DELTA-MENDOTA SUBBASIN
GROUNDWATER SUSTAINABILITY PLAN
November 19, 2024
2 Landmark legislation passed in 2014
§ First comprehensive groundwater legislation in California § Provides a framework for the sustainable management of groundwater basins
§ Promotes local groundwater management
• Led by local Groundwater Sustainability Agencies (GSAs) • Preparing and implementing a Groundwater Sustainability Plan (GSP) § Sets regulatory deadlines for submitting GSPs, reporting progress, and achieving sustainable management
What is the Sustainable Groundwater Management
Act (SGMA)?
What is Sustainable Management?
• Management and use of groundwater in a manner that can be maintained without causing undesirable results:
3 Chronic lowering of
Groundwater Levels
Reduction of Groundwater
Storage
Land Subsidence
Seawater Intrusion
Groundwater Quality Degradation
Depletion of Interconnected
Surface Water
What is a Groundwater Sustainability Plan or GSP?
• A GSP is:
§ A Plan meeting SGMA requirements that provides for a sustainably managed groundwater basin
§ Sets the metrics and criteria for evaluating if sustainability has been achieved § Outlines how the GSA(s) will implement, manage, and measure specific actions for the health and viability of a basin
§ DWR will evaluate the GSPs and provide the GSA(s) with an assessment and/or determination of the GSP and any necessary recommendations within two years of submittal
SGMA Requirements
• Adopt and submit one or more Groundwater
Sustainability Plans (GSPs) detailing the pathway to
sustainability
o Due by January 31, 2020 for critically-overdrafted basins o Due by January 31, 2022 for all other high- and medium-priority basins
• “Sustainable groundwater management” must occur
within 20 years
o By 2040 for critically-overdrafted basins
o By 2042 for all other high- and medium-priority basins 2014
2015
2017
Jan 2020
Jan 2022
Jun 2022
Mar 2023
Mar/Apr 2025(?)
SGMA legislation passed
SGMA implementation begins
Formation of 23 GSAs in Delta-Mendota Subbasin
Submittal of 6 GSPs, including Northern & Central Delta-Mendota GSP Incomplete Determination by DWR
Resubmission of 6 GSPs
Inadequate Determination by DWR
Probationary Hearing with SWRCB
SGMA Compliance Timeline
Basin Response – Prepare single GSP for Subbasin
Single GSP Compliance Timeline
Delta-Mendota GSP
GSP Sections
Executive Summary
Introduction
Plan Area
Basin Setting
Sustainable Management Criteria
Monitoring Network
Projects and Management Actions
Plan Implementation
References Studies
• Appendix A – GSP Submittal Checklist
• Appendix B – DWR Determination Letters
• Appendix C – Board Resolutions to Adopt
GSP
• Appendix D – MOA among DM GSAs
• Appendix E – Public Outreach and
Communications Log
• Appendix F – DM Communications Plan
• Appendix G – Comments received on GSP
• Appendix H – Modeling Memo
• Appendix I – Concentrations, Trends and
Correlations of COCs
• Appendix J – Conceptual Master Plan for
Subsidence Monitoring and Management
• Appendix K – Freshwater Species in Basin
• Appendix L – Hydrographs for RMW-WLs
• Appendix M – Well Impact Analysis for
Production Wells
• Appendix N – Well Mitigation Policy
Appendices
§ Addresses potential impacts to domestic and small community wells from the chronic lowering of groundwater levels.
§ Well Impacts Analysis
§ Worst-case scenario - 98 drinking water wells are expected to be impacted § Accommodates more than 10 drinking water wells reported as dry in any given year and at least 170 dry wells by 2040
§ Individual GSAs to investigate MT exceedances for all monitoring wells and take pre-emptive action to avoid dewatering of a domestic well
§ Applies to domestic wells installed prior to GSP adoption or screened at depths deeper than local groundwater level MTs.
§ Well users applying for mitigation will receive an emergency water supply within 2 business days, assuming application appears to meet requirements. § Potential mitigations:
§ Lowering the well pump
§ Deepening the well
§ Installing a new well
§ Connection to a municipal water supply
Well Mitigation Program
1. Monitoring and data collection policy
§ Quarterly groundwater level measurements and annual water quality sampling § Meter GW production, or estimate with an equivalently effective method § Replace composite or active production RMWs with dedicated monitoring wells
2. Overdraft mitigation policy
§ GSAs will collectively reduce total pumping by at least 42,000 AFY § Incremental reduction in overdraft from 20% by 2026 to 100% by 2030 § May include pumping reduction achieved under Subsidence mitigation policy
3. GWL-MT avoidance policy
§ Define RMW-specific groundwater level triggers and zone of influence § Develop RMW-specific pumping reduction plan
4. WQ-MT exceedance policy
§ Define RMW-specific groundwater level triggers
§ Investigate cause of exceedance – Pumping/GWL decline or other management actions § Develop and implement mitigation plan
5. Subsidence mitigation policy
§ Set trigger as 3-year moving average rate of subsidence that exceeds 0.2 ft/year § Lower aquifer pumping will be limited to 0.25 AF/acre within the zone of influence (0.5 mile of critical infrastructure)
Five-Part Pumping Reduction Framework
Consistent MOA, if GSA(s) have GWL MT exceedances for two consecutive years and/or fail to achieve their minimum pumping reduction required under the overdraft mitigation policy, GSA(s) will be required to implement a groundwater allocation program.
Pumping Reduction Framework Timeline
July
2024
October
2024
January
2025 … 2030
Adopt GSP
Develop
Implementation
Plan
Implementation
Plan
Achieve
42,000 AFY
Pumping
Reduction
What Next?
• Adopt single Delta-Mendota Subbasin Groundwater
Sustainability Plan
• Complete and formalize Pumping Reduction Framework
o Normalized in GSP
o Different details for different regions
• Delivery of a single Subbasin GSP to SWRCB
• Active engagement and continued communication with the regulatory agencies (DWR and State Board)
• Preparation for March/April 2025 State Board Hearing
• Continue GSP implementation
QUESTIONS?