ground Surface for Wells in Stanislaus County ...................................... 1-42 Table 1 4: Groundwater Sustainability Workgroup Interests (Collected During Development of 2020 GSP) ............ 1-47 Table 1 5: Stakeholder Database Summary ............................................................................................................. 1-55 Table 2 1: Eastern San Joaquin Subbasin Watershed Details .................................................................................. 2-25 Table 2 2: Generalized Stratigraphic Column, Formation Descriptions, and Water-Bearing Properties ................... 2-40 Table 2 3: Production Zone Capacities ..................................................................................................................... 2-68 Table 2 4: Wells within Water-Bearing Zones ........................................................................................................... 2-69 Table 2 5: Summary of Chloride Data by Decade ................................................................................................... 2-106 Table 2 6: Summary of Chloride Data by Depth (1940s-2010s) ............................................................................. 2-106 Table 2 7: Summary of TDS Data by Depth (2015-2018) ....................................................................................... 2-111 Table 2 8: Nitrate as N Concentrations by Decade ................................................................................................. 2-113 Table 2 9: Arsenic Concentrations by Decade ........................................................................................................ 2-118 Table 2 10: MCLs for Common Petroleum Hydrocarbons and MTBE .................................................................... 2-122 Table 2 11: MCLs for Common Synthetic Organic Constituents ............................................................................. 2-123 Table 2 12: Chloride Concentrations after 2015...................................................................................................... 2-144 Table 2 13: Summary of Water Budget Assumptions (Historical, Current, and Projected Periods) ........................ 2-169 Table 2 14: Average Annual Water Budget for Revised ESJWRM (Version 3.0) – Stream System (AF/year) ....... 2-177 Table 2 15: Average Annual Water Budget for Revised ESJWRM – Land Surface System (AF/year) ................... 2-179 Table 2 16: Average Annual Water Budget for Revised ESJWRM – Groundwater System (AF/year) .................... 2-181 Table 2 17: Average Annual Values for Key Components of Historical Water Budget by Year Type ..................... 2-186 Table 2 18: Average Annual Values for Key Components of Projected Water Budget by Year Type ..................... 2-193 Table 2 19: Average Annual Values for Key Components of Projected Conditions with Climate Change Water Budget by Year Type ........................................................................................................................................................... 2-197 Table 2 20: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL Version 3.0 and PCBL-DR Version 3.0 ............................................................................................................................................. 2-199 Table 2 21: ESJ Subbasin Hydrologic Groundwater Budget Annual Average Comparison Between PCBL Version 3.0 and PCBL-DR Version 3.0 ...................................................................................................................................... 2-202 Table 2 22: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL-CC Version 3.0 and PCBL-CC-DR Version 3.0 ................................................................................................................................ 2-204 Table 2 23: ESJ Subbasin Hydrologic Groundwater Budget Annual Average Comparison Between the PCBL-CC and the PCBL-CC-DR Version 3.0 ................................................................................................................................. 2-207 Table 2 24: Summary of ESJWRM Category A Projects Surface Water Deliveries ................................................ 2-210 Table 2 25: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL Version 3.0 and PCBL-PMA Version 3.0 ........................................................................................................................................... 2-212 Table 2 26: ESJ Hydrologic Groundwater Budget Annual Average Comparison Between the PCBL (Version 3.0) and the PCBL-PMA (Version 3.0) .................................................................................................................................. 2-215 Table 2 27: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL-CC Version 3.0 and PCBL-CC-PMA Version 3.0 ............................................................................................................................. 2-216 Table 2 28: ESJ Hydrologic Groundwater Budget Annual Average Comparison Between the PCBL-CC and the PCBL-CC-PMA Version 3.0 ...........2-219Table 3 1: Minimum Thresholds for Chronic Lowering of Groundwater Levels .................................................................................................................................................................................... 3-9 Table 3 2: Measurable Objective for Chronic Lowering of Groundwater Levels ....................................................... 3-10 Table 3 3: Interim Milestones for Chronic Lowering of Groundwater Levels ............................................................. 3-12 Table 3 4: Salinity Tolerances of Major Subbasin Crops .......................................................................................... 3-18 Table 3 5: Measurable Objective and Interim Milestones for Degraded Water Quality for Total Dissolved Solids (mg/L TDS) .......................................................................................................................................................................... 3-21 Table 3 6: Measurable Objective and Interim Milestones for Degraded Water Quality for Chloride (mg/L chloride) 3-22 ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan vii
Table of Contents November 2024
Table 3 7: Minimum Thresholds for Interconnected Surface Water .......................................................................... 3-29 Table 3 8: Measurable Objectives and Interim Milestones for Interconnected Surface Water .................................. 3-32 Table 4 1: Representative Monitoring Wells for Groundwater Levels ......................................................................... 4-2 Table 4 2: DWR Monitoring Well Density Recommendations ..................................................................................... 4-7 Table 4 3: Groundwater Level Monitoring Network Density ........................................................................................ 4-7 Table 4 4: Representative Monitoring Network Wells for Water Quality...................................................................... 4-9 Table 4 5: Historical Groundwater Quality Monitoring Frequency at Identified Local Water Quality Wells ............... 4-11 Table 4 6: Groundwater Quality Monitoring Network Density ................................................................................... 4-11 Table 4 7: Representative Monitoring Network for Inelastic Land Subsidence ......................................................... 4-13 Table 4 8: Representative Monitoring Wells for Interconnected Surface Water ........................................................ 4-15 Table 4 9: Considerations for Well Selection and Well Installation ........................................................................... 4-22 Table 5 1: Data Management System User Types ..................................................................................................... 5-2 Table 5 2: Data Collection Site Information ................................................................................................................. 5-3 Table 5 3: Data Types and Their Associated Parameters Configured in the DMS ..................................................... 5-8 Table 5 4: Sources of Data Included in the Data Management System ...................................................................... 5-9 Table 6 1: List of SGMA Projects ................................................................................................................................ 6-4 Table 6 2: Overview of Project Types and Available Funding Mechanisms .............................................................. 6-59 Table 7 1: GSP Schedule for Implementation 2020 to 2040 ....................................................................................... 7-2 Table 7 2: Costs to GSAs and GSP Implementation Costs ........................................................................................ 7-6 Table 7 3: Funding Mechanisms for Proposed Projects and Management Actions .................................................. 7-13 Table 7 4: Potential Funding Sources for GSP Implementation ................................................................................ 7-18 ATTACHMENT 2
2024 Amended Groundwater Sustainability Plan viii
Table of Contents November 2024
Figures
Figure 1 1: Interconnected Planning and Modeling Efforts for Water Resource Protection ....................................... 1-2 Figure 1 2: Plan Manager and Agency Contact Information ..................................................................................... 1-2 Figure 1 3: Eastern San Joaquin Groundwater Sustainability Agencies .................................................................... 1-4 Figure 1 4: Placement within the San Joaquin Valley Groundwater Basin............................................................... 1-12 Figure 1 5: Neighboring Groundwater Subbasins .................................................................................................... 1-13 Figure 1 6: Underlying and Surrounding Counties ................................................................................................... 1-14 Figure 1 7: City Boundaries ...................................................................................................................................... 1-15 Figure 1 8: Disadvantaged Communities (DACs) .................................................................................................... 1-16 Figure 1 9: Land Use................................................................................................................................................ 1-17 Figure 1 10: Land Use by Crop Type ....................................................................................................................... 1-18 Figure 1 11: US Fish and Wildlife Service, California State Parks, and California Department of Fish and Wildlife Boundaries .................................................................................................................................. 1-20 Figure 1 12: Density of Domestic Wells per Square Mile ......................................................................................... 1-21 Figure 1 13: Density of Public Wells per Square Mile .............................................................................................. 1-22 Figure 1 14: Density of Production Wells per Square Mile ....................................................................................... 1-23 Figure 1 15: Eastern San Joaquin GMP Region Setting .......................................................................................... 1-31 Figure 1 16: Locations of Groundwater Recharge Projects Prior to SGMA Implementation .................................... 1-35 Figure 2 1: Depth of All Wells in Water Data Library.............................................................. 2-12 Figure 2 2: Depth Distribution of Wells in Water Data Library................................................ 2-13 Figure 2 3: GAMA Monitoring Well Network .......................................................................... 2-14 Figure 2 4: Number of Chloride Measurements Taken at GAMA Monitoring Sites (2005-2017) 2- 15 Figure 2 5: AEM Flight Lines across ESJ Subbasin ................................................................................................. 2-18 Figure 2 6: Geologic Time Scale .............................................................................................................................. 2-19 Figure 2 7: Topography ............................................................................................................................................ 2-22 Figure 2 8: Major Hydrologic Features ..................................................................................................................... 2-23 Figure 2 9: Eastern San Joaquin Subbasin Watersheds .......................................................................................... 2-26 Figure 2 2 10: Soil Depositional Areas ..................................................................................................................... 2-27 Figure 2 11: Hydrologic Soil Groups ........................................................................................................................ 2-29 Figure 2 12: Occurrence of Hardpan within the Eastern San Joaquin Subbasin ..................................................... 2-30 Figure 2 13: Areal Extents of Alluvial Fans, Interfans, and Pre-Modesto Formations .............................................. 2-32 Figure 2 14: Existing Areas of Groundwater Recharge (ESJWRM Version 3.0) ...................................................... 2-34 Figure 2 15: Average Percent Coarse Fraction in Near-Surface Materials .............................................................. 2-35 Figure 2 16: Potential Recharge Areas .................................................................................................................... 2-36 Figure 2 17: Generalized Geologic Section and Eastern San Joaquin Subbasin Setting ........................................ 2-37 Figure 2 18: Geologic Map ....................................................................................................................................... 2-38 Figure 2 19: Faults and Structural Features ............................................................................................................. 2-45 Figure 2 20: Base of Fresh Water Elevation and Stockton Fault ............................................................................. 2-46 Figure 2 21: Cross-Section, by Formation, Location Map ........................................................................................ 2-48 Figure 2 22: Hydrogeologic Cross-sections A-A’ and B-B’ ....................................................................................... 2-49 Figure 2 23: Hydrogeologic Cross-sections C-C’ and D-D’ ...................................................................................... 2-50 Figure 2 24: Hydrogeologic Cross- section E-E’ ...................................................................................................... 2-51 Figure 2 25: Cross-Section, by Percent Coarseness, Location Map ........................................................................ 2-52 Figure 2 26: Percent Coarse Cross-Section F-F’ ..................................................................................................... 2-53 Figure 2 27: Percent Coarse Cross-Section G-G’ .................................................................................................... 2-54 Figure 2 28: Percent Coarse Cross-Section H-H’ .................................................................................................... 2-55 Figure 2 29: Percent Coarse Cross-section I-I’ ........................................................................................................ 2-56 Figure 2 30: Bottom Elevation of Water-Bearing Zones (Shallow) ........................................................................... 2-61 ATTACHMENT 2
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Table of Contents November 2024
Figure 2 31: Bottom Elevation of Water-Bearing Zones (Deep and Intermediate) ................................................... 2-62 Figure 2 32: Elevation of Base of Continental Deposits ........................................................................................... 2-65 Figure 2 33: Sand and Gravel Isopach Map............................................................................................................. 2-67 Figure 2 34: Total Number of Cation/Anion Measurements in the Eastern San Joaquin Subbasin ......................... 2-72 Figure 2 35: Trilinear Diagrams ................................................................................................................................ 2-73 Figure 2 36: TDS Annual Variation .......................................................................................................................... 2-74 Figure 2 37: TDS Concentrations in 2017 ................................................................................................................ 2-75 Figure 2 38: Chloride Annual Variation .................................................................................................................... 2-76 Figure 2 39: Chloride Concentrations in 2017 .......................................................................................................... 2-77 Figure 2 40: Sulfate Annual Variation ...................................................................................................................... 2-78 Figure 2 41: Sulfate Concentrations in 2017 ............................................................................................................ 2-79 Figure 2 42: Hydrographs of Selected Wells ............................................................................................................ 2-83 Figure 2 43: Summary of Groundwater Elevation Data, 1940-2018......................................................................... 2-85 Figure 2 44: Precipitation Stations ........................................................................................................................... 2-86 Figure 2 45: First Quarter 2017 Groundwater Elevation .......................................................................................... 2-88 Figure 2 46: Fourth Quarter 2017 Groundwater Levels ........................................................................................... 2-89 Figure 2 47: Map of Nested and/or Clustered Well Sites (as of 2020 GSP Development) ...................................... 2-91 Figure 2 48: Nested Well Hydrographs: CCWD 004-006 (as of 2020 GSP Development) ...................................... 2-92 Figure 2 49: Nested Well Hydrographs: CCWD 010-012 (as of 2020 GSP Development) ...................................... 2-92 Figure 2 50: Nested Well Hydrographs: Sperry Well (as of 2020 GSP Development) ............................................. 2-93 Figure 2 51: Nested Well Hydrographs: Swenson Golf Course (as of 2020 GSP Development) ............................ 2-93 Figure 2 52: Nested Well Hydrographs: STK-1 (as of 2020 GSP Development) ..................................................... 2-94 Figure 2 53: Nested Well Hydrographs: STK-2 (as of 2020 GSP Development) ..................................................... 2-94 Figure 2 54: Nested Well Hydrographs: STK-4 (as of 2020 GSP Development) ..................................................... 2-95 Figure 2 55: Nested Well Hydrographs: STK-5 (as of 2020 GSP Development) ..................................................... 2-95 Figure 2 56: Nested Well Hydrographs: STK-6 (as of 2020 GSP Development) ..................................................... 2-96 Figure 2 57: Nested Well Hydrographs: STK-7 (as of 2020 GSP Development) ..................................................... 2-96 Figure 2 58: Nested Well Hydrographs: Lodi MW-21 (as of 2020 GSP Development) ............................................ 2-97 Figure 2 59: Nested Well Hydrographs: Lodi MW-24 (as of 2020 GSP Development) ............................................ 2-97 Figure 2 60: Nested Well Hydrographs: Lodi MW-25 (as of 2020 GSP Development) ............................................ 2-98 Figure 2 61: Nested Well Hydrographs: Lodi SMW-1 (as of 2020 GSP Development) ............................................ 2-98 Figure 2 62: Nested Well Hydrographs: Lodi WMW-1 (as of 2020 GSP Development) ........................................... 2-99 Figure 2 63: Nested Well Hydrographs: Lodi WMW-2 (as of 2020 GSP Development) ........................................... 2-99 Figure 2 64: Historical Modeled Change in Storage............................................................................................... 2-100 Figure 2 65: Historical Modeled Change in Annual Storage with Water Use and Year Type ................................. 2-101 Figure 2 66: Maximum Chloride Concentration Greater Than 250 mg/L (1940s-2010s) ....................................... 2-104 Figure 2 67: Maximum Chloride Concentration Above 250 mg/L by Decade......................................................... 2-105 Figure 2 68: Maximum Chloride Concentration Above 250 mg/L by Well Depth (1940s-2010s) ........................... 2-107 Figure 2 69: Maximum TDS Concentrations 2015-2018 ........................................................................................ 2-109 Figure 2 70: Average TDS Concentrations 2015-2018 .......................................................................................... 2-110 Figure 2 71: Maximum TDS Concentrations in Shallow Wells 2015-2018 ............................................................. 2-111 Figure 2 72: Maximum TDS Concentrations in Deep Wells 2015-2018 ................................................................. 2-112 Figure 2 73: Nitrate as N Concentrations by Decade ............................................................................................. 2-115 Figure 2 74: Arsenic Concentrations by Decade .................................................................................................... 2-117 Figure 2 75: Maximum Arsenic Concentrations 2015-2018 ................................................................................... 2-118 Figure 2 76: Active Investigation and Remediation Sites as of 2019 ..................................................................... 2-120 Figure 2 77: Active Sites with the Potential to Cause Plumes ................................................................................ 2-121 Figure 2 78: Subsidence (Annual Rate of Vertical Displacement) ......................................................................... 2-124 Figure 2 79: Stream Connectivity to the Groundwater System .............................................................................. 2-126 Figure 2 80: Losing and Gaining Streams .............................................................................................................. 2-127 Figure 2 81: Natural Communities Commonly Associated with Groundwater (NCCAGs) ...................................... 2-129 ATTACHMENT 2
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Table of Contents November 2024
Figure 2 82: NCCAGs Identified as Data Gap Areas for Future Refinement, Likely to Access Non-groundwater Water Supplies ..................................................................................................................................... 2-132 Figure 2 83: Areas Identified as GDEs ................................................................................................................... 2-134 Figure 2 84: Fourth Quarter 2019 Groundwater Elevation (WY 2020) ................................................................... 2-136 Figure 2 85: First Quarter 2020 Groundwater Levels (WY 2020) ........................................................................... 2-137 Figure 2 86: Fourth Quarter 2022 Groundwater Elevation (WY 2023) ................................................................... 2-138 Figure 2 87: First Quarter 2023 Groundwater Levels (WY 2023) ........................................................................... 2-139 Figure 2 88 : Number of Reported Dry Wells in San Joaquin County between WY 2020-2023 ............................. 2-140 Figure 2 89: Modeled Change in Annual Storage with Water Use and Year Type ................................................ 2-141 Figure 2 90: 2023 Annual Groundwater Pumping .................................................................................................. 2-143 Figure 2 91: Average Chloride Concentrations Post-2015 ..................................................................................... 2-145 Figure 2 92: Monitoring Frequency for Wells Measuring Total Dissolved Solids ................................................... 2-146 Figure 2 93: Wells with Recent TDS Observations by Well Depth ......................................................................... 2-147 Figure 2 94: Maximum Concentrations for Wells Measuring Total Dissolved Solids ............................................. 2-148 Figure 2 95: CGPS Station MTWK – Subsidence Time Series .............................................................................. 2-150 Figure 2 96: CGPS Station P309 – Subsidence Time Series ................................................................................ 2-151 Figure 2 97: CGPS Station CMNC – Subsidence Time Series .............................................................................. 2-152 Figure 2 98: CGPS Station CA1S – Subsidence Time Series ............................................................................... 2-153 Figure 2 99: Subsidence Rates (inches per year) Throughout the Subbasin ......................................................... 2-154 Figure 2 100: CGPS Station MTWK: Subsidence Time Series .............................................................................. 2-155 Figure 2 101: CGPS Station CNDR – Time Series of Subsidence and Groundwater Levels ................................ 2-156 Figure 2 102: Stream Reaches in ESJWRM .......................................................................................................... 2-158 Figure 2 103: Surface Waters Connected with the Groundwater System at least 75% of All Months in ESJWRM under Current Conditions .......................................................................................................... 2-159 Figure 2 104: Diagram of Gaining and Losing Connected Streams ....................................................................... 2-160 Figure 2 105: Current Conditions Average Annual Stream Gains by Stream Node ............................................... 2-162 Figure 2 106: Mapping of Potential Groundwater Dependent Ecosystems ............................................................ 2-164 Figure 2 107: Generalized Water Budget Diagram ................................................................................................ 2-165 Figure 2 108: 55-Year Historical Precipitation and Cumulative Departure from Mean Precipitation ...................... 2-167 Figure 2 109: Historical Average Annual Water Budget – Stream System ............................................................ 2-183 Figure 2 110: Historical Average Annual Water Budget – Land Surface System ................................................... 2-184 Figure 2 111: Historical Average Annual Water Budget Estimates – Groundwater System................................... 2-185 Figure 2 112: Current Average Annual Water Budget Estimates – Stream System .............................................. 2-187 Figure 2 113: Current Average Annual Water Budget Estimates – Land Surface System ..................................... 2-188 Figure 2 114: Current Average Annual Water Budget Estimates – Groundwater System ..................................... 2-189 Figure 2 115: Projected Average Annual Water Budget Estimates – Stream System ........................................... 2-191 Figure 2 116: Projected Average Annual Water Budget Estimates – Land Surface System ................................. 2-191 Figure 2 117: Projected Average Annual Water Budget Estimates – Groundwater System .................................. 2-192 Figure 2 118: Projected Average Annual Water Budget Estimates with Climate Change – Stream System ......... 2-194 Figure 2 119: Projected Average Annual Water Budget Estimates with Climate Change – Land Surface System 2-195 Figure 2 120: Projected Average Annual Water Budget Estimates with Climate Change – Groundwater System 2-196 Figure 2 121: ESJ Subbasin Projected Agricultural Demand in the PCBL-DR Version 3.0 ................................... 2-200 Figure 2 122: ESJ Subbasin Projected Urban Demand in the PCBL-DR Version 3.0 ........................................... 2-200 Figure 2 123: ESJ Subbasin Projected Hydrologic Groundwater Budget in PCBL-DR Version 3.0 ....................... 2-202 Figure 2 124: ESJ Subbasin Projected Agricultural Demand in the PCBL-CC-DR Version 3.0 ............................. 2-205 Figure 2 125: ESJ Subbasin Projected Urban Demand in the PCBL-CC-DR Version 3.0 ..................................... 2-206 Figure 2 126: ESJ Subbasin Projected Hydrologic Groundwater Budget in the PCBL-CC-DR Version 3.0 .......... 2-208 Figure 2 127: ESJ Subbasin Projected Agricultural Demand in the PCBL-PMA .................................................... 2-213 Figure 2 128: ESJ Subbasin Projected Urban Demand in the PCBL-PMA ............................................................ 2-213 Figure 2 129: ESJ Subbasin Projected Hydrologic Groundwater Budget in the PCBL-PMA Version 3.0 .............. 2-215 Figure 2 130: ESJ Subbasin Projected Agricultural Demand in the PCBL-CC-PMA Version 3.0 .......................... 2-217 ATTACHMENT 2
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Figure 2 131: ESJ Subbasin Projected Urban Demand in the PCBL-CC-PMA Version 3.0 .................................. 2-218 Figure 2 132: Eastern San Joaquin Subbasin Projected Hydrologic Groundwater Budget in the PCBL-CC-PMA 2-220 Figure 3 1: Sustainable Management Criteria Definitions Graphic (Groundwater Levels Example) .......................... 3-2 Figure 3 2: Location of Representative Monitoring Wells for Groundwater Levels ..................................................... 3-8 Figure 3 3: Location of Representative Monitoring Wells for Water Quality ............................................................. 3-19 Figure 3 4: Defined Critical Infrastructure in the Eastern San Joaquin Subbasin..................................................... 3-25 Figure 3 5: Location of Representative Monitoring Sites for Subsidence ................................................................. 3-27 Figure 3 6: Location of Representative Monitoring Sites for Interconnected Surface Water .................................... 3-30 Figure 4 1: Representative Monitoring Network for Groundwater Levels ................................................................... 4-5 Figure 4 2: Representative Monitoring Network for Groundwater Quality .................................................................. 4-8 Figure 4 3: Representative Monitoring Network for Inelastic Land Subsidence ....................................................... 4-14 Figure 4 4: Representative Monitoring Network for Interconnected Surface Water ................................................. 4-17 Figure 4 5: Proposed New Monitoring Well Locations (Shown as Orange Diamonds) ............................................ 4-21 Figure 5 1: Opti DMS Screenshot .............................................................................................................................. 5-1 Figure 5 2: DMS Data Entry Tool ............................................................................................................................... 5-4 Figure 5 3: Landing Page of Groundwater Portal ....................................................................................................... 5-5 Figure 5 4: Progress-At-A-Glance Dashboard ........................................................................................................... 5-6 Figure 5 5: Typical DMS Data Display ....................................................................................................................... 5-6 Figure 6 1: Location of Category A Projects............................................................................................................. 6-12 Figure 6 2: Location of Category B Projects............................................................................................................. 6-13 Figure 7 1: GSP Implementation Schedule ................................................................................................................ 7-4 ATTACHMENT 2
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Acronyms
µg/L micrograms per liter
1,2,3-TCP 1,2,3-Trichloropropane
AB Assembly Bill
ACS American Community Survey
AEM Airborne Electromagnetic
AEM airborne electromagnetic survey
AF acre-feet
AF/day acre-feet per day
AF/year acre-feet per year
AMI Advanced Metering Infrastructure
AMI automated metering infrastructure
ASR aquifer storage and recovery
AWMP Agricultural Water Management Plan
B.P. before present
Bay-Delta Plan Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Estuary
bgs below ground surface
BMP best management practice
BTEX benzene, toluene, ethylbenzene, and xylenes
C&E Plan Communication and Engagement Plan
C2VSim-FG California Central Valley Simulation Model – Fine Grid Cal Water California Water Service Company Stockton District California State Parks California Department of Parks and Recreation CALSIMETAW California Simulation of Evapotranspiration of Applied Water CalTrans California Department of Transportation
CASGEM California Statewide Groundwater Elevation Monitoring CC climate change
CCR California Code of Regulations
CCR Consumer Confidence Report
CCWD Calaveras County Water District
CDEC California Data Exchange Center
CDFW California Department of Fish and Wildlife
CDP census designated place
CDPH California Department of Public Health
CDPR California Department of Pesticide Regulation
CDWA Central Delta Water Agency
CEDEN California Environmental Data Exchange Network
CEQA California Environmental Quality Act
cfs cubic feet per second
CGPF CalSim II Generated Perturbation Factors
CGPS continuous global positioning system
CNRA California Natural Resources Agency
CSJWCD Central San Joaquin Water Conservation District
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CVFPB Central Valley Flood Protection Board
CVRWQCB Central Valley Regional Water Quality Control Board CV-SALTS Central Valley Salinity Alternatives for Long-Term Sustainability CWC California Water Code
CWSRF Clean Water State Revolving Fund
DAC Disadvantaged Community
DBCP 1,2-dibromo-3-chloropropane
DDW Division of Drinking Water
Delta Sacramento-San Joaquin River Delta
DER Department of Environmental Resources
DFW Department of Fish and Wildlife
DMS data management system
DOGGR Division of Oil, Gas, and Geothermal Resources
DPC Delta Protection Commission
DPR Department of Pesticide Regulation
DPW San Joaquin County Department of Public Works
DTSC Department of Toxic Substances Control
DWR Department of Water Resources
Eastside GSA Eastside San Joaquin GSA
EBMUD East Bay Municipal Utility District
EC electrical conductivity
EDB ethylene dibromide
EO Executive Order
EPA Environmental Protection Agency
ERTs Encoder Receiver Transmitters
ESJ Eastern San Joaquin
ESJGWA Eastern San Joaquin Groundwater Authority
ESJGWA Board Eastern San Joaquin Groundwater Authority Board of Directors ESJWRM Eastern San Joaquin Water Resources Model
ETo evapotranspiration
EWMPs efficient water management practices
ft. bgs feet below ground surface
ft/mi feet per mile
GAMA Groundwater Ambient Monitoring and Assessment
GBA Groundwater Basin Authority
GCM global climate model
GDE groundwater dependent ecosystem
GICIMA Groundwater Information Center Interactive Mapping Application GIS Geographic Information System
GMP Groundwater Management Plan
gpd gallons per day
gpm gallons per minute
GSA Groundwater Sustainability Agency
GSP Groundwater Sustainability Plan
GWL groundwater level
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HCM Hydrogeologic Conceptual Model
ICU Program Integrated Conjunctive Use Program
IDW inverse distance weighted
ILRP Irrigated Lands Regulatory Program
InSAR interferometric synthetic aperture radar
IRWM Integrated Regional Water Management
IRWMP Integrated Regional Water Management Plan
ISW interconnected surface water
IWFM Integrated Water Flow Model
JPA Joint Powers Agreement
JPL Jet Propulsion Laboratory
LCSD Lockeford Community Services District
LCWD Linden County Water District
LLNL Lawrence Livermore National Laboratory
LOCA local analogs
MAC Mokelumne-Amador-Calaveras
MAF million acre-feet
MAR managed aquifer recharge
MCL maximum contaminant level
mg/L milligrams per liter
MGD million gallons per day
MHI median household income
MICUP Mokelumne River Integrated Conjunctive Use Program µmhos/cm micromhos per centimeter
MO measurable objective
MOA memorandum of agreement
MokeWISE Mokelumne Watershed Interregional Sustainability Evaluation MSL mean sea level
MT minimum threshold
MtBE methyl tertiary-butyl ether
MUD Municipal Utilities Department
MWH Montgomery Watson Harza
NAD 83 North American Datum of 1983
NASA National Aeronautics and Space Administration
NAVD 88 North American Vertical Datum of 1988
NCCAG Natural Communities Commonly Associated with Groundwater NDWA North Delta Water Agency
NEPA National Environmental Policy Act
NGS National Geodetic Survey
NOI Notice of Intent
NPDES National Pollutant Discharge Elimination System
NRCS Natural Resource Conservation Service
NSJWCD North San Joaquin Water Conservation District
NWIS National Water Information System
O&M operations and maintenance
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OES San Joaquin County Office of Emergency Services
OID Oakdale Irrigation District
OSWCR Online System for Well Completion Reports
PCBL Projected Conditions Baseline
PCE perchloroethylene
PDA Protest Dismissal Agreement
pdf portable document format
PFOA perfluorooctantoic acid
PFOS perfluorooctanesulfonic acid
PG&E Pacific Gas and Electric Company
PMA Projects and Management Actions
PMC Project Management Committee
PRISM Precipitation-Elevation Regressions on Independent Slopes Model PS persistent scatter
RCA recommended corrective action
RCD Resource Conservation District
RCP representative climate pathways
RD Reclamation District
RFP request for proposal
RL Reporting Limit
RMN representative monitoring network
RMW representative monitoring well
RWQCB Regional Water Quality Control Board
SAGBI Soil Agricultural Groundwater Banking Index
SAW Stakeholder Advisory Workgroup
SB Senate Bill
SCADA supervisory control and data acquisition
SCWSP South County Water Supply Program
SDACs Severely Disadvantaged Communities
SDWA South Delta Water Agency
SEWD Stockton East Water District
SGM Sustainable Groundwater Management
SGMA Sustainable Groundwater Management Act
SJC San Joaquin County
SJC POC San Joaquin Valley Point of Contacts
SJCFCWCD San Joaquin County Flood Control and Water Conservation District SJV San Joaquin Valley
SMC sustainable management criteria
SMCL secondary maximum contaminant levels
SNMP Salt and Nutrient Management Plan
SOPAC Scripps Orbit and Permanent Array Center
SRA State Recreation Area
SS specific storage
SSJ South San Joaquin
SSJ GSA South San Joaquin GSA
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SSJID South San Joaquin Irrigation District
SVRA State Vehicular Recreation Area
SWRCB State Water Resources Control Board
SWTF Surface Water Treatment Facility
SY specific yield
TAC Technical Advisory Committee
TAFY thousand acre-feet per year
TCE trichloroethene
TDS total dissolved solids
TNC The Nature Conservancy
TSS Technical Support Services
UNAVCO University Navstar Consortium
UNGL University of Nevada Geodetic Laboratory
USACE United States Army Corps of Engineers
USBR United States Bureau of Reclamation
USDA United States Department of Agriculture
USEPA U.S. Environmental Protection Agency
USFWS United States Fish & Wildlife Service
USGS United States Geological Survey
UTM Universal Transverse Mercator
UWMP Urban Water Management Plan
UWMPs Urban Water Management Plans
VFD variable frequency drive
VIC Variable Infiltration Capacity
VOC volatile organic compound
Water Code California Water Code
WDL Water Data Library
WDR Waste Discharge Requirement
WID Woodbridge Irrigation District
WIIN Water Infrastructure Improvements for the Nation
Workgroup Groundwater Sustainability Workgroup
WPCF Water Pollution Control Facility
WRFP Water Recycling Funding Program
WRIMS Water Resource Integrated Modeling System
WY water year

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Eastern San Joaquin Groundwater
Subbasin
2024 Groundwater
Sustainability Plan Amendment:

Executive Summary
Prepared by:

November 2024
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Executive Summary November 2024
Acronyms
AF acre-feet
AF/year acre-feet per year
Cal Water California Water Service Company Stockton District CASGEM California Statewide Groundwater Elevation Monitoring CCWD Calaveras County Water District
CDWA Central Delta Water Agency
CGPS continuous global positioning system
CSJWCD Central San Joaquin Water Conservation District
Delta Sacramento-San Joaquin River Delta
DMS data management system
DWR Department of Water Resources
Eastside GSA Eastside San Joaquin GSA
ESJGWA Eastern San Joaquin Groundwater Authority
ESJGWA Board Eastern San Joaquin Groundwater Authority Board of Directors ESJWRM Eastern San Joaquin Water Resources Model
GAMA Groundwater Ambient Monitoring and Assessment
GSA Groundwater Sustainability Agency
GSP Groundwater Sustainability Plan
InSAR Interferometric Synthetic Aperture Radar
LCWD Linden County Water District
LCSD Lockeford Community Services District
Letter Consultation Initiation Letter
MAF million acre-feet
mg/L milligrams per liter
NSJWCD North San Joaquin Water Conservation District
OID Oakdale Irrigation District
PMAs projects and management actions
PMC Project Management Committee
RWQCB Regional Water Quality Control Board
SDWA South Delta Water Agency
SEWD Stockton East Water District
SGMA Sustainable Groundwater Management Act
SMCL secondary maximum contaminant levels
SSJID South San Joaquin Irrigation District
TDS total dissolved solids
TSS Technical Support Services
USACE United States Corps of Engineers
USGS United States Geological Survey
WID Woodbridge Irrigation District
Workgroup Groundwater Sustainability Workgroup
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2024 Groundwater Sustainability Plan Amendment ES-1
Executive Summary November 2024

EXECUTIVE SUMMARY
ES-1. INTRODUCTION
In 2014, the California legislature enacted the Sustainable Groundwater Management Act (SGMA) in response to continued overdraft of California’s groundwater resources. The Eastern San Joaquin Groundwater Subbasin (Eastern San Joaquin Subbasin, or Subbasin) is one of 21 basins and subbasins identified by the California Department of Water Resources (DWR) as being in a state of critical overdraft. SGMA requires preparation of a Groundwater Sustainability Plan (GSP) to address measures necessary to attain sustainable conditions in the Subbasin. Within the framework of SGMA, sustainability is generally defined as long-term reliability of the groundwater supply and the absence of undesirable results.

The Eastern San Joaquin Groundwater Authority (ESJGWA) was formed in 2017 in response to SGMA. A Joint Exercise of Powers Agreement establishes the ESJGWA, which is composed of 16 Groundwater Sustainability Agencies (GSAs): Central Delta Water Agency (CDWA), Central San Joaquin Water Conservation District (CSJWCD), City of Lodi, City of Manteca, City of Stockton, Eastside San Joaquin GSA (Eastside GSA) (composed of Calaveras County Water District [CCWD], Calaveras County, Stanislaus County, and Rock Creek Water District), Linden County Water District (LCWD), Lockeford Community Services District (LCSD), North San Joaquin Water Conservation District (NSJWCD), Oakdale Irrigation District (OID), San Joaquin County No. 1, San Joaquin County No. 2 (with participation from California Water Service Company Stockton District [Cal Water]), South Delta Water Agency (SDWA), South San Joaquin GSA (composed of South San Joaquin Irrigation District [SSJID] including Woodward Reservoir, City of Ripon, and City of Escalon), Stockton East Water District (SEWD), and Woodbridge Irrigation District (WID). The ESJGWA is governed by a 16-member Board of Directors (ESJGWA Board), with one representative from each GSA. The Board is guided by a Steering Committee, also with one representative from each GSA, that is tasked with making recommendations to the ESJGWA Board on technical and substantive matters.

SGMA requires development of a GSP that achieves groundwater sustainability in the Subbasin by 2040. The GSP outlines the need to reduce overdraft conditions and has identified 43 projects for potential development that either replace groundwater use (offset) or supplement groundwater supplies (recharge) to meet current and future water demands. Although current analysis indicates that groundwater pumping offsets and/or recharge on the order of 95,000 acre-feet per year (AF/year) may be required to achieve sustainability, additional efforts are needed to confirm the level of pumping offsets and/or recharge required to achieve sustainability. These efforts include collecting additional data and a review of the Subbasin groundwater model, along with other efforts as outlined in the GSP.

To address the requirements prescribed in SGMA and outlined in the GSP Emergency Regulations (2016), the Subbasin GSAs prepard and submitted a Final GSP by the initial January 31, 2020 deadline. On January 28. 2022, the ESJGWA received a Determiniation Letter from DWR. The Letter identified two deficiencies in the Subbasin GSPs which precluded DWR’s approval, as well as potential corrective actions to address each potential deficiency. The Letter initiated consultation between DWR, the Plan Manager, the ESJGWA, and the Subbasin’s GSAs. On July 27, 2022, the GSAs submitted the 2022 Revised GSP to DWR. In a July 6, 2023 Determination Letter, DWR concluded that the GSAs has taken sufficient actions to correct the deficienes identified by DWR and approved the 2022 Revised Plan. This 2023 Determiniation Letter also outlined eight recommended corrective actions that the GSAs could consider addressing Critical Dates for the Eastern San Joaquin Subbasin
☒ 2020 By January 31: Submit GSP to DWR
☒ 2025 Evaluate GSP and update if warranted
☐ 2030 Evaluate GSP and update if warranted
☐ 2035 Evaluate GSP and update if warranted
☐ 2040 Achieve sustainability for the Subbasin
Figure ES-1: GSP Plan Area within
the San Joaquin Valley
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during preparation of the first Periodic Evaluation. The ESJGWA determined that a Plan Amendment was required to adequately address the recommended corrective actions.

A Public Draft of the 2024 GSP Amendment was prepared and made available for public review and comment on October 1, 2024 for a period of 31 days ending on October 31, 2024. The ESJGWA received numerous comments from the public, reviewed and prepared responses to comments, and revised the Draft 2024 GSP Amendment. This Final 2024 GSP Amendment includes those edits and revisions, as well as edits to address the eight recommended corrective actions in DWR’s 2023 Determination Letter.

ES-2. PLAN AREA
The ESJGWA’s jurisdictional area is defined by the boundaries of the Eastern San Joaquin Subbasin in DWR’s 2003 Bulletin 118 as updated in 2016 and 2018. The Subbasin underlies the San Joaquin Valley, as shown in Figure ES-1.

ES-3. OUTREACH EFFORTS
A stakeholder engagement strategy was developed to enable the interests of beneficial users of groundwater in the Subbasin to be considered. The strategy incorporated bi-monthly Project Management Committee (PMC) meetings, Steering Committee meetings, ESJGWA Board meetings, public meetings, an informational open house event, and information distribution to property owners and residents in the Subbasin.

To support the 5-year Periodic Evaluation of the GSP
and development the 2024 GSP Amendment, the
Steering Committee recommended that the chair of
the ESJGWA form an Ad Hoc Project Management
Committee (PMC). Approved by the Steering
Committee in December 2023, the PMC was
comprised of six GSA volunteers representing the
varied interests in the Subbasin and covering both
urban and agricultural areas. The PMC met bi-monthly
during the GSP Periodic Evaluation and GSP Amendment process, and was tasked with driving the review and update process and coordinating other SGMA implementation efforts, including development of a Domestic Well Mitigation Program, coordination of stakeholder outreach and engagement, and annual and long-term budgeting. PMC members reviewed draft work products and other meeting materials to provide input and direction as needed at the bi-monthly meetings. The PMC was also responsible for recognizing and flagging items requiring discussion and direction from stakeholders, the Steering Committee, and the ESJGWA.

Public Meeting Type Number of
Meetings
ESJGWA Board Meetings 5
Steering Committee Meetings 5
Project Management Committee Meetings 20
Public Events (Meetings & Informational Open House
Events)
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ES-4. BASIN SETTING
The Subbasin is located to the west of the SacramentoSan Joaquin River Delta (Delta) and is bounded by the Sierra Nevada foothills to the east, the San Joaquin
River to the west, Dry Creek to the north, and
Stanislaus River to the south. In the eastern portion of the Subbasin, groundwater flows from east to west and
generally mirrors the westward sloping topography of
the geologic formations. In the western portion of the
Subbasin, groundwater flows eastward toward areas
with relatively lower groundwater elevation. Surface
water generally flows from east to west, with the major river systems traversing the Subbasin being the
Calaveras, Mokelumne, and Stanislaus rivers. Multiple
smaller streams flow into the San Joaquin River, which
flows from south to north. The location of the Subbasin is shown in Figure ES-3.

ES-5. EXISTING GROUNDWATER

CONDITIONS
Groundwater levels in some portions of the Subbasin have been declining for many years, while groundwater levels in other areas of the Subbasin have remained stable or increased in recent years. The change in groundwater levels varies across the Subbasin, with the greatest declines occurring in the central portion of the Subbasin. The western and southern portions of the Subbasin have experienced less change in groundwater levels, in part due to the minimal groundwater pumping in the Delta area to the west and the import of surface water for agricultural and urban uses. In the most recent years, groundwater levels show a general trend of increasing as a result of two signficantly wet water years following two critically dry water years.

It has also been established through isotope analysis that the implementation of the Tecklenberg project has added to groundwater levels in the project area.

Groundwater quality in the Subbasin varies by location. Areas along the western margin have historically had higher levels of salinity. Salinity may be naturally occurring or the result of human activity. Sources of salinity in the Subbasin include Delta sediments, deep saline groundwater, and irrigation return water. Total dissolved solids (TDS), which is a measure of all inorganic and organic substances present in a liquid in molecular, ionized, or colloidal suspended form, and chloride are commonly used to measure salinity. The Groundwater Ambient Monitoring and Assessment (GAMA) Program includes numerous water quality monitoring sites in the Subbasin compiled from different sources, shown in Figure ES-4. Maximum TDS concentrations across the Subbasin have been reported as high as 2,500 milligrams per liter (mg/L) along portions of the Subbasin’s western boundary. Maximum chloride concentrations have been reported at concentrations greater than 2,000 mg/L, with higher concentrations measured in the central and western regions of the Subbasin. For drinking water, California has three secondary maximum contaminant level (SMCL) standards for TDS, all based on aesthetic considerations such as taste and odor, not public health concerns. These are 500 mg/L (recommended limit), 1,000 mg/L (upper limit), and 1,500 mg/L (short-term limit). TDS concentrations decrease significantly to the east, to typically less than 500 mg/L (the recommended limit for aesthetic considerations). The SMCL for chloride is 250 mg/L. Chloride concentrations are typically low across the Subbasin with the majority of measurements falling within the 0-250 mg/L range. Elevated concentrations of other constituents, such as nitrate, arsenic, and point-source contaminants, are generally localized and not widespread and are Figure ES-3: Basin Setting
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generally related to natural sources or land use activities. The GSP establishes ongoing monitoring of salinity (as TDS and chloride) and uses publicly available groundwater quality data to assess groundwater quality relative to arsenic, nitrate, and a number of other common water quality constituents to fill data gaps and identify potential trends of concern.

While the total volume of groundwater in storage in the Subbasin has declined over time, groundwater storage
reduction has not historically been an area of concern in the Subbasin, as there are large volumes of fresh water stored in the aquifer. The total fresh groundwater in storage was estimated at over 50 million-acre-feet (MAF) in 2015. The amount of groundwater in storage has decreased by
approximately 0.01 percent per year (or -0.34 MAF per year) between 1995 and 2023. As such, it is highly unlikely the Subbasin will experience conditions under which the volume of stored groundwater poses a concern, although the depth to access that groundwater does pose a concern.

Land subsidence has not historically been an area of concern in the Subbasin, and there are no records of land subsidence caused by groundwater pumping in the Subbasin.

Seawater intrusion is not considered an applicable sustainability indicator for the Eastern San Joaquin Subbasin as the adjoining Sacramento-San Joaquin River Delta (Delta) is managed as a freshwater body, there is minimal pumping near the Delta, and there are relatively low chloride concentrations in the Subbasin.

Surface waters can be hydraulically interconnected with the groundwater system, where the stream baseflow is either derived from the aquifer (gaining stream) or recharged to the aquifer (losing stream). If the water table beneath the stream substantially lowers as a result of groundwater pumping, the stream may disconnect entirely from the underlying aquifer. Major river systems in the Subbasin are highly managed to meet instream flow requirements for fisheries, water quality standards, and water rights of users downstream. The Eastern San Joaquin Water Resources Model (ESJWRM) Version 3.0 was used to identify interconnected reaches of rivers and streams contained within or bounding the Subbasin by comparing monthly groundwater elevations from the historical calibration of the ESJWRM to streambed elevations along the streams represented. The Mokelumne, Stanislaus, and lower San Joaquin Rivers were found to be connected at least 80 percent of the time over the model simulation period, and the Calaveras River less than 20 percent of the time. ESJWRM Version 3.0 was also used to evaluate current conditions to those simulated for Water Year 2015 (representing dry conditions with low groundwater levels after a multi-year drought). The resultant trends were very similar to historical gains and losses, with the exception of the Stanislaus River, which has a high number of stream nodes in the center portion of the river that are losing under current conditions. ESJWRM Version 3.0, while the best available tool at the time of analysis, contains uncertainty preventing the GSAs from having sufficient data to determine if or when streams or reaches are connected to the groundwater table with this level of granularity. The GSAs will be collecting more data with the new ISW monitoring wells to help inform this analysis going forward.

Figure ES-4: GAMA Water Quality
Sampling Locations
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ES-6. SUSTAINABLE MANAGEMENT CRITERIA
SGMA introduces several terms to measure sustainability, including:

Sustainability Indicators – Sustainability indicators refer to any of the effects caused by groundwater conditions occurring throughout the Subbasin that, when significant and unreasonable, cause undesirable results. The six sustainability indicators identified by DWR are the following:
• Chronic lowering of groundwater levels indicating a significant and unreasonable depletion of supply if continued over the planning and implementation horizon
• Significant and unreasonable reduction of groundwater storage • Significant and unreasonable seawater intrusion
• Significant and unreasonable degraded water quality
• Significant and unreasonable land subsidence that substantially interferes with surface land uses • Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water
Sustainability Goal – This goal is the culmination of conditions resulting in a sustainable condition (absence of undesirable results) within 20 years.

Undesirable Results – Undesirable results are the significant and unreasonable occurrence of conditions that adversely affect groundwater use in the Subbasin, including reduction in the long-term viability of domestic, agricultural, municipal, or environmental uses of the Subbasin’s groundwater. Categories of undesirable results are defined through the sustainability indicators.

Minimum Thresholds – Minimum thresholds are numeric values for each sustainability indicator and are used to define when undesirable results occur. Undesirable results occur if minimum thresholds are exceeded in an established percentage of sites in the Subbasin’s representative monitoring network.

Measurable Objectives – Measurable objectives are a specific set of quantifiable goals for the maintenance or improvement of groundwater conditions.

The method prescribed by SGMA to measure undesirable results involves setting minimum thresholds and measurable objectives for a series of representative monitoring wells or sites for each sustainability indicator. Representative monitoring wells are identified to provide a basis for measuring groundwater conditions (levels and quality) throughout a basin or subbasin without having to measure each well, which would be cost prohibitive. In the Eastern San Joaquin Subbasin, representative wells were selected based on history of recorded groundwater level and/or quality data and potential to effectively represent the groundwater conditions. For the sustainability indicator relating to inelastic land subsidence, representative montioring locations measure ground surface elevations. Similar to the monitoring networks for groundwater levels and quality, monitoring sites were selected based on the history of recorded data and the potential to effectively represent conditions across the Subbasin. As determined following further evaluation, the sustainability indicator relating to significant and unreasonable seawater intrusion was deemed not applicable to the Eastern San Joaquin Subbasin as the Subbasin is not on the coast, and saltwater intrusion through the Delta is managed by upstream reservoir releases to maintain salinity concentrations around 2 parts per thousand.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-6
Executive Summary November 2024
A total of 23 representative wells were identified for measurement of groundwater levels in the Subbasin, 21 representative wells were identified for groundwater quality monitoring, and 12 representive wells were identified for monitoring related to interconnected surface water. For measurements related to inelastic land subsidence, four CGPS stations and six survey benchmarks were selected to form the monitoring network for this sustainability indicator. The GSP uses groundwater level data as the basis for evaluating conditions for groundwater storage.

Minimum thresholds and measurable objectives
were developed for each of the representative
monitoring sites. Figure ES-5 shows a typical
relationship of the minimum thresholds,
measurable objectives, and historical
groundwater level data for a sample groundwater
level representative monitoring well. Similar
analyses can be made for groundwater quality
and land subsidence.

Minimum thresholds for groundwater levels were
developed with reference to historical drought low
conditions and domestic well depths. Specifically,
minimum thresholds were established based on
the historical (2015) drought low plus a buffer of
the historical fluctuation or the 10th percentile
domestic well depth, whichever is shallower –
establishing levels that are protective of 90
percent of domestic wells and wells that community water systems may rely on. In municipalities with ordinances requiring the use of City water (water provided by the City’s municipal wells), the 10th percentile municipal well depth is used in place of the 10th percentile domestic well depth criteria.

Measurable objectives for groundwater levels were established based on the historical (2015) drought low and provide a buffer above the minimum threshold. A table summarizing minimum thresholds and measurable objectives is included in Chapter 3 of this Amended GSP. Graphs showing the minimum threshold and measurable objective for each of the representative wells are contained in an appendix to the GSP.

The minimum thresholds and measurable objectives for groundwater levels are used for the groundwater storage sustainability indicator, as this sustainability indicator is strongly linked to groundwater levels. The groundwater levels minimum thresholds are found to be protective of groundwater storage
Minimum thresholds for groundwater quality were defined by considering two primary beneficial uses at risk of undesirable results related to salinity: drinking water and agriculture uses. Minimum thresholds are 1,000 mg/L total dissolved solids (TDS), 250 mg/L chloride, or the groundwater concentration of those constituents as measured in 2015 at the representative monitoring location, whichever is greater. These values reflect the Secondary Maximum Contaminant Limit (SMCL) for the two constituents of concern (TDS and chloride), plus ackowledges groundwater quality degradation that was already occurring in 2015. Furthermore, these values reflect the agricultural nature of the Subbasin.

Measurable objectives for groundwater quality were set at 600 mg/L for TDS, and the maximum maximum recent historical measurement (as measured between 2015 and 2023) for chloride. The TDS measurable objective of 600 mg/L was developed based on the TDS recommended SMCL for drinking water of 500 mg/L with an added 100 mg/L buffer. A measurable objective of 600 mg/L TDS is close to the recommended SMCL of 500 mg/L and significantly below the upper limit SMCL of 1,000 mg/L, and is considered adequate for drinking water and agricultural uses. The chloride measurable objective was set equal to the Figure ES-5: Sample Relationship Between Minimum
Threshold and Measurable Objective
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-7
Executive Summary November 2024
maximum measured chloride concentration as measured during recent historical conditions (between 2015 and 2023), accounting for fluctuations in constituent concentrations with hydrologic conditions.

The minimum threshold for inelastic land subsidence in the Subbasin was set at no more than 0.2 foot/year [2.4 inches/year] in any five-year period between 2020 and 2040, resulting in no more than a total additional 2 feet (24 inches) of land subsidence by 2040. This is set within the same magnitude of estimated error of the InSAR data (+/- 0.1 foot [0.03 m]), which is currently the most comprehensive tool available for measuring subbasin-wide land subsidence consistently each year, based on historical subsidence rates. Additionally, the minimum threshold of 24 inches of additional subsidence by 2040 reflects the historical subsidence level with an added buffer, and is in line (both by method and magnitude) with the minimum thresholds established by other nearby basins overlying the Corcoran Clay.

The measurable objective for inelastic subsidence is based on the long-term avoidance of land subsidence: 0 ft/year, on a long-term average. This measurable objective is set recognizing the interconnectedness of the Subbasin with surrounding subbasins, and the ability to meet this objective is dependent on the successful management of all nearby subbasins Finally, the minimum thresholds and measurable objectives established for interconnected surface water representative monitoring wells both use groundwater levels as a metric. Groundwater level data are used to calculate water table gradients and, therefore, the volume of water gained and lost. The interconnected surface water minimum thresholds and measurable objectives for wells with historical groundwater level observations are the same as for the chronic lowering of groundwater levels minimum thresholds. Analyses were conducted to demonstrate that the groundwater level minimum thresholds are protective of stream depletions and stream-aquifer interactions (stream connectivity, stream gains and losses, and stream gains and losses as a percentage of streamflow), and therefore the use of these minimum thresholds is justified. For new representative montiroing wells without historic data sets, minimum thresholds and measurable objectives will be established after at least four years of data have been collected, including data for at least one wet year and one dry or critical year during that time period, utilizing the methodologies outlined in Chapter 3 of this GSP.

ES-7. WATER BUDGETS
The Eastern San Joaquin Subbasin has been in an overdraft condition for many years. Overdraft occurs when the amount of groundwater extracted exceeds the long-term average
groundwater recharged.

The groundwater evaluations conducted as a part of the
developmnet of this GSP Amendment provide revised
estimates of the historical, current, and projected
groundwater budget conditions. The current analysis was prepared using the best available information and through updates to the Subbasin’s groundwater modeling tool, the Eastern San Joaquin Water Resources Model (ESJWRM),
Version 3.0. It is anticipated that as additional information becomes available, the model will continue to be updated to continuously refine estimates of annual pumping and
overdraft .

As part of the 5-year Periodic Evaluation and preparation of this Amended GSP, the ESJWRM was updated to Version

3.0 to incorporate new data relating to layering, streams, land use, urban water demand, surface water supply and water deliveries and to extend the simulation period through Water Year 2023. The model was then recalibrated for the extended Figure ES-6: Subbasin-Wide Total Groundwater Pumping
and Offsets Required to Achieve Sustainability
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-8
Executive Summary November 2024
period, and water budgets were updated for historical conditions, current conditions, projected conditions baseline, and projected conditions with the impacts of climate change. Projected conditions scenarios were also updated to incorporate an updated list of projects and management actions as well as updates to the sustainable yield estimate.

Based on these analyses, at projected groundwater pumping levels, the long-term groundwater pumping offset and/or recharge required for the Subbasin to achieve a 0 AF/year change in storage is approximately 95,000 AF/year. Groundwater levels are expected to continue to decline based on projections of current land and water uses. Projects and management actions that offset groundwater pumping and/or increase recharge will help the Subbasin reach sustainability, as illustrated in Figure ES-6.

The projected Subbasin water budget was also evaluated
under climate change conditions, which simulate higher
demand requiring increased groundwater pumping despite
more precipitation and streamflows. The updated version of the Projected Conditions Baseline with Climate Change (PCBL-CC) largely used the same perturbation factors
(2070 Central Tendency climate change conditions) as the original simulation, but the updated PCBL-CC extended the simulation time period by three additional years. The
overdraft modeled under climate change conditions is
simulated to increase above projected conditions without climate change, requiring long-term groundwater pumping offset and/or recharge required for the Subbasin to achieve a 0 AF/year change in storage is approximately 166,000
AF/year.

ES-8. MONITORING NETWORKS
This GSP Amendment outlines the representative monitoring networks for five of the six sustainability indicators. (Seawater intrusion is no longer considered an applicable sustainability indicator for the Eastern San Joaquin Subbasin.) The objective of these monitoring networks is to monitor conditions across the Subbasin and to detect trends toward undesirable results.

Specifically, the monitoring networks were developed to do the following:
• Monitor impacts to the beneficial uses or users of groundwater • Monitor changes in groundwater conditions and land surface elevations relative to measurable objectives and minimum thresholds
• Demonstrate progress toward achieving measurable objectives described in the GSP There are four representative monitoring networks in the Eastern San Joaquin Subbasin: two representative networks for water levels (one for the chronic lowering of groundwater levels sustainability indicator and one for the interconnected surface waters sustinability indicator), a representative network for groundwater quality, and a representative network for inelastic land subsidence. Representative networks are used to determine compliance with the minimum thresholds.

The monitoring networks were designed by evaluating data from the DWR’s California Statewide Groundwater Elevation Monitoring (CASGEM) Program, the United States Geological Survey (USGS), the United States Army Corps of Engineers (USACE), the California Department of Transportation (CalTrans), the San Joaquin County Department of Public Works, and participating GSAs. The groundwater level and interconnected surface water monitoring networks consist largely of wells that are already being used for monitoring in the Subbasin. New wells were added to the monitoring networks, including one well located in the Delta, two deep, multi-completion monitoring wells constructed under DWR’s Technical Support Services (TSS) Figure ES-7: Monitoring Sites
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-9
Executive Summary November 2024
program, and five new shallow monitoring wells for interconnected surface water assessment. Figure ES-7 shows the location of existing monitoring sites for all representative monitoring networks.

Wells in the monitoring networks for water levels (for both the groundwater level and interconnected surface water sustainability indicators) and groundwater quality will be measured on a semi-annual schedule. Monitoring for subsidence will also occur semi-annually. Historical measurements have been entered into the Subbasin Data Management System (DMS), and future data will also be stored in the DMS.

A summary of the monitoring sites in the representative monitoring networks is shown in the table below.

Summary of Representative Monitoring Network Wells/Stations Data Collected Well/Station
Count
Groundwater Level 23
Interconnected Surface Water 12
Groundwater Quality 21
Subsidence (CGPS stations and survey benchmarks) 10
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-10
Executive Summary November 2024
ES-9. DATA MANAGEMENT SYSTEM
The Eastern San Joaquin DMS was built on a flexible, open software platform that uses familiar Google maps and charting tools for analysis and visualization. The DMS serves as a data-sharing portal that enables use of the same data and tools for visualization and analysis. These tools support sustainable groundwater management and create transparent reporting about collected data and analysis results.

The DMS is web-based; the public can easily
access this portal using common web
browsers such as Google Chrome, Firefox,
and Microsoft Edge. The DMS is currently
populated with available historical data.

Future data will also be entered into the
system as it is collected.

The DMS portal provides easy access and
the ability to query information stored in the
system. Groundwater data can be plotted for
any of the available data points, providing a
pictorial view of historical and current data.

Recently, a mobile and tablet interface was
developed for the DMS to facilitate the realtime upload of data collected in the field. The mobile interface is implemented using the
Esri ArcGIS Field Maps mobile app (or the
Collector app if already installed) and is
integrated with the DMS via web services to
ArcGIS Online*. The mobile interface is
intended to provide all ESJGWA staff and
their consultants with an easy-to-use
interfaces to collect well and groundwater
related data in the field. Data collected using
the mobile interfaces are pulled into the DMS
on a nightly basis where it is quality controlled
prior to insertion into the database.

The DMS can be accessed at this link using
the Guest Login:
https://opti.woodardcurran.com/esj/
Figure ES-8: Opti DMS Screenshot
Figure ES-9: Typical DMS Data Display
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-11
Executive Summary November 2024
ES-10. PROJECTS AND MANAGEMENT ACTIONS
Achieving sustainability in the Subbasin requires implementation of projects and management actions. The Subbasin will achieve sustainability by implementing water supply projects that either replace groundwater use or supplement groundwater supplies to attain the current estimated pumping offset and/or recharge need of 95,000 AF/year. It should be noted that this number will be reevaluated in the future after additional data are collected and analyzed. In addition, three projects have been identified that support demand conservation and reduction activities, including water use efficiency upgrades. While the implementation of projects to address sustainabilty has been and will continue to be the cornerstone of the ESJ GSP, the Subbasin is committed to developing a Demand Management Program that would include pumping restrictons if projects are not implemented as expected.

Although the ESJGWA does not have direct authority to require GSAs to implement projects, the ESJGWA will coordinate analysis of GSA-level demands and will compile annual or biannual reports to evaluate progress. If projects do not progress, or if monitoring efforts demonstrate that the projects are not effective in achieving stated recharge and/or offset targets, the Subbasin’s Demand Management Program, a new management action in this GSP, will be implemented.

Projects to increase water supply availability in the Subbasin were identified by individual GSAs. The initial set of projects was reviewed with the ESJGWA Board, Steering Committee, and Workgroup. A final list of 41 potential projects are included in the GSP, representing a variety of project types including direct and in-lieu1recharge, intra-basin water transfers, demand conservation, water recycling, and stormwater reuse. Four new additional projects were approved by the ESJGWA Board at their September 11, 2024 meeting, and are not included in below. More information on these projects is included in Appendix 6-A. With the addition of these four projects, the GSP now includes 45 total projects. Projects are classified into two categories based on project status: Category A and Category B. Category A projects are those that are completed or are anticipated to advance in the next five years and have existing water rights or agreements. Category B projects are those that are not anticipated to advance in the next five years, but may be implemented in the future. Category A projects were simulated in the projected water budget to evaluate their effectiveness on achieving Subbasin sustainability. Category B projects may be elevated to a Category A project should feasibility studies demonstrate a viable project, if water rights or contracts are firmly identified, if partnerships are formed, and if economic evaluation demonstrate that the projects are cost effective, and remain part of the overall adaptive management strategy that the Subbasin is utilizing in GSP implementation to achieve and maintain Subbasin sustainability. These projects are summarized below. 1 In-lieu recharge refers to the use of surface water or recycled water supplies for applications where groundwater is currently used.

This “in-lieu” use reduces groundwater pumping and allows groundwater to remain in the aquifer.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-12
Executive Summary November 2024
Project
Name Project Type Project Proponent
Measurable
Objective
Expected to
Benefit
Current Status
Time-table
(initiation and
completion)
Estimated Costs Required
Permitting and
Regulatory
Process1
Maximum
Recharge
Benefit
(AF/year)
Capital Annual O&M
Category A Projects - projects that were completed or are anticipated to advance in the next five years and have existing water rights or agreements Lake Grupe Inlieu RechargeIn-lieu Recharge SEWD Groundwater levels
Completed 2020-2023 $2.3 M $330,000 Installation for
new intake and
pipeline requires
permits from

DFW, CVFPB,
RWQCB, and
USACE
4,900
SEWD Surface
Water
Implementation
Expansion
In-lieu Recharge SEWD Groundwater
levels
Implementation 2019-2029 $750,000 $100,000 Permit approvals from DFW,
RWQCB,
CVFPB, and
USACE by
private
landowners
19,000
White Slough
Water Pollution
Control Facility
Expansion
Recycling/
In-lieu
Recharge/Direct
Recharge
City of Lodi Groundwater
levels
Construction complete 2019-2020 $6 M $4,664 None (permitting complete)
1,000
CSJWCD Capital
Improvement
Program
In-lieu Recharge CSJWCD Groundwater
levels
Can be implemented
immediately
2020-2027, ongoing with 7-
year completion
cycles
N/A $50,000 Individual
applications
need CSJWCD
Board approval
and possible
streambed
alteration
permits
24,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-13
Executive Summary November 2024
Project
Name Project Type Project Proponent
Measurable
Objective
Expected to
Benefit
Current Status
Time-table
(initiation and
completion)
Estimated Costs Required
Permitting and
Regulatory
Process1
Maximum
Recharge
Benefit
(AF/year)
Capital Annual O&M
NSJWCD South
System
Modernization
In-lieu Recharge NSJWCD Groundwater
levels
Environmental review
complete, funding
secured for Phases 1, 2
and 3. Landowner
improvement district
formed. Phases 1-2
complete.
2018-2025 for
Phases 1, 2, 3;
2025-2028 for
Phase 4; 2028-
2035 for future
phases
Phase 1&2:
$7 M
Phase 3:
$4 M
Phase 4:
$8 M
Future
Phases:
$10-20 M
Phase 1&2:
$200,000
Phase 3:
$200,000
Phase 4:
$200,000
Future Phases:
$200,000
Permits for
pump station
work have been
completed;
minor grading
and road
encroachment
permits may be
needed
10,000
Long-term Water
Transfer to
SEWD and
CSJWCD
Transfers SSJ GSA Groundwater
levels
Infrastructure is in
place. CEQA completed
and agreements in
place
2019-2021 N/A $9 M Project must
comply with
CEQA
20,000
South System
Groundwater
Banking with
East Bay
Municipal Utilities
District (EBMUD)
In-lieu Recharge NSJWCD Groundwater
levels
Pilot Dream Project will
be complete by
February 2024.

Working on expanded
banking project
2020-2024 $5 M $400,000
SWCRB change
petition for
Permit 10478
and San Joaquin
County
groundwater
export permit,
and regulatory
permits as
needed
4,000
NSJWCD North
System
Modernization/
Lakso Recharge
In-Lieu Recharge NSJWCD Groundwater
levels
Constructed Phase 1A,
in progress on Phase
1B. Planning Phase 2
2021-2026 $7 M $150,000
Regulatory
permits as
needed
4,000
Tecklenburg
Recharge Project Direct Recharge NSJWCD Groundwater levels Substantially complete 2022-2024 $1 M $400,000 CEQA review
and possible
grading permit
2,000
City of Stockton
Phase 1:

Groundwater
Recharge Project
Direct Recharge City of
Stockton
Groundwater
levels
Basin design in
progress. Construction
to begin spring 2025.
2022-2026 $11.5 M To be
Determined
Project must
comply with
CEQA
20,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-14
Executive Summary November 2024
Project
Name Project Type Project Proponent
Measurable
Objective
Expected to
Benefit
Current Status
Time-table
(initiation and
completion)
Estimated Costs Required
Permitting and
Regulatory
Process1
Maximum
Recharge
Benefit
(AF/year)
Capital Annual O&M
West
Groundwater
Recharge Basin
Direct Recharge SEWD Groundwater
levels
Ongoing 2032 To be
Determined
To be
Determined
To be
Determined
16,000
NSJWCD Private
Pump
Partnerships
In-Lieu
Recharge/Direct
Recharge
NSJWCD Groundwater
levels Ongoing 2024 To be Determined
To be
Determined
To be
Determined 3,000
Oakdale
Irrigation District
In-lieu and Direct
Recharge Project
Direct Recharge/InLieu Recharge OID Groundwater
levels Ongoing 2023-2032 To be Determined
To be
Determined
To be
Determined 25,000
City of Stockton
Advanced
Metering
Infrastructure
Conservation City of
Stockton
Groundwater
levels
In progress. Contract
awarded in March 2024.
2023-2028 $17 M To be
determined
Not determined 2,000
Total Category A 154,900
Category B Projects - projects that are not anticipated to advance in the next five years, but may be implemented in the future, particularly if Category A projects do not fully achieve stated recharge and/or offset targets or do not produce a response as simulated in the model City of
Manteca
Advanced
Metering
Infrastructure
Conservation City of
Manteca
Groundwater
levels
Experiencing Delays Not determined $650,000 $300,000 None 272 City of Lodi
Surface Water
Facility
Expansion &
Delivery
Pipeline
In-lieu Recharge City of
Lodi
Groundwater
levels
Planning phase 2030-2033 $4 M $2,340,000 SWRCB
permitting and
CEQA required
4,750
BNSF Railway
Company
Intermodal
Facility
Recharge
Pond
Direct Recharge CSJWCD Groundwater
levels
Planning phase 2020-2025 N/A $50,000 Streambed
alteration permit
1,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-15
Executive Summary November 2024
Project
Name Project Type Project Proponent
Measurable
Objective
Expected to
Benefit
Current Status
Time-table
(initiation and
completion)
Estimated Costs Required
Permitting and
Regulatory
Process1
Maximum
Recharge
Benefit
(AF/year)
Capital Annual O&M
Manaserro
Recharge
Project
Direct Recharge NSJWCD Groundwater
levels
Planning phase 2023-2025 $500,000 $50,000 CEQA review,
possible grading
permit, possible
water right
change petition
8,000
City of Escalon
Wastewater
Reuse
Recycling/
In-lieu Recharge/
Transfers
SSJ GSA Groundwater
levels
Planning phase 2020-2028 To be
determined$18
M
To be
determined$40
0,000
CEQA review,
RWQCB
permits, and
road
encroachment
permits
672
City of Ripon
Surface Water
Supply
In-lieu Recharge SSJ GSA Groundwater
levels
Design complete;
environmental
permitting underway;
negotiations for the right
to connect are
underway.
2028-2030 To be
determined
To be
determined
NEPA
Categorical
Exclusion,
CEQA Mitigated
Negative
Declaration, and
road
encroachment
permits
6,000
City of Escalon
Connection to
Nick DeGroot
Water
Treatment
Plant
In-lieu Recharge SSJ GSA Groundwater
levels
Conceptual design;
environmental review
complete; Council
approval are pending
further design work and
rate study
2028-2030 To be
determined
To be
determined
Road
encroachment
permits
2,015
Farmington
Dam
Repurpose
Project
Direct Recharge SEWD Groundwater
levels
Planning/Initial Study 2030-2050 To be
determined
To be
determined
Permits and
approvals form

SWRCB, USBR,

DFW, RWQCB,
CVFPB, and
USACE
60,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-16
Executive Summary November 2024
Project
Name Project Type Project Proponent
Measurable
Objective
Expected to
Benefit
Current Status
Time-table
(initiation and
completion)
Estimated Costs Required
Permitting and
Regulatory
Process1
Maximum
Recharge
Benefit
(AF/year)
Capital Annual O&M
Mobilizing
Recharge
Opportunities
Direct Recharge San
Joaquin
County
Groundwater
levels
Project Development 2024-2040 Not
determined
Not determined Not determined 158,000
NSJWCD
Winery
Recycled
Water
Recycling/
In-Lieu Recharge/
Direct Recharge
NSJWCD Groundwater
levels
Conceptual planning
and discussion
2025-2027 To be
determined
To be
determined
WDR permitting
through the
RWCQB and
minor permits for
pipeline
construction
750
SSJID Storm
Water Reuse
Storm Water/
In-lieu Recharge/
Direct Recharge
SSJ GSA Groundwater
levels
Planning phase 2027-2030 To be
determined$30
M
To be
determined$30,
000
CEQA review
and road
encroachment
permits
1,100
WallaceBurson
Conjunctive
Use Program
Conjunctive
Use/Direct Recharge
Eastside
GSA
Groundwater
levels
Conceptual planning
and discussion 2030-2040 To be determined
To be
determined Not determined 3,000
Calaveras
River
Wholesale
Water Service
Expansion
In-Lieu Recharge Eastside
GSA
Groundwater
levels Conceptual planning 2020-2040 To be determined
To be
determined Not determined 600
Recycled
Water to
Manteca Golf
Course
Recycling City of
Manteca
Groundwater
levels
12-in pipeline installed.

Waiting for DWR to
determine grant
recipients
To Be
Determined
To be
determined
To be
determined Not determined 406
Threfall Ranch
Reservoir, InLieu and Direct
Recharge
Project
In-Lieu
Recharge/Direct
Recharge
Eastside
GSA
Groundwater
levels Design 2025 To be determined
To be
determined Not determined 2,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-17
Executive Summary November 2024
Project
Name Project Type Project Proponent
Measurable
Objective
Expected to
Benefit
Current Status
Time-table
(initiation and
completion)
Estimated Costs Required
Permitting and
Regulatory
Process1
Maximum
Recharge
Benefit
(AF/year)
Capital Annual O&M
Perfecting
Mokelumne
River Water
Right
In-Lieu Recharge
San
Joaquin
County
Groundwater
levels Planning 2024-2025
$125,000
(spent to date)
Total TBD
To be
determined Not determined 158,000
North System
Groundwater
Recharge
Project - Phase
2 Direct Recharge NSJWCD Groundwater
levels
Design phase with
planned construction in
2025-2026
2026-2029 $10 M $100,000 Not determined 3,000
Stormwater
Collection,
Treatment, and
Infiltration
Direct Recharge/
Stormwater
City of
Manteca
Groundwater
levels Planning/Initial Study To Be Determined
To be
determined
To be
determined Not determined To Be Determined
Off-Stream
Regulating
Reservoir
Direct Recharge SEWD Groundwater
levels Conceptual Phase 2026-2050 To be determined
To be
determined Not determined To Be Determined
On-Farm
Recharge
Project
Direct Recharge SEWD Groundwater
levels Planning/Initial Study 2024-2030 N/A $100,000 Not determined To Be Determined Bellota Weir
Modifications
Project
Direct Recharge/
Stormwater SEWD Groundwater
levels
SRF loan application
submitted. $12.3M
grant received. Minor
construction started
2023-2030 $ 85 M $1.5M
USACE,

FWS,CVFPB,CE

QA,NEPA
5,200
Water Supply
Enhancement
Project -
Distribution
Pipelines
In-Lieu
Recharge/Direct
Recharge
SEWD Groundwater
levels Design 2024-2040 $7M To be determined

RWQCB,CEQA,

USACE,CVFPB,
DFW
17,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-18
Executive Summary November 2024
Project
Name Project Type Project Proponent
Measurable
Objective
Expected to
Benefit
Current Status
Time-table
(initiation and
completion)
Estimated Costs Required
Permitting and
Regulatory
Process1
Maximum
Recharge
Benefit
(AF/year)
Capital Annual O&M
Water
Treatment
Plant Aquifer
Storage
Recovery Well
- 7401
Direct Recharge SEWD Groundwater
levels Implementation 2024-2026 $1.5 M To be determined

RWQCB,CEQA,
NEPA 2,420
Beckman Well Direct Recharge SEWD Groundwater
levels Refurbish 2024-2028 $200,000 N/A RWQCB,CEQA 800
West Linden
Project
In-Lieu
Recharge/Direct
Recharge
SEWD Groundwater
levels Planning/Design 2024-2035 $60M To be determined

CEQA,RWQCB,
road
encroachment
permits
60,000
Water Supply
Enhancement
Project - Direct
Recharge
Direct Recharge SEWD Groundwater
levels Design 2024-2030 To be determined
To be
determined Not determined To Be Determined
SSJID Water
Master Plan -
System
Improvements
In-Lieu Recharge SSJ GSA Groundwater
levels
Feasibility study
complete 2023-2040 $ 30 – 40 M To be determined Not determined 15,000 Total Category B 509,985
1 Acronyms defined: Stockton East Water District (SEWD), Central San Joaquin Water Conservation District (CSJWCD), North San Joaquin Water Conservation District (NSJWCD), California Department of Fish and Wildlife (DFW), Central Valley Flood Protection Board (CVFPB), Regional Water Quality Control Board (RWQCB), and U.S. Army Corps of Engineers (USACE), State Water Resources Control Board (SWRCB), California Environmental Quality Act (CEQA), U.S. Bureau of Reclamation (USBR), National Pollutant Discharge Elimination System (NPDES), Waste Discharge Requirements (WDR).

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-19
Executive Summary November 2024
ES-11. GSP IMPLEMENTATION
The overdraft condition in the Subbasin requires either projects to offset groundwater pumping and/or increase recharge, or pumping reduction. The exact amount of required offset/recharge will be reevaluated after additional data are collected and analyzed. As previously noted, the overarching philosophy of the ESJ GSP is to implement projects to address the overdraft condition. Should the projects be delayed or not provide the benefits identified, the Subbasin will implement the Demand Management Program, a new management action in this GSP.

Projects will be administered by the GSA project proponents. GSAs may elect to implement projects individually or jointly with one or more GSAs or with the ESJGWA.

Implementing the GSP will require numerous management activities that will be undertaken by the ESJGWA, including the following:
• Monitoring and recording of groundwater levels and groundwater quality data • Maintaining and updating the Subbasin DMS with newly collected data • Maintaining and updating the Subbasin Data Management System (DMS) with newly collected data • Addressing identified data gaps
• Annual monitoring of progress toward sustainability
• Annual reporting of Subbasin conditions to DWR as required by SGMA • Refining Subbasin model and water budget planning estimates • Evaluating the GSP once every 5 years and amending the plan if warranted The ESJGWA Board adopted a preliminary schedule for project implementation. Project implementation is scheduled to begin in 2020, with full implementation by 2040. This approach provides adequate time to put in place methods necessary to refine model estimates and verify project cost effectiveness.

ES-12. FUNDING
Implementation of the GSP requires funding sources. To the degree they become available, outside grants will be sought to assist in reducing cost of implementation to participating agencies, residents, and landowners of the Subbasin. However, there will be a need to collect funds to support implementation.

The areas associated with ESJGWA-wide management and GSP implementation will be borne by the ESJGWA through contributions from the member GSAs, under a cost-sharing arrangement. These costs include:
• ESJGWA administration
• Groundwater level monitoring and reporting
• Groundwater quality monitoring and reporting
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ES-20
Executive Summary November 2024
• Inelastic land subsidence monitoring and reporting
• Water use estimation
• Data management
• Stakeholder engagement
• Oversight of management actions
• Annual Report preparation and submittal to DWR
• Developing and implementing a funding mechanism
• Grant applications
• GSP evaluation and updates, if warranted (every 5 years) For budgetary purposes, the estimated initial cost of these activities is on the order of $600,000 to $1 million per year excluding projects and management actions costs and costs associated with the installation of new monitoring wells and grant writing.

Additional one-time costs, such as model refinement, are estimated to be on the order of $350,000.

GSAs will individually fund implementation of projects in their respective areas. Options for GSA funding include fees based on groundwater pumping, acreage, or combinations of these, and pursuit of any available grant funds. The GSAs will evaluate options for securing the needed funding on an individual basis.

The estimated initial costs of projects range from on the order of $50,000 to $85 million, depending on the project. Annual project costs range from $3,000 to $9 million per year to provide funds for operations and maintenance.

ATTACHMENT 2
Eastern San Joaquin Groundwater
Subbasin
2024 Groundwater
Sustainability Plan Amendment:

Agency Information, Plan Area,
and Communication
Prepared by:

November 2024
ATTACHMENT 2
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ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment i
Agency Information, Plan Area, and Communication November 2024

TABLE OF CONTENTS
SECTION PAGE NO.

1. AGENCY INFORMATION, PLAN AREA, AND COMMUNICATION...............................................................1-1

1.1 Introduction and Agency Information.....................................................................................................1-1

1.1.1 Purpose of the Groundwater Sustainability Plan .................................................................1-1

1.1.2 Sustainability Goal...............................................................................................................1-2

1.1.3 Contact Information .............................................................................................................1-2

1.1.4 Agency Information..............................................................................................................1-3

1.1.5 GSP Organization..............................................................................................................1-10

1.2 Plan Area.............................................................................................................................................1-10

1.2.1 Description of Plan Area ....................................................................................................1-11

1.2.2 Water Resources Monitoring and Management Programs................................................1-23

1.2.3 Land Use Elements or Topic Categories of Applicable General Plans ..............................1-35

1.2.4 Additional GSP Elements ..................................................................................................1-41

1.3 Notice and Communication..................................................................................................................1-43

1.3.1 Beneficial Uses and Users in the Basin.............................................................................1-43

1.3.2 List of Public Meetings Where the 2024 GSP was Discussed...........................................1-44

1.3.3 Decision-Making Process ..................................................................................................1-45

1.3.4 Opportunities for Public Engagement and How Public Input was Used.............................1-45

1.3.5 Inter-basin Coordination ....................................................................................................1-56

1.3.6 Notice of Intent to Adopt the GSP......................................................................................1-56 Tables
Table 1-1: Minimum Depth of Seal Below Ground Surface for Wells in San Joaquin County.................................. 1-39 Table 1-2: Minimum Depth of Seal Below Ground Surface for Wells in Calaveras County...................................... 1-40 Table 1-3: Minimum Depth of Seal Below Ground Surface for Wells in Stanislaus County ..................................... 1-41 Table 1-4: Groundwater Sustainability Workgroup Interests (Collected During Development of 2020 GSP) .......... 1-46 Table 1-5: Stakeholder Database Summary ............................................................................................................ 1-54 Figures
Figure 1-1: Interconnected Planning and Modeling Efforts for Water Resource Protection ....................................... 1-2 Figure 1-2: Plan Manager and Agency Contact Information ..................................................................................... 1-2 Figure 1-3: Eastern San Joaquin Groundwater Sustainability Agencies.................................................................... 1-4 Figure 1-4: Placement within the San Joaquin Valley Groundwater Basin .............................................................. 1-12 Figure 1-5: Neighboring Groundwater Subbasins.................................................................................................... 1-13 Figure 1-6: Underlying and Surrounding Counties................................................................................................... 1-14 Figure 1-7: City Boundaries ..................................................................................................................................... 1-15 Figure 1-8: Disadvantaged Communities (DACs) .................................................................................................... 1-16 Figure 1-9: Land Use ............................................................................................................................................... 1-17 Figure 1-10: Land Use by Crop Type....................................................................................................................... 1-18 Figure 1-11: US Fish and Wildlife Service, California State Parks, and California Department of Fish and Wildlife Boundaries .................................................................................................................................. 1-20 Figure 1-12: Density of Domestic Wells per Square Mile......................................................................................... 1-21 Figure 1-13: Density of Public Wells per Square Mile.............................................................................................. 1-22 Figure 1-14: Density of Production Wells per Square Mile....................................................................................... 1-23 ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ii
Agency Information, Plan Area, and Communication November 2024 Figure 1-15: Eastern San Joaquin GMP Region Setting.......................................................................................... 1-31 Figure 1-16: Locations of Groundwater Recharge Projects Prior to SGMA Implementation.................................... 1-35 Appendices
Appendix 1-A Eastern San Joaquin Groundwater Authority JPA Agreement and Bylaws Appendix 1-B Legal Authority of Eastern San Joaquin GSAs Appendix 1-C Agency Resolutions to Become GSAs
Appendix 1-D DWR Preparation Checklist
Appendix 1-E Community Water Systems
Appendix 1-F Relevant General Plan Goals and Policies
Appendix 1-G Freshwater Species in the Eastern San Joaquin Subbasin Appendix 1-H 2024 Eastern San Joaquin Subbasin Communication and Engagement Plan Update Appendix 1-I Public Comments Received
Appendix 1-J Response to Public Comments
Appendix 1-K Notice of Intent to Adopt the 2024 GSP Amendment ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment iii
Agency Information, Plan Area, and Communication November 2024 Acronyms
AB Assembly Bill
ACS American Community Survey
AEM Airborne Electromagnetic
AF acre-feet
AF/year acre-feet per year
AWMPs Agricultural Water Management Plans
Cal Water California Water Service Company Stockton District California State Parks California Department of Parks and Recreation CASGEM California Statewide Groundwater Elevation Monitoring CCR Consumer Confidence Report
CCWD Calaveras County Water District
CDEC California Data Exchange Center
CDFW California Department of Fish and Wildlife
CDP census designated place
CDPH California Department of Public Health
CDPR California Department of Pesticide Regulation
CDWA Central Delta Water Agency
C&E Plan Communication and Engagement Plan
CEDEN California Environmental Data Exchange Network
CEQA California Environmental Quality Act
CGPS continuous global positioning system
CNRA California Natural Resources Agency
CSJWCD Central San Joaquin Water Conservation District
CVRWQCB Central Valley Regional Water Quality Control Board CV-SALTS Central Valley Salinity Alternatives for Long-Term Sustainability DACs Disadvantaged Communities
DDW Division of Drinking Water
DER Department of Environmental Resources
DPR Department of Pesticide Regulations
DWR Department of Water Resources
EBMUD East Bay Municipal Utility District
Eastside GSA Eastside San Joaquin GSA
EO Executive Order
ESJGWA Eastern San Joaquin Groundwater Authority
ESJGWA Board Eastern San Joaquin Groundwater Authority Board of Directors ESJWRM Eastern San Joaquin Water Resources Model
EWMPs efficient water management practices
GAMA Groundwater Ambient Monitoring and Assessment
GBA Groundwater Basin Authority
GDE groundwater dependent ecosystem
GICIMA Groundwater Information Center Interactive Mapping Application GMP Groundwater Management Plan
GSA Groundwater Sustainability Agency
GSP Groundwater Sustainability Plan
ICU Program Integrated Conjunctive Use Program
ILRP Irrigated Lands Regulatory Program
InSAR Interferometric Synthetic Aperture Radar
IRWMP Integrated Regional Water Management Plan
JPL Jet Propulsion Laboratory
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment iv
Agency Information, Plan Area, and Communication November 2024 JPA Joint Powers Agreement
LCSD Lockeford Community Services District
LCWD Linden County Water District
LLNL Lawrence Livermore National Laboratory
MAC Mokelumne-Amador-Calaveras
MHI median household income
MOA memorandum of agreement
MokeWISE Mokelumne Watershed Interregional Sustainability Evaluation MUD Municipal Utilities Department
NASA National Aeronautics and Space Administration
NDWA North Delta Water Agency
NOI Notice of Intent
NSJWCD North San Joaquin Water Conservation District
NWIS National Water Information System
OID Oakdale Irrigation District
OSWCR Online System for Well Completion Reports
PG&E Pacific Gas and Electric Company
PMC Project Management Committee
PS persistent scatter
RCD Resource Conservation District
RD Reclamation District
SAW Stakeholder Advisory Workgroup
SB Senate Bill
SCWSP South County Water Supply Program
SDACs Severely Disadvantaged Communities
SDWA South Delta Water Agency
SEWD Stockton East Water District
SGMA Sustainable Groundwater Management Act
SJCFCWCD San Joaquin County Flood Control and Water Conservation District SJC POC San Joaquin Valley Point of Contacts
SNMP Salt and Nutrient Management Plan
SRA State Recreation Area
SSJID South San Joaquin Irrigation District
SVRA State Vehicular Recreation Area
SWRCB State Water Resources Control Board
TDS total dissolved solids
UNAVCO University NAVSTAR Consortium
UNGL University of Nevada Geodetic Laboratory
USBR United States Bureau of Reclamation
USDA United States Department of Agriculture
USFWS United States Fish & Wildlife Service
USGS United States Geological Survey
UWMPs Urban Water Management Plans
Water Code California Water Code
WDL Water Data Library
WDR Waste Discharge Requirement
WID Woodbridge Irrigation District
Workgroup Groundwater Sustainability Workgroup
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-1
Agency Information, Plan Area, and Communication November 2024

1. AGENCY INFORMATION, PLAN AREA, AND COMMUNICATION

1.1 INTRODUCTION AND AGENCY INFORMATION

1.1.1 Purpose of the Groundwater Sustainability Plan
The purpose of this Groundwater Sustainability Plan (GSP) is to meet the regulatory requirements set forth in the three-bill legislative package consisting of Assembly Bill (AB) 1739 (Dickinson), Senate Bill (SB) 1168 (Pavley), and SB 1319 (Pavley), collectively known as the Sustainable Groundwater Management Act (SGMA). SGMA defines sustainable groundwater management as “management and use of groundwater in a manner that can be maintained during the planning and implementation horizon without causing undesirable results”, which are defined by SGMA as any of the following effects caused by groundwater conditions occurring throughout the basin (CA DWR, 2018):
• Chronic lowering of groundwater levels indicating a significant and unreasonable depletion of supply if continued over the planning and implementation horizon
• Significant and unreasonable reduction of groundwater storage • Significant and unreasonable seawater intrusion
• Significant and unreasonable degraded water quality, including the migration of contaminant plumes that impair water supplies
• Significant and unreasonable land subsidence that substantially interferes with surface land uses • Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water
The Eastern San Joaquin Groundwater Subbasin (Eastern San Joaquin Subbasin or Subbasin) was identified by the Department of Water Resources (DWR) as critically overdrafted. The Eastern San Joaquin Groundwater Sustainability Plan (Eastern San Joaquin GSP, GSP, or the Plan) was originally developed to meet SGMA regulatory requirements by the January 31, 2020 deadline for critically-overdrafted basins while reflecting local needs and preserving local control over water resources. The 2020 GSP was subsequently revised in 2022 to address comments from DWR in their determination letter dated January 28, 2022. This 2024 GSP Amendment addresses comments in DWR’s July 6, 2023 determination letter approving the 2022 Revised GSP, and continues to provide a path to achieve and document sustainable groundwater management within 20 years following initial Plan adoption, promoting the long-term sustainability of locally-managed groundwater resources now and into the future.

While the Eastern San Joaquin GSP offers a new and significant approach to groundwater resource protection, it was developed within an existing framework of comprehensive planning efforts. Throughout the Eastern San Joaquin Region, several separate yet related planning efforts have occurred previously or are concurrently proceeding. The following figure (Figure 1-1) shows flagship reports from these efforts, which include integrated regional water management, urban water management, agricultural water management, watershed management, habitat conservation, and general planning. The Eastern San Joaquin GSP fits in with these prior planning efforts, building on existing local management and basin characterization. A description of prior planning efforts can be found in Section

1.2.2.7 of this document.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-2
Agency Information, Plan Area, and Communication November 2024 Figure 1-1: Interconnected Planning and Modeling Efforts for Water Resource Protection

1.1.2 Sustainability Goal
A sustainability goal is the culmination of conditions resulting in a sustainable condition (absence of undesirable results) within 20 years of the GSP’s initial adoption in 2020. The sustainability goal reflects this requirement and succinctly states the GSP’s objectives and desired conditions of the Subbasin.

The sustainability goal description for the Eastern San Joaquin Subbasin is to maintain an economically-viable groundwater resource for the beneficial use of the people of the Eastern San Joaquin Subbasin by operating the Subbasin within its sustainable yield or by modification of existing management to address future conditions. This goal will be achieved through the implementation of a mix of supply and demand type projects consistent with the GSP implementation plan (see Chapter 6: Projects and Management Actions).

Additional discussion of the sustainability goal can be found in Chapter 3: Sustainable Management Criteria.

1.1.3 Contact Information
The San Joaquin County Department of Public Works Director has been designated as Plan Manager and record keeper. As Plan Manager, the Public Works Director is tasked with submitting a single, jointly-composed GSP to DWR on behalf of the entire Subbasin.

Contact information for the submitting agency and Plan Manager is provided in Figure 1-2.

Figure 1-2: Plan Manager and
Agency Contact Information
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-3
Agency Information, Plan Area, and Communication November 2024

1.1.4 Agency Information
The Eastern San Joaquin GSP was developed jointly by the members of the Eastern San Joaquin Groundwater Authority (ESJGWA), which is a joint powers authority formed by the 16 groundwater sustainability agencies (GSAs) within the Eastern San Joaquin Subbasin. The ESJGWA includes the Central Delta Water Agency (CDWA), Central San Joaquin Water Conservation District (CSJWCD), City of Lodi, City of Manteca, City of Stockton, Eastside San Joaquin GSA (Eastside GSA) (composed of Calaveras County Water District [CCWD], Calaveras County, Stanislaus County, and Rock Creek Water District), Linden County Water District (LCWD), Lockeford Community Services District (LCSD), North San Joaquin Water Conservation District (NSJWCD), Oakdale Irrigation District (OID), San Joaquin County No. 1, San Joaquin County No. 2, South Delta Water Agency (SDWA), South San Joaquin GSA (composed of South San Joaquin Irrigation District [SSJID] including Woodward Reservoir, City of Ripon, and City of Escalon), Stockton East Water District (SEWD), and Woodbridge Irrigation District (WID). Collectively, these 16 GSAs will be referred to as “GSAs.” Figure 1-3 below indicates the jurisdictional boundaries of the individual GSAs.

The GSAs represent a diverse range of water management organizations. The agencies include water agencies, irrigation districts, water conservation districts, and local governments at the city and county level. The GSAs work through the ESJGWA to coordinate implementation of the GSP by each GSA to cover the entire geographic extent encompassed by the boundaries of the Eastern San Joaquin Subbasin.

California Water Service Company Stockton District (Cal Water) formed a partnership with San Joaquin County to participate in the process as part of the San Joaquin County No. 2 GSA, since its status as an investor-owned utility prohibited it from forming its own GSA under SGMA regulations until later amendments under SB 13 (Pavley). As a major purveyor of water in the Stockton region, Cal Water’s participation is considered essential to the development and implementation of a comprehensive plan for sustainable groundwater management in the Subbasin.

The portion of the City of Lathrop located east of the San Joaquin River was initially involved in the Eastern San Joaquin Subbasin 2020 GSP development process as a 17th GSA (City of Lathrop GSA) and was part of the ESJGWA. The City of Lathrop GSA voluntarily withdrew its status from the ESJGWA in March 2019 following DWR’s approval of their request for a basin boundary modification between the Eastern San Joaquin Subbasin and the neighboring Tracy Subbasin, which moved the City of Lathrop entirely within the Tracy Subbasin.

WID voluntarily withdrew its status as a GSA and its membership in the ESJGWA in December 2018; WID reinstated its status as a GSA and its membership in the ESJGWA in October 2019.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-4
Agency Information, Plan Area, and Communication November 2024 Figure 1-3: Eastern San Joaquin Groundwater Sustainability Agencies ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-5
Agency Information, Plan Area, and Communication November 2024

1.1.4.1 Eastern San Joaquin Groundwater Authority Joint Powers Agreement The Joint Powers Agreement (JPA) provides the basis for forming the ESJGWA. The ESJGWA submitted an Initial Notification to jointly develop a GSP for the Eastern San Joaquin Subbasin on February 8, 2017. The agreement and bylaws are provided in Appendix 1-A.

The purpose of the ESJGWA is to act as the coordinating agency and cooperatively carry out the purposes of SGMA in the Eastern San Joaquin Subbasin. The ESJGWA is a public entity separate from the member organizations and holds the authority to coordinate and exercise the common powers of its members within the geographical area of the Eastern San Joaquin Subbasin consistent with the terms and conditions of the JPA.

Since its formation, the ESJGWA has employed a consensus-based approach in its goal to provide a dynamic, costeffective, and collegial organization to achieve initial and ongoing SGMA compliance within the Subbasin. Collaboration among the ESJGWA member agencies has strengthened the potential for broad public support for groundwater management activities as well as the ability to leverage local, state, and federal funds (Eastern San Joaquin GWA, 2017b).

1.1.4.2 Organization and Management Structure of the GSAs The governing body of the ESJGWA, the ESJGWA Board of Directors (ESJGWA Board), convenes every second Wednesday of the month at 10:30 a.m. to coordinate efforts to implement the GSP by debating and finalizing key discussion points and decisions incorporated into the Plan. Each of the 16 GSAs has a voice on the ESJGWA Board and has appointed two representatives to serve: one Board member and one Alternate member to attend in the Board member’s absence.

The ESJGWA Board is tasked with developing actions including, but not limited to, the following:
• Approving budget(s) and appropriate cost sharing for any project or program that requires funding from the ESJGWA
• Proposing guidance and options for obtaining grant funding • Adopting rules, regulations, policies, and procedures related to the JPA • Approving any contracts with consultants or subcontractors that would undertake work on behalf of the GSAs and/or relate to Basin-wide issues and, if applicable, recommend the funding that each GSA should contribute towards the costs of such contracts
• Reporting to the GSA’s respective governing boards
• Approving and implementing a GSP
The ESJGWA Board is guided by a Steering Committee that is made up of one representative from each GSA and convenes every second Wednesday of the month at 8:30 a.m. The Steering Committee is responsible for developing recommendations on technical and substantive Subbasin-wide matters. The Steering Committee is tasked with developing actions including, but not limited to, the following:
• Recommending the action and/or approval of technical or policy elements for the implementation of the GSP, including groundwater conditions, thresholds, and projects and management actions • Recommending the action and/or approval of a GSP
To support the 5-year Periodic Evaluation of the GSP and development the 2024 GSP Amendment, the Steering Committee recommended that the chair of the ESJGWA form an Ad Hoc Project Management Committee (PMC).

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-6
Agency Information, Plan Area, and Communication November 2024 Approved by the Steering Committee in December 2023, the PMC was comprised of six GSA volunteers representing the varied interests in the Subbasin and covering both urban and agricultural areas. At the time of the development of the 2024 GSP Amendment, the six members of the PMC represented the following GSAs: City of Stockton, North San Joaquin Water Conservation District, Oakdale Irrigation District, San Joaquin County, South San Joaquin Irrigation District, and Stockton East Water District. The PMC met bi-monthly during the GSP Periodic Evaluation and GSP amendment process, and was tasked with driving the review and update process and coordinating other SGMA implementation efforts, including development of a Well Mitigation Program, coordination of stakeholder outreach and engagement, and annual and long-term budgeting. PMC members reviewed draft work products and other meeting materials to provide input and direction as needed at the bi-monthly meetings. The PMC was also responsible for recognizing and flagging items requiring discussion and direction from stakeholders, the Steering Committee, and the ESJGWA. While the PMC informed administrative concepts and reviewed draft work products at the staff level, they did not have decision-making authority.

Decisions of the ESJGWA Board are made by an affirmative majority of Board members, except in the following cases which require a two-thirds supermajority vote: approval or modification or amendment of the ESJGWA annual budget; decisions related to the levying of taxes, assessments, or property-related fees and charges; decisions related to the expenditure of funds by the ESJGWA beyond expenditures approved in the annual budget; adoption of rules, regulations, policies, bylaws, and procedures related to the function of the ESJGWA; decisions related to the establishment of the members’ percentage obligations for payment of the ESJGWA’s operating and administrative costs; approval of any contract over $250,000 or contracts for terms that exceed two years; decisions regarding the acquisition and the holding, use, sale, letting, and disposal of real and personal property including water rights, and the construction, maintenance, alteration, and operation of works or improvements; decisions related to the limitation or curtailment of groundwater pumping; and approval of a GSP. Each member of the ESJGWA Board has one vote. A process for dispute resolution and noncompliance, including internal resolution and mediation prior to judicial or administrative remedies, is set forth in the ESJGWA Bylaws in Appendix 1-A.

GSAs share in the general operating and administrative costs of the ESJGWA in accordance with percentages determined by the ESJGWA Board.

1.1.4.3 Description of Participating Agencies
A brief description of each of the GSAs that make up the ESJGWA is provided in the sections below.

Central Delta Water Agency – The Central Delta Water Agency (CDWA) service area encompasses a total of 52,000 acres in the northwestern portion of the Eastern San Joaquin Subbasin. The primary land use in this area is agriculture with crops such as vineyards, fruit and nut trees, row crops, and field crops. CDWA protects water supply within its service area (which extends outside of the Subbasin), assists landowners and reclamation districts with water issues, and represents landowners in flood control matters. CDWA does not own any facilities, and surface water from the Delta is the area’s only utilized source of water, along with limited private groundwater pumping. Approximately 5,000 acres of the GSA overlap with the sphere of influence of the City of Stockton (Eastern San Joaquin County GBA, 2014).

Central San Joaquin Water Conservation District – The Central San Joaquin Water Conservation District (CSJWCD) was formed in 1959 under provisions of the California Water Conservation Act of 1931. The CSJWCD includes approximately 73,000 largely agricultural acres, of which 6,300 acres are within the sphere of influence of the City of Stockton. To mitigate declining groundwater levels, the CSJWCD contracted with the United States Bureau of Reclamation (USBR) for 80,000 acre‐feet per year (AF/year) from New Melones Reservoir on the Stanislaus River.

Irrigation facilities have been installed and operated by individual landowners through a surface water incentive program sponsored by the CSJWCD. At the regional level, CSJWCD has participated as a member agency of the Eastern Water Alliance and the Groundwater Basin Authority (GBA), two preceding efforts to the ESJGWA that focused on groundwater management (Eastern San Joaquin County GBA, 2014).

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-7
Agency Information, Plan Area, and Communication November 2024 City of Lodi – The City of Lodi is located northeast of the City of Stockton along Highway 99. The City of Lodi relies on both groundwater and surface water to satisfy customer needs. In 2003, Lodi entered into a 40‐year agreement with WID for up to 6,000 AF/year of Mokelumne River water. The City of Lodi built the Lodi Surface Water Treatment Plant and associated conveyance facilities necessary to deliver this supply, which were completed and operational at the end of 2012. The City of Lodi currently provides up to 3,000 AF/year of treated wastewater to agricultural land in the vicinity of the wastewater treatment plant, White Slough Water Pollution Control Facility. The GSA for the City of Lodi covers 9,000 acres and includes the White Slough Water Pollution Control Facility area (City of Lodi, 2015).

City of Manteca – The City of Manteca’s approximately 13,000 acres straddles Highway 99 south of the City of Stockton. Potable water supplies consist of a combination of groundwater and treated surface water from the South County Water Supply Program (SCWSP). Manteca currently receives up to 11,500 AF/year of treated surface water and ultimately can receive up to 18,500 AF/year in Phase II of the SCWSP. Up to 700 AF/year of reclaimed wastewater is applied to fodder crops on City-owned and leased lands (City of Manteca, 2020).

City of Stockton – The City of Stockton Municipal Utilities Department (MUD) service area generally encompasses portions of the City of Stockton north of the Calaveras River and south of the Cal Water service area. Water use measured in 2015 shows approximately 27 percent of the Stockton MUD’s water deliveries come from groundwater, with 73 percent from treated surface water from SEWD and the Delta Water Supply Project. The Delta Water Supply Project came online in 2012 and utilizes surface water both from the San Joaquin River (City of Stockton water right) and Mokelumne River through a 40-year agreement with WID initiated in 2008 for up to 6,500 AF/year with more water as the City of Stockton grows. The City of Stockton GSA (approximately 39,000 acres) overlaps with the extent of the Cal Water service area (City of Stockton, 2015).

Eastside San Joaquin GSA – Eastside San Joaquin GSA (Eastside GSA) is a partnership between Calaveras County Water District, Calaveras County, Stanislaus County, and Rock Creek Water District. The area covers over 126,000 acres, stretching into the western portion of Calaveras County and northern portion of Stanislaus County. • Calaveras County Water District – The Calaveras County Water District (CCWD) provides water service to approximately 13,360 municipal and residential customers in six service areas and shares the same boundaries as Calaveras County. Supply for CCWD comes from reservoir releases on the Calaveras, Stanislaus, and Mokelumne Rivers for a total of approximately 6,000 AF/year for primarily agricultural and residential use. CCWD has several customers with riparian rights along the Calaveras River, has one service area that relies solely on groundwater, and has several areas that utilize recycled water. • Calaveras County – Calaveras County has a total area of 1,037 square miles and extends beyond the boundaries of the Eastern San Joaquin Subbasin. Calaveras County Water District is the only public water supplier to residents located in the portion of the County overlying the Subbasin. The only incorporated city, Angels Camp, is located outside of the Subbasin. Calaveras County had one of the fastest growing annual percent increases in population in California between 2000 and 2010 (CCWD, 2020). For the portion of Calaveras County that falls within the Eastern San Joaquin Subbasin, there are numerous domestic, municipal, and monitoring wells.
• Stanislaus County – Stanislaus County has a total area of 973,000 acres and nine incorporated cities and extends beyond Eastern San Joaquin Subbasin. There are approximately 30 water suppliers that serve water to Stanislaus County for domestic, commercial, and agricultural uses. The majority of the county’s population resides in incorporated cities due to urban development and steady population growth within city boundaries.

These incorporated cities are outside of the Subbasin. The portions of Stanislaus County that fall within the Eastern San Joaquin Subbasin not already included in a GSA have partnered with CCWD, Calaveras County, and Rock Creek Water District as the Eastside GSA. The land is mostly unirrigated, and water needs are met by private pumping.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-8
Agency Information, Plan Area, and Communication November 2024 • Rock Creek Water District – Rock Creek Water District was formed in 1941 and covers approximately 1,800 acres in northeastern Stanislaus County. Through the Salt Spring Valley Reservoir in Calaveras County, Rock Creek Water District delivers agricultural water for irrigation (Stanislaus LAFCO, 2018).

Linden County Water District – Linden County Water District (LCWD) provides water and wastewater services to the 300 acres of the unincorporated community of Linden. LCWD is located approximately 12 miles northeast of the City of Stockton along State Route 26. LCWD lies entirely within the boundaries of the SEWD. Between 2000 and 2010, the population in Linden increased by 61 percent from approximately 1,100 to 1,800 residents. LCWD relies on groundwater to meet residential demands in Linden (SJC, 1992).

Lockeford Community Services District – Lockeford Community Services District (LCSD) was established in 1976 and superseded the San Joaquin County Water Works District No. 1 and Lockeford Sanitary District. LCSD provides water and wastewater services to approximately 3,200 residents (as of 2010) in the unincorporated urban community of Lockeford located 17 miles northeast of the City of Stockton on State Routes 12 and 88. LCSD lies within the boundaries of the NSJWCD; however, LCSD’s jurisdiction area is its own GSA and is not part of the NSJWCD GSA.

LCSD’s GSA area is approximately 800 acres and encompasses primarily residential and commercial uses. LCSD anticipates that, as community build-out occurs, it may serve over 5,000 residents. Groundwater from the Eastern San Joaquin Subbasin is LCSD’s only source of potable water (SJC, 2016a).

North San Joaquin Water Conservation District GSA – North San Joaquin Water Conservation District (NSJWCD), organized in 1948 under provisions of the Water Conservation District Act of 1931, includes approximately 149,000 acres east of the City of Lodi, including about 70,000 acres of irrigated agriculture. NSJWCD also includes approximately 4,740 acres within the Lodi city limits and the community of Lockeford. Pursuant to agreements between NSJWCD, Lockeford, and Lodi, the Lodi and Lockeford acreage is excluded from the NSJWCD GSA. NSJWCD straddles the Mokelumne River and has Dry Creek as its northern boundary. Prior to a basin boundary modification approved in 2016, NSJWCD was located in both the Cosumnes and the Eastern San Joaquin Subbasins. NSJWCD has a 20,000 AF Mokelumne River surface water right which is generally available in normal to wet years. NSJWCD provides surface water deliveries to irrigated acreage and conducts groundwater recharge, but much of the NSJWCD area relies on private groundwater pumping. At the regional level, NSJWCD has participated as a member agency of the Eastern Water Alliance and the GBA, two preceding efforts to the ESJGWA that focused on groundwater management (Eastern San Joaquin County GBA, 2014).

Oakdale Irrigation District – Oakdale Irrigation District (OID) comprises about 81,000 acres, primarily located in the northern portion of Stanislaus County, but with a small portion located within San Joaquin County. A little less than 40 percent of the District’s area overlies the Eastern San Joaquin Subbasin (over 31,000 acres), and the remaining portion overlies the Modesto Subbasin. SSJID and OID jointly own facilities to provide water from the Stanislaus River for agricultural use (Eastern San Joaquin County GBA, 2014).

San Joaquin County – The San Joaquin County GSA consists of 51,000 acres of areas within the Eastern San Joaquin Subbasin not covered by the other GSAs. Overlapping agencies include North Delta Water Agency (NDWA), unincorporated county, riparian land along Stanislaus River, and areas in the City of Stockton served by the City of Stockton MUD. In collaboration with the Northeast San Joaquin County Groundwater Banking Authority, San Joaquin County led the development of the Eastern San Joaquin Groundwater Basin Groundwater Management Plan in 2004 to review, enhance, and coordinate existing groundwater management policies and programs in the region and to develop new policies and programs for the long-term sustainability of groundwater resources. San Joaquin County has also supported the development of studies and plans in the region, such as the Groundwater Basin Authority System Plan and San Joaquin County Water Management Plan.
• North Delta Water Agency – The NDWA was formed by a special act of the Legislature in 1973 to protect the water supply against seawater intrusion and to ensure a reliable water supply to meet current and future water needs. The NDWA service area now includes approximately 277,000 acres within the counties of Sacramento, San Joaquin, Solano, and Yolo. Most of the land is devoted to agriculture use and supplied with surface water ATTACHMENT 2
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Agency Information, Plan Area, and Communication November 2024 from the Delta (NDWA, 2015). The reclamations districts within the NDWA and the Eastern San Joaquin Subbasin include Reclamation District (RD) 38 – Staten Island, RD 2086 – Canal Ranch, and RD 348 – New Hope Tract.

San Joaquin County No. 2 (Cal Water) – San Joaquin County No. 2 GSA includes approximately 7,000 acres of the unincorporated San Joaquin County portion of the Cal Water Service Area. Cal Water is an investor-owned public utility regulated by the California Public Utilities Commission; it is a signatory to the California Urban Water Conservation Council. Cal Water has approximately 42,000 connections in the greater Stockton area, primarily south of the Calaveras River. Cal Water utilizes surface water delivered from SEWD and groundwater pumped by Cal Water wells to meet customer demands. Cal Water's Stockton District was formed in 1927 with the purchase of the water system from Pacific Gas and Electric Company (PG&E).

South Delta Water Agency – The South Delta Water Agency (SDWA) was originally formed to address local water supply and water quality concerns in the south Delta area. The SDWA encompasses a total of approximately 150,000 acres within its boundaries, and almost 18,000 acres overlap with the southwestern portion of the Eastern San Joaquin Subbasin. The SDWA does not own any facilities or water rights. Instead, the SDWA protects property owners who have individual water rights. Surface water is the primary source of water used within the agency boundaries given that most of the groundwater is highly saline (Eastern San Joaquin County GBA, 2014).

South San Joaquin GSA – South San Joaquin GSA’s 64,000 acres encompass most of the South San Joaquin Irrigation District (SSJID), including Woodward Reservoir and canals leading to SSJID; the City of Ripon; and the City of Escalon. The portion of SSJID within the incorporated City of Manteca is included in the City of Manteca GSA. • South San Joaquin Irrigation District – SSJID was formed in 1909 under the Irrigation District Act and covers approximately 72,000 acres in the southeastern portion of San Joaquin County located within the Eastern San Joaquin Subbasin boundaries. The cities of Manteca, Ripon, and Escalon account for approximately 20,000 acres of the SSJID area. SSJID in 2005 began the delivery of up to 32,000 AF/year currently (and up to 43,000 AF/year in Phase II) of treated surface water from Woodward Reservoir to the cities of Manteca, Lathrop, and Tracy for the SCWSP, with Escalon to receive water in the future (Eastern San Joaquin County GBA, 2014).
• City of Ripon – The City of Ripon is located at the southern edge of San Joaquin County along Highway 99.

The population in 2015 was approximately 16,000 people and is expected to grow to about 30,800 people by 2040 (U.S. Census Bureau, 2020). The city’s potable water is provided by city groundwater wells and supplied over 4,000 acre-feet (AF) in 2015. Non-potable groundwater and surface water from SSJID are used for irrigation purposes and recharge (City of Ripon, 2015). • City of Escalon – The City of Escalon is located within the San Joaquin County boundaries along State Route 120. Incorporated in 1957, the City of Escalon was home to approximately 7,400 residents in 2020 (U.S.

Census Bureau, 2020). The City of Escalon has an allotment of 2,015 AF of treated water from the SSJID and the SCWSP; however, the city is not utilizing its allotment and currently relies solely on groundwater wells to serve the city’s population as well as commercial customers. The City of Escalon is selling its allotment of treated water to the City of Tracy but intends to construct a pipeline to convey SSJID water to meet domestic and industrial needs in the City of Escalon (SSJID, 2015b).

Stockton East Water District – Stockton East Water District (SEWD) was formed in 1948, includes a total of 143,300 acres, overlaps with portions of WID, and includes the entire City of Stockton and the entire Cal Water service area. The SEWD GSA covers 101,000 acres of the district, with the remaining SEWD areas covered by the City of Stockton, San Joaquin County, and San Joaquin County No. 2 GSAs. SEWD is guaranteed 56.5 percent of New Hogan Reservoir’s yield and is provided a total amount of 75,000 AF/year from New Melones Reservoir through agreements with USBR. SEWD delivers wholesale drinking water to the City of Stockton, Cal Water, San Joaquin County, and Woodbridge Irrigation District (WID) areas in the Stockton MUD (Eastern San Joaquin County GBA, 2014). At the ATTACHMENT 2
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Agency Information, Plan Area, and Communication November 2024 regional level, SEWD has participated as a member agency of the Eastern Water Alliance and the GBA, two efforts preceding the current ESJGWA that focused on groundwater management (Eastern San Joaquin County GBA, 2014).

Woodbridge Irrigation District – WID, organized in 1924 under the California Irrigation District Act, encompasses a gross area of approximately 42,900 acres with over 29,000 acres covered by the WID GSA. WID is discontiguous, resulting in patches of non‐district lands within its boundary, and overlaps with portions of NSJWCD, SEWD, and the City of Lodi. WID owns and operates the Woodbridge Diversion Dam, located on the Lower Mokelumne River northeast of the City of Lodi, as well as an extensive canal system serving approximately 13,000 acres west of Lodi and north of Stockton. Recent improvements made to the new Woodbridge Diversion Dam include state‐of‐the‐art fish and diversion works which enable WID to keep Lodi Lake full year‐round. At the regional level, WID has participated as a member agency in regional groundwater management efforts, including the GBA.

1.1.4.4 Legal Authority
Any local public agency that has water supply, water management, or land use responsibilities in a basin can decide to become a GSA under SGMA. A single local agency can become a GSA, or a combination of local agencies can decide to form a GSA by using either a JPA, a memorandum of agreement (MOA), or other legal agreement (CA DWR, 2016a).

In the Eastern San Joaquin Subbasin, the ESJGWA has legal authority to jointly prepare, adopt, and implement a GSP consistent with the terms of the JPA Agreement and the ESJGWA Bylaws (Eastern San Joaquin GWA, 2017a). The ESJGWA's JPA calls out the following powers granted to GSAs by SGMA:
• Become a GSA individually or collectively;
• Approve any portion, section, or chapter of the GSP adopted by the ESJGWA; • Act through GSAs to implement SGMA and the GSP; and
• Exercise the powers conferred to GSAs by SGMA.

Each GSA that is a member of the ESJGWA has its own legal authorities. For example, NSJWCD has the legal authorities granted to a GSA under the California Water Code (Water Code) as well as the legal authorities granted to a Water Conservation District pursuant to Water Code § 74000 et seq. The legal authorities of each GSA are listed in Appendix 1-B. Agency resolutions to become GSAs are provided in Appendix 1-C.

1.1.4.5 Estimated Costs and Approach to Meeting Costs
Implementation of the GSP requires funding sources. To the degree they become available, outside grants will be sought to assist in reducing the cost of implementation to participating agencies, residents, and landowners of the Subbasin. However, there will be a need to collect funds to support implementation.

For budgetary purposes, the estimated initial cost of these activities is on the order of $600,000 to $1 million per year excluding projects and management actions costs and costs associated with the installation of new monitoring wells and grant writing. Additional one-time costs, such as model refinement, are estimated to be on the order of $315,000.

The ESJGWA Board will evaluate options for securing the needed funding. Additional detail on GSP implementation costs and funding sources are detailed in Chapter 7: Plan Implementation.

1.1.5 GSP Organization
This GSP is organized according to DWR’s “GSP Annotated Outline” for standardized reporting (CA DWR, 2016b).

The Preparation Checklist for GSP Submittal in DWR formatting can be found in Appendix 1-D (CA DWR, 2016d).

1.2 PLAN AREA
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2024 Groundwater Sustainability Plan Amendment 1-11
Agency Information, Plan Area, and Communication November 2024

1.2.1 Description of Plan Area
This section provides a detailed description of the Eastern San Joaquin Subbasin, including major streams and creeks, institutional entities, agricultural and urban land uses, locations of groundwater wells, and locations of state lands. The Plan Area document also describes existing surface water and groundwater monitoring programs, existing water management programs, and general plans in the Plan Area.

1.2.1.1 Summary of Jurisdictional Areas and Other Features The Eastern San Joaquin Subbasin falls within the larger San Joaquin Valley Groundwater Basin (see Figure 1-4).

Basin designations by DWR were first published in 1952 in Water Quality Investigations Report No. 3, Ground Water Basins in California, and subsequently updated in Bulletin 118 in 1975, 1980, 2003, and 2020. The San Joaquin River Hydrologic Region contains 11 distinct subbasins, where the Eastern San Joaquin Subbasin (Bulletin 118 Basin Number 5-022.01) is bordered to the north by the Cosumnes Subbasin (Bulletin 118 Basin Number 5-022.16), the South American Subbasin (Bulletin 118 Basin Number 5-021.65), and the Solano Subbasin (Bulletin 118 Basin Number 5-021.66); to the south by the Modesto Subbasin (Bulletin 118 Basin Number 5-022.02); and to the west by the Tracy Subbasin (Bulletin 118 Basin Number 5-022.15) and East Contra Costa Subbasin (Bulletin 118 Basin Number 5-022.19) (see Figure 1-5).

The Eastern San Joaquin Subbasin includes lands south of Dry Creek between the San Joaquin River on the west and the crystalline basement rock of the Sierra Nevada foothills on the east. The Eastern San Joaquin Subbasin boundary to the south stretches along the San Joaquin County line and continues along the Stanislaus River into Calaveras County to the east. Geologic units in the Eastern San Joaquin Subbasin consist of consolidated rocks and unconsolidated deposits (CA DWR, 2006).

No adjudicated areas or areas covered by an alternative to a GSP exist within the Eastern San Joaquin Subbasin.

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Agency Information, Plan Area, and Communication November 2024 Figure 1-4: Placement within the San Joaquin Valley Groundwater Basin ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-13
Agency Information, Plan Area, and Communication November 2024 Figure 1-5: Neighboring Groundwater Subbasins
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2024 Groundwater Sustainability Plan Amendment 1-14
Agency Information, Plan Area, and Communication November 2024 The Eastern San Joaquin Subbasin underlies areas of San Joaquin, Stanislaus, and Calaveras Counties. Figure 1-6 shows the location of these three counties within the State of California as well as the three other counties bordering the Eastern San Joaquin Subbasin: Sacramento, Amador, and Contra Costa.

Figure 1-6: Underlying and Surrounding Counties
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2024 Groundwater Sustainability Plan Amendment 1-15
Agency Information, Plan Area, and Communication November 2024 Figure 1-7 shows the Eastern San Joaquin Subbasin and the Subbasin’s key geographic features. The Subbasin encompasses an area of about 1,195 square miles. There are eight entities within the region with land use jurisdiction:
the County of San Joaquin, the County of Calaveras, the County of Stanislaus, the City of Stockton, the City of Lodi, the City of Manteca, the City of Escalon, and the City of Ripon. The cities of Lodi, Escalon, Manteca, and Ripon are contained entirely within the Subbasin, while western portions of San Joaquin County and the City of Stockton, and eastern portions of Calaveras and Stanislaus counties lie in neighboring subbasins or outside of groundwater subbasins altogether. The Eastern San Joaquin Subbasin encompasses the following unincorporated communities:

Acampo, Adela, Atlanta, August, Bear Creek, Burson, Clements, Collierville, Country Club, Dogtown, East Oakdale, Eugene, Farmington, French Camp, Garden Acres, Goodmans Corner, Jenny Lind, Kennedy, Knights Ferry, Lake Camanche Ranches, Lincoln Village, Linden, Lockeford, Milton, Morada, Mormon, Oak Grove, Peters, South Camanche Shore, Taft Mosswood, Terminous, Thornton, Valley Home, Valley Springs, Victor, Wallace, Waterloo, Woodbridge, and Youngstown.

Figure 1-7: City Boundaries
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2024 Groundwater Sustainability Plan Amendment 1-16
Agency Information, Plan Area, and Communication November 2024 Figure 1-8 shows the spatial extent of Disadvantaged Communities (DACs) and Severely Disadvantaged Communities (SDACs) in the Eastern San Joaquin Subbasin. DWR defines DACs as census geographies (census tracts, census block groups, and census-designated places) with an annual median household income (MHI) that is less than 80 percent of the statewide annual MHI. SDACs are defined as census geographies with an MHI less than 60 percent of the statewide annual MHI. DWR uses the most recently available 5-year American Community Survey (ACS) dataset to identify these areas. For this GSP, the 2016-2020 ACS dataset was used, establishing statewide MHI as $78,672 (CA DWR, Mapping Tools).

Figure 1-8: Disadvantaged Communities (DACs)
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2024 Groundwater Sustainability Plan Amendment 1-17
Agency Information, Plan Area, and Communication November 2024 Figure 1-9 shows a map of land use in the Eastern San Joaquin Subbasin across four general categories: cropland, industrial, undeveloped, and urban. These categories were mapped based on categories identified from the United States Department of Agriculture’s (USDA) CropScape 2022 dataset.

Land use patterns in the Eastern San Joaquin Subbasin are dominated by agricultural uses, including nut and fruit trees, vineyards, row crops, grazing, and forage. Both agricultural and urban land use rely on a combination of surface water and groundwater, with some agricultural lands using recycled or reusing water. Land use is primarily controlled by local agencies. Land use patterns in the low foothills to the east are dominated by native vegetation and unirrigated pasture lands (USDA, 2022).

Figure 1-9: Land Use
Crop type varies by region, with fruit and nut trees and vine crops comprising the majority of agriculture in the Subbasin.

Almond orchards dominate the southern portion of the Subbasin, cherry and walnut orchards dominate the central portion of the Subbasin, and vineyards dominate the northern portion (Figure 1-10). Irrigated crop acreage in the Subbasin are 37 percent fruit and nut trees, 24 percent vineyards, and 11 percent alfalfa and irrigated pasture, according to the 2022 CropScape dataset (USDA, 2022).

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2024 Groundwater Sustainability Plan Amendment 1-18
Agency Information, Plan Area, and Communication November 2024 Figure 1-10: Land Use by Crop Type
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2024 Groundwater Sustainability Plan Amendment 1-19
Agency Information, Plan Area, and Communication November 2024 Figure 1-11 shows a map with boundaries of federal and state public lands within the region that includes the Eastern San Joaquin Subbasin. The United States Fish and Wildlife Service (USFWS) manages the San Joaquin River National Wildlife Refuge situated in Stanislaus County where the Tuolumne, Stanislaus, and San Joaquin rivers meet.

Established in 1987 to provide habitat for migratory birds and endangered species, the refuge is 7,000 acres and is located just outside the southern boundary of the Subbasin (USFWS, 2012).

The California Department of Parks and Recreation maintains the Caswell Memorial State Park located along the Stanislaus River near Ripon (California State Parks, 2019). The Caswell Memorial State Park protects a riparian oak woodland and is home to the riparian brush rabbit, an endangered species (California State Parks, 2019). This is the only state park within the Eastern San Joaquin Subbasin boundary. The Franks Tract State Recreation Area (SRA) and the Carnegie State Vehicular Recreation Area (SVRA) are also managed by California State Parks; however, both of these areas are located outside of the Subbasin boundary.

The California Department of Fish and Wildlife (CDFW) owns 880 acres of man-made ditches, canals, and marshes with both grassland and riparian habitat, recognized as the White Slough Wildlife Area. The property was designated by the Fish and Game Commission in 1980 and provides recreational opportunities such as fishing, hunting, and hiking (CDFW, 2019a). CDFW also maintains the 353-acre Woodbridge Ecological Reserve to protect primarily the sandhill crane population, but also other migratory waterfowl. The sandhill crane was listed as a threatened species in 1983.

Woodbridge Ecological Reserve and the greater Stockton Delta wetlands make up the largest freshwater marsh in California (CDFW, 2019b). Lastly, Vernalis Ecological Reserve is also shown in Figure 1-11. It serves as a public access area owned by CDFW for hunting and wildlife viewing (CDFW, 2019c).

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Agency Information, Plan Area, and Communication November 2024 Figure 1-11: US Fish and Wildlife Service, California State Parks, and California Department of Fish and Wildlife Boundaries
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2024 Groundwater Sustainability Plan Amendment 1-21
Agency Information, Plan Area, and Communication November 2024 Figure 1-12 to Figure 1-14 shows the density, as of 2019, of domestic, public, and production wells per square mile in the Eastern San Joaquin Subbasin, as classified by the DWR Online System for Well Completion Reports (OSWCR), which is discussed in Section 1.2.2.1. This includes approximately 1,000 unique wells collected primarily from DWR’s Water Data Library (WDL), but also other state, regional, and local monitoring entities (CA DWR, n.d.). Though there are overlaps and discrepancies in the designation of wells, domestic wells are largely private residential wells, public wells are municipal-operated wells, and production wells are for irrigation, municipal, public, and industrial purposes (CA DWR, 2019). Areas with few wells exist in the Subbasin, particularly in the northwestern corner of the Subbasin and to the east. Wells containing groundwater level data are described further in Section 1.2.2.1. Community water systems, defined by the State Water Resources Control Board (SWRCB) as wells serving 15 or more connections or more than 25 people per day, are identified in Appendix 1-E. Appendix 1-E contains additional detail on where community water systems are found in the Subbasin.

Figure 1-12: Density of Domestic Wells per Square Mile
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Agency Information, Plan Area, and Communication November 2024 Figure 1-13: Density of Public Wells per Square Mile
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Agency Information, Plan Area, and Communication November 2024 Figure 1-14: Density of Production Wells per Square Mile

1.2.2 Water Resources Monitoring and Management Programs The existing monitoring and management landscape within the Eastern San Joaquin Subbasin is a patchwork of local, regional, state, and federal programs, each serving its own specific function. This patchwork provides valuable data that have supported past needs and will assist in meeting monitoring needs under SGMA. This patchwork of programs includes redundancies, inconsistent protocols, and inconsistent timing of monitoring that may be improved during SGMA implementation.

Existing monitoring within the Eastern San Joaquin Subbasin is extensive, complex, and performed for a variety of purposes by a variety of entities. During a review of existing groundwater monitoring data and programs, data were collected from the following agencies and programs. Programs and agencies are listed by the jurisdiction they operate across: statewide, regional, or local. The sections that follow describe in detail the programs most heavily relied upon in the development of the GSP and are organized by data type. Section 1.2.2.3 addresses the interconnection between databases.

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2024 Groundwater Sustainability Plan Amendment 1-24
Agency Information, Plan Area, and Communication November 2024 Statewide Monitoring Programs (Agencies and Databases):
• California Data Exchange Center (CDEC)
• California Department of Pesticide Regulation (CDPR)
• California Environmental Data Exchange Network (CEDEN) • California State Water Resources Control Board (SWRCB), Division of Drinking Water (DDW) • Department of Water Resources (DWR):
o Airborne Electromagnetic (AEM) Surveys
o California Statewide Groundwater Elevation Monitoring (CASGEM) o California Statewide Groundwater Elevation Monitoring Groundwater Information Center Interactive Mapping Application (GICIMA)
o Online System for Well Completion Reports (OSWCR)
o Water Data Library (WDL)
• Groundwater Ambient Monitoring and Assessment (GAMA) Program • GeoTracker
• University NAVSTAR Consortium (UNAVCO)
• United States Bureau of Reclamation (USBR)
• United States Geological Survey (USGS)
Regional Monitoring Programs:
• Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) • California Department of Public Health (CDPH)
• Central Valley Regional Water Quality Control Board (CVRWQCB) Waste Discharge Requirement (WDR) dairy data, Dairy Cares
• USGS’s National Water Information System (NWIS)
• Central Valley Dairy Representative Monitoring Program • EnviroStor
• Groundwater Quality Trend Monitoring Program through SWRCB Irrigated Lands Regulatory Program (ILRP) • San Joaquin River Restoration Program
Local Monitoring Agencies
• Cal Water
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2024 Groundwater Sustainability Plan Amendment 1-25
Agency Information, Plan Area, and Communication November 2024 • Calaveras County Water District
• City of Lodi
• City of Manteca
• City of Stockton
• Linden County Water District
• Lockeford Community Services District
• North San Joaquin Water Conservation District
• Oakdale Irrigation District
• San Joaquin County
• South San Joaquin Irrigation District
• Stockton East Water District
A description of the monitoring programs that will be used in GSP implementation is provided in Chapter 4: Monitoring Networks.

1.2.2.1 Groundwater Level Monitoring and Data Sources

1.2.2.1.1 CASGEM
DWR maintains several groundwater level monitoring programs, tools, and resources covering California. The California Statewide Groundwater Elevation Monitoring (CASGEM) Program is DWR’s primary resource for groundwater level data and has been used extensively in the development of this GSP. The CASGEM Program was authorized in 2009 by SB X7-6 to establish collaboration between local monitoring parties and DWR to collect and make public statewide groundwater elevation data. The program provides the framework for local agencies or other organizations to “assume responsibility for monitoring and reporting groundwater elevations in all or part of a basin or subbasin” (Water Code §10927). As part of SGMA implementation, wells that are in the Subbasin’s representative monitoring network have been migrated out of CASGEM and into SGMA; all other pre-existing CASGEM wells remain in that program under voluntary monitoring status.

Three CASGEM monitoring entities exist in the Eastern San Joaquin Subbasin: CCWD, San Joaquin County Flood Control and Water Conservation District (SJCFCWCD), and Stanislaus County. These three agencies have completed separate CASGEM Monitoring Plans, which are included in the references section. • CCWD CASGEM Monitoring Plan: CCWD adopted a CASGEM Monitoring Plan in November 2012, with the following objectives:
o Collect semi-annual groundwater levels from a selected monitoring well network o Upload groundwater levels to the CASGEM website after data quality steps have been completed o Maintain and update the monitoring well network plan documents including additions and removals from the monitoring network
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2024 Groundwater Sustainability Plan Amendment 1-26
Agency Information, Plan Area, and Communication November 2024 These objectives are helpful to this planning effort, as they include regular monitoring of groundwater levels and data upload to CASGEM. The CCWD plan also includes a description of the CASGEM monitoring network and groundwater level measurements. The monitoring network includes two USGS nested monitoring wells equipped with pressure transducers, which continuously monitor groundwater levels. The monitoring network also includes seven other wells that are not USGS wells. These wells are not equipped with pressure transducers, and manual groundwater elevation measurements are taken at all wells twice a year. As stated in the CCWD CASGEM plan, the non-USGS wells are owned by private landowners, and additional wells may need to be added in the future if owners opt out of the monitoring network (CCWD, 2012). This monitoring network covers the portion of Calaveras County within the Eastern San Joaquin Subbasin. • SJCFCWCD CASGEM Monitoring Plan: The SJCFCWCD CASGEM Monitoring Plan provides a description of the CASGEM monitoring network and groundwater conditions in San Joaquin County. This plan covers the portions of the Eastern San Joaquin and Tracy Subbasins within San Joaquin County. The SJCFCWCD has been taking semi-annual water level measurements since 1971 at wells owned by a variety of entities and by private individuals. A large portion of wells in the district’s network are privately owned (SJCFCWCD, 2006).

SJCFCWCD sent out consent forms to these private well owners to release well information to CASGEM; about 40 of these forms were signed and returned, and construction information for these wells was uploaded to CASGEM. This information includes attributes such as well depth, coordinates, reference point elevation, and depth of screened interval.
• Stanislaus County CASGEM Monitoring Plan: The Stanislaus County Department of Environmental Resources (DER) established a CASGEM monitoring plan in 2016 to cover the portion of Stanislaus County within the Eastern San Joaquin Subbasin, often referred to as the northern triangle. This plan details the groundwater level monitoring history, protocols, and network for the northern triangle portion of Stanislaus County. This area is rural and most of the development exists between the Stanislaus River and near the Woodward Reservoir. Wells selected for the CASGEM program are in the developed areas. 17 wells are included in this CASGEM plan to be measured semi-annually, consisting of one domestic and ten irrigation wells, plus six wells that are of unknown type. Well information such as depth and screened interval was uploaded to CASGEM for these wells (Stanislaus County DER, 2016).

1.2.2.1.2 San Joaquin County Flood Control and Water Conservation District The SJCFCWCD publishes semi-annual groundwater reports covering groundwater conditions in San Joaquin County.

These reports include tables, hydrographs, and maps on groundwater levels. Groundwater level results from each semi-annual report are compared with values from the previous period. Groundwater level data collected by the district include the data mentioned in the CASGEM section, above, and additional data that are not incorporated into CASGEM.

The data are maintained by the SJCFCWCD.

1.2.2.1.3 Water Data Library
DWR’s WDL contains measurements of groundwater elevations from water supply and monitoring wells monitored by numerous entities, such as DWR and local agencies. Groundwater level measurements available from the WDL are either continuously or periodically measured. Continuous measurements are provided by automatic water level measuring devices that take readings at wells; periodic measurements are manual recordings typically occurring at monthly or semi-annual time intervals. Measurements displayed through the WDL are taken through other programs, such as CASGEM. The WDL lists the organization responsible for collecting each water level measurement. The WDL water level measurements are available through the California Natural Resources Agency (CNRA) Open Data website as a bulk download, or through the WDL website on a per station basis.

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Agency Information, Plan Area, and Communication November 2024

1.2.2.1.4 USGS – National Water Information System
The NWIS is a USGS program comprising several water datasets, including groundwater level measurements, river flow, and river stage data. Like the WDL, NWIS contains continuous and periodic water measurements for recent and historical conditions. Within the Eastern San Joaquin Subbasin, there are only a few active NWIS sites and many inactive sites with historical records. For stream measurements, active sites are largely along major streams, such as the Mokelumne River, the Stanislaus River, and the San Joaquin River; along Delta waterways; or in the Sierra Nevada foothills, upstream of reservoirs.

1.2.2.1.5 Data Received Directly from GSAs
A number of the GSAs collect water level and water quality information within their GSAs at varying frequencies and detail. These data were provided as part of the Eastern San Joaquin Water Resources Model (ESJWRM) data collection efforts and were compared with and included in groundwater level and water quality datasets analyzed for updates to the ESJWRM model and the preparation of this GSP.

The development and update of the ESJWRM took place in an open and transparent process. Coordination efforts took place through the Eastern San Joaquin County GBA, the organizational structure for agency coordination that proceeded SGMA regulations and the formation of the ESJGWA, and through the Subbasin Steering Committee.

Through this effort, many of the staff and consultants representing the GSAs forming the ESJGWA participated as a forum to review model input data and assumptions. The group facilitated major modeling decisions and provided input data, including groundwater pumping records, surface water delivery records, urban demand, and local water levels and quality data.

Local agencies with consistent representation in meetings related to the development of the ESJWRM included San Joaquin County, WID, City of Lodi, NSJWCD, LCSD, CCWD, City of Stockton, Cal Water, SEWD, City of Lathrop, City of Manteca, SSJID, City of Escalon, OID, and Stanislaus County. Other agencies contributed local data to information collection efforts later in the GSP development and revision process.

Online System for Well Completion Reports – The OSWCR is a DWR program used to document and compile boring or well completion records throughout California. There are as many as 2 million domestic, irrigation, and monitoring water wells in California included in this dataset, including approximately 10,000 domestic wells located in the Eastern San Joaquin Subbasin. When a well is constructed, modified, or destroyed, drilling contractors are required to submit a Well Completion Report to DWR for upload to the interactive OSWCR web site. OSWCR is used as a data source for wells identified for monitoring. In this GSP, the OSWCR database was used to describe the Plan area and identify sustainable management criteria.

1.2.2.2 Groundwater Quality Monitoring and Data Sources

1.2.2.2.1 Groundwater Ambient Monitoring and Assessment Program The GAMA Program is an extensive groundwater quality monitoring program that was established by the SWRCB in 2000. The program compiles groundwater quality data from several agencies including the DWR, USGS, Department of Pesticide Regulations (DPR), Lawrence Livermore National Laboratory (LLNL), and others. Agencies submit data from monitoring wells for 258 constituents including total dissolved solids (TDS), nitrates and nitrites, arsenic, and manganese. GAMA data for the Eastern San Joaquin Subbasin contains water quality results collected by the SWRCBDDW (formerly DHS-DDW), DPR, DWR, LLNL, and USGS from the 1940s to present. Figure 2-3 in Chapter 2: Basin Setting shows the GAMA well locations throughout the Eastern San Joaquin Subbasin, roughly 6,800 monitoring points.

1.2.2.2.2 Water Data Library
DWR’s WDL contains groundwater quality data in addition to the groundwater level records described previously. This information includes data from discrete groundwater quality samples collected by DWR and other cooperating entities.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-28
Agency Information, Plan Area, and Communication November 2024 These water quality data list the entity responsible for taking the sample but do not specify what program the sample was taken under. The WDL water quality measurements are available through the CNRA Open Data website as a bulk download, or through the WDL website on a per-station basis. WDL water quality measurements in this GSP are utilized for basin characterization but are acquired from the other programs.

1.2.2.2.3 National Water Information System
The USGS NWIS contains groundwater quality data, in addition to the groundwater level measurements previously discussed. Groundwater quality results in NWIS relate to GAMA records, but there is no direct link between the two databases. Some NWIS sites have a State ID listed, which is a common identifier used for wells. This indicates these wells can be connected to other databases using the State ID information. However, differences in the format of the State ID between NWIS and other databases create challenges in cross referencing between databases. In this GSP, NWIS water quality measurements are utilized for basin characterization but are acquired from the other programs.

1.2.2.2.4 Division of Drinking Water
The SWRCB DDW monitors public water system wells for Title 22 requirements such as organic and inorganic compounds, metals, microbial, and radiological analytes. Data are available for active and inactive drinking water sources for water systems that serve the public – defined as wells serving 15 or more connections or more than 25 people per day. Data are electronically transferred from certified laboratories to DDW daily. Data generated from this program are used for regulatory compliance by water purveyors and become part of Consumer Confidence Reports (CCR) and GAMA.

1.2.2.2.5 GeoTracker
GeoTracker, operated by the SWRCB, contains records for sites that require cleanup, such as leaking underground storage tank sites, Department of Defense sites, and cleanup program sites. GeoTracker also contains records for various unregulated projects as well as permitted facilities including: ILRP, future CV-SALTS, oil and gas production, operating permitted underground storage tanks, and land disposal sites. GeoTracker receives records and data from SWRCB programs and other monitoring agencies.

1.2.2.2.6 Irrigated Lands Regulatory Program
The Irrigated Lands Regulatory Program (ILRP) is a program established by the CVRWQCB focused on monitoring and regulating the concentration of pesticides, toxicity, and nutrients (such as TDS and nitrates) in surface and groundwater. General orders under the ILRP require agricultural users in the Central Valley to prevent sediment, fertilizer, pesticides, manure, and other materials used in farming from leaving the field in irrigation or stormwater and entering surface waters or leaching below the root zone to groundwater. Agricultural users biannually sample and submit data for irrigation and domestic wells. As part of the ILRP, the San Joaquin County & Delta Water Quality Coalition members monitor drinking water wells on enrolled parcels for nitrates. This requirement began January 1, 2019, based on the February 7, 2018 revision of ILRP WDR (Order) for the Eastern San Joaquin River Watershed by the SWRCB. The ILRP program is in the process of developing a comprehensive monitoring network for future use to address the ILRP data objectives. The San Joaquin County & Delta Water Quality Coalition members also monitor domestic wells for nitrate in high vulnerability areas.

1.2.2.2.7 Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) The Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) program was launched by the CVRWQCB in 2006 in an effort to develop sustainable salinity and nitrate management plans and solutions to the salinity problem in the Central Valley. CV-SALTS is a coalition of agricultural, business, and industry parties along with local, regional, and state governments which facilitate and fund efficient management systems of salinity, technical studies, and the 2017 Final Salt and Nitrate Management Plan (SNMP). The 2017 SNMP was developed based on a ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-29
Agency Information, Plan Area, and Communication November 2024 detailed water quality analysis conducted for salinity (represented by TDS) and nitrates using measurements from wells across multiple agencies from 2000-2016. Appendices to the SNMP and supporting documents contain summary information about these constituents by Subbasin, including Eastern San Joaquin. Basin Plan Amendments identify specific actions and recommendations for individual basins in the Central Valley. Efforts are underway to implement a salinity monitoring program and the CV-SALTS program will likely require monitoring and data submittal.

1.2.2.3 Interconnection of Databases
Several of the databases discussed above utilize the same water level or water quality data. These records often specify the monitoring entity responsible for the measurement. Although these data overlap between databases, the correlation between databases is not specified. For example, water level data in the WDL are also in CASGEM, but this link is not mentioned in WDL records. This lack of connection poses problems for gathering water level and quality data in the Eastern San Joaquin Subbasin and throughout California. For instance, if certain water level data are gathered through CASGEM but not uploaded to NWIS, users who gather water level measurements through NWIS would miss the CASGEM data. Efforts have been made in the development of this Plan to overcome the issue related to overlap and poor correlation between databases, but the issue remains. It is recommended that agencies work together to utilize a common unique identifier to ease use of multiple datasets.

1.2.2.4 Land Subsidence Monitoring
Subsidence monitoring is performed using continuous global positioning system (CGPS) stations, extensometers, and Interferometric Synthetic Aperture Radar (InSAR) surveys. CGPS data are primarily available from two programs.

UNAVCO’s Plate Boundary Observatory Program – Reporting since 2004, the UNAVCO (formerly University Navigation Satellite Timing and Ranging or NAVSTAR Consortium) Plate Boundary Observatory network consists of a network of about 1,100 continuous global positioning system (CGPS) and meteorology stations in the western United States to measure deformation resulting from the constant motion of the Pacific and North American tectonic plates in the western United States. Stations located within the Subbasin contain data from at least 2006 to current and include station P309 located east of Linden and station P273 located west of Lodi. Other stations are also available in nearby Subbasins.

University of Nevada Geodetic Laboratory (UNGL) - Several additional CGPS stations from the University of Nevada Geodetic Laboratory (UNGL) were also located in the Subbasin. These stations provide additional subsidence data for the Subbasin; however, these stations have drawbacks, such as data gaps, and discontinuous monitoring, and are used on an academic/research basis that may result in increased monitoring gaps. Station CA15 is located north of the city of Stockton and has a continuous period of record between September 2013 and October 2021. Station CMNC is located along the southern edge of the Camanche Reservoir and has observations in 2020 and between February 2022 through January 2024. These locations also provided additional spatial coverage to the UNAVCO and SOPAC CGPS stations
Subsidence analyses have also been conducted using satellite-based methods over limited time periods, as described below.

United States Geological Survey – The USGS report Land Subsidence along the Delta-Mendota Canal in the Northern Part of the San Joaquin Valley, California, 2003-10 (Sneed et al., 2013) presents land subsidence data in the southwestern portion of the Eastern San Joaquin Subbasin from 2007 to 2010. Data for about 100 square miles of the Subbasin were recorded using Interferometric Synthetic Aperture Radar (InSAR) processing, a satellite-based remote sensing technique that can detect ground-surface deformation. Two InSAR techniques were used: conventional InSAR and persistent scatter (PS) InSAR. Both sources of data were collected from the Japanese Aerospace Exploration Agency’s Advanced Land Observing Satellite.

California Department of Water Resources -– DWR has made two InSAR datasets available for SGMA application:

TRE Altamira InSAR point and raster data and the National Aeronautics and Space Administration’s Jet Propulsion ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-30
Agency Information, Plan Area, and Communication November 2024 Laboratory’s (NASA JPL) raster data. Vertical displacement approximations in both datasets are collected by the European Space Agency’s Sentinel-1A satellite. The two different datasets represent two different processing results, one by TRE Altamira Inc. and one by NASA JPL. The TRE Altamira data have coverage between January 2015 and June 2018. Both annual and total raster datasets from TRE Altamira are available and represent interpolations of the vertical displacement point features. The NASA JPL processed dataset spans Spring of 2015 to Summer of 2017 (CA DWR, 2019). The TRE Altamira dataset is mapped in Figure 2-64 and discussed in Section 2.2.5.

There are no DWR or USGS extensometers in the Eastern San Joaquin Subbasin.

1.2.2.5 Groundwater Storage Monitoring
There are no existing programs that conduct regular monitoring specific to groundwater storage in the Eastern San Joaquin Subbasin. The ESJWRM historical model was used to generate estimates for historical groundwater storage based on a series of inputs including historical groundwater elevation data. The ESJWRM generated estimates for current and projected volumes of groundwater in storage based on assumptions for how future conditions may change relative to historical conditions.

1.2.2.6 Interconnected Surface Water Monitoring
There are no existing programs that conduct regular monitoring specific to the interconnection of surface water to groundwater in the Eastern San Joaquin Subbasin. However, surface water monitoring and groundwater level monitoring will be integrated to characterize spatial and temporal exchanges between surface water and groundwater and to estimate potential depletions of surface water caused by groundwater extractions. Additional information on how the depletions monitoring network was developed, monitoring frequency, and summary protocols is provided in Chapter 4: Monitoring Networks. Sources of groundwater level data are described in Section 1.2.2.1. Surface water data on stream flows and levels from stream gages are available from the USGS, CDEC, and local agencies.

1.2.2.7 Other Water Management Programs and Plans
The subsections below contain descriptions of historical and current water management programs and plans, including Integrated Regional Water Management Plans (IRWMPs), Agricultural Water Management Plans (AWMPs), and Urban Water Management Plans (UWMPs) that apply to the Eastern San Joaquin Subbasin.

1.2.2.7.1 Groundwater Management Plan
The Eastern San Joaquin Groundwater Basin Groundwater Management Plan (GMP), developed by the Northeastern San Joaquin County Groundwater Banking Authority in September 2004, was a collaborative effort between local water interests with historically diverse viewpoints to reinforce local control and provide direction for the sustainable development of groundwater resources. The GMP covered a geographic region that included the entire Eastern San Joaquin Subbasin that falls within San Joaquin County but excluded portions within Calaveras and Stanislaus counties to the east. The GMP boundaries were generally defined by the San Joaquin County line to the east, the San Joaquin River to the west, Dry Creek to the north, and the Stanislaus River to the south. A map of the Eastern San Joaquin GMP Region is shown in Figure 1-15.

Now a legacy document superseded by the Eastern San Joaquin GSP, the 2004 GMP provided valuable resources related to potential concepts, projects, and monitoring strategies that were leveraged in the early versions of this GSP (Northeastern San Joaquin County Groundwater Banking Authority, 2004). The following management objectives influenced the development and implementation of the GSP:
• Maintain or enhance groundwater elevations to meet the long-term needs of groundwater users within the Groundwater Management Area
ATTACHMENT 2
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Agency Information, Plan Area, and Communication November 2024 • Maintain or enhance groundwater quality underlying the Basin to meet the long-term needs of groundwater users within the Groundwater Management Area
• Minimize impacts to surface water quality and flow due to continued Basin overdraft and planned conjunctive use
• Prevent inelastic land subsidence due to continued groundwater overdraft Figure 1-15: Eastern San Joaquin GMP Region Setting

1.2.2.7.2 Integrated Regional Water Management Plan
The Eastern San Joaquin Integrated Regional Water Management Plan (Eastern San Joaquin IRWMP) is a collaborative regional planning document that was published in June 2014, with an Addendum released in February 2021. The IRWMP defines and integrates key water management strategies to establish protocols and courses of action to implement the Eastern San Joaquin Integrated Conjunctive Use Program (ICU Program). The ICU Program was designed to implement a comprehensive, prioritized set of projects and management actions to meet adopted ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-32
Agency Information, Plan Area, and Communication November 2024 Best Management Objectives, moving the Eastern San Joaquin County Region toward the goal of sustainable and reliable water supplies (San Joaquin County, 2021).

The following IRWMP objectives related to groundwater use would potentially influence implementation of the GSP:
• Minimize adverse impacts to agriculture, communities, and the environment • Maximize efficiency and beneficial use of supplies
• Protect and enhance water rights and supplies

1.2.2.7.3 Mokelumne Interregional Sustainability Program Report The Mokelumne Watershed Interregional Sustainability Evaluation (MokeWISE) was formed following efforts made by the Mokelumne River Forum over seven years by a diverse set of stakeholders in the Upper and Lower Mokelumne River watersheds, with the objective to develop and evaluate alternatives to optimize water resources management within the Mokelumne-Amador-Calaveras (MAC) and Eastern San Joaquin IRWM planning regions. The plan offers a bi-regional approach by bringing together stakeholders, and it brings together the interregional sections of two IRWM regions identified as the Mokelumne River Forum (San Joaquin GBA, 2015).

The following MokeWISE objectives related to groundwater use would potentially influence implementation of the GSP:
• Groundwater is not considered a viable additional source in Amador and Calaveras counties • The Eastern San Joaquin Subbasin is considered critically overdrafted • Groundwater is not considered a viable additional supply source in Amador and Calaveras counties due to low yield, unreliability, age of groundwater, and limited storage options, although conjunctive use and recharge opportunities may be available

1.2.2.7.4 Agricultural Water Management Plans
AWMPs were developed and adopted by OID, SEWD, SSJID, and WID in 2015 in compliance with SB X7-7 of 2009, which requires certain agricultural water suppliers to prepare an AWMP and implement Efficient Water Management Practices (EWMPs). The Critical EWMPs include:
• Measure the volume of water delivered to customers with sufficient accuracy to comply with requirements of the Water Code
• Adopt a pricing structure based at least in part on quantity delivered (Volumetric Pricing) Applicable Conditional EWMPs that have the benefit of less applied water or increasing system efficiency include:
• Facilitate alternative land use for lands with exceptionally high water duties • Facilitate use of available recycled water
• Facilitate financing of capital improvements for on-farm irrigation systems • Implement an incentive pricing structure that promotes one or more of the goals identified in the Water Code • Expand line or distribution systems, construct regulating reservoirs to increase distribution system flexibility and capacity, decrease maintenance, and reduce seepage
• Increase flexibility in water ordering by, and delivery to, water customers within operational limits ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-33
Agency Information, Plan Area, and Communication November 2024 • Construct and operate supplier spill and tailwater recovery systems • Increase planned conjunctive use of surface water and groundwater • Automate canal control structures
• Facilitate or promote customer pump testing and evaluation • Designate a water conservation coordinator who will develop and implement the water management plan and prepare progress reports
• Provide for the availability of water management services to water users • Evaluate the policies of agencies that provide the supplier with water to identify the potential for institutional changes to allow more flexible water deliveries and storage • Evaluate and improve the efficiencies of the supplier’s pumps The updated 2020 AWMPs provide a framework of management practices to help meet water management goals that align with the goals of the Eastern San Joaquin GSP.

1.2.2.7.5 Urban Water Management Plans
UWMPs are developed by Cal Water, CCWD, City of Lodi, City of Manteca, City of Ripon, City of Stockton, SSJID, and SEWD every five years according to requirements of the Water Code.

Agencies acting as GSAs use the following actions to encourage conservation and efficient use of water:
• Water waste prohibition ordinances
• Metered distribution systems
• Tiered water rates and conservation pricing
• Public education and outreach efforts
• Water conservation program coordination and staffing support • Free residential plumbing retrofit devices
• Washing machine rebate program

1.2.2.8 Canal Diversions and Seepage
Canal seepage in the Eastern San Joaquin Subbasin is tracked on a district-by-district basis. All of the major irrigation districts utilize a combination of natural watercourses, canals, and pipelines to distribute surface water diversions to their customers.

OID diverts water from the Stanislaus River at Goodwin Reservoir through the Joint Main Canal on the north side and the South Main Canal on the south side. Approximately 330 miles of laterals carry water to landowners off of the main canals. While the entire lateral system historically consisted of open, unlined ditches, 100 miles of the laterals have been converted to pipelines; 105 miles are open, concrete-lined ditches; and the rest remain unlined. Approximately 40 percent of the OID service area is within the Eastern San Joaquin Subbasin.

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2024 Groundwater Sustainability Plan Amendment 1-34
Agency Information, Plan Area, and Communication November 2024 In SSJID, similarly, the primary source of recharge in the groundwater system is conveyance seepage and deep percolation of applied water. SSJID diverts from the Stanislaus River initially and then sends the water through a system of lateral canals to its customers. Like OID, the entire system was open and unlined, but over time it has been slowly concrete lined and replaced with buried pipelines.

SEWD uses two unlined canal systems to deliver water from the Stanislaus River: Upper Farmington Canal and Lower Farmington Canal. SEWD also uses natural watercourses to distribute their water, such as rivers, creeks, and sloughs.

CSJWCD also uses the Upper Farmington Canal for distribution, as well as natural watercourses within its boundaries.

Historically, WID has also made efforts to improve the efficiency of the delivery infrastructure it maintains. Water for WID is diverted from the Mokelumne River and from the Delta at the end of Beaver Slough. In 2015, WID had about 100 miles of lined and unlined canals, and pipelines.

Canal seepage, generally considered a loss to districts in the short term, provides groundwater recharge and has played and will continue to play a crucial role in the long-term sustainability of groundwater resources in the Eastern San Joaquin Subbasin.

1.2.2.9 Conjunctive Use Programs Prior to SGMA Implementation Conjunctive use is the use of surface water to allow the Subbasin to recharge and store additional water supply, either through in-lieu use or direct recharge. This section describes conjunctive use programs that were in place in the Eastern San Joaquin Subbasin prior to the beginning of SGMA implementation in 2020, including both in-lieu recharge and direct recharge projects.

In-lieu recharge occurs for both agricultural and municipal purposes wherever surface water is being delivered to offset the use of groundwater. Agencies that conducted in-lieu recharge prior to SGMA implementation include CCWD, City of Lodi, City of Manteca, City of Stockton, CSJWCD, OID, SEWD, SSJID, and WID. Riparian users of surface water also benefit from in-lieu recharge.

Direct recharge projects existed in NSJWCD and SEWD, as shown below in Figure 1-16. NSJWCD’s Tracy Lake Groundwater Recharge Project includes direct recharge of 500 to 1,000 AF/year by placing surface water in the bed of South Tracy Lake to allow for percolation. The Cal-Fed/Costa Recharge project includes direct recharge of about 300 AF/year by flooding about 20 acres of vineyards post-harvest. NSJWCD is expanding these programs to add additional in-lieu and direct recharge projects in its service area. SEWD’s Farmington Groundwater Recharge Program was developed in 2001 with a conceptual plan to recharge surface water via field flooding on about 1,200 acres. SEWD has operated a 60-acre recharge site since 2003 as a result of the Farmington Program with additional 73 acres added in 2020. The observed recharge amount ranges from 2,800 AF/year to 5,800 AF/year with an average of 4,400 AF/year for a total recharge volume of about 65,000 AF since the inception of the project. SEWD also has several wells to pump some of this recharged water for municipal supply during especially dry years.

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Agency Information, Plan Area, and Communication November 2024 Figure 1-16: Locations of Groundwater Recharge Projects Prior to SGMA Implementation

1.2.3 Land Use Elements or Topic Categories of Applicable General Plans

1.2.3.1 General Plans in the Plan Area
San Joaquin County has jurisdiction over land use planning for the majority of the surface area of the Subbasin.

Stanislaus County, Calaveras County, and the incorporated cities of Stockton, Manteca, Lodi, Ripon, and Escalon make up the remaining area. Implementation of the Eastern San Joaquin GSP may be affected by the policies and regulations outlined in the San Joaquin County General Plan, as well as the General Plans for the five cities, given that the long-term land use planning decisions that would affect the Subbasin are under the jurisdiction of the counties and respective cities.

This section describes how implementation of the various General Plans may change water demands in the Subbasin, how the General Plans may influence the GSP’s ability to achieve sustainable groundwater use, and how the GSP may affect implementation of General Plan land use policies. Policies outlined in the General Plans that will potentially influence implementation of the GSP are discussed below and listed in Appendix 1-F.

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Agency Information, Plan Area, and Communication November 2024

1.2.3.1.1 San Joaquin County General Plan
The San Joaquin County General Plan describes the official county “blueprint” on the location of future land use, type of development encouraged, and decisions regarding resource conservation. Stakeholder input informed the development of the county’s vision and guiding principles, which represent the county’s core values and establish benchmarks for the General Plan’s goals and policies. The General Plan encourages preservation of the San Joaquin County’s groundwater resources and states that future urban and agricultural growth should occur within the sustainable capacity of these resources (SJC, 2016b).

1.2.3.1.2 Calaveras County General Plan
The Calaveras County General Plan has provided a framework for growth and development in Calaveras County. The Calaveras County General Plan, initially developed in 1996, underwent an extensive update process in collaboration with local stakeholders and policymakers to understand the challenges facing the community and to enact a common vision for the future. This update, with its various elements, was finalized in 2019. (The Housing Element was finalized in 2023.)
The Calaveras County General Plan recognizes that water is a limited and valuable resource and that the region is experiencing localized problems with both water supply and quality. To mitigate these issues, the General Plan delineates policies and goals that promote sustainable water resources management in the region (Calaveras County, 2019).

1.2.3.1.3 Stanislaus County General Plan
The Stanislaus County General Plan provides a comprehensive, long-term plan to guide development within the Stanislaus County boundaries through 2035. The General Plan was updated and adopted in 2016 to reflect the evolving conditions of the region. While Stanislaus County’s economic base remains predominantly agricultural, the county's land use and economy continue to diversify in response to increased pressure to convert productive agricultural lands to non-agricultural uses. To address the region’s changing water needs, the Stanislaus County General Plan supports goals, policies, and implementation measures that promote sustainable water management and protect the local groundwater sources (Stanislaus County, 2016).

1.2.3.1.4 City of Stockton General Plan
The City of Stockton General Plan establishes the City’s 2040 vision and provides supporting goals, policies, and actions needed to achieve it. The General Plan for the 2040 vision was built upon the prior 2035 Stockton General Plan (adopted in 2007) and was a collaborative process that involved a diverse group of stakeholders and interests. The General Plan update incorporated feedback from City Council study sessions, Planning Commission study sessions, community workshops, and numerous other public meetings and outreach events (City of Stockton, 2016).

The City of Stockton’s General Plan recognizes that groundwater supplies are vital to Stockton’s ability to meet current and future water demands. The city has focused attention on optimizing available surface water supplies and cooperating with agencies in the region to manage the groundwater resources at a sustainable yield and to address regulatory pressures, droughts, and saline intrusion (City of Stockton, 2016).

1.2.3.1.5 City of Lodi General Plan
The City of Lodi General Plan Update, published in 2010, outlines a vision for Lodi’s future and provides a set of policies and programs that guide community growth and development. The 2010 General Plan Update replaced the 1991 General Plan and was informed by input from community members and stakeholders who participated in the planning process through different avenues, including public workshops and meetings, mail surveys, interviews, presentations, and newsletters (City of Lodi, 2010).

ATTACHMENT 2
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Agency Information, Plan Area, and Communication November 2024 The General Plan recognizes that groundwater contamination and overdraft in the Eastern San Joaquin Subbasin can threaten the city’s ability to meet current water demands and limit future development (City of Lodi, 2010).

1.2.3.1.6 City of Manteca General Plan
The City of Manteca adopted the current Manteca General Plan in February 2024 to reflect the current conditions of the city. This recent version updated the 2003 General Plan and was the result of a collaborative process between community members, city staff, and decision-makers to produce a General Plan that is current, progressive, flexible, and viable. The General Plan Update also reevaluates the existing vision for Manteca through 2040, incorporates new planning strategies, and brings the General Plan into compliance with recent social and environmental justice policies and laws (City of Manteca, 2024).

The Manteca General Plan Update recognizes that groundwater is a large source of potable water supply for the city and that the Eastern San Joaquin Subbasin is in overdraft. To address groundwater overdraft in the city, a significant number of policies in the General Plan promote increased understanding of the Eastern San Joaquin Subbasin.

1.2.3.1.7 City of Escalon General Plan
The Escalon General Plan was developed by the city in 1994 and updated in 2010 to reflect the most current conditions of the city and to provide comprehensive planning for future development. The Escalon General Plan was developed through a cooperative effort involving the City Council and Planning Commission, city staff and their consultants, and stakeholders (City of Escalon, 2010). The Escalon General Plan delineates policies that support the long-term preservation of water supplies and water quality in the Eastern San Joaquin Subbasin (City of Escalon, 2010).

1.2.3.1.8 City of Ripon General Plan
The City of Ripon’s General Plan was updated in 2006 to guide the use of private and public lands within the community’s boundaries through 2040. The General Plan update provides a framework for promoting growth and reevaluates where growth should be located. The General Plan development process was informed by community members representing a wide variety of interests, city department heads, and staff representatives of public agencies (City of Ripon, 2006).

The General Plan supports the preservation of groundwater quantity and quality as it is an important source of water supply for the City of Ripon. Future development within the planning area is expected to have minimal effects on groundwater supplies, although it is unknown how development will impact groundwater quality. The General Plan predicts that the City of Ripon may have to abandon a large number of wells as sources of potable water due to localized contamination, and, as a result, additional development may be prohibited until an adequate source of potable water can be identified. Surface water is expected to meet water demands for surrounding agricultural uses (City of Ripon, 2006).

1.2.3.2 Effect of GSP Implementation on Applicable General Plans The General Plans in the Subbasin provide guidelines to facilitate anticipated growth within the sustainable capacity of existing resources. Successful land use planning also promotes sustainable water supply and use within the region.

Due to the complementary nature of the General Plans and the GSP, the goals and policies in the General Plans support the ability of the GSAs to achieve sustainability.

Implementation of the GSP, including changes in groundwater management, may influence the type of land use and location of future development, depending on the level of changes set forth by the GSP, such as enacted programs, plans, and policies. While General Plan implementation may result in land use changes and changes in water consumption, minimal change in water demand is expected from GSP implementation. The potential for future management actions, which could impact water supplies and development, is discussed in Section 6.5. Most of the land within the Eastern San Joaquin Subbasin is currently developed to some use, and conversion from agricultural ATTACHMENT 2
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Agency Information, Plan Area, and Communication November 2024 uses to urban uses is not anticipated to increase water demand. However, conversion from agriculture to urban use may have an effect on water source, depending on the location in the Subbasin, and may shift supply from groundwater to surface water.

1.2.3.3 Land Use Plans Outside the Plan Area
Land use decisions in neighboring areas experiencing overdraft are likely to affect groundwater conditions in the Eastern San Joaquin Subbasin. Ongoing coordination with neighboring groundwater subbasins will include updates on major land use planning that may impact the groundwater system. The cities of Tracy, Lathrop, Modesto, Galt, and Elk Grove are the largest urban areas neighboring the Eastern San Joaquin Subbasin. The portions of the Tracy and the Delta-Mendota Subbasins that are adjacent to the Eastern San Joaquin Subbasin are also located within San Joaquin County. These land use planning areas are covered by the San Joaquin County General Plan described in Section

1.2.3.1.1. The City of Tracy, located within San Joaquin County and the Tracy Subbasin, updated its General Plan in 2011. The City of Tracy General Plan identifies the Tracy Subbasin as a source of water supply for the city. The City of Tracy is working towards reducing its reliance on groundwater and reserving its use for emergency situations and droughts (City of Tracy, 2011).

The City of Lathrop, located within San Joaquin County and the Tracy Subbasin, relies on potable water supplies consisting of a combination of groundwater and treated surface water from the South County Water Supply Program.

The General Plan for the City of Lathrop was first adopted in 1991 and last amended in 2022. The General Plan reflects the city’s long-range aspirations by defining goals and policies for current and future development and by providing guidance on proposed projects.

The City of Modesto, located in Stanislaus County, relies on the Modesto and Turlock Subbasins for its groundwater supplies. The City of Modesto General Plan, last updated in March 2019, identifies historical declining groundwater levels as a result of increased urban demands. While steps have been taken to address groundwater levels, the General Plan calls for continued protection and conservation of groundwater sources while pursuing additional water supplies to meet continued growth (City of Modesto, 2019).

The City of Galt, located in Sacramento County, is on the southern edge of the Cosumnes Subbasin and last updated its General Plan in 2009. Groundwater from the Cosumnes Subbasin is the sole source of water supply for the city.

The General Plan outlines policies to ensure groundwater availability and protection (City of Galt, 2009).

The City of Elk Grove, located in Sacramento County, relies heavily on groundwater from the South American Subbasin. To address years of drought conditions and low precipitation, the City of Elk Grove Draft General Plan outlines several goals and policies to protect groundwater supplies while meeting increased water demands from agricultural production and a growing population (City of Elk Grove, 2018).

1.2.3.4 Well Permitting
On 28 March 2022, Governor Newsom signed Executive Order (EO) N-7-22 to amend prior proclamations of states of emergency due to California’s ongoing drought conditions. EO N-7-22 required that additional steps be taken by well permitting agencies to approve a permit for the construction of a new well or alternation of an existing well located in a medium- or high- priority basin subject to SGMA. For applicable wells, permitting agencies must obtain written verification from the GSA managing the area of the basin where the proposed well is to be located that the well would not conflict with the GSP or decrease the likelihood of the basin reaching its Sustainability Goal. EO N-7-22 was subsequently rescinded once the drought-related state of emergency was lifted.

On 13 February 2023, Governor Newsom signed EO N-3-23 to keep in place some of the provisions originally contained EO N-7-22 One of the provisions retained by EO N-3-23 is the requirement that well permitting agencies not approve a permit for a new well or alteration of an existing well without first obtaining written verification of GSA approval that ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-39
Agency Information, Plan Area, and Communication November 2024 groundwater extraction by the proposed well would not be inconsistent with the GSP and the programs it contains. The EO exempts de minimis new wells and new wells that replace existing, actively permitted wells with wells that will produce an equivalent quantity of water when the existing well is being replaced because it has been acquired by eminent domain or while under threat of condemnation.

The Basin GSAs are working with the permitting agencies (i.e., counties) to review and provide written verifications for permit applications within their jurisdictions as required under the EO. As described above, several counties have already amended their well permitting processes to incorporate GSA verification.

1.2.3.4.1 San Joaquin County
San Joaquin County oversees a well permitting program for any new, replacement, back-up, and de minimis well construction. The purpose of this program is to prevent groundwater contamination and safety hazards by regulation of the location, construction, repair, and destruction of water supply, monitoring, and geophysical wells and borings.

Pursuant to Water Code §13808, all new wells that do not meet the exemption criteria must submit additional information prior to the issuance of a permit by the Environmental Health Department. The permit program is enforced by Ordinance Code of San Joaquin County §9-1115, and Municipal Codes of Stockton, Lodi, Manteca, Tracy, Escalon, and Ripon. Applicants must provide information about groundwater elevation estimates, land elevation estimates, extraction volume estimates, depth of Corcoran Clay, and other basic well characteristics.

San Joaquin County has established water well standards for new wells that define property line setbacks (at least 10 feet depending on well type), casing perforations, gravel packing, well seals, backflow prevention, disinfection requirements, sampling taps, and more, as well as the requirement for installing monitoring device(s) for groundwater extraction, elevation, and/or water quality. Other setbacks for potential sources of contamination or pollution require at least 50 feet depending on the contamination source and well type.

The San Joaquin County Well Standards outline well grouting and construction standards to prevent contamination, pollution, and degradation of water wells and of the groundwater by intrusion of poor-quality water. Wells must have a watertight annular seal near the land surface to keep surface water and other potential contamination out of the well.

The minimum depth of the annular seal depth for wells in San Joaquin County is summarized in Table 1-1 (SJC EHD, 1993).

Table 1-1: Minimum Depth of Seal Below Ground Surface
for Wells in San Joaquin County
Well Type Feet
Public Water Supplies 100
Individual Domestic Well 100
Industrial Wells 100
Agricultural Wells 50
In response to EO N-3-23, San Joaquin County updated its well permitting process to require applicants to fill out either a Well Exemption Statement (for exempt wells) or a New Well Information Form (for non-exempt wells). For non-exempt wells, the New Well Information Form is forwarded with the rest of the application to the applicable GSA for review and consideration for a written verification.

1.2.3.4.2 Calaveras County
The Calaveras County Board of Supervisors adopted a well construction and destruction ordinance in 1998. The ordinance mandates that a permit must be obtained from the Calaveras County Environmental Health Department prior to development or modification of any well within the Calaveras County boundaries. The purpose of the program is to regulate the construction, alteration, abandonment, and destruction of wells such that groundwater will not be ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-40
Agency Information, Plan Area, and Communication November 2024 contaminated and that groundwater supplies will not jeopardize the health, safety, or welfare of Calaveras County residents.

To prevent polluted or contaminated water from entering the well, the well program established a minimum depth at which the annular space should be filled as well as minimum horizontal setback requirements. Horizontal setbacks from property lines range from 10 feet (for small parcels) to 150 feet (for underground storage with nearby wells at least 25 feet away). The minimum annular seal depths for wells in Calaveras County are summarized in Table 1-2 (Calaveras County Board of Supervisors, 2008).

Table 1-2: Minimum Depth of Seal Below Ground Surface for Wells in Calaveras County Well Type Feet
Public drinking water well 50
Commercial well 50
Industrial well 50
Individual domestic well 20
Agricultural well 20
Vertical geothermal exchange wells 20
Wells within 25 feet of a water way 20 feet below the bed of the water way In response to EO N-3-23, Calaveras County updated its well permitting process to require applicants to fill out either a Well Exemption Statement (for exempt wells) or a New Well Information Form (for non-exempt wells). For nonexempt wells, the New Well Information Form is forwarded with the rest of the application to the applicable GSA for review and consideration for a written verification.

1.2.3.4.3 Stanislaus County
Pursuant to Chapter 9.36 of the Stanislaus County Code, well owners must first receive a valid permit from Stanislaus County to construct, install, repair, or destroy any well or well seal within the county. Stanislaus County DER is responsible for reviewing the applications and issuing permits. The Stanislaus County Code also states that all wells must have an annular seal, except for agricultural wells that are not used for domestic purposes and are located more than 300 feet from a domestic well (Stanislaus County, 2019a).

In 2014, the DER adopted a groundwater ordinance to prohibit unsustainable extraction of groundwater in unincorporated areas of the county. The DER reviews each well permit application and determines whether the well is subject to, or exempt from, the prohibitions in the Groundwater Ordinance. Permit applications for wells intended to extract 2 AF/year of groundwater or less are exempt from the prohibitions in the groundwater ordinance (Stanislaus County, 2019b). If the permit applicant is not exempt, a non-exempt wells supplemental application must be submitted and show that the groundwater pumped from the well is being sustainably extracted and will not cause any of the “Undesirable Results” listed in § 97.030 (9) of the groundwater ordinance. Additional permit application fees may be required, and the application review is conducted at the expense of the applicant (Stanislaus County, 2019c).

The minimum annular seal depths for wells in Stanislaus County are summarized in, and are consistent with the state well standards (CA DWR, 1991).

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-41
Agency Information, Plan Area, and Communication November 2024 Table 1-3: Minimum Depth of Seal Below Ground Surface for Wells in Stanislaus County Well Type Feet
Community water supply well 50
Industrial well 50
Individual domestic well 20
Agricultural well 20
Air conditioning well 20
All other types 20
In response to EO N-3-23, Stanislaus County updated its well permitting process to refer applicable well permits to the GSAs for approval. If a GSA finds that a well permit application is not consistent with requirements in its GSP to prevent Undesirable Results, the applicant must provide substantial evidence that the proposed extraction is will not cause or contribute to their occurrence in accordance with Stanislaus County’s Discretionary Well Permitting Implementation Guidelines.

1.2.3.4.4 Sacramento County
Sacramento County, which borders the northern boundary of the Eastern San Joaquin Subbasin (see Figure 1-6), oversees well permitting within their jurisdiction and requires property owners to obtain a permit for work including well construction, modification, repair, inactivation, destruction, installation, and replacement. Each well or pump requires its own permit application and fee, but waivers can be considered for multiple wells or exploratory borings of similar construction (Sacramento County, 2019).

The Sacramento County Code water well standards are designed to meet or exceed the water well standards in DWR’s Bulletin 74-81 and 74-90. These standards apply to all types of monitoring wells, vapor extraction wells where applicable, and any other well installed in an area where special precautions are necessary to protect groundwater quality. The Sacramento County Environmental Management Department has the power under special circumstances to grant a variance from provisions in Chapter 6.28 of the Sacramento County Code and to prescribe alternative requirements in their place (Sacramento County, 2019).

The minimum annular seal depth for wells in Sacramento County is 50 feet for all well types, except for in cases of special approval (Sacramento County, 2019).

1.2.4 Additional GSP Elements
The Additional GSP Elements section of the GSP provides GSAs with the opportunity to discuss “any additional Plan elements included in Water Code §10727.4 that the Agency determined to be appropriate”. These additional elements include:
• Control of saline water intrusion
• Wellhead protection areas and recharge areas
• Migration of contaminated groundwater
• A well abandonment and well destruction program
• Replenishment of groundwater extractions
• Activities implementing, opportunities for, and removing impediments to, conjunctive use or underground storage
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-42
Agency Information, Plan Area, and Communication November 2024 • Well construction policies
• Measures addressing groundwater contamination cleanup, groundwater recharge, in-lieu use, diversions to storage, conservation, water recycling, conveyance, and extraction projects • Efficient water management practices, as defined in Water Code §10902, for the delivery of water and water conservation methods to improve the efficiency of water use • Efforts to develop relationships with state and federal regulatory agencies • Processes to review land use plans and efforts to coordinate with land use planning agencies to assess activities that potentially create risks to groundwater quality or quantity • Impacts on groundwater dependent ecosystems
Each of the Additional Elements listed are relevant and important to the Eastern San Joaquin Subbasin, and are discussed throughout this GSP, as identified below.

Control of saline water intrusion – Section 2.2.3 describes the current status of saline water intrusion in the Subbasin.

Section 3.2.4 addresses seawater intrusion as a sustainability indicator. Actions to identify and monitor for saline water intrusion is described in Section 3.3.3.

Wellhead protection areas and recharge areas – Section 1.2.3.4 addresses wellhead protection programs in San Joaquin County, Calaveras County, and Stanislaus County.

Migration of contaminated groundwater – The migration of contaminated groundwater that may impair water supplies is addressed in Section 3.3.3.

A well abandonment and well destruction program – Requirements and procedures for well destruction and abandonment are discussed in Section 1.2.3.4.

Replenishment of groundwater extractions – Proposed projects and management actions that will facilitate replenishment of groundwater extraction are discussed in Chapter 6: Projects and Management Actions. Areas where potential groundwater replenishment could occur through direct recharge are described in Section 2.1.4.5.

Activities implementing, opportunities for, and removing impediments to, conjunctive use or underground storage – Existing conjunctive use projects are identified in Section 1.2.2.9. The proposed projects and management actions that will address implementing, opportunities for, and removing impediments to, conjunctive use or underground storage projects in the Subbasin are discussed in Chapter 6: Projects and Management Actions.

Well construction policies – Section 1.2.3.4 addresses well construction policies in San Joaquin County, Calaveras County, and Stanislaus County. Annular well seal depth requirements are tabulated in Tables 1-1, 1-2, and 1-3.

Measures addressing groundwater contamination cleanup, groundwater recharge, in-lieu use, diversions to storage, conservation, water recycling, conveyance, and extraction projects – Proposed projects and management actions that address groundwater recharge, in-lieu use, diversions to storage, conservation, and water recycling are discussed in Chapter 6: Projects and Management Actions.

Efficient water management practices, as defined in Section 10902, for the delivery of water and water conservation methods to improve the efficiency of water use – Ongoing efforts to implement efficient water management practices are described in Section 1.2.2.7. Conservation methods and efficiency of water use are also noted in many local or regional general plans, detailed in Section 1.2.3. Projects relevant to this topic are discussed in Chapter 6: Projects and Management Actions.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-43
Agency Information, Plan Area, and Communication November 2024 Efforts to develop relationships with state and federal regulatory agencies – A strong relationship between the GSAs and existing regulatory agencies is valuable to the success of this GSP. Efforts to develop this relationship are described in Chapter 7: Plan Implementation.

Processes to review land use plans and efforts to coordinate with land use planning agencies to assess activities that potentially create risks to groundwater quality or quantity – Summaries of land use plans both inside the Subbasin and in nearby Subbasins can be found in Section 1.2.3. Efforts are being made at the local level to develop a formal opportunity for GSAs to provide input on the land use and water-related elements of future General Plans and California Environmental Quality Act (CEQA) documentation to promote consistency with the GSP.

Impacts on groundwater dependent ecosystems – Groundwater dependent ecosystems (GDEs) are defined in Section 2.2.7. The methodology for identifying GDEs can be found in Section 2.2.7.1. A map of identified GDEs in the Subbasin is shown in Section 2.2.7.2. Adverse impacts to GDEs are described under Depletions of Interconnected Surface Water, Section 3.3.6, as part of the undesirable results discussion.

1.3 NOTICE AND COMMUNICATION

1.3.1 Beneficial Uses and Users in the Basin
The CVRWQCB designates all groundwaters in the Sacramento River Basin and San Joaquin River Basin as suitable or potentially suitable, at a minimum, for municipal and domestic water supply, agricultural supply, industrial service supply, and industrial process supply (CVRWQCB, 2016).

As listed in Water Code §10723.2, beneficial uses and users of groundwater in the region include the following interests:
• Agricultural users and domestic well owners that hold overlying groundwater rights. • Public water systems/municipal well operators in the Subbasin. • Community water systems (wells serving 15 or more connections or more than 25 people per day). 433 community water systems were identified in the Eastern San Joaquin Subbasin and are presented in Appendix 1-E Of these 433 community water systems, 182 are located in DAC or SDAC areas, shown also in Appendix 1-E.
• Local agencies that have land use planning jurisdiction. These include counties of San Joaquin, Calaveras, and Stanislaus, and cities of Stockton, Lodi, Manteca, Escalon, and Ripon. • Environmental users of groundwater, including species and habitat reliant on instream flows, as well as wetlands and GDEs. Identified GDEs are mapped in Figure 2-69 in Section 2.2.7.2. Freshwater species in the Eastern San Joaquin Subbasin are listed in Appendix 1-G. • Irrigation districts in the Subbasin that divert surface water to deliver to their customers. • Lands managed by the federal government. The San Joaquin River National Wildlife Refuge lies just outside of the Subbasin boundary. While managed by the State of California, Caswell Memorial SP is in the Subbasin and Carnegie SVRA and Franks Tract SRA are situated just outside of the Subbasin. • DACs and SDACs. DACs and SDACs are mapped in Figure 1-8 and are primarily in the western portions of the Subbasin. Approximately 27 percent of the Subbasin area is considered disadvantaged and 5.4 percent is considered severely disadvantaged. 33 percent of the Subbasin population is considered either DAC or SDAC; within that, 16.5 percent of the population is SDAC. DACs include the following census designated ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-44
Agency Information, Plan Area, and Communication November 2024 places (CDPs)1: Stockton City CDP, Terminous CDP, Taft Mosswood CDP, and French Camp CDP. Severely disadvantaged communities include: Kennedy CDP, August CDP, Garden Acres CDP, and Thornton CDP. • Entities that monitor and report groundwater elevations. Monitoring in the Subbasin is extensive. A list of monitoring agencies can be found in Section 1.2.2.
• California Native American tribes

1.3.2 List of Public Meetings Where the 2024 GSP was Discussed During the 2024 update of the ESJ GSP, meetings of the ESJGWA Board and Steering Committee were open to the public with meeting information noticed, as appropriate, and posted to the ESJGWA website (discussed below in Section 1.3.4.2.2). In addition, public meetings and an informational open house event were held throughout the GSP update process (see Section Error! Reference source not found.).

Below is a list of the public meetings where elements of this 2024 GSP Amendment were discussed.

Meeting Type Date
Steering Committee Meeting November 8, 2023
Steering Committee Meeting December 13, 2023
ESJGWA Board Meeting January 10, 2024
Steering Committee Meeting March 13, 2024
ESJGWA Board Meeting March 13, 2024
Steering Committee Meeting April 10, 2024
ESJGWA Board Meeting June 12, 2024
Stakeholder Advisory Workgroup
Meeting #1
June 27, 2024
Stakeholder Advisory Workgroup
Meeting #2
July 17, 2024
Steering Committee Meeting August 14, 2024
ESJGWA Board Meeting August 14, 2024
1 A census designated place is a concentration of population identified by the United States Census Bureau for statistical purposes. CDPs are delineated for each decennial census as the statistical counterparts of incorporated places, such as cities, towns, and villages.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-45
Agency Information, Plan Area, and Communication November 2024 Meeting Type Date
Steering Committee Meeting September 11, 2024
GSA Open House September 25, 2024
ESJGWA Board Meeting December 11, 2024

1.3.3 Decision-Making Process
The ESJGWA Board is tasked with the vote and approval of policy decisions for the development and implementation of this GSP. The ESJGWA Board receives input from the Steering Committee, the PMC, and the public, as described in Section 1.1.4.2.

The governing bodies of each of the individual GSAs take action and provide direction to their Board member representatives and must individually adopt the final GSP Amendment. Projects will be administered by the GSA project proponents. Although the ESJGWA does not provide direct authority to require GSAs to implement projects, the ESJGWA will be working on GSA-level water budgets and evaluating the best ways to evaluate progress. Work toward implementing projects and management actions is further described in Sections 6.2 and 6.3, respectively. If the implementation of projects is not sufficient to achieve sustainability goals, a demand management policy, included as a management action in the 2024 GSP Amendment, provides a framework for how the GSAs of the Subbasin plan to achieve sustainability through other means. A description of the agencies that comprise the GSAs can be found in Section 1.1.4.3.

1.3.4 Opportunities for Public Engagement and How Public Input was Used Throughout the process of the initial development of the GSP and this particular update, the ESJGWA engaged both stakeholders and the public. This effort has been greatly aided by the facilitation support provided through DWR’s Facilitation Support Services Program. In some cases, outreach and engagement opportunities were specific to the initial development of the 2020 GSP; these are detailed in Section 1.3.4.1. In other cases, outreach and engagement opportunities began during the 2020 GSP development process and have been adapted or modified for this 2024 GSP Amendment; these are discussed in Section 1.3.4.2.

1.3.4.1 Opportunities Specific to the 2020 GSP Development Process

1.3.4.1.1 Groundwater Sustainability Workgroup
When developing the initial 2020 GSP, the ESJGWA convened a Workgroup in order to promote stakeholder input and relied upon the Workgroup when developing the 2020 GSP. The Workgroup began with an application process to ensure a diverse cross section of populations were represented to serve on the Workgroup. Workgroup members participated and provided valuable input throughout the 2020 GSP development process.

Applications were distributed to organizations within every GSA to establish a Workgroup that represented the region’s broad interests, perspectives, and geography. The Workgroup included members from a variety of organizations who represent one or more of the interested parties’ groups. Table 1-4 lists the organizations and interests represented on the Workgroup. While this Workgroup was not active during the 2024 GSP amendment process, the information collected during their involvement remains relevant and a guiding factor in this update and GSP implementation activities.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-46
Agency Information, Plan Area, and Communication November 2024 Table 1-4: Groundwater Sustainability Workgroup Interests (Collected During Development of 2020 GSP) Eastern San Joaquin Groundwater Authority
Groundwater Sustainability Workgroup – Interests Represented AG
CM
ENV
FM
GU
Agricultural
Community Neighborhood
Environmental
Flood Management
Groundwater User
BUS
DAC
INST
NA
Business
Disadvantaged Communities
Institutional
Native American
Role/Organization AG BUS CM DAC ENV FM GU INST NA Application Notes 2Q Farming ✓ ✓ ✓
2Q Farming is interested in making a
difference for agriculture and communities,
and in preserving water rights for future
generations so they will have the ability to
irrigate and access the water necessary for
life.

Agricultural Business – Farmer
Representative
✓ ✓ ✓ ✓ ✓ ✓ ✓
As a representative of agricultural business,
this member sees SGMA as an opportunity to
manage the Subbasin while keeping
jurisdiction, implementation, monitoring, and
oversight at the local level.

Calaveras County Resource
Conservation District ✓ ✓ ✓ ✓ ✓ ✓ ✓
Calaveras County RCD hopes to partner with
groundwater users in the western part of
Calaveras County to address sustainability
and recharge.

California Sportfishing Protection Alliance ✓ ✓ ✓ ✓ ✓
California Sportfishing Protection Alliance,
longtime Mokelumne River stakeholder, is
interested in reducing groundwater overdraft,
managing surface water responsibly, and
resolving longstanding conflicts.

Representative is interested in the technical
aspects of groundwater management and
gaining a better understanding of recharge.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-47
Agency Information, Plan Area, and Communication November 2024 Eastern San Joaquin Groundwater Authority
Groundwater Sustainability Workgroup – Interests Represented AG
CM
ENV
FM
GU
Agricultural
Community Neighborhood
Environmental
Flood Management
Groundwater User
BUS
DAC
INST
NA
Business
Disadvantaged Communities
Institutional
Native American
Role/Organization AG BUS CM DAC ENV FM GU INST NA Application Notes Catholic Charities of the Diocese of
Stockton ✓ ✓ ✓ ✓ ✓
The Environmental Justice Program of the
Catholic Charities of the Diocese of Stockton
works with disadvantaged communities.

Some of these communities have concerns
regarding drinking water quality and toxic
contamination of groundwater supplies.

Environmental Justice Coalition for Water ✓ ✓ ✓ ✓
The Environmental Justice Coalition for Water
is interested in ensuring that environmental
justice interests are present, informed, and
meaningfully engaged in a process that bears
considerable importance for health, wealth,
and growth.

J.R. Simplot Co. ✓ ✓ ✓
As a local industry representative with a stake
in groundwater quality, this representative
sees benefit in being part of the stakeholder
process.

Lima Ranch ✓ ✓ ✓ ✓ ✓
Lima Ranch views water as a precious
commodity that must be conserved and used
sustainably. Representative values preserving
water rights and using water efficiently.

Machado Family Farms ✓ ✓ ✓
Representative manages a family farm and
brings agricultural experience and experience
with the California Public Utilities Commission
to provide a balanced perspective.

Manufacturers Council of the Central Valley ✓ ✓ ✓ ✓ ✓
Through their involvement as a stakeholder,
Manufacturer's Council of the Central Valley
provides resources to manufacturers
impacted by the implementation of GSPs and
to GSAs looking to work with the sector.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-48
Agency Information, Plan Area, and Communication November 2024 Eastern San Joaquin Groundwater Authority
Groundwater Sustainability Workgroup – Interests Represented AG
CM
ENV
FM
GU
Agricultural
Community Neighborhood
Environmental
Flood Management
Groundwater User
BUS
DAC
INST
NA
Business
Disadvantaged Communities
Institutional
Native American
Role/Organization AG BUS CM DAC ENV FM GU INST NA Application Notes Restore the Delta ✓ ✓ ✓ ✓ ✓
Representative is interested in the link
between surface water flows for the
Sacramento-San Joaquin Delta and
groundwater management. Additionally, this
member brings connections for broad
environmental justice outreach.

San Joaquin Audubon ✓
San Joaquin Audubon is interested in overall
water use and environmental issues.

San Joaquin County Environmental Health
Department
✓ ✓ ✓
The San Joaquin County Environmental
Health Department plays a role in protecting
the area's groundwater resource, drinking
water, and public health.

San Joaquin Farm Bureau ✓ ✓ ✓ ✓ ✓
The San Joaquin Farm Bureau is interested in
helping manage and utilize the groundwater
reservoir to better supply all needs for the
short and long term.

Sequoia ForestKeeper ✓
Sequoia ForestKeeper has been submitting
comments on water-related issues to the
SWRCB since 2015.

Sierra Club - Delta-Sierra Group ✓ ✓ ✓ ✓ ✓ ✓
Sierra Club cares about the future of the
Eastern San Joaquin Subbasin and
sustainability. They believe that
representation of individuals is lacking and
there is insufficient outreach.

Spring Creek Golf & Country Club ✓ ✓ ✓ ✓ ✓
Representative is golf course superintendent
at Spring Creek Golf & Country Club and is
interested in groundwater rights and
contributing to the stakeholder Workgroup.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-49
Agency Information, Plan Area, and Communication November 2024 Eastern San Joaquin Groundwater Authority
Groundwater Sustainability Workgroup – Interests Represented AG
CM
ENV
FM
GU
Agricultural
Community Neighborhood
Environmental
Flood Management
Groundwater User
BUS
DAC
INST
NA
Business
Disadvantaged Communities
Institutional
Native American
Role/Organization AG BUS CM DAC ENV FM GU INST NA Application Notes The Hartmann Law Firm ✓ ✓ ✓ ✓ ✓
Representative is Advisory Water
Commissioner, District Counsel for multiple
reclamation districts.

The Wine Group ✓ ✓ ✓ ✓
The Wine Group has technical knowledge
and provides a unique viewpoint that supports
the successful development of a GSP for the
Eastern San Joaquin Subbasin.

Trinchero Family Estates and Sutter Home
Winery
✓ ✓ ✓ ✓ ✓
Trinchero Family Estates and Sutter Home
Winery is interested in helping develop a
balanced approach for communities and
businesses.

University of the Pacific ✓ ✓ ✓
Representative is an Emeritus Professor of
Operations/Engineering Management at the
University of the Pacific and is engaged in
research on stream flow diversion for
groundwater recharge.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-50
Agency Information, Plan Area, and Communication November 2024

1.3.4.1.2 Situation Assessment
During development of the initial 2020 GSP, the ESJGWA applied for and received facilitation support through DWR’s Facilitation Support Services Program to conduct a Situation Assessment, the purpose of which was to facilitate the stakeholder engagement process by determining stakeholder concerns related to the GSP development process. The facilitation services supported third-party interviews conducted with the members of the Workgroup in the winter of 2018 as part of the Situation Assessment. All Workgroup members were invited to participate in the Situation Assessment, and 17 were interviewed during a series of in-person and phone interview sessions. Assessment summary and highlights are available on the ESJGWA website.

Situation Assessment questions covered topics including:
• Outreach and engagement approach
• Meeting presentations
• Meeting discussions
• Strengthening the Workgroup process
• Decision making and input
• GSP development and plan content
• Resource and management conditions data
• Implementation considerations
Based on Situation Assessment findings, changes were made to the 2020 GSP development process, including meeting presentations and discussions, the draft GSP, and its review schedule.

1.3.4.2 Continuing Opportunities for Public Engagement
The sections below detail the opportunities for public engagement that were specific to this 2024 GSP Amendment.

Many began with the development of the initial 2020 GSP and have been continued and modified as appropriate to fit the needs of this particular GSP Amendment process.

1.3.4.2.1 Communication and Engagement Plan
With the support of the Workgroup, the ESJGWA developed an initial Stakeholder Outreach and Engagement Plan in June 2018 during the development of the 2020 GSP. This plan was updated as part of the 2024 GSP amendment process and renamed the Eastern San Joaquin Communication and Engagement Plan (C&E Plan). The ESJGWA supported the update of this Plan (see Appendix 1-H) for the San Joaquin Subbasin, which details communications and engagement recommendations for GSAs to consider as the GSP continues to be implemented and the needs of interested parties in the region evolves. The original goals of the Outreach and Engagement Plan are still relevant in the recent iterations of this plan:
• Keep interested list of stakeholders informed and aware of opportunities for involvement through email communications and/or their preferred mode of communication • Engage DWR for facilitated support to aid in the development of the GSP • Open ESJGWA planning efforts to the public with agendas and meeting minutes published on the ESJGWA website
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-51
Agency Information, Plan Area, and Communication November 2024 • Inform and obtain comments from the general public through public meetings held on an approximately quarterly basis
• Facilitate productive dialogue among participants at Advisory Committee, Workgroup, and public meetings through the use of qualified facilitators to obtain, consider, and integrate feedback accordingly throughout the planning process
• Seek the input of interest groups during the implementation of the GSP and any future planning efforts • Obtain input about preferred locations to conduct public informational meetings to reach diverse audiences and disadvantaged communities
• Provide timely and accurate public reporting of planning milestones through the distribution of outreach materials and posting of materials on the ESJGWA website for the GSP • Secure quality media coverage that is accurate, complete, and fair • Maintain an active communications tracking tool to capture stakeholder engagement and public outreach activities and to demonstrate the reporting of GSP outreach activities The ESJGWA used various methods to engage with and solicit input from interested parties during the 2020 GSP development process. In order to evolve the updated C&E Plan with the needs of the community, the development process started with a review of previously established commitments made by Subbasin GSAs and the ESJGWA in various SGMA-related documents and by the needs and ideas presented by interested parties. Seven individual or small group interviews were conducted between March and July of 2023 with key interested parties in the Subbasin to gather feedback on communication and engagement strategies taken during GSP implementation. Interviewees represented diverse interests, including disadvantaged communities, municipal and industrial, agricultural, domestic well, and those representing environmental water users.

Gaps or inefficiencies throughout GSP implementation were identified, showing a consistent lack of adequate support in key areas:
• Concerns over Demand Management Program: Respondents expressed concerns about potential demand reduction strategies that could be overly restrictive and disruptive to their lives and livelihoods. • Lack of Clarity on Sustainability Approaches: There was a perceived lack of clear answers and progress regarding long-term sustainability approaches.
• Cost Concerns: High water management costs and increased water rates were a concern, indicating a lack of public understanding around GSAs approach to funding. • Bureaucratic Processes: Respondents noted overly bureaucratic processes that might limit the effectiveness of the GSAs and the ESJGWA if things escalate beyond the local level. • Lack of Consistency and Transparency: There was a significant lack of consistency and transparency, particularly in how, where, and when GSAs share information and engage with each other and the public.

In order to address these key areas, the C&E Plan details the following strategies that could be implemented or expanded:
• Communications and Engagement Tracker: A strategy that involves the GSAs establishing a record-keeping system to catalogue the type and timing of outreach activities, enhancing their level of organization and compliance with requirements, with the support of the ESJGWA where necessary and feasible.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-52
Agency Information, Plan Area, and Communication November 2024 • Outreach Toolkit: A comprehensive approach by the GSAs to create a suite of standardized outreach materials and a library of relevant guides, aiming to ensure consistent messaging and best practices in communications and engagement, with the support and coordination of the ESJGWA. • Interested Parties Database: GSAs create a shared and comprehensive database, supported by the ESJGWA, to distribute information tailored to different jurisdictions and audiences, with the database managed by a third-party platform for easy maintenance, access, and tracking of public engagement. • Targeted Outreach: GSAs, in compliance with applicable regulations, implement specific efforts to identify, contact, educate, and engage with underrepresented groundwater users and non-English speakers on groundwater resource management, with coordination and collaboration support from the ESJGWA. • Workgroups and Committees: GSAs, in compliance with applicable regulations, consider establishing a committee or workgroup focused on small and underrepresented communities to engage on well protection and other related projects affecting these groundwater users, with support from the ESJGWA, • Native American Heritage Commission: GSAs submit and receive a Tribal and Sacred Land tribal contact list to the Native American Heritage Commission, ensuring they stay informed and in contact with recognized Indigenous communities in the region, a core component of inclusive engagement, especially for project implementation, with support from the ESJGWA
• Website Management: GSAs, in compliance with applicable regulations, establish and maintain web pages on their own or the ESJGWA websites, containing clear and accessible information, updates, and resources related to groundwater management, with the choice of management depending on the GSAs’ comfort and discretion.
• Enterprise Management System Management and Transparency: GSAs and/or the ESJGWA, in compliance with applicable regulations, maintain a catalog of data management systems and publish their methodology for maintaining and using the collected data, ensuring full transparency. • Comment Portal: GSAs and/or the ESJGWA, in compliance with applicable regulations, establish, maintain, and respond to public comments through an email contact portal, which collects data on the commenter and allows for categorization of comments, with links to the portal clearly available on their websites. • Funding and Financing: ESJGWA, in compliance with applicable regulations, coordinate with its member agencies to evaluate funding, grant, or in-kind support resources for facilitation, media relations, or outreach coordination services, supporting the addition of new staff or a dedicated outreach coordinator for the Subbasin to enhance communications and engagement efforts related to GSP implementation. • Outreach Coordinator: Recommendation to contract with an outreach coordinator to assist the ESJGWA and its member agencies with the tactics listed in the C&E Framework and any other ongoing communications and engagement efforts in the Subbasin, in compliance with all applicable codes and regulations.

1.3.4.2.2 ESJGWA Website
The ESJGWA website has been online since 2018 and continues to be maintained on a regular basis at www.esjgroundwater.org. It contains an introduction to SGMA, details on member agencies, and ESJGWA Board updates with meeting information and materials posted regularly. There are detailed sections for GSP resources, technical reports and data, educational materials, and meeting notices with the accompanying presentation materials and minutes. A section of the website is devoted to press releases, newsletters, public notices, and other major events and accomplishments. Contact information is readily available for interested parties to communicate with ESJGWA members and staff, and members of the public can subscribe to the ESJGWA mailing list to receive updates on GSP ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-53
Agency Information, Plan Area, and Communication November 2024 development and outreach events. Improvements to the website itself and the approach for its use will be continuously updated to meet the public engagement goals of the Subbasin.

1.3.4.2.3 Stakeholder Database
The ESJGWA developed a database of stakeholders who represent the region’s interests, perspectives, and geography. The database was developed by leveraging existing stakeholder lists and databases from prior Eastern San Joaquin Subbasin engagement efforts, conducting new research, and obtaining referrals from key stakeholders and stakeholder groups.

During the initial development of the stakeholder database, the ESJGWA worked with those responsible for implementing the GSP to obtain contact lists of interested parties within the Subbasin as well as other diverse contact lists they maintain.

This robust stakeholder list of interested parties includes, but is not limited to, the following:
• Community water systems
• Agricultural well owners
• Domestic well owners
• Municipal well operators
• Groundwater users (including agricultural)
• Local land use planning agencies
• Government agencies
• Nonprofit organizations
• Environmental organizations
• Higher education institutions
• Community based organizations
• Neighborhood organizations
• California Native American Tribes
• Disadvantaged communities
• Private citizens
The Stakeholder Database has been regularly updated by adding additional parties who expressed interest at public meetings and through website signups. Contacts were updated or removed as needed. The database continues to serve as the foundation for targeted outreach and communication and was also used to:
• Provide a single repository to collect, store, and organize information on Subbasin stakeholders • Allow individuals to self-identify their SGMA interests when they sign up as an interested stakeholder • Identify the interests and concerns of organization contacts and individual stakeholders ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-54
Agency Information, Plan Area, and Communication November 2024 • Plan meetings and send notices to stakeholders based upon their identified interests and role • Document all stakeholders invited to GSP development meetings and their primary input at the meetings • Post meeting agendas and minutes
• Produce communication and engagement summary reports
Table 1-5 provides a summary breakdown of the number of parties and interests represented in the Stakeholder Database.

Table 1-5: Stakeholder Database Summary
Eastern San Joaquin Groundwater Authority
Stakeholder Database
Interest Represented Number of Stakeholders
Government Agency (i.e. County, State) 64
Business (i.e. Consultant, Local Business, Legal
Representation) 41
Nonprofit (i.e. Environmental Organization, Thinktank) 5 Higher Education 3
Community Based Organization (i.e. Farm Bureau) 2
Water Purveyors (i.e. Public Utilities, Irrigation Districts) 77 No Affiliation Provided 93
Total 285
Outreach materials promoting informational open house events were distributed via email to the stakeholder database, and hard copies were distributed to this list throughout implementation process since the 2020 GSP.

The following section describes the stakeholder education and outreach activities completed during the development of the 2024 GSP Amendment.

1.3.4.2.4 Stakeholder Education and Outreach
Recognizing that an inclusive outreach and education process supports the success of a well-prepared GSP, the ESJGWA has prioritized stakeholder involvement and outreach in plan development and implementation, dedicating staff and financial resources for this high‐priority effort. • The ESJGWA held two public Stakeholder Advisory Workgroup (SAW) meetings and one informational open house event devoted to SGMA outreach and providing information to the public on the 2024 GSP Amendment development process. The purpose was to provide participants with information on GSP development, seek feedback from stakeholders and the public, provide a forum for the public to interact with their GSA representatives, and address questions in a transparent manner. These events were held on an approximately quarterly basis in different locations throughout the Subbasin, as listed below. o June 26, 2024 – Robert J. Cabral Agricultural Center, Stockton (23 attendees) o July 17, 2024 – Robert J. Cabral Agricultural Center, Stockton (18 attendees) o September 25, 2024 – Robert J. Cabral Agricultural Center, Stockton (40 attendees) • Additionally, GSA member agencies hosted local informational community meetings related to the SGMA process and to publicize the release of the Public Draft GSP for public comment.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-55
Agency Information, Plan Area, and Communication November 2024 • Individually, member GSAs provided targeted outreach materials to their constituencies through the distribution of outreach and informational materials
• Community events, including guided tours of facilities for the community, grower outreach meetings, and a tour for community leaders, were held to promote recharge projects and plans, and discuss challenges. • Member GSAs provided SGMA and project related updates to their Boards and other leadership bodies, including the Water Advisory Committee and the Linden-Peters Chamber of Commerce. • Factsheets, email announcements, and newsletters were used to raise awareness about topics and events relevant to the GSP and SGMA.
• Social media channels, such Facebook, were used to distribute targeted information relevant to SGMA, the GSP, and specific projects.
• Comment cards, provided in postcard format at the public informational open house, allowed the public and stakeholders to contribute written comments, solicit additional information, make suggestions, and submit other feedback as appropriate.

1.3.4.2.5 Incorporation of Stakeholder Feedback
The development of this GSP was informed and supported by stakeholder feedback, which was documented, addressed, and incorporated at numerous points throughout the development process. The public was invited to provide input at each Steering Committee and ESJGWA Board meeting. Information provided for GSP development was refined based on input from public meetings. Stakeholder involvement was additionally supported through the two public meetings and the open house held in September 2024 to solicit input on the draft Amended GSP from a wide range of beneficial users of groundwater in the Subbasin. Questions raised by participants at these meetings were addressed and, as needed, follow-up content presented and discussed at subsequent meetings.

In addition to influencing GSP development and decisions related to groundwater management, feedback from stakeholders played a key role in enhancing education and outreach efforts, and the stakeholder involvement process more broadly. Interviews in the initial stages of the C&E Plan development and survey responses received during the later stages, both provided valuable insight into how engagement can be improved. The second in-person SAW meeting also yielded some feedback, centering on two areas. • How to fund efforts toward sustainability, both at the GSA level and the ESJGWA level. • How to increase involvement of more diverse interests beyond water managers.

1.3.4.2.6 Draft 2024 GSP Amendment Public Comment Review Period The Public Draft 2024 GSP Amendment was posted on the ESJGWA website for a 31-day public comment period from October 1, 2024 through October 31, 2024. Notices and press releases were provided in English and Spanish publicizing the public comment period and inviting members of the public to attend the September 2024 informational open house event for more information. This event was scheduled to align with the release of the Public Draft 2024 GSP Amendment to provide a forum for the public to receive information, ask questions, and provide input. Hard copies were made available upon request.

The ESJGWA received 52 public comment submissions from a range of interested parties, including non-government organizations, neighboring subbasins, ESJGWA GSAs, state and federal agencies, and others. These individuals and organizations are listed below, and comments are provided in Appendix 1-I. • Barton Ranch, Inc.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-56
Agency Information, Plan Area, and Communication November 2024 • Calaveras County Water District
• California Department of Fish and Wildlife
• City of Stockton
• Sierra Club, Delta-Sierra Group
• NV5
• Restore the Delta
The PMC was responsible for reviewing and summarizing public comments, and drafting proposed response to comment recommendations for approval by the ESJGWA Board. The ESJGWA’s responses to comments are provided in Appendix 1-J.

1.3.5 Inter-basin Coordination
As part of the SGMA process, stakeholder outreach includes inter-basin coordination efforts. To date, ESJGWA has participated in the San Joaquin Valley Point of Contacts (SJC POC) meetings hosted quarterly, as well as initial introductory meetings with its neighboring subbasins. Given that the ESJ Subbasin was the first of its neighbors to submit a plan, the majority of neighboring basins were not in a position to begin meaningful coordination until recently.

There have been discussions about the establishment of annual meetings between representatives of the ESJGWA and the neighboring subbasins to begin a more formal coordination process. The purpose of these coordination meetings will be to share and discuss elements relevant to the subbasins, including water budget estimates, boundary flow assumptions, shared interconnected surface waters, and minimum thresholds.

A summary of the initial inter-basin coordination meetings with neighboring subbasins is below. • Cosumnes Subbasin – April 15, 2019
• Tracy Subbasin – June 20, 2019
• Modesto Subbasin – July 10, 2019
• South American, Solano, and East Contra Costa Subbasins – July 19, 2019 • Tracy Subbasin – September 25, 2024
To establish these annual coordination meetings, the ESJGWA plans to reach out to neighboring subbasins as part of GSP implementation to set more formal coordination between neighboring subbasins.

1.3.6 Notice of Intent to Adopt the GSP
A Notice of Intent (NOI) to adopt a GSP was signed by the Plan Manager on behalf of the GSAs and distributed on July 24, 2024. The NOI was posted to the ESJGWA website homepage and hard copies were mailed cities and counties within the Subbasin, including the following:
• County of Calaveras
• County of Stanislaus
• County of San Joaquin
• City of Escalon
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 1-57
Agency Information, Plan Area, and Communication November 2024 • City of Manteca
• City of Ripon
• City of Stockton
The signed NOI is provided in Appendix 1-K.

ATTACHMENT 2
Eastern San Joaquin Groundwater
Subbasin
2024 Groundwater
Sustainability Plan Amendment:

Basin Setting
Prepared by:

November 2024
ATTACHMENT 2
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ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment i
Basin Setting November 2024

TABLE OF CONTENTS
SECTION PAGE NO.

2. BASIN SETTING ...........................................................................................................................................2-10

2.1 Hydrogeologic Conceptual Model........................................................................................................2-10

2.1.1 Data Compilation ...............................................................................................................2-10

2.1.2 Regional Geologic and Structural Setting..........................................................................2-19

2.1.3 Geologic History ................................................................................................................2-20

2.1.4 Near-Surface Conditions ...................................................................................................2-20

2.1.5 Geologic Formations and Stratigraphy ..............................................................................2-35

2.1.6 Faults and Structural Features...........................................................................................2-43

2.1.7 Geologic Cross-Sections ...................................................................................................2-46

2.1.8 Basin Boundaries...............................................................................................................2-57

2.1.9 Principal Aquifer.................................................................................................................2-58

2.1.10 HCM Data Gaps ................................................................................................................2-79

2.2 Historical Groundwater Conditions ......................................................................................................2-80

2.2.1 Groundwater Elevation ......................................................................................................2-80

2.2.2 Groundwater Storage ........................................................................................................2-99

2.2.3 Seawater Intrusion...........................................................................................................2-101

2.2.4 Conditions as of 2019: Groundwater Quality ...................................................................2-101

2.2.5 Conditions in 2019: Land Subsidence .............................................................................2-123

2.2.6 Conditions in 2019: Interconnected Surface Water Systems...........................................2-124

2.2.7 Conditions in 2019: Groundwater-Dependent Ecosystems .............................................2-127

2.3 Current Groundwater Conditions .......................................................................................................2-135

2.3.1 Groundwater Elevation ....................................................................................................2-135

2.3.2 Groundwater Storage ......................................................................................................2-140

2.3.3 Seawater Intrusion...........................................................................................................2-141

2.3.4 Groundwater Quality........................................................................................................2-145

2.3.5 Land Subsidence.............................................................................................................2-148

2.3.6 Interconnected Surface Water Systems ..........................................................................2-156

2.3.7 Groundwater-Dependent Ecosystems .............................................................................2-162

2.4 Water Budgets...................................................................................................................................2-164

2.4.1 Water Budget Background Information............................................................................2-164

2.4.2 Identification of Hydrologic Periods..................................................................................2-166

2.4.3 Use of the ESJWRM and Associated Data in Water Budget Development .....................2-167

2.4.4 Water Budget Definitions and Assumptions.....................................................................2-168

2.4.5 Water Budget Estimates ..................................................................................................2-175

2.4.6 Projected Water Budget with Demand Reduction Estimates (ESJWRM PCBL-DR Version

3.0) ..................................................................................................................................2-197

2.4.7 Projected Water Budget with Climate Change and Demand Reduction Estimates (ESJWRM PCBL-CC-DR Version 3.0) ..............................................................................................2-203

2.4.8 Projected Water Budget with PMAs Estimates (ESJWRM PCBL-PMA Version 3.0).......2-207

2.4.9 Projected Water Budget with Climate Change and PMAs Estimates (ESJWRM PCBL-CCPMA Version 3.0).............................................................................................................2-214 ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment ii
Basin Setting November 2024
Tables
Table 2-1: Eastern San Joaquin Subbasin Watershed Details ................................................................................ 2-24 Table 2-2: Generalized Stratigraphic Column, Formation Descriptions, and Water-Bearing Properties.................. 2-39 Table 2-3: Production Zone Capacities.................................................................................................................... 2-67 Table 2-4: Wells within Water-Bearing Zones.......................................................................................................... 2-68 Table 2-5: Summary of Chloride Data by Decade.................................................................................................. 2-105 Table 2-6: Summary of Chloride Data by Depth (1940s-2010s) ............................................................................ 2-105 Table 2-7: Summary of TDS Data by Depth (2015-2018)...................................................................................... 2-111 Table 2-8: Nitrate as N Concentrations by Decade................................................................................................ 2-113 Table 2-9: Arsenic Concentrations by Decade....................................................................................................... 2-118 Table 2-10: MCLs for Common Petroleum Hydrocarbons and MTBE ................................................................... 2-122 Table 2-11: MCLs for Common Synthetic Organic Constituents............................................................................ 2-123 Table 2-12: Chloride Concentrations after 2015 .................................................................................................... 2-144 Table 2-13: Summary of Water Budget Assumptions (Historical, Current, and Projected Periods)....................... 2-170 Table 2-14: Average Annual Water Budget for Revised ESJWRM (Version 3.0) – Stream System (AF/year)...... 2-177 Table 2-15: Average Annual Water Budget for Revised ESJWRM – Land Surface System (AF/year).................. 2-179 Table 2-16: Average Annual Water Budget for Revised ESJWRM – Groundwater System (AF/year) .................. 2-181 Table 2-17: Average Annual Values for Key Components of Historical Water Budget by Year Type.................... 2-186 Table 2-18: Average Annual Values for Key Components of Projected Water Budget by Year Type.................... 2-193 Table 2-19: Average Annual Values for Key Components of Projected Conditions with Climate Change Water Budget by Year Type ............................................................................................................................. 2-197 Table 2-20: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL Version 3.0 and PCBL-DR Version 3.0......................................................................................................... 2-199 Table 2-21: ESJ Subbasin Hydrologic Groundwater Budget Annual Average Comparison Between PCBL Version 3.0 and PCBL-DR Version 3.0......................................................................................................... 2-202 Table 2-22: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL-CC Version 3.0 and PCBL-CC-DR Version 3.0 .................................................................................................. 2-203 Table 2-23: ESJ Subbasin Hydrologic Groundwater Budget Annual Average Comparison Between the PCBL-CC and the PCBL-CC-DR Version 3.0 ................................................................................................... 2-205 Table 2-24: Summary of ESJWRM Category A Projects Surface Water Deliveries............................................... 2-209 Table 2-25: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL Version 3.0 and PCBL-PMA Version 3.0...................................................................................................... 2-211 Table 2-26: ESJ Hydrologic Groundwater Budget Annual Average Comparison Between the PCBL (Version 3.0) and the PCBL-PMA (Version 3.0)..................................................................................................... 2-214 Table 2-27: ESJ Subbasin Land and Water Use Budget Annual Average Comparison Between PCBL-CC Version 3.0 and PCBL-CC-PMA Version 3.0................................................................................................ 2-215 Table 2-28: ESJ Hydrologic Groundwater Budget Annual Average Comparison Between the PCBL-CC and the PCBL-CC-PMA Version 3.0....................................................................................................... 2-218 ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment iii
Basin Setting November 2024
Figures
Figure 2-1: Depth of All Wells in Water Data Library................................................................................................ 2-12 Figure 2-2: Depth Distribution of Wells in Water Data Library.................................................................................. 2-13 Figure 2-3: GAMA Monitoring Well Network ............................................................................................................ 2-14 Figure 2-4: Number of Chloride Measurements Taken at GAMA Monitoring Sites (2005-2017) ............................. 2-15 Figure 2-5: AEM Flight Lines across ESJ Subbasin................................................................................................. 2-18 Figure 2-6: Geologic Time Scale.............................................................................................................................. 2-19 Figure 2-7: Topography............................................................................................................................................ 2-21 Figure 2-8: Major Hydrologic Features..................................................................................................................... 2-22 Figure 2-9: Eastern San Joaquin Subbasin Watersheds ......................................................................................... 2-25 Figure 2-2-10: Soil Depositional Areas .................................................................................................................... 2-26 Figure 2-11: Hydrologic Soil Groups ........................................................................................................................ 2-28 Figure 2-12: Occurrence of Hardpan within the Eastern San Joaquin Subbasin ..................................................... 2-29 Figure 2-13: Areal Extents of Alluvial Fans, Interfans, and Pre-Modesto Formations.............................................. 2-31 Figure 2-14: Existing Areas of Groundwater Recharge (ESJWRM Version 3.0)...................................................... 2-33 Figure 2-15: Average Percent Coarse Fraction in Near-Surface Materials.............................................................. 2-34 Figure 2-16: Potential Recharge Areas.................................................................................................................... 2-35 Figure 2-17: Generalized Geologic Section and Eastern San Joaquin Subbasin Setting ........................................ 2-36 Figure 2-18: Geologic Map....................................................................................................................................... 2-37 Figure 2-19: Faults and Structural Features ............................................................................................................ 2-44 Figure 2-20: Base of Fresh Water Elevation and Stockton Fault ............................................................................. 2-45 Figure 2-21: Cross-Section, by Formation, Location Map........................................................................................ 2-47 Figure 2-22: Hydrogeologic Cross-sections A-A’ and B-B’....................................................................................... 2-48 Figure 2-23: Hydrogeologic Cross-sections C-C’ and D-D’...................................................................................... 2-49 Figure 2-24: Hydrogeologic Cross- section E-E’ ...................................................................................................... 2-50 Figure 2-25: Cross-Section, by Percent Coarseness, Location Map ....................................................................... 2-51 Figure 2-26: Percent Coarse Cross-Section F-F’..................................................................................................... 2-52 Figure 2-27: Percent Coarse Cross-Section G-G’.................................................................................................... 2-53 Figure 2-28: Percent Coarse Cross-Section H-H’ .................................................................................................... 2-54 Figure 2-29: Percent Coarse Cross-section I-I’........................................................................................................ 2-55 Figure 2-30: Bottom Elevation of Water-Bearing Zones (Shallow)........................................................................... 2-60 Figure 2-31: Bottom Elevation of Water-Bearing Zones (Deep and Intermediate)................................................... 2-61 Figure 2-32: Elevation of Base of Continental Deposits........................................................................................... 2-64 Figure 2-33: Sand and Gravel Isopach Map ............................................................................................................ 2-66 Figure 2-34: Total Number of Cation/Anion Measurements in the Eastern San Joaquin Subbasin......................... 2-71 Figure 2-35: Trilinear Diagrams ............................................................................................................................... 2-72 Figure 2-36: TDS Annual Variation .......................................................................................................................... 2-73 Figure 2-37: TDS Concentrations in 2017................................................................................................................ 2-74 Figure 2-38: Chloride Annual Variation .................................................................................................................... 2-75 Figure 2-39: Chloride Concentrations in 2017.......................................................................................................... 2-76 Figure 2-40: Sulfate Annual Variation ...................................................................................................................... 2-77 Figure 2-41: Sulfate Concentrations in 2017............................................................................................................ 2-78 Figure 2-42: Hydrographs of Selected Wells............................................................................................................ 2-82 Figure 2-43: Summary of Groundwater Elevation Data, 1940-2018 ........................................................................ 2-84 Figure 2-44: Precipitation Stations ........................................................................................................................... 2-85 Figure 2-45: First Quarter 2017 Groundwater Elevation .......................................................................................... 2-87 Figure 2-46: Fourth Quarter 2017 Groundwater Levels ........................................................................................... 2-88 Figure 2-47: Map of Nested and/or Clustered Well Sites (as of 2020 GSP Development) ...................................... 2-90 Figure 2-48: Nested Well Hydrographs: CCWD 004-006 (as of 2020 GSP Development)...................................... 2-91 Figure 2-49: Nested Well Hydrographs: CCWD 010-012 (as of 2020 GSP Development)...................................... 2-91 ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment iv
Basin Setting November 2024
Figure 2-50: Nested Well Hydrographs: Sperry Well (as of 2020 GSP Development)............................................. 2-92 Figure 2-51: Nested Well Hydrographs: Swenson Golf Course (as of 2020 GSP Development) ............................ 2-92 Figure 2-52: Nested Well Hydrographs: STK-1 (as of 2020 GSP Development)..................................................... 2-93 Figure 2-53: Nested Well Hydrographs: STK-2 (as of 2020 GSP Development)..................................................... 2-93 Figure 2-54: Nested Well Hydrographs: STK-4 (as of 2020 GSP Development)..................................................... 2-94 Figure 2-55: Nested Well Hydrographs: STK-5 (as of 2020 GSP Development)..................................................... 2-94 Figure 2-56: Nested Well Hydrographs: STK-6 (as of 2020 GSP Development)..................................................... 2-95 Figure 2-57: Nested Well Hydrographs: STK-7 (as of 2020 GSP Development)..................................................... 2-95 Figure 2-58: Nested Well Hydrographs: Lodi MW-21 (as of 2020 GSP Development)............................................ 2-96 Figure 2-59: Nested Well Hydrographs: Lodi MW-24 (as of 2020 GSP Development)............................................ 2-96 Figure 2-60: Nested Well Hydrographs: Lodi MW-25 (as of 2020 GSP Development)............................................ 2-97 Figure 2-61: Nested Well Hydrographs: Lodi SMW-1 (as of 2020 GSP Development) ........................................... 2-97 Figure 2-62: Nested Well Hydrographs: Lodi WMW-1 (as of 2020 GSP Development) .......................................... 2-98 Figure 2-63: Nested Well Hydrographs: Lodi WMW-2 (as of 2020 GSP Development) .......................................... 2-98 Figure 2-64: Historical Modeled Change in Storage ................................................................................................ 2-99 Figure 2-65: Historical Modeled Change in Annual Storage with Water Use and Year Type ................................ 2-100 Figure 2-66: Maximum Chloride Concentration Greater Than 250 mg/L (1940s-2010s) ....................................... 2-103 Figure 2-67: Maximum Chloride Concentration Above 250 mg/L by Decade ........................................................ 2-104 Figure 2-68: Maximum Chloride Concentration Above 250 mg/L by Well Depth (1940s-2010s)........................... 2-106 Figure 2-69: Maximum TDS Concentrations 2015-2018........................................................................................ 2-108 Figure 2-70: Average TDS Concentrations 2015-2018.......................................................................................... 2-109 Figure 2-71: Maximum TDS Concentrations in Shallow Wells 2015-2018............................................................. 2-111 Figure 2-72: Maximum TDS Concentrations in Deep Wells 2015-2018................................................................. 2-112 Figure 2-73: Nitrate as N Concentrations by Decade............................................................................................. 2-115 Figure 2-74: Arsenic Concentrations by Decade.................................................................................................... 2-117 Figure 2-75: Maximum Arsenic Concentrations 2015-2018................................................................................... 2-118 Figure 2-76: Active Investigation and Remediation Sites as of 2019 ..................................................................... 2-120 Figure 2-77: Active Sites with the Potential to Cause Plumes ............................................................................... 2-121 Figure 2-78: Subsidence (Annual Rate of Vertical Displacement) ......................................................................... 2-124 Figure 2-79: Stream Connectivity to the Groundwater System.............................................................................. 2-126 Figure 2-80: Losing and Gaining Streams ............................................................................................................. 2-127 Figure 2-81: Natural Communities Commonly Associated with Groundwater (NCCAGs) ..................................... 2-129 Figure 2-82: NCCAGs Identified as Data Gap Areas for Future Refinement, Likely to Access Non-groundwater Water Supplies..................................................................................................................................... 2-132 Figure 2-83: Areas Identified as GDEs .................................................................................................................. 2-134 Figure 2-84: Fourth Quarter 2019 Groundwater Elevation (WY 2020)................................................................... 2-136 Figure 2-85: First Quarter 2020 Groundwater Levels (WY 2020) .......................................................................... 2-137 Figure 2-86: Fourth Quarter 2022 Groundwater Elevation (WY 2023)................................................................... 2-138 Figure 2-87: First Quarter 2023 Groundwater Levels (WY 2023) .......................................................................... 2-139 Figure 2-88 : Number of Reported Dry Wells in San Joaquin County between WY 2020-2023 ............................ 2-140 Figure 2-89: Modeled Change in Annual Storage with Water Use and Year Type ................................................ 2-141 Figure 2-90: 2023 Annual Groundwater Pumping.................................................................................................. 2-143 Figure 2-91: Average Chloride Concentrations Post-2015..................................................................................... 2-145 Figure 2-92: Monitoring Frequency for Wells Measuring Total Dissolved Solids ................................................... 2-146 Figure 2-93: Wells with Recent TDS Observations by Well Depth......................................................................... 2-147 Figure 2-94: Maximum Concentrations for Wells Measuring Total Dissolved Solids ............................................. 2-148 Figure 2-95: CGPS Station MTWK – Subsidence Time Series.............................................................................. 2-150 Figure 2-96: CGPS Station P309 – Subsidence Time Series ................................................................................ 2-151 Figure 2-97: CGPS Station CMNC – Subsidence Time Series.............................................................................. 2-152 Figure 2-98: CGPS Station CA1S – Subsidence Time Series ............................................................................... 2-153 Figure 2-99: Subsidence Rates (inches per year) Throughout the Subbasin......................................................... 2-154 ATTACHMENT 2
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Figure 2-100: CGPS Station MTWK: Subsidence Time Series.............................................................................. 2-155 Figure 2-101: CGPS Station CNDR – Time Series of Subsidence and Groundwater Levels ................................ 2-156 Figure 2-102: Stream Reaches in ESJWRM.......................................................................................................... 2-158 Figure 2-103: Surface Waters Connected with the Groundwater System at least 75% of All Months in ESJWRM under Current Conditions .......................................................................................................... 2-159 Figure 2-104: Diagram of Gaining and Losing Connected Streams....................................................................... 2-160 Figure 2-105: Current Conditions Average Annual Stream Gains by Stream Node............................................... 2-162 Figure 2-106: Mapping of Potential Groundwater Dependent Ecosystems............................................................ 2-164 Figure 2-107: Generalized Water Budget Diagram................................................................................................ 2-165 Figure 2-108: 55-Year Historical Precipitation and Cumulative Departure from Mean Precipitation...................... 2-167 Figure 2-109: Historical Average Annual Water Budget – Stream System............................................................ 2-183 Figure 2-110: Historical Average Annual Water Budget – Land Surface System .................................................. 2-184 Figure 2-111: Historical Average Annual Water Budget Estimates – Groundwater System .................................. 2-185 Figure 2-112: Current Average Annual Water Budget Estimates – Stream System.............................................. 2-187 Figure 2-113: Current Average Annual Water Budget Estimates – Land Surface System .................................... 2-188 Figure 2-114: Current Average Annual Water Budget Estimates – Groundwater System..................................... 2-189 Figure 2-115: Projected Average Annual Water Budget Estimates – Stream System........................................... 2-191 Figure 2-116: Projected Average Annual Water Budget Estimates – Land Surface System................................. 2-191 Figure 2-117: Projected Average Annual Water Budget Estimates – Groundwater System.................................. 2-192 Figure 2-118: Projected Average Annual Water Budget Estimates with Climate Change – Stream System......... 2-194 Figure 2-119: Projected Average Annual Water Budget Estimates with Climate Change – Land Surface System2-195 Figure 2-120: Projected Average Annual Water Budget Estimates with Climate Change – Groundwater System 2-196 Figure 2-121: ESJ Subbasin Projected Agricultural Demand in the PCBL-DR Version 3.0 ................................... 2-200 Figure 2-122: ESJ Subbasin Projected Urban Demand in the PCBL-DR Version 3.0 ........................................... 2-200 Figure 2-123: ESJ Subbasin Projected Hydrologic Groundwater Budget in PCBL-DR Version 3.0....................... 2-202 Figure 2-124: ESJ Subbasin Projected Agricultural Demand in the PCBL-CC-DR Version 3.0............................. 2-204 Figure 2-125: ESJ Subbasin Projected Urban Demand in the PCBL-CC-DR Version 3.0..................................... 2-205 Figure 2-126: ESJ Subbasin Projected Hydrologic Groundwater Budget in the PCBL-CC-DR Version 3.0 .......... 2-206 Figure 2-127: ESJ Subbasin Projected Agricultural Demand in the PCBL-PMA.................................................... 2-212 Figure 2-128: ESJ Subbasin Projected Urban Demand in the PCBL-PMA............................................................ 2-212 Figure 2-129: ESJ Subbasin Projected Hydrologic Groundwater Budget in the PCBL-PMA Version 3.0.............. 2-214 Figure 2-130: ESJ Subbasin Projected Agricultural Demand in the PCBL-CC-PMA Version 3.0 .......................... 2-216 Figure 2-131: ESJ Subbasin Projected Urban Demand in the PCBL-CC-PMA Version 3.0 .................................. 2-217 Figure 2-132: Eastern San Joaquin Subbasin Projected Hydrologic Groundwater Budget in the PCBL-CC-PMA 2-219 Appendices
2-A Eastern San Joaquin Water Resources Model (ESJWRM) Report 2-B Eastern San Joaquin Water Resources Model (ESJWRM) Report Version 2.0 Update 2-C Eastern San Joaquin Water Resources Model (ESJWRM) Report Version 3.0 Update ATTACHMENT 2
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Acronyms
µg/L micrograms per liter
1,2,3-TCP 1,2,3-Trichloropropane
AEM airborne electromagnetic
AF acre-feet
AF/day acre-feet per day
AF/year acre-feet per year
B.P. before present
bgs below ground surface
BMP best management practice
BTEX benzene, toluene, ethylbenzene, and xylenes
C2VSim-FG California Central Valley Simulation Model – Fine Grid CALSIMETAW California Simulation of Evapotranspiration of Applied Water CalTrans California Department of Transportation
CASGEM California Statewide Groundwater Elevation Monitoring CC climate change
CCR California Code of Regulations
CCWD Calaveras County Water District
CDFW California Department of Fish and Wildlife
CEQA California Environmental Quality Act
cfs cubic feet per second
CGPF CalSim II Generated Perturbation Factors
CGPS continuous global positioning system
CNRA California Natural Resources Agency
CSJWCD Central San Joaquin Water Conservation District
CV-SALTS Central Valley Salinity Alternatives for Long-Term Sustainability CWC California Water Code
DBCP 1,2-dibromo-3-chloropropane
DDW Department of Drinking Water
Delta Sacramento-San Joaquin River Delta
DOGGR Division of Oil, Gas, and Geothermal Resources
DPC Delta Protection Commission
DPW San Joaquin County Department of Public Works
DTSC Department of Toxic Substances Control
DWR Department of Water Resources
EDB ethylene dibromide
ESJGWA Eastern San Joaquin Groundwater Authority
ESJWRM Eastern San Joaquin Water Resources Model
ETo evapotranspiration
ft/mi feet per mile
GAMA Groundwater Ambient Monitoring and Assessment
GCM global climate model
GDE groundwater dependent ecosystem
GIS Geographic Information System
gpd gallons per day
gpm gallons per minute
GSA groundwater sustainability agency
GSP Groundwater Sustainability Plan
HCM Hydrogeologic Conceptual Model
IDW inverse distance weighted
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ILRP Irrigated Lands Regulatory Program
InSAR Interferometric Synthetic Aperture Radar
ISW interconnected surface water
IWFM Integrated Water Flow Model
LOCA local analogs
MAF million acre-feet
MAR managed aquifer recharge
MCL maximum contaminant level
mg/L milligrams per liter
MSL mean sea level
MtBE methyl tertiary-butyl ether
MWH Montgomery Watson Harza
NAD 83 North American Datum of 1983
NAVD 88 North American Vertical Datum of 1988
NCCAG Natural Communities Commonly Associated with Groundwater NRCS Natural Resource Conservation Service
NSJWCD North San Joaquin Water Conservation District
OID Oakdale Irrigation District
OSWCR Online System for Well Completion Reports
PCBL Projected Conditions Baseline
PCE perchloroethylene
pdf portable document format
PFOA perfluorooctantoic acid
PFOS perfluorooctanesulfonic acid
PMA Projects and Management Actions
PRISM Precipitation-Elevation Regressions on Independent Slopes Model RCP representative climate pathways
RL Reporting Limit
RWQCB Regional Water Quality Control Board
SAGBI Soil Agricultural Groundwater Banking Index
SEWD Stockton East Water District
SGMA the Sustainable Groundwater Management Act
SJCFCWCD San Joaquin County Flood Control and Water Conservation District SJV San Joaquin Valley
SMCL secondary maximum contaminant levels
SOPAC Scripps Orbit and Permanent Array Center
SS specific storage
SSJID South San Joaquin Irrigation District
SWRCB State Water Resources Control Board
SY specific yield
TAFY thousand acre-feet per year
TCE trichloroethene
TDS total dissolved solids
TNC The Nature Conservancy
UNAVCO University Navstar Consortium
UNGL University of Nevada Geodetic Laboratory
USACE United States Army Corps of Engineers
USDA United States Department of Agriculture
USEPA U.S. Environmental Protection Agency
USGS United States Geological Survey
UTM Universal Transverse Mercator
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UWMPs Urban Water Management Plans
VIC Variable Infiltration Capacity
VOC volatile organic compound
WDL Water Data Library
WDR waste discharge requirement
WID Woodbridge Irrigation District
WRIMS Water Resource Integrated Modeling System
WY water year
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2. BASIN SETTING
This Basin Setting chapter contains three main sections as follows:
• Hydrogeologic Conceptual Model – Section 2.1 (Hydrogeologic Conceptual Model) provides the geologic information needed to understand the framework under which water moves through the Subbasin. It focuses on geologic formations, aquifers, structural features, and topography. • Current and Historical Groundwater Conditions – Section 2.2 (Historical Groundwater Conditions) and Section 2.3 (Current Groundwater Conditions) describe and present groundwater trends, levels, hydrographs and level contour maps, estimated changes in groundwater in storage, identify groundwater quality issues, address land subsidence, and address surface water interconnection. • Water Budgets – Section 2.4 (Water Budgets) describes the data used to develop the water budget. This section also discusses how the water budgets were calculated and provides water budget estimates for historical conditions, current conditions, and projected conditions.

2.1 HYDROGEOLOGIC CONCEPTUAL MODEL

2.1.1Data Compilation
This section describes the hydrogeologic conceptual model (HCM) for the Eastern San Joaquin Subbasin (Subbasin), as was included in the 2020 Groundwater Sustainability Plan (GSP) and reconsidered during the 2024 Periodic Evaluation. The regulatory framework is based on the California Code of Regulations (CCR) Title 23 § 354.14. The HCM presents the physical characteristics used to define water movement throughout the Subbasin.

Data supporting development of the Eastern San Joaquin Subbasin HCM is available to the public from a variety of local, state, and federal agencies, as well as from non-governmental entities. The data presented herein were compiled from numerous studies conducted in the eastern portion of the San Joaquin Valley (SJV). Information from several online databases that support ongoing monitoring and development of the groundwater resources within the Eastern San Joaquin Subbasin and across California were amassed, digitized, evaluated, and reconfigured in support of the HCM. Most information was compiled during the development of the 2020 GSP. Where new data available between 2020 and 2024 provide additional information to the HCM, it has been incorporated into this chapter. New data support the original understanding of the Subbasin HCM and therefore, the original HCM remains in the 2024 GSP with additional detail incorporated where additional insights can be made.

To accomplish the data compilation task, software programs such as Microsoft Excel, ArcGIS, QGIS, CrossView, and Python1 platforms for entering, storing, displaying, and evaluating the volume of data available were used. The following subsections describe the online programmatic databases from which much of the data were sourced and provide insight on the unique obstacles within each.

2.1.1.1 Groundwater Level Data
The California Statewide Groundwater Elevation Monitoring (CASGEM) and San Joaquin County monitoring well networks provided the basis for determining groundwater levels across the Eastern San Joaquin Subbasin in the 2020 GSP. CASGEM maintains a website that allows users to download site locations and groundwater level information.

San Joaquin County’s monitoring well data came from the San Joaquin County Flood Control and Water Conservation District (SJCFCWCD).
1 Python version 3.11 was used as well as the Pandas, NumPy, Matplotlib, GeoPandas, Rasterio, Shapely, and cmocean packages
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Since the 2020 GSP, all groundwater level data have been centralized in the California Department of Water Resource’s (DWR) Water Data Library (WDL) database. Well information can be found in WDL, and all available historical data can be downloaded for each well.

There are approximately 1,000 unique wells across the Eastern San Joaquin Subbasin. Despite the large number of wells, horizontal and vertical data gaps still exist. Large areas of the Subbasin contain very few wells, particularly in the northwest and southeast portions of the Subbasin (see Figure 2-1).Substantial efforts have been made to fill these data gaps since the 2020 GSP. Section 7.1 describes what has been done as part of GSP implementation between 2020 and 2024 to address these gaps.

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Figure 2-1: Depth of All Wells in Water Data Library
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Figure 2-2 shows the distribution of well depths of WDL wells within the Subbasin, a large number of which do not have construction depth or screen interval information. This makes determining groundwater levels for depth-discrete aquifer intervals impossible. Groundwater elevation contour maps were prepared for the Subbasin’s single principal aquifer, consistent with CCR Title 23 § 354.16 Groundwater Conditions requirements. Despite uncertainties due to limited construction information, this GSP presents maps that provide a useful description of groundwater conditions.

Figure 2-2: Depth Distribution of Wells in Water Data Library

2.1.1.2 Groundwater Quality Data
This GSP relies on groundwater quality data from the Groundwater Ambient Monitoring and Assessment (GAMA) Program. GAMA includes water quality data from numerous sources, such as United States Geological Survey (USGS) and DWR. The GAMA database contains approximately 6,800 well sites throughout the Eastern San Joaquin Subbasin with over 1.6 million water quality measurements (Figure 2-3).

Although GAMA provides data on many groundwater parameters and wells throughout the Eastern San Joaquin Subbasin, significant data gaps remain. For instance, there are inconsistencies in the parameters measured, as well as in the sampling periods. Some wells are sampled at regular intervals (i.e., quarterly or annually), while others are sampled irregularly. Such assorted schedules make analysis over a given period of time difficult. Data gaps are also apparent when looking at parameters over a longer timeframe. For example, chloride, an important and commonly measured groundwater quality parameter, is reported in only a small fraction of the total number of GAMA wells. As shown in Figure 2-4, out of the over 6,800 wells listed in GAMA for the Eastern San Joaquin Subbasin, no more than 700 chloride measurements were taken during any year since 2005.

No new groundwater quality sources have been identified since the development of the 2020 GSP that are as comprehensive as GAMA.
0 50
100
150
200
250
300
350
400
No Depth Data 0- 100 100-250 250 - 500 > 500
Number of Wells
Depth (ft.)
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Figure 2-3: GAMA Monitoring Well Network
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Figure 2-4: Number of Chloride Measurements Taken at GAMA Monitoring Sites (2005-2017) Below is a list of attributes for each groundwater quality result in GAMA:
• Well ID
• Results
• Chemical
• Units
• Qualifier
• RL (Reporting Limit)
• Approximate Latitude
• Approximate Longitude
• Well Type
• Well Depth
• Top of Screen
• Screen Length
• Source
• Source Name
• Other Names
The attributes of each well in the GAMA database are not always complete or accurate. Well depths and screen interval data, where available, promote vertical analysis of groundwater quality data because these data can be correlated to depth-discrete aquifer zones. Additional depth-specific water quality monitoring is a focus of the monitoring network for this GSP, as discussed in Chapter 4 of this GSP.

2.1.1.3 Stratigraphic Data
The Online System for Well Completion Reports (OSWCR) provided a majority of the groundwater well logs used in developing the HCM. This online database, developed and maintained by DWR, is a compilation of well completion reports accessible to the public for viewing and downloading. Tables of water well records are also available which contain attributes such as construction depth and well type (e.g., domestic or agricultural). However, not every well record is complete within the tables or only a few attributes may be listed. None of the stratigraphic or geologic data are provided in the tables. Stratigraphic or geologic data must be obtained from the individual well completion reports, which are only available as scanned images downloadable in portable document format (pdf). Once the well completion reports are retrieved from the database, the geologic information can then be manually digitized into Microsoft Excel or other database software.

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Critical information needed from the well completion reports are construction depth, screen interval, and borehole stratigraphy. The quality and completeness of the reports are, however, highly variable. Very few well logs contain all of the critical data; many more list only a few of the key attributes or none at all. Descriptions of the borehole stratigraphy also vary widely, from comprehensive geologic descriptions to single-word captions (e.g., sand, sandstone, or clay).

Given the volume of wells in the Eastern San Joaquin Subbasin and the critical importance of the data being retrieved, great attention was paid to this aspect of the data compilation effort.

Once compiled, the well construction and stratigraphic data from OSWCR were correlated with well data available from the CASGEM and San Joaquin County monitoring well databases. To accomplish this task, individual well logs from OSWCR were assigned a unique location and then matched to a specific well within the CASGEM and San Joaquin County datasets (CA DWR, 2000).

Although the State ID format does not allow for matching between OSWCR, CASGEM, and San Joaquin County databases, well completion reports from OSWCR were correlated to wells in the other databases. This connection was made by plotting CASGEM/San Joaquin County well locations in Geographic Information System (GIS) software and correlating well completion reports to nearby wells with similar attributes. For instance, the State ID of the CASGEM/San Joaquin County wells and the modified State ID of the OSWCR were used to locate the features within the same Township/Range/Section. Well completion reports were matched to wells by attributes such as screen interval and seal depth or based on written location descriptions or hand-drawn sketches of the location.

To further support spatial analysis, well completion reports from OSWCR with no corresponding well in any database were added to the data set. Well completion reports for wells from other sources, including USGS nested wells and municipal wells, were also added. Well completion reports from OSWCR that did not correspond to wells in a different database were plotted using latitude and longitude coordinates listed in OSWCR. These coordinates are often approximations of the actual location; many latitude and longitude values are the geometric center of the section containing each well. All totaled, the borehole stratigraphy from approximately 330 groundwater wells was digitized to provide horizontal spatial coverage.

While groundwater wells provide valuable data in the shallower portion of the basin that are mostly accessed for groundwater use, the hydrostratigraphic units within the Eastern San Joaquin Subbasin are much deeper, reaching a maximum depth of approximately 1,000 feet. Data from the Division of Oil, Gas, and Geothermal Resources (DOGGR) were used to assess the geologic strata at the depths important to the HCM, as these wells are typically much deeper than groundwater wells.

Interpretation of geologic formations from the well completion reports and DOGGR well logs was undertaken after digitizing stratigraphic data from the various sources. This process relied heavily on the distinguishing features of each formation (Section 2.1.5), surficial geologic maps (Section 2.1.5), location and depth of borehole (Section 2.1.7), and professional judgement.

2.1.1.4 Airborne Electromagnetic (AEM) Surveys
Airborne Electromagnetic (AEM) surveys were completed across the state since the 2020 GSP. The data collected provides additional data to inform the HCM of the surveyed basins. Data are collected from a helicopter carrying geophysical equipment on a large hexagonal frame about 30 meters above the ground. This equipment sends a weak electromagnetic signal into the ground and measures the response received back. An electrical resistivity profile of the subsurface down to depths of as much as 300 meters can be developed using the received data. The Eastern San Joaquin Subbasin was included in Survey Area 6, which also included the Cosumnes, Tracy, and East Contra Costa Subbasins and Livermore Valley Groundwater Basin.

Figure 2-5 shows where the survey’s flight lines were completed across the Subbasin (CA DWR, 2023 and CA DWR, 20024).

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Aquifers are typically composed of sands and gravels that have high resistivities, while aquitards are composed of silt and clays that have low resistivities. The resistivity profiles help in mapping the overall dimensions and extent of the aquifer systems. The AEM survey data is analyzed in detail, correlated with data from nearby wells, and modeled to produce subsurface maps of the resistivity, lithology (the physical characteristics of rocks), and an initial hydrostratigraphic model (a description of the water-bearing and water-confining properties of rocks). Well lithology and oil and gas well geophysical logs located along the AEM flight lines were compiled to provide additional data to support the surveys. Groundwater levels and water quality data were also compiled.

DWR processed the collected AEM data to filter out potential noise in the data and, if necessary, remove the data where interference is too great to effectively interpret. Resistivity models were produced that provide profiles indicative of areas with relatively coarser-grained (sands and gravels) and finer-grained (silts and clays) material, represented by areas of higher and lower resistivities, respectively. The resistivity data were then processed, combining the detailed high-quality well lithologic data with information on the spatial heterogeneity from the resistivity to provide an interpretation of lithology. The resistivity and coarse fraction data were combined to produce an initial hydrostratigraphic model for each subbasin, designating areas or layers of the subsurface having similar hydrogeologic properties (Department of Water Resources (CA DWR), 2023).

The resistivity data, and the texture interpretation DWR developed, are useful as an additional source of information to contribute to local understanding of the Subbasin’s hydrogeology and structural features. These data were incorporated into the following pieces of the GSP:
• New cross-sections in the HCM
• Additional shallow subsurface texture map included in the HCM • Refinements to the model stratigraphy in ESJWRM, described in detail in the ESJWRM Version 3.0 Model Documentation TM included in Appendix 2-C.

Python was used to process the data provided by DWR.

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Figure 2-5: AEM Flight Lines across ESJ Subbasin

2.1.1.5 GIS Data
In accordance with CCR Title 23 §354.14, maps of various basin attributes are required as part of the HCM. To produce these maps, GIS software was used to store, manage, and analyze spatial and tabular data. GIS software was also used to extrapolate data through complex processes in cases where information or guidance was limited. For example, in accordance with CCR Title 23 §354.16, groundwater elevation contour maps are required based on the best available information. This requirement does not specify methods to use for producing the data, but the DWR Best Management Practice (BMP) for HCM suggests techniques used in Tonkin, M. and Larson, S. (2002), which uses geostatistical methods in conjunction with logical interpretations of groundwater level data to provide an adequate level of detail and accuracy.

Certain GIS software programs, including QGIS and ArcGIS, were relied on heavily. QGIS is a powerful open-source program, whereas ArcGIS is the industry standard. Both are capable of completing the required elements for the GSP.

QGIS provided the graphical capabilities for final map production. ArcGIS was specifically utilized because of a thirdparty extension, CrossView, which is capable of generating hydrogeologic cross-sections that are presented in Section

2.1.7. The Universal Transverse Mercator (UTM) coordinate system and North American Datum of 1983 (NAD 83) were utilized along with the North American Vertical Datum of 1988 (NAVD 88) for all spatial data.

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2.1.2Regional Geologic and Structural Setting
The Eastern San Joaquin Subbasin lies within the San Joaquin Valley, which is part of the Central Valley of California.

The Central Valley is a 400-mile-long, 50-mile-wide, northwestward trending asymmetrical structural trough filled with geologic units deposited over a long period of time. See Table 2-2 (Section 2.1.5) for the generalized stratigraphic column and Figure 2-6 below for the geologic time scale. The Sierra Nevada Mountain Range, east of the Central Valley, consists of pre-Tertiary igneous and metamorphic continental rocks. The Coast Range, to the west, consists of pre-Tertiary and Tertiary semi-consolidated to consolidated marine sedimentary and continental rocks. The material sources for the Central Valley continental deposits are the Coast Range and the Sierra Nevada, which are composed primarily of granite, related plutonic rocks, and metasedimentary and metavolcanic rocks from Late Jurassic to Ordovician age (Bertoldi et al., 1991).

Figure 2-6: Geologic Time Scale
Millions of
Years Ago
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2.1.3Geologic History
The origin of geologic formations within the Eastern San Joaquin Subbasin varies in geologic time ranging from recent to Pre-Cretaceous bedrock or basement. Six to 10 miles of sediment have been deposited within the Central Valley and include both marine and continental deposits consisting of gravels, sands, silts, and clays. During the middle Cretaceous (~100 million years ago), parts of the Central Valley were inundated by the Pacific Ocean resulting in deposition of marine deposits. Marine conditions persisted through the middle to late Tertiary period (~3-30 million years ago) after which time sedimentation changed from marine to continental deposits due to the retreat of the sea and the regional rising of land mass previously inundated by the ocean. Intermittent volcanism dominated with the deposition of rhyolites and andesites (CA DWR, 1967).

2.1.4Near-Surface Conditions

2.1.4.1 Topography
Ground surface elevations vary extensively across the Eastern San Joaquin Subbasin, from almost 1,000 feet above mean sea level (MSL) in the upland areas in the east to around sea level in the flat lying valley floor to the west. The Eastern San Joaquin Subbasin topographic map is provided as Figure 2-7.

The modern-day physiographic features are a direct result of the geologic history of the region. Surficial features on the valley floor in the Eastern San Joaquin Subbasin can be divided into physiographic units as described by DWR (1967) and Burow and others (2004): river flood plains, channels, and overflow lands; low alluvial plains and fluvial fans; and dissected uplands. The dissected uplands lie along the flanks of the valley between the Sierra Nevada to the east and the alluvial plains and fluvial fans to the west. Local relief ranges in excess of 100 feet in the form of dissected hills and gently rolling lands. The most extreme slopes are observed in Calaveras County, which are steeper than 25 percent. West of the dissected uplands is a belt of coalescing fluvial fans of low relief (less than 10 feet) that forms the low alluvial plains and fans that range in width from about 14 to 20 miles. These fans lie between the dissected uplands and the nearly flat surface of the valley trough. River floodplains and channels occur as narrow, disconnected strips along the channels of the major rivers. Overflow lands of the valley trough tributary to the San Joaquin River define the area inundated by rivers when floods are highest under natural conditions.

2.1.4.2 Major Hydrologic Features
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Figure 2-8. The Subbasin is bounded on all sides except to the east by streams. Adjacent groundwater subbasins also share an interest in the impacts of the Sustainable Groundwater Management Act (SGMA) on these boundary streams.

In the Eastern San Joaquin Subbasin, the major rivers running east-west have headwaters high in the Sierra Nevada and flow west toward the axis of the valley (
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Figure 2-8). Little deposition is taking place currently, and the rivers are cutting downward on the upper reaches of the fans where the river floodplains are commonly entrenched to depths of 50 to 80 feet. However, toward the lower ends of the fans where river gradients are low, many small streams and tributaries of the major rivers are actively aggrading their beds.

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Figure 2-7: Topography
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Figure 2-8: Major Hydrologic Features
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The San Joaquin River is the principal drainage outlet of the northern San Joaquin Valley, flowing northward on the west margin of the Eastern San Joaquin Subbasin to its confluence with the Sacramento River in the Sacramento-San Joaquin River Delta (Delta) (Burow et al., 2004). Three major westerly flowing tributaries to the San Joaquin River within or adjacent to the Eastern San Joaquin Subbasin are the Stanislaus River (Subbasin south boundary), the Mokelumne River (north portion of Subbasin), and the Calaveras River (central portion of Subbasin).

The Stanislaus River drains a watershed of about 1,040 mi2(Burow et al., 2004) and flows through the dissected uplands between the communities of Knights Ferry and Oakdale, along the low alluvial plains and fans near the City of Riverbank to the confluence with the San Joaquin River near Vernalis (see Figure 2-9). Most of the watershed area falls within Modesto Subbasin. The flow in the Stanislaus River varies seasonally from less than 134 acre-feet per day (AF/day) during the dry season in early fall to over 16,400 AF/day during wet season in winter. These flows correlate to discharges from 68 to over 8,270 cubic feet per second (cfs) recorded at the Orange Blossom Bridge gauging station approximately one mile east of Oakdale and eight miles west of the Subbasin boundary along the river (CA DWR, 2019).

The Mokelumne River drains a watershed of about 5,550 km2(2,140 mi2) and flows through the dissected uplands between the communities of Jackson and San Andreas into Pardee Reservoir where it is released to flow downstream into Camanche Reservoir and out along the alluvial plains and fans toward its confluence with the San Joaquin River near Isleton. On the north boundary of the Eastern San Joaquin Subbasin is Dry Creek and the Lower Dry Creek Watershed, the majority of which is within Cosumnes Subbasin. Dry Creek is mapped as an ephemeral drainage and is tributary to the Mokelumne River with its confluence near Thornton. Flow in the Mokelumne River below Camanche Reservoir varies seasonally and is dependent on discharges from the on-stream reservoir, from less than 200 AF/day during the dry season to 9,900 AF/day during the wet season. These flows correlate to discharges from as low as 100 to no more than 5,000 cfs reported by the USGS below the Camanche Dam. Major watersheds of the river are the Upper Mokelumne River (most of which is outside of the Subbasin to the east, with a small portion overlapping with Cosumnes Subbasin) and the Lower Mokelumne River (mostly contained in the Subbasin, with a small portion intersecting the South American and Solano Subbasins).

The Calaveras River, also with headwaters in the Sierra Nevada, drains a watershed of about 1,370 km2(530 mi2) and flows into and across the Subbasin to its confluence with the San Joaquin River on the northwest side of Stockton.

Flow in the Calaveras River below the New Hogan Reservoir varies seasonally from 608 AF/day to 19,800 AF/day and is dependent on discharges from the on-stream reservoir. These flows correlate to discharges from 223 to over 10,000 cfs reported by the USGS below the New Hogan Reservoir.

In addition to the Stanislaus, Mokelumne, and Calaveras Rivers, 10 watersheds extend into and across the Eastern San Joaquin Subbasin. Three of these watersheds extend beyond the western boundary of the Eastern San Joaquin Subbasin into the East Contra Costa or Tracy Subbasins: Middle River-San Joaquin, Five Mile Creek-San Joaquin, and Lone Tree Creek-San Joaquin. The Lone Tree Creek-San Joaquin watershed has its headwaters in the Coast Range foothills. Figure 2-9 depicts the Eastern San Joaquin Subbasin and the watersheds that overlie the Subbasin.

Table 2-1 is a list of watersheds that overlie the Subbasin.

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Table 2-1: Eastern San Joaquin Subbasin Watershed Details Watershed Name Total Area
(square miles)
Area within
Subbasin
(square miles)
Percentage of
Watershed within
Subbasin
Lower Mokelumne River 223 202 91
Lower Dry Creek 88 47 53
French Camp Slough 88 88 100
Upper Mokelumne River 93 15 16
Lone Tree Creek 158 158 100
Little Johns Creek 122 63 52
Rock Creek 107 44 41
Calaveras River 224 133 60
Middle River-San Joaquin River 213 49 23
Mormon Slough 75 75 100
Lower Stanislaus River 218 37 17
Lone Tree Creek-San Joaquin River 169 98 58
Five Mile Creek-San Joaquin River 154 62 40
Bear Creek 127 127 100
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Figure 2-9: Eastern San Joaquin Subbasin Watersheds
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2.1.4.3 Surface Soils
Soils in the Eastern San Joaquin Subbasin are one of the primary controlling factors on surface water percolation rates through the vadose zone down to the groundwater table. As described in CA DWR (1967), soils in the region of the Eastern San Joaquin Subbasin can be grouped into five main categories:

1. Alluvial fan and flood plain soils

2. Organic basin soils

3. Basin soils

4. Lower terrace soils

5. Higher terrace and upland soils
These groupings coincide in part with the geologic formations in that the oldest soils are found on the nearly level high terraces and old fluvial fans in the eastern part of the area. The oldest soils typically have claypan or hardpan layers at depths of two feet or less. The youngest soils are forming on the recently deposited alluvium along stream bottoms and on recently exposed surfaces. These soils are generally deep and rich in nutrients. The soils at intermediate stages of development are on the low terraces. Figure 2-2-10 shows the areal distribution of the five soil types in San Joaquin County (CA DWR, 1967).

Alluvial fan and floodplain deposits are
present in three areas of the Eastern
San Joaquin Subbasin bounding major
east-west rivers: Mokelumne,
Calaveras, and Stanislaus Rivers.

Figure 2-2-10 depicts soil depositional
areas within the Subbasin. These areas
have the best infiltration rates,
exclusive of the peat locales in the
Delta (northwest portion adjacent to the
Mokelumne River).

Soils of the Mokelumne and Stanislaus
River fans have young soil profiles of
sandy loam to loam. Infiltration rates of
the soils are predominantly between

0.6 to 2 inches per hour. Areas of silt
loam are also common especially in the
floodplain and have a lower infiltration
rate of less than 0.6 inches per hour.

Soils in the alluvial fans tend to coarsen
toward the apex of the fan. The soil
types show little compaction and slight
accumulation of lime or clay. Hardpan
development, which would preclude
infiltration, is minimal.

Figure 2-2-10: Soil Depositional Areas
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The soils of the Calaveras fan have deeper profiles of loam and clay loam with an infiltration rate of less than 0.6 inches per hour. These soils tend to be darker and heavier than the Stanislaus and Mokelumne River fan soils likely due to the source area being restricted to metamorphic or pre-Tertiary sedimentary material, whereas the Mokelumne and Stanislaus Rivers received large contributions from a granitic source (CA DWR, 1967).

The organic basin soils are restricted to the lower Delta portion of the Eastern San Joaquin Subbasin. Peat, muck, and clay loam are terms commonly applied to soils in this group. The organic basin soils have variable infiltration capacity.

Where peat is the dominant soil constituent, infiltration is high (greater than 2 inches per hour); where clay loam or muck occurs, infiltration is low (less than 0.6 inches per hour) (CA DWR, 1967).

The interfan and basin soils lie between the Mokelumne, Calaveras, and Stanislaus River fans in a northwesterly trending belt and around the periphery of the organic basin soils. These soils generally have well-developed profiles, medium-to-heavy textures, and fairly well compacted subsoils. Locally, hardpan overlies silty to silty clay loams.

Consequently, these soils have low infiltration rates (less than 0.6 inches per hour).

The terrace and upland soils have profiles containing moderately dense accumulation of clay and claypan, relatively near the surface. These layers are impervious barriers to the local downward movement of water, except where root holes and other breaks permit infiltration.

The Natural Resource Conservation Service (NRCS) categorizes soils by hydrologic soil groups. The hydrologic soil group is an estimation of the infiltration rate of the first five feet of soil based on depositional characteristics (mostly grain size and sorting) and secondary characteristics (compaction, lithification, and weathering). Hydrologic soil groups and their relative infiltration rates are listed below:
• A (high)
• B (medium)
• C (slow)
• D (very slow)
Figure 2-11 shows the distribution of soils mapped by hydrologic soil group across the Eastern San Joaquin Subbasin.

The broad geologic features of the Eastern San Joaquin Subbasin reflecting the river drainage elevations, areas, and percent above snowline are also apparent in the map of soils distribution. The Stanislaus and Mokelumne River alluvial fans have the overall highest infiltration rate followed by the Calaveras River fan. The smaller foothill watersheds have the lowest average infiltration rates. The relatively high permeability of windblown sands on the Mokelumne and Stanislaus River fans and the recent alluvium of the current Mokelumne and Calaveras River floodplains are also recognizable (Figure 2-11).

Hardpan is a strongly cemented weathering profile that limits infiltration unless it is modified by ripping or excavating.

Some hardpan is discontinuous and relatively shallow (located at a depth of five feet or less) and often is ripped with a bulldozer for agricultural purposes. However, in other areas, particularly in the older pre-Modesto formations, the hardpan is more continuous and extends to depths that cannot be reached by ripping methods.

The Farmington Groundwater Recharge/Seasonal Habitat Study Final Report, prepared by Montgomery Watson Harza (MWH) and dated August 2001 (MWH, 2001), overlaid the NRCS’s interpretation of where hardpan soils would be found under natural conditions. The extent of the thickest hardpan is shown in Figure 2-12 in dark blue cross hatching.

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Figure 2-11: Hydrologic Soil Groups
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Figure 2-12: Occurrence of Hardpan within the Eastern San Joaquin Subbasin ATTACHMENT 2
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2.1.4.4 Imported Water
The Eastern San Joaquin Subbasin does not rely on imported water supplies. All surface water used within the Subbasin originates from sources either within or directly tributary to the Subbasin. Several districts receive surface water from the Stanislaus River with a point of diversion approximately four miles upstream of the eastern boundary of the Subbasin (located in the Sierra Nevada foothills and not part of a Bulletin 118 groundwater basin). While this diversion point occurs outside of the Subbasin boundary, this water naturally enters the Subbasin by diversion or by surface-groundwater interaction.

2.1.4.5 Groundwater Recharge and Discharge Areas
Groundwater recharge and discharge is driven by both natural and anthropogenic (human-influenced) factors. Areas of recharge and discharge within the Eastern San Joaquin Subbasin are discussed below. Quantitative information about all natural and anthropogenic recharge and discharge is provided in Section 2.4.

2.1.4.5.1 Description of Recharge Areas
The recharge potential of soils and formations encountered in the Eastern San Joaquin Subbasin varies considerably and is dependent on primary and secondary geologic effects. Primary geologic patterns that influence permeability relate to grain size and sorting as a result of depositional characteristics. Secondary geologic effects that influence soil recharge characteristics are associated with post-depositional events such as consolidation, lithification, and weathering, including the development of hardpan soils (MWH, 2001). Additional information on geologic formations is provided in Section 2.1.5.

The primary (original) geologic permeability of the pre-Modesto formations is variable depending on grain size, but in general is low due to secondary (post-depositional) effects including the development of hardpan soils. However, the units are heterogeneous (variable), and permeable channels are common beneath the hardpan. The primary permeability of the Modesto Formation varies both east-west and north-south due to grain size differences in the original depositional environments. On any given drainage, the alluvium is generally coarsest (and most permeable) in the east where the gradient is steepest, and the relatively high energy stream carries and deposits a high proportion of coarse bedload sand and gravel (the proximal fan). Suspended sediment (clay and silt) is generally not deposited until it is carried farther west to a lower energy environment (the distal fan). As a result, the average permeability, and thus the average recharge rates, of the alluvial fan decreases overall from east to west (MWH, 2001).

The grain size distribution produced from each watershed depends on several characteristics, including the type of geologic materials in the source area, the watershed's gradient and total area, and the portions of the watershed subject to rainfall and snowmelt runoff. During the Pleistocene Epoch when the Modesto and Riverbank formations were deposited (approximately 1 million to 10,000 years ago), a colder, wetter climate produced a lower snowline than at present, and coarse glacial outwash dominated the major streams originating in the interior of the Sierra Nevada (Mokelumne and Stanislaus River fans). Alluvium of the smaller foothill watersheds consists primarily of fine-grained material in interfan areas (Bear Creek and Little Johns/Rock Creek drainages). The Calaveras River drainage is intermediate between the two, forming a moderately coarse alluvial fan between the Calaveras River and Mormon Slough (MWH, 2001). Figure 2-13 depicts the aerial extents of the alluvial fans, interfan areas, and pre-Modesto formations.

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Figure 2-13: Areal Extents of Alluvial Fans, Interfans, and Pre-Modesto Formations ATTACHMENT 2
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Within this overall framework, the alluvial fans of each drainage contain coarse-grained channel and levee deposits of relatively high permeability within finer-grained overbank and floodbasin deposits of low permeability. Stream channels migrate and abruptly jump to new locations over time in this depositional environment, creating deposits that are heterogeneous both laterally and vertically. As a result of this depositional environment, localized silt and clay lenses are common even in the alluvial fan areas. However, no regional clay layer is expected to exist that would severely reduce or inhibit vertical migration of water. The recent (Holocene) alluvium in the current incised river floodplains (Mokelumne and Calaveras Rivers) and windblown (eolian) sand deposits are of limited extent but relatively permeable (MWH, 2001). These present and historical alluvial depositional factors are useful in understanding rainfall percolation rates when the soil moisture deficit is zero and groundwater recharge occurs; groundwater system preferential vertical movement pathways through the principal aquifer and aquitards; and future groundwater management alternatives.

The Eastern San Joaquin Water Resources Model (ESJWRM) estimates the recharge that occurs in different areas of the Eastern San Joaquin Subbasin, largely due to the percolation of rainfall and applied irrigation water. Figure 2-14 shows the spatial distribution of percolation in the Subbasin, with generally less percolation occurring in finer soil areas (e.g., Hydrologic Soil Group D) and areas without extensive irrigation (i.e., native landscape). The higher percolation areas are those that substantially contribute to the replenishment and recharge in the Subbasin. Section 1.2.2.9 describes conjunctive use programs that were in place prior to the implementation of SGMA, and Figure 1-16, shown previously in Chapter 1: Agency Information, Plan Area, and Communication, maps direct recharge areas in the Subbasin.

DWR’s texture interpretation of the AEM data provided an additional data source for evaluating near-surface conditions in terms of percent coarseness of the material. Figure 2-15 shows the average percent coarseness (coarse fraction) in the top 50 ft of the subsurface along the survey flight lines. Darker blues represent finer material, while greens and yellows represent coarser material. On the eastern side of the Subbasin, where the alluvial fans identified in Figure 2-13 lie, the resistivity data indicate that the near-surface material is relatively coarser than in other areas of the Subbasin. This is consistent with general understanding of alluvial fan structure, where coarser materials are found further east where the gradient is higher. Increasingly to the west, the material becomes increasingly finer. Resistivitybased coarse fraction data complements ESJWRM model output, Hydrologic Soil Group mapping, Soil Agricultural Groundwater Banking Index (SAGBI) mapping, and geologic maps to identify areas in which natural groundwater recharge is occurring.

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Figure 2-14: Existing Areas of Groundwater Recharge (ESJWRM Version 3.0) Note: Figure shows the distribution of deep percolation of precipitation and applied water based on ESJWRM Version 3.0 model outputs. It does not include recharge from rivers and streams, boundary flows, or recharge projects.

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Figure 2-15: Average Percent Coarse Fraction in Near-Surface Materials

2.1.4.5.2 Description of Discharge Areas
Groundwater discharge primarily occurs through groundwater production wells. Groundwater production in Eastern San Joaquin Subbasin is discussed further in Section 2.2. Groundwater also discharges to rivers and streams where groundwater elevations are higher than river stage. Other sources of groundwater discharge are evapotranspiration from riparian areas, phreatophyte woodlands, and other groundwater-dependent ecosystem (GDE) communities.

Groundwater discharge to streams is described more in Section 2.2.6 and discusses analyses based on modeling results from the ESJWRM for approximately 1,700 stream nodes (locations along simulated streams where calculations are made related to stream flows and interaction with groundwater) in the Eastern San Joaquin Subbasin.

2.1.4.5.3 Description of Potential Recharge Areas
Figure 2-16 shows areas with their potential for groundwater recharge, as identified by the Soil Agricultural Groundwater Banking Index (SAGBI). SAGBI provides an index for the groundwater recharge for agricultural lands by considering deep percolation, root zone residence time, topography, chemical limitations, and soil surface condition.

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SAGBI data are derived from “modified” SAGBI data. “Modified” SAGBI data show higher potential for recharge than unmodified SAGBI data because the modified data assume that the soils have been or will be ripped to a depth of 6 feet, which can break up fine grained materials at the surface to improve percolation. Modified SAGBI data categorize 310,098 acres out of 610,890 acres (51 percent) of agricultural and grazing land within the Subbasin as moderately good, good, or excellent for groundwater recharge (University of California, Davis, 2018).

Figure 2-16: Potential Recharge Areas

2.1.5 Geologic Formations and Stratigraphy
Geologic formations within the Central Valley and Eastern San Joaquin Subbasin are generally grouped as either eastside or westside formations based on their location relative to the San Joaquin River and the source of the sedimentary material of which they are composed. The Eastern San Joaquin Subbasin is located to the east of the San Joaquin River. Eastside continental formation material generally originates from deposits from the Sierra Nevada and westside continental formation material generally originates from the deposits of the Coast Range. Rising land masses contributed to the erosion and deposition of alluvial sands and fan deposits. Glaciation in the Pleistocene also contributed to the steepening of streams during melt water periods (CA DWR, 1967).

The block diagram of the Central Valley (Figure 2-17) provides a generalized geologic cross-sectional view of the geologic setting. The Eastern San Joaquin Subbasin is located in the foothills margin between the roughly horizontal alluvial sediments of the Central Valley geomorphic province, labeled “Central Valley” in Figure 2-17, and the granitic Sierra Nevada geomorphic province, labeled “Sierra Nevada” in Figure 2-17.

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Sediment deposits can be subdivided into consolidated and unconsolidated deposits, with the consolidated sediments underlying the unconsolidated sediments. The most important fresh water-bearing formations in the Eastern San Joaquin Subbasin are the sands within the consolidated Mehrten and Laguna Formations and the unconsolidated younger alluvial deposits consisting of the Riverbank and Modesto Formations.

Figure 2-17: Generalized Geologic Section and Eastern San Joaquin Subbasin Setting With depth, the stratigraphy of unconsolidated sediments consists initially of Recent to Pleistocene Age alluvial deposits of the Post-Modesto deposits and the Modesto and Riverbank Formations. The sediments of these units are typically unconsolidated sands and gravels interbedded with considerable silts and clays. These clays separate the upper sediments over the lower Late Plio-Pleistocene Age Laguna Formation and the older Eocene to Pliocene Age Mehrten Formation. The Laguna and Mehrten Formations are characterized by poorly consolidated sediments and are differentiated based on color and sand type. The Laguna Formation is typically light brown, and the differentiating characteristic of the Mehrten is black sands derived from volcanic detritus. The Valley Springs and Ione Formations are encountered below the Mehrten Formation. The formations have a distinct geologic dip and thickness to the west.

The geologic map shown in Figure 2-18 illustrates the surface deposits of the Pleistocene-aged Modesto Formation and Turlock Lake Formation largely within the valley floor (Wagner et al., 1981; Wagner et al., 1991). The knolls and ridges to the east represent outcrops of the Tertiary-aged Laguna, Mehrten, Valley Springs, and Ione Formations. The geologic stratigraphic column is provided on Table 2-2.

Eastern San Joaquin Subbasin
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Figure 2-18: Geologic Map
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Table 2-2: Generalized Stratigraphic Column, Formation Descriptions, and Water-Bearing Properties Era*
Period*
Epoch* Formation &
Map Symbol
Thickness
Maximum (feet) Rock Characteristics and
Environment
Water-Bearing
Properties

CENOZOIC
Quaternary
Holocene Stream Channel
Deposits
50± Continental unconsolidated
gravel and coarse to medium
sand deposited along present
stream channels.

High permeability,
significant avenue for
percolation to
underlying formations.

Late Pliocene Modesto (Qm) 65-130± Continental fan and interfan material, locally some basin
types, lenticular gravel, sand,
silt, clay.

Moderate
permeabilities.

Unconfined aquifer.

Pliocene Riverbank (Qr) 150 to 250 Continental fan and interfan material, locally some basin
types, lenticular gravel, sand,
silt, clay. Reddish clay-rich
duripan caps the unit.

Moderate
permeabilities.

Unconfined aquifer.

Recent to PlioPleistoceneFlood Basin
Deposits (Qb)
Turlock Lake
Formation (Qtl)
0-1,000± Continental basinal equivalent
of Laguna, Tulare & younger
formations. Clay, silt & sand,
organic in part.

Generally low
permeabilities,
saturated environment,
unconfined to confined.

Plio-Pleistocene Laguna (Tl) 0-1000± Continental, semi-to unconsolidated silt, sand &
gravel, poorly sorted, includes
Arroyo Seco Gravel pediment
of Mokelumne R. area.

Moderate permeability,
Unconfined to locally
semi-confined.

Restricted perched
bodies in some areas.

Tertiary
Mio-Pliocene Mehrten (Tm) 0-600± Continental andesitic
derivatives of silt, sand and
gravel & their indurated
equivalents; tuff; breccia;
agglomerate.

Moderate permeability
to high where "black
sands" occur. Confined
to unconfined.

Miocene Valley Springs
(Tvs)
0-500± Continental rhyolitic ash, clay,
sand & gravel and their
indurated equivalent.

Low permeability. Not
considered as
significant in
groundwater studies.

Eocene Ione (Tl) 0-500± Light colored clay and sand.

Marine shale, siltstone and
sandstone
Contains saline waters
except where flushed
in outcrop areas.

MESOZOIC
Creta- ceous
Cretaceous
Jurassic
Undifferentiated
Bedrock
Igneous, metamorphics and
ultramafics.

Contains saline waters.

Not relevant to fresh
water basin except as
possible contaminant
source.

Pre- Cretace- ous
Sources: CA DWR, 1967; Burow et al., 2004
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2.1.5.1 Geologic Formation Descriptions
The Tertiary-age units that overlie the basement rocks and generally outcrop within the Eastern San Joaquin Subbasin are discussed in the following sections, from oldest to youngest.

2.1.5.1.1 Pre-Ione Eocene Rocks
The pre-Ione Eocene rocks, as described by Chapman and Bishop (1975), were deposited in a pre-Ione bedrock paleochannel system. Their composition includes sedimentary rocks of marine origin with biotite, chlorite, and muscovite. Feldspar is a significant component of this unit (Creely & Force, 2007). The thickness of this unit is highly variable in the foothill area as it is controlled by basement complex topography. The unit “wedges out” to the east and assumes a more uniform regional thickness to the west in the Central Valley Mesozoic-Cenozoic sediment pile (Creely & Force, 2007). Depictions and full geologic formation detail are provided in Table 2-2. The Tertiary volcanic and sedimentary rocks and terrace deposits are separated from the Jurassic volcanic/metamorphic basement by an angular unconformity from small-scale faulting. The Franciscan Group, Cretaceous, and Eocene Undifferentiated deposits have been impacted by the east-west Stockton Fault (CA DWR, 1967).

2.1.5.1.2 Ione Formation
The Eocene Age Ione Formation has been mapped along the eastern margin of the Eastern San Joaquin Subbasin and, as described by Loyd (1983), contains interbedded kaolinitic clay, quartz sand, sandy clay, and lignite. The Ione Formation is characteristically light in color, with color influenced by iron oxide, lignite, and carbonaceous mud rocks and shale (Creely & Force, 2007). Pask and Turner (1952) subdivided the Ione Formation into upper and lower members based on mineralogy. The upper and lower members contain kaolinite (anauxite) clays. Deposits can include coarse-grained sand (up to 2 mm diameter).

Ione sand is one of the most important sources of commercial clay and silica sand in the Ione Formation (Creely & Force, 2007). Ione sand has a white color with a pearly luster and appears massive; however, closer examination usually reveals cross stratification, heavy mineral laminae, and burrows (Creely & Force, 2007). Quartz is abundant with varying feldspar content in both members.

The lower member contains 8 to 10 percent feldspar, with the upper member containing 20 to 25 percent feldspar. The minerals biotite and chlorite are rare in the lower member and common in the upper member. Heavy mineral deposits vary. The lower member contains mature minerals like zircon and ilmenite. The upper member contains hornblende and epidote. Chromite is also commonly found in the Ione Formation. The upper member is largely absent north of Jackson Valley due to erosion and deposition during the development of the overlying Valley Springs Formation. The Ione Formation is deposited in both marine and fluvial continental environments (Creely & Force, 2007).

2.1.5.1.3 Valley Springs Formation
The Oligocene-Age Valley Springs Formation is described by Loyd (1983) as stream channel and alluvial deposits derived mainly from rhyolitic volcanic rocks, including some white, welded tuffs, and ash flows. The basal contact of the Valley Springs Formation is characterized, locally, by the presence of rhyolitic conglomerate. These tuffs may display alteration to clays, and, in extreme cases, only a claystone bed with relict tuffaceous texture remains. Pure deposits of rhyolitic ash exist in areas, while many sand and ash beds are present. In general, the clay beds of the Valley Springs Formation are greenish in color, may contain silt, sand, and large pumice fragments. The sandstones range in grain-size from fine to coarse and are typically well cemented. Predominantly composed of quartz and preCretaceous material, the relatively sparse conglomerate lenses within the tuff, clay, and sandstone may also contain pumice fragments. In general, the Valley Springs Formation is predominantly fine-grained, containing less coarsegrained deposits. In the Central Valley, the Valley Springs Formation is considered to be largely non-water-bearing.

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2.1.5.1.4 Mehrten Formation
Overlying the Valley Springs Formation is the Miocene Age Mehrten Formation, described as being stream channel, alluvial, and mudflow deposits derived mainly from andesitic volcanic rocks. The Mehrten Formation is considered the oldest significant fresh water-bearing formation within the Eastern San Joaquin Subbasin.

Bartow (1992) generally describes the Mehrten in the east-central portion of the Central Valley as being sandstone composed of amphiboles, pyroxenes, and pebbles (mostly volcanic) with lenticular bedding and gray to blue color.

Bartow discusses a major change in regional volcanism as the rhyolitic pyroclastic deposits of the Late Oligocene and earliest Miocene were replaced near the end of the Early Miocene by reestablished andesitic arc volcanism in the northern Sierra Nevada. This andesitic volcanism provided the source materials for the Mehrten Formation.

Ferriz (2001) discusses how the Mehrten Formation outcrops discontinuously along the eastern flank of the Valley and was laid down in the Mokelumne area by streams carrying andesitic debris from the Sierra Nevada. The Mehrten thickens in the northeastern part of the San Joaquin Valley; generally, it can be more than 700 to 1,200 feet thick at depths ranging from more than 300 feet below ground on the east side of the valley to depths exceeding 1,400 feet along the central portion of the valley. The contact between the Mehrten Formation and underlying Valley Springs Formation is a non-distinct unconformity.

The Mehrten Formation is subdivided into upper and lower units. The upper unit contains finer grained deposits (black sands interbedded with brown-to-blue clay), and the lower unit consists of dense tuff breccia. Deep wells in the Stockton area indicate that the upper portion of the Mehrten Formation contains a high percentage of clay, suggesting that the upper portion of the unit may be finer grained than the middle or lower portions with resulting semi-confined conditions (CA DWR, 1967).

The black sands of the Mehrten Formation (black andesite detrital grains) generally have moderate to high permeability and yield large quantities of fresh water to wells, which makes them a preferred exploration target for groundwater supply in the eastern half of the Central Valley (Davis & Hall, 1959; CA DWR, 1967). East of Jack Tone Road, a large number of wells produce water from the relatively permeable “black sands” commonly described as hard sandstones (CA DWR, 1967).

2.1.5.1.5 Laguna Formation
The Pliocene to Pleistocene Laguna Formation is composed of discontinuous lenses of unconsolidated to semiconsolidated alluvial sands, gravels, and silts and is typically light brown. These poorly exposed stream-laid alluvial deposits form high terraces and are associated with the last major uplift in the Sierra Nevada.

The Laguna Formation outcrops in the northeastern part of San Joaquin County and dips at 90 feet per mile and reaches a maximum thickness of 1,000 feet, with the thickest areas (400 to 1000 feet) observed near the Mokelumne River in the Stockton Area (CA DWR, 1967). The Laguna Formation is moderately permeable with some reportedly highly permeable coarse-grained fresh water-bearing zones.

2.1.5.1.6 Turlock Lake Formation
The Turlock Lake Formation consists primarily of arkosic alluvium, mostly fine sand, silt, and in places clay, at the base grading upward into coarse sand and occasional coarse pebbly sand or gravel (Marchand & Allwardt, 1981). The age of the Turlock Lake Formation is about 600,000 to greater than 730,000 years old, but younger than about 1 million years. The Turlock Lake commonly stands topographically above the younger fans and terraces throughout the northeastern San Joaquin Valley, in a broad band between the Merhten, Laguna, and the younger Riverbank and Modesto alluvial fans to the west. A buried soil separates the Turlock Lake Formation into two units (upper and lower) in the northeastern San Joaquin Valley. The thickness of the Turlock Lake is variable and appears to increase toward the east. Estimates of thickness in the subbasins to the south range from 295 to 850 feet for eastern Stanislaus County, 1,000 feet for northern Merced County, and 160 to 720 feet in the Chowchilla area.

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The Turlock Lake Formation is differentiated from the west to east by its Corcoran Clay member that is present in the southwest corner of the Subbasin near Manteca, and dominates the area west of Highway 99 south of the Eastern San Joaquin Subbasin. The Corcoran Clay becomes interbedded with the sands and silt of the upper Turlock Lake Formation and is not found in the central and northern portions of the Subbasin. The Corcoran Clay is found ranging in thickness from a feather edge to 160 feet beneath the present bed of Tulare Lake. The Turlock Lake Formation is dominant within the basins to the south.

2.1.5.1.7 Riverbank Formation
The Riverbank Formation consists primarily of arkosic sediment derived mainly from the interior Sierra Nevada, which forms at least three sets of terraces and coalescing alluvial fans along the eastern San Joaquin Valley (Marchand & Allwardt, 1981). The Riverbank Formation is about 130,000 to 450,000 years old. The Riverbank, as exposed in the northeastern San Joaquin Valley, is primarily sand, containing some scattered pebbles, gravel lenses, and some interbedded fine sand and silt. The Riverbank unconformably overlies the Laguna Formation, and its terraces and fans truncate or are cut into Turlock Lake alluvium or fill post-Turlock Lake gullies and ravines, which, in turn, are cut and filled near the foothills by terraces of the lower member of the Modesto Formation. The Riverbank Formation is informally subdivided into three units (lower, middle, and upper) which appear to coarsen upward, like those of the older Turlock Lake Formation. The Riverbank Formation also shows a variable thickness that tends to increase toward the major river channels; 150 to 200 feet is reported in northern Merced and eastern Stanislaus Counties, 260 feet along the Merced River, and about 65 feet along the Chowchilla River.

2.1.5.1.8 Modesto Formation
The Modesto Formation is composed of mainstream arkosic sediments and associated deposits of local derivation laid down during the last major series of aggradation events in the eastern San Joaquin Valley (Marchand & Allwardt, 1981). Gravel, sand, and silt were deposited as a series of coalescing alluvial fans extending continuously from the Kern River drainage on the south to the Sacramento River tributaries in the north. They occur in a wide band immediately east of the San Joaquin Valley axis and to the west of the Riverbank and older fan remnants. Radiocarbon dating estimates the age of the Modesto Formation to be older than 9,000 years before present (B.P.) to 42,000 years B.P. Most of the prime agricultural land and many of the major cities are located in the young alluvial soils associated with the undissected Modesto terrace and fan surfaces. Modesto deposits overlie late Riverbank alluvium and older units and are locally incised or covered along modern channels by post-Modesto deposits.

The materials of the Modesto Formation are virtually identical to those of the Laguna, Turlock Lake, and Riverbank Formations, but their association with low terraces and young fans and their moderate to slight degree of erosional modification and soil profile development clearly differentiate them from older alluvium. The total thickness of the Modesto deposits is reported to be 50 to 100 feet in eastern Stanislaus County, 130 feet along the Merced River, and about 65 feet along the Chowchilla River fan. The Modesto Formation also thickens toward each river channel and toward the south; there is significant evidence of local facies changes laterally. Exposed sections differ substantially from exposures near the foothills and from exposures along the westward draining rivers.

2.1.5.1.9 Post-Modesto Deposits – Recent Alluvium and Basin Deposits In general, these younger units are less consolidated and sedimentary in nature, representing a sequence of young alluvial fills including alluvial fans, channel, point bar, levee, crevasse splay, interdistributary, and floodbasin alluvium.

The alluvial fan deposits are much smaller than the late Modesto fans. The age of these deposits ranges from 9,000 years B.P to modern time. Lacustrine, swamp, and marsh deposits are presently accumulating in poorly drained areas on the alluvial fan toes. In oxbow lakes on river flood plains, near the edge of the Delta where Holocene sea level rise caused alluviation of the lower Mokelumne and Cosumnes Rivers, lakes and swamps have formed where tributary gullies have been blocked by mainstream aggradation (Marchand and Allwardt, 1981).

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2.1.6Faults and Structural Features
The Stockton Fault – The Stockton Fault is the largest fault in the Eastern San Joaquin Subbasin, shown in Figure 2-19. It is a large reverse fault with displacements of up to 3,600 feet (1,100 m) that trends transverse to the regional structure and bounds the Stockton Arch on the north. Bartow (1985) shows relative movement along the fault as northside-down. The timing of the vertical movement is predominantly post-Eocene (Hoffman, 1964), and the latest movements appear to have been subsequent to deposition of the basal part of the Valley Springs Formation, probably during Miocene time.

The Vernalis Fault – The Vernalis Fault is a reverse fault with northwest-southeast trend that bounds the TracyVernalis anticlinal trend that is mapped outside of the west boundary of the Eastern San Joaquin Subbasin. East-sidedown movement of as much as 1,500 feet (460 m) probably took place at the same time as the major movements on the Stockton Fault (Bartow, 1985). The relative thickness of sediments can be inferred from the elevations of the base of the freshwater aquifer system shown in Figure 2-20. The freshwater aquifer system on the north side of the Stockton Fault extends approximately 600 feet deeper than the aquifer system south of the fault. Relative movement along the fault is north-side-down, thus allowing for greater accumulation of the continental Tertiary sediments and deepening of the aquifer materials in this area.

Stockton Arch – The Stockton Arch is a broad transverse structure that underlies the southern half of the Eastern San Joaquin Subbasin. The arch is bounded on the north by the Stockton Fault, and the southern limit is the line of truncation of Paleogene strata south of Modesto (Bartow, 1985). Indications of northward-shallowing marine facies in the lower Paleogene sequence suggests that the arch was present by Paleocene time. Erosion during the Oligocene time apparently reduced whatever physiographic expression the arch may have had and left a nearly flat plain prior to deposition of the later Tertiary units.

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Figure 2-19: Faults and Structural Features
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As a result of the north-side-down movement along the Stockton Fault, the Tertiary sediments are thicker north of the fault and thinner south of the fault. This feature also influences the location, depth, and thickness of the “base of the fresh water,” as shown below in Figure 2-20. The base of fresh water is discussed further in Sections 2.1.7 and 2.1.8.2.

Figure 2-20: Base of Fresh Water Elevation and Stockton Fault Angular unconformities – There are a series of angular unconformities formed during the Cenozoic-related to uplift of the Sierra Nevada to the east (Bartow, 1985). The Cenozoic history of the Sierra Nevada is one of progressive westward tilting, perhaps episodic, with an increasing rate in the late Cenozoic. The subtle angular unconformities that separate the Tertiary units are evidence of this progressive tilting. The Tertiary units rarely have dips of more than 2 degrees; the difference in dip between the Ione and the Valley Springs Formations, for example, may be less than 1 degree. The discordances are most apparent in terms of gradients of depositional surfaces measured in distances of several miles. The largest discordances are between the Ione Formation (about 1,500 feet/mile) and the Valley Springs Formation (94 - 120 feet/mile), between the Mehrten Formation (99 - 131 feet/mile) and the Laguna Formation (52 - 79 feet/mile), and between the Laguna Formation and the Quaternary deposits (less than 18 feet/mile). The Ione-Valley Springs unconformity represents the Oligocene regression that affected most of central and southern California, and the Mehrten-Laguna unconformity probably marks the accelerated uplift of the Sierra Nevada beginning 3 to 5 million years ago (Huber, 1981) in the central part of the range. The Sierra Nevada was relatively stable through the Miocene with only a minor discordance between the Valley Springs and Mehrten Formations; their lithological difference reflects primarily a change from rhyolitic to andesitic volcanism in the source area. Uplift of the Sierra Nevada continued through the Quaternary, but the record is complicated by Quaternary climatic events (e.g., glaciation) which were the principal controlling factor in Quaternary sedimentation for the east side of the Great Valley.

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2.1.7Geologic Cross-Sections
Five geologic cross-sections (A-A’, B-B’, C-C’, D-D’, and E-E’) were developed for the Eastern San Joaquin Subbasin based on the stratigraphic information amassed as part of the data compilation efforts. A geologic cross-section is an interpretive diagram of the lateral and vertical subsurface relationships of geologic formations. A cross-section location map with locations of groundwater and oil and gas wells reviewed in the development process is provided as Figure 2-21. Three of the cross-sections (A-A’ through C-C’) are along east-west transects in the north, central, and southern portion of the Subbasin, respectively; two of the cross-sections (D-D’ and E-E’) are generally along north-south transects. Cross-section D-D’ generally transects the cities of Lodi, Stockton, and Manteca in the west portion of the Subbasin, and cross-section E-E’ transects the Eastern San Joaquin Subbasin along the alignment of Jack Tone Road from the northeast to the southwest portion of the Subbasin. Each of the five geologic cross-sections are provided in Figure 2-22, Figure 2-23, and Figure 2-24.

Four additional cross-sections (F-F’, G-G’, H-H’, and I-I’) were added as part of the 2024 Amended GSP, following the release of DWR’s AEM data. To supplement the existing cross-sections by geologic formation, these additional crosssections show an estimate of percent coarseness of the subsurface material. Percent coarseness estimations were developed by DWR, derived from AEM resistivity data through a comprehensive translation process in which texture characteristics of the subsurface are related to the collected resistivity measurements. Cross-sections by coarse fraction represent multiple flown survey lines stitched together to show a continuous line. Darker brown areas represent relatively finer materials (lower coarse fraction) and lighter yellow areas represent coarser materials (higher coarse fraction). Lithology logs used by DWR to generate the texture interpretation of the resistivity data are included on each cross-section. Figure 2-25 shows the locations of these four additional cross-sections. Cross-sections F-F’, G-G’, HH’, and I-I’ are included in Figure 2-26, Figure 2-27, Figure 2-28, Figure 2-29, respectively.

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Figure 2-21: Cross-Section, by Formation, Location Map
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Figure 2-22: Hydrogeologic Cross-sections A-A’ and B-B’ ATTACHMENT 2
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Figure 2-23: Hydrogeologic Cross-sections C-C’ and D-D’ ATTACHMENT 2
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Figure 2-24: Hydrogeologic Cross- section E-E’
SOUTH
E’
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Figure 2-25: Cross-Section, by Percent Coarseness, Location Map ATTACHMENT 2
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Figure 2-26: Percent Coarse Cross-Section F-F’
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Figure 2-27: Percent Coarse Cross-Section G-G’
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Figure 2-28: Percent Coarse Cross-Section H-H’
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Figure 2-29: Percent Coarse Cross-section I-I’
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Stratigraphic data fromwell completion reports of hundreds of water wells and oil and gas wells (indicated by an asterisk on the cross-sections) were used to develop the geologic cross-sections. Stratigraphy (e.g., clays and silts, sands and gravels, sedimentary rock, metamorphic and igneous rock) is presented directly on the cross-sections along with the well screen interval (shown in red). The deeper oil and gas wells are shown extending to the bottom depth of the crosssections, but many extend several hundred to thousands of feet beyond the depictions provided.

The analysis interpreted geologic formations from the borehole data after digitizing stratigraphic data from the various well log sources. This process relied heavily on the distinguishing features of each formation. Particularly, the black sands prevalent in the Mehrten Formation and evidence of shells noted in the descriptions that likely indicated a change to marine sediments of the Ione Formation were often mentioned in well logs. The analysis used surficial geology, location, and depth of the borehole to determine geologic formations. The analysis inferred formation contacts in places where data were limited, including areas on the east and west limbs of the cross-sections, as well as vertically throughout.

As evident on the east-west geologic cross-section transects, the oldest formations are present on the east side of the Eastern San Joaquin Subbasin, shown overlapping the older sedimentary and/or basement rocks of the Sierra Nevada (A-A’), with progressively younger formations present to the west and vertically occupying shallower depth intervals.

The east-west depictions also show the contacts of the formations steeply dipping in the east and nearly flat lying or at low gradients to the west. The northwest-southeast trending cross-section D-D’ shows the formations in their relatively flat-lying positions, with oldest formations on the bottom and progressively younger formations above. This crosssection transect is essentially normal to the dip of the beds. In slight contrast to D-D’, the transect of cross-section E-E’ is somewhat oblique to the dip of the beds, thus there is an apparent down-dip toward the south. This effect is seen because the transect is moving into younger materials from the south toward the north.

The base of fresh water is superimposed on the cross-sections as supported by works from Page (1974) and Williamson (1989), as represented in Figure 2-20. The base of the fresh water represents the vertical extent of fresh non-saline groundwater within the Eastern San Joaquin Subbasin principal aquifer. The sands of the Mehrten Formation are thickest in the northeast portion of the basin and there is a corresponding deepening of the freshwater aquifer on the north side of the Stockton Fault, as shown on cross-sections A-A’ and B-B’. The depth of the base of fresh water is shallower south of the Stockton Fault in the southern portion of the Eastern San Joaquin Subbasin.

Further discussion of the principal aquifer is provided in Section 2.1.9.

Well depths generally decrease in total depth from north to south across the Subbasin and locally within proximity of the major surface water drainages. In general, coarser sands are found at shallower depths within the lower unit of the Laguna Formation and upper Mehrten Formation (C-C’) in the area of the Stanislaus River Drainage. Similarly, shallow well completions evident on cross-section D-D’ and the southern portion of E-E’ are indicative of the sandier nature of the recent alluvial deposits, the Turlock Lake Formation, and the Laguna Formation near the San Joaquin River.

2.1.8Basin Boundaries

2.1.8.1 Lateral Boundaries and Boundaries with Neighboring Subbasins The Eastern San Joaquin Subbasin is within the larger San Joaquin Valley, which comprises the southernmost portion of the Great Valley Geomorphic Province of California. Groundwater subbasins bounding the Eastern San Joaquin Subbasin are shown in Figure 1-5 and include:
• Cosumnes Subbasin to the north of Dry Creek
• Modesto Subbasin to the south of the Stanislaus River • South American Subbasin to the northwest of the Mokelumne River • Solano Subbasin to the northwest of the Mokelumne River ATTACHMENT 2
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• East Contra Costa Subbasin to the west of the San Joaquin River • Tracy Subbasin to the west of the San Joaquin River
Foothill and bedrock highs are to the east within Calaveras and Amador Counties.

2.1.8.2 Definable Bottom of the Basin
The base of the fresh water defines the bottom of the basin, the maximum vertical extent of fresh non-saline groundwater within the Eastern San Joaquin Subbasin. While water-bearing materials exist below this depth, the saline nature of the groundwater, in addition to the depth itself, generally makes accessing deeper groundwater not economically viable.

Because of the extreme depths to the base of fresh water shown in Figure 2-20, efforts by the USGS have been used to define the “base of fresh water” through the interpretation of the California DOGGR well logs and deep oil well geophysical logs as depicted on maps and cross-sections above. Base of fresh water (encountered saline) has been observed as shallow as 650 feet below ground surface (bgs) in the eastern part of the basin to over 2,000 feet bgs in the northern part of the basin as depicted on the surface contour map and supported by work completed by Williamson (1989).

2.1.9Principal Aquifer
The Eastern San Joaquin Subbasin HCM has one principal aquifer that provides water for domestic, irrigation, and municipal water supply and that is composed of three water production zones. The zones have favorable aquifer characteristics that deliver a reliable water resource because of their basin location and sand thickness.

The zones are:
• Shallow Zone that consists of the alluvial sands and gravels of the Modesto, Riverbank, and Upper Turlock Lake Formations
• Intermediate Zone that consists of the Lower Turlock Lake and Laguna Formations • Deep Zone that consists of the consolidated sands and gravels of the Mehrten Formation Details on the formations are provided in Section 2.1.5.

2.1.9.1 Zones within Principal Aquifer
Zones within the principal aquifer are based on the compilation of five hydrogeologic cross-sections (see Figure 2-22 through Figure 2-24). Cross-sections were based on over 330 well logs in the Subbasin. From these data, well depths for municipal and irrigation wells range from 75 to over 800 feet bgs, with an average depth of 350 feet bgs.

Well logs were reviewed for the following information used in preparing the cross-sections:
• Depth of water table
• Depth and thickness of saturated fine to coarse grained sand and gravel layers • Depth and thickness of discrete layers of sands
• Depth and thickness of discrete clay or silt layers that locally confine groundwater • Depth of water-bearing aquifer materials (e.g., sands and gravels) down to the base of fresh water and deeper, where available
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Analyses identified significant permeable zones with high production rates and good water quality at relatively shallow depths (less than 700 feet bgs) due to the following conditions:
• The relatively shallow depths of production wells had high specific capacity that met the water supply demand and reduced the cost associated with drilling deeper • The base of fresh groundwater is deep; ranging from depths of 700 to 1,900 feet bgs • Deeper water is saline and not considered suitable for potable or agricultural use These results were cross-checked with the AEM data to validate the texture of shallow deposits, such as alluvial fans and sediments that interact with streams, and were used in updates to the hydrogeological conceptual model and the ESJWRM model stratigraphy. See Appendix 2-C for more detail on how AEM texture data were incorporated into the representation of Subbasin hydrostratigraphy.

Figure 2-30 and Figure 2-31 depict the wells used during this hydrogeologic characterization effort. Information compiled was used to detail the three permeable water-bearing zones described from surface downward in the following sections.

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Figure 2-30: Bottom Elevation of Water-Bearing Zones (Shallow) ATTACHMENT 2
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Figure 2-31: Bottom Elevation of Water-Bearing Zones (Deep and Intermediate)

2.1.9.1.1 Shallow Zone
The shallow water-bearing zone is composed of permeable sediments from recent alluvium, Modesto/Riverbank Formations, and the upper unit of the Turlock Lake Formation that are present west of the older geologic formations and extend across the majority of the Eastern San Joaquin Subbasin. This zone is generally unconfined above the aquitards (clays/silts, including Corcoran clay, and old soil horizons/hardpan layers).

The depositional structure on the eastern side of the valley trough is depicted on the hydrogeologic cross-sections A-A’ through E-E’ (see Figure 2-22, Figure 2-23, and Figure 2-24). This structure results in the groundwater flow that follows both the dip of the beds and hydraulic head differentials. Erosional and depositional features dominate aquifer characteristics. The cross-sections also depict the aquifer thickness from 30 feet to greater than 300 feet.

The Shallow Zone characteristics are supported by the sand thickness information detailed below along with review of basin aquifer parameters and AEM texture data. This zone has high yielding wells. Aquifer characteristic values range as follows (CA DWR, 1967; Burow et al., 2004):
• Transmissivities up to 90,000 gpd/feet
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• Specific yields up to 17 percent
• Vertical permeability estimates up to 0.1 feet/day

2.1.9.1.2 Intermediate Zone
As depicted on the hydrogeologic cross-sections A-A’ through E-E’ (see Figure 2-22, Figure 2-23, and Figure 2-24), sands, typically from 10 to over 60 feet thick, are found below the low permeable clay layers or aquitards. The sands and gravels are developed with one relatively continuous sand unit at 350 feet bgs, within the top of the lower unit of the Turlock Lake Formation and Laguna Formation, thinning out at topographic highs to the east. Eastern basin depositional structure shows a pinching, wedging, and combination water-bearing zones with the surficial alluvium.

The aquifer characteristics are supported by the sand thickness information detailed herein for the principal aquifer.

The eastern distribution of this water-bearing zone near the surface suggests unconfined groundwater conditions.

Typically, this zone is found under semi-confined conditions with high yielding wells and is considered the current primary production zone. Area groundwater numerical models support the CA DWR (1967) and Burow and others (2004) aquifer characteristic values range as follows:
• Transmissivities up to 59,500 gallons per day (gpd)/feet • Storage coefficients typically 0.00001 (unitless)
• Vertical permeability estimates up to of 0.07 feet/day

2.1.9.1.3 Deep Zone
The water-bearing “black sands” of the semi-consolidated Mehrten Formation are considered a significant source of water for Eastern San Joaquin Subbasin production wells. The formation is thick in the west, with a limited number of deep wells that penetrate the entire depth of this unit as depicted on the hydrogeologic cross-sections A-A’ through E-E’ (see Figure 2-22, Figure 2-23, and Figure 2-24). This water-bearing zone is confined due to the thick overlying clay units, consolidation, and basin location. Semi-confined conditions are more likely to the east because of the dipping of beds and stratigraphic layer thinning and erosion of clay/silt beds. The beds of the Mehrten Formation dip are at a steeper slope of 90 to 180 feet per mile westward. Consolidated sediments of the Mehrten and Valley Springs Formations are at valley bottom depth and exposed on the eastern foothills. Recharge to these aquifer formations occurs because of the high topographic setting with increased rainfall and exposure of weathered surface and runoff from the adjacent fractured Sierran bedrock.

As depicted on the hydrogeologic cross-sections A-A’ through E-E’ (see Figure 2-22, Figure 2-23, and Figure 2-24), boring logs indicate a significant 30-foot thick gravel encountered at a depth from 140 to 170 feet. Thickly bedded sands were found to exceed 250 feet. At the eastern margins of the basin, consolidated portions of the Mehrten, Valley Spring, and Ione Formations are important for low-yielding bedrock wells and are considered aquifer recharge sources for the Eastern San Joaquin Subbasin. The relatively low permeability and consolidated nature of the Valley Springs and Ione Formations act as the bottom of the Deep Zone (Burow et al., 2004).

The aquifer characteristics are supported by the sand thickness information. The well yields are high in this zone, over 1,000 gallons per minute (gpm). Area groundwater numerical models support the CA DWR (1967) and Burow and others (2004) aquifer characteristic values range as follows:
• Transmissivities up to 250,000 gpd/feet
• Storage coefficients that are typically 0.0001
• Vertical permeability estimates up to of 0.05 feet/day ATTACHMENT 2
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2.1.9.1.4 Limited Aquitards
The Corcoran Clay member of the Turlock Lake Formation and other interbedded clay/silts are aquitards that inhibit groundwater flow. The Corcoran Clay (found at the base of the upper unit of the Turlock Formation) is present at a depth of about 200 feet bgs. The Corcoran Clay has a limited distribution in the extreme southwestern extent of the Subbasin, southwest of the City of Manteca. The clay is typically 20 to over 100 feet thick and is locally eroded and interfingered with coarser materials at its margin. Groundwater below the Corcoran Clay is confined. The Corcoran Clay is found more significantly in subbasins to the south where it is a significant vertical barrier to flow.

Thick clay and silt layers are found within the Laguna and Mehrten Formations. These two formations each have two documented upward coarsening alluvial sequences (Burow et al., 2004). Significant clay and paleosols divide the water-bearing zones at the base of each sequence. The cross-sections (Figure 2-22, Figure 2-23, and Figure 2-24) show both the clay and silt horizons range in thickness from less than 10 feet to over 150 feet. The vertical permeability estimates range from 0.01 to 0.007 feet per day (Burow et al., 2004).

Discontinuous clay horizons have been eroded significantly by the movement of the ancestral rivers. As depicted on the cross-sections, thickest sequences of uppermost permeable units and overbank fines below these layers have been observed. The general thickness and depth are supported by a southeast to northwest movement of river channels to the existing channel location.

Hydraulic connection for the entire depth of the principal aquifer is supported by cross-section depictions that indicate the laterally extensive interbeds of high and low permeable layered deposits. The historical erosional and depositional history supports the referenced hydraulic interconnection. This observation is consistent with the possible thinning and wedging out of the regional clay units due to reworking or ancestral erosion (Davis et al., 1959). In addition to the natural connectivity, the number of water wells drilled through these zones also indicates additional hydraulic connection because of the construction of long well gravel packs that connect the water-bearing zones.

2.1.9.1.5 Deep Saline Groundwater
Connate or saline water occurs from the base of fresh water (shown in Figure 2-20 or Figure 2-31) to the base of continental deposits (shown in Figure 2-32), forming a saline layer that ranges in thickness from 50 to 2,250 feet from the east to the west across the Subbasin. The deep saline layer is not currently a water production zone for consumption or land application. Information used in developing the thickness of the saline water above continental deposits is from Page’s 1974 Base and Thickness of the Post Eocene Continental Deposits in the Sacramento Valley and the thickness of the aquifer developed by Williamson and others (1989).

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Figure 2-32: Elevation of Base of Continental Deposits
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2.1.9.2 Aquifer Characteristics and Groundwater Quality Because of the horizontal and vertical distribution of sediments and hydraulic connection between the water-bearing zones, one Principal Aquifer is defined.

An important step in aquifer characterization includes the completion of sand and gravel thickness (isopach) maps. An isopach map illustrates thickness variations within a tabular layer or stratum. Isopachs are contour lines of equal thickness over an area. The combined isopach map for the principal aquifer is depicted on Figure 2-33. The isopach map details are as follows:
• Over 313 water supply well logs with depths to 1,000 feet were used, with an average depth of 540 feet bgs. • Average sand and gravel thickness is 140 feet.
• The thickest sand and gravel sequences ranged from 500 to 700 feet near the Stanislaus River, south of Woodward Reservoir and northeast of Oakdale.
• Thicknesses from 200 to 400 feet were observed west of Morada along Bear Creek and toward the Delta. • The 200 to 500 feet thickness contours were observed near Stockton along the Duck Creek historical drainage.

Recognizing the sand and gravel thickness and the relative hydraulic conductivity of these permeable units, a more comprehensive understanding of the aquifer transmissivity can be made as detailed in Section 2.1.9.2.1.

As discussed in Section 2.1.4.3, soils facilitate rainfall and applied water infiltration, which is a significant recharge source for the Shallow Zone. Other recharge takes place through infiltration and percolation of surface water bodies and via groundwater flow from upgradient areas to the zones within the entire principal aquifer and potentially from flow between subbasins from the north, south, and west. The Intermediate and Deep Zones are recharged via infiltration near sand and gravel layers that are typically thicker near historical riverbeds. Vertical movement of water through sand deposits is more rapid compared to the confining clay deposits. In the high topographic areas along the east margin of the Subbasin, water-bearing zone sediments are exposed at the surface and considered significant to recharge.

2.1.9.2.1 Aquifer Parameters and Production Zone Well Capacities The GSP uses several sources to summarize the field-tested aquifer characteristics and production zone well capacity information for the principal aquifer.

For depiction purposes, Table 2-3 includes four investigation areas encompassing the entire Subbasin: Calaveras County, Farmington, Manteca, and near the Stanislaus Triangle Area (Riverbank). For these examples, the maximum well yields range from greater than 100 to 2,800 gpm. The range in specific capacity is 27 to 90 gpm/ft of drawdown.

These numbers relate to the testing of individual well capacities and the anticipated pumping water level related to the pumping rate. Transmissivity and storage values relate to the aquifer character anticipated at a distance away from a pumping well. Specific yield (SY) is defined as a unit volume of water released from an aquifer per unit decline in water table. Specific storage (SS) of a saturated aquifer is defined as the amount of water released from storage per unit decline in hydraulic head (Freeze and Cherry, 1979).

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Figure 2-33: Sand and Gravel Isopach Map
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Table 2-3: Production Zone Capacities
Sources/Well
Information
Maximum
Well
Yield
(gpm)
Maximum
Well
Specific
Capacity
(gpm/ft
drawdown)
Maximum
Transmissivity
(gpd/ft)
Maximum
Specific
Yield
(Unconfined
[%])
Specific
Storage
(Confined
[Unitless])
Sand and
Gravel
Thickness
Encountered
Mehrten
Depth, (feet)
Entire Eastern
San Joaquin
Subbasin
(CA DWR, 2006)
1,500 n/a n/a 7.3 % >150 400-600
Calaveras County
(WRIME, 2003)
>100 >10 >35,000 >6 % >120 At Surface
Farmington
(DE, 2012)
800 27 19,600 >5 % 0.001 >110 230
Manteca
(NV5, 2017)
2,500 90 61,000 >10 % 0.0001 >130 350
Stanislaus
Triangle
(BookmanEdmonston, 2005)
>2,800 >40
(DE, 2007)
35,000 17 % 0.001 >150 Dip to the
West
Using the basic physical properties of groundwater flow, a confined aquifer transmissivity is defined by:

T = Kb
Where: T is transmissivity
K is the hydraulic conductivity (rate of flow under a unit hydraulic gradient through a unit cross-sectional area)
b is the aquifer thickness.

Using a typical clean sand hydraulic conductivity value of 500 gpd/feet 2 and a thickness of 120 feet, the aquifer
transmissivity averages approximately 60,000 gpd/feet, which is similar to the documented values reported above (Freeze and Cherry, 1979). For additional comparison, data for the five layers of the ESJWRM were provided in the ESJWRM Model Report and Version 3.0 Model Documentation Updates TM (see Appendix 2-A and Appendix 2-C, respectively)
The distribution of production wells and monitoring wells is provided on Figure 2-30 and Figure 2-31. Table 2-4 provides descriptors for the three water-bearing zones:
• Number of wells for each zone
• Well depths
• Wells used on the cross-sections
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Additional aquifer parameter confirmation is provided by the ESJWRM as follows (Woodard & Curran, 2018):
• Horizontal Hydraulic Conductivity – The horizontal hydraulic conductivity varies across the non-saline model layers ranging from 1.1 ft/day to 72.7 feet/day or 0.148 to 10 gal/day/feet 2 .
• Specific Storage and Yield – SS and SY are used to represent the available storage at nodes in confined and unconfined aquifers. SS values range from 4.18 x 10-6to 2.05 x 10-4. SY values range from 4 to 10 percent.

Table 2-4: Wells within Water-Bearing Zones
All Wells
Water-Bearing Zone Number of
Wells
Average Construction
Depth (feet bgs)
Average Construction Bottom
Elevation (feet MSL)
Shallow 452 165 -82
Intermediate and Deep 201 539 -411
Pumping Wells
Water-Bearing Zone Number of
Wells
Average Bottom of
Screen Depth (feet bgs)
Average Bottom of Screen
Elevation (feet MSL)
Shallow 148 270 -238
Intermediate and Deep 113 369 -300
Groundwater Wells Used in Cross-Sections, by Formation
Water-Bearing Zone Number of
Wells
Average Bottom of
Borehole Depth (feet
bgs)
Average Bottom of Borehole
Elevation (feet MSL)
Shallow 39 234 -144
Intermediate and Deep 273 672 -566
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2.1.9.2.2 Regional Historical Groundwater Flow and Surface Water Interaction The horizontal groundwater flow direction for the Eastern San Joaquin Subbasin is typically towards areas of lower groundwater near the center of the Subbasin. The flow generally mirrors topography and is relatively consistent over time. The flow direction follows the overall west dipping gradient of the geologic formations in the eastern portions of the Subbasin. Higher groundwater elevations are in the foothills on the east side of the Subbasin, and the elevations decrease following the topography. In the western portion of the Subbasin, groundwater flows east toward areas with relatively lower groundwater elevation. Horizontal groundwater flow is further discussed in Section 2.2.

The GSP evaluates vertical groundwater gradients using the USGS nested wells in the Eastern San Joaquin Subbasin.

Clark and others (2012) drilled and assessed several nested wells or multiple well sites in the Eastern San Joaquin Subbasin. These nested well sites include three to five monitoring wells per borehole with screen intervals at depths of approximately 100 to 900 feet (Clark et al., 2012). Groundwater elevation in these monitoring wells, measured from 2006 to 2008, usually indicate the same trend. Groundwater elevation is typically lower in monitoring wells with deeper screen placement, suggesting a downward flow of groundwater. The difference in groundwater elevations from the shallowest to deepest monitoring wells within each borehole is typically between 5 and 20 feet (Clark et al., 2012).

Additional discussion regarding differences and distribution across the Subbasin is provided in Section 2.2.

Historical groundwater-surface water interaction in the context of the twenty-seven years of the historical model (ESJWRM) is discussed in Section 2.2.6.

2.1.9.2.3 General Groundwater Quality

2.1.9.2.3.1 Geologic Formation Groundwater Quality
The USGS and other government agencies completed several major studies concerning groundwater quality in the Central Valley of California, which includes the Eastern San Joaquin Subbasin. Repeatedly mentioned in these studies is the natural geochemical effects on groundwater quality that is specific to geologic formations (Creely & Force, 2007; Faunt, 2009; CA DWR, 1967). This natural effect is of great interest for the GSP implementation because groundwater level fluctuations from overdraft and recharge may result in water quality changes that is specific to geologic formations.

Natural geochemical reactions can be highly variable, even from well to well, as reactions depend on a number of factors, including the amount of 1) reactive surface area of the formation sediments; 2) available oxygen in the formation as affected by fluctuations in groundwater elevation, depth to groundwater, and oxygenated near-surface recharge; and 3) potentially inorganic-oxidizing bacteria.

For the Eastern San Joaquin Subbasin, igneous and metamorphic rocks of the Sierra Nevada Mountains underlie the upstream drainages. These rocks predominately contain oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium (Creely & Force, 2007). Rivers draining areas of granitic rocks typically have better water quality than metamorphic or volcanic rocks (CA DWR, 1967). For example, the Mokelumne River drains areas of granitic origin and has a lower salt content than the Calaveras River, which drains an area of primarily metamorphic rocks (CA DWR, 1967). Streams originating from either igneous or metamorphic rocks have relatively low amounts of dissolved solids, compared to marine sedimentary rocks that make up the Coast Range west of the Subbasin (Faunt, 2009). However, marine formations also underlie continental deposits in the Eastern San Joaquin Subbasin and have considerable amounts of chlorine, sulfur, bromine, and boron from connate water (Creely & Force, 2007). Connate water originates from fluids that are trapped in the pores of the sedimentary rocks as they are deposited and can contain many mineral components as ions in solution. Above these marine formations are continental deposits described in Section 2.1.5.

Groundwater quality in wells in Calaveras County is characterized by Metzger and others in a 2012 study, Test Drilling and Data Collection in the Calaveras County Portion of the Eastern San Joaquin Groundwater Subbasin, California, December 2009 – June 2011 (Metzger et al., 2012). These wells are in the eastern portion of the Eastern San Joaquin Subbasin, in an area underlain by the Ione and Valley Springs Formations. This study assessed groundwater samples and identified three water types present: calcium-magnesium-bicarbonate, sodium-bicarbonate, and mixed cationATTACHMENT 2 2024 Groundwater Sustainability Plan Amendment 2-72
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mixed anion water. The mixed cation-mixed anion group consisted mostly of sodium and chloride. These groundwater samples also showed high levels of arsenic, which were attributed to pH level variation or redox potential (Metzger et al., 2012). The Ione Formation, for instance, is known to have high sulfate levels in groundwater related to the pH influence on pyrite-sulfide rich coal deposits.

Arsenic is of particular concern because it is naturally occurring in the Eastern San Joaquin Subbasin and is hazardous to human health. Izbicki and other’s (2008) study, Source, Distribution, and Management of Arsenic in Water from Wells, Eastern San Joaquin Groundwater Subbasin, California, assesses the concentration and sources of arsenic in various wells. Arsenic was detected mostly in San Joaquin County, and the largest concentrations were in the western portion of the Subbasin (Izbicki et al., 2008). The surficial geology in this area consists of the Modesto and Riverbank Formations, which are underlain by the Turlock Lake and Laguna Formations (see Figure 2-18, Figure 2-22, Figure 2-23, and Figure 2-24). Sources of arsenic include weathering of minerals containing arsenic, desorption of arsenic under certain pH values, and release of arsenic in redox conditions (Izbicki et al., 2008).

Another element of great importance is nitrogen as it is included in many compounds that are by-products of agriculture, which heavily dominates the landscape of the Eastern San Joaquin Subbasin. Elevated levels of nitrate can typically occur as a result of fertilizer application, manure and septic waste, and natural sources. Extensive work by Holloway and others (1998) showed the Mokelumne River watershed contained significant quantities of nitrogen from bedrock lithology. The upper part of the watershed, outside the Eastern San Joaquin Subbasin, is underlain by igneous and metamorphic rock, but the metasedimentary and metavolcanic rocks contained the highest levels of nitrogen (Holloway et al., 1998).

General water quality of principal aquifers is summarized in the following sections, as required by CCR Title 23 §354.14.

General water quality can be determined by assessing commonly measured inorganic parameters as indicators of change. Evaluating these inorganic parameters involves looking at historical trends and comparing results to certain thresholds, as well as determining water types. These parameters include major cations and anions, listed below:

Anions Cations
Bicarbonate Calcium
Carbonate Magnesium
Chloride Potassium
Sulfate Sodium

2.1.9.2.3.2 Ion Composition
Evaluating the historical trends of these parameters is not straightforward. GAMA records include some groundwater quality results for the Eastern San Joaquin Subbasin going back to the 1940s. However, a thorough analysis requires a large amount of data on all the major cations and anions mentioned above. A large number of measurements of this kind were taken from 2005 to 2017, as shown in Figure 2-34. This analysis was not updated as part of this GSP amendment as basic groundwater chemistry reflects the geology of origin, which has not varied considerably since the preparation of the 2020 GSP.

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Figure 2-34: Total Number of Cation/Anion Measurements in the Eastern San Joaquin Subbasin ATTACHMENT 2
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General water quality of the Subbasin can be determined by assessing water type over specific years, in this case, within the time frame of 2005 to 2017. Evaluating the years 2005, 2011, and 2017 provides an even spread over the selected time frame and gives an idea of possible water type trends. Trilinear diagrams for each of these years show relative concentrations of the major cations and anions (see Figure 2-35). Each symbol in the diagram represents a water sample collected. Water samples, represented by the same symbol, are plotted in the two lower triangle diagrams for each year based on their relative cation (left) and anion (right) concentrations. The top diagram represents a projection of the two ternary diagrams for easier comparison.

Due to the difference in sampling locations, the years 2005 and 2011 show carbonate and bicarbonate-rich waters, and 2017 displays increased chloride and sulfate concentrations in some wells. These dates correlate to both data size increases and heavier rainfall periods. Chloride concentrations in 2017 are generally less than 150 milligrams per liter (mg/L), with some higher measurements reaching 2,000 mg/L. Sulfate
concentrations in 2017 are mostly under 300 mg/L, but a few extremely high levels up to 100,000 mg/L exist near the City of Manteca.

GAMA groundwater quality data in the northern portion of the San Joaquin Valley Groundwater Basin were assessed by
Bennett et al. in 2006. Groundwater samples were compared to thresholds such as the U.S. Environmental Protection Agency (USEPA) secondary maximum contaminant levels (SMCL).

None of the major cations and anions measured in the Eastern San Joaquin Subbasin resulted in exceedances of the SMCLs (Bennett et al., 2006). These measurements took place in December 2004 to February 2005. Additional parameters were sampled in this study and are discussed further in Section 2.2 (Historical Groundwater Conditions).

Figure 2-35: Trilinear Diagrams
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2.1.9.2.3.3 Total Dissolved Solids
A wide range of total dissolved solids (TDS) values exist in the Eastern San Joaquin Subbasin. Based on data in the GAMA database from 2005 to 2017, TDS values generally varied from 100 to 2,000 mg/L (Figure 2-36), with a median value of 520 mg/L. Over the 13-year period shown in Figure 2-36, the median concentration of TDS has steadily increased from approximately 400 mg/L in 2005 to approximately 600 mg/L in 2017. Figure 2-37 shows the variation of TDS concentrations across the basin in 2017. Sources of TDS in the Subbasin include Delta sediments, deep deposits, and irrigation return water, as discussed in Section 2.2.4.1. Additional details on TDS concentrations are provided in Section 2.2 (Historical Groundwater Conditions).

Figure 2-36: TDS Annual Variation
Note: This Box-and-Whisker plot represents a summary of five different statistic values of the distribution. Minimum and maximum values are represented by the end points of the extended lines. The center line indicates the median. The top and bottom of the rectangle indicate the first quartile (25th percentile) and third quartile (75th percentile) of the distribution, respectively.

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Figure 2-37: TDS Concentrations in 2017

2.1.9.2.3.4 Chloride
Chloride concentrations also vary considerably across the Eastern San Joaquin Subbasin. Based on data in the GAMA database from 2005 to 2017, chloride values generally varied from non-detect to 300 mg/L (Figure 2-38), with a median value of 50 mg/L. Over the 13-year period shown in Figure 2-38, the median concentration of chloride has remained fairly stable. Higher chloride concentrations during 2017 are apparent near the cities of Manteca and Stockton (
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Figure 2-39). Sources of chloride in the Subbasin are similar to those for TDS and include Delta sediments, deep deposits, and irrigation return water. Additional details on chloride concentrations are provided in Section 2.2 (Historical Groundwater Conditions).

Figure 2-38: Chloride Annual Variation
Note: This Box-and-Whisker plot represents a summary of five different statistic values of the distribution. Minimum and maximum values are represented by the end points of the extended lines. The center line indicates the median. The top and bottom of the rectangle indicate the first quartile (25th percentile) and third quartile (75th percentile) of the distribution, respectively.

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Figure 2-39: Chloride Concentrations in 2017

2.1.9.2.3.5 Sulfate
Sulfate concentrations vary considerably across the Eastern San Joaquin Subbasin ranging from non-detect to around 250 mg/L with a median value of around 25 mg/L Figure 2-40, based on data in the GAMA database from 2005 to 2017. Over the 13-year period shown in Figure 2-40, the median concentration of sulfate, like chloride, has remained fairly stable and does not show any obvious trends. Higher sulfate concentrations during 2017 are apparent near the cities of Manteca and Stockton Figure 2-41
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Figure 2-40: Sulfate Annual Variation
Note: This Box-and-Whisker plot represents a summary of five different statistic values of the distribution. Minimum and maximum values are represented by the end points of the extended lines. The center line indicates the median. The top and bottom of the rectangle indicate the first quartile (25th percentile) and third quartile (75th percentile) of the distribution, respectively.

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Figure 2-41: Sulfate Concentrations in 2017
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2.1.10 HCM Data Gaps
All hydrogeologic conceptual models contain a certain amount of uncertainty and can be improved with additional data and analysis. The Eastern San Joaquin Subbasin HCM data gaps are present in the understanding of the HCM presented in this GSP. While recent efforts have been made to address these data gaps, as noted below, the following data gap elements still require additional information and will be updated with future monitoring, modeling, and data refinement efforts.

Aquifer Characteristics
• Aquifer characteristics (such as hydraulic conductivity) have a significant impact on how projects and management actions in one part of the Subbasin may influence sustainability in other parts of the Subbasin.

While this data gap has been filled to some extent with the airborne electromagnetic (AEM) data collected by DWR and the boring logs from the new monitoring wells constructed in the Subbasin, improving the understanding of the Subbasin aquifer system and leading to the addition of a shallow alluvium layer and other refinements to ESJWRM numerical flow model refinements, much still remains unknown. Aquifer characteristics should be confirmed through additional aquifer testing or additional monitoring wells.

Groundwater Level Data
• Depth- or zone-specific water levels to assess vertical interconnection, including zones within the principal aquifer. This data gap has been partially addressed by the recent construction of the two Technical Support System (TSS) and Delta multi-completion well.
• Additional shallow groundwater data near surface waters and natural communities commonly associated with groundwater (NCCAGs). This data gap has been partially addressed by the recent construction of five new shallow monitoring wells near interconnected surface waters. • Additional groundwater level data in the east and northwest areas of the Subbasin. This data gap has been partially addressed by recent improvements to the groundwater level representative monitoring network. See Chapter 4 for additional information.
• Additional groundwater level data near major creeks and rivers to improve quantification and understanding of subsurface flows between groundwater subbasins and surface water-groundwater interaction. This data gap has been partially addressed by the recent construction of five new shallow monitoring wells near interconnected surface waters and formation of a representative monitoring network specific for monitoring impacts to interconnected surface waters.

Groundwater Quality Data
• Water quality of the three zones within the principal aquifer. This data gap has been partially addressed through recent refinements to the representative monitoring network for groundwater quality. See Chapter 4 for additional information.
o Additional monitoring at various depths for different constituents will help inform the understanding of water quality. This can be achieved through installation of new monitoring wells or through determination of screened intervals of existing monitoring wells. o Additional depth-specific water quality data will inform minimum thresholds for the degraded water quality sustainability indicator and help monitor and identify potential undesirable results.

Subsurface Conditions
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• Stockton Fault extent and impact on the base of fresh water. • Improved characterization of near-surface soil conditions as they relate to recharge. • Further definition of aquifer characteristics (e.g., hydraulic conductivity, transmissivity, and storage parameters) within and near Subbasin boundary areas to the east, southeast, north, and northwest, including aquifer tests.

2.2 HISTORICAL GROUNDWATER CONDITIONS
This section describes historical groundwater conditions in the Eastern San Joaquin Subbasin as of the development of the 2020 GSP. As such, this section includes both historical conditions in the Subbasin prior to 2019, and the current conditions as of the development of the 2020 GSP in 2019. These sections are maintained in the GSP to provide a context of the conditions occurring at the time the 2020 GSP was developed.

As required by the GSP regulations, the groundwater conditions section includes:
• Definition of current groundwater conditions in the Subbasin (as of 2020 GSP development) • Description of historical groundwater conditions in the Subbasin • Description of the distribution, availability (storage), and quality of groundwater • Identification of interactions between groundwater, surface water, groundwater dependent ecosystems, and subsidence
The groundwater conditions described in this section present the historical availability, quality, and distribution of groundwater which are the basis of this Plan’s sustainable management criteria and monitoring network. The current and historical conditions discussed are further expanded upon in Chapter 3: Sustainable Management Criteria and are used to define undesirable results and to establish measurable objectives, interim milestones, and minimum thresholds.

Historically, the two aspects of greatest focus for groundwater management in the Eastern San Joaquin Subbasin have been groundwater elevation and, in some areas of the Subbasin, groundwater quality. As discussed herein, a groundwater depression exists in the central portion of the Subbasin, while higher groundwater levels characterize the west portion of the Subbasin. Additionally, there are elevated levels of salinity and nitrate in some areas, along with naturally occurring constituents commonly seen throughout the Central Valley. Detailed descriptions of these conditions are provided in the following sections as part of a discussion of the historical and current conditions for each of the six sustainability indicators:
• Groundwater Elevation (Section 2.2.1)
• Groundwater Storage (Section 0)
• Seawater Intrusion (Section 0)
• Groundwater Quality (Section 2.2.4)
• Land Subsidence (Section 0)
• Interconnected Surface Water (Section 2.2.6)
Details of GDEs are provided in Section 2.2.7 and Section 2.3.7 to support the sustainability indicator discussions.

2.2.1Groundwater Elevation
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2.2.1.1 Historical Groundwater Elevations
Data sources for groundwater elevation are abundant in the Eastern San Joaquin Subbasin. As discussed in Section 2.1, the CASGEM and San Joaquin County databases constitute the groundwater level data used for this analysis. These sources provide a robust dataset of groundwater levels going back to 1940.

To visually show long-term trends in groundwater elevations in the Eastern San Joaquin Subbasin, 10 wells that have periods-of-record greater than 40 years and that are relatively evenly distributed across the Subbasin were selected from available data (see Figure 2-42). Long-term hydrographs prepared for these wells show that, throughout most of the Eastern San Joaquin Subbasin, groundwater elevations have declined over time.

Average groundwater level decline was quantified for 1996-2015. In Section 2.3 (Water Budgets), the Historical Water Budget from the 2020 GSP uses 1996-2015 as a representative hydrologic period which includes an average annual precipitation of 14.7 inches, very close to the long-term average of 15.4 inches. The 1996-2015 period also includes the recent 2012-2015 drought, the wet years of 2010-2011, and periods of normal precipitation. Based on data from the 10 selected wells in Figure 2-42, the average groundwater level decline was -0.5 ft/year from 1996-2015.

Hydrographs for wells numbered #2, #5, and #6 show the largest decrease in groundwater elevation. These wells are located to the east of the City of Stockton. Hydrograph #9, which corresponds to a well located on the north edge of the Subbasin, shows the least decrease in groundwater elevation from 1996-2015. Hydrograph #4 corresponds with a well located in the western side of the Subbasin and is the only well to show an increasing trend in groundwater elevations. The northeast corner of the Subbasin is an area without a nearby representative hydrograph and was identified as a data gap in Section 2.1.10 (HCM Data Gaps).

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Figure 2-42: Hydrographs of Selected Wells
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Figure 2-43 shows the distribution of the groundwater elevations from the CASGEM and San Joaquin County databases compared to average precipitation in and near the Subbasin. Figure 2-43 shows an overall decreasing trend in groundwater elevation levels with larger variability over time. The increasing variability comes partly due to a larger number of wells being sampled through time in more varied topography, but also reflects the long-term changes in groundwater levels described above and in Figure 2-42.

Periods of increases in groundwater elevation moderately correspond to the amount of precipitation in the Eastern San Joaquin Subbasin. A correlating trend can be seen with groundwater elevation increases in several hydrographs in the early 1980s and late 1990s, associated with periods of high precipitation.

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Figure 2-43: Summary of Groundwater Elevation Data, 1940-2018

1. Each vertical bar in Figure 2-43 (a) represents the full range of groundwater level measurements recorded in a given year. The central gray box represents the middle 50% of measurements (ranging from the 25th percentile to the 75th percentile), with the horizontal line showing the median. The capped lines below and above the central box represent the minimum and maximum, respectively.

2. Precipitation monitoring depicted in Figure 2-43 (a) began in 1951.

3. The average annual precipitation line presented in Figure 2-43 (b) is based on an average of data collected at 7 stations which are mapped in Figure 2-44.
(b) Number of Groundwater Level Measurements
(a) Box-and-Whisker Plot with Precipitation
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Figure 2-44: Precipitation Stations

1. These stations are operated by California Irrigation Management Information System (CIMIS) (“A”), National Oceanic and Atmospheric Administration (NOAA) (“C”), and PestCast (University of California Statewide Integrated Pest Management Program [UC IPM] and Department of Pesticide Regulation [DPR]) (“P”).

Additionally, extensive reports and research examining the groundwater conditions of the Central Valley are available from a variety of sources, including the USGS and DWR. These documents supplement the water level data provided by the CASGEM and San Joaquin County databases and were used to assess current and historical groundwater elevations.

USGS Water Supply Paper 780 – One of the earliest discussions of measured groundwater levels in the Eastern San Joaquin Subbasin is the USGS Water Supply Paper 780. The report details river stage of the Mokelumne River and the surrounding groundwater table from roughly 1900 to 1930. Groundwater levels in wells around the Mokelumne River varied, but mostly declined due to an increase in groundwater pumping.

Even between years of minimal groundwater pumping, from 1927 to 1933, the water table decreased in elevation, most drastically in areas northeast and southeast of the City of Lodi (Piper et al., 1939).

DWR Bulletin 146 – DWR’s Bulletin 146 (1967) discusses water levels and flow directions in the 1960s and earlier, which provides added historical context to current groundwater conditions. Figures 4 and 5 of Bulletin 146 show groundwater elevation in most of the Eastern San Joaquin Subbasin in fall of 1950 and 1964, ATTACHMENT 2
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respectively. Both maps show groundwater levels at the lowest elevation underneath the City of Stockton, which is attributed to heavy groundwater pumping. This groundwater depression is attributed as causing groundwater from the Delta to flow toward the City of Stockton and is described as having relatively worse water quality due to natural mineral salts. Barriers between the poorer quality water from the Delta and higher quality water from the Sierra Nevada Mountains noted in previous studies around the City of Stockton are not apparent (CA DWR, 1967).

Williamson, 1989 – Groundwater conditions provided in the groundwater model report by Williamson (1989) included horizontal and vertical flows. A westerly groundwater flow direction that roughly parallels the ground surface in the Eastern San Joaquin Subbasin was confirmed, as depicted on Figure 14 of that report.

Estimates of groundwater elevations for before-human-development were provided. Vertical flow characteristics before considerable human development were characterized and mapped; areas of wells that flowed without pumps are shown throughout the valley and in the western portion of the Eastern San Joaquin Subbasin. This is in contrast to current conditions, where wells flowing without pumps have not been currently observed in the Subbasin. At present, USGS nested monitoring wells confirm downward vertical flows (Williamson, 1989).

2.2.1.2 Conditions as of 2019: Groundwater Elevations
For the purposes of the 2020 GSP, current groundwater elevation conditions were characterized as first quarter 2017 (seasonal high, measured in spring 2017) and fourth quarter 2017 (seasonal low, measured in fall 2017) groundwater elevation measurements. At the time of the 2020 GSP, those records constituted the most complete dataset.

Groundwater elevations were mapped using the CASGEM dataset (including voluntarily monitored wells) and the San Joaquin County dataset.

Figure 2-45 and Figure 2-46 show the groundwater elevations for the first and fourth quarters of 2017, respectively. A pumping depression at the center of the Subbasin, east of the City of Stockton, existed during both of these periods. A localized pumping depression is shown expanding from the Cosumnes Subbasin across Dry Creek to the Eastern San Joaquin Subbasin in fourth quarter of 2017. However, from the perspective of the entire Eastern San Joaquin Subbasin, the central pumping depression to the east of the City of Stockton is most significant to achieving sustainability in the Subbasin. Groundwater generally flows from the outer edges of the Subbasin towards the depression in the middle of the Subbasin. Along the eastern side of the Subbasin, the lateral gradient of groundwater levels ranged from approximately 21 feet per mile (ft/mi) during the seasonal high to 16 ft/mi during the seasonal low. Along the western side of the Subbasin, the lateral gradient rangef from approximately 7 ft/mi during the seasonal high to 6 ft/mi during the seasonal low. The steeper gradients on the east side of the Subbasin compared to the west side are primarly due to the steeper topography in that area.

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Figure 2-45: First Quarter 2017 Groundwater Elevation
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Figure 2-46: Fourth Quarter 2017 Groundwater Levels
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2.2.1.2.1 Vertical Gradients
A vertical gradient drives the movement of groundwater perpendicular to the ground surface and is typically measured by comparing the elevations of groundwater in nested and/or clustered wells, wells with multiple completions at different depths. If groundwater elevations in the shallower completions are higher than in the deeper completions, the gradient is identified as a downward gradient. A downward gradient is one where groundwater is moving downward through the subsurface. If groundwater elevations in the shallower completions are lower than in the deeper completions, the gradient is identified as an upward gradient. An upward gradient is one where groundwater is moving upward through the subsurface. If groundwater elevations are the same throughout the completions, there is no vertical gradient.

Knowledge about vertical gradients is required by regulation and is useful for understanding how groundwater moves in the Subbasin.

Vertical flow characteristics before considerable human development are characterized and mapped by Williamson (1989), showing that wells flowing without pumps existed in the western portion of the Eastern San Joaquin Subbasin, also corresponding with areas of upward vertical gradients. This contrasts with current conditions, where wells flowing without pumps have not been currently observed in the Subbasin. At present, USGS nested monitoring wells confirm downward vertical gradients (Williamson, 1989).

As of the 2020 GSP, there were 16 nested and/or clustered well sites located in the Eastern San Joaquin Subbasin.

The locations of the wells are shown in Figure 2-47. The majority of these wells are located in the northwest portion of the Subbasin near the cities of Stockton and Lodi. Hydrographs with groundwater elevations for each respective set of nested wells are shown in Figure 2-48 through Figure 2-63. 10 out of 16 sets of wells consistently show elevations in shallower completions that are higher than in the deeper completions which indicates a downward gradient. The remaining six wells are located in the City of Lodi. Four of these wells exhibit a minimal downward gradient and two show no downward gradient.

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Figure 2-47: Map of Nested and/or Clustered Well Sites (as of 2020 GSP Development) ATTACHMENT 2
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Figure 2-48: Nested Well Hydrographs: CCWD 004-006 (as of 2020 GSP Development) Figure 2-49: Nested Well Hydrographs: CCWD 010-012 (as of 2020 GSP Development) ATTACHMENT 2
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Figure 2-50: Nested Well Hydrographs: Sperry Well (as of 2020 GSP Development) Figure 2-51: Nested Well Hydrographs: Swenson Golf Course (as of 2020 GSP Development) ATTACHMENT 2
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Figure 2-52: Nested Well Hydrographs: STK-1 (as of 2020 GSP Development) Figure 2-53: Nested Well Hydrographs: STK-2 (as of 2020 GSP Development) ATTACHMENT 2
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Figure 2-54: Nested Well Hydrographs: STK-4 (as of 2020 GSP Development) Figure 2-55: Nested Well Hydrographs: STK-5 (as of 2020 GSP Development) ATTACHMENT 2
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Figure 2-56: Nested Well Hydrographs: STK-6 (as of 2020 GSP Development) Figure 2-57: Nested Well Hydrographs: STK-7 (as of 2020 GSP Development) ATTACHMENT 2
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Figure 2-58: Nested Well Hydrographs: Lodi MW-21 (as of 2020 GSP Development) Figure 2-59: Nested Well Hydrographs: Lodi MW-24 (as of 2020 GSP Development) ATTACHMENT 2
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Figure 2-62: Nested Well Hydrographs: Lodi WMW-1 (as of 2020 GSP Development) Figure 2-63: Nested Well Hydrographs: Lodi WMW-2 (as of 2020 GSP Development) ATTACHMENT 2
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2.2.2 Groundwater Storage
The ESJWRM was used to estimate historical change in storage of the Eastern San Joaquin Subbasin from 1995-2023.

Figure 2-64 shows annual total storage for the combined ESJWRM Version 3.0 fresh groundwater layers (not including the deep saline layer). Figure 2-65 shows the cumulative change in storage against annual storage change and water year type. In 2015, the total fresh groundwater storage was estimated as 74.0 million acre-feet (MAF). An additional

95.0 MAF in the deepest simulated layer of the model (not pictured) is saline water. More information about the layers of the ESJWRM Version 3.0 and calculation of storage changes can be found in model documentation in Appendix 2- C.

Figure 2-64: Historical Modeled Change in Storage
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Figure 2-65: Historical Modeled Change in Annual Storage with Water Use and Year Type Notes:

1. Water Year Types based on San Joaquin Valley Water Year Index (CA DWR, 2024)

2. “Other Recharge” includes managed aquifer recharge, recharge from unlined canals and/or reservoirs, and recharge from ungauged watersheds.

3. “Change in Storage” is placed to balance the water budget. For instance, if annual outflows (-) are greater than inflows (+), there is a decrease in storage, but this would be shown on the positive side of the bar chart to balance out the increased outflows on the negative side of the bar chart.

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2.2.3 Seawater Intrusion
The Eastern San Joaquin Subbasin is not in a coastal area and seawater intrusion is not present. While the Delta ecosystem evolved with a natural salinity cycle that brought brackish tidal water in from the San Francisco Bay, levees installed to allow development of agriculture, followed by development and operation of the Central Valley Project and the State Water Project, have altered the inward movement of seawater through the Delta. Current management practices endeavor to maintain freshwater flows through a combination of hydraulic and physical barriers and alterations to existing channels (Water Education Foundation, 2019). Portions of the Subbasin do, however, experience water quality issues related to salinity, which are addressed under Section 2.2.4.1 (Salinity). As described in Section

2.2.4.1, salinity in the Subbasin is due to other factors and are not the result of seawater intrusion.

2.2.4 Conditions as of 2019: Groundwater Quality
While groundwater quality in the Eastern San Joaquin Subbasin is generally sufficient to meet beneficial uses, a number of constituents of concern are either currently impacting groundwater use or have the potential to impact it in the future. Depending on the water quality constituent, the source may be anthropogenic in origin or naturally occurring, and the issue may be widespread or localized.

The primary naturally occurring water quality constituents of concern are salinity and arsenic, while the primary water quality constituents related to human activity include nitrates, salinity, and various point-source contaminants.

The sections herein provide information on the historical and current (as of the 2020 GSP) groundwater quality conditions for constituents including:
• Salinity (Section 2.2.4.1)
• Nitrate (Section 2.2.4.2)
• Arsenic (Section 2.2.4.3)
• Point-source contamination (Section 2.2.4.4), which includes petroleum hydrocarbons, solvents, and emerging contaminants
CCR Title 22 establishes water quality standards for drinking water contaminants. A primary maximum contaminant level (MCL) or SMCL is defined for a variety of parameters. For the purposes of this GSP, comparing parameter concentrations to their MCL or SMCL is used as the basis for describing groundwater quality concerns in the Eastern San Joaquin Subbasin. Comparisons to the MCL or SMCL must be considered in context as the measured concentrations represent raw water that may be treated or blended prior to delivery to meet the standard or may not be used for potable uses. Water quality is generally not known to have significantly adversely affected beneficial uses of groundwater in the Eastern San Joaquin Subbasin.

2.2.4.1 Salinity
As identified in prior planning efforts, and as referenced in Section 2.2 (Historical Groundwater Conditions) and Section

2.3 (Current Groundwater Conditions), localized salinity issues are a concern for some areas of the Eastern San Joaquin Subbasin. Pumping in excess of recharge has resulted in declining groundwater levels that have contributed to an increase of salinity in groundwater wells since the 1950s. As identified through isotopic typing, elevated salinity concentrations in the Subbasin are the result of natural processes and overlying land use activities (O’Leary et al., 2015). Within the Subbasin, there are three primary sources of salinity:

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1. Delta Sediments – Evaporation of groundwater in discharge areas introduces naturally occurring soluble salts into Delta sediments.

2. Deep Deposits – Saline groundwater in the Subbasin is principally the result of the migration of a naturally occurring deep saline water body which originates in regionally deposited marine sedimentary rocks that underlie the San Joaquin Valley. This results in a saline aquifer underlying the freshwater aquifer, and well pumping can result in upwelling saline brines into the freshwater aquifer.

3. Irrigation Return Water – Irrigation return water is excess applied water that percolates into the groundwater system or flows to the stream system from an irrigated field following the application of irrigation water. Return water may include contaminants typical of agricultural practices (e.g., pesticides, herbicides) and can concentrate salts due to evapotranspiration. The return water may act as a conduit delivering these contaminants to the surrounding watershed or underlying groundwater aquifer. Areas in the Subbasin with salinity resulting from irrigation return water do not commonly exceed chloride concentrations of 100 mg/L (O’Leary et al., 2015).

Salinity is a measure of the mass of dissolved particles and ions in a volume of water. Salinity includes many different ions, including nitrate, but the most common are sodium, calcium, magnesium, chloride, bicarbonate, and sulfate.

Chloride and TDS are two common ways to measure and analyze salinity. Each is described separately in the sections below.

2.2.4.1.1 Chloride
Chloride is one way to measure salinity and is reported as a concentration of the Clion that originates from the dissociation of salts in water. The California Department of Drinking Water (DDW) SMCL of 250 mg/L for chloride is a common approach to identifying water quality concerns for this constituent. The SMCL is a secondary drinking water standard that is established for aesthetic reasons such as taste, odor, and color and is not based on public health concerns. The 250 mg/L value is “recommended” by SWRCB as a threshold below which chloride concentrations are desirable for a higher degree of consumer acceptance of drinking water. An “upper” limit of 500 mg/L is used to define a range above the “recommended” value where chloride concentration is acceptable if it is neither reasonable nor feasible to provide more suitable waters (SWRCB, 2018). Comparisons to the SMCL must be considered in context as the measured concentrations represent raw water, which may be treated or blended prior to delivery to meet the standard or may not be used for potable uses.

As shown in Figure 2-66, the majority of observed chloride concentrations above 250 mg/L occur on the western side of the Subbasin. As shown in Figure 2-67, the number of measurements with observed concentrations above 250 mg/L has decreased since the 1970s. The GAMA dataset was used for analysis.

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Figure 2-66: Maximum Chloride Concentration Greater Than 250 mg/L (1940s-2010s) ATTACHMENT 2
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Figure 2-67: Maximum Chloride Concentration Above 250 mg/L by Decade ATTACHMENT 2
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Table 2-5 shows occurrence of chloride measurements greater than 250 mg/L by decade. Chloride records have been observed above 250 mg/L both historically and more recently. Sampling frequencies increased in the 1970s and 2000s.

Table 2-5: Summary of Chloride Data by Decade
Decade
Measurement Above
250 mg/L? Range of Values (mg/L) Total Number
of Samples No Yes Minimum Average Median Maximum
1940 98% 2% 7.0 45.2 20.0 975 180
1950 93% 7% 2.3 89.4 25.0 3,750 699
1960 90% 10% 0.0 115.0 17.0 1,960 312
1970 90% 10% 1.8 85.9 19.0 3,310 1,780
1980 97% 3% 0.0 45.4 20.5 630 858
1990 99% 1% 0.0 31.2 19.0 533 663
2000 95% 5% 0.0 59.6 35.0 2,050 1,453
2010 98% 3% 0.0 34.8 39.0 2,050 986
Table 2-6 shows chloride occurrences of concentrations greater than 250 mg/L by well depth. The highest proportion of readings above 250 mg/L occur in the shallowest wells, less than 100 feet deep (8 percent). The highest maximum value also occurred at this depth range (up to 2,050 mg/L).

Figure 2-68 shows the spatial distribution of chloride occurrences greater than 250 mg/L by well depth within the Subbasin.

Table 2-6: Summary of Chloride Data by Depth (1940s-2010s) Depth (feet)
Measurement Above
250 mg/L? Range of Values (mg/L) Total Number
of Samples No Yes Minimum Average Median Maximum
No Depth Data 92% 8% 0.0 82.5 20.0 3,750 3,566
0 - 100 92% 8% 0.8 73.5 60.0 2,050 239
100 - 250 97% 3% 1.0 44.2 36.0 1,400 1,215
250 - 500 98% 2% 0.0 32.4 16.0 1,100 1,487
> 500 95% 5% 2.7 62.1 15.6 1,940 424
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Figure 2-68: Maximum Chloride Concentration Above 250 mg/L by Well Depth (1940s-2010s) ATTACHMENT 2
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A lack of depth information presents a challenge to analyzing the vertical distribution of chloride measurements which would inform identification of chloride sources. Examples of depth information include total well construction depth or screened interval depths, which vary between wells. Some wells have total depth but not screened interval depth, or vice versa. For this analysis, screened interval depth was used first, and if this information was not available, total depth was used. Approximately 4,600 of the almost 13,000 chloride measurements in the Eastern San Joaquin Subbasin are from wells lacking any construction or screen depth information. Roughly half of the measurements above 250 mg/L occur in the wells lacking depth data, which also show the highest range in values occurring above 250 mg/L.

Identifying the source of high-chloride water in wells of various depths over time requires further analysis of geochemical data.

2.2.4.1.2 Total Dissolved Solids (TDS)
TDS, which is a measure of all inorganic and organic substances present in a liquid in molecular, ionized, or colloidal suspended form, is commonly used to measure salinity. Recent TDS sample results show trends that match closely with the overall historical trends for chloride and highlight areas with elevated salinity concentrations in more recent years. TDS concentrations in the Eastern San Joaquin Subbasin ranged from 35 to 2,500 mg/L between 2015 and 2018. Spatially, the highest concentrations of TDS are found along the western margin of the Subbasin and the San Joaquin River and decrease significantly to the east, to typically less than 500 mg/L. TDS measurements, like chloride levels, are elevated near the cities of Stockton and Manteca, and in the Lodi GSA near the White Slough Water Pollution Control Facility.

Figure 2-69 shows the maximum and Figure 2-70 shows the average TDS concentrations from 2015 to 2018 as compared to the SMCL lower limit of 500 mg/L and upper limit of 1,000 mg/L. The GAMA dataset was used for analysis.

The SMCL is a secondary drinking water standard that is established for aesthetic reasons such as taste, odor, and color and is not based on public health concerns. The 500 mg/L value is “recommended” by the State Water Resources Control Board (SWRCB) as a threshold below which TDS concentrations are desirable for a higher degree of consumer acceptance of drinking water. The “upper” limit is used to define a range above the “recommended” value where TDS concentration is acceptable if it is neither reasonable nor feasible to provide more suitable waters (SWRCB, 2006).

Comparisons to the SMCL must be considered in context as the measured concentrations represent raw water, which may be treated or blended prior to delivery to meet the standard or may not be used for potable uses.

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Figure 2-69: Maximum TDS Concentrations 2015-2018
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Figure 2-70: Average TDS Concentrations 2015-2018
Elevated TDS concentrations are apparent in very shallow groundwater in close proximity to the San Joaquin River, while deep wells (depths greater than 200 feet) typically have TDS concentrations below 500 mg/L. TDS trends by depth are summarized in
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Table 2-7.

Figure 2-71 shows the maximum TDS concentrations for shallow wells in the Eastern San Joaquin Subbasin from years 2015 to 2018, and Figure 2-72 shows the maximum TDS concentrations for deep wells in the same timeframe.

As with chloride measurements, depth-dependent TDS data are not widely available.

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Table 2-7: Summary of TDS Data by Depth (2015-2018)
Depth (feet)
% Measurements in Range Range of Values (mg/L) Total
Number of
Samples
< 500
mg/L
500 – 1000
mg/L
> 1,000
mg/L Minimum Average Median Maximum
No Depth
Data 90% 8% 2% 94 339 310 1,180 451
0 - 100 N/A 0
100 - 250 54% 46% 0% 280 438 480 540 13
250 - 500 93% 7% 0% 120 344 340 560 75
> 500 N/A 0
Figure 2-71: Maximum TDS Concentrations in Shallow Wells 2015-2018 ATTACHMENT 2
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Figure 2-72: Maximum TDS Concentrations in Deep Wells 2015-2018 ATTACHMENT 2
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2.2.4.2 Nitrate
Nitrate is both naturally occurring and can be contributed a result of human activity. Nitrate can cause adverse human health effects. Anthropogenic sources of nitrate include fertilizers, septic systems, and animal waste. The DDW’s MCL of 10 mg/L for Nitrate as N delimits high levels of nitrate for drinking water use. Many measured concentrations are above this value, both historically and more recently. Comparisons to the MCL must be considered in context as the measured concentrations represent raw water, which may be treated or blended prior to delivery to meet the standard or may not be used for potable uses.

Table 2-8 provides the total number of nitrate values by decade and the percentage of those values greater than 10 mg/L. The total number of nitrate measurements has grown since 2000 as has the percentage of occurrences of concentrations greater than 10 mg/L. The GAMA dataset was used for analysis.

Table 2-8: Nitrate as N Concentrations by Decade
Decade % of Samples Number of Nitrate Samples <10 mg/L >10 mg/L 1940 88% 13% 8
1950 99% 1% 362
1960 99% 1% 240
1970 96% 4% 1,500
1980 95% 5% 420
1990 98% 2% 1,716
2000 87% 13% 9,679
2010 83% 17% 11,060
Figure 2-73 shows the historical spatial distribution of nitrate samples and detections by decade. During the 1940s, the earliest decade with nitrate measurements, very few records exist, and no significant conclusions can be made from this timeframe. The 1950s and 1960s have larger datasets, but measurements above 10 mg/L during these decades are sporadic and localized. Nitrate concentrations during the 1970s show a significant number of measurements above 10 mg/L in the northwest portion of the Eastern San Joaquin Subbasin, adjacent to Interstate 5. The 1980s and 1990s show similar patterns, with areas measurements above 10 mg/L primarily around the cities of Stockton, Lodi, and Manteca. Nitrate as N measurements above 10 mg/L are also located near the southern edge of the Eastern San Joaquin Subbasin, close to Highway 120. Although a much greater number of records exists for the 1990s than the 1980s, these decades have approximately the same spatial distribution. One possible explanation is similar wells were sampled during the 1980s and 1990s, but much more frequently in the 1990s. The 2000s and 2010s had both the greatest number of nitrate measurements and the largest number of measurements above 10 mg/L. Measurements above 10 mg/L during these decades follow previous trends: they are primarily between Highway 99 and Interstate 5, from Ripon to near Lodi.

Recent (as of 2019) nitrate measurements above the MCL correspond to the overall historical trends and highlight areas with elevated nitrate concentrations in more recent years. These areas include the cities of Stockton and Ripon, areas of the Lodi GSA near the White Slough Pollution Control Facility, the N.A. Chaderjian Youth Correctional Facility, Republic Services Landfill on South Austin Road, and the Kruger and Sons, Inc. site off Highway 4 outside Farmington.

While the extent of groundwater quality impacts from nitrate is a data gap area, increased nitrate concentrations have not been found to have a causal nexus between SGMA-related groundwater management activities in the Subbasin.

The causal nexus reflects that the degraded water quality issues are associated with groundwater pumping and other SGMA-related activities rather than water quality issues resulting from land use practices, naturally occurring water quality issues, or other issues not associated with groundwater pumping. Additional monitoring conducted through the implementation of this GSP will inform trends such that the Eastern San Joaquin Groundwater Authority (ESJGWA) can be informed to take action to address nitrite contamination if a causal nexus is identified.

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Section 3.3 of this Plan discusses Irrigated Lands Regulatory Program (ILRP) and Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS), two existing regulatory programs for the monitoring and regulation of nitrate.

Under the ILRP, the San Joaquin County & Delta Water Quality Coalition is required to test and potentially mitigate for nitrate in domestic wells. Additionally, the 2017 Salt and Nitrate Management Plan developed by CV-SALTS identifies long-term nitrate management practices (CVRWQCB, 2016).

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Figure 2-73: Nitrate as N Concentrations by Decade
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2.2.4.3 Arsenic
Arsenic is ubiquitous in nature and is commonly found in drinking water sources in California. Determining the source of arsenic in groundwater is difficult because arsenic is both naturally occurring and used in human activities such as agriculture. Public health concerns about arsenic in drinking water related to its potential to cause adverse health effects are addressed through DDW’s MCL, established at 10 micrograms per liter (µg/L). California's revised arsenic MCL of 10 μg/L became effective on November 28, 2008. A 10-μg/L federal MCL for arsenic has been in effect since January 2006. Previous California and federal MCLs for arsenic were 50 μg/L.

Figure 2-74 shows the spatial distribution of arsenic concentrations contained in the GAMA database. From the 1970s to present, the total number and percentage of arsenic values above 10 µg/L has increased (see Table 2-9). The spatial distribution of measurements above 10 µg/L is similar to nitrate, largely between Interstate 5 and Highway 99, from Manteca to Lodi. The increased arsenic concentrations near urban areas are not necessarily indicative of contamination from these areas and may partially be due to the fact that arsenic measurements are more abundant in these urban areas; GAMA water quality records are rarely evenly distributed throughout the Subbasin for any constituent. Recent (as of 2019) arsenic samples show measurements above 10 µg/L similar to the overall trends (see Figure 2-75). Measurements above 10 µg/L in years 2015, 2016, 2017, and 2018 are primarily located in the cities of Stockton and Manteca, with fewer occurring around the City of Lodi. While the extent of groundwater quality impacts from arsenic is a data gap area, increased arsenic concentrations have not been found to have a causal nexus between SGMA-related groundwater management activities in the Subbasin.

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Figure 2-74: Arsenic Concentrations by Decade
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Table 2-9: Arsenic Concentrations by Decade
Decade % of Samples Number of Arsenic Samples <10 µg/L >10 µg/L 1960 100% 0% 1
1970 86% 14% 339
1980 72% 28% 363
1990 72% 28% 645
2000 56% 44% 4,051
2010 48% 52% 5,109
Figure 2-75: Maximum Arsenic Concentrations 2015-2018
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2.2.4.4 Point Sources
Point sources are discrete or discernable sources of pollutants which may introduce undesirable constituents into groundwater and may negatively impact water quality. In the Eastern San Joaquin Subbasin, point sources include leaking underground storage tanks, landfills, dry cleaners, and others. These sites are actively investigated and monitored within the Eastern San Joaquin Subbasin in response to these known or potential sources of groundwater contamination.

The Regional Water Quality Control Board (RWQCB), the Department of Toxic Substances Control (DTSC), and the USEPA provide oversight of point-source pollution through existing regulatory programs, including management of remedial action for point-source contamination sites. Figure 2-76 shows the results of a query from both the GeoTracker database and the EnviroStor database. GeoTracker documents contaminant concerns that the RWQCB is or has been working with site owners to remediate while EnviroStor is the DTSC’s data management system to track known contamination sites undergoing cleanup, permitting, enforcement, and investigation efforts. As shown in Figure 2-76, there are 258 active sites within the Eastern San Joaquin Subbasin which are color-coded based on the site’s constituent(s) of concern: fuels (gas and/or diesel); synthetic organics (pesticides, herbicides, insecticides, etc.); or a mix of constituents (multiple constituents such as heavy metals and pesticides).

Most sites within the Eastern San Joaquin Subbasin are fuel sites (e.g., gas or diesel) that are under active investigation or remediation. Sites with the potential to cause plumes are mapped in Figure 2-77, which were identified by filtering for sites containing soluble and mobile constituents such as volatile organic compounds (VOCs); benzene, toluene, ethylbenzene, and xylenes (BTEX); and/or petroleum hydrocarbons (gas or diesel).

Sites with the potential to cause plumes are currently managed by existing regulatory programs through the RWQCB, DTSC, and USEPA, as described above. New projects undertaken by the GSAs as part of GSP implementation will evaluate contaminant plume movement in a CEQA document. Specific point source sites and contaminants are discussed in the sections below.

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Figure 2-76: Active Investigation and Remediation Sites as of 2019 ATTACHMENT 2
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Figure 2-77: Active Sites with the Potential to Cause Plumes

2.2.4.4.1 Publicized Plumes in and near the Subbasin
As indicated above, the Eastern San Joaquin Subbasin has numerous open cleanup sites, including areas contaminated by chlorinated solvents, methyl tertiary-butyl ether (MtBE), pesticides and herbicides, and leaking underground storage tanks. Plume sites are often clustered around urban centers but are also found near sites where historical industrial or agricultural practices have released contaminants of concern. While other plumes exist in and around the Subbasin, three specific plumes have been highly publicized: the Lodi Plumes, the Sharpe Army Depot Plume, and the Occidental Chemical Corporation Plume.

In the late 1980s, the City of Lodi discovered the chlorinated solvents perchloroethylene (PCE) and trichloroethene (TCE) in drinking water supplies and pursued a groundwater investigation that revealed a series of five separate plume areas located in the northeastern portion of the city: the Northern, Western, Central, Southern, and Busy Bee plumes.

The Busy Bee plume, named after a dry cleaner business that previously operated on the site, now has regulatory closure, with cleanup moving toward completion under CVRWQCB oversite (Water Resources Control Board, 2011).

Groundwater contamination plumes in the City of Lathrop, located just outside the Subbasin boundary, include the Sharpe Army Depot and Occidental Chemical Corporation sites. Contamination of groundwater at the Sharpe Army ATTACHMENT 2
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Depot consists primarily of trichloroethene, tetrachloroethene, and cis-1,2-dichloroethene from historical industrial activities related to military activities. Due to concerns of potential contamination, the City of Lathrop abandoned their wells in the area. Three groundwater extraction and treatment systems are located at Sharpe Army Dept and are used to treat existing groundwater (EKI Environment & Water, 2015).

The Occidental Chemical Corporation Plume was discovered in the late 1970s and is the result of former leaking wastewater holding ponds containing pesticides and chemicals used for equipment cleaning by the Occidental Chemical Corporation. Contaminants of concern include the pesticides 1,2-dibromo-3-chloropropane (DBCP) and ethylene dibromide (EDB), lindane, 2,3,4,5-tetrahydrothiopene-1, 1-dioxide, sulfate, nitrate, chloride, and BHC (RWQCB, 2012). Since the discovery of these plumes in the 1980s, groundwater monitoring and evaluation at point source locations has led to the implementation of remedial activities such as the installation of groundwater extraction and remedial systems, implementation of a Salinity Reduction Plan, and mandated waste discharge requirements (WDRs) (CVRWQCB, 2012).

2.2.4.4.2 Petroleum Hydrocarbons
Approximately 134 sites in the Eastern San Joaquin Subbasin are identified as actively investigating or remediating an unauthorized release of petroleum hydrocarbons, according to the GeoTracker and EnviroStor databases. At these sites, petroleum hydrocarbon constituents are most commonly fuels (diesel, gasoline, motor oil, or aviation fuel) and VOCs commonly added to fuels, including MTBE and BTEX constituents. Concentrations of petroleum hydrocarbons have not been modeled across the Subbasin; concentrations are local and site specific. A summary description of the aforementioned constituents is provided in Table 2-10 below:

Table 2-10: MCLs for Common Petroleum Hydrocarbons and MTBE Constituent Source Primary MCL
MTBE Oxygenate commonly added to gasoline 13 µg/L
BTEX
Benzene Industrial solvent added to crude oil paint, varnish, and lacquer thinner 1 µg/L
Toluene Aromatic hydrocarbon used in industrial feedstock, as a solvent, and to produce benzene and added to gasoline 150 µg/L
Ethylbenzene Used as a solvent and added to fuel, asphalt, and naphthalene 300 µg/L Xylenes Naturally occurring in petroleum, coal and wood tar 1.750 mg/L Source: (SWRCB, 2018)

2.2.4.4.3 Synthetic Organics
Approximately 47 sites in the Eastern San Joaquin Subbasin are identified as actively investigating or remediating an unauthorized release of synthetic organics, according to the GeoTracker and EnviroStor databases. At these sites, pesticides, herbicides, fertilizer, and pesticides are the most common constituents. Other constituents include VOCs such as PCE and TCE. Concentrations of synthetic organics have not been modeled across the Subbasin; concentrations are local and site specific. For context, a brief description of the aforementioned VOCs is provided in Table 2-11.

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Table 2-11: MCLs for Common Synthetic Organic Constituents Constituent Source Primary MCL1
TCE Used as a solvent in manufacturing facilities and dry cleaners 5 µg/L PCE Used as a solvent in manufacturing facilities, dry cleaners, printing shops, and auto repair facilities 5 µg/L
Note:
1 Source: (SWRCB, 2018)

2.2.4.4.4 Mixed Constituents
Approximately 28 sites in the Eastern San Joaquin Subbasin are identified as actively investigating or remediating an unauthorized release of mixed constituents, according to the GeoTracker and EnviroStor databases. Sites with mixed constituents are those that include a release of more than one type of contaminant, such as a mix of heavy metals, diesel, inorganics, and/or organics. At these sites, the most common constituents include a mixture of heavy metals (chromium, arsenic, and lead), inorganics, and solvents. The sources and primary MCL for many contaminants found in the ‘mixed constituents’ classification have been discussed throughout Section 2.2.4.

2.2.4.4.5 Emerging Contaminants
Many chemical and microbial constituents that have not historically been considered as contaminants are occasionally, and in some cases with increasing frequency, detected in groundwater. These newly recognized (or emerging) contaminants are commonly derived from municipal, agricultural, industrial wastewater, and domestic wastewater sources and pathways. These newly recognized contaminants are dispersed to the environment from domestic, commercial, and industrial uses of common household products and include caffeine, artificial sweeteners, pharmaceuticals, cleaning products, and other personal care products. Residual waste products of genetically modified organisms are also of potential concern. Several studies, such as by Watanabe et al. in 2010, have recently been published or are underway regarding the potential link between dairies and the occurrence of pharmaceuticals in shallow groundwater in the San Joaquin Valley.

Perfluorooctanesulfonic acid (PFOS) and perfluorooctantoic acid (PFOA) are organic chemicals synthesized for water and lipid resistance, used in a wide variety of consumer products as well as fire-retarding foam and various industrial processes. These chemicals tend to accumulate in groundwater, though typically in a localized area in association with a specific facility, such as a factory or airfield (California Water Boards, 2018). There are currently no MCLs for PFOS or PFOA; however, the USEPA is moving forward with establishing the MCL and is recommending municipalities notify customers at levels at or greater than 70 parts per trillion in water supplies (USEPA, 2019). California’s DDW has established notification levels at 6.5 parts per trillion for PFOS and 5.1 parts per trillion for PFOA (SWRCB, 2019). 1,2,3-Trichloropropane (1,2,3-TCP) is a solvent and is typically found in industrial or hazardous waste sites. Along with an industrial solvent, 1,2,3-TCP is a cleaning and degreasing agent and associated with pesticide products. Though there is currently no federal MCL, the MCL for 1,2,3-TCP in California is 0.005 µg/L (SWRCB, 2019).

Currently, data on PFOS, PFOA, and 1,2,3-TCP are limited in the Eastern San Joaquin Subbasin since these are emerging contaminants.

2.2.5 Conditions in 2019: Land Subsidence
Despite long-term declining groundwater levels, there are no historical records of significant and unreasonable impacts from subsidence in the Eastern San Joaquin Subbasin. Figure 2-78 shows regional subsidence produced from TRE Altamira Interferometric Synthetic Aperture Radar (InSAR) data, provided by DWR for SGMA application. InSAR is a satellite-based method for showing ground-surface displacement over time. This figure illustrates that subsidence has historically been minimal in the Subbasin and surrounding areas (ranging from -0.1 to 0.1 feet of vertical displacement annually). The error range of a single InSAR measurement is +/- 5 millimeters (TRE Altamira, 2019). See Section 2.1.5 for a discussion of the soils and clays within the Subbasin, including the extent of Corcoran Clay.

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Figure 2-78: Subsidence (Annual Rate of Vertical Displacement) Note: This dataset represents measurements of vertical ground surface displacement in between spring 2015 and summer 2017 (TRE Altamira, 2019).

2.2.6 Conditions in 2019: Interconnected Surface Water Systems Interconnected surface waters (ISW) are surface water features that are hydraulically connected by a saturated zone to the groundwater system. In these systems, the water table and surface water features intersect at the same elevations and locations. Interconnected surface waters may be either gaining or losing, wherein the surface water feature itself is either gaining water from the aquifer system or losing water to the aquifer system.

In the Eastern San Joaquin Subbasin, stream connectivity was analyzed by comparing monthly groundwater elevations from the historical calibration of the ESJWRM to streambed elevations along the streams represented in ESJWRM.

This analysis was based on modeling results from the historical calibration of the ESJWRM for approximately 900 stream nodes in the Eastern San Joaquin Subbasin, which represents that best available information for current and historical conditions related to interconnected surface water systems. Figure 2-79 shows locations where streams ATTACHMENT 2
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are interconnected at least 75 percent of the time (shown in blue) or interconnected less than 25 percent of the time (shown in green).

Disconnected streams will always be losing streams, but interconnected streams may be either losing or gaining, depending on the surface water and groundwater conditions. Groundwater discharge from the aquifer is primarily through groundwater pumping, however, groundwater also discharges to streams where groundwater elevations are higher than the streambed elevations. Figure 2-80 shows mostly gaining streams in blue where groundwater discharges to rivers more than 75 percent of the time, mostly losing streams in red where streams lose water to the groundwater system more than 75 percent of the time, and mixed streams (gaining or losing less than 75 percent of the time) in orange.

Due to limited model calibration based on insufficient calibration information, stream nodes in the Delta area and along stretches of streams near the foothill boundary of the Subbasin are not shown on Figure 2-79 and Figure 2-80.

Interconnected surface water is highlighted as a data gap in Section 4.7.3 due to a lack of data from shallow monitoring wells near streams. Future improvements to the understanding of interconnected surface water include proposed monitoring wells in Section 4.7.5 that are largely located along streams or in areas of the foothills where current monitoring coverage is lacking and a specific project in Section 6.2 to improve understanding of losses along Mokelumne River. Section 7.4.1 discusses model refinements over the next five years in order to improve calibration of the model and its use in analysis of GSP water budgets and sustainability criteria. The analysis in this section includes the results from the 2019 model and Appendix 3-G details an updated analysis.

Figure 2-79 and Figure 2-80 are illustrations to describe model outputs, which are subject to uncertainty and future refinements and are not intended for regulatory purposes beyond the use in this Plan.

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Figure 2-79: Stream Connectivity to the Groundwater System Note: Analysis is based on limited data recognized to have significant gaps. Interconnected surface water is a recognized data gap in the GSP as discussed in Section 4.7.

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Figure 2-80: Losing and Gaining Streams
Note: Analysis is based on limited data recognized to have significant gaps. Interconnected surface water is a recognized data gap in the GSP as discussed in Section 4.7.

2.2.7 Conditions in 2019: Groundwater-Dependent Ecosystems Groundwater-dependent ecosystems (GDEs) are defined in the GSP regulations as “ecological communities or species that depend on groundwater emerging from aquifers or on groundwater occurring near the ground surface.” SGMA requires the identification of GDEs. SGMA does not require that additional sustainable management criteria be established to specifically manage these areas, but rather includes GDEs as a beneficial user of water to be considered when developing other sustainable management criteria.

GDEs exist where vegetation accesses shallow groundwater for survival. This Plan identifies GDEs within the Eastern San Joaquin Subbasin based on determining the areas where vegetation is dependent on groundwater.

2.2.7.1 Methodology for GDE Identification
The Natural Communities Commonly Associated with Groundwater (NCCAG) database was used as a starting point to identify GDEs within the Subbasin. The NCCAG database was developed by a working group comprised of DWR, California Department of Fish and Wildlife (CDFW), and The Nature Conservancy (TNC). The working group reviewed ATTACHMENT 2
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publicly available datasets which mapped California vegetation, wetlands, springs, and seeps and conducted a screening process to retain communities known to be commonly associated with groundwater. The NCCAG database defines two habitat classes: wetland and vegetative. The wetland class includes wetland features commonly associated with the surface expression of groundwater under natural, unmodified conditions. The vegetative class includes vegetation types commonly associated with the shallow subsurface presence of groundwater (phreatophytes). Figure 2-81 shows the location of the two NCCAG classes within the Eastern San Joaquin Subbasin. The distribution of freshwater fish and wildlife species that may be dependent on GDEs is not well known and is not included in this analysis. A list of freshwater species in the Eastern San Joaquin Subbasin is provided in Appendix 1-H. Instream flows for rivers and streams interconnected with groundwater are evaluated through the Depletions of Interconnected Surface Water sustainability indicator (see Section 3.3.6).

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Figure 2-81: Natural Communities Commonly Associated with Groundwater (NCCAGs) Source: NC Dataset Viewer, CADWR Sustainable Groundwater Management (https://gis.water.ca.gov/app/NCDatasetViewer/) ATTACHMENT 2
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This Plan uses the NCCAG database as a starting point for identifying potential GDEs. To identify NCCAG areas that are potential GDEs, the analysis identified communities in areas where groundwater levels are shallower than 30 feet bgs, as these areas are thought to be reachable by the root zone of vegetation. 1 Oak trees are considered the deepestrooted plant in the region with a root zone of roughly 25 feet.2 This value is considered conservative, as this depth is unlikely to support recruitment of new oak seedlings. NCCAG-identified communities in areas with groundwater shallower than 30 feet were considered as potential GDEs. Communities in areas deeper than 30 feet were identified as data gap areas for future refinement and are labeled on Figure 2-82 as “Depth to Water > 30 ft”. These areas will be refined in future analyses to identify potential existing GDEs that may have been misclassified through this screening process. Additional information regarding plans to fill GDE-related data gaps can be found in Section 4.7.4.

The NCCAG database was then further refined to identify communities without access to alternate water supplies, as those communities would not be dependent on groundwater. This was done by screening for the following: 1) areas not close to managed wetlands, 2) areas not adjacent to irrigated agriculture, and 3) areas not near perennial surface water bodies. NCCAG-identified communities with access to shallow water (less than 30 feet bgs) and without access to alternate water supplies were classified as GDEs. Communities with access to alternate water supplies were identified as data gap areas requiring additional investigation to determine the reliability of the alternate supply. • Proximity to Managed Wetlands – Managed wetlands receive supplemental water to support wildlife habitat.

Managed wetlands, and areas within 150 feet of a managed wetland, are assumed to be able to access this supplemental delivered water regardless of the condition of the underlying aquifer. Areas farther than 150 feet from a managed wetland that meet the other GDE criteria in this section are assumed to be dependent on groundwater and were identified as GDEs. A criterion of 150 feet was used to reflect ponded conditions at the wetlands. Identified wetlands were reviewed with local water managers to verify supplemental water deliveries.

NCCAG-identified communities not identified as GDEs through this analysis are identified as data gap areas for future refinement and are labeled on Figure 2-82 as “Managed Wetland”. These areas will be refined in future analyses to determine if the alternate source of surface water is reliable over time and to identify potential existing GDEs that may have been misclassified through this screening process. • Adjacent to Irrigated Agriculture – Irrigated agricultural lands are dependent on regular irrigation. This irrigation benefits not only the crops, but also the surrounding vegetation. Irrigated lands, and areas within 50 feet of irrigated lands, are assumed to be able to access this supplemental delivered water regardless of the condition of the underlying aquifer. Areas farther than 50 feet from irrigated lands that meet the other GDE criteria in this section are assumed to be dependent on groundwater and were identified as GDEs. A criterion of 50 feet was used to reflect non-ponded conditions in the fields.

NCCAG-identified communities not identified as GDEs through this analysis are identified as data gap areas for future refinement and are labeled on Figure 2-82 as “Adjacent to Agriculture”. These areas will be refined in future analyses to determine if the alternate source of surface water is reliable over time and to identify potential existing GDEs that may have been misclassified through this screening process. • Proximity to Perennial Surface Water Bodies – Perennial surface water bodies provide year-round water supplies that can be accessed by adjacent vegetation. These water bodies include much of the Delta; large, managed rivers; and smaller water bodies that flow throughout the summer due to agricultural deliveries or 1 This analysis uses 2015 groundwater levels (winter, spring, summer, and fall), which may be deeper than representative levels due to drought conditions, a factor which will be considered in future GDEs analyses. 2 Quercus chrysolepis (canyon live oak) has a maximum rooting depth of 7.3 meters (23.95 feet) (Canadell et al., 1996).

Quercus lobata (valley oak) has a maximum rooting depth of 7.41 meters (24.31 feet), although available data are from fractured rock aquifers (Lewis & Burgy 1964 and Schenk, H. J. and Jackson, R. B. 2002, as cited in TNC, 2019).

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tailwater. Areas within 150 feet of such surface water bodies are assumed to be able to access that surface water regardless of the condition of the underlying aquifer. Areas father than 150 feet from such surface water bodies that meet the other GDE criteria in this section are assumed to be dependent on groundwater and were identified as GDEs. A criterion of 150 feet was used to reflect open water conditions in the surface water bodies.

NCCAG-identified communities not identified as GDEs through this analysis are identified as data gap areas for future refinement and are labeled on Figure 2-82 as “Perennial Surface Water Bodies”. These areas will be refined in future analyses to determine if the alternate source of surface water is reliable over time and to identify potential existing GDEs that may have been misclassified through this screening process.

Next, areas identified as GDEs were ground-truthed electronically with GSA staff and Groundwater Sustainability Workgroup (Workgroup) members. Through this process, areas identified GDEs were investigated, and areas identified as known irrigated parcels such as parks were reclassified. These areas are labels on Figure 2-82 as “Stakeholder Comment.”
This methodology was developed to focus groundwater management activities on the most appropriate areas. The distinction between GDEs and other wetland or vegetative areas is important from a management perspective, as GDEs are expected to be more responsive to changes in groundwater management. Management of communities that access alternate supplies, on the other hand, may require greater focus on land use protection or irrigation activities, for which the GSAs have limited authority to manage through SGMA.

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Figure 2-82: NCCAGs Identified as Data Gap Areas for Future Refinement, Likely to Access Non-groundwater Water Supplies ATTACHMENT 2
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2.2.7.2 Areas Identified as GDEs
Following the methodology presented above, this Plan identifies several GDEs, primarily located along the western boundary of the Subbasin and in the Delta areas where groundwater is typically shallow. These areas are divided into two categories: Vegetative GDEs and Wetland GDEs, as shown in Figure 2-83.

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Figure 2-83: Areas Identified as GDEs
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2.3 CURRENT GROUNDWATER CONDITIONS
This section describes the current groundwater conditions in the Eastern San Joaquin Subbasin since development of the 2020 GSP.

As required by the GSP regulations, the current groundwater conditions section includes:
• Definition of current groundwater conditions in the Subbasin • Description of the distribution, availability (storage), and quality of groundwater • Identification of interactions between groundwater, surface water, groundwater dependent ecosystems, and subsidence
Current conditions are generally assumed to be the conditions of the Subbasin roughly between WY 2020 and WY 2023, unless otherwise noted in the below sections.

2.3.1Groundwater Elevation

2.3.1.1 Groundwater Levels
For the purposes of the 2024 GSP, the most current groundwater elevation conditions were characterized as fourth quarter 2022 (recent seasonal low, measured in fall 2022) and first quarter 2023 (recent seasonal high, measured in spring 2023) groundwater elevation measurements. However, WY 2023 represented a wetter than average water year.

For comparison, fourth quarter 2019 and first quarter 2020 of WY 2020 are also included. WY 2020 was a dry year.

Groundwater elevations were mapped using wells with available data in WDL.

Figure 2-84 and Figure 2-85 show the groundwater elevations for WY 2020. Figure 2-86 and Figure 2-87 show the groundwater elevations for WY 2023. A pumping depression at the center of the Subbasin, east of the City of Stockton, generally exists during periods of lower groundwater elevations, as shown in Fourth Quarter 2019, First Quarter 2020, and Fourth Quarter 2022. In wetter years, this pumping depression can recover, as shown in First Quarter 2023. Similar to historical conditions, groundwater generally flows from the outer edges of the Subbasin towards the depression in the middle of the Subbasin. The predominant hydraulic gradient across the Subbasin is from east to west.

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Figure 2-84: Fourth Quarter 2019 Groundwater Elevation (WY 2020) ATTACHMENT 2
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Figure 2-85: First Quarter 2020 Groundwater Levels (WY 2020) ATTACHMENT 2
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Figure 2-86: Fourth Quarter 2022 Groundwater Elevation (WY 2023) ATTACHMENT 2
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Figure 2-87: First Quarter 2023 Groundwater Levels (WY 2023) Hydrographs are reported annually to DWR in the Annual Reports for 76 single completion wells and 52 nested wells.

The most recent hydrographs for these wells can be found in the WY 2023 ESJ Subbasin Annual Report, available on DWR’s SGMA Portal (https://sgma.water.ca.gov/portal/). All hydrographs show yearly cycles of groundwater level declines in summer due to typical patterns in groundwater pumping and recharge during winter recovery.

2.3.1.2 Reported Dry Wells
According to DWR’s Dry Well Reporting System, San Joaquin County has had 106 reported dry wells since the start of WY 2020 (CA Department of Water Resources, 2023). Figure 2-88 shows the number of reports made to DWR by month between WY 2020 and WY 2023. However, it is important to note that dry wells are reported for many reasons other than a failure due to increasing depth to groundwater. Staff interviews with DWR confirmed that the system does not determine the cause of the well failure unless monitored by outside parties. As expected, reports of dry wells were higher in the critical years of WY 2021 and 2022 than in WY 2023, a wet year.

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Figure 2-88 : Number of Reported Dry Wells in San Joaquin County between WY 2020-2023

2.3.2Groundwater Storage
The ESJWRM was used to estimate historical change in storage of the Eastern San Joaquin Subbasin from 1995-2023.

Figure 2-89 shows the cumulative change in storage against annual storage change and water year type, including current condition years WY 2020 through 2023. The cumulative change in storage from 1996 to 2023 was estimated as on average -0.34 million acre-feet per year (MAF/year). More information about the layers of the ESJWRM and calculation of storage changes can be found in model documentation in Appendix 2-C.

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Figure 2-89: Modeled Change in Annual Storage with Water Use and Year Type Notes:

4. Water Year Types based on San Joaquin Valley Water Year Index (CA DWR, 2024)

5. “Other Recharge” includes managed aquifer recharge, recharge from unlined canals and/or reservoirs, and recharge from ungauged watersheds.

6. “Change in Storage” is placed to balance the water budget. For instance, if annual outflows (-) are greater than inflows (+), there is a decrease in storage, but this would be shown on the positive side of the bar chart to balance out the increased outflows on the negative side of the bar chart.

2.3.3Seawater Intrusion
The northwest corner of the Eastern San Joaquin (ESJ) Subbasin overlies a portion of the Delta. The Delta originally experienced groundwater fluctuations closely tied to tidal cycles, with a mix of brackish, saline ocean water, and fresh streamflow typical of an inland river delta and estuary. However, after decades of land reclamation and the implementation of managed operations as a result of the State Water Project and Central Valley Project, the Delta is now managed as a freshwater body. Saline water is no longer able to migrate eastward beyond the extensive network of levees and engineering alterations to the original natural channels. As a result, seawater intrusion has not historically been observed within the Subbasin nor is it likely to occur in the future.

The following section provides analysis supporting this claim, demonstrating that:

1. The Delta is managed as a freshwater body in the Subbasin

2. There is minimal pumping near the Delta

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Further detail can be found in Appendix 3-F.

2.3.3.1 Delta is Managed to Maintain Freshwater Flows
The Subbasin is located in the Delta region. Prior to the construction of the Shasta Dam in 1943, brackish water had entered the surface waterways throughout the Delta. The Delta ecosystem naturally adapted to a salinity cycle that brought brackish tidal water from the San Francisco Bay. However, the construction of levees for agricultural development, followed by the development and operation of the Central Valley Project and the State Water Project, has changed the pattern of seawater movement into the Delta (Water Education Foundation, 2019). Historically, some saltwater may have infiltrated the aquifers locally affecting groundwater quality. Current management practices aim to maintain freshwater flows in the Delta through a combination of hydraulic and physical barriers and modifications to existing channels (Water Education Foundation, 2019). The ”X2” barrier, where the salinity is approximately 2 parts per thousand (ppt), is located well outside of the Subbasin boundary further downstream in the Delta (Cloern, 2012). (For reference purposes, the salinity of the ocean is about 35 ppt.) Various agencies and regulations, such as the Delta Protection Commission (DPC), Delta Stewardship Council, San Joaquin County & Delta Water Quality Coalition, and State Water Board Resolution No. 2009-011, contribute to managing and maintaining salinity conditions in the Delta region.

2.3.3.2 Minimal Groundwater Pumping Near the Delta
Figure 2-90 presents the Subbasin’s 2023 average groundwater pumping in feet across the Subbasin. The majority of pumping is in the northwest portion of Subbasin, areas adjacent to the Delta pump less than half a foot of groundwater per year.

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Figure 2-90: 2023 Annual Groundwater Pumping
This figure reflects groundwater pumping from the 2023 Eastern San Joaquin Annual Report. Results may vary with the updated 2024 Eastern San Joaquin Water Resources Model.

2.3.3.3 Low Chloride Concentrations
Historical and current chloride concentrations were analyzed in the Subbasin. A variety of groundwater quality data were collected and examined. The datasets used for this analysis include (1) the Groundwater Ambient Monitoring and Assessment (GAMA) database, (2) The National Water (NWQMC) database, (3) the region’s Opti Data Management System (DMS), and (4) SGMA Data Viewer (DWR). From these datasets, 4,000 unique wells were utilized with approximately 19,500 chloride observations.

Most wells had chloride concentrations well below the SMCL of 250 mg/L for chloride. (Secondary MCLs are established as guidelines to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color, and odor. Contaminants with SMCLs are not considered to present a risk to human health and are not enforced.) Chloride concentrations throughout the Subbasin have remained relatively low. Table 2-12 shows the percentage of chloride measurements after 2015 that exceed thresholds of 250 mg/L, 500 mg/L, and 2,000 mg/L.

Notably, the majority of measurements (80%) fell within the 0–250 mg/L range, indicating low chloride levels throughout the Subbasin. Additionally, 14% of chloride observations were in the 250–500 mg/L range. Overall, 94% of measurements are below the 500 mg/L threshold. This analysis demonstrates that chloride concentrations in the Subbasin are generally low.

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Table 2-12: Chloride Concentrations after 2015
Threshold Concentration Percentage of Measurements after 2015 above Threshold
250 mg/L 14%
500 mg/L 5%
2,000 mg/L 1%
Chloride measurements in Table 2 are based on approximately 19,500 observations from 4,000 unique wells.

Figure 2-91 shows the average chloride concentration in the Subbasin since January 2015. These results are consistent with the ranges shown in Table 2-12. As shown in Figure 2-91, the majority of chloride concentrations in the Subbasin are within the 0 to 250 mg/L range. There are instances of higher concentrations in the 250 to 500 mg/L range, localized within the central and western regions of the Subbasin. Notably, these areas of relatively higher chloride concentrations are not located only in the Delta area and do not form a seawater intrusion front pattern. Overall, concentrations of chloride in the Subbasin are minimal and seawater intrusion is not occurring in the Subbasin or expected to occur in the future.

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Figure 2-91: Average Chloride Concentrations Post-2015

2.3.4Groundwater Quality
In addition to the chloride data shown in Section 2.3.3, available recent TDS data from the Groundwater Ambient Monitoring and Assessment (GAMA) Program were also analyzed to characterize current groundwater quality conditions. The locations, observations, and concentrations of the new set of monitoring wells were examined, as shown in Figure 2-92 through Figure 2-94.

Figure 2-92 illustrates the count of TDS groundwater quality observations for each well between January 2015 and January 2024. The majority of wells have 10 or fewer observations, indicating that most wells were not sampled on an annual basis. Several wells closer to the City of Stockton have up to 50 groundwater quality observations. The wells with the highest sample count appear to be located near groundwater cleanup sites. Ideally, wells in the representative monitoring network for groundwater quality would have been sampled regularly; however, some wells in the specific areas have not sampled frequently (greater than 10 times) in recent years.

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Figure 2-93 displays wells with TDS observations in recent years (2015 through early 2024) by well depth. The threshold between shallow and deep wells was set at 200 feet for consistency with the 2020 GSP. There were several wells without perforation or depth information. Between shallow, deep, and unknown well depths, there is a similar distribution of high- and low-quality groundwater. In other words, TDS was not observed in just the shallow portions or just the deep portions of the aquifer.

Figure 2-94 illustrates the maximum TDS concentrations since January 2015. The majority of wells have TDS concentrations below 600 mg/L (the measurable objective for TDS). However, some wells have recent TDS concentrations above 1,000 mg/L (the minimum threshold for TDS). These wells are primarily located near the City of Stockton. Public water purveyors closely monitor groundwater quality and source and treat their water accordingly.

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Figure 2-93: Wells with Recent TDS Observations by Well Depth ATTACHMENT 2
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Figure 2-94: Maximum Concentrations for Wells Measuring Total Dissolved Solids

2.3.5Land Subsidence
SGMA requires monitoring and reporting on inelastic land subsidence. In the Subbasin, subsidence concerns, if any, are focused on the non-Delta area as the Delta region contains peaty soils. Peaty soils can subside due to peaty soil oxidation. Peat oxidation occurs when the peaty soils dewater and come into contact with air, causing the soils to break down and compress, and is not a mechanism caused by groundwater overdraft.

Within the Eastern San Joaquin Subbasin, there are three primary sources of subsidence data, each with different periods of record and methods of data collection:
• CGPS vertical displacement data from the DWR SGMA Data Viewer • InSAR subsidence rates from the SGMA Data Viewer
• Survey benchmarks from U.S. Geological Survey (USGS), the U.S. Army Corps of Engineers (USACE), California Department of Transportation (CalTrans), the San Joaquin County Department of Public Works, and local agencies.

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There are no DWR or USGS extensometers in the Eastern San Joaquin Subbasin. The datasets used are detailed further below.

2.3.5.1 CGPS Data
Vertical displacement data from CGPS stations are available for download from the DWR SGMA Data Viewer (DWR, 2024). Two CGPS stations are monitored by UNAVCO and two by Scripps Orbit and Permanent Array Center (SOPAC). Of the SOPAC stations, Station P309, is the northeast region of the Subbasin north of the Calaveras River and has a period of record from March 4, 2006, to January 19, 2024. Station P273, in the northwest region of the Subbasin, has data from November 10, 2005, to December 28, 2020. P273 lies in the Delta region of the Subbasin.

The two UNAVCO CGPS stations are CNDR and MTWK. CNDR, in the western region of the Subbasin, has data from April 30, 1999, to February 14, 2006, but is no longer monitored. MTWK, in the southern region of the Subbasin south of the city of Manteca, has data from December 12, 2019, to January 19, 2024. This is the closest CGPS station to the location of the Corcoran Clay. Clay-rich zones are prioritized for monitoring since groundwater over-extraction in these areas can lead to dewatering and compression of the clay aquitards, and inelastic land subsidence.

Several additional CGPS stations from the University of Nevada Geodetic Laboratory (UNGL) are also monitored for subsidence (UNGL, 2024). Station CA15 is located north of the city of Stockton and has a continuous period of record between September 2013 and October 2021. Station CMNC is located along the southern edge of the Camanche Reservoir and has observations in 2020 and between February 2022 through January 2024. These locations also provided additional spatial coverage to the UNAVCO and SOPAC CGPS stations.

Figure 2-95 through Figure 2-98 show time series graphs of subsidence for the four CGPS stations in this analysis.

Between 2015 and 2023, all of the CGPS stations showed that less than one foot of subsidence was observed throughout the Subbasin. The accuracy of GPS data is estimated to be ± 2 inches (CA DWR, 2017).

Figure 2-95 shows a time series graph of subsidence for CGPS Station MTWK. The graph indicates a slight downward trend, reflecting a small increase in subsidence in the Subbasin. From January 2023 to July 2023, subsidence increased slightly more, though overall subsidence remains minimal. The trend line's slope of -0.0295 inches per month (or -0.354 inches per year) confirms that subsidence is occurring in the Subbasin, but at insignificant levels.

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Figure 2-95: CGPS Station MTWK – Subsidence Time Series Figure 2-96 shows a time series graph of subsidence for CGPS Station P309. The graph indicates a very slight downward trend, reflecting a small increase in subsidence in the Subbasin. However, the displacement data varies to a great degree, increasing and decreasing throughout 2006 to current conditions. From June 2015 to June 2016, subsidence increased slightly more, with an overall subsidence of approximately 0.7 inches. This data point represents the largest observed subsidence across the four CGPS stations but still shows no inelastic subsidence. The trend line's slope of -0.0004 inches per month (-0.005 inches per year) confirms that subsidence occurring in this region is elastic and negligible.
y = -0.0295x + 0.1815
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0.2 0.7

1.2 2019-112020-052020-072020-092020-112021-012021-032021-052021-072021-092021-112022-012022-032022-052022-072022-092022-112023-012023-032023-052023-072023-092023-112024-01 Vertical Displacement (in)
CGPS Station MTWK
Ave Displacement (in) Linear (Ave Displacement (in))
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Figure 2-96: CGPS Station P309 – Subsidence Time Series Figure 2-97 shows a time series graph of subsidence for CGPS Station CMNC, located in the northeastern region of the Subbasin, along the southern edge of the Camanche Reservoir. Overall, there is a very slight rise in ground elevation that could be due to several factors, such as swelling of clay soils in wet winters. There is no inelastic subsidence occurring at this CGPS station. As previously mentioned, CPGS Station CMNC is being monitored by UNGL and its data are subject to data gaps and discontinuous monitoring due to its academic nature. While the dataset does not have a long period of record, it supports the observation that subsidence has not historically been an issue in the Subbasin.
y = -0.0004x + 0.2946
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1.2 2006-022006-102007-062008-022008-102009-062010-022010-102011-062012-022012-102013-062014-022014-102015-062016-022016-102017-062018-022018-102019-062020-022020-102021-062022-022022-10 Vertical Displacement (in)
CGPS Station P309
Ave Displacement (in) Linear (Ave Displacement (in))
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Figure 2-97: CGPS Station CMNC – Subsidence Time Series Figure 2-98 shows a time series graph of subsidence for CGPS Station CA1S, located in the western region of the Subbasin, north of the City of Stockton. The graph indicates a downward trend, reflecting a small increase in subsidence in the Subbasin. The subsidence observed for CGPS Station CA1S shows that subsidence was generally increasing in the Subbasin, and this is reflected in the slope of the trendline. The trend line's slope of -0.0286 inches per month (-0.34 inches per year) shows that the rate of subsidence at this region of the Subbasin is relatively greater than that of the other three CGPS stations but is still relatively minimal as compared to the overall accuracy of the data.

The largest observed vertical displacement in this period of record was -0.261 inches, from December 2022 to January 2023, which is a small degree of subsidence. Important to note that, like CGPS Station CMNC, this dataset is obtained by UNGL and subject to data gaps and discontinuous monitoring. y = 7E-07x - 0.0275
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1.2 Vertical Displacement (in)
CGPS Station CMNC
Ave Displacement (inches)
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Figure 2-98: CGPS Station CA1S – Subsidence Time Series

2.3.5.2 InSAR
InSAR data were collected from the SGMA Data Viewer sourced from the California Natural Resources Agency (CNRA). Included in this dataset are point data that represent average vertical displacement values for raster data for total and annual vertical displacement rates in monthly time steps. The longest period of record, at the time of analysis, was from June 13, 2015, to October 1, 2023.

The subsidence analysis using InSAR data revealed minimal subsidence rates across the Subbasin. The highest observed subsidence rate was in the central region, averaging 0.92 inches per year between 2015 and 2023. In contrast, subsidence is not occurring in the eastern region of the Subbasin; instead, the ground elevation has increased due to the swelling of clayey soil in the foothills. This observation is supported by the subsidence analysis for CGPS Station CMNC in the eastern Subbasin which showed positive vertical displacement, indicating a rise in ground elevation. The western region of the Subbasin, adjacent to the Delta, is likely experiencing land subsidence due to peat oxidation rather than groundwater extraction. Figure 2-99 illustrates that the central portion of the Subbasin in the cone of depression area is more prone to land subsidence. Despite this, overall subsidence in the Subbasin remains minimal and is not expected to cause undesirable effects.
y = -0.0286x + 0.2332
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-0.3

0.2 0.7

1.2 2021-102021-112021-122022-012022-022022-032022-042022-052022-062022-072022-082022-092022-102022-112022-122023-012023-022023-032023-042023-052023-062023-072023-082023-09 Vertical Displacement (in)
CGPS Station CA1S
Ave Displacement (in) Linear (Ave Displacement (in))
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Figure 2-99: Subsidence Rates (inches per year) Throughout the Subbasin Note: InSAR period of the record displayed in the figure above is June 13, 2015, to October 1, 2023 While CGPS data are more accurate than InSAR vertical displacement measurements, InSAR can estimate subsidence rates over a large land area. Compared to CGPS stations, InSAR has a 16 mm vertical accuracy at a 95% confidence level and an estimated 12 mm (0.47 inches) accuracy near Eastern San Joaquin (Towill, 2020).

2.3.5.3 Survey Benchmarks
Survey benchmark data were collected from USGS, ACOE, CalTrans, the San Joaquin County Department of Public Works (DPW), and local agencies. While there is a high density of benchmarks in the Subbasin, they are not surveyed regularly.

In March 2024, Stockton East Water District (SEWD) conducted benchmark surveys for subsidence monitoring. The aim was to verify claims by the DWR that approximately 7 inches of subsidence had occurred in the area over the past seven years. SEWD surveyed the current elevations of six National Geodetic Survey (NGS) benchmarks with published elevations to compare the historical data with current measurements. These benchmarks, all established in 1962, are located along Comstock Road. The survey results indicated that the average subsidence from the published elevations (1962) to current conditions (March 2024) is approximately 9.3 inches, with a range of subsidence spanning 12.72 ATTACHMENT 2
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inches. The greatest subsidence observed was at NGS Survey Benchmark H-956, which showed a subsidence of

16.56 inches over the 62-year period, or 0.27 inches per year. Due to the temporal differences in subsidence observations, this 62-year period does not provide a precise measurement to directly compare with DWR's InSAR 8- year subsidence data from 2015 to 2023 with an average subsidence rate of 0.92 inches per year.

It is also noteworthy that the six surveyed benchmarks are all located in the central region of the Subbasin, where InSAR data indicated the highest subsidence rate of 0.92 inches per year. While the subsidence of 16.56 inches at NGS Survey Benchmark H-956 is significant, it must be considered within the context of the 62-year period. The benchmark survey results suggest that subsidence in the Subbasin is not occurring at significant levels and is not expected to cause undesirable effects.

2.3.5.4 Relationship with Groundwater Levels
Historically, the Subbasin has not had significant or undesirable effects caused by inelastic land subsidence. Examining recent CGPS vertical displacement data, less than one foot of subsidence was observed throughout the Subbasin between 2015 and 2023. While the 2020 GSP originally considered groundwater levels as a proxy for subsidence, a strong correlation was not observed.

Figure 2-100 shows a time series graph of subsidence (vertical displacement of land surface) and groundwater elevation for CGPS Station MTWK, with Manteca 18 as the respective groundwater level RMW. The graph indicates a slight downward trend in land surface elevation, reflecting a small increase in subsidence rates in the Subbasin. From January 2023 to July 2023, land surface elevations increased slightly more when groundwater levels declined, though overall subsidence remains minimal. It is important to note that, while there was a significant drop in groundwater elevations during September 2023, when groundwater levels recovered in the winter of 2024, subsidence reversed.

This shows elastic subsidence that can recover with sustainable groundwater levels. Note that the historical groundwater levels in this example did not decline below MT for that RMW.

Figure 2-100: CGPS Station MTWK: Subsidence Time Series Figure 2-101 shows a time series graph of subsidence (vertical displacement of land surface) and groundwater elevations for CGPS Station CNDR, with Woodbridge 03N06E05N003 as the respective RMW. The graph indicates a slight downward trend in land surface elevations, reflecting a small increase in subsidence in the Subbasin. The trend line's slope of -0.0105 inches per month confirms that subsidence is occurring in the Subbasin, but at very low levels.

There was a significant decrease of 70 feet in groundwater elevation between March 1, 2000, and November 1, 2000, ATTACHMENT 2
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at this location; however, it is important to note that while there was a sharp decline in groundwater elevation during October 2000, subsidence appears to be unaffected. The Woodbridge 03N06E05N003 groundwater level representative monitoring well was selected for analysis because it is the only representative monitoring well that has historically declined below its respective minimum threshold. CNDR CGPS station was selected because it is the only CGPS station with historical observations during the period when the groundwater levels were below minimum thresholds.

Figure 2-101: CGPS Station CNDR – Time Series of Subsidence and Groundwater Levels

2.3.6Interconnected Surface Water Systems

2.3.6.1 Definitions
Section 2.2.6 detailed the original depletions analysis in the 2020 GSP. This section provides an update to that analysis based on guidance provided by DWR and updates to ESJWRM to reflect current conditions as of the development of this 2024 Amended GSP. More detail can be found in Attachment 3-F, including an extensive update to the historical ISW conditions analysis. As described in Depletions of ISW: An Introduction (CA DWR, 2024), the first of three guidance documents on ISWs released by DWR, the consideration and interpretation of ISWs can be based on five example cases of nearby groundwater elevation data (Figure 5 of Depletions of ISW: An Introduction). Of the examples provided, Figure 5d is most applicable to Eastern San Joaquin Subbasin due to a lack of shallow monitoring wells and associated historic data near the rivers and creeks in the Subbasin (shown in the DWR guidance document and Appendix 3-G). This lack of shallow groundwater level data near surface water courses translates to a low degree of confidence in model calibration around these surface water features and therefore uncertainty around what is or is not a connected reach or model node.

GSP regulations require the identification of ISWs within a basin (and therefore identification of the degree of connectivity) and an estimate of the timing and quantity of depletions of those systems, where depletions are defined as “conditions where groundwater pumping results in reductions in flow or water levels of ISW.” However, the DWR guidance document notes that “the definition above differs from how depletions may be defined in other hydrologic contexts, where they can refer to any surface water losses without considering the cause.” A good faith effort was conducted to isolate stream depletions in the ESJ Subbasin due solely to groundwater pumping by comparing (1) pumping and no-pumping scenarios and (2) a pumping “pulse” scenario to examine the delayed impact of pumping on stream depletions, both using the integrated Eastern San Joaquin Water Resources Model Version 3.0 (ESJWRM).

However, the analyses resulted in an inconclusive understanding of depletions due to pumping since an equilibrium was not reached within the simulation period and depletions were heavily influenced by initial and boundary conditions.

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of cause. This allows the GSAs to have more confidence in the results and be able to manage and report depletions in future Annual Reports without limitations and uncertainties from the existing toolset. At the time of the 2024 GSP, the additional guidance documents from DWR (Techniques for Estimating Depletions of Interconnected Surface Water and Examples of Approaches for Estimating Depletions of Interconnected Surface Water) had not yet been released.

The timing, location, and volume of depletions in the ESJ Subbasin will be revised at a later time in coordination with further guidance from DWR.

2.3.6.2 Stream Connectivity
Stream connectivity was analyzed by comparing monthly groundwater elevations from the historical calibration of the ESJWRM to streambed elevations along the streams represented in ESJWRM. The reaches in ESJWRM are displayed in Figure 2-102. Layer 1 groundwater levels were used since the new Layer 1 in ESJWRM represents the shallow, generally unconsolidated sediments where stream interaction is happening. Stream connectivity was also analyzed under current conditions, represented by Water Year 2020 through 2024 in the historical ESJWRM model. “75% Connected” streams were defined as Layer 1 groundwater levels at or above the streambed elevation at least 75 percent of the time. The definition of ISWs is not limited to surface waters that the ESJGWM indicates are connected to the shallowest modeled groundwater level at least 75 percent of the time. The GSAs understand that an ISW may be seasonally connected and/or connected in only wetter water year types. The GSAs currently do not have sufficient data to determine if or when streams or reaches are connected to the groundwater table with this level of granularity. The GSAs will be collecting more data with the new ISW monitoring wells to help inform this analysis going forward. Using ESJWRM Version 3.0, which was the best available tool at the time of analysis, ATTACHMENT 2
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Figure 2-103 shows that the 75 percent connected streams are the Mokelumne River, Stanislaus River, and lower San Joaquin River. Streams that are not connected at least 75 percent of the time are Dry Creek, Calaveras River, and Mormon Slough. Other smaller creeks are not represented in ESJWRM.

Figure 2-102: Stream Reaches in ESJWRM
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Figure 2-103: Surface Waters Connected with the Groundwater System at least 75% of All Months in ESJWRM under Current Conditions
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2.3.6.3 Stream Gains and Losses
Disconnected streams will always be losing streams, but interconnected streams may be either losing or gaining, depending on the surface water and groundwater conditions. Groundwater discharge from the aquifer is primarily through groundwater pumping; however, groundwater also discharges to streams where groundwater elevations are higher than the streambed elevations and stream levels or stage. Figure 2-104, from DWR’s Depletions of ISW: An Introduction (CA DWR, 2024), illustrates connected gaining streams (on the left) where groundwater levels are higher than the stream stage, and losing streams (on the right) where groundwater levels are lower than the stream stage.

Figure 2-104: Diagram of Gaining and Losing Connected Streams ATTACHMENT 2
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Figure 2-105 shows the average annual volume of stream gains under current conditions (Water Year 2020 through 2023). While the Mokelumne River is a connected river in most years, it is losing water from the stream to the aquifer system upstream of the Cosumnes River, and gaining water from the aquifer system downstream of the Cosumnes River, on average. The Stanislaus River has a high number of stream nodes in the center portion of the river that are losing under current conditions. The lower San Joaquin River is gaining in many sections near the confluence with the Stanislaus River, Calaveras River, and in the Delta region.

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Figure 2-105: Current Conditions Average Annual Stream Gains by Stream Node

2.3.7Groundwater-Dependent Ecosystems
In the Eastern San Joaquin Subbasin, the primary environmental beneficial users are groundwater dependent ecosystems. In the 2020 GSP, potential GDEs were mapped across the Subbasin. The mapping relied on the Natural Communities Commonly Associated with Groundwater (NCCAG) database, from which additional refinements were made to remove areas that met the following criteria:
• Areas where groundwater levels were deeper than 30 feet below the ground surface (ft bgs). • Areas with access to alternate water supplies that may not be dependent on groundwater (i.e., communities close to managed wetlands, irrigated agriculture, or perennial surface water bodies).

The resulting desktop mapping was then considered by GSA staff and technical workgroup members before inclusion in the GSP. Further detail on this approach to mapping potential GDEs is described in Appendix 3-C of this GSP Amendment.

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Before conducting the analysis to evaluate the potential impacts of the groundwater level SMC on potential GDEs, it was verified that no changes to the NCCAG dataset within the ESJ Subbasin have been made since 2020. The NCCAG database still represents the most comprehensive source of potential GDEs within this Subbasin. Polygons in the NCCAG dataset were removed where the vegetative community’s average maximum rooting depths do not intersect with groundwater. In other words, if the vegetation is not able to access groundwater within its rooting depth, then it is assumed that the ecosystem is not a potential GDE. This average maximum rooting depth is estimated to be 30 feet below ground surface for the majority of phreatophytes (The Nature Conservancy, 2021). The original mapping completed as part of the 2020 GSP was retained in this GSP Amendment.

The map of potential GDEs included in the 2020 GSP is shown in Figure 2-106. This mapping of potential GDEs represents a desktop analysis that will continue to be improved through field verification.

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Figure 2-106: Mapping of Potential Groundwater Dependent Ecosystems

2.4 WATER BUDGETS

2.4.1Water Budget Background Information
Water budgets are developed to provide a quantitative account of water entering and leaving the Eastern San Joaquin Subbasin. Water entering and leaving the Subbasin includes flows at the surface and in the subsurface environment.

Water enters and leaves due to natural conditions, such as precipitation and streamflow, and/or through human activities, such as groundwater pumping or recharge from applied water. Additionally, interconnection between the groundwater system and rivers/streams accounts for other components of the water budget. Figure 2-107 depicts the major components of a water budget and their interconnection as presented in the context of stream, land surface, and groundwater systems.

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Figure 2-107: Generalized Water Budget Diagram
Quantities presented for the water budget components of the Eastern San Joaquin Subbasin provide information on historical, current, and projected conditions as they relate to hydrology, water demand, water supply, land use, population, climate variability, groundwater and surface water interaction, and groundwater flow. This information can assist in the management of the Subbasin by identifying the relationship between different components affecting the water budget of the Subbasin, which provides context in the development and implementation of strategies and policies to achieve Subbasin groundwater sustainability conditions. Water budget quantities presented are based on the simulation results from the ESJWRM.

The ESJWRM was developed to be the primary analysis tool supporting the development of the GSP for the Subbasin.

The ESJWRM is a quasi-three-dimensional finite element model developed using the Integrated Water Flow Model (IWFM) simulation code (Dogrul et al., 2024a and Dogrul et al,. 2024b). Using data from federal, state, and local resources, the ESJWRM was originally calibrated for the 20-year hydrologic period of October 1995 to September 2015 (water years 1996 through 2015) for the 2020 GSP by comparing simulated groundwater levels and streamflow records with historical observed records. Development of the model involved the study and analysis of hydrogeologic conditions, agricultural and urban water demands, agricultural and urban water supplies, and an evaluation of regional water quality conditions. The Historical ESJWRM has undergone nine updates to date, of which three were major updates:

1. Major Update: Development and Calibration of Historical ESJWRM Version 1.1 (WY 1995 through 2015) for November 2020 GSP

2. Extension of Data in Historical ESJWRM Version 1.1 from WY 2016 through 2019 for WY 2019 Annual Report

3. Extension of Data in Historical ESJWRM Version 1.1 through WY 2020 for WY 2020 Annual Report

4. Major Update: Model Update and Recalibration Resulting in Historical ESJWRM Version 2.0 (WY 1995 through 2020) for Revised June 2022 GSP

5. Extension of Data in Historical ESJWRM Version 2.0 through WY 2021 for WY 2021 Annual Report ATTACHMENT 2
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6. Updated Monthly Agricultural Demand Distribution in Fall 2022 Resulting in Historical ESJWRM Version 2.2

7. Extension of Data in Historical ESJWRM Version 2.2 through WY 2022 for WY 2022 Annual Report

8. Extension of Data in Historical ESJWRM Version 2.2 through WY 2023 for WY 2023 Annual Report

9. Major Update: Model Update and Recalibration Resulting in Historical ESJWRM Version 3.0 for 2024 Periodic Evaluation and GSP Amendment
Only ESJWRM Version 3.0 water budget results are presented in Section 2.4. Version 3.0 development is documented in a report, “Eastern San Joaquin Water Resources Model (ESJWRM) Version 3.0 Update,” published in August 2024 and available in Appendix 2-C.

Consistent with CCR Title 23 § 354.18, the water budgets presented in this document encompass the combined surface and groundwater system of the Eastern San Joaquin Subbasin. The Subbasin water budget focuses on the full water year (12 months spanning October 1 of the previous year to September 30 of the year in question), with some consideration of monthly variability.

The Regulations require that the annual water budget quantify three different conditions: historical, current, and projected. Budgets are developed to capture typical conditions during these time periods. Typical conditions are developed through selecting historical hydrologic periods that incorporate droughts, wet periods, and normal periods.

By incorporating these varied conditions within the budgets, the Subbasin is analyzed under certain hydrologic conditions, such as drought or very wet events, along with long-term averages. This Plan relies on historical hydrology to identify time periods for water budget analysis and uses the ESJWRM and associated data to develop the water budget and resulting budget estimates. The water budget components developed for the Eastern San Joaquin Subbasin are based upon estimates developed from historical and projected data as well as modeling assumptions.

The water budget assumptions may be refined in the future, the water budget may change, and the conclusions and recommendations derived from the water budget may also change.

2.4.2Identification of Hydrologic Periods
The historical hydrologic periods used in this Plan were selected to meet the requirements of developing historical, current, and projected water budgets. The Regulations require that the projected water budget reflect a 50-year hydrologic period in order to project how the Subbasin’s land and groundwater systems may react under long-term average hydrologic conditions. Consistent with the Regulations, the ESJWRM Version 3.0’s 55-year historical record characterizes future conditions with respect to precipitation, evapotranspiration, and streamflow. Historical precipitation or rainfall in the Eastern San Joaquin Subbasin was used to identify a hydrologic period that would provide a representation of wet and dry periods and long-term average conditions needed for water budget analyses. Rainfall data for the Subbasin are derived from the PRISM (Precipitation-Elevation Regressions on Independent Slopes Model) dataset of the DWR’s California Simulation of Evapotranspiration of Applied Water (CALSIMETAW) model.

Precipitation-Elevation Regressions on Independent Slopes Model (PRISM) is a spatial estimation of rainfall data developed using monitoring network point data and interpolated using a variety of factors (Oregon State University, 2023).

Wet and dry hydrologic periods were identified by evaluating the cumulative departure from mean precipitation. Under this method, the long-term average precipitation is subtracted from annual precipitation within each water year to develop the departure from mean precipitation for each water year. Wet years have a positive departure and dry years have a negative departure; a year with exactly average precipitation would have zero departure. Starting at the first year analyzed, the departures are added cumulatively for each year. So, if the departure for Year 1 is 5 inches and the departure for Year 2 is -2 inches, the cumulative departure would be 5 inches for Year 1 and 3 inches (5 plus -2) for Year 2. Figure 2-108 graphically illustrates the cumulative departure of the spatially averaged rainfall within the Eastern San Joaquin Subbasin. The figure includes bars displaying annual precipitation for each water year from 1969 through 2023 and a horizontal line representing the mean precipitation of 15.6 inches. The cumulative departure from mean precipitation is based on these data sets and is displayed as a line that highlights wet periods with upward slopes ATTACHMENT 2
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(positive departure) and dry periods with downward slopes (negative departure). More severe events are shown by steeper slopes and greater changes. For example, the period from 1975 to 1977 illustrates a short period with dramatically dry conditions (6-inch decline per year in cumulative departure).

The PRISM estimates for rainfall in the Subbasin were confirmed by comparing the cumulative departure from mean precipitation results to the water year types in the San Joaquin Valley Water Year Hydrologic Classification (CA DWR, 2023), which classifies water years 1901 through 2023 as wet, above normal, below normal, dry, and critical based on inflows to major reservoirs or lakes. Wet (W) or Above Normal (AN) years generally show upward sloping cumulative departures, while Below Normal (BN), Dry (D), or Critical (C) water year types show downward trending cumulative departures (Figure 2-108). As the San Joaquin Valley Water Year Hydrologic Classification determines water year types based on inflows for streams throughout the entire San Joaquin Valley, a more locally relevant index to the Subbasin may be developed in the future.

Figure 2-108: 55-Year Historical Precipitation and Cumulative Departure from Mean Precipitation

2.4.3Use of the ESJWRM and Associated Data in Water Budget Development This Plan developed water budgets utilizing the ESJWRM, a fully integrated surface and groundwater flow model covering the Eastern San Joaquin Subbasin, as well as the Cosumnes Subbasin to the north and the Modesto Subbasin to the south. The adjacent subbasins were included in the ESJWRM boundaries to be consistent with past local modeling efforts and to better simulate boundary flows to/from the north and south of the Subbasin. This Plan provides a water budget for the Eastern San Joaquin Subbasin portion of the ESJWRM.

With the ESJWRM Version 3.0 as the underlying framework, four model scenarios were developed representing historical, current, projected, and projected with climate change conditions in the Eastern San Joaquin Subbasin, as discussed below:
• Historical water budget represents the historical model calibration period, which covers water years 1996 through 2023 (28 years).

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• Current water budget represents an estimate of averaged recent historical conditions in the Subbasin, based on water years 2019 through 2023 (5 years).
• Projected water budget represents estimated long-term conditions of the Subbasin under the foreseeable future level of development over a long-term period of hydrologic conditions (the 55-year period represented by water years 1969 through 2023).
• Projected water budget, with climate change represents the projected water budget, with the impacts of climate change on streamflow, evapotranspiration, and precipitation.

2.4.4Water Budget Definitions and Assumptions
Definitions and assumptions for the historical, current, and projected water budgets are provided in the sections below and summarized in Table 2-13: Summary of Water Budget Assumptions (Historical, Current, and Projected Periods)
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Water Budget Type Historical5 Current Projected5
Projected with Climate
Change5
Model Version
Historical
ESJWRM
Version 3.0
Historical
ESJWRM
Version 3.0

ESJWRM PCBL
Version 3.0

ESJWRM PCBL-CC
Version 3.0
Scenario Historical
Calibration
Current
Conditions
Projected
Conditions
Baseline
Projected Conditions
Baseline with Climate
Change
Hydrologic Years Water Years
1996-2023
Water Years
2019-2023
Water Years 1969-
2023
Water Years 1969-2023
with perturbation
Level of Development1 Historical Current
General Plan or
Sphere of Influence
Buildout
General Plan or Sphere of
Influence Buildout
Agricultural Demand2 Historical
Current
(average of WY
2019-2023)
Current (2022, less
urban expansion)
Current (2022, less urban
expansion, with increased
ET)
Urban Demand3 Historical Current Projected based on
UWMP data
Projected based on
UWMP data
Water Supplies4 Historical Current Projected based on
local information
Projected based on local
information (with an
adjustment for climate
change impact on
precipitation and
streamflow)
Notes:
1 The level of development describes the footprint of the urban areas. Historical is the footprint in the historical model period (water years 1996-2023), current is the footprint at the end of the historical model period (water years 2019-2023), and projected reflects the footprint after general plan or sphere of influence urban buildout (approximately water year 2040). 2 Agricultural demand is based on historical cropping patterns and evapotranspiration rates. Projected agricultural cropping patterns are assumed to be consistent with DWR’s statewide crop mapping of 2022, less urban buildout. For the current and projected water budgets, future evapotranspiration rates are assumed to remain the same as historical. 3 Historical urban demand includes actual demand and population from Urban Water Management Plans (UWMPs) or other planning efforts. Current demand is assumed to represent average demands and population between WY 2019-2023.

Projected demand uses projected demand and population from UWMPs or other planning efforts and uses numbers for a buildout level of development (approximately water year 2040). 4 Historical water supplies rely on local district information and records. Projected water supplies were assumed for approximately water year 2040 and may include projects or expansions of supplies currently begun or with funding secured.

Current water supplies represent water supplies averaging approximately water years 2019-2023 in the historical records. 5 For more information on historical and projected modeling, see the published model report (Appendix 2-C). .

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Table 2-13: Summary of Water Budget Assumptions (Historical, Current, and Projected Periods) Water Budget Type Historical5 Current Projected5
Projected with Climate
Change5
Model Version
Historical
ESJWRM
Version 3.0
Historical
ESJWRM
Version 3.0

ESJWRM PCBL
Version 3.0

ESJWRM PCBL-CC
Version 3.0
Scenario Historical
Calibration
Current
Conditions
Projected
Conditions
Baseline
Projected Conditions
Baseline with Climate
Change
Hydrologic Years Water Years
1996-2023
Water Years
2019-2023
Water Years 1969-
2023
Water Years 1969-2023
with perturbation
Level of Development1 Historical Current
General Plan or
Sphere of Influence
Buildout
General Plan or Sphere of
Influence Buildout
Agricultural Demand2 Historical
Current
(average of WY
2019-2023)
Current (2022, less
urban expansion)
Current (2022, less urban
expansion, with increased
ET)
Urban Demand3 Historical Current Projected based on
UWMP data
Projected based on
UWMP data
Water Supplies4 Historical Current Projected based on
local information
Projected based on local
information (with an
adjustment for climate
change impact on
precipitation and
streamflow)
Notes:
1 The level of development describes the footprint of the urban areas. Historical is the footprint in the historical model period (water years 1996-2023), current is the footprint at the end of the historical model period (water years 2019-2023), and projected reflects the footprint after general plan or sphere of influence urban buildout (approximately water year 2040). 2 Agricultural demand is based on historical cropping patterns and evapotranspiration rates. Projected agricultural cropping patterns are assumed to be consistent with DWR’s statewide crop mapping of 2022, less urban buildout. For the current and projected water budgets, future evapotranspiration rates are assumed to remain the same as historical. 3 Historical urban demand includes actual demand and population from Urban Water Management Plans (UWMPs) or other planning efforts. Current demand is assumed to represent average demands and population between WY 2019-2023.

Projected demand uses projected demand and population from UWMPs or other planning efforts and uses numbers for a buildout level of development (approximately water year 2040). 4 Historical water supplies rely on local district information and records. Projected water supplies were assumed for approximately water year 2040 and may include projects or expansions of supplies currently begun or with funding secured.

Current water supplies represent water supplies averaging approximately water years 2019-2023 in the historical records. 5 For more information on historical and projected modeling, see the published model report (Appendix 2-C).

2.4.4.1 Assumptions Used in the Historical Water Budget The historical water budget is intended to evaluate availability and reliability of past surface water supply deliveries, aquifer response to water supply, and demand trends relative to water year type. The historical calibration of the ESJWRM reflects the historical conditions in the Eastern San Joaquin Subbasin over water years 1996-2023. The hydrologic period has an average annual precipitation of approximately 15.5 inches and includes the recent 2012-2015 and 2020-2022 droughts, the wetter years of 1996-2000, 2017, and 2023, and periods of normal precipitation.

Regulations require the use of a minimum of 10 years to develop the historical water budget. The entire historical calibration period of the ESJWRM was used to be inclusive of all the data used in developing the ESJWRM and to average over a broader range of different hydrologic conditions. The historical water budget applied an evolving level of development and agricultural demand throughout a 28-year historical hydrology.

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Additional details of the data used in the development of the historical calibration can be found in the published model report (Appendix 2-C).

The historical calibration includes the following:
• Hydrologic period: Water Years 1996-2023 (28-year hydrology) • Stream Flows for Water Years 1996-2023:
o Dry Creek: No streamflow gaging stations were available for Dry Creek; as such, flow estimates from the DWR’s California Central Valley surface and groundwater Model (C2VSim-FG v1.01) were used for water years 1996-2015 . For 2015-2023, an average of historical data by month and water year type was used. o Mokelumne River: Historical records from USGS (Mokelumne River below Camanche Dam, CA) o Calaveras River: New Hogan Dam releases
o Stanislaus River: Historical records from USGS (Stanislaus River below Goodwin Dam near Knights Ferry, CA)
o San Joaquin River: Historical records from USGS (San Joaquin River near Vernalis, CA) • Reservoir Operations: Upstream reservoirs regulating streamflows into the Subbasin include Pardee Reservoir and Camanche Reservoir on the Mokelumne River; New Hogan Reservoir on the Calaveras River; and New Melones Reservoir, Tulloch Reservoir, and Goodwin Reservoir on the Stanislaus River. As reservoir releases are regulated, no changes to the historical operations of the reservoirs are assumed. In addition, two other local reservoirs are included in the model: Woodward and Farmington. The model estimates seepage contributions from these reservoirs to the groundwater system. Water supply deliveries from these reservoirs are based on records provided by the agencies responsible for operation of these reservoirs. • Land use and cropping patterns are based on the DWR land use surveys (assumed to represent water year 1995), and the recent, comprehensive, and Subbasin-wide land use survey from DWR as prepared by Land IQ from 2016-2022 (CA DWR, 2014). Local data and information were also utilized to refine and update the cropping patterns, as needed. To fill the gap between 1995 and 2016, all land use and crop categories were interpolated at the spatial resolution level of the model elements to simulate the geographic distribution of various crops.
• Urban water demand is calculated for all the urban areas in the model. Urban centers in Eastern San Joaquin Subbasin are City of Escalon, Linden, Lockeford, City of Lodi, City of Manteca, City of Ripon, and City of Stockton. Demands for other domestic areas are estimated based on rural population. Urban water demand is based on:
o Urban water use from 2020 Urban Water Management Plans (Cal Water; Calaveras County Water District [CCWD], Cities of Lodi, Manteca, and Stockton; Stockton East Water District [SEWD]; and South San Joaquin Irrigation District [SSJID]) or municipal pumping records, used to calculate the per capita water use for each urban center.
o Urban center population from Urban Water Management Plans (UWMPs), United States Census Bureau, or the California Department of Finance.
• Surface Water Deliveries:

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o Deliveries to agricultural areas: Obtained from agricultural entities in the Subbasin, including Central San Joaquin Water Conservation District (CSJWCD), North San Joaquin Water Conservation District (NSJWCD), Oakdale Irrigation District (OID), SEWD, SSJID, and Woodbridge Irrigation District (WID) o Deliveries to urban areas: Cities of Lodi, Manteca, and Stockton (including Cal Water and City of Stockton service areas, and unincorporated San Joaquin County areas) o Recharge projects: SEWD’s Farmington Groundwater Recharge Program; NSJWCD’s Tracy Lakes Recharge Project; NSJWCD’s CALFED groundwater recharge project; Tecklenburg Recharge Project; and NSJWCD’s FloodMAR recharge projects
o Riparian diversions: CCWD, Delta areas, and data from C2VSim-FG for riparian diversions off major streams (Dry Creek, Mokelumne River, Calaveras River and related streams, Stanislaus River, San Joaquin River) (C2VSim-FG v1.01)
• Groundwater Pumping:
o District pumping for agricultural/landscape uses: City of Manteca, OID, City of Ripon, and SSJID o District pumping for urban uses: Cal Water, City of Escalon, Linden County WD, Lockeford CSD, City of Lodi, City of Manteca, City of Ripon, SEWD, and City of Stockton o Data on private pumping was not available on a consistent basis across the model, so private pumping was estimated as that which would be required to meet agricultural and rural residential water needs as calculated by the ESJWRM model based on consumptive use methodology (Refer to the ESJWRM documentation for details).

2.4.4.2 Assumptions Used in the Current Water Budget
A current conditions estimate using the Historical ESJWRM Version 3.0 was developed for use in estimating the current water budget. The current conditions estimate is comprised of the average of historical model water years 2019-2023 in order to estimate current inflows and outflows for the Subbasin. Current conditions are not necessarily indicative of one year and are instead a compilation of data assumed representative of Subbasin recent conditions. The definition of current conditions, by nature, will continuously change. The current water budget represents the current conditions as of the time of the 2024 GSP.

2.4.4.3 Assumptions Used in the Projected Water Budget
The projected water budget is intended to assess the conditions of the Subbasin under future conditions of water supply and agricultural and urban demand, including quantification of uncertainties in the components. The projected conditions scenario applies future land and water use conditions and uses the 55-year hydrologic period of water years 1969-2023. Projections are assumed to represent a buildout level of development (approximately year 2040) and are represented using projected population, land use, and water demand and supply projections. Results of the projected conditions scenario under potential climate change conditions (changes to precipitation, stream flows, and evapotranspiration) are presented in Section Error! Reference source not found..

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-175
Basin Setting November 2024
The projected conditions scenario includes the following conditions:
• Hydrologic Period: Water Years 1969-2023 (55-year hydrology) • Stream Flows for Water Years 1969-2023:
o Dry Creek: No streamflow gaging stations were available for Dry Creek; as such, flow estimates from the DWR’s C2VSim-FG were used (C2VSim-FG v1.01)
o Mokelumne River: Historical records from USGS (Mokelumne River below Camanche Dam, CA) o Calaveras River: Historical records from USGS (Calaveras River below New Hogan Dam near Valley Springs, CA) and New Hogan Dam releases
o Stanislaus River: Historical records from USGS (Stanislaus River below Goodwin Dam near Knights Ferry, CA)
o San Joaquin River: Historical records from USGS (San Joaquin River near Vernalis, CA) • Reservoir Operations: Upstream reservoirs regulating streamflows into the Subbasin include Pardee Reservoir and Camanche Reservoir on the Mokelumne River; New Hogan Reservoir on the Calaveras River; and New Melones Reservoir, Tulloch Reservoir, and Goodwin Reservoir on the Stanislaus River. The projected conditions scenario assumes that the historical operations of the reservoirs over the 50-year hydrologic records were in place and no changes are made. • Land use and cropping patterns are based on the most recent, comprehensive, and Subbasin-wide land use survey from DWR as prepared by Land IQ (CA DWR, 2014), with adjustments based on local information and input. Urban areas expand to either the sphere of influence or general plan boundaries and are held constant during the simulation. Cropping acreage is reduced only where urban expansion occurs. • Urban water demands are calculated for all the urban areas in the model. Urban centers in Eastern San Joaquin Subbasin are City of Escalon, Linden, Lockeford, City of Lodi, City of Manteca, City of Ripon, and City of Stockton. Demands for other domestic areas are estimated based on rural population. Urban water demand is based on:
o Urban water use estimated from projections in the 2020 Urban Water Management Plans (Cal Water; CCWD, Cities of Lodi, Manteca, Ripon, and Stockton; SEWD; and SSJID) or municipal pumping records, used to calculate the per capita water use for each urban center in the future (approximately 2040 or 2045).
o Urban center population projections from the San Joaquin Council of Governments. • Surface water delivery projections for the 55-year period were estimated based on the historical records of diversions by water year type, surface water rights or agreements, and potential planned changes/upgrades to the surface water diversion facilities. Surface water diversion estimates reflecting projected conditions using currently available information and knowledge were provided to each GSA for review and comment, and appropriate adjustments were made to the estimated record to reflect the surface water diversion projections for each entity. Surface water deliveries include:
o Deliveries to agricultural areas: CSJWCD, NSJWCD, OID, SEWD, SSJID, and WID o Deliveries to urban areas: Cities of Lodi, Manteca, and Stockton (including Cal Water and City of Stockton service areas, and unincorporated San Joaquin County areas) ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-176
Basin Setting November 2024
o Recycling or recharge projects: Recycled water for Cities of Lodi and Manteca; SEWD’s Farmington Groundwater Recharge Program; NSJWCD’s Tracy Lakes Recharge Project; and NSJWCD’s CALFED groundwater recharge project
o Riparian: CCWD, Delta areas, and data from C2VSim for riparian diversions off major streams (Dry Creek, Mokelumne River, Calaveras River, Stanislaus River, and San Joaquin River) • As private groundwater pumping was estimated by ESJWRM in the historical calibration, there is no local estimate of projected private groundwater pumping available on a consistent basis across the model.

Therefore, groundwater pumping to meet agricultural and rural residential needs is calculated by the model based on meeting remaining demands after surface water deliveries are made. Demand in areas with no access to surface water is completely met by groundwater pumping. Additional details on the estimation of private groundwater pumping in ESJWRM can be found in the published model report (Appendix 2-A).

Additional details of the data used in the development of the projected conditions baseline can be found in the published model report (Appendix 2-C).

2.4.4.4 Assumptions Used in the Projected Water Budget, with Climate Change The projected water budget with climate change is intended to assess the conditions of the Subbasin under future conditions of water supply and agricultural and urban demand, with the additional impact of climate change on the available water supply and agricultural demand. The projected conditions scenario with climate change is based on the projected conditions scenario without climate change and therefore all assumptions listed in Section Error! R eference source not found. remain, except where noted below. A future scenario of 2070 climate forecasts was evaluated in this analysis, consistent with DWR guidance. DWR combined 10 global climate models (GCMs) for two different representative climate pathways (RCPs) to generate the central tendency scenarios in the datasets used in this analysis. The “local analogs” method (LOCA) was used to downscale these 20 different climate projections to a scale usable for California (DWR, 2018a). The 2070 central tendency (2070 CT) among these projections serves to assess impacts of climate change over the long-term planning and implementation period.

The following model inputs were adjusted in the 2070 CT climate change scenario:
• Stream Flow: Flows for Central Valley rivers are divided into impaired and unimpaired. In the Subbasin, Dry Creek and Mokelumne River are unimpaired rivers. Projected conditions scenario stream flows are modified by applying perturbation factors provided by DWR. Calaveras, San Joaquin, and Stanislaus Rivers are all impaired rivers. CalSim II estimated flows, also provided by DWR, were used to simulate stream flows under climate change for impaired rivers.
• Precipitation: Precipitation was modified using the perturbation factors provided by DWR, where available. • Evapotranspiration: Evapotranspiration (ET) was modified using the perturbation factors provided by DWR, where available.

Additional details of the data used in the development of the projected conditions with climate change scenario can be found in the published model report (Appendix 2-C).

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-177
Basin Setting November 2024

2.4.4.5 Updates to Water Budgets
Following submittal of the Eastern San Joaquin Subbasin GSP in January of 2020, the ESJWRM was revised to correct data relating to historical surface water deliveries and to include additional data for Water Year (WY) 2016 through WY 2023. Specifically, the following data sets were updated in ESJWRM:
• The hydrologic period was extended to include WY 2016-2023 with the precipitation data mapped accordingly. • Model layering was updated based on Airborne Electromagnetic (AEM) data • Changes to land use were made with the simulated land uses mapped to the statewide crop mapping released by DWR in 2016 through 2022. USDA CropScape data was removed from the model and interpolation was updated from 1995 to 2016 datasets.
• Stream inflows were extended through WY 2023 using the same data sources as in the original version. • Populations were updated for WY 2016 through 2023, and urban demands revised accordingly. Rural residential urban demand was updated to use
• Surface water deliveries were extended to WY 2023 and additional surface water deliveries that were not previously simulated were added to the model, including Farmington Reservoir seepage. • Groundwater pumping volumes were extended to WY 2023 and the Modesto Subbasin wells, additional OID, Cal Water, Manteca, and SSJID wells were added to the model. • Agricultural water operations were updated to extend through WY 2023.

The ESJWRM simulation period was extended to simulate Water Years 1995 through 2023 and the model recalibrated for the extended period. As a result of the two major model updates, both the historical and projected water budgets were revised in 2021 and 2024 to reflect the new data sets used in the model. See Appendix 2-C for additional details on the updates made to the ESJWRM.

2.4.5Water Budget Estimates
The ESJWRM simulates the major hydrologic processes that affect the land surface, stream, and groundwater systems in the Eastern San Joaquin Subbasin. The major hydrologic processes can be represented by separate water budgets which detail inflows and outflows occurring at the stream scale (budget on surface water flows occurring in the Subbasin), land surface scale (budget balancing how demands on urban, agricultural, and native lands are met by rainfall, surface water deliveries, or groundwater pumping), and groundwater scale (budget detailing flows occurring within the groundwater aquifers of the Subbasin).

The primary components of the stream system are:
• Inflows:
o Stream inflows
o Stream gain from the groundwater system
o Runoff to the stream system from precipitation
o Return flow to the stream system from irrigation water • Outflows:

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-178
Basin Setting November 2024
o Stream outflows
o Stream seepage (i.e., losses to the groundwater system) o Surface water diversions
o Riparian intake from streams
The primary components of the land surface system are:
• Inflows:
o Precipitation
o Surface water supplies to meet agricultural or urban and industrial uses o Groundwater pumping (i.e., groundwater supplies to meet agricultural or urban and industrial uses) o Riparian intake from streams
• Outflows:
o Evapotranspiration
o Runoff to the stream system
o Return flow to the stream system
o Deep percolation from precipitation, applied water (surface water and groundwater) for agricultural lands, and applied water (surface water and groundwater) for outdoor use in the urban areas or industrial purposes
The primary components of the groundwater system are:
• Inflows:
o Deep percolation from precipitation, applied water (surface water and groundwater) for agricultural lands, and applied water (surface water and groundwater) for outdoor use in the urban areas or industrial purposes
o Stream seepage (i.e., losses to the groundwater system) o Other recharge (including unlined canals/reservoir seepage, local tributaries seepage, and Managed Aquifer Recharge [MAR] projects)
o Subsurface inflow
• Outflows:
o Groundwater outflow to streams (i.e., stream gain from the groundwater system) o Groundwater pumping
o Subsurface outflow
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-179
Basin Setting November 2024
• Change in Groundwater Storage (Inflows Minus Outflows): This reflects average annual change in groundwater storage
The revised ESJWRM Version 3.0 estimated water budgets for the historical, current conditions, projected conditions, and projected conditions with climate change scenarios are provided below, with results summarized in Error! R eference source not found. through Error! Reference source not found.. Differences between the original and revised scenarios are discussed further in the documentation in Appendix 2-C.

Table 2-14: Average Annual Water Budget for Revised ESJWRM (Version 3.0) – Stream System (AF/year)
Component
Historical
Calibration
(AF/year)
Current
Conditions
(AF/year)
Projected
Conditions
(AF/year)
Projected
Conditions with
Climate Change
(AF/year)
Model Version
Historical
ESJWRM Version

3.0 Historical
ESJWRM Version

3.0 ESJWRM PCBL
Version 3.0
ESJWRM PCBLCC Version 3.0
Hydrologic Period
Water Years
1996-2023
(28-Year period)
Water Years
2019-2023
(5-Year average)
Water Years
1969- 2023
(55-Year period)
Water Years
1969- 2023
(55-Year period)
Inflows
Stream Inflows1 4,221,000 4,224,000 4,519,000 4,929,000 Stream Gain from
Groundwater2
145,000 130,000 121,000 115,000
Eastern San Joaquin
Subbasin 75,000 63,000 57,000 53,000
Dry Creek11 0 0 0 0
Mokelumne River 14,000 13,000 10,000 8,000
Calaveras River 1,000 1,000 1,000 1,000
Stanislaus River 28,000 18,000 17,000 16,000
San Joaquin River 31,000 31,000 29,000 27,000
Other Subbasins4 70,000 67,000 65,000 62,000
Dry Creek 23,000 29,000 28,000 27,000
Mokelumne River 0 0 0 0
Stanislaus River 27,000 19,000 17,000 16,000
San Joaquin River 20,000 20,000 19,000 18,000
Runoff to the Stream System5 629,000 741,000 656,000 753,000 Return Flow to Stream System6 96,000 95,000 111,000 112,000 Total Inflow10 5,092,000 5,190,000 5,407,000 5,908,000
Outflows
Stream Outflows7 4,426,000 4,469,000 4,655,000 5,108,000 Stream Seepage2 284,000 331,000 374,000 420,000
Eastern San Joaquin
Subbasin 236,000 267,000 298,000 330,000
Dry Creek 2,000 2,000 2,000 2,000
Mokelumne River 125,000 135,000 150,000 160,000
Calaveras River 37,000 37,000 39,000 41,000
Stanislaus River 36,000 55,000 67,000 82,000
San Joaquin River 37,000 37,000 40,000 45,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-180
Basin Setting November 2024
Other Subbasins4 47,000 65,000 76,000 90,000
Dry Creek 2,000 2,000 2,000 2,000
Mokelumne River 3,000 3,000 3,000 4,000
Stanislaus River 30,000 47,000 56,000 69,000
San Joaquin River 12,000 12,000 14,000 14,000
Surface Water Diversions8 340,000 353,000 340,000 340,000 Riparian Intake from Streams9 42,000 37,000 37,000 40,000 Total Outflow10 5,092,000 5,190,000 5,407,000 5,908,000 Notes:
1 Stream inflows into Eastern San Joaquin Subbasin include flows from Dry Creek, Mokelumne River, Calaveras River, Stanislaus River, San Joaquin River, and estimated tributary flows. Differences between historical and current/projected flows are due to differing hydrologic periods.
2 Stream gain from groundwater and stream seepage represent the interaction of surface water and groundwater. Differences between the scenarios are related to differences in streamflows and long-term average groundwater elevations. Projected scenarios and even current condition averages represent lower groundwater levels, causing less stream interaction. 3 Local tributaries include Bear Creek and related streams, Little Johns Creek, Duck Creek, and Lone Tree Creek. 4 Other subbasins include the Cosumnes, Modesto, South American, Solano, East Contra Costa, and Tracy Subbasins. Streamaquifer interaction with the other subbasins was included for streams on the boundaries of the Eastern San Joaquin Subbasin. 5 Runoff to the stream system is due to precipitation. As urban areas are assumed to have greater runoff of precipitation (due to more paved areas), the changes in runoff between the model scenarios are due to differences in the urban areas in the scenarios, as well as the amount of precipitation occurring. The historical calibration, with both less precipitation (due to more dry years than wet in the 28-year period) and smaller urban areas, has a corresponding smaller runoff. The current conditions scenario uses urban areas at the end of the historical calibration, while the projected scenario includes urban buildout to sphere of influence or general plan boundaries and therefore has more runoff. 6 Return flow to the stream system is due to applied water, either surface water or groundwater used for agricultural or municipal purposes. Differences between the scenarios is primarily related to the urban growth in the projected conditions scenario causing higher urban demand and therefore correspondingly higher applied water to meet that demand resulting in greater urban return flows (i.e., discharge of treated wastewater).
7 Stream outflows occur at the edge of Eastern San Joaquin Subbasin at the confluence of the San Joaquin and Mokelumne Rivers.
8 Surface water diversions shown in this table are the volumes of water taken directly off the river prior to any losses due to evaporation or canal seepage. These numbers do not include surface water directly diverted from simulated stream nodes (i.e., water taken off Stanislaus River occurs just upstream in the Subbasin). Differences between scenarios are due to differences in historical, current, and planned surface water diversions. 9 Riparian intake from streams is the portion of the riparian vegetation evapotranspiration met by streamflows. Differences between scenarios may be due to availability of streamflows or extent of riparian vegetation, which may be affected by growth in urban areas.
10 Summations in table may not match the numbers in the table. This is due to the rounding of model results. 11 Values smaller than 500 AF/year are represented by a dash (-).

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-181
Basin Setting November 2024
Table 2-15: Average Annual Water Budget for Revised ESJWRM – Land Surface System (AF/year) Component
Historical
Calibration
(AF/year)
Current
Conditions
(AF/year)
Projected
Conditions
(AF/year)
Projected
Conditions with
Climate Change
(AF/year)
Model Version
Historical
ESJWRM
Version 3.0
Historical
ESJWRM
Version 3.0

ESJWRM PCBL
Version 3.0
ESJWRM PCBLCC Version 3.0
Hydrologic Period
Water Years
1996-2023
(28-Year period)
Water Years
2019-2023
(5-Year average)
Water Years
1969- 2023
(55-Year period)
Water Years
1969- 2023
(55-Year period)
Inflows
Precipitation1
(Precipitation, inches)
988,000
(15.5)
1,063,000
(16.7)
992,000
(15.6)
1,087,000
(17.1)
Total Surface Water Supply2 568,000 562,000 525,000 525,000 Agricultural 512,000 497,000 452,000 452,000
Urban and Industrial 56,000 65,000 73,000 73,000
Total Groundwater Supply3 732,000 830,000 799,000 879,000 Agricultural 666,000 777,000 732,000 812,000
Urban and Industrial 66,000 53,000 67,000 67,000
Riparian Intake from Streams4 30,000 26,000 26,000 29,000 Total Inflow10 2,318,000 2,481,000 2,342,000 2,521,000
Outflows
Evapotranspiration5 1,309,000 1,352,000 1,302,000 1,384,000 Agricultural 1,006,000 1,080,000 999,000 1,089,000
Municipal and Domestic 59,000 58,000 80,000 81,000
Refuge, Native, and Riparian 243,000 213,000 214,000 214,000 Runoff to the Stream System6 629,000 741,000 656,000 753,000 Return Flow to the Stream System7 96,000 95,000 111,000 112,000 Agricultural 22,000 22,000 25,000 26,000
Municipal and Domestic 75,000 73,000 86,000 86,000
Deep Percolation8 275,000 284,000 270,000 268,000
Precipitation 60,000 53,000 55,000 52,000
Applied Surface Water –
Agricultural 85,000 82,000 73,000 70,000
Applied Surface Water – Urban
and Industrial 9,000 11,000 12,000 11,000
Applied Groundwater –
Agricultural 111,000 129,000 119,000 125,000
Applied Groundwater – Urban and
Industrial 11,000 9,000 11,000 10,000
Other Flows9 8,000 9,000 4,000 5,000
Total Outflow10 2,318,000 2,481,000 2,342,000 2,521,000 Notes:
1 Precipitation is discussed in the identification of the hydrologic periods in 2.4.2. The projected conditions scenarios utilize the same 55 years of hydrology (water years 1969-2023) with perturbations in the climate change scenario causing more precipitation. The historical calibration has a shorter hydrologic period (28 years from 1996-2023) with slightly less precipitation on average. Current conditions represent recent years with 2 wet years (2019 and 2023) and 3 dry or critical years (2020, 2021, and 2022).

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-182
Basin Setting November 2024
2 Total surface water supply shown in this table is the volume of surface water diverted or transported to meet agricultural and urban demands minus estimated losses due to evaporation or canal seepage. Differences between scenarios are due to differences in historical, current, and planned surface water deliveries. 3 Total groundwater supply in the scenarios is calculated based on meeting remaining demands after surface water deliveries occur. Differences in demand largely drive the amount of groundwater pumped. 4 Riparian intake from streams is the portion of the riparian vegetation evapotranspiration met by streamflows. Differences between scenarios may be due to availability of streamflows or extent of riparian vegetation, which may be affected by growth in urban areas.
5 Evapotranspiration is the demand required by agricultural land (i.e., crops); municipal and domestic areas (i.e., industrial and urban demands); and refuge, native and riparian areas. Differences in evapotranspiration are largely related to differences in urban areas between the scenarios and the loss of agricultural or native/riparian land as urban growth occurs. 6 Runoff to the stream system is due to precipitation. As urban areas are assumed to have greater runoff (e.g., more paved areas), the changes in runoff between the model scenarios are due to differences in the urban areas in the scenarios, as well as the amount of precipitation occurring. The historical calibration, with both less precipitation and smaller urban areas, has a corresponding smaller runoff. The current conditions scenario uses urban areas at the end of the historical calibration, while the projected scenario includes urban buildout to sphere of influence or general plan boundaries and therefore has more runoff. 7 Return flow to the stream system is due to applied water, either surface water or groundwater used for agricultural or municipal purposes. Differences between the scenarios is primarily related to the urban growth in the projected conditions scenario causing higher urban demand and therefore correspondingly higher applied water to meet that demand. 8 Deep percolation is the amount of infiltrated water ultimately reaching the groundwater aquifer. The source of the water may be from precipitation or either applied surface water or groundwater used for agricultural or urban and industrial purposes.

Differences between scenarios are related to differences between these sources of water and differences in the infiltration parameters related to land use.
9 Other Flows captures the gains and losses due to land expansion and temporary storage in the root-zone and unsaturated (vadose) zones.
10 Summations in table may not match the numbers in the table. This is due to the rounding of model results.

ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-183
Basin Setting November 2024
Table 2-16: Average Annual Water Budget for Revised ESJWRM – Groundwater System (AF/year) Component
Historical
Calibration
(AF/year)
Current
Conditions
(AF/year)
Projected
Conditions
(AF/year)
Projected
Conditions with
Climate Change
(AF/year)
Model Version
Historical
ESJWRM
Version 3.0
Historical
ESJWRM
Version 3.0

ESJWRM PCBL
Version 3.0
ESJWRM PCBLCC Version 3.0
Hydrologic Period
Water Years
1996-2023
(28-Year period)
Water Years
2019-2023
(5-Year average)
Water Years
1969- 2023
(55-Year period)
Water Years
1969- 2023
(55-Year period)
Inflows
Deep Percolation1 275,000 284,000 270,000 268,000
Precipitation 60,000 53,000 55,000 52,000
Applied Surface Water – Agricultural 85,000 82,000 73,000 70,000 Applied Surface Water – Urban and
Industrial 9,000 11,000 12,000 11,000
Applied Groundwater – Agricultural 111,000 129,000 119,000 125,000 Applied Groundwater – Urban and
Industrial 11,000 9,000 11,000 10,000
Stream Seepage2 236,000 267,000 298,000 330,000
Dry Creek 2,000 2,000 2,000 2,000
Mokelumne River 125,000 135,000 150,000 160,000
Calaveras River 37,000 37,000 39,000 41,000
Stanislaus River 36,000 55,000 67,000 82,000
San Joaquin River 37,000 37,000 40,000 45,000
Other Recharge 170,000 174,000 165,000 168,000
Carriage/Canal Recharge 103,000 109,000 98,000 98,000
Managed Aquifer Recharge 5,000 9,000 11,000 11,000
Reservoir Seepage 17,000 14,000 14,000 14,000
Ungauged Watershed Drainage 45,000 42,000 45,000 48,000 Subsurface Inflow3 176,000 188,000 204,000 222,000
Cosumnes Subbasin 28,000 34,000 35,000 35,000
Sierra Nevada Mountains 55,000 54,000 57,000 55,000
Modesto Subbasin 30,000 32,000 37,000 41,000
South American Subbasin 3,000 4,000 5,000 6,000
Solano Subbasin 19,000 19,000 22,000 27,000
East Contra Costa Subbasin 9,000 10,000 11,000 13,000
Tracy Subbasin 31,000 34,000 37,000 44,000
Total Inflow5 857,000 912,000 937,000 988,000
Outflows
Groundwater Outflow to Streams2 75,000 63,000 57,000 53,000 Dry Creek6 0 0 0 0
Mokelumne River 14,000 13,000 10,000 8,000
Calaveras River 1,000 1,000 1,000 1,000
Stanislaus River 28,000 18,000 17,000 16,000
San Joaquin River 31,000 31,000 29,000 27,000
Groundwater Pumping4 732,000 830,000 799,000 879,000
Agricultural 666,000 777,000 732,000 812,000
Urban and Industrial 66,000 53,000 67,000 67,000
Subsurface Outflow3 96,000 104,000 110,000 111,000
Cosumnes Subbasin 27,000 32,000 36,000 37,000
Modesto Subbasin 40,000 44,000 44,000 46,000
ATTACHMENT 2
2024 Groundwater Sustainability Plan Amendment 2-184
Basin Setting November 2024
Component
Historical
Calibration
(AF/year)
Current
Conditions
(AF/year)
Projected
Conditions
(AF/year)
Projected
Conditions with
Climate Change
(AF/year)
Model Version
Historical
ESJWRM
Version 3.0
Historical
ESJWRM
Version 3.0

ESJWRM PCBL
Version 3.0
ESJWRM PCBLCC Version 3.0
Hydrologic Period
Water Years
1996-2023
(28-Year period)
Water Years
2019-2023
(5-Year average)
Water Years
1969- 2023
(55-Year period)
Water Years
1969- 2023
(55-Year period)
South American Subbasin6 1,000 1,000 0 0
Solano Subbasin 11,000 11,000 11,000 10,000
East Contra Costa Subbasin 2,000 2,000 2,000 2,000
Tracy Subbasin 16,000 14,000 17,000 16,000
Total Outflow5 903,000 997,000 965,000 1,043,000
Change in Groundwater Storage (Inflows Minus Outflows)
Change in Groundwater Storage5(48,000) (89,000) (30,000) (56,000) Notes:
1 Deep percolation is the amount of infiltrated water ultimately reaching the groundwater aquifer. The source of the water may be from precipitation, as well as either applied surface water or groundwater used for agricultural or urban and industrial purposes.

Differences between scenarios are related to differences between these sources of water and differences in urban versus agricultural land use totals.
2 Stream gain from groundwater and stream seepage represent the interaction of surface water and groundwater. Differences between the scenarios are related to differences in streamflows and long-term average groundwater elevations. 3 The goal of projecting inter-basin flows is to maintain a reasonable balance between the neighboring groundwater subbasins.

The resulting projected conditions scenario flows are within 10-15% of historical calibration flows, considered a reasonable range given the availability of projected land use, population, surface water delivery, and groundwater production data from areas outside of the Eastern San Joaquin Subbasin. Continuing inter-basin coordination may refine these numbers. 4 Groundwater pumping is estimated by the ESJWRM based on the need for additional water to meet remaining demands after surface water deliveries occur. Differences in demand largely drive the amount of groundwater pumped. 5 Summations in table may not match the numbers in the table. This is due to the rounding of model results. 6 Values smaller than 500 AF/year are represented by a dash (-).

ATTACHMENT 2
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2.4.5.1 Historical Water Budget Estimates (Historical ESJWRM Version 3.0) The historical water budget is a quantitative tabulation of the historical surface and groundwater supply represented in the historical calibration of the ESJWRM covering the 28-year period of water years 1996-2023. The ESJGWA selected this period as the representative hydrologic period to calibrate and reduce the uncertainty of the ESJWRM. Proper analysis and calibration of water budgets using the ESJWRM assures the hydrologic characteristics of the groundwater basin are well simulated. The historical calibration is discussed in detail in the historical model documentation (Appendix 2-A). CCR Title 23 § 354.18, the water budget includes estimates for supply and demand, while summarizing flows within the Subbasin, including the movement of all primary sources of water such as precipitation, agricultural water supplies, streamflow, and subsurface flows.

Subsequent to completion and submittal of the GSP in January of 2020, the ESJWRM was updated to include new data sets extending the simulation period to encompass WY 1996 through 2020. It was then updated again in 2024 to extend the simulation period from WY 1996 through 2023. These model updates, recalibration, and the associated results are documented in Appendix 2-C of this GSP.

The existing stream network supplies water to multiple agricultural water users and municipalities in the Eastern San Joaquin Subbasin. When analyzing the water budget for the stream system, it is important to note potentially significant effects due to the interactions and managed operations of adjacent groundwater subbasins on streams coinciding with the boundaries of the Subbasin (i.e., Dry Creek, portions of the Mokelumne River, San Joaquin River, and Stanislaus River). The summary of water budget assumptions presented in Table 2-13 and Figure 2-109 not only quantifies the surface water system within the Subbasin, but also estimates contributions from adjoining subbasins.

The stream system inflows through or along the Subbasin boundary simulated in the historical calibration average is

5.1 MAF/year. The majority of these flows, almost 4.2 MAF/year, enter the Subbasin as stream inflows to the Subbasin.

Three other surface water inflows are estimated stream gains from the groundwater system (145,000 AF/year), runoff of precipitation to the stream system (629,000 AF/year), and return flow of applied water to the stream system (96,000 AF/year). Outflows of the Eastern San Joaquin Subbasin stream system total 5.1 MAF/year and include downstream outflows leaving the Subbasin (almost 4.4 MAF/year), stream seepage to the groundwater system (284,000 AF/year), surface water diversions (340,000 AF/year), and riparian vegetation intake from streams (42,000 AF/year).

Figure 2-109: Historical Average Annual Water Budget – Stream System ATTACHMENT 2
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The land surface system water budget in the historical calibration of the Eastern San Joaquin Subbasin, shown below in Figure 2-110, estimates almost 2.3 MAF/year of inflows, a combination of precipitation (988,000 AF/year), surface water supply (568,000 AF/year), groundwater supply (732,000 AF/year), and riparian intake from streams (30,000 AF/year). The outflow from the land surface system in the historical calibration estimates evapotranspiration (close to 1.3 MAF/year), runoff of precipitation to the stream system (629,000 AF/year), return flow of applied water to the stream system (96,000 AF/year), deep percolation of precipitation or applied water (275,000 AF/year), and a small component representing other flows (8,000 AF/year), which includes uncertainties in other components due to land expansion and temporary storage in the root-zone and unsaturated (vadose) zones.

Figure 2-110: Historical Average Annual Water Budget – Land Surface System The groundwater system of the Eastern San Joaquin Subbasin includes 905,000 AF/year of inflows in the historical calibration (not including change in groundwater storage), of which 275,000 AF/year is deep percolation of precipitation or applied water. There is also stream seepage (236,000 AF/year), other recharge (170,000 AF/year), and subsurface inflows (176,000 AF/year) from the Sierra Nevada Mountains and the neighboring groundwater subbasins of Cosumnes, Modesto, South American, Solano, East Contra Costa, and Tracy. On average, the inflows do not meet the entire groundwater demand. The primary outflow from the groundwater system is pumping (732,000 AF/year), followed by groundwater outflow to streams (75,000 AF/year), and subsurface outflow to the neighboring groundwater subbasins (96,000 AF/year).

The Eastern San Joaquin Subbasin average historical groundwater budget has greater outflows than inflows, leading to an estimated average annual decrease in groundwater storage of approximately 48,000 AF/year. Figure 2-111 summarizes the average historical calibration groundwater inflows and outflows of the Eastern San Joaquin Subbasin.

A groundwater change in storage, or overdraft, estimate of 48,000 AF/year represents a refinement over previous efforts which have estimated levels of overdraft for the Subbasin to be between 70,000 AF and 150,000 AF annually.

Such previous efforts include the DWR’s 2003 Bulletin 118 study (CA DWR, 2003) and modeling conducting as part of the SJCFCWCD’s 2001 Water Management Plan (SJCFCWCD, 2001) and presented in the 2004 Eastern San Joaquin Groundwater Basin Groundwater Management Plan (NSJCGBA, 2004). The analysis presented in this Plan represents the best available information to date. These estimates, which are the result of several years of collaboration between ATTACHMENT 2
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agencies prior to Plan development, utilize new data and modeling capabilities not captured in prior modeling efforts.

A portion of the reduction seen in the overdraft estimate is also the result of converting from groundwater use to surface water supplies that has occurred since the development of previous estimates. For additional discussion of refinements that occurred in the development of the ESJWRM (Woodard & Curran, 2018), see Appendix 2-A.

Figure 2-111: Historical Average Annual Water Budget Estimates – Groundwater System Historical inflows and outflows change by water year type as defined by the San Joaquin Valley Water Year Hydrologic Classification (CA DWR, 2018a). In wet years, precipitation meets more of the water demand and greater availability of surface water reduces the need for groundwater pumping. However, in dry years, more groundwater is pumped to meet the demand not met by surface water or precipitation. This may lead to an increase in groundwater storage in wet years and a decrease in dry years. Table 2-17breaks down the average historical water supply and demand by water year type.

The historical calibration focuses on representing changing conditions and operations, such as new agricultural land or crop types, new surface water diversions, and population growth. The timing of these changes is often independent of the hydrologic conditions of the year in question; therefore, looking at supplies and demands averaged by water year type does not necessarily present clear results. Furthermore, the 28 years represented in the historical calibration do not include an equal number of each water year type, making averages less reliable to gather historical trends. As the projected conditions scenario considered the water year type in some of the model inputs and the 55-year hydrologic period allows for greater repetition of the water year types, the projected conditions results presented later in Section

2.4.5.3 are more consistent with the trends expected when averaging by water year type.

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Table 2-17: Average Annual Values for Key Components of Historical Water Budget by Year Type Component
Water Year Type (San Joaquin River Index)
Wet Above
Normal
Below
Normal1
Dry Critical 28-Year
Number of Years2 9 3 2 7 7 28
Precipitation, AF/year
(Precipitation, inches)
1,409,000
(22.1)
944,000
(14.8)
867,000
(13.6)
805,000
(12.6)
684,000
(10.7)
988,000
(15.5)
Water Demand (AF/year)
Ag Demand3 1,143,000 1,114,000 1,168,000 1,167,000 1,225,000 1,168,000 Urban Demand4 117,000 122,000 122,000 125,000 123,000 122,000 Total Demand7 1,260,000 1,236,000 1,290,000 1,293,000 1,348,000 1,290,000 Water Supply (AF/year)
Total Surface Water
Supply5
556,000 597,000 557,000 572,000 569,000 568,000
Agricultural 503,000 544,000 501,000 517,000 507,000 512,000 Urban and Industrial 53,000 53,000 56,000 55,000 62,000 56,000 Total Groundwater
Supply6
713,000 648,000 741,000 731,000 791,000 732,000
Agricultural 648,000 578,000 675,000 660,000 728,000 666,000 Urban and Industrial 65,000 70,000 67,000 71,000 62,000 66,000 Total Supply (AF/year)7 1,268,000 1,245,000 1,298,000 1,303,000 1,360,000 1,300,000 Change in
Groundwater Storage
(AF/year)7
78,000 13,000 -82,000 -105,000 -170,000 -48,000
Notes:
1 There was only two below normal water yeas in the historical calibration (water year 2003 and 2018), so averages are just based on model results for two water years. Since there weren’t any more below normal years to use in the average, results for the below normal water year type may not follow expected trends. 2 List of historical water budget water years by water year type:

Wet: 1996, 1997, 1998, 2005, 2006, 2011, 2017, 2019, 2023 Above Normal: 1999, 2000, 2010
Below Normal: 2003, 2018
Dry: 2001, 2002, 2004, 2009, 2012, 2016, 2020
Critical: 2007, 2008, 2013, 2014, 2015, 2021, 2022
3 Agricultural demand is based on evapotranspiration by crop and acreages by crop. As agricultural land use changes over the historical calibration through changes in crop types and urbanization, averaging of the resulting agricultural demand is less a function of water year type than of the time in the simulation when that year type fell. 4 Urban demands in the historical water budget are reported values from cited sources. Averaging urban demands by water year type may not explicitly depict urban growth patterns during the historical calibration period. 5 Total surface water supply is based on information received from local entities and varied historically based on when surface water rights or agreements occurred. As some entities received new surface water sources during the historical calibration period, averaging by water year type depends more on when the water year types occurred in the simulation. 6 Total groundwater supply is pumping as estimated by the ESJWRM is a function of demand, precipitation, and surface water.