Arroyo Seco Area Groundwater Sustainability Plan Draft
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ARROYO SECO GROUNDWATER SUSTAINABILITY AGENCY Arroyo Seco Area Groundwater Sustainability Plan Draft May 18, 2020 2490 Mariner Square Loop, Suite 215 Alameda, CA 94501 510.747.6920 www.toddgroundwater.com PROFESSIONAL CERTIFICATION Eugene B. (Gus) Yates Professional Geologist #7178 Certified Hydrogeologist #740 Table of Contents Executive Summary .................................................................................................................................. ES-1 1. Introduction ....................................................................................................................................... 1-1 1.1 Purpose of the Groundwater Sustainability Plan (GSP) ............................................................. 1-1 1.2 Agency Information ................................................................................................................... 1-1 1.3 GSP Organization ....................................................................................................................... 1-2 2 Description of Plan Area .................................................................................................................... 2-1 2.1 Summary of Jurisdictional Areas and Other Features ............................................................... 2-1 2.2 Water Resources Monitoring and Management Programs ....................................................... 2-1 2.3 Land Use and Land Use Planning ............................................................................................. 2-10 3 Basin Setting ....................................................................................................................................... 3-1 3.1 Hydrogeologic Conceptual Model ............................................................................................. 3-1 3.2 Historical, Current and Future Groundwater Conditions .......................................................... 3-8 3.3 Water Budget Information ....................................................................................................... 3-30 3.4 Management Areas .................................................................................................................. 3-37 4 Sustainable Management Criteria ..................................................................................................... 4-1 4.1 Sustainability Goal...................................................................................................................... 4-1 4.2 Sustainability Indicators ............................................................................................................. 4-1 4.3 Undesirable Results, Minimum Thresholds and Measurable Objectives .................................. 4-2 4.4 Groundwater Levels ................................................................................................................... 4-3 4.5 Groundwater Storage .............................................................................................................. 4-10 4.6 Seawater Intrusion ................................................................................................................... 4-13 4.7 Land Subsidence ...................................................................................................................... 4-13 4.8 Water Quality ........................................................................................................................... 4-15 4.9 Interconnected Surface Water ................................................................................................. 4-21 5 Monitoring Network Details .............................................................................................................. 5-1 5.1 Introduction ............................................................................................................................... 5-1 5.2 Monitoring for Water Levels ...................................................................................................... 5-3 5.3 Monitoring for Groundwater Storage ........................................................................................ 5-5 5.4 Monitoring for Seawater Intrusion ............................................................................................ 5-5 5.5 Monitoring for Subsidence ........................................................................................................ 5-5 Arroyo Seco DRAFT Groundwater Sustainability Plan i Todd Groundwater 5.6 Monitoring for Water Quality .................................................................................................... 5-5 5.7 Monitoring for Interconnected Surface Water .......................................................................... 5-6 5.8 Data Management System ......................................................................................................... 5-7 6 Project and Management Action Details ........................................................................................... 6-1 6.1 General Provisions ..................................................................................................................... 6-1 6.2 Future No-Action Scenarios ....................................................................................................... 6-1 6.3 Management Action 1: Reservoir Reoperation ......................................................................... 6-6 6.4 Management Action 2: Salinity Management Studies ............................................................ 6-10 6.5 Management Action 3: Improve Rural Residential Water Quality .......................................... 6-13 6.6 Management Action 4: Oppose New Dams on the Arroyo Seco ............................................. 6-14 6.7 Additional GSP Elements .......................................................................................................... 6-15 7 Plan Implementation ......................................................................................................................... 7-1 7.1 Implementation Activities .......................................................................................................... 7-1 7.2 Roles and Responsibilities .......................................................................................................... 7-2 7.3 Cost of Implementation ............................................................................................................. 7-2 7.4 Funding Sources ......................................................................................................................... 7-2 8 References Cited ................................................................................................................................ 8-1 Appendices Appendix A. Notice of Declaration to Become a GSA Appendix B. List of Public Meetings Appendix C. Comments and Responses Appendix D. GSP Contents Checklist Appendix E. Data and Analysis for Water Quality Appendix F. Documentation for Rainfall-Runoff-Recharge Model Appendix G. Documentation for Groundwater Model Appendix H. Documentation for Reservoir Operations Model Appendix I. Water Budget Tables Appendix J. Intrabasin Coordination Agreement Appendix K. Water Level Monitoring Protocols Arroyo Seco DRAFT Groundwater Sustainability Plan ii Todd Groundwater Tables (in text) 3.1-1 Soil Types in the ASGSA Area 3.1-2 Perforated Intervals of Wells 4.4-1 Minimum Threshold and Maximum Desirable Water Levels at Indicator Wells 4.8-1 Statistics of Nitrate Concentrations in ASGSA Area Wells in 2017-2018 4.8-2 Statistics of Specific Conductance in ASGSA Area Wells in 2017-2018 Figures (at end of each section) 2.0-1 Regional Location Map 2.0-2 Location of Arroyo Seco GSA 2.1-1 Federal Lands 2.2-1 Locations of Water-Level Monitoring Wells 2.2-2 Sample MCWRA Pumping Summary 2.2-3 Parcels Enrolled in ILRP 2.3-1 Monterey County General Plan Land Use 3.1-1 Boundary of Arroyo Seco Cone 3.1-2 Topography of ASGSA Area 3.1-3 Salinas River Sub-Watersheds 3.1-4 Surficial Geology 3.1-5 Soils 3.1-6 Hydrogeologic Cross Section 3-3’ 3.1-7 Hydrogeologic Cross Section 4-4’ 3.1-8 Hydrogeologic Cross Section 5-5’ 3.1-9 Hydrogeologic Cross Section 8-8’ 3.1-10 Hydrogeologic Cross Section 9-9’ 3.1-11 Hydrogeologic Cross Section 10-10’ 3.1-12 Recharge Locations 3.1-13 Domestic Well Density 3.1-14 Production Well Density 3.2-1 Annual Discharge in Arroyo Seco, 1902-2018 3.2-2 Groundwater Hydrographs 1939-2018 3.2-3 Groundwater Elevation in February 1952 3.2-4 Water Level Declines During Droughts 3.2-5 Groundwater Elevation in March 1998 3.2-6 Groundwater Elevation in December 2016 3.2-7 Groundwater Elevation in March 2010 3.2-8 Groundwater Elevation in October 2010 3.2-9 Simulated Hydrographs for Future Baseline Scenario 3.2-10 Cumulative Subsidence Arroyo Seco DRAFT Groundwater Sustainability Plan iii Todd Groundwater 3.2-11 Groundwater Nitrate Trends 3.2-12 Recent Nitrate Trends in Greenfield 3.2-13 Groundwater Salinity Trends 3.2-14 Map of Groundwater Salinity in 1994 3.2-15 Mixing Model Projection of Future Groundwater Salinity 3.2-16 Salinas River Elevation Profile 3.2-17 Arroyo Seco Elevation Profile 3.2-18 Arroyo Seco Flow Loss in Spring, 1995-2018 3.2-19 Salinas River Flow at Soledad, 1984-2018 3.2-20 Releases and Flow at Soledad 3.2-21 Arroyo Seco Riparian Vegetation 3.2-22 Cottonwood Trees along the Salinas River in April 2019 3.3-1 Diagram of Rainfall-Runoff-Recharge Model Processes 3.3-2 Future Baseline