SURFACE WATER AND GROUNDWATER AVAILABILITY ASSESSMENT MONO CITY AREA MONO COUNTY, CALIFORNIA PREPARED ON SEPTEMBER 27, 2006 FOR MONO COUNTY PLANNING DEPARTMENT MAMMOTH LAKES, CALIFORNIA PREPARED BY SURFACE WATER AND GROUNDWATER AVAILABILITY ASSESSMENTS MONO CITY AREA MONO COUNTY, CALIFORNIA TABLE OF CONTENTS SECTION PAGE 1.0 INTRODUCTION....................................................................................................................1 1.1 PURPOSE AND SCOPE ................................................................................................1 1.2 LOCATION AND PHYSIOGRAPHIC SETTING ................................................................2 1.3 LAND USE.................................................................................................................2 1.4 WATER RESOURCE MANAGEMENT ...........................................................................2 1.5 DATA SOURCES.........................................................................................................3 2.0 SURFACE WATER AVAILABILITY ASSESSMENT .................................................................4 2.1 GENERAL CONDITIONS ..............................................................................................4 2.2 AVAILABLE RECORDS...............................................................................................4 2.3 SURFACE WATER FLOW / RUNOFF............................................................................4 2.4 SURFACE WATER USE...............................................................................................5 2.4.1 In-Stream Requirements ..............................................................................5 2.4.2 Present Development and Water Use ..........................................................5 2.4.3 Existing Water Rights..................................................................................6 2.5 FUTURE DEVELOPMENT AND SURFACE WATER USE.................................................6 3.0 GROUNDWATER AVAILABILITY ASSESSMENT....................................................................7 3.1 REGIONAL HYDROGEOLOGY.....................................................................................8 3.2 HYDROGEOLOGIC UNITS...........................................................................................9 3.3 GEOLOGIC STRUCTURE ...........................................................................................10 3.4 GROUNDWATER OCCURRENCE AND MOVEMENT ....................................................10 3.5 HYDRAULIC PROPERTIES ........................................................................................11 3.6 GROUNDWATER INFLOW.........................................................................................11 3.6.1 Groundwater Recharge from Precipitation .................................................11 3.6.2 Seepage From Virginia Creek Diversion...................................................12 3.6.3 Percolation from Septic Tanks...................................................................13 3.7 GROUNDWATER OUTFLOW .....................................................................................13 3.7.1 Groundwater Pumping................................................................................13 3.7.2 Evapotranspiration .....................................................................................13 3.7.3 Seepage to Streams ....................................................................................14 3.7.4 Springs .......................................................................................................14 3.7.5 Subsurface Outflow ...................................................................................14 3.8 GROUNDWATER IN STORAGE ..................................................................................14 3.9 GROUNDWATER LEVELS AND DISCUSSION OF INFLOW AND OUTFLOW COMPONENTS.........................................................................................14 3.10 CHEMICAL QUALITY ...............................................................................................16 3.9.1 Potential Impacts to Groundwater Quality ................................................16 3.11 POTENTIAL FUTURE GROUNDWATER USE ..............................................................16 4.0 CONCLUSIONS ...................................................................................................................18 5.0 RECOMMENDATIONS .........................................................................................................20 5.1 KEY ISSUES TO BE EVALUATED ..............................................................................20 5.2 DATA COLLECTION.................................................................................................20 5.3 EVALUATION OF EVAPOTRANSPIRATION.................................................................20 5.4 WELL-LOGGING......................................................................................................20 5.5 AQUIFER TESTING FOR NEW WELLS .......................................................................21 5.6 WATER QUALITY ANALYSES ..................................................................................21 5.7 PREPARATION OF A GROUNDWATER MANAGEMENT PLAN FOR THE MONO CITY AREA ......................................................................................................................21 6.0 REFERENCES......................................................................................................................22 7.0 CONDITIONS AND LIMITATIONS........................................................................................24 LIST OF TABLES Table Title TABLE 1 MILL CREEK PRIORITY RIGHTS TABLE 2 SUMMARY OF PRECIPITATION DATA TABLE 3 RECHARGE SUMMARY LIST OF FIGURES Figure Title FIGURE 1 GENERAL AREA MAP FIGURE 2 MONO CITY AREA MAP FIGURE 3 SUBWATERSHED MAP FIGURE 4 PRECIPITATION VS. ELEVATION LIST OF APPENDIXES Appendix Title APPENDIX A STREAMFLOW DATA FOR MILL AND WILSON CREEKS APPENDIX B WATER RIGHTS DATABASE SUMMARY APPENDIX C ENVIRONMENTAL DATABASE SEARCH RESULTS SURFACE WATER AND GROUNDWATER AVAILABILITY ASSESSMENTS MONO CITY AREA MONO COUNTY, CALIFORNIA 1.0 INTRODUCTION This report summarizes the results of a surface water and groundwater availability assessment performed by TEAM Engineering & Management, Inc. (TEAM) for the Mono City area, Mono County, California. Surface water and groundwater are both considered in this report because both surface and groundwater are interconnected components of a single resource. Therefore, describing the conditions of both surface water and groundwater is key to understanding the water resources of the Mono City area. This report is one of a series of watershed assessment reports designed to provide the Mono County Planning Department with key information to evaluate and identify future development issues in the outlying, but rapidly growing, areas of the county. Additionally, this report provides recommendations concerning future studies and water management issues. This report is consistent with published guidelines for groundwater investigation reports (California Board for Geologists and Geophysicists, 1998). Mono City was identified by county staff as a community to be evaluated as part of this project. This work is being prepared for the Mono County Planning Department under a grant that the County received from the California State Water Resources Control Board (Agreement No. 03- 008-556-0). 1.1 PURPOSE AND SCOPE The purpose of this report is to provide an overview of the water resources (both quantity and quality) of the Mono City area. Additionally, this report addresses potential future water resource issues of concern for the area, and needs for additional data and analysis. The work described above included the following key tasks: • Literature Search and Review • Surface Water Availability Assessment • Groundwater Availability Assessment • Report Preparation The literature search and review included the evaluation of government technical reports (U.S. Geological Survey, Inyo National Forest, California Department of Water Resources), the California Regional Water Quality Control Board – Lahontan Region Basin Plan, precipitation data for regional precipitation stations, streamflow data for Mill Creek and Wilson Creek, an environmental database search, and water rights information. The surface water availability assessment includes a summarization of surface water conditions including stream flows, an evaluation of existing surface water usage versus availability, a review of surface water quality issues, a review of regulatory issues associated with surface water usage, and qualitative analyses of potential areas for surface water development (if available) and associated potential impacts. The groundwater availability assessment includes the development of groundwater recharge estimates for Mono City area subwatersheds as represented in Mono County’s existing geographic information system (GIS), evaluation of existing groundwater pumping and resulting groundwater availability, a review of groundwater quality issues, and qualitative analyses of potential groundwater development areas and potential impacts due to groundwater development. 1.2 LOCATION AND PHYSIOGRAPHIC SETTING Mono City is located approximately 3-1/2 miles north of Lee Vining, California, and east of U.S. Highway 395 (Figures 1 and 2). Access to the area is via the north-south