ARROYO SECO GROUNDWATER SUSTAINABILITY AGENCY Arroyo Seco Area Groundwater Sustainability Plan Draft Chapters 1-4 October 2, 2019 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 1 Introduction ..................................................................................................................................... i 1.1 Purpose of the Groundwater Sustainability Plan (GSP) ............................................................. 1 1.2 Agency Information .................................................................................................................. 1 1.2.1 Organization and Management of Arroyo Seco Groundwater Sustainability Agency ......... 1 1.2.2 Legal Authority of Arroyo Seco Groundwater Sustainability Agency .................................. 2 1.2.3 Outreach and Communication .......................................................................................... 2 1.3 GSP Organization ..................................................................................................................... 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 2.2.1 Active Water Resources Monitoring Programs ............................................................... 2-2 2.2.2 Active Water Resources Management Programs ........................................................... 2-5 2.3 Land Use and Land Use Planning ......................................................................................... 2-10 2.3.1 Federal and State Lands Management ......................................................................... 2-10 2.3.2 California Department of Water Resources .................................................................. 2-10 2.3.3 Monterey County Agricultural Commissioner .............................................................. 2-11 2.3.4 California Department of Conservation........................................................................ 2-11 2.3.5 Monterey County General Plan .................................................................................... 2-11 2.3.6 City of Greenfield General Plan .................................................................................... 2-11 2.3.7 Interaction of GSP and Land Use Plans ......................................................................... 2-12 3 Basin Setting ................................................................................................................................. 3-1 3.1 Hydrogeologic Conceptual Model .......................................................................................... 3-1 3.1.1 Topography ................................................................................................................... 3-1 3.1.2 Watersheds and Surface Water Bodies .......................................................................... 3-2 3.1.3 Surficial Geology ............................................................................................................ 3-2 3.1.4 Soils ............................................................................................................................... 3-3 3.1.5 Basin Fill Materials......................................................................................................... 3-4 3.1.6 Recharge and Discharge Areas ....................................................................................... 3-5 3.1.7 Wells ............................................................................................................................. 3-6 3.1.8 Mineral Resources ......................................................................................................... 3-7 Arroyo Seco DRAFT Groundwater Sustainability Plan i Todd Groundwater 3.2 Historical, Current and Future Groundwater Conditions ........................................................ 3-8 3.2.1 Groundwater Elevations ................................................................................................ 3-9 3.2.2 Groundwater Storage .................................................................................................. 3-13 3.2.3 Seawater Intrusion ...................................................................................................... 3-14 3.2.4 Subsidence .................................................................................................................. 3-14 3.2.5 Water Quality .............................................................................................................. 3-15 3.2.6 Depletion of Interconnected Surface Water ................................................................. 3-21 3.2.7 Groundwater-Dependent Ecosystems ......................................................................... 3-25 3.3 Water Budget Information .................................................................................................. 3-30 3.3.1 Overview and Approach .............................................................................................. 3-30 3.3.2 Rainfall-Runoff-Recharge Model .................................................................................. 3-30 3.3.3 Groundwater Flow Model ............................................................................................ 3-31 3.3.4 Reservoir Operations Model ........................................................................................ 3-32 3.3.5 Simulation of Future Water Budgets ............................................................................ 3-32 3.3.6 Surface Water Budgets ................................................................................................ 3-33 3.3.7 Groundwater Budgets ................................................................................................. 3-35 3.3.8 Sustainable Yield ......................................................................................................... 3-36 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 4.4.1 Undesirable Results ....................................................................................................... 4-3 4.4.2 Minimum Threshold ...................................................................................................... 4-4 4.4.3 Measurable Objective.................................................................................................... 4-8 4.4.4 Management Actions .................................................................................................... 4-8 4.5 Groundwater Storage ............................................................................................................ 4-9 4.5.1 Undesirable Results ....................................................................................................... 4-9 4.5.2 Minimum Threshold ...................................................................................................... 4-9 4.5.3 Measurable Objective.................................................................................................. 4-11 4.5.4 Management Actions .................................................................................................. 4-11 4.6 Seawater Intrusion .............................................................................................................. 4-11 Arroyo Seco DRAFT Groundwater Sustainability Plan ii Todd Groundwater 4.7 Land Subsidence ................................................................................................................. 4-12 4.7.1 Undesirable Results ..................................................................................................... 4-12 4.7.2 Minimum Threshold .................................................................................................... 4-12 4.7.3 Measurable Objective.................................................................................................. 4-14 4.7.4 Management Actions .................................................................................................. 4-14 4.8 Water Quality...................................................................................................................... 4-14 4.8.1 Undesirable Results ..................................................................................................... 4-14 4.8.2 Minimum Threshold ...................................................................................................