LITTLE LAKE VALLEY GROUNDWATER MANAGEMENT PLAN Final Draft PREPARED FOR CITY OF WILLITS August 18, 2020 City of Willits Contact: Andrea Trincado, Project Manager City of Willits Engineering Department Prepared by: LACO Associates 776 S. State St., Suite 103 Ukiah, California 95482 (707) 462-0222 LACO Project No. 8509.07 Little Lake Valley Groundwater Management Plan FINAL DRAFT Prepared for City of Willits TABLE OF CONTENTS 1.0 Introduction 5 1.1 Purpose of the Plan ......................................... 5 1.2 Background and Legal Authority for Local Groundwater Management ................................. 5 1.3 Plan Components .............................................. 7 1.4 Plan Development Process ................................. 7 1.5 Previous Studies .............................................. 9 2.0 Public Outreach and Involvement ............................ 10 2.1 Public Workshops ........................................... 11 2.2 Issues of Concern to the Public ........................ 12 3.0 Study Area 12 3.1 Location and Description ................................. 12 3.2 Physical Geography and Geology ..................... 13 3.2.1 Geologic Formations ............................. 15 3.3 Climate 15 3.4 Land Use and Population ................................. 18 3.5 Water Use 21 3.5.1 Municipal Water Use ............................ 21 3.5.2 Rural Water Use .................................. 23 3.5.3 Tribal Water Use ................................. 23 3.5.4 Environmental Water Use ....................... 23 4.0 Hydrogeology 23 4.1 Principal Aquifers ......................................... 23 4.1.1 Aquifer I – Holocene Alluvium ................ 24 August 18, 2020 Page 1 of 49 Little Lake Valley Groundwater Management Plan FINAL DRAFT Prepared for City of Willits 4.1.2 Aquifer II – Pliocene to Pleistocene Continental Basin Deposits ..................... 25 4.1.3 Jurassic-Cretaceous Franciscan Complex .. 26 4.2 Recharge Sources ........................................... 27 4.3 Historic Variations in Groundwater Levels ......... 27 5.0 Surface Water Hydrology ...................................... 29 5.1 Surface Water Systems and Waterbodies ........... 29 5.1.1 Streams 29 5.1.2 Little Lake .......................................... 31 5.1.3 Surface Water Facilities ....................... 31 5.2 Surface Water Quality ................................... 33 5.2.1 Naturally Occurring .............................. 33 5.2.2 Point Source Impacts ............................ 33 5.2.3 Non-Point Source Impacts ...................... 34 6.0 Components of the Groundwater Management Plan ..... 34 6.1 Goals and Objectives ..................................... 34 6.1.1 Groundwater Management Goals ............. 34 6.1.2 Basin Management Objectives ................ 35 6.2 Groundwater Monitoring ................................. 35 6.2.1 Monitoring of Groundwater Levels and Storage 36 6.2.2 Monitoring of Groundwater Quality ......... 37 6.2.3 Inelastic Land Subsidence Monitoring ...... 38 6.3 Groundwater Resource Protection ..................... 38 6.3.1 Wellhead and Recharge Area Protection .. 38 August 18, 2020 Page 2 of 49 Little Lake Valley Groundwater Management Plan FINAL DRAFT Prepared for City of Willits 6.3.2 Replenishment of Groundwater Extracted by Water Producers .................................. 39 6.3.3 Mitigation of Conditions of Overdraft ..... 39 6.3.4 Well Construction, Maintenance, Protection, Abandonment, and Destruction ................ 39 6.3.5 Construction and Operation of Groundwater Projects 40 6.3.6 Control of Saline Intrusion .................... 40 6.4 Groundwater Management Coordination ............. 41 6.4.1 Facilitate Conjunctive Use Operations ..... 41 6.4.2 Develop and Maintain Relationships with Local, State, and Federal Entities ........... 43 6.4.3 Review and Coordination of Land Use Issues 43 7.0 Groundwater Management Plan Implementation and Financing 44 7.1 Plan Implementation ....................................... 44 7.2 Plan Financing 45 8.0 References 46 August 18, 2020 Page 3 of 49 Little Lake Valley Groundwater Management Plan FINAL DRAFT Prepared for City of Willits FIGURES Figure 1-1 Plan Area Figure 1-2 Local Agency Boundaries Figure 3-1 Existing Monitoring in Little Lake Valley Figure 3-2 Geologic Map of Little Lake Valley Figure 3-3 Cross Sections of Little Lake Valley Figure 3-4 Land Cover Map Figure 3-5 Unincorporated Area Land Use Map Figure 3-6 Well Density within the Little Lake Valley Groundwater Basin Figure 5-1 Outlet Creek Watersheds and Subbasins Map Figure 5-2 FEMA Flood Zone Map APPENDICES Appendix A Resolution of Intention Appendix B GWMP Components Appendix C Public Outreach Documentation August 18, 2020 Page 4 of 49 Little Lake Valley Groundwater Management Plan FINAL DRAFT Prepared for City of Willits 1.0 INTRODUCTION This Little Lake Valley Groundwater Management Plan (GWMP) represents the initial effort on the part of the City of Willits to develop a plan for sustainable management of groundwater in the Little Lake Valley. This GWMP seeks to provide a framework for advancing the level of understanding and for facilitating future coordination regarding management of groundwater resources in the Little Lake Valley. 1.1 Purpose of the Plan This voluntary, non-regulatory GWMP describes existing local groundwater management policies and recommends a range of actions that the City of Willits may take within the boundaries of its legal authority, to monitor, analyze, and interpret characteristics of the Little Lake Valley groundwater basin (Basin). This plan is also intended to identify and develop potential, effective management practices for utilizing and protecting valuable groundwater resources within the Basin. For the purposes of carrying out the goals and objectives established in this GWMP, the boundaries of the GWMP area include all of the land within the City of Willits jurisdictional authority, including the land within the City limits and City-owned properties outside the City limits, as shown on Figure 1-1. Any land outside of the jurisdictional authority of the City of Willits is not included in this GWMP. Although this GWMP is limited to the jurisdictional boundaries of the City of Willits, this GWMP seeks to improve the understanding and sustainable management of groundwater resources in the entire Little Lake Valley, where mismanagement can impact water users within the Little Lake Valley and the surrounding areas. In addition, this GWMP will allow the City of Willits and other entities within the Basin, if they choose to adopt this GWMP, to be eligible for grant funding administered through the Department of Water Resources (DWR) for projects related to groundwater. 1.2 Background and Legal Authority for Local Groundwater Management In early 2019, the City of Willits submitted a preliminary grant application for Integrated Regional Water Management (IRWM) funding, administered by the DWR for a groundwater supply project which would greatly improve drinking water supply reliability for the community, especially in times of drought. The project was selected for funding; however, as outlined in the IRWM Grant Program Guidelines (2019), as a condition for receiving the funding, the City of Willits must commit to adopting a groundwater management plan that meets the requirements of Water Code §10753.7 by September 6, 2020 (within one year of the final grant application submittal date of September 6, 2019). On December 11, 2019, the City of Willits City Council formally approved Resolution No. 2019-59 noticing its intent to prepare a groundwater management plan for the portion of the Little Lake Valley groundwater basin within its jurisdictional authority (resolution of intention). The resolution of intention is included as Appendix A. The development of a groundwater management plan is governed by the Groundwater Management Act, which was codified into law in 1992 as California Water Code (CWC) §10750 et seq. and was subsequently amended in 2002 and 2011. CWC §10750 et seq. allows development of a groundwater management plan by local agencies to efficiently manage and maximize groundwater supplies, assure long term water supplies, and distribute costs, benefits, and water sharing in an equitable manner. Pursuant to CWC § 10753 (a), as a local agency whose service area includes a portion of a groundwater basin, as defined in CWC § 10752, the City of Willits has the legal authority to adopt and implement a groundwater management plan within all or a portion of its service area. Adoption and implementation of this GWMP by the City of Willits will August 18, 2020 Page 5 of 49 LITTLE LAKE VALLEY GROUNDWATER MANAGEMENT PLAN JRG FIGURE PROJECT BY 1-1 RMD CLIENT CITY OF WILLITS CHECK LACO JOB NO. 6/08/2020 EUREKA ● UKIAH ● SANTA ROSA LOCATION WILLITS, CALIFORNIA DATE 8509.07 1-800-515-5054 www.lacoassociates.com PLAN AREA REUSE OF DOCUMENTS: This document and the ideas and design incorporated herein, as an instrument of professional service, is the property of LACO Associates and shall not be reused in whole or part for any other project without LACO Associates express written authorization. NOTE: THE INFORMATION ILLUSTRATED IN THIS MAP WAS DERIVED FROM PUBLICLY AVAILABLE GIS DATA. LACO ASSOCIATES MENDOCINO CANNOT GUARANTEE THE ACCURACY OF COUNTY THE DATA. PACIFI C OCEAN PLAN AREA 101 CITY OF WILLITS GROUNDWATER TREATMENT SYSTEM WILLITS 20 CITY OF WILLITS RESERVOIRS & 0 6,000 SURFACE WATER Feet TREATMENT PLANT LEGEND STATE HIGHWAYS CITY OF WILLITS