Groundwater Sustainability Plan for the Northern and Central Delta-Mendota Regions Common Chapter
Appendix B
Appendix B
Northern & Central Delta-Mendota Region GSP
Groundwater Sustainability Plan
30November2019; Revised June 2022
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For the Delta-Mendota Subbasin Groundwater Sustainability Plan August 2019; revised June 2022
Common Chapter
FARMERS
WATER DISTRICT
Delta-Mendota
Groundwater Subbasin
Groundwater Sustainability Plan:
Revised Common Chapter
August 2019; Revised June 2022
Prepared by:
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If you have difficulty accessing any material in this document, please contact us in writing or via telephone and we will work with you to make the information available. You can direct your request to:
ATTN: John Brodie
San Luis and Delta-Mendota Water Authority
842 6th Street
Los Banos, CA 93635
Telephone (209) 826-1872Email: [email protected]
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Table of Contents
DISCLAIMER........................................................................................................................................... IV
1. INTRODUCTION ............................................................................................................................. 1
1.1 Purpose of Common Chapter .......................................................................................... 1
1.2 Delta-Mendota Subbasin................................................................................................. 1
1.3 Disadvantaged Communities within the Delta-Mendota Subbasin....................................... 2
1.4 Economically Disadvantaged Areas within the Delta-Mendota Subbasin ............................. 4
2. DELTA-MENDOTA SUBBASIN GOVERNANCE ...................................................................... 8
2.1 GSA and GSP Coordination and Governance ................................................................. 13
2.1.1 Delta-Mendota Subbasin SGMA Governance Structure ....................................... 13
2.1.2 Intra-Basin Coordination................................................................................... 18
2.1.3 Inter-basin Agreements ..................................................................................... 24
3. DELTA-MENDOTA SUBBASIN PLAN AREA .......................................................................... 25
3.1 Plan Area Definition .................................................................................................... 25
3.2 Plan Area Setting ......................................................................................................... 28
3.3 General Plans in Plan Area ........................................................................................... 44
3.4 Existing Land Use Plans and Impacts to Sustainable Groundwater Management ................ 46
3.5 Existing Water Resources Monitoring and Management Programs ................................... 46
3.6 County Well Construction/Destruction Standards and Permitting ..................................... 48
4. SUBBASIN SETTING .................................................................................................................... 50
4.1 Hydrogeologic Conceptual Model ................................................................................. 50
4.1.1 Regional Geologic and Structural Setting ........................................................... 50
4.1.2 Geologic History .............................................................................................. 52
4.1.3 Geologic Formations and Stratigraphy ............................................................... 54
4.1.4 Faults and Structural Features............................................................................ 55
4.1.5 Basin Boundaries ............................................................................................. 55
4.1.6 Definable Bottom of Basin ................................................................................ 57
4.1.7 Principal Aquifers and Aquitards ....................................................................... 57
4.1.8 Structural Properties and Restricted Groundwater Flow ....................................... 71
4.1.9 Water Quality .................................................................................................. 71
4.1.10 Topography, Surface Water, Recharge, and Imported Supplies ............................. 73
4.2 Delta-Mendota Subbasin Groundwater Conditions .......................................................... 83
4.2.1 Useful Terminology ......................................................................................... 83
4.2.2 Groundwater Elevations.................................................................................... 84
4.2.3 Groundwater Storage ........................................................................................ 98
4.2.4 Seawater Intrusion............................................................................................ 99 Delta-Mendota Subbasin Groundwater Sustainability Plan
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4.2.5 Groundwater Quality ........................................................................................ 99
4.2.6 Land Subsidence .............................................................................................. 99
4.2.7 Interconnected Surface Water Systems ............................................................. 114
4.2.8 Data Gaps ..................................................................................................... 130
4.3 Delta-Mendota Subbasin Water Budgets ...................................................................... 130
4.3.1 Coordinated Assumptions ............................................................................... 131
4.3.2 GSP-Level Water Budgets .............................................................................. 141
4.3.3 Coordinated Water Budgets ............................................................................ 141
4.3.4 Sustainable Yield ........................................................................................... 150
5. SUSTAINABLE MANAGEMENT CRITERIA ........................................................................ 153
5.1 Coordinated Assumptions and Data ............................................................................. 153
5.2 Coordinated Sustainability Goal and Undesirable Results .............................................. 153
5.3 GSP-Level Sustainable Management Criteria ............................................................... 154
5.4 Delta-Mendota Subbasin Sustainable Management Criteria ........................................... 154
5.4.1 Chronic Lowering of Groundwater Levels ........................................................ 155
5.4.2 Reduction in Groundwater Storage .................................................................. 162
5.4.3 Degraded Groundwater Quality ....................................................................... 163
5.4.4 Inelastic Land Subsidence ............................................................................... 171
5.4.5 Depletion of Interconnected Surface Water ....................................................... 176
6. SUBBASIN MONITORING PROGRAM .................................................................................. 180
6.1.1 Coordinated Assumptions and Data ................................................................. 180
6.1.2 Coordinated Monitoring Activities ................................................................... 180
6.1.3 GSP-Level Monitoring Networks .................................................................... 184
6.1.4 Delta-Mendota Subbasin Monitoring Networks................................................. 184
7. SUBBASIN DATA COLLECTION AND MANAGEMENT .................................................... 191
8. STAKEHOLDER OUTREACH .................................................................................................. 193
8.1 Situation Assessment and Communications Plan ........................................................... 193
8.2 Public Noticing and Information.................................................................................. 194
8.3 List of Public Meetings Where the GSPs were Discussed .............................................. 194
8.4 Comments Regarding the GSPs ................................................................................... 196
8.5 Subbasin Decision Making Process.............................................................................. 196
8.6 Opportunities for Public Engagement and How Public Input was Used ........................... 196
8.6.1 Opportunities for Public Engagement ............................................................... 197
8.6.2 How Public Input and Response was Used in the Development of the GSP.......... 198
8.7 Revisions to Common Chapter and Subbasin GSPs ....................................................... 198
9. REFERENCES .............................................................................................................................. 200 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Tables
Table CC-1: DACs as a Percentage of the Delta-Mendota Subbasin ..................................................... 3 Table CC-2: DAC and SDAC Census Designated Places in Delta-Mendota Subbasin ............................ 3 Table CC-3: EDAs as a Percentage of the Delta-Mendota Subbasin ..................................................... 4 Table CC-4: Delta-Mendota Subbasin Coordination Committee Members .......................................... 14 Table CC-5: Subsidence Monitoring Trends ................................................................................... 100 Table CC-6: Estimated Quantity of Gains/Depletions for Interconnected Stream Reaches, San Joaquin River .................................................................................................................. 116 Table CC-7: List of Potential Freshwater Species ........................................................................... 121 Table CC-8: Historical and Current Water Budgets Data Sources ..................................................... 139 Table CC-9: Projected Water Budgets Data Sources ....................................................................... 140 Table CC-10: Delta-Mendota Subbasin Historical Water Budget, Land Surface Budget ..................... 143 Table CC-11: Delta-Mendota Subbasin Historical Water Budget, Groundwater Budget...................... 143 Table CC-12: Delta-Mendota Subbasin Current Water Budget, Land Surface Budget ........................ 144 Table CC-13: Delta-Mendota Subbasin Current Water Budget, Groundwater System......................... 144 Table CC-14: Delta-Mendota Subbasin Projected Water Budget, Land Surface Budget ...................... 145 Table CC-15: Delta-Mendota Subbasin Projected Water Budget, Groundwater Budget ...................... 147 Table CC-16: Delta-Mendota Subbasin SMC ................................................................................ 155 Table CC-17: Numeric SMC for the Chronic Lowering of Groundwater Levels ................................ 157 Table CC-18: Delta-Mendota Subbasin SMC ................................................................................ 163 Table CC-19: Delta-Mendota Subbasin SMC ................................................................................ 165 Table CC-20: Numeric SMC for Degraded Groundwater Quality ..................................................... 166 Table CC-21: Delta-Mendota Subbasin SMC ................................................................................ 171 Table CC-22: Numeric SMC for Inelastic Land Subsidence ............................................................. 173 Table CC-23: Delta-Mendota Subbasin SMC ................................................................................ 176 Table CC-24: Coordinated Public Workshops ................................................................................ 195 Figures
Figure CC-1: Delta-Mendota Subbasin and GSP Regions .................................................................... 5 Figure CC-2: Disadvantaged and Severely Disadvantaged Communities in the Delta-Mendota Subbasin . 6 Figure CC-3: Economically Distressed Areas in the Delta-Mendota Subbasin ....................................... 7 Figure CC-4: GSAs in the Delta-Mendota Subbasin – Stanislaus County ............................................ 10 Figure CC-5: GSAs in the Delta-Mendota Subbasin – Merced County ................................................ 11 Figure CC-6: GSAs in the Delta-Mendota Subbasin – Fresno and Madera Counties ............................. 12 Figure CC-7: Governance Structure of the Delta-Mendota Subbasin ................................................... 17 Figure CC-8: Neighboring Subbasins of the Delta-Mendota Subbasin ................................................ 26 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-9: Delta-Mendota Groundwater Subbasin Plan Area ......................................................... 27 Figure CC-10: Local Watersheds .................................................................................................... 29 Figure CC-11: Wildlife Refuges and Wetland Habitat Areas in the Delta-Mendota Subbasin ................ 30 Figure CC-12: Communities Dependent on Groundwater .................................................................. 33 Figure CC-13: Domestic Well Density in the Delta-Mendota Subbasin ............................................... 34 Figure CC-14: Production Well Density in the Delta-Mendota Subbasin ............................................. 35 Figure CC-15: Public Well Density in the Delta-Mendota Subbasin ................................................... 36 Figure CC-16: 100-Year Floodplain, Delta-Mendota Subbasin........................................................... 39 Figure CC-17: Typical Land Use .................................................................................................... 40 Figure CC-18: Land Use Planning Entities ....................................................................................... 41 Figure CC-19: Federal and State Lands............................................................................................ 43 Figure CC-20: 2014 Land Use in the Delta-Mendota Subbasin........................................................... 45 Figure CC-21: Regional Geologic Setting ........................................................................................ 51 Figure CC-22: Generalized Geology................................................................................................ 53 Figure CC-23: Subbasin Faults ....................................................................................................... 56 Figure CC-24: Representative Cross-Sections .................................................................................. 61 Figure CC-25: Cross-Section A-A’ (Hotchkiss, 1972) ....................................................................... 62 Figure CC-26: Cross-Section B-B’ (Hotchkiss, 1972) ....................................................................... 63 Figure CC-27: Cross-Section C-C’ (Hotchkiss, 1972) ....................................................................... 64 Figure CC-28: Cross-Section D-D’ (Hotchkiss & Balding, 1971) ....................................................... 64 Figure CC-29: Cross-Section E-E’ (Hotchkiss & Balding, 1971) ........................................................ 65 Figure CC-30: Cross-Section F-F’ (Hotchkiss, 1972) ........................................................................ 66 Figure CC-31: Depth to Corcoran Clay ............................................................................................ 67 Figure CC-32: Non-Corcoran Clay Layers ....................................................................................... 68 Figure CC-33: Thickness of Corcoran Clay ...................................................................................... 69 Figure CC-34: Soil Hydraulic Conductivity ..................................................................................... 70 Figure CC-35: Ground Surface Elevation ......................................................................................... 75 Figure CC-36: Surface Water Features ............................................................................................ 76 Figure CC-37: SAGBI Soils Map .................................................................................................... 79 Figure CC-38: Tile Drains .............................................................................................................. 80 Figure CC-39: Recharge Areas, Seeps and Springs ........................................................................... 81 Figure CC-40: Imported Supplies .................................................................................................... 82 Figure CC-41: Wells with Known Screened Interval Depths .............................................................. 90 Figure CC-42: Select Graphs of Groundwater Elevations, Upper Aquifer ........................................... 91 Figure CC-43: Select Graphs of Groundwater Elevations, Various Depths .......................................... 92 Figure CC-44: Select Graphs of Groundwater Elevations, Lower Aquifer ........................................... 93 Figure CC-45: Spring 2013 Upper Aquifer Groundwater Contour Map............................................... 94 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-46: Fall 2013 Upper Aquifer Groundwater Contour Map................................................... 95 Figure CC-47: Spring 2013 Lower Aquifer Groundwater Elevation Measurements .............................. 96 Figure CC-48: Fall 2013 Lower Aquifer Groundwater Elevation Measurements .................................. 97 Figure CC-49: Calculated Upper Aquifer Change in Storage, Annual and Cumulative ......................... 98 Figure CC-50: Calculated Lower Aquifer Change in Storage, Annual and Cumulative ......................... 99 Figure CC-51: UNAVCO and Delta-Mendota Canal Subsidence Monitoring Locations ..................... 103 Figure CC-52: Vertical Elevation Change at UNAVCO CGPS P255, Spring 2007 to 2018 ................. 104 Figure CC-53: Vertical Elevation Change at UNAVCO CGPS P259, Spring 2006 to 2018 ................. 105 Figure CC-54: Vertical Elevation Change at UNAVCO CGPS P252, Spring 2006 to 2018 ................. 106 Figure CC-55: Vertical Elevation Change at UNAVCO CGPS P303, Spring 2006 to 2018 ................. 107 Figure CC-56: Vertical Elevation Change at UNAVCO CGPS P301, Spring 2005 to 2018 ................. 108 Figure CC-57: Vertical Elevation Change at UNAVCO CGPS P304, Spring 2005 to 2018 ................. 109 Figure CC-58: Land Subsidence, December 2011 to December 2014 ............................................... 110 Figure CC-59: Recent Land Subsidence at Key San Joaquin Valley Locations .................................. 111 Figure CC-60: Vertical Displacement, April 2015 to April 2016 ...................................................... 112 Figure CC-61: Elevation Change along the Delta-Mendota Canal, 2014 through 2018 ....................... 113 Figure CC-62: Groundwater Dependent Ecosystems, Wetlands........................................................ 119 Figure CC-63: Groundwater Dependent Ecosystems, Vegetation ..................................................... 120 Figure CC-64: Change in Storage, Delta-Mendota Subbasin Projected Water Budget......................... 149 Figure CC-65: Groundwater Level Representative Monitoring Locations with SMC – Upper Aquifer . 160 Figure CC-66: Groundwater Level Representative Monitoring Locations with SMC – Lower Aquifer 161 Figure CC-67: Groundwater Quality Representative Monitoring Locations with SMC – Upper Aquifer .......................................................................................................................... 169 Figure CC-68: Groundwater Quality Representative Monitoring Locations with SMC – Lower Aquifer .......................................................................................................................... 170 Figure CC-69: Land Subsidence Representative Monitoring Locations with SMC ............................. 175 Figure CC-70: Interconnected Surface Water Representative Monitoring Locations with SMC ........... 179 Figure CC-71: Data Flow in Delta-Mendota Subbasin ..................................................................... 182 Figure CC-72: Delta-Mendota Monitoring and Data Management Roles and Responsibilities ............. 183 Figure CC-73: Upper Aquifer Groundwater Level Monitoring Network ........................................... 185 Figure CC-74: Lower Aquifer Groundwater Level Monitoring Network ........................................... 186 Figure CC-75: Upper Aquifer Groundwater Quality Monitoring Network ......................................... 187 Figure CC-76: Lower Aquifer Groundwater Quality Monitoring Network ........................................ 188 Figure CC-77: Interconnected Surface Water Monitoring Network................................................... 189 Figure CC-78: Land Surface Elevation Monitoring Network............................................................ 190 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Appendices
Appendix A – Coordination Agreement
Appendix B – Common Technical Memoranda
Appendix C – Preparation Checklist for GSP Submittal
Appendix D – Interbasin Agreements
Appendix E – Delta-Mendota Subbasin Communications Plan Appendix F – Summaries of Coordinated Public Workshops
Appendix G – Examples of Promotional Materials from Public Workshops Appendix H – List of Stakeholders and Community Organizations Contacted Delta-Mendota Subbasin Groundwater Sustainability Plan
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Acronyms
AB 3030 1992 California Assembly Bill 3030
AWMP Agricultural Water Management Plan
BMP Best Management Practice
CASGEM California Statewide Groundwater Elevation Monitoring CCC Columbia Canal Company
CCF Climate Change Factors
CCID Central California Irrigation District
CDEC California Data Exchange Center
CDFW California Department of Fish and Wildlife
cfs cubic feet per second
CVO Central Valley Operations
CVP Central Valley Project
CVRWQCB Central Valley Regional Water Quality Control Board DAC Disadvantaged Community
DMC Delta-Mendota Canal
DPWD Del Puerto Water District
DWR California Department of Water Resources
ET Evapotranspiration
ETc Total Crop Evapotranspiration
ETiw Crop Evapotranspiration of Irrigation Water
ETmisc Miscellaneous Evapotranspiration including; canal evaporation, consumptive use of phreatophytes, etc.
FCWD Firebaugh Canal Water District
FNF Full Natural Flow
GAMA Groundwater Ambient Monitoring and Assessment
gpm gallons per minute
GRCD Grassland Resource Conservation District
GSA Groundwater Sustainability Agency
GSP Groundwater Sustainability Plan
GWD Grassland Water District
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Acronyms
HCM Hydrogeologic Conceptual Model
HMRD Henry Miller Reclamation District
IM interim milestone
IRWM Integrated Regional Water Management
JPA Joint Powers Authority
KDSA Kenneth D. Schmidt and Associates
MAF million acre-feet
MO measurable objective
MSL Mean Sea Level
MT minimum threshold
NASA JPL National Aeronautics and Space Administration Jet Propulsions Laboratory P&P Provost and Pritchard Consulting Group
RCD Resource Conservation District
RWQCB Regional Water Quality Control Board
SB 372 2017 California Senate Bill 372
SGMA Sustainable Groundwater Management Act
SGWP Sustainable Groundwater Planning
SJREC San Joaquin River Exchange Contractors
SJRECWA San Joaquin River Exchange Contractors Water Authority SJRIP San Joaquin River Improvement Program
SJRRP San Joaquin River Restoration Program
SLDMWA San Luis & Delta-Mendota Water Authority
SMC Sustainable Management Criteria
SWP State Water Project
SWRCB State Water Resources Control Board
TAF thousand acre-feet
TDS Total Dissolved Solids
TIWD Turner Island Water District
TNC The Nature Conservancy
UNAVCO University NAVSTAR Consortium
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Acronyms
USACE U.S. Army Corps of Engineers
USBR U.S. Bureau of Reclamation
USF&WS U.S. Fish & Wildlife Service
USGS United States Geological Survey
UWMP Urban Water Management Plan
WDL Water Data Library
WMP Water Management Plan
WSIP Water Storage Investment Program
WWD Westlands Water District
WY Water Year
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1. INTRODUCTION
1.1 Purpose of Common Chapter
The 23 Groundwater Sustainability Agencies (GSAs) overlying the Delta-Mendota Subbasin (Subbasin) have prepared six Groundwater Sustainability Plans (GSPs) that, together, encompass the entire Subbasin area (Figure CC-1). These GSPs have been prepared in a coordinated manner under the oversight of the Delta-Mendota Subbasin Coordination Committee (Coordination Committee) and in accordance with the Delta-Mendota Subbasin Coordination Agreement (Coordination Agreement) for the Subbasin. This Common Chapter has been prepared as means of integrating key parts of the six GSPs to meet subbasinlevel requirements per the Sustainable Groundwater Management Act (SGMA) and the Emergency GSP regulations (DWR, 2016).
On January 21, 2022, the Subbasin received a Consultation Initiation Letter (CIL) from the California Department of Water Resources (DWR). The CIL identified four potential deficiencies across the six Subbasin GSPs which may preclude DWR’s approval, as well as potential corrective actions to address each potential deficiency. The CIL thus initiated consultation between DWR, the Subbasin Point of Contact, Plan Managers, and the Subbasin’s GSAs. This Common Chapter has been revised to incorporate changes required to reflect the Subbasin’s response to the deficiencies identified in the CIL, based on direction provided by the Coordination Committee, the Delta-Mendota Technical Working Group (Technical Working Group), the Subbasin GSAs and DWR. This revised Common Chapter, along with the attached cover letter, are intended to document how the deficiencies identified in the CIL were addressed in the revised Subbasin GSPs and this revised Common Chapter.
This revised Common Chapter, along with the six Subbasin GSPs, Coordination Agreement (Appendix A) and Common Technical Memoranda (Appendix B), meets regulatory requirements established by DWR as shown in the completed Preparation Checklist for GSP Submittal (Appendix C). The Common Technical Memoranda summarize the common data sets, assumptions and methodologies used during preparation of the six Subbasin GSPs. The reader is referred to the individual GSP (and their associated Executive Summaries) for information, data, and GSP requirements specific to each GSP Plan Area.
1.2 Delta-Mendota Subbasin
The Delta-Mendota Subbasin (DWR Basin 5-022.07) is located in the San Joaquin Valley Groundwater Basin and adjoins nine (9) subbasins of the San Joaquin Valley Groundwater Basin. The Delta-Mendota Subbasin boundaries generally correspond to DWR’s California’s Groundwater Bulletin 118 – Update 2003 (Bulletin 118) groundwater basin boundaries. Changes made to the Subbasin boundaries as part of the SGMA planning process include the following:
A jurisdictional internal boundary modification made in 2016 to extend the boundary of the Delta-Mendota Subbasin eastward to include all of Aliso Water District. A jurisdictional internal boundary modification made in 2016 to bring areas that straddle the Delta-Mendota Subbasin and adjacent subbasins fully within the Delta-Mendota Subbasin. This modification adjusted areas from the southern boundary of the Delta-Mendota Subbasin and the Westside Subbasin in coordination with Westlands Water District, and moved the eastern boundary of the Delta-Mendota Subbasin from the Madera Subbasin into the Delta-Mendota Delta-Mendota Subbasin Groundwater Sustainability Plan
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Subbasin in coordination with Aliso Water District. The modification also moved areas from the Tracy Subbasin into the Delta-Mendota Subbasin so that Del Puerto Water District and West Stanislaus Irrigation District were fully within the Delta-Mendota Subbasin, and cleaned up boundaries between the Delta-Mendota Subbasin and the Kings Subbasin to conform with the boundaries of Tranquillity Irrigation District and the Traction Ranch property (bounded on the east by Mid-Valley Water District).
A jurisdictional internal boundary modification made in 2018 to modify the boundary between the Delta-Mendota and the Chowchilla Subbasins to follow the western boundary of Triangle T Water District and the southern boundary of Clayton Water District. This modification moved approximately 700 acres of land from the Chowchilla Subbasin into the Delta-Mendota Subbasin.
The western San Joaquin Valley is a highly agricultural region with an economy dependent on that industry. There are no large cities or industries in the Delta-Mendota Subbasin to provide an alternative economic base; hence the availability of Central Valley Project (CVP) imported supplies and surface water supplies (primarily from the San Joaquin and Kings River) are essential elements to the economic health of the region. Other uses of CVP and surface water in the Subbasin are for municipal and industrial (M&I) purposes and wildlife refuge water supply.
Groundwater is a key component of overall water supplies in the Delta-Mendota Subbasin. Agricultural and wildlife refuge needs may be supplemented by groundwater for areas with access to CVP water.
Other landowners within the Subbasin may rely wholly on groundwater for irrigation and/or potable purposes. Municipal and industrial (M&I) water use, which is a small share of total water use in the Subbasin, occurs primarily within the cities, and predominantly uses groundwater to meet those demands.
The largest M&I use areas in the Delta-Mendota Subbasin, based on 2015 population estimates from the U.S. Census Bureau, are the cities of Patterson (population 21,498) and Los Banos (population 37,457) (U.S. Census Bureau, 2015).
As previously noted, most communities within the Delta-Mendota Subbasin have economies greatly dependent on agricultural production. These communities include Patterson, Grayson, Tranquillity, Mendota, Firebaugh, Dos Palos, Los Banos, Santa Nella, Newman, Gustine, Crows Landing, Westley, Volta, and Vernalis.
1.3 Disadvantaged Communities within the Delta-Mendota Subbasin A disadvantaged community (DAC) is defined as a community with a Median Household Income (MHI) less than 80% of the California statewide MHI. The California Department of Water Resources (DWR) compiled U.S. Census Bureau’s American Community Survey (ACS) data from 2012 to 2016; these data were used in GIS to identify DACs within the Delta-Mendota Subbasin. California’s average statewide MHI from 2012 to 2016 is $63,783; thus, a community with an MHI less than or equal to $51,026 is considered a DAC. Based on these criteria, 93% of the geographic area of the Subbasin is considered disadvantaged. Furthermore, a community with an MHI of less than 60% of the California statewide MHI, meaning an MHI of less than or equal to $38,270, is considered a severely disadvantaged community (SDAC). According to the U.S. Census ACS 2012-2016 data, there are a number of SDACs throughout the Subbasin. See Figure CC-2 for a map of the DACs and SDACs throughout the DeltaMendota Subbasin.
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As noted above, a significant portion of the Subbasin contains DACs. Of the total population of 117,120 within the Subbasin, 80% of the population lives within a DAC, with 93% of the Subbasin’s total geographic area consisting of DACs. Table CC-1 includes the proportion of DACs in the Subbasin based on population and geographic area.
Table CC-1: DACs as a Percentage of the Delta-Mendota Subbasin Area
Geographic Area
(Square Miles)
% Based on
Geographic Area Population
% Based on
Population
DAC (including SDAC) 1,109 93% 93,786 80%
Delta-Mendota Subbasin 1,194 117,120
Table CC-2 includes Census Designated Places that are DACs in the Delta-Mendota Subbasin, with their associated MHIs and percentage of the California MHI from the ACS 5-Year 2012-2016 average. Several DACs in the Subbasin have considerably lower MHI than 80% of the California Statewide MHI and are further designated as Severely Disadvantaged Communities (SDACs). In Table CC-2, SDACs are indicated in bold text. Note that according to the U.S. Department of the Interior Indian Affairs, as of January 2017, there are no listed federally recognized tribes within the Region (Mosley, 2017).
Table CC-2: DAC and SDAC Census Designated Places in Delta-Mendota Subbasin Census
Designated Place
(CDP)
Median
Household
Income
(MHI)
% of CA MHI
City of Dos Palos $36,509 57%
City of Firebaugh $36,181 57%
City of Gustine $37,770 59%
City of Los Banos $45,751 72%
City of Mendota $26,094 41%
City of Newman $52,783 83%
Crows Landing $26,786 42%
Dos Palos Y (CDP) $16,656 26%
Grayson $29,787 47%
Madera County $45,490 74%
Merced County $43,066 70%
Fresno County $45,963 72%
Santa Nella $27,778 44%
South Dos Palos $41,992 66%
Tranquillity $30,441 48%
Volta $48,250 76%
Westley $23,375 37%
Data Sources:
1. U.S. Census ACS data from 2012 to 2016 provided by DWR Mapping Tool.
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Census
Designated Place
(CDP)
Median
Household
Income
(MHI)
% of CA MHI
2. MHI data are from the 2016 Census, and percent of CA MHI is calculated based on the 2012-2016 Statewide MHI. Bold rows indicate severely disadvantaged communities (less than 60% of CA Statewide MHI).
1.4 Economically Disadvantaged Areas within the Delta-Mendota Subbasin An economically distressed area (EDA) is defined by the State of California as a “municipality with a population of 20,000 persons or less, a rural county, or a reasonably isolated and divisible segment of a larger municipality where the segment of the population is 10,000 persons or less, with an annual median household income that is less than 85% of the statewide median household income, and with one or more of the following conditions as determined by the (sic) Department of Water Resources:
1. Financial hardship
2. Unemployment rate at least two percent higher than the statewide average
3. Low population density (CA Assembly, 2014).”
U.S. Census GIS data provided by DWR were used to identify EDAs in the Delta-Mendota Subbasin.
Figure CC-3 shows the location of EDAs within the Delta-Mendota Subbasin A significant portion of the Subbasin contains EDAs. Of the total population of 117,120 within the Subbasin, 87% live in areas that meet EDA Criterion 2, 20% live in areas that meet EDA Criterion 3, and 87% live in areas that meet Criteria 2 or 3. In all, 93% of the geographic area within the Subbasin consists of areas considered to meet either EDA Criteria 2 or 3. Table CC-3 includes the proportion of EDAs in Subbasin based on population and geographic area.
Table CC-3: EDAs as a Percentage of the Delta-Mendota Subbasin Area
Geographic Area
(Square Miles)
% Based on
Geographic Area Population
% Based on
Population
EDA Criterion 2 1,112 93% 102,407 87%
EDA Criterion 3 1,004 84% 23,688 20%
EDA Criteria 2 or 3 1,112 93% 102,407 87%
Delta-Mendota Subbasin 1,194 117,120
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Figure CC-1: Delta-Mendota Subbasin and GSP Regions
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Figure CC-2: Disadvantaged and Severely Disadvantaged Communities in the DeltaMendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-3: Economically Distressed Areas in the Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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2. DELTA-MENDOTA SUBBASIN GOVERNANCE
This section includes information pursuant to Article 5. Plan Contents, Subarticle 1. Administrative Information, § 354.6 (Agency Information) as well as Subarticle 8. Interagency Agreements (§ 357.2 Interbasin Agreements and § 357.4 Coordination Agreements), as required by the Groundwater Sustainability Plan (GSP) Regulations. Agency Contact information for the Delta-Mendota Subbasin and the plan manager is included in this section. The organization and management structure, as well as the legal authority of each Groundwater Sustainability Agency (GSA) in the Delta-Mendota Subbasin, is detailed and accompanied by GSA boundary maps and a description of intra-basin and inter-basin coordination agreements in place for the development and implementation of the GSPs overlying the Delta-Mendota Subbasin.
Agency Contact Information
This Common Chapter to the six GSPs for the Delta-Mendota Subbasin has been prepared in a cooperative manner by the following GSAs in the Delta-Mendota Subbasin:
Northern & Central Delta-Mendota Region GSP
Patterson Irrigation District GSA
West Stanislaus Irrigation District GSA
DM-II GSA
City of Patterson GSA
Northwestern Delta-Mendota GSA
Central Delta-Mendota GSA
Widren Water District GSA
Oro Loma Water District GSA
San Joaquin River Exchange Contractors (SJREC) GSP
San Joaquin River Exchange Contractors Water Authority GSA Turner Island Water District-2 GSA
City of Mendota GSA
City of Firebaugh GSA
City of Los Banos GSA
City of Dos Palos GSA
City of Gustine GSA
City of Newman GSA
Madera County – 3 GSA
Portion of Merced County – Delta-Mendota GSA
Portion of Fresno County Management Area B GSA
Grassland GSP
Grassland GSA
Portion of Merced County – Delta-Mendota GSA
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Aliso Water District GSP
Aliso Water District GSA
Farmers Water District GSP
Farmers Water District GSA
Fresno County GSP
Fresno County Management Area A GSA
Portion of Fresno County Management Area B GSA
The plan areas covered by each of the six Subbasin GSPs is show in Figure CC-1. Figure CC-4 through Figure CC-6 show the location of the GSAs comprising the six GSP regions. These GSAs are coordinating development and implementation of the six GSPs under the Coordination Agreement, as described below in Section 2.1.
The current Plan Manager for the coordinated Delta-Mendota Subbasin GSPs is John Brodie, Water Resources Program Manager for San Luis & Delta-Mendota Water Authority (SLDMWA). Mr. Brodie can be contacted as follows:
Mr. John Brodie, Plan Manager
Delta-Mendota Subbasin
842 6th Street
Los Banos, CA 93635
Phone: (209) 826-1872/ Fax (209) 833-1034
[email protected]
Contact information for each GSP plan administrator can be found in the respective GSPs. The DWR Point of Contact is shown below.
Department of Water Resources Point of Contact
The point of contact for the Delta-Mendota Subbasin is:
Christopher Olvera
Department of Water Resources
[email protected]
(559) 230-3373
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Figure CC-4: GSAs in the Delta-Mendota Subbasin – Stanislaus County Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-5: GSAs in the Delta-Mendota Subbasin – Merced County Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-6: GSAs in the Delta-Mendota Subbasin – Fresno and Madera Counties Delta-Mendota Subbasin Groundwater Sustainability Plan
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2.1 GSA and GSP Coordination and Governance
This section includes a description of intra-basin coordination agreements, which are required where there is more than one GSP prepared for a groundwater basin, and inter-basin coordination agreements, which are optional agreements between neighboring groundwater subbasins, pursuant to Article 8. Interagency Agreements, § 357.4. Coordination Agreements and § 357.2 Interbasin Agreements.
2.1.1 Delta-Mendota Subbasin SGMA Governance Structure
The GSAs within the Delta-Mendota Subbasin adopted and executed a Coordination Agreement on December 12, 2018 to comply with the SGMA requirement that multiple GSAs within a given subbasin must coordinate when developing and implementing their GSPs (see Intra-Agency Coordination subsection above for more information). Additionally, a Cost Sharing Agreement was signed and executed by the same parties on December 12, 2018. Figure CC-5 shows the SGMA governance structure within the Delta-Mendota Subbasin. In addition to the two members appointed to represent each of the Northern & Central Delta-Mendota GSP Region and the San Joaquin River Exchange Contractors (SJREC) GSP Region on the Delta-Mendota Subbasin Coordination Committee as voting members, the Grassland GSP Region, Farmers Water District GSP Region, Fresno County Management Areas A & B GSP Region, and Aliso Water District GSP Region all have appointed one voting member each for a total of eight voting members.
Three working groups were formed under the auspices of the Delta-Mendota Subbasin Coordination Committee: the Technical Working Group, the Communications Working Group and the DMS Working Group. Representatives of each GSP region participate in each working group.
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Table CC-4: Delta-Mendota Subbasin Coordination Committee Members GSP GSA Agency
Coordination Committee Members
Primary Alternate
Northern & Central DeltaMendota Region GSP
Northern Delta Mendota Region Management Committee
Patterson Irrigation District GSA
Patterson Irrigation District
Vince Lucchesi Walt Ward
Twin Oaks Irrigation District
West Stanislaus Irrigation District GSA
West Stanislaus Irrigation District
DM-II GSA
Del Puerto Water District
Oak Flat Water District
City of Patterson GSA City of Patterson Northwestern DeltaMendota GSA Merced County Fresno County Central DeltaMendota Region Management Committee
Central Delta-Mendota GSA
San Luis Water District
Ben Fenters Lacey Kiriakou
Panoche Water District Tranquillity Irrigation District Fresno Slough Water District Eagle Field Water District Pacheco Water District Santa Nella County Water DistrictMercy Springs Water District Merced County Fresno County Widren Water District GSA Widren Water District Oro Loma Water District GSA Oro Loma Water District Delta-Mendota Subbasin Groundwater Sustainability Plan
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GSP GSA Agency
Coordination Committee Members
Primary Alternate
San Joaquin River Exchange Contractors GSP
San Joaquin River Exchange Contractors Water Authority GSA Central California Irrigation District
Jarrett Martin, Alejandro Paolini
Chris White, John Wiersma
Columbia Canal Company Firebaugh Canal Water DistrictSan Luis Canal Company Turner Island Water District-2 GSA Turner Island Water District City of Mendota GSA City of Mendota City of Firebaugh GSA City of Firebaugh City of Los Banos GSA City of Los Banos City of Dos Palos GSA City of Dos Palos City of Gustine GSA City of Gustine City of Newman GSA City of Newman County of Madera – 3 GSA County of Madera Portion of Merced County – Delta-Mendota GSA County of Merced Portion of Fresno County Management Area B GSA County of Fresno Grassland GSP
Grassland GSA
Grassland Water District
Ric Ortega Ken Swanson
Grassland Resource Conservation District
Portion of Merced County Delta-Mendota GSA County of Merced Farmers Water District GSP Farmers Water District GSA Farmers Water District Jim Stilwell Don Peracchi Fresno County GSP Fresno County – Management Area A County of Fresno Buddy Mendes Glenn Allen or Augustine Ramirez Delta-Mendota Subbasin Groundwater Sustainability Plan
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GSP GSA Agency
Coordination Committee Members
Primary Alternate
Fresno County – Management Area B County of Fresno
Aliso Water District GSP Aliso Water District GSA Aliso Water District Joe Hopkins Board Secretary (Ross Franson) Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-7: Governance Structure of the Delta-Mendota Subbasin
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2.1.2 Intra-Basin Coordination
The Delta-Mendota Subbasin Coordination Agreement (Coordination Agreement), effective as of December 12, 2018, has been signed by all participating agencies in the Delta-Mendota Subbasin; a copy of this agreement is included in Appendix A. The purpose of the Agreement, including technical reports to be developed after the initial execution of this Agreement, is to comply with SGMA requirements and to ensure that the multiple GSPs within the Subbasin are developed and implemented utilizing the same datasets, methodologies and assumptions, that the elements of the GSPs are appropriately coordinated to support sustainable subbasin management of groundwater resources, and to ultimately set forth the information necessary to show how the multiple GSPs in the Subbasin will achieve the sustainability goal as determined for the Subbasin in compliance with SGMA and its associated regulations.
A key goal of basin-wide coordination is to ensure that the Subbasin GSPs utilize the same data and methodologies during their plan development and that elements of the Plans necessary to achieve the sustainability goal for the basin are based upon consistent interpretations of the basin setting, as required by SGMA and associated regulations. The Coordination Agreement defines how the coordinated efforts will be achieved and documented, and also sets out the process for identifying the Plan Manager. The Coordination Agreement is part of each individual GSP within the Delta-Mendota Subbasin.
The Coordination Agreement for the Delta-Mendota Subbasin covers the following topics:
1. Purpose of the Agreement, including:
a. Compliance with SGMA and
b. Description of Criteria and Function;
2. General Guidelines, including:
a. Responsibilities of the Parties and
b. Adjudicated or Alternative Plans in the Subbasin;
3. Role of San Luis & Delta-Mendota Water Authority (SLDMWA), including:
a. Agreement to Serve,
b. Reimbursement of SLDMWA, and
c. Termination of SLDMWA’s Services;
4. Responsibilities for Key Functions, including:
a. Coordination Committee,
b. Coordination Committee Officers,
c. Coordination Committee Authorized Action and Limitations, d. Subcommittees and Workgroups,
e. Coordination Committee Meetings, and
f. Voting by Coordination Committee;
5. Approval by Individual Parties;
6. Exchange of Data and Information, including:
a. Exchange of Information and
b. Procedure for Exchange of Information;
7. Methodologies and Assumptions, including:
a. SGMA Coordination Agreements,
b. Pre-GSP Coordination, and
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c. Technical Memoranda Required;
8. Monitoring Network
9. Coordinated Water Budget
10. Coordinated Data Management System
11. Adoption and Use of the Coordination Agreement, including:
a. Coordination of GSPs and
b. GSP and Coordination Agreement Submission;
12. Modification and Termination of the Coordination Agreement, including:
a. Modification or Amendment of Exhibit “A” (Groundwater Sustainability Plan Groups including Participation Percentages),
b. Modification or Amendment of Coordination Agreement, and c. Amendment for Compliance with Law;
13. Withdrawal, Term, and Termination;
14. Procedures for Resolving Conflicts;
15. General Provisions, including:
a. Authority of Signers,
b. Governing Law,
c. Severability,
d. Counterparts, and
e. Good Faith; and
16. Signatories of all Parties
Coordination During GSP Implementation
The Coordination Agreement ensures that the multiple GSAs are working cooperatively and collaboratively to ensure GSPs within the Subbasin are developed and implemented utilizing the same methodologies and assumptions and to ultimately establish the processes necessary to show how the multiple GSPs in the Subbasin will be sustainably managed to achieve the Delta-Mendota Subbasin’s sustainability goal. The Coordination Committee intends to continue to meet and confer following the submittal of the Subbasin’s GSPs and will develop guidelines for GSP implementation between the GSP Groups and update the Coordination Agreement as the Parties to the Agreement deem necessary.
The Coordination Committee will continue meeting regularly following submittal of the Subbasin GSPs in order to develop the guidelines for coordinated implementation of GSPs. The intent of the guidelines will be to outline processes that will ensure the GSAs are progressing toward the Subbasin sustainability goal, while meeting the Annual Reporting requirements or any other requirements agreed upon for purposes of coordination.
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Agency Responsibilities
In meeting the terms of the Coordination Agreement, all Parties (meaning the Delta-Mendota Subbasin GSAs) agree to work collaboratively to meet the objectives of SGMA and the Coordination Agreement.
Each Party to the Agreement is a GSA and acknowledges that it is bound by the terms of the Coordination Agreement as an individual party.
The Parties have established a Coordination Committee to provide a forum to accomplish the coordination obligations of SGMA. The Coordination Committee operates in full compliance with the Brown Act and is composed of a Chairperson and Vice Chairperson, Secretary, Plan Manager, and a GSP Group Representative and Alternate Representative for each of the six GSP groups. The Chairperson and Vice Chairperson are rotated annually among GSP Groups in alphabetical order. The Secretary assumes primary responsibility for Brown Act compliance. The GSP Group Representatives, who are identified in Table CC-4, are selected by each respective GSP Group at the discretion of the respective GSP Group, and such appointments are effective upon providing written notice to the Secretary and to each Group Contact. The Coordination Committee recognizes each GSP Group Representative and GSP Group Alternate Representative until the Group Contact provides written notice of removal and replacement to the Secretary and to every other Group Contact. Each GSP Group is required to promptly fill any vacancy created by the removal of its Representative or Alternate Representative so that each GSP Group has the number of validly designated representatives.
Each GSP Group Representative is entitled to one vote at the Coordination Committee, where the Alternate Representative is authorized to vote in the absence of the GSP Group Representative. The unanimous vote of the GSP Representatives from all GSP Groups is required on most items upon which the Coordination Committee is authorized to act, with the exception of certain ministerial and administrative items. Voting procedures to address a lack of unanimity take place upon a majority vote of a quorum of the Coordination Committee and include straw polls, provisional voting, and delay of voting (see Section 5.6.3 – Voting Procedures to Address Lack of Unanimity of the Coordination Agreement).
Where the law or the Coordination Agreement require separate written approval by each of the Parties, such approval is evidenced in writing by providing the resolution, Motion, or Minutes of their respective Board of Directors to the Secretary of the Coordination Committee. Minutes of the Coordinate Committee are kept and prepared by the Secretary’s appointee and maintained by the Secretary as Coordination Agreement records and are available to the Parties and the public upon request. Meeting agenda and minutes are posted on the Delta-Mendota website (www.deltamendota.org).
The Coordination Committee may appoint subcommittees, working groups, and otherwise direct staff made available by the Parties. Subcommittees or working groups may include qualified individuals possessing the knowledge and expertise to advance the goals of the Coordination Agreement on the topics being addressed by the subcommittee or working group, whether or not such individuals are GSP Group Representatives or Alternate Representatives. Tasks assigned to subcommittees, working groups, or staff made available by the Parties may include developing technical data, supporting information, and/or recommendations on specialized matters to the Coordination Committee. One GSP Group Representative or Alternate Representative is required to vote on behalf of the GSP Group at the subcommittee level. If no GSP Group Representative or Alternate Representative is present, one individual working on a subcommittee on behalf of the Parties in a GSP Group votes on behalf of the GSP Group. Subcommittees report voting results and provide information to the Coordination Committee but are not entitled to make determinations or decisions that are binding on the Parties.
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The Coordination Committee is authorized to act upon the following items:
1. The Coordination Committee reviews, and consistent with the requirements of SGMA, approves the Technical Memoranda that compose the Common Chapter (see Coordinated Data and Methodology);
2. The Coordination Committee is responsible for ongoing review and updating of the Technical Memoranda as needed; assuring submittal of annual reports; providing five-year assessments and recommending any needed revisions to the Coordination Agreement; and providing review and assistance with coordinated projects and programs, once the GSPs have been submitted to and approved by DWR;
3. The Coordination Committee reviews and approves work plans, and in accordance with the budgetary requirements of the respective Parties, approves annual budget estimates of Coordinated Plan Expenses presented by the Secretary and any updates to such estimates provided that such estimates or updates with supporting documentation are circulated to all Parties for comment at least thirty (30) days in advance of the meeting at which the Coordination Committee will consider approval of the annual estimate;
4. The Coordination Committee is authorized to approve changes to Exhibit “A” (Groundwater Sustainability Plan Groups including Participation Percentages) to the Agreement and to recommend amendments to terms of the Agreement;
5. The Coordination Committee may assign work to subcommittees and workgroups as needed, provide guidance and feedback and ensure that subcommittees and workgroups prepare work products in a timely manner;
6. The Coordination Committee directs the Plan Manager in the performance of its duties under SGMA; and
7. The Coordination Committee provides direction to its Officers concerning other administrative and ministerial issues necessary for the fulfillment of the above-enumerated tasks.
Additional information regarding the roles, responsibilities, and duties of the Coordination Committee can be found in Section 5 – Responsibilities for Key Functions of the Coordination Agreement.
Exchange of Information
Timely exchange of information is a critical aspect of GSP coordination. All parties to the Coordination Agreement have agreed to exchange public and non-privileged information through collaboration and/or informal requests made at the Coordination Committee level or through subcommittees designated by the Coordination Committee. To the extent it is necessary to make a written request for information to another Party, each Party designates a representative to respond to information requests and provides the name and contact information of the designee to the Coordination Committee. Requests may be communicated in writing and transmitted in person or by mail, facsimile machine, or other electronic means to the appropriate representative as named in the Coordination Agreement. The designated representative is required to respond in a reasonably timely manner. Nothing in the Agreement shall be construed to prohibit any Party from voluntarily exchanging information with any other Party by any other mechanism separate from the Coordination Committee.
The Parties agree that each GSP Group shall provide the data required to develop the Subbasin-wide coordinated water budget but, unless required by law, will not be required to provide individual well or parcel-level information in order to preserve confidentiality of individuals to the extent authorized by law, including but not limited to Water Code Section 10730.8, subdivision (b). To the extent that a court order,
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subpoena, or the California Public Records Act is applicable to a party, the Party in responding to a request made pursuant to that Act for release of information exchanged from another Party shall notify each other Party in writing of its proposed release of information in order to provide the other Parties with the opportunity to seek a court order preventing such release of information.
Dispute Resolution
Procedures for conflict resolution have been established within the Coordination Agreement. In the event that a dispute arises among Parties as it relates to the Coordination Agreement, the disputing Party or Parties are to provide written notice of the basis of the dispute to the other Parties within thirty (30) calendar days of the discovery of the events giving rise to the dispute. Within thirty (30) days after such written notice, all interested Parties are to meet and confer in good faith to informally resolve the dispute.
All disputes that are not resolved informally shall be settled by arbitration. In such an event, within ten (10) days following the failed informal proceedings, each interested Party is to nominate and circulate to all other interested Parties the name of one arbitrator. Within ten (10) days following the nominations, the interested Parties are to rank their top three among all nominated arbitrators, awarding three points to the top choice, two points to the second choice, and one point to the third choice and zero points to all others.
Each interested Party will then forward its tally to the Secretary, who tabulates the points and notifies the interested Parties of the arbitrator with the highest cumulative score, who shall be the selected arbitrator.
The Secretary may also develop procedures for approval by the Parties for selection of an arbitrator in the case of tie votes or in order to replace the selected arbitrator in the event such arbitrator declines to act.
The arbitration is to be administered in accordance with the procedures set forth in the California Code of Civil Procedure, Section 1280, et seq., and of any state or local rules then in effect for arbitration pursuant to said section. Upon completion of arbitration, if the controversy has not been resolved, any Party may exercise all rights to bring legal action relating to the controversy.
Coordinated Data and Methodology
Pursuant to SGMA, the Coordination Agreement ensures that the individual GSPs utilize the same data and methodologies for developing assumptions used to determine: 1) groundwater elevation; 2) groundwater extraction data; 3) surface water supply; 4) total water use; 5) changes in groundwater storage; 6) water budgets; and 7) sustainable yield. The Parties have agreed to develop agreed-upon methodologies and assumptions for the aforementioned items prior to or concurrent with the individual development of GSPs. This development is facilitated through the Coordination Committee’s delegation to a subcommittee or working group of the technical staff provided by some or all of the Parties. The basis upon which the methodologies and assumptions have been developed includes existing data/information, best management practices, and/or best modeled or projected data available and may include consultation with DWR as appropriate.
The data and methodologies for assumptions described in Water Code §10727.6 and Title 23, California Code of Regulations, Section 357.4 to prepare coordinated plans are set forth in Technical Memoranda prepared by the Coordination Committee for each of the following elements: Data and Assumptions; Hydrogeologic Conceptual Model; Coordinated Water Budgets; Sustainable Management Criteria (SMC); Coordinated Monitoring Network; Coordinated Data Management System, and Adoption and Use of the Coordination Agreement. The Technical Memoranda have been subject to the unanimous approval of the Coordination Committee and once approved, have been attached to and incorporated by reference into the Coordination Agreement without formal amendment of the Coordination Agreement being required. The Parties have agreed that they will not submit this Coordination Agreement to DWR until the Technical Memoranda described herein have been added to the Coordination Agreement. The Technical Memoranda created pursuant to the Coordination Agreement are to be utilized by the Parties during the development and implementation of their individual GSPs in order to assure coordination of
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the GSPs is in compliance with SGMA. The Technical Memoranda have been included as an appendix to this GSP as a part of the Common Chapter.
Plan Implementation and Submittal
Under the Coordination Agreement, the Parties have agreed to submit their respective GSPs to DWR through the Coordination Committee and Plan Manager, in accordance with all applicable requirements.
Subject to the subsequent attachment of the Technical Memoranda as appendices to the Common Chapter, the Parties intend that the described Coordination Agreement fulfill the requirements of providing an explanation of how the GSPs implemented together satisfy the requirements of SGMA for the entire Subbasin. The Coordination Agreement does not otherwise affect each Party’s responsibility to implement the terms of its respective GSP in accordance with SGMA. Rather, this Coordination Agreement is the mechanism through which the Parties will coordinate their respective GSPs to the extent necessary to ensure that such GSP coordination complies with SGMA.
Each Party is responsible for ensuring that its own GSP complies with the statutory requirements of SGMA, including but not limited to the filing deadline. The Parties to this Coordination Agreement intend that their individual GSPs be coordinated together in order to satisfy the requirements of SGMA and to be in substantial compliance with the California Code of Regulations. The collective GSPs will satisfy the requirements of Water Code Sections 10727.2 and 10727.4 by providing a description of the physical setting and characteristics of the separate aquifer systems within the Subbasin, the measurable objectives for each such GSP, interim milestones (IMs), and monitoring protocols that together provide a detailed description of how the Subbasin as a whole will be sustainably managed.
The Parties agree to submit their respective GSPs to DWR through the Coordination Committee and Plan Manager, in accordance with all applicable requirements. The Coordination Committee is responsible for assuring submittal of annual reports, five-year updates, and for providing assessments recommending any needed revisions to the Coordination Agreement.
Coordinated Data Management System
The Delta-Mendota Subbasin GSAs have developed and will maintain a coordinated Data Management System that is capable of storing and reporting information relevant to the reporting requirements and/or implementation of the GSPs and monitoring network of the Subbasin.
The Parties may also develop and maintain separate Data Management Systems. Each separate Data Management System developed for each GSP will store information related to implementation of each individual GSP, monitoring network data and monitoring sites requirements, and water budget data requirements. Each system will be capable of reporting all pertinent information to the Coordination Committee. After providing the Coordination Committee with data from the individual GSPs, the Coordination Committee will ensure the data are stored and managed in a coordinated manner throughout the Subbasin and reported to DWR on an annual basis.
Adjudicated Areas and Alternative Plans
There are no adjudicated areas within the Delta-Mendota Subbasin, and no Alternative Plans have been submitted by the local agencies within the Subbasin.
Legal Bindings of the Delta-Mendota Subbasin Coordination Agreement The Coordination Agreement, as contained herein, is reflected in the same manner and form as in the six Subbasin GSPs. All parties understand that the Delta-Mendota Subbasin Coordination Agreement is part of the GSPs for participating Subbasin GSAs and will be a primary mechanism by which the six Subbasin
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GSPs will be implemented in a coordinated fashion. Further, all parties to the Coordination Agreement understand that DWR will evaluate the agreement for compliance with the procedural and technical requirements of GSP Regulations §357.4 (Coordination Agreement) to ensure that the agreement is binding on all parties and that provisions of the agreement are sufficient to address any disputes between or among parties to the agreement.
The Coordination Agreement will continue to be the framework under which the six Delta-Mendota Subbasin GSPs will be implemented and will be reviewed as part of the five-year assessment and revised as necessary, dated, and signed by all parties.
2.1.3 Inter-basin Agreements
SLDMWA, on behalf of the Northern and Central Delta-Mendota Regions, and the SJREC GSA executed inter-basin data sharing agreements with Westlands Water District (the lead entity encompassing the adjoining Westside Subbasin). The purpose of the agreement is to establish a set of common assumptions on groundwater conditions on either side of the boundary between the Westside Subbasin and the DeltaMendota Subbasin to be used for the development of GSPs in support of implementation of SGMA. In this agreement, the parties agree to provide each other with recorded, measured, estimated, and/or simulated modeling data located within five (5) miles of the boundary between the Westside Subbasin and the Delta-Mendota Subbasin. A list of data types to be shared between the parties to the agreement can be found in Appendix D.
Data provided under this agreement are understood to be shared with consultants and other stakeholders in the respective basins (Delta-Mendota Subbasin and Westside Subbasin), and that the information will be made public through the development of the respective Parties’ (meaning SLDMWA/SJREC and Westlands Water District) GSPs and the supporting documentation of the GSPs. Other than publishing information for those purposes, neither Party will disclose the other Party’s information to any third party, except if the other Party determines, at its sole discretion, the disclosure is required by law. Each Party may review preliminary results before publishing the information.
It is recognized that many of the sustainability indicators, notably groundwater quality, inelastic land subsidence and change in storage, are regional issues that may require future inter-basin discussions and coordination. Memorandum of Intent (MOI) are being discussed with the surrounding subbasins to demonstrate/confirm the subbasins’ desires to coordinate during GSP implementation. These agreements, to be discussed further following submittal of GSPs, will allow for thoughtful consideration of the intent, structure, and need for future coordination with respect to data collection, reporting, regular meetings, and updates prior to annual reporting.
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3. DELTA-MENDOTA SUBBASIN PLAN AREA
This section describes the Delta-Mendota Subbasin, including major streams and creeks, institutional entities, agricultural and urban land uses, locations of state lands (including wetlands), and geographic boundaries of surface water runoff areas. The reader is referred to the individual Subbasin GSPs for descriptions of existing surface water and groundwater monitoring programs, existing water management programs, and general plans in the individual GSP Plan Areas. The information contained in this section reflects information from publicly available sources and may not reflect all information that will be used for GSP technical analysis.
This section of the GSP satisfies Section 354.8 of the SGMA regulations.
3.1 Plan Area Definition
The Plan Area for the six coordinated GSPs is the Delta-Mendota Subbasin (DWR Basin 5-022.07). As previously noted, the Delta-Mendota Subbasin is one of nine subbasins that lie completely within the San Joaquin Valley Hydrologic Region and adjoins the following subbasins (Figure CC-8):
Tracy
Eastern San Joaquin
Modesto
Turlock
Merced
Chowchilla
Madera
Kings
Westside
As described in California’s Groundwater, DWR Bulletin 1188 (2016), the Delta-Mendota Subbasin is in the San Joaquin Valley Groundwater Basin, located along the western edge of the San Joaquin Valley and includes portions of San Joaquin, Stanislaus, Merced, Fresno, San Benito, and Madera Counties. The northern boundary begins just south of Tracy in San Joaquin County, and the eastern boundary generally follows the San Joaquin River and Fresno Slough. The southern boundary is near the small town of San Joaquin, and the Subbasin is bounded on the west by the Coast Range. The Subbasin boundaries are further described in Section 4.1.5, Basin Boundaries, and is shown in relation to each of the six counties in Figure CC-9.
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Figure CC-8: Neighboring Subbasins of the Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-9: Delta-Mendota Groundwater Subbasin Plan Area Delta-Mendota Subbasin Groundwater Sustainability Plan
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3.2 Plan Area Setting
As previously noted, the Delta-Mendota Subbasin lies along the western margin of the San Joaquin Valley. This valley is part of the large, northwest-to-southeast-trending asymmetric trough of the Central Valley, which has been filled with up to six vertical miles of sediment. This sediment includes both marine and continental deposits ranging in age from Jurassic to Holocene. The San Joaquin Valley lies between the Coast Range Mountains on the west and the Sierra Nevada on the east and extends northwestward from the San Emigdo and Tehachapi Mountains to the Sacramento-San Joaquin Delta (Delta) near the City of Stockton. The San Joaquin Valley is 250 miles long and 50 to 60 miles wide. The relatively flat alluvial floor is interrupted occasionally by low hills. Foothills adjacent on the west are composed of folded and faulted beds of mainly marine shale in the north and sandstone and shale in the south.
The San Joaquin Valley floor is divided into several geomorphic land types, including dissected uplands, low alluvial fans and plains, river floodplains and channels, and overflow lands and lake bottoms.
Alluvial plains cover most of the valley floor and comprise some of the most intensely developed agricultural lands in the San Joaquin Valley. In general, alluvial sediments of the western and southern parts of the San Joaquin Valley tend to have lower permeability than east side deposits.
This section provides additional information relating to water resources in and around the Delta-Mendota Subbasin.
Watersheds
The Delta-Mendota Subbasin lies in the Middle San Joaquin-Lower Merced-Lower Stanislaus watershed and the Middle San Joaquin-Lower Chowchilla watershed (Figure CC-10). Historically, the San Joaquin Valley Basin was a large floodplain of the San Joaquin River that supported vast expanses of permanent and seasonal marshes, lakes, and riparian areas. Approximately 90 percent of the basin’s wetlands have been lost, with approximately 58,000 flooded acres remaining on State, federal and private wildlife refuges. Approximately 100,000 acres of managed wetland, upland and riparian habitat is found within the Grassland Plan area, and together with the 12,000-acre Mendota Wildlife Area (found in the Fresno County Plan area), encompasses the vast majority of the remaining wetlands found in the basin (Figure CC-11).
The San Joaquin River Basin (Basin) includes the entire area drained by the San Joaquin River. The San Joaquin River Basin drains 13,513 square miles (mi2
) before it flows into the Sacramento-San Joaquin
Delta near the town of Vernalis. The Merced, Tuolumne and Stanislaus Rivers are the three major tributaries that join the mainstream San Joaquin River from the east before it flows into the Delta.
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Figure CC-10: Local Watersheds
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Figure CC-11: Wildlife Refuges and Wetland Habitat Areas in the Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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Surface Water Use
Surface water is a primary water supply for agriculture within the Delta-Mendota Subbasin. Surface water supplies are brought into the Subbasin using an extensive series of water systems relied upon by multiple water agencies, cities, and private water users. Major water-related infrastructure in the Subbasin includes the facilities required to deliver Central Valley Project (CVP) supplies to CVP water supply contractors, in addition to key infrastructure of the State Water Project (SWP) utilized to deliver water to SWP water supply contractors and surface water diversions (e.g., intakes) to divert and distribute water from the San Joaquin and Kings Rivers.
The San Luis & Delta-Mendota Water Authority (SLDMWA) is a joint powers authority consisting of 28 member agencies that provide water to approximately 1.2 million acres of highly productive farmland, 2 million California residents, and millions of waterfowl dependent upon the nearly 200,000 acres of managed wetlands within this area of the Pacific Flyway. The SLDMWA operates and maintains portions of the CVP, including the Delta Cross Channel, the C.W. “Bill” Jones Pumping Plant, the Delta-Mendota Canal (DMC), O’Neill Pumping-Generating Plant, and the San Luis Drain, and provides emergency assistance when requested on the Delta Cross Channel and the Tracy Fish Collection Facility. The California Department of Water Resources (DWR) operates and maintains the SWP facilities, designed to deliver nearly 4.2 million acre-feet of water per year to 29 long-term SWP water supply contractors. Joint federal-state facilities include the California Aqueduct, Banks Pumping Plant, O’Neill Dam and Forebay, Sisk Dam and San Luis Reservoir, and Dos Amigos Pumping Plant. Surface water diversion facilities are owned and operated by individual water and irrigation districts and typically include some form of intake (e.g., fish screen, open water intake, flumes) plus facilities to convey the diverted surface water to a distribution system.
Groundwater Use
Groundwater is a key component of water supplies in the Delta-Mendota Subbasin. To protect the longterm sustainability of groundwater resources, pumping has significantly reduced in past years (2017- 2019), allowing the groundwater levels in the Subbasin to recover to some extent. During the most recent drought period, groundwater was heavily relied upon throughout the Subbasin for irrigation as surface water deliveries were significantly severely reduced for many water users (especially those with junior surface water rights), resulting in increased groundwater pumping.
There are many communities within the Subbasin that are partially or completely reliant on groundwater for municipal and domestic water supplies, including the cities of Patterson, Newman, Gustine, Los Banos, Firebaugh, and Mendota and the communities of Grayson, Westley, Crows Landing, Santa Nella, Volta, Dos Palos Y, and Tranquillity (Figure CC-12). Other unincorporated areas of the Subbasin also rely on groundwater as the sole water supply source. There are several areas of de minimis groundwater extractors in the Subbasin, which are defined as well owners who extracts two acre-feet or less per year from a parcel for domestic purposes (SWRCB, n.d. (a)).
Figure CC-13, Figure CC-14, and Figure CC-15 show the density per square mile (PLSS Section) of domestic, production, and public wells in the Delta-Mendota Subbasin as identified by DWR’s Well Completion Report Map Application. Domestic wells are defined as individual domestic wells which supply water for the domestic needs of an individual residence or systems of four or less service connections (DWR, 1981). Within the Delta-Mendota Subbasin, the majority of PLSS Sections contain five or fewer domestic wells (Figure CC-13). Production well statistics include wells that are designated as irrigation, municipal, public, and industrial on well completion reports, generally indicating wells designed to obtain water from productive zones containing good-quality water (DWR, 1991). The majority of PLSS Sections in the Subbasin contain only zero, one, or two production wells (Figure CC- Delta-Mendota Subbasin Groundwater Sustainability Plan
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14). The highest concentration of production wells can be found in the south of the Subbasin, near Mendota. Public wells are defined as wells that provide water for human consumption to 15 or more connections or regularly serves 25 or more people daily for at least 60 days out of the year (SWRCB, n.d. (b)). Compared to domestic and production wells, public wells are less common in the Subbasin. The status of the wells (e.g., active, abandoned, destroyed) contained in the DWR Well Completion Report Map Application has not been independently confirmed. Additionally, the reader is referred to each of the six Subbasin GSPs for more information regarding wells in the Delta-Mendota Subbasin.
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Figure CC-12: Communities Dependent on Groundwater
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Figure CC-13: Domestic Well Density in the Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-14: Production Well Density in the Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-15: Public Well Density in the Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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Flood Management
In general, the Delta-Mendota Subbasin slopes toward the San Joaquin River with steeper slopes along the western boundary (near the Coast Range), tapering off closer to the San Joaquin River. The flood management system in the San Joaquin Valley includes reservoirs to regulate snowmelt from elevations greater than 5,000 feet, bypasses at lower elevations, and levees that line major rivers.
Severe rain events in 1997/98, 2005/2006, 2011 and 2017 flooded communities, agricultural lands and refuges adjacent to the San Joaquin River in the Delta-Mendota Subbasin (specifically the communities of Firebaugh, Newman, Gustine and Mendota) and produced some localized flooding of farmland and refuges caused by runoff impoundment by elevated canal banks. Based on the recent historical events, the primary threat of flooding to urban areas will be for those along (and immediately adjacent to) the San Joaquin River. Areas within the 100-year floodplain within the Subbasin are shown in Figure CC-16.
Major Land Use Divisions
The Delta-Mendota Subbasin consists mostly of agricultural land use types (Figure CC-17). Typical land uses are described in the following sections and consist predominantly of the following:
Pasture/Rangeland
Agricultural Land (including rice, field crops and grains) Deciduous Forest
Idle and Retired Farmland/Rangeland
Riparian/Wetland
Urban
The primary land use planning entities in the Delta-Mendota Subbasin include San Joaquin, Stanislaus, Merced, Fresno, and Madera Counties, as well as the cities of Patterson, Newman, Gustine, Los Banos, Dos Palos, Firebaugh, and Mendota, and Community of Santa Nella, as shown in Figure CC-18.
Pasture/Rangeland
Grasslands in the Central Valley were originally dominated by native perennial grasses such as needlegrass and alkali sacaton. Currently, grassland vegetation is characterized by a predominance of annual or perennial grasses in an area with few or no trees and shrubs. Annual grasses found in grassland vegetation include wild oats, soft chess, ripgut grass, medusa head, wild barley, red brome, and slender fescue. Perennial grasses found in grassland vegetation are purple needlegrass, Idaho fescue, and California oatgrass. Forbs commonly encountered in grassland vegetation include long-beaked filaree, redstem filaree, dove weed, clovers, Mariposa lilies, popcornflower, and California poppy. Vernal pools found in small depressions with an underlying impermeable layer are isolated wetlands within grassland vegetation. Pastures can consist of both irrigated and unirrigated lands dominated by perennial grasses used predominantly for grazing.
Rangeland communities are composed of similar grasses, grass-like plants, forbs, or shrubs which are grazed by livestock. Rangelands are classified into three basic types: shrub and brush rangeland, mixed rangeland, and herbaceous rangeland. The shrub and brush rangeland are dominated by woody vegetation and is typically found in arid and semiarid regions. Mixed rangelands are ecosystems where more than one-third of the land supports a mixture of herbaceous species and shrub or brush rangeland species.
Herbaceous rangelands are dominated by naturally occurring grasses and forbs as well as some areas that have been modified to include grasses and forbs as their principal cover. Rangelands are, by definition, areas where a variety of commercial livestock are actively maintained.
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Agricultural Land
General agricultural types occurring in the Delta-Mendota Subbasin include row crops, grains, orchards, and vineyards. Management of agricultural lands often includes intensive management, including soil preparation activities, crop rotation, grazing, and the use of chemicals.
Row Crops
Most row crops grown in the San Joaquin Valley and harvested for food are annual species and are managed with a crop rotation system. During the year, several different crops may be produced on a given parcel of land either concurrently or in succession. Typical crops grown in the Delta-Mendota Subbasin include tomatoes, melons, grain crops (such as barley, wheat, corn, and oats), rice, cotton, and beans.
Orchards and Vineyards
Orchard and vineyards consist of cultivated fruit or nut-bearing trees or grapevines. Orchards are typically open, single-species, tree-dominated habitats and are planted in a uniform pattern and intensively managed. Understory vegetation is usually sparse. Vineyards are typically managed in a similar manner for producing grapes for wine and/or direct consumption.
Deciduous Forest
Deciduous forests are composed of trees that lose their leaves in the winter. These include species such as the various California oaks, California buckeye, Fremont Cottonwoods, Goodding Willows, and California Sycamores. The interior live oak, which is not deciduous, is also found in deciduous forests.
Valley oak woodlands are found in the Sacramento and San Joaquin Valleys and usually occur below elevations of 2,000 feet.
Idle or Retired Farmland/Rangeland
Lands of this category are similar to abandoned farmlands in ruderal (disturbed) areas. Plants on these parcels may consist of either native and/or non-native species.
Riparian/Wetland
Riparian and wetland communities are both natural and man-made. Managed wetlands are classified as riparian and are flooded for overwintering migratory bird habitat. In the spring the wetlands are drained to promote grasses such as swamp timothy and watergrass which are an important waterfowl food supply.
Although some grazing continues on managed wetlands, historically, many of these lands were irrigated and used as rangeland throughout the summer months. Today, managed wetlands are irrigated in the spring to maximize wetland productivity and provide nesting and sensitive species habitat. Managed wetlands also contain emergent vegetation such as cattail and tule and are often adjacent to riparian corridors.
Urban
Urban land uses include cities and smaller communities, in addition to other lands used for industrial and/or commercial practices.
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Figure CC-16: 100-Year Floodplain, Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-17: Typical Land Use
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Figure CC-18: Land Use Planning Entities
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Regional Economic Issues and Trends
The western San Joaquin Valley is a highly agricultural region. There are no large cities or industries in the Subbasin to provide an alternative economic base. The economy of this region is predominately driven by agricultural production and therefore, the availability of surface water supplies (predominantly in the form of CVP agricultural water and diversions from the San Joaquin and Kings Rivers) is an essential element to the economic health of the region. Other uses of surface water in the Subbasin are used for M&I purposes and wildlife refuge water supply.
Depending on water supply conditions, about 800,000 acres in the Delta-Mendota Subbasin are partially or solely irrigated with surface water. Other economic base industries include travel on the Interstate 5 (I5) corridor, some petroleum extraction, and tourism. State, federal, and private wildlife refuges benefit local economies by attracting hunters, anglers, outdoor recreationists to the region. Managed wetland water conveyance infrastructure is maintained and improved by many contractors and local agency staff.
Large scale conveyance improvements and habitat restoration projects, including mitigation banks, are also common throughout the Subbasin. M&I water use, which is a small share of total water use in the Subbasin, occurs primarily within the cities and smaller communities. The largest M&I use areas in the Delta-Mendota Subbasin, based on 2018 population estimates from the U.S. Census Bureau, are the cities of Patterson (population 22,352) and Los Banos (population 30,074) (U.S. Census Bureau, 2017).
All communities within the Delta-Mendota Subbasin have economies greatly dependent on agricultural production. These communities include Patterson, Tranquillity, Grayson, Mendota, Firebaugh, Dos Palos, Los Banos, Santa Nella, Newman, Gustine, Crows Landing, and Westley. All of these communities are strongly affected by the reliability of agricultural water supplies. Some of them are dependent upon groundwater for M&I use.
Plan Area Jurisdictional Boundaries
Jurisdictional areas within the Delta-Mendota Subbasin include counties, cities, water districts, irrigation districts, mutual water companies, and federal and state agencies. There are no federal- or staterecognized tribal communities in the Subbasin. Federal and State Lands are shown in Figure CC-19.
More detail on specific jurisdictional areas within each GSP area can be found in the respective GSP.
In general, all municipal, water/irrigation districts and counties within the Delta-Mendota Subbasin are participating in GSP development either as a separate GSA or as members of a GSA. The California Department of Fish and Wildlife boundaries and the U.S. Fish and Wildlife Service boundaries overlay the wildlife refuges and areas and state parks within the Subbasin. DWR manages the SWP and the California Aqueduct, and the U.S. Bureau of Reclamation (USBR), through the SLDMWA, manages the CVP and the Delta-Mendota Canal. The California Department of Transportation (Caltrans) is responsible for managing the State and Interstate highways in the Subbasin, including Interstate- (I-) 5, and State Highways 132, 33, 140, 152, and 165.
Figure CC-9 depicts the Subbasin’s extent relative to the boundaries of the various counties that overlie the Subbasin. Merced County has jurisdiction over the largest portion of the Subbasin (525 square miles), in the central portion of the Subbasin. Stanislaus County has jurisdiction over most of the area on the northern end of the Subbasin (covering 223 square miles). Fresno and Madera Counties have jurisdiction over the southern extent of the Delta-Mendota Subbasin (400 square miles). Finally, San Benito County covers the smallest portion of the Subbasin (5 square miles) in the southwestern portion of the Subbasin near San Luis Reservoir.
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Figure CC-19: Federal and State Lands
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Land Use Elements
Land use in the Delta-Mendota Subbasin is predominantly agricultural with wildlife habitat areas and areas of municipal, industrial, and commercial use. Predominant crops grown in the region include grain and hay crops, nut and fruit trees, and row crops. Figure CC-20 shows the distribution of different land use types across the Delta-Mendota Subbasin.
Conjunctive use of surface water and groundwater is practiced throughout much of the Delta-Mendota Subbasin. Urban centers, such as the City of Patterson, and most unincorporated county areas rely solely on groundwater for their water supplies. Several water and irrigation districts hold water rights to divert from the San Joaquin River and/or the Kings Rivers. Other water purveyors receive water from the CVP and use groundwater and non-CVP-acquired surface waters to supplement demand, while some water districts rely solely on groundwater for their supplies. Refer to each GSP for detailed discussions of the water sources used by each agricultural, wetland, and urban water supplier.
Agriculture is the predominant water use sector throughout the Delta-Mendota Subbasin (Figure CC-20).
Urban water uses are mostly concentrated within and surrounding cities (such as Patterson and Los Banos). Non-irrigated land includes any idle or native riparian land classifications, which are scattered throughout the Regions.
3.3 General Plans in Plan Area
Within each GSP, General Plans and/or Community Specific Plans overlie the area. These include County general plans for Fresno, Merced, San Benito, San Joaquin, Stanislaus, and Madera Counties, and specific plans for cities and communities. Each GSP contains a detailed list of General Plan policies and objectives relevant to water resources management in the applicable GSP area. Refer to discussions in the individual GSPs which satisfy §354.8(f) of the GSP Emergency Regulations under SGMA.
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Figure CC-20: 2014 Land Use in the Delta-Mendota Subbasin Delta-Mendota Subbasin Groundwater Sustainability Plan
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3.4 Existing Land Use Plans and Impacts to Sustainable Groundwater Management
Numerous policies in each County’s and Community’s General Plan compliment the GSPs’ plans to conserve and sustainably manage groundwater resources. In general, the County and City General Plans guide future growth and development (and associated demands) within their respective jurisdictional areas. This additional growth may impact groundwater sustainability by placing additional demands on groundwater resources in an area where surface water resources are scarce or are otherwise unavailable.
The General Plans also promote water conservation (in both the urban and agricultural sectors), which could potentially offset the additional demands associated with future urban development. In addition to conservation, some (though not all) General Plans promote groundwater recharge, the protection of recharge areas and wetlands, and the use of water transfers to further benefit groundwater sustainability.
Most General Plans within the Delta-Mendota Subbasin include goals focused on preserving agriculture, efficient use of existing and future water sources in both the urban and agricultural sectors, connecting smaller rural communities to larger water systems, and water quality protection. With respect to the protection of water quality and groundwater dependent ecosystems, the General Plans generally protect riparian and wetland habitats, encourage the protection of water quality (including through the remediation of contamination that may impact groundwater quality, requiring the use of septic systems in rural areas that are designed to be protective of groundwater quality and/or the use of community wastewater systems in urban areas), and promote flood control and management (including the associated impacts of erosion and sedimentation of surface water-courses).
The Fresno County General Plan, in particular, promotes sustainability by managing new wells in urban areas, supporting monitoring of water resources and associated habitats, and through the formation of a water resources document repository.
While the magnitude of impacts of these policies over the planning and implementation horizon are not known, such policies have been considered in this GSP, primarily through the use of the General Plans and associated zoning maps to identify future land use types and projected growth areas. These General Plans and mapping were used along with available water master plans, urban water management plans, agricultural water management plans, and other relevant planning documents to determine projected future land use and estimate future water demands by land use sector for use in the projected future water budgets.
Just as the General Plans complement the GSPs, the GSPs in the Delta-Mendota Subbasin may influence the General Plans’ goals and policies. Sustainable management of groundwater resources through a GSP may change the pace, location, and type of development and/or land use that will occur in the Subbasin.
GSP implementation is anticipated to be consistent with the General Plans’ goals to sustainably manage land development and water resources in the Subbasin.
3.5 Existing Water Resources Monitoring and Management Programs As required by §354.8I and (d) of the GSP Emergency Regulations, the following section describes key existing water resources-related management and monitoring programs, and a discussion of how these programs will either impact GSP implementation and/or will be incorporated into the GSPs. The information shown below is a high-level summary of key existing programs; please see the individual GSPs for additional relevant management and monitoring programs.
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Irrigated Lands Regulatory Program (ILRP)
In 1999, the California Legislature passed Senate Bill 390, which eliminated a blanket waiver of water quality regulations for agricultural waste discharges. The Bill required the Regional Water Quality Control Boards to develop a program to regulate agricultural lands under the Porter-Cologne Water Quality Control Act. In 2003, the Central Valley Regional Water Quality Control Board (CV-RWQCB) issued an order that sets Waste Discharge Requirements (WDRs) for irrigated lands to protect both surface and groundwater throughout the Central Valley, primarily to address nitrates, pesticides, and sediment discharge. The resulting Irrigated Lands Regulatory Program (ILRP) regulates wastes from commercial irrigated lands that discharge into surface and groundwater. The program is administered by the CV-RWQCB working directly with a regional or crop-based coalition as well as directly with irrigators. The goal of the ILRP is to protect surface water and groundwater and to reduce impacts of irrigated agricultural discharges to waters of the State. As a result of the ILRP, monitoring reports, assessment reports, management plans, surface water quality data, and groundwater quality data are made available to the public.
Implementation of the IRLP in the Delta-Mendota Subbasin is managed primarily by the Westside San Joaquin River Watershed Coalition and the Grassland Drainage Area Coalition under the San Joaquin Valley Drainage Authority, a California Joint Powers Authority (JPA). This region specifically emphasizes nitrogen, sediment, and erosion control.
CV-SALTS
The Central Valley Salinity Alternatives for Long-Term Sustainability (CV-SALTS) is an initiative to reduce salt and nitrate impacts, restore groundwater quality, and provide safe drinking water supplies.
Developed by a group of stakeholders (federal, state, and local agencies, dischargers and growers, and environmental groups) called the Central Valley Salinity Coalition, the Central Valley Salt and Nitrate Management Plan (SNMP) was released in 2017.
The Central Valley SNMP recommends revised and flexible regulations for existing Basin Plans and includes recommended interim solutions for salt and nutrient management in high priority basins in addition to long-term salt management strategies. Under the Central Valley SNMP, dischargers are provided two compliance pathways: (1) traditional permitting as an individual discharger or as a coalition (i.e., irrigated lands coalition), or (2) groundwater management zone permitting. Zone permitting allows dischargers to work as a collective in collaboration with the CV-RWQCB to provide safe drinking water with the option to extend time to achieve nitrogen balance. At this time, the Central Valley SNMP is not currently enforced.
Integrated Regional Water Management Program
Three Integrated Regional Water Management Plans (IRWMPs) overlie the Delta-Mendota Subbasin.
The Westside-San Joaquin IRWMP covers most of the Subbasin, while smaller portions of the Subbasin are covered by the East Stanislaus and Madera IRWM Plans.
Integrated Regional Water Management (IRWM) is a collaborative effort to identify and implement water management solutions on a regional scale that increase regional self-reliance, reduce conflict, and manage water to concurrently achieve social, environmental, and economic objectives. Developed by Regional Water Management Groups, the IRWMPs seek to deliver higher value for investments in water resources and management by considering all interests, providing multiple benefits, and working across jurisdictional boundaries. Examples of multiple benefits include improved water quality, better flood management, restored and enhanced ecosystems, and more reliable surface and groundwater supplies.
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Please see the individual GSPs for additional details regarding the IRWM program in their GSP Plan areas.
California State Groundwater Elevation Monitoring Program (CASGEM) Since 2009, the California Statewide Groundwater Elevation Monitoring (CASGEM) Program has tracked seasonal and long-term groundwater elevation trends in groundwater basins statewide. The program’s mission is to establish a permanent, locally-managed program of regular and systematic monitoring in all of California’s alluvial groundwater basins. This early attempt to monitor groundwater continues to exist as a tool to help achieve the goals set out under the Sustainable Groundwater Management Act (SGMA) with mandatory annual water elevation monitoring and reporting.
San Joaquin River Restoration Program (SJRR)
The San Joaquin River Restoration Program (SJRRP) is a comprehensive, long-term effort to restore flows to the San Joaquin River from Friant Dam to the confluence of Merced River and restore a selfsustaining Chinook salmon fishery in the river while reducing or avoiding adverse water supply impacts from Restoration Flows. The program has two general goals resulting from the San Joaquin River Restoration Settlement reached in 2006:
Restoration: To restore and maintain fish populations in “good condition” in the main stem of the San Joaquin River below Friant Dam to the confluence of the Merced River, including naturally reproducing and self-sustaining populations of salmon and other fish. Water Management: To reduce or avoid adverse water supply impacts to all of the Friant Division long-term contractors that may result from the Interim Flows and Restoration Flows provided for in the Settlement.
The program includes the implementation of projects, reintroduction activities and associated monitoring to assess progress towards achieving the Settlement goals.
USGS Land Subsidence Monitoring
The USGS maintains and monitors a large system of monitoring locations nationwide using interferometric synthetic aperture radar (InSAR), continuous GPS (CGPS) measurements, campaign global positioning system (GPS) surveying, and spirit-leveling surveying. Aquifer-system compaction is measured by using extensometers to aid in the understanding of the depths at which compaction is occurring. The USGS shares these results to support decision making relative to groundwater basin management with the goal of minimizing future inelastic land subsidence.
3.6 County Well Construction/Destruction Standards and Permitting DWR has developed well standards for the state per California Water Code Sections 13700 to 13806.
These standards have been adopted by the State Water Resources Control Board (SWRCB) into a statewide model well ordinance (Resolution No. 89-98) for use by the Regional Boards for enforcing well construction standards where no local well design ordinance exists that meets or exceeds the DWR standards. DWR’s Well Standards are presented in Bulletin 74-81 and Bulletin 74-90.
Each GSP lists the counties within their GSP Plan areas and the respective permitting agencies and local ordinances for well construction and destruction standards. Discussion of these standards and the Delta-Mendota Subbasin Groundwater Sustainability Plan
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respective permitting process as well as well abandonment and destruction procedures can be found in the individual GSPs.
3.7 Existing and Planned Conjunctive Use Programs
Conjunctive use programs in the Subbasin are currently implemented and planned by single agencies as well as through multi-agency partnerships. Maximizing the beneficial use of surface water, groundwater, and recycled water resources is of critical concern to water managers throughout the Delta-Mendota Subbasin with the ultimate goal of using all of these water sources more efficiently to avoid overdraft and to sustainably manage groundwater resources. Each GSP describes efforts to utilize existing water resources conjunctively and demonstrate feasibility to continue to implement conjunctive use projects in the future. These may include projects such as groundwater recharge and conveyance facilities, new wells, improved monitoring systems, improved delivery efficiency, water recycling, and water quality improvements and treatment.
Underground recharge and storage occur throughout the Delta-Mendota Subbasin through stormwater applied water and managed wetland recharge. Stormwater collects both naturally and artificially and eventually percolates through the ground and into aquifers for beneficial use for both urban and agriculture. Recharge from agricultural and wetland water conveyance and irrigation percolates into the ground and eventually into aquifers where it can be pumped again for use. This natural and unmanaged recharge creates future opportunities for conjunctive use programs; however, this recharge may decline as farmers move toward more precise and water efficient irrigation methods.
3.8 Plan Elements from California Water Code Section 10727.4 Each GSP may contain, as deemed appropriate, a detailed discussion of the additional plan elements as identified in California Water Code (CWC) Section 10727.4. These elements are:
Control of saline water intrusion
Wellhead protection areas and recharge areas
Migration of contaminated groundwater
Well abandonment and well destruction programs
Activities implementing, opportunities for, and removing impediments to conjunctive use or underground storage
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 Section 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 risk to groundwater quality or quantity Impacts on Groundwater Dependent Ecosystems
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4. SUBBASIN SETTING
This Delta-Mendota Subbasin Settings section contains three main subsections as follows:
Hydrogeologic Conceptual Model (HCM) – The HCM section (Section 4.1) provides the geologic information needed to understand the framework that water moves through in the Subbasin. It focuses on geologic formations, aquifers, structural features, and topography. Groundwater Conditions – The Groundwater Conditions section (Section 4.2) describes and presents groundwater trends, levels, hydrographs and level contour maps, estimates changes in groundwater storage, identifies groundwater quality issues, addresses subsidence, and addresses surface water interconnection.
Water Budget – The Water Budget section (Section 4.3) describes the data used to develop the water budget. Additionally, this section discusses how the budget was calculated, provides water budget estimates for historical conditions, and current conditions and projected conditions
4.1 Hydrogeologic Conceptual Model
This section describes the hydrogeologic conceptual model (HCM) for the Delta-Mendota Subbasin based on technical studies and qualified maps that characterize the physical components and interaction of the surface water and groundwater systems, pursuant to Article 5, Plan Contents, Subarticle 2, Basin Setting, § 354.14 Hydrogeologic Conceptual Model of the GSP Emergency Regulations. The physical description of the Delta-Mendota Subbasin is based on information originally published in the Western San Joaquin River Watershed Groundwater Quality Assessment Report (GAR) (LSCE, 2015), Grassland Drainage Area Groundwater Quality Assessment Report (LSCE, 2016), and Groundwater Overdraft in the DeltaMendota Subbasin (KDSA, 2015).
4.1.1 Regional Geologic and Structural Setting
The Delta-Mendota Subbasin is located in the northwestern portion of the San Joaquin Valley Groundwater Basin within the southern portion of the Central Valley (Figure CC-21). The San Joaquin Valley is a structural trough up to 200 miles long and 70 miles wide filled with up to 32,000 feet of marine and continental sediments deposited during periodic inundation by the Pacific Ocean and by erosion of the surrounding Sierra Nevada and Coast Range mountains, respectively (DWR, 2006).
Continental deposits shed from the surrounding mountains form an alluvial wedge that thickens from the valley margins toward the axis of the structural trough. This depositional axis is slightly west of the series of rivers, lakes, sloughs, and marshes which mark the current and historic axis of surface drainage in the San Joaquin Valley.
The Delta-Mendota Subbasin (DWR Basin No. 5-22.07) is bounded on the west by the tertiary and older marine sediments of the Coast Ranges, on the north generally by the San Joaquin-Stanislaus County line, on the east generally by the San Joaquin River and Fresno Slough, and on the south by the Tranquillity Irrigation District boundary near the community of San Joaquin. Surface waters converge from the Fresno, Merced, Tuolumne, and Stanislaus Rivers into the San Joaquin River, which drains to the north toward the Sacramento-San Joaquin Delta.
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Figure CC-21: Regional Geologic Setting
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4.1.2 Geologic History
Approximately three million years ago, tectonic movement of the Oceanic and Continental plates associated with the San Andreas Fault system resulted in the formation of the Coast Range which sealed off the Central Valley from the Pacific Ocean (LSCE, 2015). As this occurred, the floor of the San Joaquin Valley began to transition from a marine depositional environment to a freshwater system with ancestral rivers bringing alluvium to saltwater bodies (Mendenhall et al., 1916). The Coast Ranges on the western side of the San Joaquin Valley consist mostly of complexly folded and faulted consolidated marine and non-marine sedimentary and crystalline rocks ranging from Jurassic to Tertiary age, dipping eastward and overlying the basement complex in the region (Croft, 1972; Hotchkiss and Balding, 1971).
The Central Valley Floor, in which the Delta-Mendota Subbasin lies, consists of Tertiary and Quaternaryaged alluvial and basin fill deposits (Figure CC-22). The fill deposits mapped throughout much of the valley extend vertically for thousands of feet, and the texture of sediments varies in the east-west direction across the valley. Coalescing alluvial fans have formed along the sides of the valley created by the continuous shifting of distributary stream channels over time. This process has led to the development of thick fans of generally coarse texture along the margins of the valley and a generally fining texture towards the axis of the valley (Faunt et al., 2009 and 2010).
Deposits of Coast Range and Sierra Nevada sources interfinger within the Delta-Mendota Subbasin.
Steeper fan surfaces, with slopes as high as 80 feet per mile, exist proximal to the Coast Range, whereas more distal fan surfaces consist of more gentle slopes of 20 feet per mile (Hotchkiss and Balding, 1971).
In contrast to the east side of the valley, the more irregular and ephemeral streams on the western side of the valley floor have less energy and transport smaller volumes of sediment resulting in less developed alluvial features, including alluvial fans which are less extensive, although steeper, than alluvial fan features on the east side of the valley (Bertoldi et al., 1991). Lacustrine and floodplain deposits also exist closer to the valley axis as thick silt and clay layers. Lakes present during the Pleistocene epoch in parts of the San Joaquin Valley deposited great thicknesses of clay sediments.
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Figure CC-22: Generalized Geology
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4.1.3 Geologic Formations and Stratigraphy
Distinct geomorphic units exist within the Delta-Mendota Subbasin defining areas of unique hydrogeologic environments. The geomorphic units are mapped and described by Hotchkiss and Balding (1971) and Davis et al. (1959) and are shown in Figure CC-22. The two primary geomorphic units within the Central Valley Floor area of the Delta-Mendota Subbasin include the overflow lands geomorphic unit and the alluvial fans and plains geomorphic unit. Overflow lands are defined as areas of relatively poorly draining soils with a shallow water table. The overflow lands geomorphic unit is located in the southeastern portion of the Subbasin and is dominated by finer-grained floodplain deposits that are the result of historical episodic flooding of this low-land area. This has formed poorly-draining soils with generally low hydraulic conductivity characteristics. In contrast, the alluvial fans and plains geomorphic unit is characterized by relatively better drainage conditions, with sediments comprised of coalescing and somewhat coarser-grained alluvial fan materials deposited by higher-energy streams flowing out of the Coast Range (Hotchkiss and Balding, 1971). The alluvial fans and plains geomorphic unit covers much of the Delta-Mendota Subbasin along the western margins of the Central Valley Floor at the base of the Coast Range.
The primary groundwater bearing units within the Delta-Mendota Subbasin consist of Tertiary and Quaternary-aged unconsolidated continental deposits and older alluvium of the Tulare Formation.
Subsurface hydrogeologic materials covering the Central Valley Floor consist of lenticular and generally poorly sorted clay, silt, sand, and gravel that make up the alluvium and Tulare Formation. These deposits are thickest along the axis of the valley with thinning along the margins towards the Coast Range mountains (DWR, 2003; Hotchkiss and Balding, 1971). A zone of very shallow groundwater, generally within 25 feet of the ground surface, exists throughout large areas of the Subbasin, with considerable amounts (greater than 50 percent) of farmland in the area estimated to have very shallow depths to groundwater of less than 10 feet (Hotchkiss and Balding, 1971). Many of these areas are naturally swampy lands adjacent to the San Joaquin River.
The Tulare Formation extends to several thousand feet in depth and to the base of freshwater throughout most of the area and consists of interfingered sediments ranging in texture from clay to gravel of both Sierra Nevadan and Coast Range origin. The formation is composed of beds, lenses, and tongues of clay, sand, and gravel that have been alternatively deposited in oxidizing and reducing environments (Hotchkiss and Balding, 1971).
Terrace deposits of Pleistocene age lie up to several feet higher than present streambeds and are comprised of yellow, tan, and light-to-dark brown silt, sand, and gravel with a matrix that varies from sand to clay (Hotchkiss and Balding, 1971). The water table generally lies below the bottom of the terrace deposits; however, the relatively large grain size of the terrace deposits suggests their value as possible recharge sites. Alluvium is composed of interbedded, poorly to well-sorted clay, silt, sand, and gravel and is divided based on its degree of dissection and soil formation. The flood-basin deposits are generally composed of light-to-dark brown and gray clay, silt, sand, and organic material with locally high concentrations of salt and alkali. Stream channel deposits of coarse sand and gravel are also included.
The Tulare Formation also includes the Corcoran Clay (E-Clay) member, a diatomaceous clay or silty clay of lakebed origin which is a prominent aquitard in the San Joaquin Valley, separating the upper zone from the lower zone and distinguishing the semi-confined Upper Aquifer from the confined Lower Aquifer (Hotchkiss and Balding, 1971). The depth and thickness of the Corcoran Clay are variable within the Central Valley Floor, and it is not present in peripheral areas (outside the Central Valley Floor) of the Subbasin. Within the Upper Aquifer, additional clay layers exist and also provide varying degrees of confinement, including other clay members of the Tulare Formation and layers of white clay identified by Hotchkiss and Balding (1971). These clays are variable in extent and thickness, but the white clay is Delta-Mendota Subbasin Groundwater Sustainability Plan
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noted to be as much as 60 feet thick in areas providing very effective confinement of underlying zones (Croft, 1972; Hotchkiss and Balding, 1971). The Tulare Formation is hydrologically the most important geologic formation in the Delta-Mendota Subbasin because it contains most of the fresh water-bearing deposits. Most of the natural recharge that occurs in the Subbasin is in the alluvial fan apex areas along Coast Range stream channels (Hotchkiss and Balding, 1971).
4.1.4 Faults and Structural Features
The valley floor portion of the Delta-Mendota Subbasin contains no known major faults and is fairly geologically inactive. There are few faults along the western boundary of the Subbasin within the Coast Range mountains, but they are not known to inhibit groundwater flow or impact water conveyance infrastructure (Figure CC-23).
4.1.5 Basin Boundaries
The Delta-Mendota Subbasin is defined by both geological and jurisdictional boundaries. The DeltaMendota Subbasin borders all subbasins within the San Joaquin Valley Hydrologic Region with the exception of the Cosumnes Subbasin. The following subsections describe the lateral boundaries of the Subbasin, boundaries with neighboring subbasins, and the definable bottom of the Delta-Mendota Subbasin.
Lateral Boundaries
The Delta-Mendota Subbasin is geologically and topographically bounded to the west by the Tertiary and older marine sediments of the Coast Ranges, and to the east generally by the San Joaquin River. The northern, central, and southern portion of the eastern boundary are dictated by jurisdictional boundaries of water purveyors within the Delta-Mendota Subbasin.
As described in California’s Groundwater, DWR Bulletin 118 (2016), the Delta-Mendota Subbasin is in the San Joaquin Valley Groundwater Basin, located along the western edge of the San Joaquin Valley.
The northern boundary begins just south of Tracy in San Joaquin County. The eastern boundary generally follows the San Joaquin River and Fresno Slough. The southern boundary is near the small town of San Joaquin. The subbasin is bounded on the west by the coast range. The Subbasin boundary is defined by 20 segments detailed in the descriptions below. The Delta-Mendota Subbasin extends into six (6) counties:
San Joaquin, Stanislaus, Merced, Fresno, San Benito, and Madera and is shown in relation to each of the six counties in Figure CC-9.
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Figure CC-23: Subbasin Faults
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4.1.6 Definable Bottom of Basin
In the San Joaquin Valley, the bottom of the Delta-Mendota Subbasin is defined as the interface of saline water of marine origin (base of fresh water) within the uppermost beds of the Tulare Formation. The Tulare Formation is characterized by blue and green fine-grained rocks and principally composed of finegrained silty sands, silt, and clay (Foss and Blaisdell 1968). The Tulare Formation is predominantly marine in origin and is considered late Pliocene and possibly early Pleistocene in age. This formation is the upper shaley part of the Pliocene sequence. The top of the Tulare Formation is generally encountered around -2,000 feet mean sea level throughout the Delta-Mendota Subbasin. As agreed upon by the DeltaMendota Subbasin GSP Groups, the base of freshwater is specifically defined by an electrical conductivity of 3,000 micromhos per centimeter at 25 °C, as presented by Page (1973). If and when significant use of water beyond the defined bottom takes place, the definition of the bottom will be revised appropriately.
4.1.7 Principal Aquifers and Aquitards
DWR’s Groundwater Glossary defines an aquifer as “a body of rock or sediment that is sufficiently porous and permeable to store, transmit, and yield significant or economic quantities of groundwater to wells, and springs”. There are two primary aquifers within the Delta-Mendota Subbasin: a semi-confined aquifer above the Corcoran Clay and a confined aquifer below the Corcoran Clay, with the Corcoran Clay acting as the principal aquitard within the Delta-Mendota Subbasin. Figure CC-24 shows the locations of the representative cross-sections for the Delta-Mendota Subbasin, where Figure CC-25 through Figure CC-30 show the hydrostratigraphy of the representative cross-sections.
While the two-aquifer system described above is generally true across the Delta-Mendota Subbasin, there are portions of the Subbasin where the Corcoran Clay does not exist (predominantly along the western margin of the Subbasin) and hydrogeology is generally controlled by localized interfingering clays, and/or where local hydrostratigraphy results in shallow groundwater conditions that differ, to some extent, from that seen in the Subbasin as a whole. Additionally, in the southern portion of the Subbasin in the Mendota, Aliso and Tranquillity areas, there are A and C Clay layers in addition to the Corcoran Clay that inhibit vertical groundwater flow. However, while there are localized complexities throughout the Subbasin, the Corcoran Clay (or E Clay) extends through much of the Delta-Mendota Subbasin, generally creating a two-aquifer system.
Principal Aquifers
In the Delta-Mendota Subbasin, there are two primary aquifers composed of alluvial deposits separated by the Corcoran Clay (KDSA, 2015): a semi-confined Upper Aquifer (generally the ground surface to the top of the Corcoran Clay), and a confined Lower Aquifer starting at the bottom of the Corcoran Clay to the base of fresh water. However, as previously described, the localized presence of the A and C Clay layers in the southern portion of the Subbasin, the absence of the Corcoran Clay at the western margin of the Subbasin, and/or local hydrostratigraphy result in differing shallow groundwater conditions and/or perched groundwater conditions in some portions of the Subbasin. See the individual GSPs for more detailed descriptions of hydrostratigraphy in the respective Plan areas.
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Upper Aquifer
The Upper Aquifer is represented by materials extending from the upper groundwater table to the top of the Corcoran Clay. The Upper Aquifer includes shallow geologic units of younger and older alluvium and upper parts of the Tulare Formation. Sediments within the upper Tulare Formation have variable sources, and subdivision of units can be distinguished between eastern and western sourced materials. Alluvial fan materials above the Corcoran Clay in the Delta-Mendota Subbasin are generally more extensive than older alluvial fan deposits within the Tulare Formation below the Corcoran Clay. As shown in Figure CC31 by the depth to the top of the Corcoran Clay, the Upper Aquifer extends to depths ranging between approximately 150 feet and greater than 350 feet. Other notable mapped clay units also exist within the upper part of the Tulare Formation in the Delta-Mendota Subbasin, including the A and C Clay members of the Tulare Formation and a white clay mapped by Hotchkiss and Balding (1971).
Lower Aquifer
The Lower Aquifer is the portion of the Tulare Formation that is confined beneath the Corcoran Clay, extending downward to the underlying San Joaquin Formation and the interface of saline water of marine origin within its uppermost beds. The Lower Aquifer is generally characterized by groundwater that tends to be dominantly sodium-sulfate type, which is often of better quality than the Upper Aquifer (Davis et al., 1957; Hotchkiss and Balding, 1971). Exceptions to this quality do exist in the Subbasin, particularly in the southwestern portion of the Subbasin. Because of its relatively shallow depth within the DeltaMendota Subbasin and lower salinity in areas when compared to other groundwater resources, the Lower Aquifer is heavily utilized as a source of groundwater for agricultural and drinking water uses within the Subbasin.
The base of the Lower Aquifer generally decreases from south to north, changing in depth from about 1,100 to 1,200 feet deep in the south to about 600 feet to the north. Depth to the top of the Corcoran Clay ranges from less than 100 feet on the west near Interstate 5 (I-5) to more than 500 feet in the area near Tranquillity. The Corcoran Clay pinches out or is above the water level near the California Aqueduct in the western part of the Subbasin, where the Upper and Lower Aquifers merge into interfingered layers of sand, gravel, and clay.
Corcoran Clay
The Corcoran Clay, as a regional aquitard, is a notable hydrogeologic feature throughout most of the Delta-Mendota Subbasin, impeding vertical flow between the Upper and Lower Aquifers. The Corcoran Clay is present at varying depths across most of the Central Valley floor (Figure CC-31 and Figure CC33). The depths to the top of the Corcoran Clay ranges between approximately 100 and 500 feet below the ground surface throughout most of the Subbasin, with a general spatial pattern of deepening to the south and east. In the far southeastern area of the Subbasin, in the vicinity of Mendota and Tranquillity, the top of the Corcoran Clay is at depths of greater than 350 feet (Figure CC-31). The thickness of the Corcoran Clay, which likely influences the degree of hydraulic separation between the Upper and Lower Aquifers, is greater than 50 feet across most of the Delta-Mendota Subbasin with thicknesses of more than 75 feet in central Subbasin areas in the vicinity of Los Banos and Dos Palos, and 140 feet in the eastern portions of the Subbasin. The Corcoran Clay appears thinner in areas north of Patterson, between Patterson and Gustine, and also in the vicinity of Tranquillity to the south (Figure CC-33). Along the westernmost portions of the Delta-Mendota Subbasin, the Corcoran Clay layer is generally non-existent or it exists as Corcoran-equivalent clays (clays existing at the same approximate depth but not part of the mapped aquitard).
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Aquifer Properties
The following subsections include discussion of generalized aquifer properties within the Delta-Mendota Subbasin. These include hydraulic conductivity, transmissivity, specific yield and specific storage.
DWR defines hydraulic conductivity as the “measure of a rock or sediment’s ability to transmit water” and transmissivity as the “aquifer’s ability to transmit groundwater through its entire saturated thickness” (DWR, 2003). High hydraulic conductivity values correlate with areas of transmissive groundwater conditions with transmissivity generally equaling hydraulic conductivity times the saturated thickness of the formation. Storage of water within the aquifer system can be quantified in terms of the specific yield for unconfined groundwater flow and the storage coefficient for confined flow, respectively (Faunt et al., 2009). Specific yield represents gravity-driven dewatering of shallow, unconfined sediments at a declining water table, but also accommodates a rising water table. The specific yield is dimensionless and represents the volume of water released from or taken into storage per unit head change per unit area of the water table. Specific yield is a function of porosity and specific retention of the sediments in the zone of water-table fluctuation.
Where the aquifer system is confined, storage change is governed by the storage coefficient, which is the product of the thickness of the confined-flow system and its specific storage. The specific storage is the sum of two component specific storages – the fluid (water) specific storage and the matrix (skeletal) specific storage, which are governed by the compressibility of the water and skeleton, respectively (Jacob, 1940). Specific storage has units of 1 over length and represents the volume of water released from or taken into storage in a confined flow system per unit change in head per unit volume of the confined flow system (Faunt et al., 2009). Therefore, the storage coefficient of a confined flow system is dimensionless and, similar to specific yield, represents the volume of water released from or taken into storage per unit head change.
Hydraulic Conductivity
Figure CC-34 shows the saturated C-horizon hydraulic conductivity of surficial soils within the DeltaMendota Subbasin based on the National Resource Conservation Service (NRCS) Soil Survey Geographic Database (SSURGO). Soil survey data for counties within the Subbasin were combined using the weighted harmonic mean of these representative layers to depict the saturated hydraulic conductivity of the C-horizon for each soil map unit. The soil profile represented by these data is variable but commonly extends to a depth of six or more feet.
Floodplain deposits are evident as soils with relatively low hydraulic conductivity (less than 0.5 feet per day [ft/day]) blanket much of the Central Valley Floor, although localized areas of soils with higher hydraulic conductivity are present in association with modern and ancient surface waterways and alluvial fan features (Figure CC-34). Coarse soils of distributary alluvial fan sediments deposited by Del Puerto Creek, Orestimba Creek, Los Banos Creek, Ortigalita Creek, and Little Panoche Creek, in addition to other ephemeral northeasterly creek flows off the Coast Ranges, are notably apparent as areas of soils of high hydraulic conductivity located along active and inactive stream channels extending eastward from the fan apex areas along the Valley Floor margins to the current alignment of the San Joaquin River in the valley axis. Additionally, soils in areas adjacent to the active channel of the San Joaquin River also exhibit high hydraulic conductivities, including values of greater than 4 ft/day which are particularly apparent in an area north of Mendota. Soils of similarly high hydraulic conductivity trending as linear features in a general northwest-southeast alignment to the north of Dos Palos and Los Banos are likely the result of historical depositional processes and paleochannels associated with the San Joaquin River (Figure CC-34). In areas peripheral to the Central Valley floor, soils tend to be characterized by relatively low hydraulic conductivity, although soils of somewhat higher hydraulic conductivity Delta-Mendota Subbasin Groundwater Sustainability Plan
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associated with distinct geologic units are mapped across much of the peripheral area to the west of Patterson and Gustine and also in localized bands associated with surface water courses.
Transmissivity
Transmissivity varies greatly above the Corcoran Clay, within the Corcoran Clay, and below the Corcoran Clay within the Delta-Mendota Subbasin, with transmissivities in the confined Lower Aquifer generally being larger than those in the semi-confined Upper Aquifer. Based on testing conducted at multiple locations within both the Upper and Lower Aquifers of the Delta-Mendota Subbasin, average transmissivities in the Subbasin are approximately 109,000 gallons per day per square foot (gpd/ft2 )
(KDSA, 1997b).
Specific Yield
DWR defines specific yield as the “amount of water that would drain freely from rocks or sediments due to gravity and describes the proportion of groundwater that could actually be available for extraction” (DWR, 2003). Specific yield is a measurement specific to unconfined aquifers.
The estimated specific yield of the Delta-Mendota Subbasin is 0.118 (DWR, 2006). Within the southern portion of the Delta-Mendota Subbasin, specific yield ranges from 0.2 to 0.3 (Belitz et al., 1993). Specific yield estimates for the Delta-Mendota Subbasin are fairly limited in literature since the Upper Aquifer above the Corcoran Clay is semi-confined and the Lower Aquifer below the Corcoran Clay is confined.
Therefore, specific yield values only characterize the shallow, unconfined groundwater within the Subbasin.
Specific Storage
Values for specific storage were extracted from the Central Valley Hydrologic Model 2 (CVHM2), which is currently under development by the United States Geological Survey (USGS) and includes refinements for the Delta-Mendota Subbasin. Specific storage varies above, within, and below the Corcoran Clay with CVMH2. Above the Corcoran Clay, specific storage ranges from 1.34 x 10-6 to 6.46 x 10-2 meters-1 (m-1) with average values ranging from 6.16 x 10-3 to 1.97 x 10-2 m-1. Specific storage within the Corcoran Clay is considerably smaller than above the Corcoran Clay, ranging between 1.41 x 10-6 and 2.35 x 10-6 m-1 and average values between 1.96 x 10-6 and 2.02 x 10-6 m-1. Below the Corcoran Clay, specific storage is comparable to within the Corcoran Clay with overall ranges the same as within the Corcoran Clay and average values ranging from 1.86 x 10-6 to 2.01 x 10-6 m-1. Therefore, specific storage is greatest within the semi-confined aquifer overlying the Corcoran Clay layer, with considerably smaller specific storage values within the low permeability Corcoran Clay and confined aquifer underlying the Corcoran Clay layer.
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Figure CC-24: Representative Cross-Sections
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Figure CC-25: Cross-Section A-A’ (Hotchkiss, 1972)
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Figure CC-26: Cross-Section B-B’ (Hotchkiss, 1972)
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Figure CC-27: Cross-Section C-C’ (Hotchkiss, 1972)
Figure CC-28: Cross-Section D-D’ (Hotchkiss & Balding, 1971) Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-29: Cross-Section E-E’ (Hotchkiss & Balding, 1971) Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-30: Cross-Section F-F’ (Hotchkiss, 1972)
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Figure CC-31: Depth to Corcoran Clay
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Figure CC-32: Non-Corcoran Clay Layers
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Figure CC-33: Thickness of Corcoran Clay
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Figure CC-34: Soil Hydraulic Conductivity
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4.1.8 Structural Properties and Restricted Groundwater Flow Under natural (pre-development) conditions, the prevailing groundwater flow within the Upper and Lower Aquifer systems of the western San Joaquin Valley was predominantly in a generally northeasterly direction from the Coast Range towards and parallel to the San Joaquin River and the Sacramento-San Joaquin Delta (LSCE, 2015; Hotchkiss and Balding, 1971; KDSA, 2015). Historically, numerous flowing artesian wells within the Lower Aquifer existed throughout the Delta-Mendota Subbasin (Mendenhall et al., 1916) and the pressure gradient for groundwater flow was upward from the Lower Aquifer to the Upper Aquifer. These flowing artesian conditions have disappeared in many areas as a result of increased development of groundwater resources within the Tulare Formation (Hotchkiss and Balding, 1971).
Additionally, the Delta-Mendota Subbasin has experienced periods of considerable decline in groundwater levels during which hydraulic heads in the Lower Aquifer decreased considerably in some areas due to heavy pumping (Bertoldi et al., 1991).
Despite the presence of local pumping depressions within parts of the Subbasin, the prevailing northeastward flow direction for groundwater in the Upper Aquifer within the region has remained (AECOM, 2011; DWR, 2010; Hotchkiss and Balding, 1971). Groundwater generally flows outward from the Delta-Mendota Subbasin, except along the southern and western margins where there is some recharge from local streams and canal seepage (KDSA, 2015), in addition to northward subbasin boundary flows. Within the Upper Aquifer, there are similar groundwater flow directions in most of the Subbasin with groundwater outflow to the northeast or towards the San Joaquin River in much of the Subbasin during wet and normal periods. One exception is in the Orestimba Creek area west of Newman where groundwater flows to the west during drought conditions and east during wet periods. Calculations based on aquifer transmissivity indicate the net groundwater outflow in the Upper Aquifer has been about three times greater during drought periods than during normal periods (KDSA, 1997a and 1997b).
Within the Lower Aquifer, there is a groundwater divide generally in the area between Mendota and the point near the San Joaquin River in the Turner Island area, northeast of Los Banos. Groundwater southwest of this divide generally flows southwest toward Panoche Water District and Westlands Water District. Groundwater northeast of this divide flows to the northeast into Madera and Merced Counties.
Net groundwater outflow in the Lower Aquifer under drought conditions has been about two and a half times greater than for normal conditions (KDSA, 1997a and 1997b). Based on current and historical groundwater elevation maps, groundwater barriers do not appear to exist in the Delta-Mendota Subbasin (DWR, 2006).
The combined effect of pumping below the Corcoran Clay and increased leakage from the Upper Aquifer to the Lower Aquifer where the Corcoran Clay does not exist or has been perforated has developed a generally downward flow gradient in the Tulare Formation which changes with variable pumping and irrigation over time (Bertoldi et al., 1991). Periods of great groundwater level declines have also resulted in inelastic compaction of fine-grained materials in some locations, particularly between Los Banos and Mendota, potentially resulting in considerable decreases (between 1.5 and 6 times) in permeability of clay members within the Tulare Formation, including the Corcoran Clay (Bertoldi et al., 1991). However, the number of wells penetrating the Corcoran Clay may be enabling vertical hydraulic communication across the Corcoran Clay aquitard and other clay layers (Davis et al., 1959; Davis et al., 1964).
4.1.9 Water Quality
Groundwater in the Delta-Mendota Subbasin is characterized by mixed sulfate to bicarbonate water types in the northern and central portion of the Subbasin, with areas of sodium chloride and sodium sulfate waters in the central and southern portions (DWR, 2003). Total Dissolved Solids (TDS) values range from 400 to 1,600 mg/L in the northern portion, and 730 to 6,000 mg/L in the southern portion of the Delta-Mendota Subbasin Groundwater Sustainability Plan
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Delta-Mendota Subbasin (Hotchkiss and Balding, 1971). The Department of Health Services (currently the Division of Drinking Water), which monitors Title 22 water quality standards, reports TDS values in 44 public supply wells in the Subbasin ranging in value from 210 to 1,750 mg/L, with an average value of 770 mg/L. Shallow, saline groundwater also occurs within about 10 feet of the ground surface over a large portion of the Delta-Mendota Subbasin. There are also localized areas of high iron, fluoride, nitrate, selenium, and boron in the Delta-Mendota Subbasin (Hotchkiss and Balding, 1971).
Alluvial sediments derived from west-side streams are composed of material from serpentine, shale, and sandstone parent rock, which results in soil and groundwater types entirely different from those on the east side of the San Joaquin Valley (LSCE, 2015). In contrast with the siliceous mineralogy of the alluvial sands and gravels on the eastern side of the Central Valley that are derived from the Sierra granitic rocks (which are coarser and more resistant to chemical dissolution), the sulfate and carbonate shales and sandstones of Coast Range sediments on the western side are more susceptible to dissolution processes.
Some soils and sediments within the western San Joaquin Valley that are derived from marine rocks of the Coast Range have notably high concentrations of naturally-occurring nitrogen, with particularly higher nitrate concentrations in younger alluvial sediments (Strathouse and Sposito, 1980; Sullivan et al., 1979). These naturally-occurring nitrogen sources may contribute to nitrate concentrations in groundwater within the Delta-Mendota Subbasin, although it is not well known where this may occur and to what degree. Naturally high concentrations of TDS in groundwater are known to have existed historically within parts of the Subbasin due to the geochemistry of the Coast Range rocks and the marine depositional environment, the resulting naturally-high TDS of recharge derived from Coast Range streams, the dissolvable materials within the alluvial fan complexes, and the naturally-poor draining conditions which tend to concentrate salts in the system. The chemical quality of waters in the Coast Range streams can be closely correlated with the geologic units within their respective catchments.
Groundwater flows discharging from these marine and non-marine rocks into streams introduce a variety of dissolved constituents resulting in variable groundwater types. The water quality and chemical makeup in westside streams can be highly saline, especially in more northern streams, including Corral Hollow, Panoche and Del Puerto Creeks, where historical baseflow TDS concentrations have typically exceeded 1,000 mg/L with measured concentrations as high as 1,790 mg/L (Hotchkiss and Balding, 1971). This is in contrast with TDS concentrations typically below 175 mg/L in streams draining from the Sierras. The contribution of water associated with these Coast Range sediments has resulted in naturally high salinity in groundwater within and around the Delta-Mendota Subbasin, which has been recognized as early as the 1900s (Mendenhall et al., 1916). Groundwater in some areas within the immediate vicinity of the San Joaquin River is influenced by lower-salinity surface water discharging from the east side of the San Joaquin Valley Groundwater Basin (Davis et al., 1957).
Areas of historical high saline groundwater documented by Mendenhall et al. (1916) indicate somewhat high TDS concentrations approaching or greater than 1,000 mg/L in wells sampled throughout many parts of the Delta-Mendota Subbasin. Areas of locally higher TDS concentrations (1,500-2,400 mg/L) have existed between Mendota and Los Banos; whereas the trend in deeper groundwater (average well depth of 450 feet) south of Mendota near Tranquillity indicates slightly lower historical salinity conditions, but still somewhat high with an average TDS concentration of greater than 1,000 mg/L. In the northern part of the Subbasin, north of Gustine, the average historical TDS concentration of wells was also relatively high (930 mg/L). Historically low TDS concentrations (<500 mg/L) existed in groundwater from wells with an average depth of 209 feet in the central Subbasin area between Los Banos and Gustine.
The general chemical composition of groundwater in the Subbasin is variable based on location and depth. Groundwater within the Upper Aquifer is largely characterized as transitional type with less area characterized as predominantly of chloride, bicarbonate, and sulfate water types. Transitional water types, in which no single anion represents more than 50 percent of the reactive anions, occurs in many different combinations with greatly ranging TDS concentrations. Chloride-type waters occur generally in grassland Delta-Mendota Subbasin Groundwater Sustainability Plan
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areas east of Gustine and around Dos Palos, with sodium chloride water present in northern areas near Tracy and also extending south from Dos Palos. These waters also exhibit greatly varying salinity with typical TDS concentrations, ranging from less than 500 mg/L to greater than 10,000 mg/L and of high sodium makeup (50-75 percent of cations present) (Hotchkiss and Balding, 1971). Areas of bicarbonate groundwater within the Upper Aquifer of relatively lower TDS concentrations are directly associated with intermittent streams of the Coast Range near Del Puerto, Orestimba, San Luis, and Los Banos Creeks.
Sulfate water in the central and southern Subbasin areas has TDS concentrations decreasing from west (1,200 mg/L) to east (700 mg/L) towards the San Joaquin River, similar to the bicarbonate water areas, although areas of sulfate water south of Dos Palos have much higher TDS concentrations (1,900 to 86,500 mg/L) (Hotchkiss and Balding, 1971).
Groundwater in the Lower Aquifer below the Corcoran Clay is also spatially variable, consisting of mostly transitional sulfate waters in the northern part of the Delta-Mendota Subbasin to more sodium-rich water further south in the grassland areas. In the northern part of the Delta-Mendota Subbasin, the Lower Aquifer exhibits relatively lower TDS concentrations, ranging from 400 to 1,600 mg/L, with a sulfatechloride type makeup near the valley margin trending to sulfate-bicarbonate type near the valley axis.
Farther south, TDS concentrations in the Lower Aquifer increase (Hotchkiss and Balding, 1971).
Natural conditions of groundwater salinity exist throughout the Upper and Lower Aquifers as a result of the contribution of salts from recharge off the Coast Range mountains. Surface water and groundwater flowing over and through Coast Range sediments of marine origin have dissolved naturally-occurring salts, contributing to the historical and current presence of salinity in groundwater within the DeltaMendota Subbasin. In addition to natural salinity contributed from the Coast Range sediments, a number of other mechanisms are believed to further contribute to increased salinity in the groundwater in the region. Poorly draining soil conditions are extensive within some of the southern and eastern areas of the Subbasin, extending from the vicinity of Tranquillity to near Gustine, and these types of soil, combined with a shallow water table, contribute to a build-up of soil salinity.
4.1.10 Topography, Surface Water, Recharge, and Imported Supplies This section describes the topography, surface water, soils, and groundwater recharge potential in the Delta-Mendota Subbasin.
Topography
As previously described, the Delta-Mendota Subbasin lies on the western side of the Central Valley and extends from the San Joaquin River on the east, along the axis of the Valley, to the Coast Range on the west side (LSCE, 2015). The Subbasin has ground surface elevations ranging from less than 100 feet above mean sea level (msl) along parts of the eastern edge to greater than 1,600 feet msl in the Coast Range mountains (Figure CC-35). Most of the lower elevation areas occur east of Interstate 5, in the eastern parts of the Delta-Mendota Subbasin; although some lower elevation areas also extend westward into the Coast Range, such as in Los Banos Creek Valley. Low elevation areas generally coincide with the extent of the Central Valley floor. Topography within the Delta-Mendota Subbasin consists largely of flat areas across the Central Valley floor, where slopes are generally less than 2 percent, with steepening slopes to the west. The topography outside of the Central Valley floor in the Coast Range mountains is characterized by steeper slopes, generally greater than 6 percent.
Surface Water Bodies
The San Joaquin River and its tributaries is the primary natural surface water feature within the DeltaMendota Subbasin, flowing from south to north along the eastern edge of the Subbasin (LSCE, 2015).
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During the 1960s, the San Joaquin River exhibited gaining flow conditions through much of the Subbasin (Hotchkiss and Balding, 1971). Numerous intermittent streams from the Coast Range enter the DeltaMendota Subbasin from the west; however, none of these maintain perennial flow and only Orestimba Creek, Los Banos Creek and Del Puerto Creek have channels that extend eastward to a junction with the San Joaquin River. Most of the flow in other notable west-side creeks, including Quinto Creek, San Luis Creek, Little Panoche Creek, and Ortigalita Creek, is lost to infiltration (Hotchkiss and Balding, 1971).
Flow from Los Banos and San Luis Creeks are impounded by dams on their respective systems. When flood releases are made from Los Banos Creek Reservoir, the vast majority of flows pass through Grassland Water District to the San Joaquin River as they tend to occur during times when agricultural and wetland demand is low. San Luis Reservoir on San Luis Creek, which is located along the western boundary of the Delta-Mendota Subbasin, is an artificial water storage facility for the Central Valley Project and California State Water Project and has no notable natural surface water inflows. Outflows from the reservoir go into the system of federal- and state-operated canals and aqueducts comprising the Central Valley and State Water Projects. Surface water use within the Delta-Mendota Subbasin is derived largely from water deliveries provided by these projects, including from the California Aqueduct (referred to as San Luis Canal in the joint-use area of the California Aqueduct) and Delta-Mendota Canal, and also from the San Joaquin River (Figure CC-36).
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Figure CC-35: Ground Surface Elevation
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Figure CC-36: Surface Water Features
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Soils
The NRCS provides soil mapping in the region. One of the combining soil groupings mapped includes hydrologic groups. The predominant soil hydrologic groups within the Delta-Mendota Subbasin are soil types C and D (Figure CC-37). Group C soils have moderately high runoff potential when thoroughly wet (NRCS, 2009) with water transmission through the soil somewhat restricted. Group C soils typically have between 20 percent and 40 percent clay and less than 50 percent sand and have loam, silt loam, sandy clay loam, clay loam, and silty clay loam textures. Group D soils have a high runoff potential when thoroughly wet and water movement through the soil is restricted or very restricted. Group D soils typically have greater than 40 percent clay, less than 50 percent sand, and have clayey textures. In some areas, they also have high shrink-swell potential.
Soil hydraulic conductivity groups are closely related to soil drainage characteristics and hydraulic conductivity. The fine-grained floodplain deposits present across much of the southeastern area of the Subbasin are evidenced as soils with lower hydraulic conductivity in Figure CC-37 and accordingly, these characteristics also make these areas poorly drained. Poorly draining soil conditions are extensive within the southern and eastern areas of the Subbasin, extending from the vicinity of Tranquillity to near Gustine (Fio, 1994; Hotchkiss and Balding, 1971). Soils in the northern and western parts of the DeltaMendota Subbasin exhibit better drainage characteristics, although areas of poorly drained soils are also present in the north and west in proximity to surface water courses, including most notably directly adjacent to portions of the San Joaquin River and Los Banos Creek channels. Many of the upland soils, which are of generally coarser texture and located proximal to sediment sources derived from the Coast Range hill slopes, are characterized as moderately well drained.
In areas with low hydraulic conductivity, corresponding to areas without adequate natural drainage, tile drains are present to remove shallow groundwater from the rooting zone. Known tile drain locations are shown in Figure CC-38, which are primarily located along the eastern boundary of the Delta-Mendota Subbasin as well as the southern portion of the Subbasin in the Grassland Drainage Area. The Grassland Drainage Area contains a tile drainage system connected to the San Joaquin River Improvement Project, which uses tile drainage water for irrigated agriculture with a high salinity tolerance.
Areas of Recharge, Potential Recharge, and Groundwater Discharge Areas The primary process for groundwater recharge within the Central Valley floor area is from percolation of applied irrigation water and seepage from canals and stream beds, although some groundwater recharge does occur in the Delta-Mendota Subbasin along the western boundary of the Subbasin due to mountain front recharge. In sandier areas, recharge ponds have been constructed within certain districts (CCC, Aliso Water District, CCID and Del Puerto Water District) to promote managed aquifer recharge.
Groundwater recharge potential on agricultural land based on the Soil Agricultural Groundwater Banking Index (SAGBI) is shown in Figure CC-39. The SAGBI is based on five major factors: deep percolation, root zone residence time, topography, chemical limitations, and soil surface conditions. Within the DeltaMendota Subbasin, SAGBI data categorizes 160,248 acres out of 744,237 acres (21%) of agricultural and grazing land within the regions as having Excellent, Good, and Moderately Good (Figure CC-39) recharge properties, and 571,573 acres out of 744,237 acres (or 77%) of agricultural and grazing land as having Moderately Poor, Poor, or Very Poor recharge properties. “Modified” SAGBI data shows higher potential for recharge than unmodified SAGBI data because the modified data assumes that soils have been or will be ripped to a depth of six feet, which can break up fine grained materials at the surface to improve percolation. The modified data set was determined to more accurately represent the DeltaMendota Subbasin due to the heavy presence of agriculture. In almost all cases, recharge from applied water on irrigated lands recharges the Upper Aquifer of the Subbasin. However, the use of percolation Delta-Mendota Subbasin Groundwater Sustainability Plan
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ponds and other managed aquifer recharge techniques must consider existing water quality in addition to soil composition and may be limited in areas where poor water quality currently exists.
The Corcoran Clay is a known barrier restricting vertical flow between the Upper and Lower Aquifers; therefore, natural recharge of the Lower Aquifer from downward percolating water is most likely restricted where the Corcoran Clay is present, including across most of the Central Valley floor. Primary recharge areas to the Lower Aquifer are most likely in western parts of the Central Valley floor where percolating water can enter formations feeding the Lower Aquifer, particularly in the vicinity and west of Los Banos, Orestimba, and Del Puerto Creeks, along the western margin of the Subbasin.
Groundwater discharge areas are identified as springs located within the Delta-Mendota Subbasin and the San Joaquin River. Figure CC-39 shows the location of historic springs identified by USGS. There are only six springs/seeps identified by USGS in their National Hydrograph Dataset, which are located in the southwestern corner of the Subbasin. The springs shown represent a dataset collected by USGS and are not a comprehensive map of springs in the Subbasin.
Imported Supplies
Both the California Aqueduct and Delta-Mendota Canal run the length of the Delta-Mendota Subbasin, primarily following the Interstate 5 corridor (Figure CC-40). The following water purveyors in the DeltaMendota Subbasin are SLDMWA Member Agencies and thus receive water from the Central Valley Project via the Delta-Mendota Canal: California Department of Fish and Wildlife, Central California Irrigation District, Columbia Canal Company, Del Puerto Water District, Eagle Field Water District, Firebaugh Canal Water District, Fresno Slough Water District, Grassland Water District, Laguna Water District, Mercy Springs Water District, Oro Loma Water District, Pacheco Water District, Panoche Water District, Patterson Irrigation District, San Luis Canal Company, San Luis Water District, Tranquillity Irrigation District, Turner Island Water District, U.S. Fish and Wildlife Service, and West Stanislaus Irrigation District. Oak Flat Water District is the only recipient of State Water Project (SWP) water in the Delta-Mendota Subbasin; Oak Flat Water District initially bought into the SWP in 1968.
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Figure CC-37: SAGBI Soils Map
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Figure CC-38: Tile Drains
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Figure CC-39: Recharge Areas, Seeps and Springs
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Figure CC-40: Imported Supplies
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4.2 Delta-Mendota Subbasin Groundwater Conditions
This section describes the current and historic groundwater conditions in the Delta-Mendota Subbasin, including data from January 1, 2015 to recent conditions for the following parameters: groundwater elevations, groundwater storage, groundwater quality, land subsidence, interconnected surface water systems, and groundwater dependent ecosystems (GDEs) (pursuant to Article 5 Plan Contents, Subarticle 2 Basin Setting, § 354.16 Groundwater Conditions of the GSP Emergency Regulations). Seawater intrusion is not discussed herein as the Delta-Mendota Subbasin is inland and is not impacted by seawater intrusion. For the purposes of this GSP, “current conditions” is represented by Water Year (WY) 2013 conditions, which is consistent with the year representing the Current Conditions Water Budget (see Section 4.3 for more information about Water Budgets). Data post-WY 2013 through present day are presented when available.
The purpose of describing groundwater conditions, as contained in this section and described in the individual GSPs, is to establish baseline conditions that will be used to monitor changes relative to measurable objectives (MOs) and minimum thresholds (MTs). Therefore, these established baseline conditions will help support monitoring to demonstrate measurable efforts in achieving the sustainability goal for the Delta-Mendota Subbasin.
4.2.1 Useful Terminology
This groundwater conditions section includes descriptions of the amounts, quality, and movement of groundwater, among other related components. A list of technical terms and a description of the terms are listed below. The terms and their descriptions are identified here to guide readers through the section and are not a definitive definition of each term:
Depth to Groundwater – The distance from the ground surface to first-detected non-perched groundwater, typically reported at a well.
Upper Aquifer – The alluvial aquifer above the Corcoran Clay (or E-clay) layer. Lower Aquifer – The alluvial aquifer below the Corcoran Clay (or E-clay) layer. Horizontal gradient – The slope of the groundwater surface from one location to another when one location is higher or lower than the other. The gradient is shown on maps with an arrow showing the direction of groundwater flow in a horizontal direction. Vertical gradient – Describes the movement of groundwater perpendicular to the ground surface. Vertical gradient is measured by comparing the elevations of groundwater in wells that are of different depths. A downward gradient is one where groundwater is moving down into the ground towards deeper aquifers and an upward gradient is one where groundwater is upwelling towards the ground surface.
Contour Map – A contour map shows changes in groundwater elevations by interpolating groundwater elevations between monitoring sites. The elevations are shown on the map with the use of a contour line, which represents groundwater being at the indicated elevation along the contour line. Contour maps can be presented in two ways:
o Elevation of groundwater above mean sea level (msl), which can be used to identify the horizontal gradients of groundwater, and
o Depth to water (i.e., the distance from the ground surface to groundwater), which can be used to identify areas of shallow or deep groundwater.
Hydrograph – A graph that shows the changes in groundwater elevation or depth to groundwater over time at a specific location. Hydrographs show how groundwater elevations change over the years and indicate whether groundwater is rising or descending over time.
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Maximum Contaminant Level (MCL) – MCLs are standards that are set by the State of California and the U.S. Environmental Protection Agency for drinking water quality. MCLs are legal threshold limits on the amount of an identified constituent that is allowed in public drinking water systems. At both the State and Federal levels, there are Primary MCLs, set to be protective of human health, and Secondary MCLs for constituents that do not pose a human health hazard but do pose a nuisance through either smell, odor, taste, and/or color. MCLs are different for different constituents and have not been established for all constituents potentially found in groundwater.
Elastic Land Subsidence – Reversible and temporary fluctuations in the elevation of the earth’s surface in response to seasonal periods of groundwater extraction and recharge. Inelastic Land Subsidence – Irreversible and permanent decline in the elevation of the earth’s surface resulting from the collapse or compaction of the pore structure within the fine-grained portions of an aquifer system. This form of subsidence is what is required by SGMA to be monitored and reported.
Gaining Stream – A stream in which groundwater flows into a streambed and contributes to a net increase in surface water flows across an identified reach. Losing Stream – A stream in which surface water is lost through the streambed to the groundwater, resulting in a net decrease in surface water flows across an identified reach. Conjunctive Use – The combined use of surface water and groundwater supplies, typically with more surface water use in wet years and more groundwater use in dry years.
4.2.2 Groundwater Elevations
This section describes groundwater elevation data utilized and elevation trends in the Delta-Mendota Subbasin. Groundwater conditions vary widely across the Subbasin. Historic groundwater conditions through present day conditions, the role of imported surface water in the Subbasin, and how conjunctive use has impacted groundwater trends temporally and spatially are discussed. Groundwater elevation contour maps associated with current seasonal high and seasonal low for each principal aquifer, as well as hydrographs depicting long-term groundwater elevations, historical highs and lows, and hydraulic gradients (both horizontal and vertical), are also described.
Available Data
Groundwater elevation data, and accompanying well construction information, within the Delta-Mendota Subbasin from the following sources and associated programs were utilized in the development of the Delta-Mendota Subbasin GSPs:
California Department of Water Resources (DWR)
o California Statewide Groundwater Elevation Monitoring Program (CASGEM) o Water Data Library (WDL)
Water level data from local monitoring programs
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Data provided by these sources included well information (such as location, well construction, owner, ground surface elevation and other related components), as well as groundwater elevation data (including information such as date measured, depth to water, groundwater surface elevation, questionable measurement code, and comments). At the time that these analyses were performed, groundwater elevation data were available for the time period from 1930 through 2018. There are many wells with monitoring data from some time in the past but no recent data, while a small number of wells have monitoring data recorded for periods of greater than 50 years.
Not all groundwater elevation data received were used in preparing the groundwater elevation contour maps for both principal aquifers (defined in this Common Chapter as the Upper and Lower Aquifers which are divided by the Corcoran Clay or E-clay layer). Some groundwater elevation data were associated with wells with unknown screened depths and/or composite well screens constructed across the Corcoran Clay. Groundwater elevation data associated with wells with composite screens and/or unknown screened depths were removed from the data set in most instances, along with any data point that appears to be an outlier when compared with surrounding data from the same period. Select wells with unknown construction were evaluated for inclusion in contour mapping efforts in areas of limited data. Duplicate well measurements were also removed prior to contouring and only one observation for a given well was used for the identified season, rather than averaging all measurements at a given well during the same season.
Figure CC-41 shows the locations of wells with known screened depths within the Delta-Mendota Subbasin as well as known spatial gaps where no well information is currently available. These wells include those monitored under CASGEM, the Delta-Mendota Canal Well Pump-in Program, and by local owners or agencies. Monitoring data available for these wells varies by local owner and agency. Well locations were provided by local agencies to the best of their knowledge at the time of writing and may include wells that have been destroyed or are no longer in service.
Historic Conditions
Historic groundwater trends changed significantly with the first deliveries of imported water deliveries to the Delta-Mendota Subbasin. Construction of the Delta-Mendota Canal and the California Aqueduct heralded the introduction of significant surface water supplies into the Subbasin and reduced dependence on groundwater as the primary water supply. These conveyance systems have resulted in significant increases in the conjunctive use of surface water and groundwater throughout the Subbasin. Various drought periods and regulations reducing delivery of supplies from the Sacramento-San Joaquin Delta also punctuate critical understandings of groundwater use patterns throughout the Subbasin, as well as what is known regarding response and recovery of groundwater levels following notable droughts.
Prior to Imported Water Deliveries (1850-1950s)
Prior to 1850, the majority of agriculture and development in the San Joaquin Valley consisted of rain-fed grain and cattle production, with irrigated development beginning sporadically during this time via river (primarily San Joaquin River) and perennial stream diversions (SWRCB, 2011). Construction of the railroad through the San Joaquin Valley from 1869 through 1875 increased demand for more extensive agriculture, making markets in larger coastal cities more accessible to valley farmers. Significant irrigation sourced from surface water and resulting production began in the western side of the San Joaquin Valley in 1872 when the San Joaquin River was diverted through the Miller and Lux canal system west of Fresno (DWR, 1965). By the 1890s and early 1900s, sizable areas of the southern San Joaquin Valley were being forced out of production by salt accumulation and shallow water tables. Much of this land lay idle until the 1920s when development of reliable electric pumps and the energy to power them accelerated the expansion of irrigated agriculture with the availability of vast groundwater Delta-Mendota Subbasin Groundwater Sustainability Plan
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resources. The resultant groundwater pumping lowered the water table in many areas (SWRCB, 1977 and Ogden, 1988) and allowed the leaching of salts, particularly near the valley trough and western side of the valley. Groundwater pumping for irrigation from around 1920 to 1950 drew the water table down as much as 200 feet in areas along the westside of the San Joaquin River (Belitz and Heimes, 1990).
Declining water tables were causing higher pumping costs and land subsidence, and farmers were finding poorer quality water as water tables continued to decline. These issues created a desire for new surface water supplies, which would be fulfilled by the Central Valley Project.
Post-Imported Water Deliveries (1950s-2012)
Surface water deliveries from the Central Valley Project via the DMC began in the early 1950s, and from the State Water Project via the California Aqueduct in the early 1970s (Sneed et al., 2013). The CVP is the primary source of imported surface water in the Delta-Mendota Subbasin, where only Oak Flat Water District receives deliveries from the SWP. Introduction of imported water supplies to the Delta-Mendota Subbasin resulted in a decrease in groundwater pumping from some parts of the Subbasin and the greater Central Valley, which was accompanied by a steady recovery of water levels. During the droughts of 1976-1977 and 1987-1992, diminished deliveries of imported surface water prompted increased pumping of groundwater to meet irrigation demands, bringing water levels to near-historic lows. Following periods of drought, recovery of pre-drought water levels has been rapid, especially in the Upper Aquifer. This trend has been observed in historic hydrographs for wells across the Subbasin.
Current Conditions
Trends similar to historic drought and subsequent recovery conditions were observed during the 2012 to 2016 drought and the 2016 to present recovery period.
Recent Drought (2012-2016)
During the most recent drought, from 2012 through 2016, similar groundwater trends were observed as during the 1976-1977 and 1987-1992 droughts. With diminished imported surface water deliveries, groundwater pumping increased throughout the Subbasin to meet irrigation needs. This resulted in historic or near-historic low groundwater levels during the height of the drought in 2014 and 2015, when CVP and SWP allocations for agricultural water service contractors were 0%, Exchange Contractors and refuge deliveries were less than 75%, and post-1914 surface water rights in the San Joaquin River watershed were curtailed. In June 2015, senior water rights holders with a priority date of 1903 or later in the San Joaquin and Sacramento watersheds and the Delta were ordered by the State Water Resources Control Board to curtail diversions (State of California, 2015). This marked the first time in recent history that pre-1914 water rights holders were curtailed.
Post-Drought (2016-present)
With wetter conditions following the 2012-2016 drought, groundwater levels began to recover. This was largely a result of increased surface water availability with CVP allocations reaching 100% and full water rights supplies available for diversion from the San Joaquin River in 2017. Additionally, inelastic land subsidence rates also drastically decreased in 2017 as imported water supplies were once again available, resulting in decreased groundwater pumping particularly from the Lower Aquifer. This pattern of increased drought-driven groundwater pumping, accompanied by declining groundwater elevations, followed by recovery is a predominant factor to be considered in the sustainable management of the Delta-Mendota Subbasin. Furthermore, subsidence mitigation projects were developed which drastically reduced the observed subsidence rate on the eastern and southern boundaries of the Subbasin.
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Groundwater Trends
Groundwater levels can fluctuate greatly throughout time due to various natural and anthropogenic factors, including long-term climatic conditions, adjacent well pumping, nearby surface water flows, and seasonal groundwater recharge or depletion (LSCE, 2015). As discussed in the Hydrogeologic Conceptual Model section of this Common Chapter (Section 4.1), the Delta-Mendota Subbasin is generally a twoaquifer system consisting of an Upper and Lower Aquifer that are subdivided by the Corcoran Clay layer, a regional aquitard. The Corcoran Clay layer, or E-Clay equivalent, restricts flow between the upper semiconfined aquifer and lower confined aquifer. The presence of a tile drain network along the Grassland Drainage Area and the Subbasin’s eastern boundary affects the lateral and vertical water movement in the shallow groundwater zone (LSCE, 2016).
The Delta-Mendota Subbasin has a general flow direction to the east in the Upper Aquifer, where it loses groundwater to the San Joaquin River and its neighboring subbasins. Most recharge throughout the Subbasin is attributed to applied irrigation water, where other sources of recharge include local streams, canal seepage, and infiltration along the western margin of the Subbasin from the Coast Range. The figures that follow were developed for inclusion in the Western San Joaquin River Watershed Groundwater Quality Assessment Report (LSCE, 2015) and the Grassland Drainage Area Groundwater Quality Assessment Report (LSCE, 2016) and are included herein with the intent of demonstrating general trends in groundwater elevations around the Delta-Mendota Subbasin. These figures are not to scale.
Please see the individual GSPs for more specific information relating to similar trends in those respective GSP Plan areas. Additionally, it is important to note that groundwater trends, such as these, are dependent on climatic conditions and are not necessarily representative of the historic and current water budgets for those respective GSP Plan areas.
Upper Aquifer
For the Upper Aquifer, Figure CC-42 presents select hydrographs illustrating temporal groundwater level trends in the Upper Aquifer wells within the Subbasin. Hydrographs shown on Figure CC-42 are displayed with different ranges of elevation values on the vertical axes. Wells in the Upper Aquifer exhibit decreasing trends to somewhat stable water levels until the mid-1980s, and increasing or stable water levels thereafter.
Similarly, Figure CC-43 presents select hydrographs illustrating temporal groundwater level trends in the areas covered by the Central Delta-Mendota, Oro Loma Water District, and Widren Water District GSAs in the Northern & Central Delta-Mendota Region GSP Group at various depths. The three select hydrographs representing wells in the Upper Aquifer each show less than 10 years of available data with two wells showing slight declines of about 10 feet or less from about 2003 through 2013, and one well showing a more drastic elevation change, ranging from 100 feet above mean sea level (ft msl) to -20 ft msl over a 5-year period from 2010 to 2016.
Lower Aquifer
Figure CC-44 presents select hydrographs illustrating temporal groundwater level trends in Lower Aquifer wells within the Subbasin. Note, hydrographs shown on Figure CC-44 displayed different ranges of elevation on the vertical axes. In the Lower Aquifer, piezometric head typically increased or remained relatively stable during the period from the 1980s through the early 2000s.
Again, similarly, Figure CC-43 presents select hydrographs illustrating temporal groundwater level trends in the Central Delta-Mendota, Oro Loma Water District, and Widren Water District GSA areas of Delta-Mendota Subbasin Groundwater Sustainability Plan
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the Northern & Central Delta-Mendota Region GSP Group at various depths. The two select hydrographs representing wells in the Lower Aquifer each show similar elevation patterns post-2010 with a total elevation change of 50 ft msl or more. USGS1000489 shows stable and increasing groundwater elevation trends from the late 1950s through the mid-1980s with a data gap from the mid-1980s through 2010, whereafter 2010 groundwater levels have a steep decline through 2016.
Vertical Gradients
Throughout most of the Delta-Mendota Subbasin, the Corcoran Clay layer acts as a regional aquitard, limiting the vertical migration of groundwater. In areas outside the Corcoran Clay layer (along the western margin of the Subbasin), localized interfingered clays minimize the downward migration of groundwater; although in areas where the clay layers are not competent or non-existent, groundwater migrates from shallower to deeper groundwater zones. Similarly, in areas where the Corcoran Clay has been compromised (due to well construction across the clay), groundwater generally flows from the Upper Aquifer to the Lower Aquifer, especially in areas where the Lower Aquifer is actively used as a water supply (lowering the potentiometric head in that zone).
Groundwater Contours
The Subbasin-wide groundwater contours reflected in Figure CC-45 and Figure CC-46 evaluate the seasonal high (Spring 2013) and seasonal low (Fall 2013) conditions of the current year (defined as WY2013 for the GSP analyses) for the Upper Aquifer. Spring is defined as groundwater surface elevation measurements collected between January 1 and April 8; where Fall is defined as groundwater surface elevation measurements collected between September 1 and October 31. For wells where multiple Spring 2013 or Fall 2013 measurements were available, the highest elevation for each season was used for contouring. Gaps in data and contours can be attributed to a lack of wells present, level measurements, or requirements to report level readings groundwater level data. Consistent with traditional contouring efforts, the quality of outlier water level data was investigated. In instances of poor quality data, the associated data was eliminated for the groundwater contouring effort. Furthermore, implementation of the CASGEM program in 2014 has reduced temporal and spatial gaps in groundwater level datasets, and implementation of the Delta-Mendota Subbasin GSPs’ monitoring programs will add to the improved data quantity and quality.
In the Upper Aquifer, during Spring 2013, the general flow of groundwater in the Delta-Mendota Subbasin was from the Coast Range along the western boundary of the Subbasin toward the San Joaquin River along the eastern boundary. Groundwater elevations tend to increase moving south throughout the Subbasin. Within Stanislaus County, groundwater elevations are the lowest, ranging between 40 and 80 feet above msl, becoming increasingly higher in Madera County, ranging between 80 and 100 feet above msl, and in Merced and Fresno counties, ranging between 80 and 140 feet above msl (Figure CC-45).
Similar flow directions (west to east and northeast) are observed in the Fall 2013. Within Stanislaus County, groundwater elevations are the lowest ranging between 40 and 80 feet above msl, showing little difference compared to Spring 2013; become increasingly higher in Madera County ranging between 60 and 100 feet above msl; in Merced County ranging between 60 and 140 feet above msl; and in Fresno County ranging from 60 and 120 feet above msl (Figure CC-46). Both maps indicate a prevailing southwest to northeast flow gradient above the Corcoran Clay. In general, little variation is apparent in groundwater elevation between seasonal high and low periods in 2013.
Due to insufficient data, groundwater elevation contour maps for the Lower Aquifer for the seasonal high and low (Spring 2013 and Fall 2013, respectively) could not be accurately prepared. Figure CC-47 and Figure CC-48 show the available groundwater elevation measurements for Spring 2013 and Fall 2013.
Available Spring 2013 measurements range from -127 to 12 feet above msl in Stanislaus County, -65 to Delta-Mendota Subbasin Groundwater Sustainability Plan
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124 feet above msl in Merced County, and -5 to 88 feet above msl in Fresno County (Figure CC-47), where no measurements are available for this time period in Madera County. Available Fall 2013 measurements range from -138 to 156 feet above msl in Stanislaus County, -94 to 19 feet above msl in Merced County, and -72 to -4 feet above msl in Fresno County (Figure CC-48), where no measurements are available for this time period in Madera County. The Lower Aquifer exhibits less seasonal difference in groundwater elevations than the Upper Aquifer. Throughout most of the Subbasin, the Lower Aquifer shows lower piezometric heads than the Upper Aquifer suggesting that potential exists for downward vertical gradient.
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Figure CC-41: Wells with Known Screened Interval Depths Delta-Mendota Subbasin Groundwater Sustainability Plan
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Note: Figure not to scale.
Source: Western San Joaquin River Watershed Groundwater Quality Assessment Report, 2016 Figure CC-42: Select Graphs of Groundwater Elevations, Upper Aquifer Delta-Mendota Subbasin Groundwater Sustainability Plan
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Note: Figure not to scale. Source: Western San Joaquin River Watershed Groundwater Quality Assessment Report, 2016.
Figure CC-43: Select Graphs of Groundwater Elevations, Various Depths Delta-Mendota Subbasin Groundwater Sustainability Plan
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Note: Figure not to scale.
Source: Western San Joaquin River Watershed Groundwater Quality Assessment Report, 2016.
Figure CC-44: Select Graphs of Groundwater Elevations, Lower Aquifer Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-45: Spring 2013 Upper Aquifer Groundwater Contour Map Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-46: Fall 2013 Upper Aquifer Groundwater Contour Map Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-47: Spring 2013 Lower Aquifer Groundwater Elevation Measurements Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-48: Fall 2013 Lower Aquifer Groundwater Elevation Measurements Delta-Mendota Subbasin Groundwater Sustainability Plan
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4.2.3 Groundwater Storage
Annual changes in groundwater storage for both the Upper and Lower Aquifers in the Delta-Mendota Subbasin were estimated as part of the development of the Historic (WY2003-2012), Current (WY2013) and Projected Water Budgets (WY2014-2070). For information on how change in storage was calculated, refer to Section 4.3.2 – Water Budgets of this Common Chapter. Figure CC-49 and Figure CC-50 show annual change in storage, cumulative change in storage, and water year type for the Upper Aquifer and Lower Aquifer, respectively, from WY 2003 through 2013 for the Delta-Mendota Subbasin. For the purposes of the water budget four water year types were utilized, wet, average (corresponding to above and below normal water years), dry (corresponding to dry and critical water years) and Shasta critical.
Change in storage is negative for 6 out of the 11-year historic and current water budget period for the Upper Aquifer, and 9 out of 11 years for the Lower Aquifer. Despite periods of wet conditions with recharge outpacing extractions, an overall declining trend in groundwater storage can be observed in both the Upper Aquifer and Lower Aquifer. Cumulative change in storage declined more rapidly in the Upper Aquifer compared to the Lower Aquifer, declining by about 624,0000 AF in the Upper Aquifer and 375,000 AF in the Lower Aquifer between WY2003 to 2013.
Figure CC-49: Calculated Upper Aquifer Change in Storage, Annual and Cumulative Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-50: Calculated Lower Aquifer Change in Storage, Annual and Cumulative
4.2.4 Seawater Intrusion
Seawater intrusion is not an applicable sustainability indicator for the Delta-Mendota Subbasin. The Subbasin is located inland from the Pacific Ocean; thus, groundwater conditions related to seawater intrusion are not applicable to the Delta-Mendota Subbasin.
4.2.5 Groundwater Quality
Groundwater quality varies considerably from west to east and north to south throughout the DeltaMendota Subbasin. In general, Upper Aquifer water quality has historically been impacted by overlying land uses with some areas showing increasing concentrations of nitrate and TDS. Areas of elevated salt concentrations can be found in the Subbasin, generally along the southern portion of the San Joaquin River and in the southern portion of the Subbasin. Lower Aquifer groundwater has, and remains in most cases, to be of generally good quality. For more information about historic and current conditions relative to groundwater quality in each GSP Group area, refer to the individual GSPs.
4.2.6 Land Subsidence
Long-term groundwater level declines can result in a one-time release of “water of compaction” from compacting silt and clay layers (aquitards) resulting in inelastic land subsidence (Galloway et al., 1999).
There are several other types of subsidence in the San Joaquin Valley, including subsidence related to hydrocompaction of moisture-deficient deposits above the water table, subsidence related to fluid withdrawal from oil and gas fields, subsidence caused by deep-seated tectonic movements, and subsidence caused by oxidation of peat soils that is a major factor in the Sacramento-San Joaquin Delta (Sneed et al., 2013). However, aquifer-system compaction caused by groundwater pumping causes the largest magnitude and areal extent of land subsidence in the San Joaquin Valley (Poland et al., 1975; Ireland et al., 1984; Farrar and Bertoldi, 1988; Bertoldi et al., 1991; Galloway and Riley, 1999).
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Land subsidence is a prevalent issue in the Delta-Mendota Subbasin as it has impacted prominent infrastructure of statewide importance, namely the DMC and the California Aqueduct, as well as local canals, causing serious operational, maintenance, and construction-design issues (Sneed et al., 2013).
Reduced freeboard and flow capacity for the DMC and California Aqueduct have rippling effects on imported water availability throughout the State. Even small amounts of subsidence in critical locations, especially where canal gradients are small, can impact canal operations (Sneed and Brandt, 2015). While some subsidence is reversible (referred to as elastic subsidence), inelastic or irreversible subsidence is caused mainly by pumping groundwater from below the Corcoran Clay, thus causing compaction and reducing storage in the fine-grained materials in the lower confined aquifer as well as damaging well infrastructure. As a result, important and extensive damages and repairs have resulted in the loss of conveyance capacity in canals that deliver water or remove floodwaters, the realignment of canals as their constant gradient becomes variable, the raising of infrastructure such as canal check stations, and the releveling of furrowed fields.
Available Data
There are six UNAVCO Continuous GPS (CGPS) locations that monitor subsidence within the DeltaMendota Subbasin (Figure CC-51). Changes in land surface elevation have also been measured at DMC Check Structures. Figure CC-52 through Figure CC-57 show the vertical change in land surface elevation from a given time point (specified on charts) for the UNAVCO CGPS stations within the DeltaMendota Subbasin, along with annual CVP allocations. Table CC-5 summarizes the greatest monthly land subsidence rate and corresponding year(s) of that change at each UNAVCO CGPS station. Overall, the greatest monthly subsidence rates occurring after January 1, 2015 occurred during the Spring of 2016 to the Spring of 2017. Land subsidence rates (in feet per year), as measured by USBR from December 2011 to December 2014, are shown in Figure CC-58. Based on these data, within the majority of the Delta-Mendota Subbasin, annual subsidence rates were between -0.15 and -0.3 feet/year during this period (or between -0.45 and -0.9 feet of total subsidence over this three-year period).
Table CC-5: Subsidence Monitoring Trends
UNAVCO CGPS Stations
Station ID
Greatest Monthly Land
Subsidence Rate as of
January 1, 2015 (feet)
Year(s) of Greatest Monthly
Subsidence Rate
P255 -0.0292 Spring 2016 to 2017
P259 -0.0183 Spring 2016 to 2017
P252 -0.033 Spring 2016 to 2017
P303 -0.2190 Spring 2016 to 2017
P301 -0.0029 Spring 2016 to 2017
P304 -0.0003 Spring 2013 to 2017
Historic Conditions
Along the DMC, in the northern portion of the San Joaquin Valley, extensive groundwater extraction from unconsolidated deposits caused subsidence exceeding 8.5 meters (or about 28 feet) between 1926 Delta-Mendota Subbasin Groundwater Sustainability Plan
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and 1970 (Poland et al., 1975), reaching 9 meters (or about 30 feet) in 1980 (Ireland, 1986). Land subsidence from groundwater pumping began in the San Joaquin Valley in the mid-1920s (Poland et al., 1975; Bertoldi et al., 1991; Galloway and Riley, 1999), and by 1970, about half of the San Joaquin Valley had land subsidence of more than 0.3 meters (or about 1 foot) (Poland et al., 1975). When groundwater pumping decreased in the Delta-Mendota Subbasin following imported water deliveries from the CVP via the DMC in the early 1950s, compaction rates were reduced in certain areas and water levels recovered.
Notable droughts of 1976-1977 and 1987-1992 saw renewed compaction during these periods, with increased groundwater pumping as imported supplies were reduced or unavailable. However, following these droughts, compaction virtually ceased, and groundwater levels rose to near pre-drought levels quite rapidly (Swanson, 1998; Galloway et al., 1999).
Subsidence contours for 1926-1970 (Poland et al., 1975) show the area of maximum active subsidence was southwest of the community of Mendota. Historical subsidence rates in the Mendota area exceeded 500 millimeters/year (or about 20 inches/year) during the mid-1950s and early 1960s (Ireland et al., 1984). The area southwest of Mendota has experienced some of the highest levels of subsidence in California, where from 1925 to 1977, this area sustained over 29 feet of subsidence (USGS, 2017).
Historical subsidence rates along Highway 152 calculated from leveling-survey data from 1972, 1988, and 2004 show that for the two 16-year periods (1972-1988 and 1988-2004), maximum subsidence rates of about 50 millimeters/year (or about 2 inches/year) were found just south of El Nido (Sneed et al., 2013). Geodetic surveys completed along the DMC in 1935, 1953, 1957, 1984, and annually from 1996- 2001 indicated that subsidence rates were greatest between 1953 and 1957 surveys, and that the maximum subsidence along the DMC (about 3 meters, or about 10 feet) was just east of DMC Check Structure Number 18.
After 1974, land subsidence was demonstrated to have slowed or largely stopped (DWR, June 2017); however, land subsidence remained poised to resume under certain conditions. Such an example includes the severe droughts that occurred between 1976 and 1977 and between 1987 and 1991. Those droughts, along with other corroborating factors, led to diminished deliveries of imported water which prompted some water agencies and farmers (especially in the western Valley) to refurbish old pumps, drill new water wells, and begin pumping groundwater to make up for cutbacks in the imported water supply. The decisions to renew groundwater pumping were encouraged by the fact that groundwater levels had recovered to near-predevelopment levels. CGPS data collected between 2007 to 2014 show seasonally variable subsidence and compaction rates, including uplift as elastic rebound occurs during the fall and winter (Sneed and Brandt, 2015). Vertical displacement at P303, near Los Banos, indicates subsidence at fairly consistent rates during and between drought periods (Sneed and Brandt, 2015). Vertical displacement at P304, near Mendota, indicates that most subsidence occurred during drought periods with very little occurring between drought periods. Finally, data from extensometers 12S/12E-16H2, located on the DMC west of Los Banos, and 14S/13E-11D6, located between the DMC and California Aqueduct west of Mendota, showed subsidence rate increases during 2014, the third year of the most recent drought (Sneed and Brandt, 2015).
Subsidence impacts to the California Aqueduct, which runs parallel and in close proximity to the DeltaMendota Canal across the Subbasin, is of statewide importance. During the construction of the California Aqueduct, it was thought that subsidence within the San Joaquin Valley would cease with the delivery of water from the Central Valley Project, though additional freeboard was incorporated into the design and construction of the Aqueduct in an attempt to mitigate for future subsidence (DWR, June 2017). After water deliveries from the Aqueduct began, subsidence rates decreased to an average of less than 0.1 inches/year during normal to wet hydrologic years. During dry to critical hydrologic years, subsidence increased to an average of 1.1 inches per year. The 2012-2015 drought produced subsidence similar to those seen before the Aqueduct began delivering water, with some areas experiencing nearly 1.25 inches of sinking per month (based on NASA UAVSAR flight measurements). Dry and critically dry water years Delta-Mendota Subbasin Groundwater Sustainability Plan
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since Aqueduct deliveries began have resulted in extensive groundwater withdrawals, causing some areas near the Aqueduct to subside nearly 6 feet.
Current Conditions
Based on subsidence rates observed over the last decade, it is anticipated that without mitigation, subsidence will continue to impact operations of the DMC and California Aqueduct. For example, recently, Reach 4A of the San Joaquin River near Dos Palos experienced between 0.38 and 0.42 feet/year in subsidence between 2008 and 2016. As a result of subsidence, freeboard in Reach 4A is projected to be reduced by 0.5 foot by 2026 as compared to 2016, resulting in a 50 percent reduction in designed flow capacity (DWR, May 2018). Reduced flow capacities in the California Aqueduct will impact deliveries and transfers throughout the State and result in the need to pump more groundwater, thus contributing to further subsidence.
More recent subsidence measuring indicates subsidence hot spots within the Subbasin include the area east of Los Banos and the Tranquillity Irrigation District (TRID) area. USGS began periodic measurements of the land surface in parts of the San Joaquin Valley over the last decade. Between December 2011 and December 2014, total subsidence in the area east of Los Banos, located within the Merced Subbasin (also referred to as the El Nido-Red Top area), over the three-year period ranged from
0.15 to 0.75 feet, or 1.8 to 9 inches respectively (KDSA, 2015). The Jet Propulsion Laboratory (JPL) at the California Institute of Technology has also been monitoring subsidence in California using interferometric synthetic aperture radar (or InSAR), and a recent progress report documenting data for the period from May of 2015 to September of 2016 indicates that the two previously-identified primary subsidence areas near the community of Corcoran and centered on El Nido was joined by a third area of significant subsidence near TRID. For the study period (as shown in Figure CC-59), maximum total subsidence of 22 inches was measured near Corcoran, while the El Nido area subsided 15 inches and the TRID area subsided around 20 inches. Analyses at two particular stations near El Nido show interesting trends. At Station P303, between 2007 and 2014, 50 mm (or nearly 2 inches) of subsidence occurred at this location. Vertical displacement at P303 (Figure CC-55) show subsidence at fairly consistent rates during and between drought periods, indicating that these areas continued to pump groundwater despite climatic variations (possibly due to a lack of surface water availability) (Sneed and Brandt, 2015).
Residual compaction may also be a factor. Vertical displacement at Station P304 indicated that most subsidence in this particular area occurred during drought periods and very little occurred between drought periods (Figure CC-57). This suggests that this area received other sources of water (most likely surface water available between drought periods) and that residual compaction was not very important in this area. These two areas demonstrate a close link between the availability of surface water, groundwater pumping, and inelastic land subsidence.
Total land subsidence from April 2015 to April 2016 in the San Joaquin Valley is shown in Figure CC-60: Vertical Displacement, April 2015 to April 2016 . Subsidence monitoring in the DeltaMendota Subbasin, and in the San Joaquin Valley as a whole, demonstrated significant inelastic land subsidence as a result of the last drought, with effects continuing to the present time (as evidenced by continued subsidence between 2016 and 2018 through surveys of the DMC). While the impacts appeared to have slowed, the temporal and spatial impacts of continued subsidence have not yet been evaluated.
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Figure CC-51: UNAVCO and Delta-Mendota Canal Subsidence Monitoring Locations Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-52: Vertical Elevation Change at UNAVCO CGPS P255, Spring 2007 to 2018 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-53: Vertical Elevation Change at UNAVCO CGPS P259, Spring 2006 to 2018 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-54: Vertical Elevation Change at UNAVCO CGPS P252, Spring 2006 to 2018 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-55: Vertical Elevation Change at UNAVCO CGPS P303, Spring 2006 to 2018 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-56: Vertical Elevation Change at UNAVCO CGPS P301, Spring 2005 to 2018 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-57: Vertical Elevation Change at UNAVCO CGPS P304, Spring 2005 to 2018 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-58: Land Subsidence, December 2011 to December 2014 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Source: Progress Report: Subsidence in California, March 2015 – September 2016, Farr et. Al. JPL, 2017 Figure CC-59: Recent Land Subsidence at Key San Joaquin Valley Locations Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-60: Vertical Displacement, April 2015 to April 2016 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-61: Elevation Change along the Delta-Mendota Canal, 2014 through 2018 Delta-Mendota Subbasin Groundwater Sustainability Plan
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4.2.7 Interconnected Surface Water Systems
Understanding the location, timing and magnitude of groundwater pumping impacts on interconnected surface water systems is important for the proper management of groundwater resources in order to minimize impacts on interconnected surface waters and the biological communities and permitted surface water diverters that rely on those resources. Historically, throughout the San Joaquin Valley, many interconnected stream reaches have transitioned from net-gaining to net-losing streams (TNC, 2014).
Gaining streams occur when streamflows increase as a result of groundwater contribution and losing streams occur when streamflows decrease due to infiltration into the bed of the stream (McBain & Trush, Inc., 2002). Increased groundwater pumping has the ability to contribute to the depletion of interconnected waters with the nature, rate, and location of increased pumping being a function of distance to the river, as well as depth, timing, and rate of groundwater pumping.
Available Data
Two communities in the Delta-Mendota Subbasin are likely most vulnerable to the loss of interconnected surface water as a result of groundwater pumping: San Joaquin River surface water diverters and groundwater dependent ecosystems (GDEs). These communities represent the primary beneficial users of interconnected surface water and groundwater. Streams stemming from the west side of the DeltaMendota Subbasin are ephemeral in nature, and only two of these creeks reach the San Joaquin River (Del Puerto Creek and Orestimba Creek). These creeks lose their flows to the underlying vadose zone (netlosing streams) and therefore do not represent areas of potential GDEs.
Groundwater dependent ecosystems are defined under Article 2 Definitions, § 351 Definitions of the GSP Emergency Regulations as “ecological communities or species that depend on groundwater emerging from aquifers or on groundwater occurring near the ground surface.” The Natural Communities Commonly Associated with Groundwater (NCCAG) dataset (2018) provided by DWR in conjunction with The Nature Conservancy (TNC) was initially used to identify GDEs within the Delta-Mendota Subbasin, following the associated guidance document provided by TNC (Rohde et al., 2018). Local verification efforts were conducted in the Delta-Mendota Subbasin by different GSA representatives to ground-truth GDEs based on local knowledge. Specifically, areas where natural communities have been urbanized or otherwise modified prior to 2015 were eliminated from the data set used to identify GDEs.
Identification of Interconnected Surface Water Systems
The San Joaquin River and Fresno Slough are the primary surface water bodies interconnected with Delta-Mendota Subbasin groundwater. For information about the sources used to determine the interconnected segments of the San Joaquin River and Fresno Slough within the Delta-Mendota Subbasin, refer to the individual GSPs.
Historic Conditions
The San Joaquin River and its tributaries drain approximately 13,500 mi2 (measured at the USGS gaging station at Vernalis) along the western flank of the Sierra Nevada and eastern flank of the Coast Range, and flows northward into the Sacramento-San Joaquin Delta where it is joined by the Calaveras and Mokelumne Rivers before combining with the Sacramento River. Typical of Mediterranean climate catchments, river flows vary widely seasonally and from year to year. Three major tributaries join the San Joaquin from the east: the Merced, Tuolumne, and Stanislaus Rivers. Smaller tributaries include the Fresno River, Chowchilla River, Bear Creek, and Fresno Slough (from the Kings River). Precipitation is predominantly snow above about 5,500 to 6,000 feet in the Sierra Nevada, with rain in the middle and Delta-Mendota Subbasin Groundwater Sustainability Plan
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lower elevations of the Sierra foothills and in the Coast Range. As a result, the natural hydrology historically reflected a mixed runoff regime dominated by winter-spring rainfall runoff and springsummer snowmelt runoff. Most flow is derived from snowmelt from the Sierra Nevada, with relatively little runoff contributed from the western side of the drainage basin in the rain shadow of the Coast Range. The unimpaired average annual water yield (WY1906-2002) of the San Joaquin River, as measured immediately above Millerton Reservoir, is 1,801,000 acre-feet (USBR, 2002); the post-Friant Dam average annual water yield (WY 1950-2000) to the lower San Joaquin River is 695,500 acre-feet (USGS, 2000). As average precipitation decreases from north to south, the San Joaquin River basin (including the Stanislaus, Tuolumne, and Merced Rivers) contributes about 22% of the total runoff to the Delta (DWR, 1998).
Current Conditions
Historically, most of the San Joaquin River, which forms the great majority of the Delta-Mendota Subbasin’s eastern border, was a gaining reach. Snowmelt runoff during the spring and early summer resulted in these conditions through a good portion of the year. However, significant decreases in groundwater elevations due to a myriad of factors, including pumping, tile drains, the channelizing of flood flows, and upstream diversions on the river, have reversed this condition so most reaches are now losing reaches. Some localized gaining reaches still remain on the lower river, such as between the Stanislaus and Merced Rivers; however, many reaches along these rivers (and along localized streams) may transition from gaining to losing depending on hydrology.
Estimates of Timing and Quantity of Depletions
Using available data and where feasible, each Delta-Mendota Subbasin GSP Group quantified the gains and/or losses from the groundwater at each interconnected reach of the San Joaquin River adjoining the Delta-Mendota Subbasin. Table CC-6 summarizes these estimates. For more information about the sources or methods used to estimate the timing and quantity of depletions, refer to the individual GSPs.
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Table CC-6: Estimated Quantity of Gains/Depletions for Interconnected Stream Reaches, San Joaquin River Landmark River Mile GSP Group Interconnected? Gaining or Losing? Quantity Gained/Loss (cfs) Notes REACH 1 267.5 to
229.0
Located outside the Delta-Mendota Subbasin
A Friant Dam 267.5
North Fork Road Bridge 266.8 Cobb Island Bridge 259.0 State Route 41 (Lanes Bridge) 255.2 Scout Island Bend 250.0 ATSF Railroad Bridge 245.0 B State Route 99 243.2
Southern Pacific Railroad 243.2 State Route 145 Bridge (Skaggs Bridge) 234.1 Gravelly Ford 229.0 REACH 2 229.0 to
204.8
A Gravelly Ford 229.0 Yes Losing when flowing
Upstream Limit of Right Bank Levee 227.0 Upstream Limit of Left Bank Levee 225.0 B Chowchilla Bypass Control Structure 216.1 Farmers
Water District
Yes Losing when flowing -4 2003 to 2013 average. High in 2010 (-8 cfs), low in 2004 and 2009 (-1 cfs)
Mendota Dam 204.8 Mendota Pool Yes Losing -40 -29,000 AFY REACH 3 204.8 to
182.0
Yes Losing -25 -18.000 AFY
Mendota Dam 204.8 Avenue 7.5 Bridge (Firebaugh) 195.2 Sack Dam 182.0 REACH 4 182.0 to
135.8
-–0 - 0 Losses when wet; gaining in some areas (but
unquantifiable)
A Sack Dam 182.0 Y–s - first 2 miles
–o - next 1.5
miles
Y–s - remaining
miles
Losing
State Route 152 Bridge 173.9 Yes Gaining
B Sand Slough Control Structure 168.5
Mariposa Slough Control Structure 168.4 Turner Island Road Bridge 157.2 Mariposa Bypass confluence 147.2 Delta-Mendota Subbasin Groundwater Sustainability Plan
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Landmark River Mile GSP Group Interconnected? Gaining or Losing? Quantity Gained/Loss (cfs) Notes Bear Creek/Eastside Bypass confluence 135.8
REACH 5 135.8 to
118.0
Yes Gaining unquantifiable Likely gaining from ag/refuge draining but unquantifiable
Bear Creek/Eastside Bypass confluence 135.8 State Route 165 Bridge (Lander Avenue) 132.9 Salt Slough con fluence 127.7 State Route 140 Bridge (Fremont Ford) 125.1 Mud Slough confluence 121.2 Merced River confluence (Hills Ferry Bridge) 118.0 Newman to Crows Landing Northern & Central DeltaMendota
Yes Gaining 50 50
Crows Landing to Patterson Northern &
Central DeltaMendota
Region
Yes Gaining -50 to 200 -50 to 200
Patterson to Vernalis Northern &
Central DeltaMendota
Region
Yes Gaining 190 6.1 cfs/mi for 30.8 miles. Based on Cooley, W. 2001.
Groundwater flow net analysis for lower San Joaquin
River Basin. Memo to CRWQCB, August 8, 2001
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Groundwater Dependent Ecosystems
A groundwater dependent ecosystem (GDE) is defined under the GSP Emergency Regulations as referring “to ecological communities or species that depend on groundwater emerging from aquifers or on groundwater occurring near the ground surface” (§351(m)). Under §354.16(g) of the GSP Emergency Regulations, each Plan is required to identify GDEs within the subbasin utilizing data provided by DWR or the best available information. The following section describes the process for verifying GDEs within the Delta-Mendota Subbasin and the location of verified and potential GDEs.
The Natural Communities Commonly Associated with Groundwater (NCCAG) dataset (2018c) provided by DWR was used in conjunction with information provided by The Nature Conservancy (TNC) to identify GDEs within the Delta-Mendota Subbasin. To further screen available information regarding GDEs, each GSP Group developed individualized criteria. Additional details regarding the screening process implemented by each GSP can be found in the individual GSPs.
Based on the screening process implemented by each individual GSP Group, GDE polygons determined not to be GDEs were removed from the mapping. Figure CC-62 and Figure CC-63 summarize the results of the GDE analysis for the Subbasin. Results are compiled into two habitat classes: wetlands (Figure CC-62) and vegetation (Figure CC-63). Wetland features are commonly associated with surface expression of groundwater under natural, unmodified conditions. Vegetation feature types are commonly associated with the sub-surface presence of groundwater (phreatophytes – deep rooted plants). Confirmed GDEs have been grouped into larger polygons based on proximity and aquifer connection.
In general, identified Possible GDEs are primarily located along the San Joaquin River corridor, within the northern portion of the Northern & Central Delta-Mendota Region GSP, the SJREC GSP, the Grassland GSP, and the Fresno GSP Plan Areas, where some possible GDEs have been identified along ephemeral streams that originate from the Coast Range. Table CC-7 includes all freshwater species within the Delta-Mendota Subbasin as identified by TNC (2018). Per TNC data, these species (listed in Table CC-7) have either been observed or have the potential to exist within the Delta-Mendota Subbasin; however, the actual presence of these species have not been verified. As a result of the identification of Possible GDEs for the purpose of SGMA, no land use protections for GDEs are conveyed unless otherwise required. Additionally, the Delta Mendota Subbasin recognizes the opportunity to present further-refined GDE delineations in the subsequent GSP Updates.
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Figure CC-62: Groundwater Dependent Ecosystems, Wetlands Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-63: Groundwater Dependent Ecosystems, Vegetation Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-7: List of Potential Freshwater Species
Scientific Name Common Name Group Federal Protection Status State Protection Status Actitis macularius Spotted Sandpiper Birds Aechmophorus clarkii Clark’s Grebe Birds Aechmophorus occidentalis Western Grebe Birds Agelaius tricolor Tricolored Blackbird Birds Bird of Conservation Concern Special Concern
Aix sponsa Wood Duck Birds Anas acuta Northern Pintail Birds Anas americana American Wigeon Birds Anas clypeata Northern Shoveler Birds Anas crecca Green-winged Teal Birds Anas cyanoptera Cinnamon Teal Birds Anas discors Blue-winged Teal Birds Anas platyrhynchos Mallard Birds Ariescriser albifrons Greater White-fronted Goose Birds
Ardea alba Great Egret Birds Ardea herodias Great Blue Heron Birds Aythya affinis Lesser Scaup Birds Aythya americana Redhead Birds Special Concern Aythya collaris Ring-necked Duck Birds Aythya marila Greater Scaup Birds Aythya valisineria Canvasback Birds Special Botaurus lentiginosus American Bittern Birds Bucephala albeola Bufflehead Birds Bucephala clangula Common Goldeneye Birds Butorides virescens Green Heron Birds Calidris alpina Dunlin Birds Calidris mauri Western Sandpiper Birds Calidris minutilla Least Sandpiper Birds Chen caerulescens Snow Goose Birds Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Chen rossii Ross’s Goose Birds Chlidonias niger Black Tern Birds Special Concern Chroicocephalus philadelphia Bonaparte’s Gull Birds Cistothorus palustris Marsh Wren Birds Cygnus columbianus Tundra Swan Birds Cypseloides niger Black Swift Birds Bird of Conservation Concern Special Concern
Dendrocygna bicolor Fulvous Whistling-Duck Birds Special Concern Egretta thula Snowy Egret Birds Empidonax traillii Willow Flycatcher Birds Bird of Conservation Concern Endangered
Fulica americana American Coot Birds Gallinago delicata Wilson’s Snipe Birds Gallinula chloropus Common Moorhen Birds Geothlypis trichas Common Yellowthroat Birds Grus canadensis Sandhill Crane Birds Haliaeetus leucocephalus Bald Eagle Birds Bird of Conservation Concern Endangered
Himantopus mexicanus Black-necked Stilt Birds Icteria virens Yellow-breasted Chat Birds Special Concern Limnodromus scolopaceus Long-billed Dowitcher Birds Lophodytes cucullatus Hooded Merganser Birds Megaceryle alcyon Belted Kingfisher Birds Mergus merganser Common Merganser Birds Mergus serrator Red-breasted Merganser Birds
Numenius americanus Long-billed Curlew Birds Numenius phaeopus Whimbrel Birds Nycticorax Black-crowned NightHeron Birds
Oxyura jamaicensis Ruddy Duck Birds Pandion haliaetus Osprey Birds Watch listPelecanus erythrorhynchos American White Pelican Birds Special Concern Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Phalacrocorax auritus
Double-crested Cormorant Birds
Phalaropus tricolor Wilson’s Phalarope Birds Plegadis chihi White-faced Ibis Birds Watch listPluvialis squatarola Black-bellied Plover Birds Podiceps nigricollis Eared Grebe Birds Podilymbus podiceps Pied-billed Grebe Birds Porzana carolina Sora Birds Rallus limicola Virginia Rail Birds Recurvirostra americana American Avocet Birds Riparia Bank Swallow Birds Threatened Setophaga petechia Yellow Warbler Birds Tachycineta bicolor Tree Swallow Birds Tringa melanoleuca Greater Yellowlegs Birds Tringa semipalmata Willet Birds Tringa solitaria Solitary Sandpiper Birds Vireo bellii Bell’s Vireo Birds Vireo bellii pusillus Least Bell’s Vireo Birds Endangered Endangered Xanthocephalus Yellow-headed Blackbird Birds Special Concern
Artemia franciscana
San Francisco Brine Shrimp Crustaceans
Branchinecta conservatio
Conservancy Fairy Shrimp Crustaceans Endangered Special Branchinecta lindahli Versatile Fairy Shrimp Crustaceans Branchinecta longiantenna Longhorn Fairy Shrimp Crustaceans Endangered Special Branchinecta lynchi Vernal Pool Fairy Shrimp Crustaceans Threatened Special Lepidurus packardi
Vernal Pool Tadpole Shrimp Crustaceans Endangered Special Linderiella occidentalis California Fairy Shrimp Crustaceans Special Oncorhynchus myki–s - CV Central Valley steelhead Fishes Threatened Special Oncorhynchus mykiss irideus Coastal rainbow trout Fishes Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Pogonichthys macrolepidotus Sacramento splittail Fishes Special Concern Actinemys marmorata Western Pond Turtle Herps Special Concern Ambystoma californiense California Tiger Salamander Herps Threatened Threatened Anaxyrus boreas Boreal Toad Herps Pseudacris regilla
Northern Pacific Chorus Frog Herps
Rana boylii
Foothill Yellow-legged Frog Herps
Under Review in the Candidate or Petition Process Special Concern Rana draytonii
California Red-legged Frog Herps Threatened Special Concern Spea hammondii Western Spadefoot Herps
Under Review in the Candidate or Petition Process Special Concern Thamnophis atratus Santa Cruz Gartersnake Herps Thamnophis elegans Mountain Gartersnake Herps Thamnophis gigas Giant Gartersnake Herps Threatened Threatened Thamnophis hammondii Two-striped Gartersnake Herps Special Concern
Thamnophis sirtalis Common Gartersnake Herps Aeshnidae fam. Aeshnidae fam. Insects & other inverts Anax junius Common Green Darner Insects & other inverts Brillia spp. Brillia spp. Insects & other inverts Callicorixa spp. Callicorixa spp. Insects & other inverts Capnia hitchcocki Arroyo Snowfly Insects & other inverts Chironomus spp. Chironomus spp. Insects & other inverts Coenagrionidae fam. Coenagrionidae fam. Insects & other inverts Corisella spp. Corisella spp. Insects & other inverts Cricotopus spp. Cricotopus spp. Insects & other inverts Ischnura cervula Pacific Forktail Insects & other inverts Ischnura denticollis Black-fronted Forktail Insects & other inverts Mesocapnia bulbosa Bulbous Snowfly Insects & other inverts Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Paraleptophlebia associata A Mayfly Insects & other inverts Paratanytarsus spp. Paratanytarsus spp. Insects & other inverts Phaenopsectra spp. Phaenopsectra spp. Insects & other inverts Procladius spp. Procladius spp. Insects & other inverts Psectrocladius spp. Psectrocladius spp. Insects & other inverts Tanypus spp. Tanypus spp. Insects & other inverts Tipulidae fam. Tipulidae fam. Insects & other inverts Trichocorixa spp. Trichocorixa spp. Insects & other inverts Castor canadensis American Beaver Mammals Lontra canadensis North American River Otter Mammals
Neovison vison American Mink Mammals Ondatra zibethicus Common Muskrat Mammals Anodonta californiensis California Floater Mollusks Special Margaritifera falcata Western Pearlshell Mollusks Special Pyrgulopsis diablensis Diablo Range Pyrg Mollusks Special Alopecurus saccatus Pacific Foxtail Plants Ammannia coccinea Scarlet Ammannia Plants Anemopsis californica Yerba Mansa Plants Arundo donax NA Plants Azolla filiculoides NA Plants Azolla microphylla Mexican mosquito fern Plants Special Baccharis salicina Plants Bacopa eisenii Gila River Water-hyssop Plants Bidens laevis Smooth Bur-marigold Plants Bolboschoenus glaucus NA Plants Bolboschoenus maritimus paludosus NA Plants Callitriche marginata Winged Water-starwort Plants Ceratophyllum demersum Common Hornwort Plants Chloropyronmoesclle hispidum Plants Special Chloropyron palmatum NA Plants Endangered Special Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Cotula coronopifolia NA Plants Crassula aquatica Water Pygmyweed Plants Crypsis vaginiflora NA Plants Cyperus erythrorhizos Red-root Flatsedge Plants Cyperus squarrosus Awned Cyperus Plants Downingia bella Hoover’s Downingia Plants Downingia pulchella Flat-face Downingia Plants Echinodorus berteroi Upright Burhead Plants Elatine brachysperma Shortseed Waterwort Plants Elatine californica California Waterwort Plants Eleocharis acicularis Least Spikerush Plants Eleocharis atropurpurea Purple Spikerush Plants Eleocharis coloradoensis Plants Eleocharis macrostachya Creeping Spikerush Plants Eleocharis montevidensis Sand Spikerush Plants Eleocharis quadrangulata NA Plants Elodea canadensis Broad Waterweed Plants Epilobium cleistogamum Cleistogamous Spikeprimrose Plants
Eragrostis hypnoides Teal Lovegrass Plants Eryngium castrense Great Valley Eryngo Plants Eryngium racemosum Delta Coyote-thistle Plants Endangered Eryngium spinosepalum Spiny Sepaled Coyotethistle Plants Special
Eryngium vaseyi vallicola Plants Eryngium vaseyi Vasey’s Coyote-thistle Plants Euthamia occidentalis Western Fragrant Goldenrod Plants
Hydrocotyle verticillata
Whorled Marshpennywort Plants
Juncus acuminatus Sharp-fruit Rush Plants Juncus xiphioides Iris-leaf Rush Plants Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Lasthenia ferrisiae Ferris' Goldfields Plants Special Lasthenia fremontii Fremont’s Goldfields Plants Lemna aequinoctialis Lesser Duckweed Plants Lemna gibba Inflated Duckweed Plants Lemna minor Lesser Duckweed Plants Lepidium jaredii Jared’s Peppergrass Plants Special Lepidium oxycarpum Sharp-pod Peppergrass Plants Limnanthes douglasii Douglas' Meadowfoam Plants Limosella acaulis Southern Mudwort Plants Lipocarpha micrantha Dwarf Bulrush Plants Ludwigia peploides NA Plants Ludwigia repens Creeping Seedbox Plants Lythrum californicum California Loosestrife Plants Marsilea vestita NA Plants Mimulus cardinalis Scarlet Monkeyflower Plants Mimulus guttatus Common Large Monkeyflower Plants
Montia fontana Fountain Miner’s-lettuce Plants Myosurus minimus NA Plants Myosurus sessilis Sessile Mousetail Plants Myriophyllum aquaticum NA Plants Najas guadalupensis Southern Naiad Plants Navarretia heterandra Tehama Navarretia Plants Navarretia leucocephala White-flower Navarretia Plants Navarretia prostrata Prostrate Navarretia Plants Special Neostapfia colusana Colusa Grass Plants Threatened Endangered Panicum dichotomiflorum NA Plants Paspalum distichum Joint Paspalum Plants Persicaria hydropiperoides Plants Persicaria lapathifolia Plants Persicaria maculosa NA Plants Persicaria pensylvanica NA Plants Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Phacelia distans NA Plants Phyla lanceolata Fog-fruit Plants Phyla nodiflora Common Frog-fruit Plants Pilularia americana NA Plants Plagiobothrys acanthocarpus Adobe Popcorn-flower Plants Plagiobothrys greenei Greene’s Popcornflower Plants
Plagiobothrys humistratus Dwarf Popcorn-flower Plants Plagiobothrys leptocladus Alkali Popcorn-flower Plants Plantago elongata Slender Plantain Plants Pluchea odorata Scented Conyza Plants Pogogyne douglasii NA Plants Pogogyne zizyphoroides Plants Potamogeton diversifolius Water-thread Pondweed Plants Potamogeton foliosus Leafy Pondweed Plants Potamogeton nodosus Longleaf Pondweed Plants Potamogeton pusillus Slender Pondweed Plants Psilocarphus brevissimus Dwarf Woolly-heads Plants Psilocarphus oregonus Oregon Woolly-heads Plants Psilocarphus tenellus NA Plants Puccinellia simplex Little Alkali Grass Plants Ranunculus sceleratus NA Plants Rorippa curvisiliqua Curve-pod Yellowcress Plants Rorippa palustris Bog Yellowcress Plants Rotala ramosior Toothcup Plants Ruppia cirrhosa Widgeon-grass Plants Ruppia maritima Ditch-grass Plants Sagittaria longiloba Longbarb Arrowhead Plants Sagittaria montevidensis calycina Plants Salix exigua Narrowleaf Willow Plants Salix gooddingii Goodding’s Willow Plants Delta-Mendota Subbasin Groundwater Sustainability Plan
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Scientific Name Common Name Group Federal Protection Status State Protection Status Schoenoplectus acutus occidentalis Hardstem Bulrush Plants Schoenoplectus americanus Three-square Bulrush Plants Sinapis alba NA Plants Sparganium eurycarpum Plants Stuckenia pectinata Plants Typha domingensis Southern Cattail Plants Typha latifolia Broadleaf Cattail Plants Veronica americana American Speedwell Plants Wolffiella lingulata Tongue Bogmat Plants Zannichellia palustris Horned Pondweed Plants Source: The Nature Conservancy (TNC). 2018. Identifying Environmental Surface Water Use–s - Freshwater Species List for Each Groundwater Basin dataset. https://groundwaterresourcehub.org/gde-tools/environmental-surface-water-beneficiaries/ Delta-Mendota Subbasin Groundwater Sustainability Plan
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4.2.8 Data Gaps
The Delta-Mendota Subbasin is an extensive subbasin covering a large area extending along the northwestern end of the San Joaquin Valley. While there is a significant amount of data available regarding various groundwater-related aspects of the Subbasin, much is still not known in multiple locations around the Subbasin. To this end, the following data gaps have been identified and will be addressed as part of the interim period between adoption of this GSP and its first 5-year update. Information regarding subsidence varies in extent around the region. While there is a large amount of land elevation survey data available in association with the DMC and the San Joaquin River Restoration Program, other areas in the Delta-Mendota Subbasin require additional data collection to both further establish and monitor future land subsidence rates. Only three shallow groundwater wells exist proximate to the northern end of the San Joaquin River (outside of the area being addressed by the San Joaquin River Restoration Program). Additional nested or clustered monitoring wells are required adjacent to the river on the northern end of the Subbasin to evaluate horizontal and vertical groundwater gradients, and in connection with river stage monitoring, to assess the interconnection between the San Joaquin River and the northeastern end of the Delta-Mendota Subbasin.
There are a large number of wells in the Delta-Mendota Subbasin where no well construction information exists or is readily available. Video surveys and other surveys should be conducted on selected wells that may potentially be added to the Subbasin monitoring network to (1) identify where the wells are screened, and (2) determine if the well(s) are appropriate as additions to the GSP Groups’ groundwater monitoring programs.
Mapping of GDEs in the Delta-Mendota Subbasin, as contained in this Common Chapter, is an initial assessment of their location. This mapping may be refined using most recent groundwater elevation/depth to water contour mapping.
Monitoring networks contained herein are preliminary and were formulated based on existing well information. As additional wells are installed in the Subbasin and additional well construction information is obtained for existing wells, these networks may need to be refined to improve on the spatial (areal and vertical) distribution of monitoring points and the data collected for evaluation of conditions of the groundwater basin.
The sustainable yield estimates and water budgets contained in this Common Chapter for both the Upper and Lower Aquifers were developed using limited data. As additional data are collected over the first five years, improved sustainable yield estimates and estimates of water in storage in both principal aquifers should be prepared utilizing the new data.
In addition to these Subbasin-level data gaps, additional data gaps have been identified for each GSP Plan Area. Please see the individual GSPs for additional identified data gaps.
4.3 Delta-Mendota Subbasin Water Budgets
This section describes the common coordinated assumptions agreed upon and utilized by each GSP Group in the Delta-Mendota Subbasin in developing the historical, current, and projected water budgets for their respective GSP Plan Areas. These coordinated historical, current, and projected water budgets were then compiled to prepare the subbasin-level water budgets required under the GSP Regulations § Delta-Mendota Subbasin Groundwater Sustainability Plan
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357.4(b)(3)(B), presented below. The sustainable yield for the Upper Aquifer and Lower Aquifer developed at the Subbasin-level and agreed upon by all GSP Groups in the Delta-Mendota Subbasin is also presented along with a description as to how the sustainable yield for each primary aquifer was calculated.
4.3.1 Coordinated Assumptions
All common coordinated assumptions agreed upon and utilized by each GSP Group in preparing their respective historical, current, and projected water budgets are presented in Technical Memoranda 3 (Assumptions for the Historical, Current, and Projected Water Budgets of the Delta-Mendota Subbasin), which is included in Appendix B of this Common Chapter.
The data and methodologies used to develop the water budgets in the six individual GSPs (and compiled herein as the Subbasin Water Budgets) were coordinated with the express objective to “rely on the best available information and best available science to quantify the water budget for the basin” (Title 23 of the California Code of Regulations [23 CCR] § 354.18(e)). Given the complex nature of the Subbasin, different data sets and methodologies were appropriate for and/or available in different portions of the Subbasin. As such, a significant effort was made by the Subbasin GSAs to: (1) identify the different sources and accuracy of the available data; (2) consolidate these data and associated methodologies into a general hierarchy for use by the GSAs to honor the local conditions, while maintaining consistency with the intent of 23 CCR § 354.18(e); and (3) standardize the terminology for purposes of the Common Chapter presentation of the Subbasin Water Budget. These standardized water budget components and data sources are presented in Error! Reference source not found. and Table CC-9 for the historic and current, and projected water budgets, respectively, and are further described below, while acknowledging that significant additional detail is presented in the six underlying GSPs. In some cases, data were not available or applicable, as acknowledged below and in the tables. Additionally, in some cases the specific terminology and/or the details of the calculations included in each underlying GSP remains unique relative to the standardized terminology and descriptions presented below; a full reconciliation of water budget nomenclature will be conducted as part of the 2025 GSP updates, as well as updates to the datasets and methodologies employed. Water use in the Subbasin is largely for agricultural purposes, with local municipal and industrial (M&I) uses. As appropriate, these M&I uses were quantified and incorporated in the individual GSP water budgets.
LAND SURFACE WATER BUDGET
The data sources/methodologies used to estimate the six major components of the Historical and Current Land Surface Water Budgets are summarized in Table CC-8 and for the Projected Land Surface Water Budgets in Table CC-9. A general description of each component and the data hierarchy that was applied by the GSAs is provided below, with further detail provided in the Water Budget sections of the six underlying GSPs. For purposes of the Subbasin GSPs, the Historical and Current Water Budgets represent Water Year (WY) 2003-2013, where the historical period is WY 2003-2012 and the current year is WY 2013. The Projected Water Budgets reflect projected conditions through 20701 and consider the impacts
1 The Subbasin GSAs agreed to use actual data from WYs 2014-2017 and assume a repeat of the historical hydrology for the years WY 2018-2070. The selected period for the projected water budgets meets SGMA requirements by establishing a 50-year period, where the timeframe is continuous between the historic, current, and projected water budgets. The historic hydrologic period for simulating the projected water budget hydrologic Delta-Mendota Subbasin Groundwater Sustainability Plan
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of climate change and projects and management actions (PMAs). To the extent possible the data sources and methodology used were consistent with those identified by the California Department of Water Resources (DWR) in Table 2 – Potential Data Sources to Support Water Budget Development and other sections of the Best Management Practices (BMP) –4 - Water Budget.1 As applicable and available,
models and tools (e.g., the Central Valley Hydrologic Model 2 [CVHM2]) were used to support the local sources and assumptions incorporated into the development of the Subbasin Groundwater Water Budget. (1) Precipitation (Inflow). For the Historical and Current Land Surface Water Budgets, total precipitation across the Subbasin was estimated using either: (1) PRISM: the PrecipitationElevation Regressions on Independent Slopes Model (PRISM); (2) CIMIS: area-weighted data from the California Irrigation Management Information System (CIMIS) stations located in the Subbasin; California Data Exchange Center (CDEC) and/or (3) data from the National Water Service Station located in Los Banos, CA. Total precipitation was further parsed into effective and non-effective precipitation, as applicable to each GSP area, based on assumptions regarding deep percolation percentages and other losses.
For the Projected Land Surface Water Budgets, for WY 2014-2017, actual data were provided consistent with the process described above for the Historical and Current Water Budgets. For the projected WY 2018-2070 period, the 2030 Central Tendency and 2070 Central Tendency climate change factors and guidance provided by DWR were applied to the historical precipitation record to project the impact of climate change on precipitation across the Subbasin. For example, either (1) the Gridded Statewide Precipitation and Change Factors developed for the Water Storage Investment Program (WSIP) using the Variable Infiltration Capacity (VIC) Macroscale Hydrology Model (DWR, 2018) were applied to the available precipitation data sets for the Subbasin, or (2) recommendations from the Perspectives and Guidance for Climate Change Analysis document prepared by the DWR Climate Change Technical Advisory Group (CCTAG) were incorporated (DWR CCTAG, 2015).
(2) Applied Water – Groundwater (Inflow). To estimate the volume of applied groundwater for the Historical and Current Land Surface Water Budgets (including both agricultural and M&I pumping, as applicable to each GSP area), the total pumping within the Subbasin was estimated using the following hierarchy of sources, depending upon existing records: (1) Flow meters:
volumetric flow meter records from pumping wells; (2) Power bills: electricity bills from pumping wells (wherein information related to the number of kilowatt-hours used was converted to a pumping volume based on assumptions related to pumping lift and efficiency); and/or (3) Consumptive use: reported crop acreages and consumptive use data based on either Irrigation Training and Research Center (ITRC)2
Mapping of Evapotranspiration with Internal Calibration (METRIC) procedure or crop coefficient methodologies (e.g., those provided in the Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 schema was chosen as WY 1979-2017, then wrapping around to include WY 1965-1978 hydrology. Actual data and hydrology were used for WY 2014- 2017 with the representative water years simulating WY 2018 and beyond (e.g., WY2018 is represented by the hydrology from WY1979; WY2019 is represented by the hydrology from WY1980, and so forth, with the caveat that 1979 would represent the fifth year of the projection and following sequentially the historical water year 1965 would represent the forty-fourth year of the projection). 1 https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/Groundwater-Management/SustainableGroundwater-Management/Best-Management-Practices-and-Guidance-Documents/Files/BMP-4-WaterBudget_ay_19.pdf 2 California Polytechnic State University, San Luis Obispo Delta-Mendota Subbasin Groundwater Sustainability Plan
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(FAO-56) (Snyder et. al., 2000, Snyder and Bali, 2008) or the ITRC Crop Coefficient data for Zone 14), corrected as applicable, for applied local and imported surface water. This volume of applied groundwater is consistent with the volume estimated under Water Budget Component (9) Extraction of the Groundwater Water Budget (see below).
For the Projected Land Surface Water Budgets, for WY 2014-2017, actual data were provided, consistent with the process described above for the Historical and Current Water Budgets. For the projected (WY 2018-2070) period, the volume of applied groundwater was estimated using various, complementary methods, including: (1) as the difference between projected demand and the assumed volumes of precipitation, surface water deliveries, and tile drainage available to meet the demand, or (2) assuming future groundwater production rates would be equivalent to historical extractions for a given year type (e.g., future dry year production rates would be equivalent to average dry year production rates over the historical record). Climate change impacts and the effects of the planned projects and management actions (PMAs) are implicitly, rather than explicitly, accounted for (i.e., to the extent that climate change and PMAs increase or decrease the amount of water otherwise available to meet applied water demands, the volume of applied groundwater will be adjusted accordingly). Total inflow to Shasta Lake dictates the amount of imported surface water available for use in the Subbasin. The WSIP model was used to analyze the impacts of climate change on the Subbasin and anticipate projected inflow to Shasta Lake, and as to whether or not the water year would be classified as Shasta Critical under the Exchange Contract, the Refuge Contract, and by municipal users. (3) Surface Water Inflow (Inflow). Surface water serves as an inflow to Subbasin water budget as both applied surface water and as seepage from streams and rivers. To estimate the volume of applied surface water for the Historical and Current Land Surface Water Budgets, the total diversions within the Subbasin over the historical and current water budget time periods were reported using the best available data for each source. Deliveries from the Central Valley Project (CVP), State Water Project (SWP), the San Joaquin River, and other local streams and rivers were compiled from records from the following sources, including, but not limited to: State Water Resources Control Board (SWRCB) diversion reports; United States Bureau of Reclamation (USBR) Central Valley Operations (CVO); Meyers Water Bank Records; CVP refuge water supply delivery data; and GSA member agency records.
To account for seepage of surface water into the Subbasin from streams and rivers for the Historical and Current Water Budgets, California Data Exchange Center (CDEC) data were used (i.e., by comparing the reductions in measured flow at successive gauging stations after accounting for other diversions) and/or from estimates of seepage losses from certain water bodies from prior water infiltration studies or modeling efforts, as described in the individual GSPs. Seepage from streams and rivers is counted either towards the Groundwater Water Budget directly or towards the Land Surface Water Budget and then, because of the lack of storage capacity in the land surface system and by way of mass balance principles, some or all of this water adds to the Groundwater Water Budget through Water Budget Component (6) Deep Percolation (see below).
For the Projected Land Surface Water Budgets, the volume of applied surface water was estimated as (1) the records of actual delivery data as available for the respective service areas for WY 2014-2017; and (2) estimates of anticipated future deliveries by WY type for WY 2018- 2070, inclusive of climate change considerations to the extent they could be reasonably estimated (i.e., directly modeled based on data provided by DWR and the USBR), or using water year types as a proxy (i.e., future dry year deliveries would reflect historical average dry year deliveries over Delta-Mendota Subbasin Groundwater Sustainability Plan
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the historical record). The impacts of planned PMAs on the availability of applied surface water volumes were also incorporated, as applicable.
For the Projected Land Surface Water Budgets, the volume of surface water seepage was adjusted, as applicable and available, based on climate change factors provided by DWR.
Changes to surface water seepage were directly estimated as a result of PMAs or other program implementation (e.g., the impact on seepage resulting from the San Joaquin River Restoration Program [SJRRP] implemented by the USBR).
(4) Surface Water Outflow (Outflow). As described above, total precipitation was parsed into effective and non-effective precipitation (i.e., the latter being that portion of the total precipitation that cannot be used by the plants because it either runs off or percolates beyond the root zone).
Similarly, a portion of the applied water can run off or deep percolate (typically termed “irrigation inefficiency”). Other surface water outflows (losses) from the Subbasin Land Surface Water Budget include agency-measured or estimated “spills” (i.e., outflow from tile drained fields, canal spills, field runoff, and precipitation runoff) and stream gauge readings, flow meter readings, and transfer pumping data. These collective data sets, sources, and methodologies were used to estimate the historical and current outflows from this component of the Subbasin Land Surface Water Budget.
For the Projected Land Surface Water Budgets, for WY 2014-2017, the data were provided consistent with the process described above for the Historical and Current Water Budgets. For the projected (WY 2018-2070) period, the volume of surface water outflows was estimated based on estimates provided by the GSA member agencies (using water year types as a proxy), while those components that may be impacted by climate change (e.g., runoff) were adjusted to reflect changes to precipitation and reference evapotranspiration (ETo). Changes to surface water outflows were directly estimated as a result of PMAs or other program implementation (e.g., water conservation programs to reduce spills) as information was available. (5) Evapotranspiration (Outflow). The largest outflow for the Historical and Current Land Surface Water Budget is evapotranspiration (consumptive use) by crops. As such, a combination of CIMIs ETo data, crop acreage, and crop coefficient data and methodologies (e.g., ITRC data and methodologies) were utilized to estimate the consumptive use, including municipal uses, of water in the Subbasin. In addition, direct evaporation from surface water bodies and phreatophytes (i.e., groundwater dependent ecosystems [GDEs]) was estimated based on the surface area and time period it was wetted.
For the Projected Land Surface Water Budgets, for WY 2014-2017, the actual data were provided consistent with the process described above for the Historical and Current Water Budgets. For the projected (WY 2018-2070) period, the 2030 Central Tendency and 2070 Central Tendency climate change factors or guidance provided by DWR were applied to the historical ETo record to project the impact of climate change on ETo across the Subbasin. For example, either the Gridded Statewide Precipitation and Change Factors developed for the WSIP using the VIC Macroscale Hydrology Model (DWR, 2018) were applied to the available ETo data sets for the Subbasin, or (2) recommendations from the Perspectives and Guidance for Climate Change Analysis document prepared by the DWR CCTAG (2015) were incorporated. (6) Deep Percolation (Outflow). For the Historical, Current, and Projected Land Surface Water Budgets, this water budget component is estimated as the sum of the other Outflow components (Water Budget Components 4 and 5) of the Land Surface Water Budget subtracted from the sum of the Inflow components (Water Budget Components 1 through 3) and represents the total Delta-Mendota Subbasin Groundwater Sustainability Plan
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volume of water that seeps past the root zone and into the Subbasin aquifer(s). This includes applied water seepage, as well as stream seepage (from the San Joaquin River, Delta-Mendota Canal, and California Aqueduct, and other canals), and delivery losses. To the extent that climate change and PMA implementation affects the volumes of Water Budget Components 1 through 5, these impacts are reflected in the resultant Outflow component, Water Budget Component (6) Deep Percolation, which serves as the inflow component, and Water Budget Component (7) Deep Percolation to the Groundwater Water Budget (see below).
GROUNDWATER WATER BUDGET
The data sources/methodologies used to estimate the Historical and Current Groundwater Water Budgets are summarized in Table CC-8 and for the Projected Groundwater Water Budgets in Table CC-9. A general description of each component and the data hierarchy that was applied by the GSAs is provided below, with further detail provided in the Water Budget sections of the six underlying GSPs. The time periods for the Groundwater Water Budgets are consistent with those used for the Land Surface Water Budgets, and likewise, to the extent possible, the data sources and methodology used were consistent with those identified by DWR in Table 2 – Potential Data Sources to Support Water Budget Development and other sections of the BMP –4 - Water Budget.1
As identified in Table CC-8 and Table CC-9, significant data gaps were identified in several of the GSPs on key aspects of the Groundwater Water Budget; additional efforts are on-going to address those data gaps and refine the water budgets as part of the 2025 GSP update. As applicable and available, models and tools (e.g., CVHM2, Westside Subbasin Groundwater Model, and a numerical flow model for the Farmers Water District and Fresno County areas) were used to validate the local sources and support assumptions used to develop the Subbasin Groundwater Water Budget.
(7) Deep Percolation (Inflow). In all instances, this component of the Groundwater Water Budget is directly linked to the Water Budget Component (6) Deep Percolation of the Land Surface Water Budget. To the extent that climate change is factored into the Historical, Current, and Projected Land Surface Water Budgets, those impacts are reflected in the varying volumes of deep percolation that are assumed to recharge the aquifer system(s) via infiltration. (8) Lateral Subsurface Flow (Inflow). For the Historical and Current Groundwater Water Budgets, this component is estimated somewhat differently for the Upper and Lower Aquifer portions of the Subbasin.
8A. Upper Aquifer. For the Upper Aquifer, lateral inflows were generally estimated using Darcy’s equation2 and estimated aquifer characteristics, or a groundwater flow model, as available.
Aquifer transmissivity values were compiled from aquifer tests, model parameters and other sources, while observed or simulated water level maps for wet, normal, and dry water year types and hydrographs were prepared to determine the elevation and direction of groundwater flow between GSP areas within the Subbasin and across Subbasin boundaries. Mountain front recharge 1 https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/Groundwater-Management/SustainableGroundwater-Management/Best-Management-Practices-and-Guidance-Documents/Files/BMP-4-WaterBudget_ay_19.pdf 2 Darcy’s equation in which groundwater flow velocity is identified as a function of the aquifer hydraulic conductivity and hydraulic gradient based upon measured water levels and aquifer properties. Freeze, R.A. and Cherry, J.A. 1979. Groundwater. Prentice Hall, Inc. Englewood Cliffs, NJ. p 16.
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from the Coastal Range was also assumed to provide an additional source of inflow to the Upper Aquifer.
8B. Lower Aquifer. To the extent possible, lateral inflows to the Lower Aquifer were estimated, primarily using Darcy’s equation and estimated aquifer characteristics, and coarse assumptions regarding contributions of other sources of inflow, or via a groundwater flow model, as available.
However, this portion of the Groundwater Budget was acknowledged as a significant data gap, which the GSAs are working to address through the collection of additional data, etc.
In instances where there was significant downward flow between the Upper and Lower Aquifers, vertical flow was estimated using Darcy’s equation, estimated aquifer characteristics, and groundwater gradients. Aquifer transmissivity values were compiled from aquifer tests, model parameters and other sources, while water level maps for wet, normal, and dry water year types were prepared to determine the elevation and groundwater gradient. Furthermore, flow to the Lower Aquifer from the Upper Aquifer is acknowledged as a data gap.
Projected Groundwater Water Budget. For the Projected Groundwater Water Budgets, for WY 2014-2017, the data were provided consistent with the process described above for the Historical and Current Water Budgets. For the projected (WY 2018-2070) period, this component is generally estimated using historical inflows by water year type as a proxy (i.e., the underflows used in the Historical and Current Water Budgets were averaged by WY type and used throughout the Projected Water Budget period). Impacts of climate change are implicitly incorporated, and expected increases in inflows as a result of PMAs (including projected groundwater banking activities) are directly incorporated to the extent the information was provided by the GSAs. As additional data are obtained during implementation of the GSPs, the inputs will be updated and improved to revise the Projected Groundwater Water Budget. (9) Extraction (Outflow). Consistent with the methodology used to estimate Water Budget Component (2), Applied Groundwater, of the Historical and Current Land Surface Water Budgets, the total pumping from the Subbasin aquifers was estimated using the following hierarchy of sources depending upon available records: (1) Flow meters: Volumetric flow meter records from pumping wells; (2) Power bills: Electricity bills from pumping wells (wherein information related to the number of kilowatt-hours used was converted to a pumping volume based on assumptions related to pumping lift and efficiency and duration of operation); and/or (3) Consumptive use: crop acreages and consumptive use data based on either ITRC-METRIC or crop coefficient methodologies. While the exact distribution of pumping from the Upper and Lower Aquifers is acknowledged as a data gap, total extractions were assumed to be partitioned between the aquifers, with the majority of extractions (80-90%) occurring in the Upper Aquifer.
Information regarding well construction obtained and compiled from the local and Subbasin Well Census and Inventory projects completed by the GSAs in 2022 will be used to further improve the estimated allocation of groundwater extraction between the aquifers in the 2025 GSP update.
For the Projected Groundwater Water Budgets, for WY 2014-2017, the data were provided, consistent with the process described above for the Historical and Current Water Budgets. For the projected (WY 2018-2070) period, the volume of pumped groundwater was estimated using various, complimentary methods, including (1) as the difference between projected demand and the assumed volumes of precipitation, surface water deliveries, and tile drainage available to meet the demand, or (2) assuming future groundwater production would be equivalent to historical extractions for a given year type (e.g., future dry year production rates would be equivalent to average dry year production rates over the historical record, with the exception of M&I pumping which was projected based on information provided in various source documents such as Urban Delta-Mendota Subbasin Groundwater Sustainability Plan
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Water Management Plans). Climate change impacts and the effect of the planned PMAs are implicitly, rather than explicitly, accounted for.
(10) Lateral Subsurface Flow (Outflow). For the Historical and Current Groundwater Water Budgets, this component was estimated somewhat differently for the Upper and Lower Aquifer portions of the Subbasin, but similarly to Water Budget Component (8) of the Groundwater Water Budget.
10A. Upper Aquifer. Lateral outflows were generally estimated using Darcy’s equation and estimated aquifer characteristics, and validated by a groundwater flow model, as available.
Aquifer transmissivity values were compiled from aquifer tests, model parameters and other sources, while observed or simulated water level maps for wet, normal, and dry water year types and hydrographs were prepared to determine the elevation and direction of groundwater flow between GSP areas within the Subbasin and across Subbasin boundaries. 10B. Lower Aquifer. To the extent possible, lateral outflows from the Lower Aquifer were estimated, primarily using Darcy’s equation and estimated aquifer characteristics, and validated by a groundwater flow model, as available. However, this portion of the Groundwater Water Budget was acknowledged as a significant data gap which the GSAs are working to address through the collection and evaluation of additional data, etc.
Projected Groundwater Water Budget. For the Projected Groundwater Water Budgets, for WY 2014-2017, the data were provided, consistent with the process described above for the Historical and Current Water Budgets. For the projected (WY 2018-2070) period, this component is generally estimated using historical outflows by water year type as a proxy (i.e., the underflows used in the Historical and Current Water Budgets were averaged by WY type and used throughout the Projected Water Budget period). Impacts of climate change are implicitly incorporated, and expected increases in outflows as a result of PMAs (including projected groundwater banking activities) are directly incorporated to the extent the information was provided by the GSAs.
(11) Change in Storage. For the Historical and Current Groundwater Water Budgets, this component was estimated somewhat differently for the Upper and Lower Aquifer portions of the Subbasin.
11A. Upper Aquifer. A sum of the Outflow components (Water Budget Components 9 through 10) of the Groundwater Water Budget was subtracted from the Inflow components (Water Budget Components 7 and 8) to assess the change in storage. These estimates were also compared in some of the GSPs to the available hydrographs, water level contour maps, and assumed aquifer storativity values from local data sets and models to assess and confirm change in storage, and assumed consumptive use data.
11B. Lower Aquifer. Approaches varied among the GSPs given the limited available data, which the GSAs are working to address through the collection of additional data, etc. Change in storage was estimated using measured subsidence as a proxy (i.e., due to compaction caused by inelastic land subsidence), as the difference between inflows and outflows based on modeled results, or as an assumed proportion of overall groundwater change in storage. These estimates were also compared in some of the GSPs to the available hydrographs, water level contour maps, and assumed aquifer storativity values from local data sets and models to assess and confirm change in storage, and assumed consumptive use data.
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Projected Groundwater Water Budgets. For the Projected Groundwater Water Budgets, for WY 2014-2017, the data were provided, consistent with the process described above for the Historical and Current Water Budgets. For the projected (WY 2018-2070) period, the change in storage volumes used in the Historical and Current Water Budgets were averaged by water year type and used throughout the projected water budget period, or were calculated as the difference between inflows and outflows.
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Table CC-8: Historical and Current Water Budgets Data Sources Water Budget Flow Direction Flow Budget Category Aliso Water District Farmers Water District Fresno County Grassland Northern & Central Delta- Mendota San Joaquin River Exchange Contractors Land Surface Inflow Precipitation
Precipitation-Elevation Regressions on Independent Slopes Model (PRISM) and California Irrigation Management Information System (CIMIS) PRISM PRISM and CIMIS PRISM and CIMIS CIMIS and National Weather Service (NWS) Land Surface Inflow Applied Wat–r - Groundwater Consumptive use Flow meters Flow meters, power bills, and consumptive use
Flow meters and consumptive use Flow meters
Land Surface Inflow Surface Water Inflow
State Water Resources Control Board (SWRCB) diversion reports; landowner records San Joaquin River inflows
United States Bureau of Reclamation (USBR) Central Valley Operations (CVO); Meyers Water Bank Records Central Valley Project (CVP) refuge water supply delivery data USBR CVO and SWRCB diversion reports
USBR CVO; California Data Exchange Center (CDEC) where available, water infiltration study used otherwise Land Surface Outflow Surface Water Outflow Non-effective precipitation Transfer pumping and San Joaquin River outflows
Transfer pumping that exceeds applied groundwater
Non-effective precipitation and agency measured spills
Evapotranspiration and noneffective precipitation) Non-effective precipitation and flow meter readings Land Surface Outflow Evapotranspiration Vegetation coefficients and CIMIS Land Surface Outflow Deep Percolation Land Surface Budget Inflow - Outflow Groundwater Inflow Infiltration Land Surface Budget Inflow - Outflow Groundwater Inflow Lateral subsurface flow - Upper Aquifer Darcy’s equation (groundwater levels and transmissivities) Groundwater Inflow Lateral subsurface flow - Lower Aquifer Unused - Data Gap Darcy’s equation (groundwater levels and transmissivities) Data G–p - Assumed 20% of total inflows. Darcy’s equation (groundwater levels and transmissivities) Groundwater Outflow Extraction - Upper Aquifer Consumptive use and irrigation efficiency Flow meters Flow meters, power bills and consumptive use Flow meters and consumptive use Flow meters Groundwater Outflow Extraction - Lower Aquifer Unused - Data Gap Flow meters Flow meters, power bills and consumptive use
Flow meters and consumptive use Assumed 10% of total pumping Groundwater Outflow Lateral subsurface flow - Upper Aquifer Darcy’s equation (groundwater levels and transmissivities) Groundwater Outflow Lateral subsurface flow - Lower Aquifer Unused - Data Gap Darcy’s equation (groundwater levels and transmissivities) Groundwater Change in Storage Upper Aquifer Inflow - Outflow Groundwater Change in Storage Lower Aquifer Land subsidence as proxy Inflow - Outflow Land subsidence as proxy Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-9: Projected Water Budgets Data Sources
Water Budget Flow Direction Flow Budget Category Aliso Water District Farmers Water District Fresno County Grassland Northern & Central Delta- Mendota San Joaquin River Exchange Contractors Land Surface Inflow Precipitation Precipitation-Elevation Regressions on Independent Slopes Model (PRISM), applying climate change factors (CCF) PRISM and California Irrigation Management Information System (CIMIS), applying CCF CIMIS and National Weather Service (NWS), applying CCF Land Surface Inflow Applied Wat–r - Groundwater Consumptive use Flow meters and consumptive use Flow meters Land Surface Inflow Surface Water Inflow State Water Resources Control Board (SWRCB) diversion reports, using water year (WY) types as a proxy San Joaquin River inflows (CDEC and United States Geological Survey [USGS]) Mendota Pool inflows - USBR CVO
USBR CVO and SWRCB diversion reports, using WY types as a proxy
USBR CVO; California Data Exchange Center (CDEC) where available, using WY types as a proxy; Water infiltration study used otherwise Land Surface Outflow Surface Water Outflow
Non-effective precipitation calculated with CCF and WY types as a proxy for quantity San Joaquin River outflows (CDEC and USGS)
Mendota Pool outflows (USBR CVO)
Non-effective precipitation and agency measured spills calculated with CCF and WY types as a proxy for quantity Non-effective precipitation
calculated with CCF and WY types
as a proxy for quantity
Non-effective precipitation and
agency measured spills calculated
with CCF and WY types as a
proxy for quantity
Land Surface Outflow Evapotranspiration Vegetation coefficients and CIMIS (calculated with CCFs and WY types as a proxy) Land Surface Outflow Deep Percolation Land Surface Inflow - Outflow Groundwater Inflow Infiltration Land Surface Budget Inflow - Outflow Groundwater Inflow Lateral subsurface flow - Upper Aquifer Darcy’s equation (groundwater levels and transmissivities) using WY types as a proxy Groundwater Inflow Lateral subsurface flow - Lower Aquifer Unused - Data Gap Darcy’s equation (groundwater levels and transmissivities) using WY types as a proxy Data Gap - Assumed 20% of total inflows. Darcy’s equation (groundwater levels and transmissivities) using WY types as a proxy Groundwater Outflow Extraction - Upper Aquifer Consumptive use and irrigation efficiency using WY type as a proxy with CCFs and PMAs Adjusted historic metered data using WY type as
a proxy with CCFs and PMAs Adjusted historic metered data and consumptive use using WY type as a proxy with CCFs and PMAs Groundwater Outflow Extraction - Lower Aquifer Unused - Data Gap Not Applicable Unused - Data Gap Adjusted historic metered data and consumptive use using WY type as a proxy with CCFs and PMAs Groundwater Outflow Lateral subsurface flow - Upper Aquifer Darcy’s equation (groundwater levels and transmissivities) using WY types as a proxy with CCFs Groundwater Outflow Lateral subsurface flow - Lower Aquifer Unused – Data Gap Darcy’s equation (groundwater levels and transmissivities) using WY types as a proxy with CCFs Data Gap - Assumed 20% of total inflows. Darcy’s equation (groundwater levels and transmissivities) with CCFs Groundwater Change in Storage Upper Aquifer Inflow - Outflow Groundwater Change in Storage Lower Aquifer Unused – Data Gap Inflow - Outflow Projected land subsidence and WY types used as a proxy with CCFs and PMAs Inflow - Outflow
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4.3.2 GSP-Level Water Budgets
Individual historical, current, and projected water budgets were developed by each GSP Group for their respective Plan Area. For more information on the development of those water budgets, as well as tabular and graphical representation of the results, refer to the respective sections of the individual GSPs.
All historical, current, and projected water budgets developed within the Delta-Mendota Subbasin are consistent with GSP Regulations §354.18 Water Budget, and DWR’s Best Management Practices for the Sustainable Management of Groundwater Water Budget BMP (2016c) document was used when and where applicable at the discretion of each GSP Group.
4.3.3 Coordinated Water Budgets
The land surface budget, groundwater budget, and annual change in storage for the historical water budget, current water budget, and projected water budget with climate change factors (CCFs) and projects and management actions for the Delta-Mendota Subbasin were developed by compiling the water budgets prepared by each of GSP Group. The land surface budget is an accounting of water flows into and out of the land surface above an aquifer within with Delta-Mendota Subbasin, where inflows and outflows include flow between GSP Groups and neighboring subbasins, the atmosphere, and the groundwater aquifer below. The groundwater budget is an accounting of groundwater flows into and out of the two principal groundwater aquifers (Upper Aquifer and Lower Aquifer) within the Delta-Mendota Subbasin, where inflows and outflows include flow between GSP Groups and neighboring subbasins as well as the above land surface.
Subsequent to the submittal of the Delta-Mendota GSP in January 2022, and in response to the Consultation Initiation Letter (CIL) received from DWR on January 21, 2022 in which DWR stated that, while the same data may have been used in developing the water budgets, the terminology used to describe those data sets were not consistent across the basin, the Delta-Mendota Subbasin GSAs acknowledge additional detail was needed to demonstrate that all water budget components across the six Subbasin GSPs utilize the same data and methodologies. As such, subsequent to receipt of the CIL, the Technical Working Group and Coordination Committee met to identify the specific data used and to develop a consistent terminology for the various water budget components. Additionally, the Technical Working Group attempted to simplify the presentation of the Subbasin water budgets through a reduction in the number of water budget components. The mapping of the original GSP water budget components into the revised simplified coordinated water budget component terminology is discussed in the prior section (Section 4.3.1 of this revised Common Chapter).
After agreeing to the set of common simplified definitions for water budget components, the six DeltaMendota GSP groups mapped their prior water budget components to the new common definitions. The revised land surface budget and groundwater budget are presented respectively for the historical water budget in Table CC-10 and Table CC-11, for the current water budget in Table CC-12 and Table CC13, and for the projected water budget with climate change factors and projects and management actions in Table CC-14 and Table CC-15. All categories presented in the land surface budget and groundwater budget tables were agreed upon by all Delta-Mendota GSP Groups, with representatives from each GSP group tasked with filling out these budget tables as appropriate to account for the unique hydrology, land use, and water use within their respective GSP regions. The tables below are simply compilations of the individual GSP water budget data as provided by their respective plan preparers, and no water budget data were modified during the mapping process.
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Individual GSAs and agencies in the Delta-Mendota Subbasin understand that the historical, current, and projected water budgets were completed using best available science and data, and efforts were made to use the same data sources throughout the Subbasin where available, though due to variability in data availability throughout the Subbasin, the best available data were used and characterized appropriately.
Where data gaps exist, the individual GSAs and agencies intend to conduct the work necessary to substantiate or improve the estimates and assumptions developed for determining their water budgets.
Nothing in this part, or in any groundwater sustainability plan adopted pursuant to this part, determines, or alters surface water rights or groundwater rights under common law or any provision of law that determines or grants surface water rights.
Figure CC-64 shows the revised average annual and cumulative change in storage in both principal aquifers under the Subbasin projected water budget (including application of climate change factors and the addition of projects and management actions).
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Table CC-10: Delta-Mendota Subbasin Historical Water Budget, Land Surface Budget Land Surface Budget
Water Year Water Year Type
Inflows Outflows
Precipitation Applied Wat–r - Groundwater Surface Water Inflows Total Inflows Surface Water Outflows Evapotranspiration Deep Percolation Total Outflows 2003 N 450,000 395,000 2,501,000 3,346,000 1,306,000 1,772,000 293,000 3,371,000 2004 D 412,000 417,000 2,433,000 3,262,000 1,206,000 1,760,000 315,000 3,281,000 2005 W 739,000 303,000 2,764,000 3,806,000 1,614,000 1,810,000 352,000 3,776,000 2006 W 571,000 293,000 3,311,000 4,175,000 2,111,000 1,804,000 296,000 4,211,000 2007 D 258,000 474,000 2,485,000 3,217,000 1,230,000 1,701,000 310,000 3,241,000 2008 D 328,000 527,000 2,295,000 3,150,000 1,140,000 1,769,000 331,000 3,240,000 2009 N 304,000 511,000 2,191,000 3,006,000 1,017,000 1,813,000 327,000 3,157,000 2010 N 539,000 380,000 2,637,000 3,556,000 1,515,000 1,655,000 406,000 3,576,000 2011 W 626,000 279,000 3,283,000 4,188,000 2,013,000 1,799,000 414,000 4,226,000 2012 D 275,000 470,000 2,582,000 3,327,000 1,301,000 1,679,000 355,000 3,335,000 Table CC-11: Delta-Mendota Subbasin Historical Water Budget, Groundwater Budget Groundwater Budget
Water Year Water Year Type
Inflows Outflows Change in Storage
Infiltration
Lateral Subsurface Flow
Total Inflows
Groundwater Extraction Lateral Subsurface Flow
Total Outflows
Estimated Annual Change in Groundwater
Storage
Upper Aquifer Lower Aquifer Upper Aquifer Lower Aquifer Upper Aquifer Lower Aquifer Upper Aquifer Lower Aquifer Total 2003 N 324,000 196,000 117,000 637,000 357,000 39,000 260,000 106,000 762,000 17,000 5,000 22,000 2004 D 345,000 180,000 114,000 639,000 376,000 42,000 286,000 132,000 836,000 (180,000) (48,000) (228,000) 2005 W 424,000 223,000 128,000 775,000 268,000 36,000 269,000 78,000 651,000 223,000 14,000 237,000 2006 W 394,000 203,000 120,000 717,000 260,000 34,000 264,000 75,000 633,000 18,000 (23,000) (5,000) 2007 D 358,000 161,000 99,000 618,000 431,000 48,000 280,000 130,000 889,000 (282,000) (67,000) (349,000) 2008 D 371,000 169,000 106,000 646,000 481,000 55,000 293,000 141,000 970,000 (341,000) (80,000) (421,000) 2009 N 361,000 195,000 112,000 668,000 466,000 53,000 273,000 117,000 909,000 (134,000) (28,000) (162,000) 2010 N 470,000 211,000 124,000 805,000 350,000 39,000 264,000 116,000 769,000 180,000 (4,000) 176,000 2011 W 515,000 205,000 124,000 844,000 248,000 32,000 277,000 83,000 640,000 125,000 (23,000) 102,000 2012 D 417,000 168,000 107,000 692,000 432,000 45,000 288,000 141,000 906,000 (171,000) (62,000) (233,000) Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-12: Delta-Mendota Subbasin Current Water Budget, Land Surface Budget Land Surface Budget
Water Year Water Year Type
Inflows Outflows
Precipitation Applied Wat–r - Groundwater Surface Water Inflows Total Inflows Surface Water Outflows Evapotranspiration Deep Percolation Total Outflows 2013 D 318,000 521,000 2,597,000 3,436,000 1,386,000 1,671,000 402,000 3,459,000 Table CC-13: Delta-Mendota Subbasin Current Water Budget, Groundwater System Groundwater Budget
Water Year Water Year Type
Inflows Outflows Change in Storage
Infiltration
Lateral Subsurface Flow
Total Inflows
Groundwater Extraction Lateral Subsurface Flow
Total Outflows
Estimated Annual Change in Groundwater
Storage
Upper Aquifer Lower Aquifer Upper Aquifer Lower Aquifer Upper Aquifer Lower Aquifer Upper Aquifer Lower Aquifer Total 2013 D 467,000 173,000 112,000 752,000 477,000 51,000 278,000 136,000 942,000 (128,000) (55,000) (183,000) Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-14: Delta-Mendota Subbasin Projected Water Budget, Land Surface Budget (containing climate change factors and projects and management actions) Land Surface Budget
Inflows Outflows
Precipitation Applied Wat–r - Groundwater Surface Water Inflow Applied Wat–r - Groundwater (Project Effect–) - NCDM Only Applied Wat–r - Imported Surface Water (Project Effect–) - NCDM Only Project Effects - All GSP Groups Total Inflows Surface Water Outflow Evapotranspiration Crop Evapotranspiration - Aliso Only Canal/Reservoir Evaporation - Aliso Only Deep Percolation Runoff (Project Effect–) - NCDM Only Project Effects - All GSP Groups Total Outflows 2014 SC 283,000 601,000 1,725,000 0 0 1,000 2,610,000 852,000 1,616,000 0 0 230,000 0 0 2,698,000 2015 SC 363,000 650,000 1,247,000 0 0 0 2,260,000 479,000 1,528,000 0 0 287,000 0 0 2,294,000 2016 D 712,000 392,000 1,605,000 0 0 0 2,709,000 631,000 1,618,000 0 0 403,000 0 0 2,652,000 2017 W 686,000 303,000 3,651,000 0 0 6,000 4,646,000 2,423,000 1,773,000 0 0 445,000 0 0 4,641,000 2018 N 527,000 389,000 2,628,000 (6,000) 0 7,000 3,545,000 1,506,000 1,660,000 0 0 403,000 0 0 3,569,000 2019 W 712,000 266,000 3,162,000 (7,000) 2,000 6,000 4,141,000 1,975,000 1,810,000 0 0 368,000 0 0 4,153,000 2020 D 434,000 394,000 2,187,000 (6,000) 9,000 7,000 3,025,000 939,000 1,726,000 0 0 343,000 0 0 3,008,000 2021 W 808,000 261,000 3,261,000 (7,000) 7,000 6,000 4,336,000 2,025,000 1,821,000 0 0 403,000 0 0 4,249,000 2022 W 1,021,000 249,000 3,266,000 (7,000) 7,000 6,000 4,542,000 2,190,000 1,834,000 0 0 449,000 0 0 4,473,000 2023 N 580,000 389,000 2,658,000 (8,000) 6,000 7,000 3,632,000 1,470,000 1,711,000 0 0 403,000 0 0 3,584,000 2024 D 573,000 387,000 2,176,000 (3,000) 6,000 6,000 3,145,000 963,000 1,726,000 0 0 374,000 0 0 3,063,000 2025 W 884,000 261,000 3,256,000 (7,000) 7,000 6,000 4,407,000 1,993,000 1,847,000 0 0 424,000 0 0 4,264,000 2026 D 575,000 483,000 2,098,000 (43,000) 52,000 9,000 3,174,000 914,000 1,785,000 0 0 412,000 0 0 3,111,000 2027 D 653,000 481,000 2,078,000 (41,000) 49,000 9,000 3,229,000 914,000 1,766,000 0 0 419,000 0 0 3,099,000 2028 D 534,000 484,000 2,115,000 (42,000) 50,000 9,000 3,150,000 934,000 1,789,000 0 0 353,000 0 0 3,076,000 2029 D 462,000 484,000 2,099,000 (46,000) 55,000 9,000 3,063,000 910,000 1,744,000 0 0 356,000 0 0 3,010,000 2030 SC 417,000 575,000 1,800,000 (47,000) 49,000 3,000 2,797,000 833,000 1,624,000 0 0 363,000 0 0 2,820,000 2031 SC 492,000 573,000 1,780,000 (48,000) 51,000 2,000 2,850,000 815,000 1,633,000 0 0 406,000 0 0 2,854,000 2032 W 832,000 269,000 3,250,000 (31,000) 46,000 6,000 4,372,000 1,963,000 1,830,000 0 0 490,000 1,000 0 4,284,000 2033 D 466,000 490,000 2,001,000 (46,000) 60,000 10,000 2,981,000 869,000 1,741,000 0 0 364,000 1,000 0 2,975,000 2034 W 851,000 252,000 3,258,000 (29,000) 47,000 7,000 4,386,000 2,003,000 1,791,000 0 0 465,000 1,000 0 4,260,000 2035 W 731,000 280,000 3,163,000 (32,000) 48,000 7,000 4,197,000 1,969,000 1,849,000 0 0 422,000 1,000 0 4,241,000 2036 W 774,000 316,000 3,268,000 (31,000) 50,000 7,000 4,384,000 2,052,000 1,867,000 0 0 494,000 1,000 0 4,414,000 2037 W 1,194,000 252,000 3,274,000 (28,000) 49,000 7,000 4,748,000 2,254,000 1,780,000 0 0 607,000 1,000 0 4,642,000 2038 N 448,000 431,000 2,689,000 (47,000) 53,000 10,000 3,584,000 1,529,000 1,660,000 0 0 381,000 0 0 3,570,000 2039 N 488,000 446,000 2,655,000 (46,000) 52,000 10,000 3,605,000 1,487,000 1,698,000 0 0 411,000 0 0 3,596,000 2040 D 534,000 423,000 2,200,000 (46,000) 66,000 9,000 3,186,000 1,001,000 1,712,000 0 0 411,000 1,000 0 3,125,000 2041 D 384,000 437,000 2,139,000 (52,000) 62,000 9,000 2,979,000 879,000 1,704,000 0 0 374,000 1,000 0 2,958,000 2042 N 530,000 469,000 2,730,000 (46,000) 51,000 10,000 3,744,000 1,532,000 1,795,000 0 0 400,000 0 0 3,727,000 Delta-Mendota Subbasin Groundwater Sustainability Plan
Revised Common Chapter
CC-146
June 2022
Land Surface Budget
Inflows Outflows
Precipitation Applied Wat–r - Groundwater Surface Water Inflow Applied Wat–r - Groundwater (Project Effect–) - NCDM Only Applied Wat–r - Imported Surface Water (Project Effect–) - NCDM Only Project Effects - All GSP Groups Total Inflows Surface Water Outflow Evapotranspiration Crop Evapotranspiration - Aliso Only Canal/Reservoir Evaporation - Aliso Only Deep Percolation Runoff (Project Effect–) - NCDM Only Project Effects - All GSP Groups Total Outflows 2043 D 488,000 437,000 2,101,000 (48,000) 68,000 11,000 3,057,000 884,000 1,797,000 0 0 331,000 1,000 0 3,013,000 2044 W 875,000 286,000 3,231,000 (37,000) 53,000 11,000 4,419,000 2,141,000 1,831,000 0 0 419,000 1,000 0 4,392,000 2045 W 622,000 313,000 3,263,000 (45,000) 53,000 12,000 4,218,000 1,971,000 1,847,000 0 0 355,000 1,000 0 4,174,000 2046 D 268,000 571,000 2,149,000 (57,000) 68,000 12,000 3,011,000 893,000 1,794,000 0 0 346,000 1,000 0 3,034,000 2047 D 402,000 575,000 2,067,000 (55,000) 64,000 12,000 3,065,000 834,000 1,820,000 0 0 383,000 0 0 3,037,000 2048 N 331,000 593,000 2,696,000 (49,000) 49,000 12,000 3,632,000 1,457,000 1,893,000 0 0 358,000 0 0 3,708,000 2049 N 658,000 407,000 2,683,000 (29,000) 62,000 12,000 3,793,000 1,525,000 1,706,000 0 0 474,000 2,000 0 3,707,000 2050 W 708,000 316,000 3,145,000 (40,000) 54,000 13,000 4,196,000 1,974,000 1,878,000 0 0 376,000 1,000 0 4,229,000 2051 D 350,000 447,000 2,110,000 (51,000) 69,000 13,000 2,938,000 858,000 1,738,000 0 0 302,000 1,000 0 2,899,000 2052 D 390,000 553,000 2,103,000 (46,000) 67,000 14,000 3,081,000 873,000 1,727,000 0 0 416,000 1,000 0 3,017,000 2053 SC 306,000 634,000 1,765,000 (44,000) 47,000 8,000 2,716,000 801,000 1,699,000 0 0 304,000 0 0 2,804,000 2054 SC 340,000 632,000 1,678,000 (29,000) 34,000 7,000 2,662,000 750,000 1,657,000 0 0 354,000 0 0 2,761,000 2055 D 630,000 453,000 1,831,000 (39,000) 49,000 14,000 2,938,000 855,000 1,742,000 0 0 385,000 1,000 0 2,983,000 2056 W 745,000 351,000 3,073,000 (44,000) 46,000 12,000 4,183,000 1,935,000 1,894,000 0 0 450,000 0 0 4,279,000 2057 W 693,000 313,000 3,150,000 (34,000) 55,000 12,000 4,189,000 1,932,000 1,893,000 0 0 401,000 1,000 0 4,227,000 2058 N 478,000 547,000 2,688,000 (49,000) 54,000 15,000 3,733,000 1,417,000 1,871,000 0 0 446,000 0 0 3,734,000 2059 W 739,000 309,000 3,154,000 (33,000) 55,000 13,000 4,237,000 1,941,000 1,888,000 0 0 425,000 1,000 0 4,255,000 2060 D 405,000 441,000 2,111,000 (52,000) 69,000 15,000 2,989,000 847,000 1,786,000 0 0 360,000 1,000 0 2,994,000 2061 W 910,000 300,000 3,276,000 (33,000) 55,000 13,000 4,521,000 2,106,000 1,896,000 0 0 512,000 1,000 0 4,515,000 2062 N 466,000 459,000 2,687,000 (50,000) 58,000 16,000 3,636,000 1,482,000 1,757,000 0 0 420,000 0 0 3,659,000 2063 N 477,000 544,000 2,674,000 (49,000) 54,000 16,000 3,716,000 1,454,000 1,861,000 0 0 397,000 0 0 3,712,000 2064 D 338,000 447,000 2,123,000 (49,000) 70,000 16,000 2,945,000 818,000 1,780,000 0 0 341,000 1,000 0 2,940,000 2065 N 725,000 443,000 2,688,000 (47,000) 58,000 17,000 3,884,000 1,502,000 1,739,000 0 0 573,000 1,000 0 3,815,000 2066 W 668,000 323,000 3,153,000 (34,000) 55,000 15,000 4,180,000 1,929,000 1,897,000 0 0 383,000 1,000 0 4,210,000 2067 W 690,000 321,000 3,262,000 (33,000) 55,000 15,000 4,310,000 1,942,000 1,898,000 0 0 394,000 1,000 0 4,235,000 2068 D 448,000 558,000 1,859,000 (52,000) 69,000 12,000 2,894,000 872,000 1,695,000 0 0 327,000 1,000 0 2,895,000 2069 D 382,000 561,000 1,824,000 (50,000) 66,000 12,000 2,795,000 788,000 1,688,000 0 0 328,000 1,000 0 2,805,000 2070 W 962,000 302,000 3,388,000 (34,000) 55,000 16,000 4,689,000 2,130,000 1,887,000 0 0 557,000 1,000 0 4,575,000 Delta-Mendota Subbasin Groundwater Sustainability Plan
Revised Common Chapter
CC-147
June 2022
Table CC-15: Delta-Mendota Subbasin Projected Water Budget, Groundwater Budget (containing climate change factors and projects and management actions) Groundwater Budget
Inflows Outflows Change in Storage
Infiltration
Lateral Subsurface
Flow
Seepage
Through
Corcoran Clay -
SJREC Only
Applied Water
Infiltration (Project
Effects) - NCDM
Only
Deep Percolation
(Project Effects) -
NCDM Only
Project
Effects
Total
Inflows
Groundwater
Extraction
Lateral Subsurface
Flow Flow to Lower Aquifer -
Grassland Only
Discharge to Surface
Water/Consumptive Use by
GDEs/Lateral Flow - Grassland
Only
Total
Outflows
Estimated Annual Change in
Groundwater Storage
Upper
Aquifer
Lower
Aquifer
Upper
Aquifer
Lower
Aquifer
Upper
Aquifer
Lower
Aquifer
Upper
Aquifer
Lower
Aquifer Total
2014 SC 275,000 162,000 115,000 0 0 0 0 552,000 513,000 101,000 321,000 191,000 0 0 1,126,000 (428,000) (234,000) (662,000) 2015 SC 333,000 154,000 113,000 0 0 0 0 600,000 558,000 101,000 325,000 202,000 0 0 1,186,000 (408,000) (234,000) (642,000) 2016 D 487,000 152,000 112,000 0 0 0 0 751,000 354,000 60,000 313,000 156,000 0 0 883,000 (89,000) (130,000) (219,000) 2017 W 525,000 198,000 128,000 0 0 0 10,000 861,000 254,000 50,000 307,000 91,000 0 0 702,000 148,000 (28,000) 120,000 2018 N 465,000 190,000 115,000 0 0 0 0 770,000 347,000 59,000 264,000 101,000 0 0 771,000 105,000 44,000 149,000 2019 W 461,000 216,000 124,000 0 0 0 10,000 811,000 231,000 38,000 279,000 74,000 0 0 622,000 122,000 11,000 133,000 2020 D 385,000 153,000 106,000 0 0 3,000 0 647,000 354,000 57,000 298,000 136,000 0 0 845,000 (185,000) (142,000) (327,000) 2021 W 464,000 218,000 125,000 0 0 10,000 0 817,000 224,000 39,000 280,000 72,000 0 0 615,000 135,000 27,000 162,000 2022 W 553,000 218,000 125,000 0 0 10,000 10,000 916,000 214,000 37,000 276,000 77,000 0 0 604,000 254,000 40,000 294,000 2023 N 449,000 186,000 117,000 0 0 3,000 0 755,000 348,000 55,000 264,000 111,000 0 0 778,000 89,000 74,000 163,000 2024 D 417,000 151,000 108,000 0 0 3,000 0 679,000 349,000 58,000 301,000 134,000 0 0 842,000 (153,000) (94,000) (247,000) 2025 W 493,000 214,000 125,000 0 0 10,000 10,000 852,000 227,000 38,000 278,000 73,000 0 0 616,000 176,000 44,000 220,000 2026 D 451,000 152,000 107,000 0 0 6,000 0 716,000 413,000 51,000 302,000 137,000 0 0 903,000 (169,000) (56,000) (225,000) 2027 D 470,000 152,000 106,000 0 0 9,000 0 737,000 411,000 52,000 303,000 131,000 0 0 897,000 (148,000) (47,000) (195,000) 2028 D 390,000 153,000 104,000 0 0 9,000 0 656,000 414,000 51,000 304,000 130,000 0 0 899,000 (225,000) (55,000) (280,000) 2029 D 395,000 154,000 103,000 0 0 10,000 0 662,000 410,000 51,000 303,000 129,000 0 0 893,000 (213,000) (67,000) (280,000) 2030 SC 400,000 159,000 97,000 0 0 9,000 0 665,000 454,000 84,000 312,000 127,000 0 0 977,000 (230,000) (104,000) (334,000) 2031 SC 442,000 158,000 97,000 0 0 9,000 0 706,000 453,000 82,000 313,000 118,000 0 0 966,000 (188,000) (89,000) (277,000) 2032 W 545,000 220,000 115,000 0 0 22,000 0 902,000 213,000 35,000 279,000 68,000 0 0 595,000 258,000 61,000 319,000 2033 D 400,000 157,000 98,000 0 0 10,000 0 665,000 402,000 50,000 308,000 133,000 0 0 893,000 (201,000) (70,000) (271,000) 2034 W 547,000 220,000 118,000 0 0 22,000 10,000 917,000 203,000 29,000 273,000 70,000 0 0 575,000 275,000 57,000 332,000 2035 W 459,000 220,000 119,000 0 0 22,000 0 820,000 225,000 34,000 276,000 76,000 0 0 611,000 162,000 55,000 217,000 2036 W 552,000 221,000 119,000 0 0 22,000 10,000 924,000 243,000 51,000 275,000 76,000 0 0 645,000 275,000 65,000 340,000 2037 W 719,000 217,000 122,000 0 0 23,000 10,000 1,091,000 202,000 31,000 269,000 80,000 0 0 582,000 442,000 53,000 495,000 2038 N 415,000 185,000 114,000 0 0 15,000 0 729,000 350,000 58,000 258,000 111,000 0 0 777,000 90,000 87,000 177,000 2039 N 455,000 197,000 117,000 0 0 15,000 0 784,000 360,000 63,000 262,000 108,000 0 0 793,000 142,000 82,000 224,000 2040 D 457,000 151,000 104,000 0 0 10,000 0 722,000 348,000 53,000 299,000 136,000 0 0 836,000 (82,000) (65,000) (147,000) 2041 D 410,000 150,000 101,000 0 0 10,000 0 671,000 352,000 56,000 299,000 130,000 0 0 837,000 (123,000) (68,000) (191,000) 2042 N 448,000 197,000 111,000 0 0 15,000 0 771,000 385,000 62,000 264,000 100,000 0 0 811,000 98,000 98,000 196,000 2043 D 368,000 151,000 100,000 0 0 10,000 0 629,000 357,000 55,000 298,000 109,000 0 0 819,000 (173,000) (58,000) (231,000) Delta-Mendota Subbasin Groundwater Sustainability Plan
Revised Common Chapter
CC-148
June 2022
Groundwater Budget
Inflows Outflows Change in Storage
Infiltration
Lateral Subsurface
Flow
Seepage
Through
Corcoran Clay -
SJREC Only
Applied Water
Infiltration (Project
Effects) - NCDM
Only
Deep Percolation
(Project Effects) -
NCDM Only
Project
Effects
Total
Inflows
Groundwater
Extraction
Lateral Subsurface
Flow Flow to Lower Aquifer -
Grassland Only
Discharge to Surface
Water/Consumptive Use by
GDEs/Lateral Flow - Grassland
Only
Total
Outflows
Estimated Annual Change in
Groundwater Storage
Upper
Aquifer
Lower
Aquifer
Upper
Aquifer
Lower
Aquifer
Upper
Aquifer
Lower
Aquifer
Upper
Aquifer
Lower
Aquifer Total
2044 W 502,000 209,000 119,000 0 0 23,000 28,000 881,000 220,000 38,000 282,000 71,000 0 0 611,000 227,000 59,000 286,000 2045 W 413,000 215,000 121,000 0 0 22,000 28,000 799,000 235,000 43,000 271,000 77,000 0 0 626,000 141,000 32,000 173,000 2046 D 382,000 151,000 101,000 0 0 10,000 0 644,000 469,000 68,000 296,000 112,000 0 0 945,000 (264,000) (85,000) (349,000) 2047 D 422,000 150,000 99,000 0 0 10,000 0 681,000 471,000 71,000 298,000 105,000 0 0 945,000 (214,000) (64,000) (278,000) 2048 N 393,000 187,000 109,000 0 0 14,000 0 703,000 475,000 92,000 263,000 100,000 0 0 930,000 (27,000) 69,000 42,000 2049 N 545,000 188,000 110,000 0 0 16,000 0 859,000 345,000 56,000 262,000 103,000 0 0 766,000 209,000 90,000 299,000 2050 W 436,000 217,000 120,000 0 0 23,000 28,000 824,000 239,000 46,000 274,000 73,000 0 0 632,000 173,000 41,000 214,000 2051 D 343,000 152,000 101,000 0 0 10,000 0 606,000 361,000 58,000 296,000 136,000 0 0 851,000 (195,000) (88,000) (283,000) 2052 D 466,000 150,000 98,000 0 0 10,000 0 724,000 463,000 66,000 296,000 105,000 0 0 930,000 (183,000) (82,000) (265,000) 2053 SC 341,000 156,000 97,000 0 0 9,000 0 603,000 499,000 99,000 312,000 104,000 0 0 1,014,000 (322,000) (95,000) (417,000) 2054 SC 392,000 156,000 96,000 0 0 8,000 0 652,000 514,000 98,000 312,000 102,000 0 0 1,026,000 (270,000) (98,000) (368,000) 2055 D 422,000 152,000 96,000 0 0 9,000 0 679,000 376,000 62,000 296,000 101,000 0 0 835,000 (138,000) (69,000) (207,000) 2056 W 511,000 222,000 115,000 0 0 22,000 28,000 898,000 258,000 58,000 278,000 67,000 0 0 661,000 244,000 48,000 292,000 2057 W 437,000 222,000 116,000 0 0 23,000 0 798,000 249,000 41,000 279,000 73,000 0 0 642,000 110,000 46,000 156,000 2058 N 479,000 205,000 108,000 0 0 15,000 0 807,000 453,000 69,000 266,000 105,000 0 0 893,000 63,000 83,000 146,000 2059 W 482,000 221,000 120,000 0 0 23,000 28,000 874,000 245,000 40,000 275,000 74,000 0 0 634,000 192,000 55,000 247,000 2060 D 395,000 150,000 101,000 0 0 10,000 0 656,000 361,000 51,000 293,000 136,000 0 0 841,000 (157,000) (76,000) (233,000) 2061 W 581,000 218,000 120,000 0 0 23,000 28,000 970,000 238,000 40,000 274,000 72,000 0 0 624,000 297,000 56,000 353,000 2062 N 454,000 198,000 113,000 0 0 15,000 0 780,000 372,000 60,000 262,000 109,000 0 0 803,000 115,000 83,000 198,000 2063 N 431,000 200,000 113,000 0 0 15,000 0 759,000 448,000 71,000 264,000 107,000 0 0 890,000 17,000 90,000 107,000 2064 D 376,000 152,000 101,000 0 0 11,000 0 640,000 368,000 52,000 299,000 134,000 0 0 853,000 (183,000) (68,000) (251,000) 2065 N 657,000 186,000 111,000 0 0 15,000 0 969,000 360,000 60,000 263,000 103,000 0 0 786,000 321,000 95,000 416,000 2066 W 419,000 218,000 120,000 0 0 23,000 0 780,000 258,000 42,000 280,000 74,000 0 0 654,000 78,000 50,000 128,000 2067 W 430,000 217,000 121,000 0 0 23,000 0 791,000 257,000 42,000 277,000 77,000 0 0 653,000 96,000 54,000 150,000 2068 D 362,000 155,000 102,000 0 0 10,000 0 629,000 451,000 64,000 311,000 113,000 0 0 939,000 (291,000) (72,000) (363,000) 2069 D 364,000 154,000 98,000 0 0 10,000 0 626,000 457,000 62,000 312,000 105,000 0 0 936,000 (297,000) (64,000) (361,000) 2070 W 638,000 211,000 118,000 0 0 23,000 28,000 1,018,000 237,000 42,000 270,000 70,000 0 0 619,000 350,000 55,000 405,000 Delta-Mendota Subbasin Groundwater Sustainability Plan
Revised Common Chapter
CC-149
June 2022
Figure CC-64: Change in Storage, Delta-Mendota Subbasin Projected Water Budget Delta-Mendota Subbasin Groundwater Sustainability Plan
Revised Common Chapter
CC-150
June 2022
4.3.4 Sustainable Yield
Under SGMA, sustainable yield is defined as “the maximum quantity of water, calculated over a base period representative of long-term conditions in the basin and including any temporary surplus, that can be withdrawn annually from a groundwater supply without causing an undesirable result.” (CWC 10721(w)). Sustainable yield estimates for the Upper Aquifer and Lower Aquifer have been developed in a coordinated fashion for the Delta-Mendota Subbasin by the Delta-Mendota Technical Working Group and approved by the Delta-Mendota Coordination Committee.
Upper Aquifer Sustainable Yield Estimate
Methodologies for calculating Upper Aquifer sustainable yield were discussed by both the Delta-Mendota Coordination Committee and an ad-hoc Technical Working Group of the Coordination Committee.
During a workshop dedicated to this effort, several basic concepts and principles were discussed to calculate the Upper Aquifer sustainable yield estimate. Consideration was given to several potential options with increasing detail, including a combination of the following: total Subbasin Upper Aquifer pumping volumes, total Subbasin Upper Aquifer change in storage, and Subbasin Upper Aquifer subsurface inflows and outflows. Inflow from certain neighboring subbasins, based on groundwater flow direction, as well as subsurface inflow from the Coast Range at existing gradients (as part of the inflow to the Northern & Central Delta-Mendota Region GSP area) was considered. Outflow to neighboring subbasins at existing gradients was also considered in certain applicable areas along the Delta-Mendota Subbasin boundary based on groundwater flow characteristics.
An overarching goal of this Subbasin is to maintain a balanced water budget by managing groundwater extractions (pumping). Therefore, the Upper Aquifer sustainable yield was estimated using the change in storage from the historic water budget (WY2003-2012). Based on these considerations, the following formula was selected for estimating Upper Aquifer sustainable yield utilizing the consolidated historic water budget components:
Upper Aquifer Sustainable Yield = (Pumping + Change in Storage) + (Subsurface Outflow – Subsurface Inflow)
The formula for determining Upper Aquifer sustainable yield was applied to the following compiled Delta-Mendota Subbasin projected water budgets (WY2014-2070):
Projected Baseline values with Climate Change Factors Projected Baseline values with Climate Change Factors and Projects and Management Actions This analysis resulted in an Upper Aquifer Sustainable Yield estimate of 403,000 acre-feet.
The Upper Aquifer sustainable yield value, derived from calculations using the best available but limited data, is considered to be a preliminary estimation only and will be updated to an anticipated higher level of accuracy in future GSP updates. The intention of the Delta-Mendota Subbasin GSAs, following GSP submission in 2020, is to increase subbasin-wide data collection efforts. Improved data, modeling results, and understanding of subsurface flows will allow the GSAs and each GSP Group to improve estimated sustainable yield values for future GSP updates. The GSP Groups are in the process of developing GSP implementation guidelines that will address future data collection efforts and other GSP implementation activities.
Delta-Mendota Subbasin Groundwater Sustainability Plan
Revised Common Chapter
CC-151
June 2022
The Upper Aquifer sustainable yield calculated range reflects the principle that the GSAs within the Delta-Mendota Subbasin reserve the right to claim or retain some portion of subbasin outflow generated by the lowering of groundwater levels from neighboring subbasins and the equitable portion of sources of recharge shared between two subbasins, by physical or non-physical means, in the future if the DeltaMendota Subbasin GSAs determine that doing so will improve Subbasin sustainability or will prevent undesirable results due to the chronic lowering of groundwater levels. Furthermore, intra-basin coordination during GSP development, followed by continuing inter-basin coordination discussions and data collection after GSP adoption, will allow the GSAs to further refine these determinations.
Lower Aquifer Sustainable Yield Estimate
Currently, within the Delta-Mendota Subbasin, the distribution of known Lower Aquifer water level data and extraction volume data are not sufficient to allow for an accurate calculation of Lower Aquifer sustainable yield utilizing the same methodology as for the Upper Aquifer. Following discussions by both the Coordination Committee and the Technical Working Group of the Coordination Committee, a consensus was reached to establish a Lower Aquifer sustainable yield estimate for the Subbasin based on a projection of existing subsidence rates as measured along the DMC with the minimum threshold established for inelastic land subsidence. In the original 2020 submittal, the calculation for the Lower Aquifer sustainable yield was based on the following. The Westlands Water District GSA recently conducted a study using groundwater modeling, in conjunction with the Westside GSP development, to estimate sustainable yield for the Westside Subbasin. Based on an analysis of available data and an initial assumption of Lower Aquifer sustainable yield equivalent to approximately 0.35 acre-feet per acre within the Westside Subbasin (Westlands Water District GSA, Groundwater Management Strategy Concepts presentation to the WWD Board on October 16, 2018), the GSA estimates a sustainable yield of 230,000 to 250,000 acre-feet, with historic conditions suggesting a range from 250,000 to 300,000 acre-feet (Westlands Water District GSA, Westside Subbasin’s Groundwater Model Forecast and Augmentation Strategies presentation to the WWD Board on April 3, 2019). Using Westlands Water District GSA’s analysis, the Delta-Mendota Coordination Committee recommended a slightly more conservative sustainable yield value of one-third (0.33) an acre-foot per acre for the Delta-Mendota Subbasin. Using this more conservative value, the estimated Lower Aquifer sustainable yield is approximately 250,000 acre-feet per year over the approximately 750,000-acre subbasin. It should be noted that sustainable management of the Lower Aquifer is governed by significant and unreasonable subsidence rather than sustainable yield. The distribution of sustainable yield is not uniform throughout the Subbasin, and it will be the responsibility of each GSA in the Subbasin to manage Lower Aquifer pumping to prevent significant and unreasonable subsidence.
Acknowledging that land subsidence is occurring at localized areas in the Subbasin, the DMCC refined the Lower Aquifer sustainable yield calculation, adjusting the value from 250,000 AF to 101,000 AF, based on observed extractions from the Lower Aquifer during WY2015. This refinement is consistent with the common definitions established across the Subbasin for all SMCs. It is important to note that subsidence will be the primary factor influencing the allowable volume of groundwater that can be extracted from the Lower Aquifer without incurring significant and unreasonable impacts on beneficial uses and users. As such, this number will be updated as data gaps are filled, particularly using the Proposition (Prop) 68 grant-funded well inventory and subsidence study and the results of the Airborne Electromagnetic (AEM) survey recently completed by DWR. Furthermore, the Subbasin will investigate the feasibility to recharge the Lower Aquifer as a means of reducing subsidence and managing future Lower Aquifer sustainable yield.
The Lower Aquifer sustainable yield estimate will be refined in the future based on data collected and compiled for the Subbasin. This current sustainable yield approximation highlights the importance of an Delta-Mendota Subbasin Groundwater Sustainability Plan
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accepted Subbasin-level subsidence monitoring program concurrent with improved estimates of subCorcoran Clay groundwater extractions.
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5. SUSTAINABLE MANAGEMENT CRITERIA
As required by Subarticle 3. Sustainable Management Criteria of the GSP regulations, the GSPs must include a sustainability goal and definitions of undesirable results, in addition to defining what is considered to be significant and unreasonable and establishing minimum thresholds, measurable objectives and 5-year interim goals. Given the variability of conditions within the Delta-Mendota Subbasin, a subbasin-wide sustainability goal and definitions of undesirable results were developed at the subbasin-level, while the definitions of significant and unreasonable, minimum thresholds, measurable objectives and 5-year interim goals were established at the GSP Plan area-level.
This section describes the coordinated sustainability goal and definition of undesirable results at a subbasin-level and the sustainable management criteria at a GSP-level. Sustainable management criteria developed by each GSP Group were further compared and coordinated between neighboring GSP Groups to avoid conflicts, particularly in setting numeric minimum thresholds, measurable objectives, and interim milestones at boundary locations. The sustainable management criteria for each GSP Group for each applicable sustainability indicator are presented herein.
5.1 Coordinated Assumptions and Data
All common coordinated assumptions and data agreed upon and implemented by each GSP Group in developing their respective sustainable management criteria for each applicable sustainability indicator are presented in Technical Memoranda 4 (Assumptions for Delta-Mendota Subbasin Management Areas, Sustainability Indicators, and GSP Documentation), which is included in Appendix B of this Common Chapter.
During preparation of the January 2020 GSP, each GSP Group drafted their respective sustainable management criteria for each applicable sustainability indicator and then met with their neighboring GSP Groups to coordinate minimum thresholds and measurable objectives to avoid conflicts and ensure each GSP Group would not negatively impact their neighboring GSP Groups from achieving sustainability. In the CIL received on January 21, 2022, DWR stated that “The GSPs have not established common definitions of undesirable results in the Subbasin.” nor did they comply with the Emergency GSP Regulations in establishing common definitions and methodologies for SMC. In response, subsequent to receipt of the CIL, the Technical Working Group and Coordination Committee met to develop, at a subbasin level, singular coordinated definitions and methods for establishing SMC for each applicable sustainability indicator.
5.2 Coordinated Sustainability Goal and Undesirable Results The sustainability goal for the Delta-Mendota Subbasin was established to succinctly state the objectives and desired conditions of the Subbasin that culminates in the absence of undesirable results by 2040. The sustainability goal for the Delta-Mendota Subbasin is as follows and was approved by the Delta-Mendota Subbasin Coordination Committee during the June 10, 2019 meeting:
The Delta-Mendota Subbasin will manage groundwater resources for the benefit of all users of groundwater in a manner that allows for operational flexibility, ensures resource availability under drought conditions, and does not negatively impact surface water diversion and conveyance and delivery capabilities. This goal will be achieved through the implementation of the proposed projects and management actions to reach identified measurable objectives and milestones through the implementation of the GSP(s), and through continued coordination with neighboring subbasins to ensure the absence of undesirable results by 2040.
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The following definitions of “undesirable results” were agreed upon during the 20222 revision of this Common Chapter for the following applicable sustainability indicators:
Chronic lowering of groundwater levels - Chronic changes in groundwater levels that diminish access to groundwater, causing significant and unreasonable impacts to beneficial uses and users of groundwater.
Reduction in groundwater storage - A chronic decrease in groundwater storage that causes a significant and unreasonable impact to the beneficial uses and users of groundwater. Degraded water quality - Degradation of groundwater quality as a result of groundwater management activities that causes significant and unreasonable impacts to beneficial uses and users of groundwater.
Land subsidence - Changes in ground surface elevation that cause damage to critical infrastructure, including significant and unreasonable reductions of conveyance capacity, impacts to natural resource areas, or conditions that threaten public health and safety. Depletions of interconnected surface wat–r - Depletions of interconnected surface water as a direct result of groundwater pumping that cause significant and unreasonable impacts on natural resources or downstream beneficial uses and users.
5.3 GSP-Level Sustainable Management Criteria
In the original 2020 GSP submittals for the Delta-Mendota Subbasin, each GSP Group defined what was considered significant and unreasonable in their Plan Area for each applicable sustainability indicator, in addition to establishing minimum thresholds, measurable objectives and 5-year interim goals for their Plan Area, consistent with GSP Regulations Article 5. Plan Contents, Subarticle 3. Sustainable Management Criteria (§ 354.2 through 354.30). DWR’s Draft Best Management Practices for the Sustainable Management of Groundwater Sustainable Management Criteria BMP (2017) document was also used when and where applicable at the discretion of each GSP Group.
Subsequent to this submittal, the Technical Working Group and Coordination Committee met to develop consistent definitions and methodologies for establishing numeric metrics for each applicable sustainability indicator. These revised SMC are discussed in the next section.
5.4 Delta-Mendota Subbasin Sustainable Management Criteria The sustainable management criteria for each sustainability indicator contains the following components:
the subbasin-wide definitions of an undesirable result and of significant and unreasonable, sustainability goals, minimum thresholds (MTs), measurable objectives (MOs), and five-year interim milestones (IMs).
Separate tables show the sustainable management criteria for chronic lowering of groundwater levelsError! Reference source not found., reduction in groundwater storageError! Reference source not found., degraded water quality, land subsidence, and depletions of interconnected surface water Error! Reference source not found.with maps showing representative monitoring sites with corresponding numeric MTs and MOs, and a table summarizing the MTs and MOs by representative monitoring location.
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5.4.1 Chronic Lowering of Groundwater Levels
Chronic Lowering of Groundwater Levels is arguably the most fundamental Sustainability Indicator, as it directly and indirectly influences several other Sustainability Indicators, such as Reduction of Groundwater Storage, Land Subsidence, and Degraded Water Quality. The Subbasin GSAs are committed to maintaining groundwater levels above historic low conditions in order to avoid undesirable results to beneficial uses and users of groundwater and to prevent further decrease of groundwater levels due to groundwater management actions performed within the Subbasin.
The GSAs developed SMCs for Chronic Lowering of Groundwater Levels using readily available historic records of groundwater level data for 61 of the 75 Representative Monitoring Sites (RMS). The MTs and MOs were developed for each RMS using common data and coordinated assumptions, as detailed in Table CC-16, and are consistent with the requirement of Title 23 of the California Code of Regulations (23 CCR) § 354.28(c) to consider trends in historic groundwater levels, water year type, projected water use in the Basin, and relationship with other sustainability indicators. The equivalent process was used in both the Upper Aquifer and Lower Aquifer within the Subbasin.
The MT is currently established as a fixed elevation at each RMS, equivalent to the historic seasonal low prior to the end of WY2016, based on available groundwater level data. The MO is to maintain water levels at or above the Water Year 2015 seasonal high at more than 50% of RMS in a GSP area. The GSAs will conduct a minimum of bi-annual groundwater level monitoring to track progress towards sustainability at the 75 RMS.
Per the definition of Undesirable Results for Chronic Lowering of Groundwater Levels, the exceedance of a MT at a single RMS is not indicative of an Undesirable Result; rather, the exceedance of MTs at 50% or more RMS within a GSP area is considered to cause significant and unreasonable impacts to locallyspecific beneficial uses and users of groundwater, namely the increased costs associated with modifying wells to access groundwater, securing alternative sources, or required mitigation of groundwater dependent ecosystems. To account for future year-to-year variations in hydrology, compliance will be assessed by comparing a four-year rolling average of groundwater level measurements to the fixed MT at each RMS within a GSP area.
In addition to the SMCs developed as part of this GSP, the GSAs will continue to coordinate to develop shorter-term (“acute”) groundwater level thresholds in the five-year GSP update that will be submitted in 2025. These thresholds will be set at levels that avoid short-term undesirable results, particularly for domestic water users, groundwater dependent ecosystems, and interconnected surface waters and subsidence when present. Each year, both the historic seasonal low MT value and the acute groundwater elevation thresholds will apply, whichever is more protective.
Table CC-16: Delta-Mendota Subbasin SMC
for Chronic Lowering of Groundwater Levels
Definition of
Undesirable Results
Chronic changes in groundwater levels that diminish access to groundwater, causing significant and unreasonable impacts to beneficial uses and users of groundwater.
Definition of
Significant and
Unreasonable
Significant and unreasonable impacts to beneficial uses and users of groundwater are substantially increased costs associated with higher total pumping lift, lowering pumps, drilling deeper wells, or otherwise modifying wells to access groundwater, securing alternative water sources, or required mitigation of groundwater dependent ecosystems. Significant Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-16: Delta-Mendota Subbasin SMC
for Chronic Lowering of Groundwater Levels
and unreasonable is quantitatively defined as exceeding the MT at more than 50% of representative monitoring sites by aquifer in a GSP area.
Sustainability Goal Maintain groundwater levels that are comparable to existing conditions (historic low conditions as of Water Year 2016) in order to continue meeting the demand of beneficial uses and users of groundwater and prevent a trend of decreasing groundwater levels. The Delta-Mendota Subbasin will continue successful and ongoing coordination with neighboring Subbasins to address chronic lowering of groundwater levels caused by pumping outside of the Subbasin.
Minimum Threshold The groundwater elevation indicating a chronic lowering of groundwater levels that may lead to undesirable results is an elevation that is lower than the historical seasonal low. The historic seasonal low is a fixed elevation at each site, based on available groundwater level data prior to the end of Water Year 2016. To account for future year-to-year variations in hydrology, compliance with the fixed historic seasonal low threshold will be compared with a 4-year rolling average of annual groundwater level measurements.
Shorter-term (“acute”) groundwater elevation thresholds will also be established at each representative monitoring site by 2025 using a coordinated methodology. Acute thresholds will be established at levels that are intended to avoid short-term undesirable results, particularly for domestic water wells, groundwater dependent ecosystems, and interconnected surface waters where present in the Upper Aquifer, and for subsidence in the Lower Aquifer. Each year, both the historic seasonal low and the acute groundwater elevation thresholds will apply, whichever is more protective. Groundwater levels are measured as water surface elevation (WSE). Each GSP area includes multiple representative monitoring sites (RMS) to which the minimum threshold applies. See Table CC-17for numeric MTs.
For any RMS without data prior to Water Year 2016, MTs and acute thresholds will be established using the aforementioned methodologies and the data resulting from the first five years of monitoring following Water Year 2016 or following construction of the well.
Measurable Objective Maintain seasonal high groundwater levels at an elevation that is at or above the Water Year 2015 seasonal high at more than 50% of representative monitoring sites in a GSP area. The Water Year 2015 seasonal high is a fixed elevation at each site, based on available groundwater level data. If data are unavailable for Water Year 2015 at a representative monitoring site, either a Water Year 2014 or Water Year 2016 Seasonal High will be used. To account for future year-to-year variations in hydrology, compliance with the fixed seasonal high threshold will be compared with a 4-year rolling average of annual groundwater level measurements. Groundwater levels are measured as water surface elevation (WSE). Each GSP area includes multiple representative monitoring sites (RMS) to which the measurable objective applies. See Table CC-17 for numeric MOs.
For any RMS without data prior to Water Year 2016, Measurable Objectives will be established using the aforementioned methodology and Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-16: Delta-Mendota Subbasin SMC
for Chronic Lowering of Groundwater Levels
the data resulting from the first five years of monitoring following Water Year 2016 or following the construction of the well.
5-Year Interim
Milestones Year 5: Gather data and complete the establishment of seasonal low and seasonal high elevations at representative monitoring sites in the Lower Aquifer for the Grassland GSP area. Develop a coordinated methodology and complete the establishment of acute groundwater elevation thresholds.
Identify chronic lowering of groundwater levels caused by pumping outside the Subbasin.
Year 10: Maintain groundwater levels at MOs. Where chronic lowering of groundwater levels is caused by pumping outside of the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
Year 15: Maintain groundwater levels at MOs. Where chronic lowering of groundwater levels is caused by pumping outside of the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
The numeric MTs and MOs by RMS are shown below in Figure CC-65 for the Upper Aquifer and Figure CC-66 for the Lower Aquifer, with the numeric SMC tabulated in Table CC-17.
Table CC-17: Numeric SMC for the Chronic Lowering of Groundwater Levels DMS ID GSP Region Principal Aquifer
Minimum
Threshold (ft
above MSL,
NAVD88)
Measurable
Objective (ft
above MSL,
NAVD88)
09‐001 Aliso Water District Upper 40.5 114.3
09‐002 Aliso Water District Upper (Composite) ‐4.0 17.1 09‐003 Aliso Water District Upper 37.4 52.9
09‐004 Aliso Water District Upper 37.7 51.9
10‐001 Farmers Water District Upper 34.0 102.7
12‐001 Fresno County Upper 98.2 103.2
13‐001 Fresno County Upper 109.4 120.5
13‐003 Fresno County Upper 48.6 116.1
13‐004 Fresno County Lower ‐59.0 ‐27.0
11‐001 Grassland Lower TBD TBD
11‐002 Grassland Lower TBD TBD
11‐003 Grassland Lower TBD TBD
11‐004 Grassland Lower TBD TBD
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DMS ID GSP Region Principal Aquifer
Minimum
Threshold (ft
above MSL,
NAVD88)
Measurable
Objective (ft
above MSL,
NAVD88)
11‐005 Grassland Lower TBD TBD
11‐006 Grassland Lower TBD TBD
11‐007 Grassland Upper 79.9 91.1
11‐008 Grassland Upper 82.3 93.2
11‐009 Grassland Upper 63.4 77.3
11‐013 Grassland Upper 76.8 80.4
11‐014 Grassland Upper 68.1 80.7
11‐015 Grassland Upper 72.8 75.7
11‐016 Grassland Upper 83.1 92.8
11‐017 Grassland Upper 90.2 116.6
11‐019 Grassland Upper 27.0 27.0
19‐003 Grassland Upper 90.5 91.8
01‐001 NCDM Lower ‐44.9 ‐13.4
01‐002 NCDM Lower ‐36.1 ‐18.9
01‐003 NCDM Lower ‐21.8 62.3
01‐004 NCDM Upper 158.9 161.8
01‐005 NCDM Upper 110.6 179.6
01‐006 NCDM Lower 77.1 94.0
01‐007 NCDM Lower 12.3 56.7
01‐008 NCDM Lower ‐44.9 2.4
02‐002 NCDM Lower ‐18.3 33.7
02‐009 NCDM Upper ‐6.2 29.8
03‐001 NCDM Upper 30.7 46.7
03‐002 NCDM Upper 7.7 67.2
03‐003 NCDM Upper TBD TBD
04‐001 NCDM Lower ‐17.6 ‐3.6
06‐001 NCDM Lower ‐52.3 16.1
06‐002 NCDM Upper 31.5 44.6
06‐003 NCDM Lower ‐9.1 18.5
06‐004 NCDM Upper 14.8 30.5
07‐002 NCDM Lower 1.6 10.8
07‐003 NCDM Upper 62.5 89.9
07‐005 NCDM Lower ‐84.7 ‐41.8
07‐007 NCDM Lower ‐53.4 ‐26.6
07‐008 NCDM Lower ‐63.0 ‐47.0
07‐009 NCDM Upper 49.3 73.9
07‐010 NCDM Upper 64.0 96.2
07‐012 NCDM Upper TBD TBD
07‐014 NCDM Lower ‐133.5 ‐47.2
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DMS ID GSP Region Principal Aquifer
Minimum
Threshold (ft
above MSL,
NAVD88)
Measurable
Objective (ft
above MSL,
NAVD88)
07‐015 NCDM Lower ‐147.0 ‐65.0
07‐016 NCDM Lower ‐2.4 74.6
07‐017 NCDM Upper TBD TBD
07‐018 NCDM Upper TBD TBD
07‐028 NCDM Lower ‐88.2 ‐64.8
07‐029 NCDM Upper TBD TBD
07‐030 NCDM Lower TBD TBD
07‐031 NCDM Lower TBD TBD
07‐032 NCDM Lower TBD TBD
07‐035 NCDM Upper ‐99.8 95.2
08‐002 NCDM Upper 50.7 83.7
14‐001 SJREC Upper 24.0 48.5
14‐002 SJREC Upper 96.5 125.7
14‐003 SJREC Upper 81.3 92.2
14‐004 SJREC Upper 78.7 92.6
14‐005 SJREC Upper 92.2 106.2
14‐006 SJREC Upper 76.7 98.2
14‐007 SJREC Upper 73.5 98.5
14‐008 SJREC Upper 70.5 98.5
14‐019 SJREC Lower ‐48.8 35.0
14‐020 SJREC Lower 38.1 57.4
14‐021 SJREC Lower ‐33.0 14.8
23‐001 SJREC Upper 102.3 120.2
T–D ‐ Numeric SMC to be determined after five years of data have been collected for this representative monitoring site.
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Figure CC-65: Groundwater Level Representative Monitoring Locations with SMC – Upper Aquifer Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-66: Groundwater Level Representative Monitoring Locations with SMC – Lower Aquifer Delta-Mendota Subbasin Groundwater Sustainability Plan
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5.4.2 Reduction in Groundwater Storage
The GSAs intend to maintain groundwater storage at volumes that will continue to meet the demands of beneficial uses and users of groundwater, provide a three-year drought buffer, and minimize reductions in groundwater storage during extended dry periods. Further, the GSAs will coordinate with neighboring subbasins to address reductions in groundwater storage caused by pumping outside of the Subbasin. The SMCs were developed using common data and coordinated assumptions, as detailed in Table CC-18 and will be monitored a minimum of bi-annually as detailed for Chronic Lowering of Groundwater Levels in Section 5.4.1 (Table CC-16) and consistent Land Subsidence monitoring as detailed in Section 5.4.4 (Table CC-21).
Pursuant to 23 CCR § 354.28(d), the MTs for Reduction of Groundwater Storage may be set by using groundwater levels as a proxy if it is demonstrated that a correlation exists between the two metrics. It is logical to link these two Sustainability Indicators for the Upper Aquifer, as the amount of groundwater in storage is directly, if not linearly, related to groundwater levels. As such, in the Upper Aquifer, it is not necessary to set a unique MT for Reduction of Groundwater Storage, and the MTs for Chronic Lowering of Groundwater Levels are used as a proxy for the Reduction of Groundwater Storage Sustainability Indicator. Similarly, the MOs for Chronic Lowering of Groundwater Levels serves as a proxy for Reduction of Groundwater Storage. Because the SMCs established for Chronic Lowering of Groundwater Levels are designed to maintain groundwater levels above historic low conditions, they are protective of the Reduction of Groundwater Storage Sustainability indicator and local beneficial uses and users of the Upper Aquifer, as the SMCs maintain sufficient water storage to maintain beneficial uses, including the conjunctive use of groundwater.
In the Lower Aquifer, the physical reduction in groundwater storage is caused by inelastic land subsidence, as detailed in Section 5.4.4 (Table CC-21). As such, the SMCs set for Land Subsidence (which are designed to reduce subsidence caused by groundwater extraction in the Subbasin, with no additional subsidence after 2040) are reasonably protective and used as a tool to calculate the Reduction of Groundwater Storage Sustainability Indicator SMCs in the Lower Aquifer1 .
1 The most significant subsidence in the Subbasin observed between from 2014-2018 was a 0.6-foot decline at Check 18 of the Delta-Mendota Canal. During those same years, the water budget calculation estimated what the change in storage was in the Lower Aquifer. Given the apparent relationship between the loss in groundwater storage and the observed subsidence, the projected allowable additional subsidence (i.e., two feet by 2040) was converted to a groundwater storage volume in the Lower Aquifer and used as the SMC.
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Table CC-18: Delta-Mendota Subbasin SMC
for Reduction in Groundwater Storage
Definition of
Undesirable Results A chronic decrease in groundwater storage that causes a significant and unreasonable impact to the beneficial uses and users of groundwater.
Definition of
Significant and
Unreasonable
A significant and unreasonable impact to beneficial uses and users of groundwater is insufficient water storage to maintain beneficial uses and natural resource areas in the Subbasin, including the conjunctive use of groundwater.
Sustainability Goal Maintain historic groundwater storage volumes in order to continue meeting the demand of beneficial uses and users of groundwater and to provide a 3- year drought buffer. Minimize reductions in groundwater storage during extended dry periods. Work with neighboring Subbasins to address reduction in groundwater storage caused by pumping outside of the Subbasin.
Minimum Threshold For the Upper Aquifer, as a reasonable proxy for an individual groundwater storage threshold, maintain groundwater levels in accordance with the minimum threshold set for Chronic Lowering of Groundwater Levels.
For the Lower Aquifer, correlate the SMCs for inelastic land subsidence with the reduction in groundwater storage that would cause undesirable results, estimated to be 1.1 million acre-feet of storage loss by 2040 attributable to groundwater extraction in the Subbasin.
Measurable Objective For the Upper Aquifer, maintain groundwater levels in accordance with the measurable objectives set for Chronic Lowering of Groundwater Levels.
For the Lower Aquifer, minimize loss of groundwater storage caused by inelastic land subsidence.
5-Year Interim
Milestones Year 5: Maintain groundwater levels in accordance with the measurable objectives. Identify reduction in groundwater storage caused by pumping outside the Subbasin.
Year 10: Maintain groundwater levels in accordance with the measurable objectives. Where reduction in groundwater storage is caused by pumping outside of the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
Year 15: Maintain groundwater levels in accordance with the measurable objectives. Where reduction in groundwater storage is caused by pumping outside of the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
5.4.3 Degraded Groundwater Quality
The GSP groups within the Delta-Mendota Subbasin are committed to preventing the migration or elevated concentrations of constituents of concern due to groundwater management activities. The primary constituent of concern in the Subbasin is salinity, frequently reported as total dissolved solids (TDS).
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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). To reflect the Subbasin’s designation as a Municipal (MUN) beneficial use, as established in the Central Valley Water Control Plans (often referred to as Basin Plans), the Subbasin has selected the upper limit of 1,000 mg/L as the Minimum Threshold.
The Delta-Mendota GSAs also recognize that a Salt Control Program for the San Joaquin Valley was recently developed through the collaborative CV-SALTS Program and was adopted into the Central Valley Basin Plans to address the long-term problem of salt accumulation in the Valley. The program recognizes that salt accumulation and water uses vary widely across the Valley. The program approach is intended to protect beneficial uses by maintaining water quality that meets applicable objectives, allow some salt accumulation in areas where salt can be stored without impairing beneficial uses of water, and, through long-term management, restore water quality where reasonable, feasible, and practicable.
A Prioritization and Optimization (P&O) Study planning process is now underway to identify potential requirements that will protect beneficial uses, improve salt management, and restore water quality where possible. During the next ten years (Phase 1), the P&O Study will: characterize the salt conditions and trends in the Valley; identify salt management needs and mechanisms; evaluate the feasibility of potential solutions; prepare an implementation plan; and review and recommend revising salinity regulations as necessary. 1
The minimum thresholds and measurable objectives for groundwater quality incorporate these standards and objectives for salinity. The minimum threshold is therefore set as 1,000 mg/L TDS, and the measurable objective is a concentration less than 1,000 mg/L TDS with acknowledgement that salinity standards are still being developed by water quality experts and regulatory agencies in the Central Valley, and thus may need to be revised in the future. Additionally, groundwater is frequently blended with other water supplies to reduce TDS concentrations to meet the salinity sensitivity of a particular beneficial use.
For any representative monitoring site that currently exceeds the TDS thresholds set forth above, the existing regulatory water quality compliance and remediation programs will apply. These include, but are not limited to, the CV-SALTS Salt Control Program, the County Drought Plan requirements for State Small Water Systems and Domestic Wells (SB 552), the Safe and Affordable Funding for Equity and Resilience (SAFER) program, and the Bureau of Reclamation’s Refuge Water Supply Program. For any future exceedance of the TDS thresholds at representative monitoring sites that do not currently exceed the objectives, the applicable GSP group is required to coordinate and publish an assessment of the effect of groundwater management activities on the documented exceedance, and propose timely actions to manage groundwater differently in order to avoid exacerbating the exceedance.
The sustainable management criteria also incorporate by reference the specific requirements for preventing the migration of contaminants adopted by the Central Valley Regional Water Quality Control Board in Cleanup and Abatement Orders for individual contaminated sites.2 1 See https://www.cvsalinity.org/salt-program/;
https://www.waterboards.ca.gov/centralvalley/water_issues/basin_plans/sacsjr_201805.pdf 2 E.g., the Cleanup and Abatement Order R5-2018-0033 for the Spreckels facility:
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Table CC-19: Delta-Mendota Subbasin SMC
for Degraded Groundwater Quality
Definition of
Undesirable Results
Degradation of groundwater quality as a result of groundwater management activities that causes significant and unreasonable impacts to beneficial uses and users of groundwater.
Definition of
Significant and
Unreasonable
Significant and unreasonable impacts to beneficial uses and users of groundwater as a result of groundwater management activities are the migration of contaminant plumes or elevated concentrations of constituents of concern that reduce groundwater availability, and the degradation of surface water quality as a result of groundwater migration that substantially impair an existing beneficial use. Significant and unreasonable is quantitatively defined as exceeding the MT at more than 50% of representative monitoring sites by aquifer in a GSP area where current groundwater quality (as established in the Subbasins GSPs) does not exceed 1,000 mg/L TDS.
Sustainability Goal Minimize further impairment of water supplies resulting from groundwater management activities that cause the migration or concentration of contaminant plumes or the increased rate of movement or concentrations of constituents of concern. Coordinate with and support compliance with existing regulatory groundwater quality orders and objectives for drinking water, agricultural irrigation, and managed wetlands. Work with neighboring Subbasins to address existing or potential impairments of groundwater quality in the Subbasin caused by groundwater management activities outside the Subbasin.
Minimum Threshold The minimum threshold for salinity is 1,000 mg/L TDS. For representative monitoring sites that currently exceed the minimum threshold, existing regulatory water quality compliance and remediation programs will apply, including but not limited to, the CV-SALTS Salt Control Program, the Irrigated Lands Regulatory Program, the County Drought Plan requirements for State Small Water Systems and Domestic Wells (SB 552), and the Safe and Affordable Funding for Equity and Resilience (SAFER) program. For any RMS without data prior to the end of Water Year 2016, current (ambient) groundwater quality will be established using data collected during the first five years of monitoring following Water Year 2016 or following construction of the well.
For representative monitoring sites that do not currently exceed the minimum threshold, but are found to exceed minimum thresholds in the future, the applicable GSP group will conduct and publish an assessment of the effect of groundwater management activities on the documented exceedance, and propose timely actions to manage groundwater differently, if needed, to avoid exacerbating the exceedance. The applicable GSP group will also coordinate with the appropriate regulatory program to address the impact.
Measurable Objective The measurable objective for salinity will be concentrations less than 1,000 mg/L TDS.
Each GSP group will participate in, provide data for, and track and report on compliance with orders and objectives adopted by the State and Central Valley Regional Water Quality Control Boards and similar regulatory agencies, in coordination with the Central Valley Groundwater Monitoring Collaborative.
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Table CC-19: Delta-Mendota Subbasin SMC
for Degraded Groundwater Quality
5-Year Interim
Milestones Year 5: Maintain salinity consistent with measurable objectives. Participate in, provide data for, and track and report on compliance with orders and objectives adopted by the State Water Resources and Central Valley Regional Water Quality Control Boards and similar regulatory agencies, in coordination with the Central Valley Groundwater Monitoring Collaborative. Develop correlation between groundwater quality and groundwater levels in order to establish methodology for the use of groundwater levels as a proxy for groundwater quality.
Year 10: Maintain water quality consistent with measurable objectives.
Continue monitoring and publishing groundwater quality data, and tracking and reporting on compliance with regulatory orders and objectives. Where water quality impairments are caused by activities outside the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
Utilizing the methodology developed by the Year 5 Interim Milestone, develop minimum thresholds and measurable objectives for groundwater quality that utilize groundwater elevations as a proxy for monitoring.
Year 15: Maintain water quality consistent with measurable objectives.
Continue monitoring and publishing groundwater quality data, and tracking and reporting on compliance with regulatory orders and objectives. Where water quality impairments are caused by activities outside the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
The numeric MTs and MOs by RMS are shown below in Figure CC-67 for the Upper Aquifer and Figure CC-68 for the Lower Aquifer, with the numeric SMC tabulated in Table CC-20.
Table CC-20: Numeric SMC for Degraded Groundwater Quality DMS ID GSP Region
Principal Aquifer Minimum Threshold
(TDS in mg/L)
Measurable
Objective
(TDS in mg/L)
09‐002 Aliso Water District Upper 1,000 < 1,000
09‐003 Aliso Water District Upper 1,000 < 1,000
09‐005 Aliso Water District Upper 1,000 < 1,000
09‐196 Aliso Water District Upper 1,000 < 1,000
10‐001 Farmers Water District Upper 1,000 < 1,000
10‐005 Farmers Water District Upper 1,000 < 1,000
12‐002 Fresno County Upper N/A N/A
12‐003 Fresno County Upper N/A N/A
12‐004 Fresno County Upper N/A N/A
12‐005 Fresno County Upper N/A N/A
12‐006 Fresno County Upper 1,000 < 1,000
12‐007 Fresno County Upper N/A N/A
13‐006 Fresno County Upper N/A N/A
13‐007 Fresno County Upper N/A N/A
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DMS ID GSP Region
Principal Aquifer Minimum Threshold
(TDS in mg/L)
Measurable
Objective
(TDS in mg/L)
13‐008 Fresno County Upper N/A N/A
11‐010 Grassland Lower TBD TBD
11‐011 Grassland Lower 1,000 < 1,000
11‐012 Grassland Lower 1,000 < 1,000
11‐021 Grassland Upper N/A N/A
19‐002 Grassland Upper 1,000 < 1,000
19‐004 Grassland Upper N/A N/A
01‐001 NCDM Lower 1,000 < 1,000
01‐002 NCDM Lower 1,000 < 1,000
01‐003 NCDM Lower N/A N/A
01‐004 NCDM Upper 1,000 < 1,000
01‐006 NCDM Lower 1,000 < 1,000
01‐007 NCDM Lower 1,000 < 1,000
01‐008 NCDM Lower 1,000 < 1,000
01‐018 NCDM Upper (assumed) 1,000 < 1,000
02‐002 NCDM Lower 1,000 < 1,000
02‐009 NCDM Upper 1,000 < 1,000
03‐001 NCDM Upper N/A N/A
03‐003 NCDM Upper N/A N/A
03‐007 NCDM Upper 1,000 < 1,000
04‐001 NCDM Lower 1,000 < 1,000
06‐001 NCDM Lower 1,000 < 1,000
06‐002 NCDM Upper 1,000 < 1,000
06‐003 NCDM Lower 1,000 < 1,000
06‐004 NCDM Upper N/A N/A
07‐002 NCDM Lower 1,000 < 1,000
07‐003 NCDM Upper 1,000 < 1,000
07‐007 NCDM Lower 1,000 < 1,000
07‐008 NCDM Lower N/A N/A
07‐012 NCDM Upper N/A N/A
07‐014 NCDM Lower 1,000 < 1,000
07‐015 NCDM Lower 1,000 < 1,000
07‐016 NCDM Lower 1,000 < 1,000
07‐017 NCDM Upper 1,000 < 1,000
07‐018 NCDM Upper N/A N/A
07‐028 NCDM Lower N/A N/A
07‐029 NCDM Upper N/A N/A
07‐030 NCDM Lower N/A N/A
07‐031 NCDM Lower N/A N/A
07‐032 NCDM Lower N/A N/A
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DMS ID GSP Region
Principal Aquifer Minimum Threshold
(TDS in mg/L)
Measurable
Objective
(TDS in mg/L)
07‐033 NCDM Upper 1,000 < 1,000
07‐034 NCDM Lower (assumed) N/A N/A
07‐035 NCDM Upper N/A N/A
08‐002 NCDM Upper N/A N/A
14‐001 SJREC Upper 1,000 < 1,000
14‐002 SJREC Upper 1,000 < 1,000
14‐003 SJREC Upper N/A N/A
14‐004 SJREC Upper 1,000 < 1,000
14‐005 SJREC Upper N/A N/A
14‐006 SJREC Upper 1,000 < 1,000
14‐007 SJREC Upper N/A N/A
14‐008 SJREC Upper 1,000 < 1,000
14‐019 SJREC Lower 1,000 < 1,000
14‐020 SJREC Lower 1,000 < 1,000
14‐021 SJREC Lower N/A N/A
23‐001 SJREC Upper 1,000 < 1,000
Notes:
1. Current TDS concentration is defined as prior to the end of WY 2016.
2. N/A ‐ Current groundwater quality exceeds 1,000 mg/L TDS.
3. TBD ‐ Numeric SMC to be determined after five years of data have been collected for this representative monitoring site.
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Figure CC-67: Groundwater Quality Representative Monitoring Locations with SMC – Upper Aquifer Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-68: Groundwater Quality Representative Monitoring Locations with SMC – Lower Aquifer Delta-Mendota Subbasin Groundwater Sustainability
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5.4.4 Inelastic Land Subsidence
The Subbasin GSAs are committed to ramping down the amount of allowable subsidence caused by groundwater extraction in the Subbasin and eliminating additional subsidence within the Subbasin by 2040. Further, the GSAs will coordinate with neighboring subbasins to address inelastic land subsidence caused by groundwater management activities that occur outside of the Subbasin.
The SMCs for Land Subsidence were coordinated at the Subbasin level and are designed to be protective of critical infrastructure, including significant and unreasonable reductions of conveyance capacity (i.e., structural damage that creates an unmanageable reduction of design capacity), impacts to natural resource areas (i.e., unmitigated decreases in the ability to irrigate or drain these areas by gravity), or conditions that threaten public health and safety (i.e., unmitigated reduction of freeboard that allows for flooding, or unmitigated damage to roads and bridges). The Subbasin-wide MT is set to prevent subsidence that exceeds the corrective design standards or established triggers for critical infrastructure, including the Delta-Mendota Canal and California Aqueduct. At the RMS, the MT is defined as two feet of additional inelastic subsidence by 2040 attributable to groundwater extraction within the Subbasin. The MO is set at no additional subsidence after 2040 based on groundwater extractions within the Delta-Mendota Subbasin.
The GSAs further developed Interim Milestones (IMs) to periodically reduce the amount of allowable subsidence and meet the MO by 2040. The IMs allow for no more than 1.0 foot of additional subsidence by 2025, 0.5 feet of additional subsidence by 2030 (1.5 feet of cumulative subsidence), 0.25 feet of additional subsidence by 2035 (1.75 feet of cumulative subsidence), and 0.25 feet of additional subsidence by 2040 (2.0 feet of cumulative subsidence). The SMCs were defined at 45 RMS in the Subbasin, and the GSAs will conduct monitoring to track progress towards sustainability. Additionally, as part of the 5-year update to the GSPs, the Subbasin Hydrogeologic Conceptual Model (HCM) will be reviewed and revised to incorporate new data, including Airborne Electromagnetic (AEM) survey data provided by DWR and data/results from the Subsidence Study prepared using Prop 68 grant funding.
Additionally, the GSAs will continue work with USBR on revisions to the CVHM2 model for simulating groundwater extraction-subsidence interactions, to re-evaluate inelastic land subsidence SMC to consider new data and studies, and to assess allowable land subsidence on a Subbasin and localized (subbasin subarea) basis.
Table CC-21: Delta-Mendota Subbasin SMC
for Inelastic Land Subsidence
Definition of
Undesirable Results
Changes in ground surface elevation that cause damage to critical infrastructure, including significant and unreasonable reductions of conveyance capacity, impacts to natural resource areas, or conditions that threaten public health and safety.
Definition of
Significant and
Unreasonable
Significant and unreasonable damage to conveyance capacity from inelastic land subsidence is structural damage that creates an unmitigated and unmanageable reduction of design capacity or freeboard.
Significant and unreasonable impacts to natural resource areas from inelastic land subsidence are unmitigated decreases in the ability to flood or drain such areas by gravity.
Significant and unreasonable threats to public health and safety from inelastic land subsidence are those that cause an unmitigated reduction of freeboard that allows for flooding, or unmitigated damage to roads and bridges.
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Table CC-21: Delta-Mendota Subbasin SMC
for Inelastic Land Subsidence
Sustainability Goal Minimize inelastic land subsidence by ramping down allowable subsidence caused by groundwater extraction in the Subbasin, with no additional subsidence after 2040. Work with neighboring Subbasins to address inelastic land subsidence caused by groundwater extraction outside of the Subbasin.
Minimum Threshold At representative monitoring sites, the change in ground surface elevation that would cause undesirable results is up to 2 feet of additional inelastic land subsidence attributable to groundwater extraction in the Subbasin. Prevent subsidence caused by groundwater extractions in the Delta-Mendota Subbasin that exceeds corrective design standards or established triggers for critical infrastructure including the Delta-Mendota Canal, California Aqueduct, and roads and bridges.
Measurable Objective Minimize inelastic land subsidence attributable to groundwater extraction within the Subbasin, with no additional subsidence after 2040. 5-Year Interim
Milestones Year 5: Interim goal of no more than 1 foot of additional inelastic land subsidence attributable to groundwater extraction in the Subbasin during the first 5-year period of SGMA implementation. Review and revise Hydrogeologic Conceptual Model (HCM) to incorporate new data. Re-evaluate inelastic land subsidence SMC to consider new data and studies and to assess allowable land subsidence on a Subbasin and localized (subbasin subarea) basis. Gather data and complete the selection or establishment of representative monitoring sites (RMS) for land subsidence, with particular attention to the locations of critical infrastructure in the Subbasin, and in coordination with the Bureau of Reclamation and Department of Water Resources. Determine the relative proportion of subsidence caused by groundwater extraction within and outside the Subbasin for each RMS. Where subsidence is caused by pumping outside the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
Year 10: Interim goal of no more than 0.5 feet of additional inelastic land subsidence attributable to groundwater extraction in the Subbasin during the second 5-year period of SGMA implementation, for a cumulative total of 1.5 feet in the first 10 years. Where subsidence is caused by groundwater extraction outside the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs. Continue work to improve understanding of interconnection between groundwater extractions and land subsidence, utilizing model simulations and/or data collection and analysis.
Year 15: Interim goal of no more than 0.25 feet of additional inelastic land subsidence attributable to groundwater extraction in the Subbasin during the third 5-year period of SGMA implementation, for a cumulative total of 1.75 feet in the first 15 years. Where subsidence is caused by groundwater extraction outside the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs. Continue work to improve understanding of interconnection between groundwater extractions and land subsidence, utilizing model simulations and/or data collection and analysis.
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The numeric MTs and MOs by RMS are shown below in Figure CC-69, with the numeric SMC tabulated in Table CC-22.
Table CC-22: Numeric SMC for Inelastic Land Subsidence
DMS ID GSP Region
Minimum Threshold (Inelastic
Land Subsidence in ft
Attributable to Groundwater
Extraction)
Measurable Objective (Inelastic
Land Subsidence in ft
Attributable to Groundwater
Extraction)
09‐006 Aliso Water District 2 0
09‐007 Aliso Water District 2 0
09‐008 Aliso Water District 2 0
10‐008 Farmers Water District 2 0
12‐010 Fresno County 2 0
13‐010 Fresno County 2 0
11‐018 Grassland 2 0
11‐019 Grassland 2 0
11‐020 Grassland 2 0
01‐009 NCDM 2 0
01‐010 NCDM 2 0
01‐011 NCDM 2 0
01‐012 NCDM 2 0
01‐013 NCDM 2 0
01‐014 NCDM 2 0
01‐015 NCDM 2 0
01‐016 NCDM 2 0
01‐017 NCDM 2 0
02‐003 NCDM 2 0
02‐004 NCDM 2 0
02‐005 NCDM 2 0
02‐006 NCDM 2 0
02‐007 NCDM 2 0
02‐008 NCDM 2 0
03‐004 NCDM 2 0
03‐005 NCDM 2 0
03‐006 NCDM 2 0
04‐003 NCDM 2 0
04‐004 NCDM 2 0
04‐005 NCDM 2 0
06‐006 NCDM 2 0
07‐019 NCDM 2 0
07‐020 NCDM 2 0
07‐021 NCDM 2 0
07‐022 NCDM 2 0
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DMS ID GSP Region
Minimum Threshold (Inelastic
Land Subsidence in ft
Attributable to Groundwater
Extraction)
Measurable Objective (Inelastic
Land Subsidence in ft
Attributable to Groundwater
Extraction)
07‐023 NCDM 2 0
07‐024 NCDM 2 0
07‐025 NCDM 2 0
07‐026 NCDM 2 0
07‐027 NCDM 2 0
14‐014 SJREC 2 0
14‐015 SJREC 2 0
14‐016 SJREC 2 0
14‐017 SJREC 2 0
14‐018 SJREC 2 0
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Figure CC-69: Land Subsidence Representative Monitoring Locations with SMC Delta-Mendota Subbasin Groundwater Sustainability Plan
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5.4.5 Depletion of Interconnected Surface Water
The GSAs are committed to managing groundwater within the Subbasin to maintain interconnected surface waters comparable to existing conditions and prevent a trend of increasing interconnected surface water losses from the San Joaquin River. The GSAs will coordinate with neighboring subbasins to address interconnected surface water losses caused by groundwater management activities that occur outside of the Subbasin.
Presently, the Depletion of Interconnected Surface Water Sustainability Indicator is identified as a data gap within the Subbasin. Until the GSAs are able to collect the additional data necessary to set quantitative SMCs for this Sustainability Indicator, the SMCs for Chronic Lowering of Groundwater Levels serve as a proxy in the Upper Aquifer, pursuant to 23 CCR §354.28(d). Because the SMCs established for Chronic Lowering of Groundwater Levels are designed to maintain groundwater levels above historic low conditions, they are understood to be protective of the Depletion of Interconnected Surface Water Sustainability indicator and local natural resources and downstream beneficial uses and users. The RMS locations and frequency are consistent with that detailed in Section 6.
The GSAs plan to establish an Interconnected Surface Water monitoring network and develop SMCs as detailed in Table CC-18. By 2025, the GSAs anticipate completing an Interconnected Surface Water monitoring network that includes nine existing sites in the San Joaquin River Restoration Program and additional sites funded by the SGMA Implementation Grant award. The additional RMS will focus on the Northern & Central Delta-Mendota and Grassland GSP areas along the San Joaquin River. By 2030, the GSAs anticipate being able to gather and analyze data from these new RMS to estimate the influence of groundwater levels on gains and losses observed on the San Joaquin River. At this point, the Subbasin GSAs will establish Interconnected Surface Water SMCs as a rate or volume of surface water depletions that have adverse impacts on beneficial uses and users and may lead to undesirable results.
Table CC-23: Delta-Mendota Subbasin SMC
for Depletions of Interconnected Surface Water
Definition of
Undesirable Results
Depletions of interconnected surface water as a direct result of groundwater pumping that cause significant and unreasonable impacts on natural resources or downstream beneficial uses and users.
Definition of
Significant and
Unreasonable
Significant and unreasonable impacts on natural resources or downstream beneficial uses and users of groundwater are a reduction in available surface water supplies for natural resource areas, and reductions in downstream water availability as a result of increased streamflow depletions along the San Joaquin River when compared to similar historic water year types.
Sustainability Goal Maintain interconnected surface waters comparable to existing conditions (historic low conditions as of Water Year 2016) in order to prevent a trend of increasing interconnected surface water losses from the San Joaquin River.
Work with neighboring Subbasins to address increased interconnected surface water losses caused by pumping outside of the Subbasin.
Minimum Threshold Interconnected Surface Water is an identified data gap in the Delta-Mendota Subbasin. As an interim minimum threshold, use the Chronic Lowering of Groundwater Level Minimum Threshold as a proxy for impacts to interconnected surface waters (see below).
The groundwater elevation indicating a chronic lowering of groundwater levels that may lead to undesirable results is an elevation that is lower than the historical seasonal low. The historic seasonal low is a fixed elevation at each Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-23: Delta-Mendota Subbasin SMC
for Depletions of Interconnected Surface Water
site, based on available groundwater level data prior to the end of Water Year 2016. To account for future year-to-year variations in hydrology, compliance with the fixed historic seasonal low threshold will be compared with a 4-year rolling average of annual groundwater level measurements. Groundwater levels are measured as water surface elevation (WSE). Each GSP area includes multiple representative monitoring sites (RMS) to which the minimum threshold applies.
For any RMS without data prior to Water Year 2016, Minimum Thresholds and acute thresholds will be established using the aforementioned methodologies and the data resulting from the first five years of monitoring following Water Year 2016 or following construction of the well.
Measurable Objective Interconnected Surface Water is an identified data gap in the Subbasin. As an interim measurable objective, use the Chronic Lowering of Groundwater Level Measurable Objective as a proxy for interconnected surface waters (see below).
Maintain seasonal high groundwater levels at an elevation that is at or above the Water Year 2015 seasonal high at representative monitoring sites in a GSP area.
The Water Year 2015 seasonal high is a fixed elevation at each site, based on available groundwater level data. If data are unavailable for Water Year 2015 at a representative monitoring site, either a Water Year 2014 or Water Year 2016 Seasonal High will be used. To account for future year-to-year variations in hydrology, compliance with the fixed seasonal high threshold will be compared with a 4-year rolling average of annual groundwater level measurements.
Groundwater levels are measured as water surface elevation (WSE). Each GSP area includes multiple representative monitoring sites (RMS) to which the measurable objective applies.
For any RMS without data prior to Water Year 2016, Measurable Objectives will be established using the aforementioned methodology and the data resulting from the first five years of monitoring following Water Year 2016 or following the construction of the well.
5-Year Interim
Milestones Year 5: Fill data gaps, establish, and manage groundwater use to avoid the rate or volume of surface water depletions that have adverse impacts on beneficial uses and users and may lead to undesirable results.
The Subbasin will complete a monitoring network of Interconnected Surface Water sites that will include six existing sites and datasets. GSP groups will complete the monitoring network with additional sites installed with SGMA Implementation Grant funding awarded to the Subbasin. The existing nine sites are part of the San Joaquin River Restoration Program and are located along the San Joaquin River at the southern end of the Subbasin. These nine sites, and the associated datasets, will continue to be utilized by the Subbasin as part of its monitoring network. Additional representative monitoring network sites for Interconnected Surface Water will focus on the Northern & Central DeltaMendota and Grassland GSP areas along the San Joaquin River.
Year 10: Gather and analyze data from Subbasin’s established representative monitoring network sites. Also gather and analyze available data in cooperation with neighboring subbasins, the U.S. Bureau of Reclamation’s San Joaquin River Restoration Program, the U.S. Geological Survey, and DWR’s California Data Exchange Center (CDEC), to estimate the influence of groundwater on gains and losses in the San Joaquin River. Establish minimum thresholds and Delta-Mendota Subbasin Groundwater Sustainability Plan
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Table CC-23: Delta-Mendota Subbasin SMC
for Depletions of Interconnected Surface Water
measurable objectives as a rate or volume of surface water depletions that have adverse impacts on beneficial uses and users and may lead to undesirable results.
Year 15: Monitor and maintain interconnected surface waters in accordance with revised minimum thresholds and measurable objectives. Where increased interconnected surface water losses are caused by pumping outside of the Subbasin, seek remedies in coordination with the Department of Water Resources and neighboring GSAs.
The RMN for this sustainability indicator is shown below in Figure CC-70. Please see Table CC-17 for the numeric SMC associated with the Chronic Lowering of Groundwater Levels.
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Figure CC-70: Interconnected Surface Water Representative Monitoring Locations with SMC Delta-Mendota Subbasin Groundwater Sustainability Plan
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6. SUBBASIN MONITORING PROGRAM
As required by Subarticle 4. Monitoring Networks of the GSP regulations, the GSPs must include a monitoring network for each sustainability indicator, in addition to describing the monitoring protocols and data management to be followed in implementing the GSP monitoring program. Given the variability of conditions within the Delta-Mendota Subbasin, each GSP Group initially developed their individual monitoring networks, in coordination with their neighboring GSP Groups, such that the subbasin-wide monitoring program is simply a compilation of those coordinated individual monitoring networks. These representative monitoring networks were then re-evaluated as part of the update to the Subbasin GSP in 2022. Please see the individual GSPs for further discussion as to how the monitoring networks were developed.
The subbasin-wide monitoring networks presented herein are the representative monitoring networks for each of the applicable sustainability indicators, as defined according to the GSP Regulations § 354.36, Representative Monitoring. It is at the representative monitoring sites where each GSP Group has defined minimum thresholds, measurable objectives, and interim milestones to evaluate progress in achieving the Subbasin’s sustainability goal by 2040. Data collected at the representative monitoring locations may be augmented with additional data, as available and appropriate, from other locations and/or publicly available datasets, in evaluating Subbasin conditions on an annual basis.
6.1.1 Coordinated Assumptions and Data
As previously noted, the required monitoring networks were initially developed at the GSP-level in order to appropriately capture the variability of hydrogeologic and water quality conditions in the DeltaMendota Subbasin, and then re-evaluated at the Subbasin level to confirm that the monitoring networks meet the necessary requirements. All common coordinated assumptions agreed upon and implemented by each GSP Group in developing their respective monitoring networks are presented in Technical Memorandum 5 (Assumptions for Delta-Mendota Subbasin Monitoring Network) which is included in Appendix B of this Common Chapter.
6.1.2 Coordinated Monitoring Activities
All Delta-Mendota Subbasin GSP Groups have agreed to utilize the following monitoring protocols, data management, and roles and responsibilities for implementing and reporting from their respective monitoring plans under SGMA to ensure consistency in data collection, analysis and management allowing for subbasin-wide evaluation of groundwater conditions relative to the Subbasin sustainability goal, as defined and agreed upon by all GSP Groups.
Monitoring Protocols
Each GSP Group will utilize agreed-upon protocols, which may be the same as, or equal to, data collection protocols (i.e., industry standards and best management practices) to ensure the collection of comparable data using comparable methods. Additionally, the following minimum monitoring frequency for each applicable sustainability indicator was agreed upon by each GSP Group during the joint DeltaMendota Subbasin Coordination Committee and Technical Working Group meeting on June 18, 2019:
Chronic lowering of groundwater levels/reduction in groundwater storage - Twice per year, with seasonal high groundwater elevation data collected between February and April, and seasonal low groundwater elevation data collected between September and October. All measurements will be collected to a tenth of a foot.
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Degraded water quality – Once per year during irrigation season, typically between May and July.
Depletions of interconnected surface water – Twice per year in conjunction with groundwater level monitoring.
Subsidence – Publicly available subsidence data will be used along with locally-collected data. At a minimum, three data points will be collected within the first five years of GSP implementation, with a baseline value from 2019 or a date prior to that.
For non-monitored data to be reported as part of the annual reports (e.g., groundwater extractions, surface water deliveries), actual metered data will be used where such data exists, and when direct data do not exist, estimated quantities will be calculated based on existing indirect data (e.g., electrical usage, crop demand, ET) and/or other industry best practices. Additionally, where available and applicable, public datasets will be used to augment monitoring data collected by the Subbasin and analyzed on an annual basis.
Data Management
Each GSP Group will be responsible for conducting quality control reviews of data collected from the monitoring networks. As described in the Coordination Agreement, each GSP Group will exchange and share collected data in order to facilitate analysis and reporting at the Subbasin level. The Coordinated Data Management System (DMS) will be the primary vehicle by which data are shared amongst the GSP Groups, and it will be the responsibility of each GSP Group to conduct a quality control review of data entered into the DMS.
Roles and Responsibilities
It will be the responsibility of each GSP Group, and the GSAs included in that group, to conduct the monitoring program as agreed upon at the Subbasin level, for reviewing the data collected, and for ensuring that these data are available at the Subbasin level. Figure CC-71 shows the general flow of data collected from the Delta-Mendota monitoring programs.
Figure CC-72 shows the roles and responsibilities of each GSA and GSP Group in the collecting, processing and reporting of data from the GSP monitoring networks. Additionally, it is the responsibility of each GSP Group, including their respective GSAs, to maintain the monitoring network and, as appropriate, revise and/or expand the monitoring networks to fill identified data gaps. Please see the individual GSPs for further information regarding data gaps and the GSAs plans for addressing those gaps.
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Figure CC-71: Data Flow in Delta-Mendota Subbasin
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Figure CC-72: Delta-Mendota Monitoring and Data Management Roles and Responsibilities Delta-Mendota Subbasin Groundwater Sustainability Plan
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6.1.3 GSP-Level Monitoring Networks
For more information on the individual GSP monitoring networks for each applicable sustainability indicator, including how the networks were developed, please refer to the individual GSPs. The monitoring networks for each applicable sustainability indicator for each GSP Group were developed in accordance with the GSP Regulations Article 5. Plan Contents, Subarticle 4. Monitoring Networks (§ 354.21 – 354.40). DWR’s Best Management Practices for the Sustainable Management of Groundwater Monitoring Protocols, Standards, and Sites BMP (2016b) and Monitoring Networks and Identification of Data Gaps BMP (2016a) documents were used when and where applicable at the discretion of each GSP group in developing monitoring networks and monitoring protocols.
6.1.4 Delta-Mendota Subbasin Monitoring Networks
The subbasin-level monitoring networks are a compilation of the representative monitoring networks developed by each individual GSP Group and reviewed and modified at the Subbasin level for consistency and appropriate coverage. The monitoring network for the chronic lowering of groundwater sustainability indicator is comprised of two parts, the Upper Aquifer (Figure CC-73) and Lower Aquifer (Figure CC-74). The monitoring networks for the reduction in groundwater storage for the Upper Aquifer and Lower Aquifer are the same as those utilized for the chronic lowering of groundwater levels.
The monitoring network for the degraded water quality sustainability indicator is also comprised of two parts, the Upper Aquifer (Figure CC-75) and Lower Aquifer (Figure CC-76). Data gaps (areas without wells of known construction) are shown for the Upper Aquifer and Lower Aquifer for the chronic lowering of groundwater and degraded water quality sustainability indicator. The interconnected surface water monitoring network for the Delta-Mendota Subbasin is shown in Figure CC-77, and the monitoring network for land subsidence for the Delta-Mendota Subbasin is shown in Figure CC-78.
The Delta-Mendota Subbasin representative monitoring networks will be periodically reviewed and revised, as appropriate, by the GSP Groups responsible for maintaining them and coordinated at the Subbasin level. Revised monitoring networks will be included in the five-year updates to the GSPs.
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Figure CC-73: Upper Aquifer Groundwater Level Monitoring Network Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-74: Lower Aquifer Groundwater Level Monitoring Network Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-75: Upper Aquifer Groundwater Quality Monitoring Network Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-76: Lower Aquifer Groundwater Quality Monitoring Network Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-77: Interconnected Surface Water Monitoring Network Delta-Mendota Subbasin Groundwater Sustainability Plan
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Figure CC-78: Land Surface Elevation Monitoring Network Delta-Mendota Subbasin Groundwater Sustainability Plan
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7. SUBBASIN DATA COLLECTION AND MANAGEMENT
As required in §352.6, Data Management System of the GSP regulations, each GSA is required to develop and maintain a data management system (DMS) that is capable of storing and reporting information relevant to the development or implementation of the GSP(s). Additionally, per §354.4, Reporting Monitoring Data to the Department, all monitoring data is to be stored in a DMS with copies of the monitoring data included in the annual report and submitted electronically on forms provided by DWR. Recognizing that GSP implementation, including annual reporting, will require some efforts at the subbasin level, the 23 GSAs overlying the Delta-Mendota Subbasin have chosen to develop a coordinated DMS that can be utilized by each GSP Group for management of their data, but which will allow for the required compendium of data sets for preparation of Subbasin annual reports. The coordinated DMS will also provide a generic framework that can be used by any GSP Group or GSA in the Subbasin for individual data management while allowing for consistent formatting and the simplified uploading of compiled datasets into the Subbasin-wide coordinated DMS.
The individual GSP Groups have also developed and will maintain separate data storage processes or DMSs. Each separate DMS developed for each GSP will store information related to implementation of each individual GSP, monitoring network data and monitoring sites requirements, and water budget data requirements. Each system will be capable of reporting all pertinent information to the respective GSA and/or GSP Group, and ultimately to the Coordination Committee. After providing the Coordination Committee with data from the individual GSPs, the Subbasin Plan Manager and Coordination Committee will ensure the data are stored and managed in a coordinated manner throughout the Subbasin and reported to DWR on an annual basis.
The DMS constructed for the Delta-Mendota Subbasin is a secured web-based application hosted on Amazon Web Services (AWS). The DMS focuses on five core business requirements including:
centralized data warehouse, security of data, permissioned based access, data visualization and reporting.
Other goals of the DMS focus around improving data collection/aggregation processes, creating data standards, gaining efficiencies in reporting and improving data sharing with stakeholders. The DMS is designed to aggregate data through import processes by GSP to support data visualization and annual report generation.
Underlying the web application is a relationship database used to store the information aggregated from GSPs across primary data types identified to support monitoring and Annual Report development. Those data types include groundwater extractions, surface water deliveries, groundwater storage, groundwater elevations, groundwater quality, interconnected surface water and land subsidence. The web application functionality includes an embedded GIS viewer, screens to view tables of time series data, and charting capabilities for hydrographs. The embedded GIS viewer contains functionality to store map layers such as reference data, GSA/GSP boundaries and derived information such as water level contours.
Section 6.1.2 describes the process by which monitoring data are collected by each GSP Group and processed for inclusion in the Coordinated DMS. In order to be able to track data by location in the Subbasin, each monitoring locations in the Delta-Mendota Subbasin is assigned a unique identifier in the DMS. The number system is in a format of ##-####, where the first two digits indicates which GSA the monitoring location is associated with, the subsequent four digits indicate which specific monitoring Delta-Mendota Subbasin Groundwater Sustainability Plan
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location in that GSA area. As shown in Figure CC-72, the general methodology agreed upon for data import and management is as follows:
Each GSA collects their respective data per agreed-upon monitoring protocols and transmits it to the GSA Representative.
Each GSA Representative then compiles the data and conducts a quality control check. The GSA Representative then transmits the compiled data set to the GSP Lead or Representative, who then aggregates the data from all GSAs and conducts a second quality control check. The GSP Lead or Representative then uploads the data set into the DMS using import wizards designed specifically for this process.
The Subbasin Plan Manager then uses the data in the DMS to compile information as required for the annual report.
Compiled data sets from the DMS are then augmented with required maps generated externally to produce the required annual report. Mapping prepared outside the DMS are subsequently imported into the DMS as GIS files to ensure all data are kept in one place and to allow for access by GSAs and other Subbasin stakeholders.
The DMS will be maintained by the San Luis & Delta-Mendota Water Authority, while acting as the Plan Manager, with a contract with the software vendor for hosting, maintenance and future maintenance.
Each GSP will pay a maintenance fee for the continued hosting and support of the Subbasin coordinated DMS.
The Coordinated DMS as described herein may be supplemented by additional DMS developed and maintained by each GSP Group in the Subbasin. The reader is referred to each of the six Subbasin GSPs for specific information relative to data collection and management in each GSP Plan area.
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8. STAKEHOLDER OUTREACH
California Code of Regulations, Title 23, §354.10 identifies the requirements for notice and communication information presented in a GSP, which includes:
A summary of information relating to notification and communication by the GSAs with other agencies and interested parties;
A description of the beneficial uses and users of groundwater in the basin, including the land uses and property interests potentially affected by the use of groundwater in the basin, the types of parties representing those interests, and the nature of consultation with those parties; A list of public meetings at which the GSP was discussed or considered by the GSAs; Comments regarding the GSP received by the GSAs and a summary of any responses by the GSAs;
A communication section of the GSP that includes an explanation of the GSAs’ decision-making process, identification of opportunities for public engagement, a discussion of how public input and response was used, a description of how the GSAs encouraged the active involvement of diverse social, cultural and economic elements of the population within the basin, and the methods used by the GSAs to inform the public about progress implementing the GSP, including the status of projects and actions.
In meeting these requirements, outreach and educational activities were conducted at the Subbasin, GSP and GSA level throughout the GSP development process. This section describes the noticing and outreach conducted at the Delta-Mendota Subbasin level for GSP development. Please refer to each individual Subbasin GSP for specific details regarding noticing and communication, and descriptions of the beneficial uses and users of groundwater at the GSP and GSA level. Information regarding Subbasin coordination and committees can be found in Section 2, Delta-Mendota Subbasin Governance, of this document.
8.1 Situation Assessment and Communications Plan
To assist in GSA formation and GSP development, agencies in the Delta-Mendota Subbasin sought and received Facilitation Support Services funding from DWR in August 2016. Under this funding, a neutral, third-party facilitation team conducted a situation assessment on behalf of the Subbasin GSAs. The purpose of the assessment was to understand how stakeholders perceived the status of the Subbasin’s groundwater resources and identify potential barriers to the successful development of the GSPs. The facilitation team, with input from local agencies, identified 30 stakeholders representing diverse interests and beneficial users in the Subbasin, together with disadvantaged communities, agricultural well owners, government and land use agencies, and environmental and ecosystem interests. From February 2017 to May 2017, the facilitators conducted over 30 phone and in-person interviews with stakeholders. The facilitators recorded the interview responses and summarized the results in a presentation made to the GSA representatives.
The assessment results were used to inform the development of the Delta-Mendota Subbasin Sustainable Groundwater Management Act Communications Plan (Communications Plan), which is provided with this document as Appendix E. The Communications Plan identifies near- and long-term outreach and engagement strategies, tactics, and tools for stakeholder engagement in GSP development and Delta-Mendota Subbasin Groundwater Sustainability Plan
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implementation. The Subbasin GSAs used the Communications Plan as a framework for conducting the stakeholder outreach and engagement activities described in this document.
The Delta-Mendota Subbasin is home to a large Hispanic or Latino population with many using Spanish as their primary language. As such, public noticing, educational materials and other outreach efforts were developed and presented in both English and Spanish throughout the GSP development process.
8.2 Public Noticing and Information
The Delta-Mendota Subbasin GSAs developed and used several coordinated tools, in addition to their own resources to inform members of the public about GSP development activities and promote opportunities for public engagement. These tools are described below. Website: The Subbasin website – www.deltamendota.org – is the primary location for information related to SGMA implementation in the Subbasin. Information provided on the website includes: an overview of SGMA, a description of each of the GSP groups, contact information for each of the GSAs, and upcoming workshops and public meetings. The website also serves as a repository for outreach collateral, workshop materials, and meeting packets and minutes for the Delta-Mendota Subbasin Coordination Committee, Technical Working Group, and Communications Working Group (described below), and provides links to the individual GSP websites maintained by each GSP Group.
Delta-Mendota Subbasin Newsletter: The Delta-Mendota Subbasin Newsletter is distributed on a monthly basis and serves as an informational tool to keep interested parties, beneficial users, and members of the general public informed about the development and status of the GSPs.
Newsletter topics include Subbasin-wide activities, general announcements, upcoming meetings and workshops, and past and upcoming GSP development activities. Copies of the newsletters are archived on the Subbasin website.
Informational Materials: GSAs in the Subbasin developed a suite of materials in English and Spanish to educate and inform members of the public about SGMA and topics covered in the GSP. These materials include bilingual presentations, fact sheets, handouts, frequently asked questions, and videos. Copies of the materials are available on the Subbasin website. GSA representatives distributed these materials before and during meetings, workshops, and other outreach activities.
8.3 List of Public Meetings Where the GSPs were Discussed Each GSP Group for the Delta-Mendota Subbasin has conducted individual outreach efforts relative to their own GSP Plan area in addition to those same efforts at the subbasin-level. Please refer to each of the individual GSPs for this information. Below is a list of the coordinated public workshops and meetings where the GSPs were discussed. These include meetings of the Delta-Mendota Subbasin Coordination Committee, the two Subbasin Working Groups and coordinated public workshops. All meetings were publicly noticed and held from June 2017 through July 2019. Meeting agenda, minutes and handouts are available on the Delta-Mendota Subbasin website at www.deltamendota.org.
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Delta-Mendota Coordination Committee Meetings
The Delta-Mendota Subbasin Coordination Committee meets on the second Monday of each month at 9:30 am at the SLDMWA Administration Offices located at 842 6th Street, Los Banos, California. These meetings are noticed as required under the Brown Act and are open to the public.
In addition to the monthly meetings, a special meeting of the Coordination Committee was held on March 8, 2019 to discuss sustainable yield estimation methodologies.
Delta-Mendota Technical Working Group Meetings
The Delta-Mendota Technical Working Group meets on the third Tuesday of each month at 10:00 am at the SLDMWA Administration Offices located at 842 6th Street, Los Banos, California. These meetings are noticed as required under the Brown Act and are open to the public.
In addition to the monthly meetings, several special meetings of the Technical Working Group were held to discuss specific topics. These additional meetings were as follows:
August 24, 2018 and September 19, 2018 meetings to discuss Groundwater Dependent Ecosystems
August 8, 2018, October 30, 2018 and December 19, 2018 meetings to discuss water budgets Delta-Mendota Communication Working Group Meetings
The Delta-Mendota Communications Working Group meets on the fourth Tuesday of each month at 1:00 pm. These meetings typically conducted via conference call. Meeting information for this working group is available on the Delta-Mendota Subbasin website.
Coordinated Public Workshops
Coordinated public workshops were held for the Delta-Mendota Subbasin shown in the table below. All workshops were advertised and conducted in both English and Spanish.
Table CC-24: Coordinated Public Workshops
Date Location, Venue Topic
Spring 2018 Workshops
May 14, 2018 Los Banos, San Luis & Delta Mendota
Water Authority
Sustainable Groundwater
Management Act overview
Delta-Mendota Subbasin overview
Opportunities for engagement
May 16, 2018 Patterson, Hammon Senior Center
May 17, 2018 Mendota, Mendota Library
Fall 2018 Workshops
October 22, 2018 Firebaugh, Firebaugh Middle School GSP development and implementation process
Data collection
Hydrogeologic Conceptual Model
Numerical and analytical models
Water budgets
October 24, 2018 Los Banos, College Greens Building
October 25, 2018 Patterson, Hammon Senior Center
Winter 2019 Workshops
February 19, 2019 Los Banos, College Greens Building Historic and current water budgets February 20, 2019 Patterson, Patterson City Hall
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Date Location, Venue Topic
March 4, 2019 Santa Nella, Romero Elementary
School
Sustainability criteria
Undesirable results
Projects and management actions
Spring 2019 Workshops
May 20, 2019 Patterson, Patterson City Hall Projected water budgets Sustainable yield
Groundwater monitoring networks
Projects and management actions
May 21, 2019 Los Banos, College Greens Building
May 22, 2019 Santa Nella, Romero Elementary
School
May 23, 2019 Mendota, Mendota Library
Please see Appendix F for summaries of the coordinated public workshops, and Appendix G for example promotional materials for the public workshops.
8.4 Comments Regarding the GSPs
Key components of the six Subbasin GSPs were presented at the public workshops conducted throughout the GSP development process. Appendix F contains summaries of the coordinated public workshops, including comments received from and feedback provided to workshop participants. Additionally, each of the GSP Groups in the Delta-Mendota Subbasin are individually responsible for the public review of their plans and for addressing any public comments received. Please see the individual GSPs for additional information regarding plan review.
8.5 Subbasin Decision Making Process
The Delta-Mendota Subbasin Coordination Agreement outlines the responsibilities of all Subbasin parties, including decision making protocols and voting structure. These are further discussed in Chapter 2 of this document.
During the GSP development process, the Technical Working Group was charged with coordinating implementation of the required technical elements of the GSP (e.g., water budgets, monitoring networks), and to provide recommendations to the Delta-Mendota Subbasin Coordination Committee. Similarly, the Communications Working Group was charged with implementing the Subbasin Communications Plan and with providing recommendations for workshops and other outreach activities to the Coordination Committee. The Coordination Committee took actions and approved recommendations and work products and provided direction to both working groups and other ad hoc committees.
In general, the coordinated decision-making process included developing agendas for each meeting of the Delta-Mendota Subbasin Coordination Committee and for each Working Group meeting. The agendas were developed in concert with the Technical and Communications Working Groups, and the respective representatives of each GSP Group. Agenda items were either educational, informational, or required direction or decision. Meeting agendas, meetings minutes and handouts have been posted on the DeltaMendota Subbasin website for public access.
8.6 Opportunities for Public Engagement and How Public Input was Used Community input was encouraged and received at all meetings of the Coordination Committee, Technical Working Group, Communications Working Group meetings and at the public workshops. The Subbasin GSPs (and therefore, this Common Chapter) was shaped by community input, Working Group input, and Coordination Committee direction and decisions.
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8.6.1 Opportunities for Public Engagement
Regular opportunities for public engagement were available throughout GSP development. The Coordination Committee, Technical and Communications Working Groups, and individual GSA staff encouraged public input throughout the development of the GSPs as described below. A list of stakeholder and community organizations contacted as part of the Subbasin coordinated outreach efforts is included in Appendix H.
Meetings and Direct Engagement
Open meetings and public workshops were held as described in Section 8.1. In addition, GSA staff made direct contact with community representatives to encourage their participation in the GSP development process. GSA representatives provided their contact information by phone, email, or mail both online (on the Subbasin website) and at workshops for stakeholder questions and comments.
Targeted Stakeholder Engagement
The Subbasin GSAs also conducted targeted outreach and engagement to hard-to-reach communities, interested parties, and stakeholders that were previously underrepresented in other engagement activities.
This included outreach to the following stakeholder types:
Agricultural Interests: Agricultural stakeholders in the Subbasin include agricultural well operators, growers, ranchers, farmworkers, and agricultural landowners. Strong agricultural representation exists within the leadership of the GSAs. To augment direct outreach being conducted by individuals GSAs, Subbasin representatives also coordinated closely with local county farm bureaus to disseminate information related to GSP development and public workshops.
School Districts: Schools districts are considered for both beneficial users of groundwater (for drinking water), as well communication channels to disseminate information about SGMA and GSP development. GSA representatives directly contacted local school districts to notify them of the public workshops. Some schools also help distributed informational materials and workshop flyers to their students and parents.
Industrial Interests: There are many industrial interested in the Subbasin, including packaging and processing plants, mining industries, and other similar facilities that use groundwater in some fashion. The GSP Groups have identified these interests within their respective Plan areas and have disseminated information related to GSP development during individual outreach efforts. Environmental/Conservation Interests: Environmental and conservation interests in the Subbasin have been contacted and communicated with during GSP development. Specific related interest groups contacted during GSP development include The Nature Conservancy, the California Department of Fish and Wildlife, Audubon, and various sportsman clubs and wetland managers.
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Disadvantaged Communities: The GSAs followed best practices identified in Collaborating for Success: Stakeholder Engagement for Sustainable Groundwater Management Act Implementation (Community Water Center, 2015) and other guidance documents to engage disadvantaged and severely disadvantaged communities. This included holding meetings in disadvantaged communities; holding meetings in the evening at known local venues, such as schools, civic centers, and community centers; translating fact sheets, meeting materials, and presentations into other languages; and providing interpreting services at all public workshops. Other Interests: Other potential groundwater users in the Subbasin (or those with groundwaterrelated interests) contacted during GSP development included the various counties in which the Delta-Mendota Subbasin lie and/or are adjoining (including San Joaquin County and San Benito County), Caltrans, the DWR State Water Project Division of Operations and Maintenance, the U.S. Bureau of Reclamation, the U.S. Geological Survey and the San Joaquin River Restoration Program.
The Reader should refer to each individual GSP for a more complete description of GSP-specific meetings and direct engagement.
GSP Section Review and Comment Periods
Each GSP Group was responsible for coordinating the individual review of their GSP. Please see each GSP for additional information as to their specific public review process. This Common Chapter to the six Delta-Mendota Subbasin GSPs was posted on the Subbasin’s website (www.deltamendota.org) following submittal of the Subbasin GSPs.
8.6.2 How Public Input and Response was Used in the Development of the GSP Each GSP Group was responsible for coordinating the individual review of their GSP and for determining how to incorporate public input and responses into their respective plans. Public input to the GSPs was solicited through the GSP development process through a number of means, including coordinated public workshops, Board of Directors presentations, City Council presentations, and growers’ meetings. Please see the individual GSPs for more information regarding GSP-specific outreach efforts and how stakeholder and public input was received and factored into the GSPs.
8.7 Revisions to Common Chapter and Subbasin GSPs
As previously noted in this document, the Delta-Mendota Subbasin received a Consultation Initiation Letter on January 21, 2022 from DWR. The CIL identified four potential deficiencies across the six Subbasin GSPs which may preclude DWR’s approval, as well as potential corrective actions to address each potential deficiency. The CIL thus initiated consultation between DWR, the Basin Manager, Plan Managers, and the Subbasin’s 23 Groundwater Sustainability Agencies (GSAs) on February 18, 2022 regarding the amount of time needed to address the potential deficiencies and corrective actions.
Subsequent meetings were held on March 7, March 30, April 19, May 24, and June 20 2022 to discuss the Subbasin’s proposed approach to addressing the identified deficiencies.
The four deficiencies identified in DWR’s CIL are summarized as follows:
Potential Deficiency 1: The GSPs do not use the same data and methodologies.
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Potential Deficiency 2: The GSPs have not established common definitions of undesirable results in the Subbasin.
Potential Deficiency 3: The GSPs in the Subbasin have not set sustainable management criteria in accordance with GSP regulations.
Potential Deficiency 4: The management areas established in the Plan have not sufficiently addressed the requirements specified in 23 CCR §354.20.
This revised Common Chapter, and associated revisions to the six Subbasin GSPs, have been prepared in response to the deficiencies identified in the CIL based on direction provided by the Delta-Mendota Subbasin Coordination Committee, the Delta-Mendota Technical Working Group, the Subbasin GSAs and DWR. It is intended to document how the deficiencies identified in the CIL were addressed in the revised GSPs and associated Common Chapter, and where those revisions are addressed in the Common Chapter.
A Notice of Intent to Adopt the revised Common Chapter and six Subbasin GSPs (known as the Amended Groundwater Sustainability Plan) was distributed on March 15, 2022. Public meetings for the adoption of the Common Chapter and Subbasin GSPs were held in June and July of 2022; please see the Subbasin’s website (www.deltamendota.org) for the respective dates for each GSAs meeting and adoption.
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