Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea Ventura County, California Prepared for: RBF Consulting and County Waterworks District No. 8 City of Simi Valley September 13, 2006 GEOSCIENCE Support Services, Inc. Tel: (909) 920-0707 Fax: (909) 920-0403 Mailing: P. O. Box 220, Claremont, CA 91711 1326 Monte Vista Ave., Suite 3, Upland, CA 91786 email: [email protected] Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea, Ventura County, California 13-Sep-06 RBF CONSULTING / VENTURA COUNTY WATERWORKS DISTRICT NO. 8 GEOHYDROLOGIC EVALUATION OF MAXIMUM PERENNIAL YIELD TAPO CANYON TRIBUTARY SUBAREA – VENTURA COUNTY, CALIFORNIA CONTENTS 1.0 EXECUTIVE SUMMARY ................................................................................................ 1 2.0 INTRODUCTION .............................................................................................................. 5 2.1 Purpose and Scope......................................................................................................... 5 2.2 Project Location............................................................................................................. 6 2.3 Previous Investigations.................................................................................................. 6 2.4 Sources of Data.............................................................................................................. 7 3.0 DESCRIPTION OF THE STUDY AREA........................................................................ 8 3.1 Physiography and Topography ...................................................................................... 8 3.2 Climate........................................................................................................................... 8 3.2.1 Precipitation..................................................................................................... 9 3.2.2 Evaporation.................................................................................................... 10 3.3 Existing Water Purveyors and Wells........................................................................... 10 3.4 Ground Water Production............................................................................................ 11 4.0 GEOLOGY........................................................................................................................ 13 4.1 Regional Geology........................................................................................................ 13 4.2 Study Area Geology.....................................................................................................13 4.2.1 Bedrock.......................................................................................................... 14 4.2.2 Quaternary Alluvial Deposits........................................................................ 16 GEOSCIENCE Support Services, Inc. RBF Consulting i Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea, Ventura County, California 13-Sep-06 5.0 GEOHYDROLOGY......................................................................................................... 17 5.1 Surface Water .............................................................................................................. 17 5.2 Ground Water .............................................................................................................. 17 5.2.1 Aquifer Characteristics.................................................................................. 19 5.2.2 Ground Water Movement.............................................................................. 19 5.2.3 Historical Ground Water Level Trends ......................................................... 20 5.2.4 Ground Water Quality................................................................................... 21 6.0 ANALYSIS OF MAXIMUM PERENNIAL YIELD - METHODOLOGY ................ 22 6.1 Ground Water Level and Production Analysis............................................................ 23 6.2 Watershed Model......................................................................................................... 23 6.2.1 Conceptual Watershed Model........................................................................ 24 6.2.1.1 Initial Abstraction............................................................................... 25 6.2.1.2 Infiltration and Interflow..................................................................... 25 6.2.1.3 Overland Flow.................................................................................... 26 6.2.1.4 Ground Water Recharge..................................................................... 26 6.2.2 Model Input................................................................................................... 27 6.2.2.1 Model Subunits................................................................................... 27 6.2.2.2 Precipitation ........................................................................................ 27 6.2.2.3 Potential Evapotranspiration............................................................... 28 6.2.2.4 Streamflow.......................................................................................... 28 6.2.3 Model Output................................................................................................. 28 6.2.3.1 Surface Runoff.................................................................................... 28 6.2.3.2 Evapotranspiration .............................................................................. 29 6.2.3.3 Ground Water Recharge..................................................................... 30 6.2.4 Model Calibration.......................................................................................... 30 GEOSCIENCE Support Services, Inc. RBF Consulting ii Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea, Ventura County, California 13-Sep-06 7.0 FINDINGS......................................................................................................................... 31 7.1 Estimate of Maximum Perennial Yield Based on Ground Water Level and Production History ......................................................................................................................... 31 7.2 Estimate of Average Annual Ground Water Recharge Based on the Watershed Model.. 32 8.0 CONCLUSIONS AND RECOMMENDATIONS.......................................................... 34 8.1 Conclusions.................................................................................................................. 34 8.2 Recommendations........................................................................................................ 35 9.0 REFERENCES.................................................................................................................. 37 FIGURES, TABLES, APPENDICES GEOSCIENCE Support Services, Inc. RBF Consulting iii Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea, Ventura County, California 13-Sep-06 FIGURES No. Description 1 Study Area Location 2 Tapo Canyon Tributary Subarea 3 Precipitation and Cumulative Departure from Mean Precipitation – Tapo Canyon Tributary Subarea 4 Well Locations 5 Ground Water Production – Tapo Canyon Ground Water Basin 6 Geology of the Tapo Canyon Area 7 Geologic Cross-Section 8 Tapo Canyon Tributary Subunits 9 Static Ground Water Elevations – Tapo Canyon Ground Water Basin 10 Water Quality Trilinear Diagram – Wells in the Tapo Canyon Tributary Subarea 11 Schematic Diagram of Watershed Model 12 Precipitation, Production and Ground Water Elevations – Tapo Canyon Tributary Subarea 13 Potential Future Well Locations GEOSCIENCE Support Services, Inc. RBF Consulting iv Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea, Ventura County, California 13-Sep-06 TABLES No. Description 1 Summary of Annual Precipitation – Tapo Canyon Tributary Subarea 2 Summary of Wells Within the Tapo Canyon Tributary Subarea 3 Tapo Canyon Ground Water Basin Annual Ground Water Production 4 Selected Water Quality – Tapo Canyon Wells GEOSCIENCE Support Services, Inc. RBF Consulting v Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea, Ventura County, California 13-Sep-06 APPENDICES Ltr. Description A Driller’s Logs B Ground Water Elevations GEOSCIENCE Support Services, Inc. RBF Consulting vi Geohydrologic Evaluation of Maximum Perennial Yield Tapo Canyon Tributary Subarea, Ventura County, California 13-Sep-06 GEOHYDROLOGIC EVALUATION OF MAXIMUM PERENNIAL YIELD TAPO CANYON TRIBUTARY SUBAREA VENTURA COUNTY, CALIFORNIA 1.0 EXECUTIVE SUMMARY This report presents the methodology, analysis, and findings of an evaluation of the maximum perennial yield of the ground water basin within the Tapo Canyon area of the Santa Susana Mountains immediately north of Simi Valley, California. Evaluation of the maximum perennial yield was conducted in order to assess potential future increase of ground water production from the area. The scope of the evaluation included: • Data collection and review, • Delineation of the drainage area encompassing Tapo Canyon, • Identification of the limits of the ground water basin, • Analysis of historical geohydrological data, • Estimation of the maximum perennial yield of the ground water basin using multiple methods, • Identification of potential future well