NOVEMBER 2014 Salt and Nutrient Management Plan Santa Clara Subbasin This page is intentionally left blank REVISED FINAL SALT AND NUTRIENT MANAGEMENT PLAN: SANTA CLARA SUBBASIN Originally posted online in November, 2014; Revised in June 2016 to add San Francisco Bay Regional Water Quality Control Board comments and Santa Clara Valley Water District responses ACKNOWLEDGMENTS PREPARED BY: Thomas Mohr, P.G., H.G. Senior Hydrogeologist UNDER THE DIRECTION OF: James Fielder Chief Operating Officer, Water Utility Enterprise Garth Hall Deputy Operating Officer Water Supply Division Behzad Ahmadi Unit Manager,Groundwater (retired) CONTRIBUTORS: Chanie Abuye, Civil Engineer Randy Behrens, Geologist Ellen Fostersmith, Geologist (retired) Ardy Ghoreishi, Engineering Technician Robert Siegfried, Soil Scientist (retired) Miguel Silva, Associate Civil Engineer Xiaoyong Zhan, Civil Engineer GRAPHICS DESIGN: Benjamin Apollo BOARD OF DIRECTORS: John L. Varela, District 1 Barbara Keegan, District 2 (Chair) Richard Santos, District 3 Linda J. LeZotte, District 4 Nai Hsueh, District 5 Tony Estremera, District 6 Gary Kremen, District 7 TABLE OF CONTENTS Page ACRONYMS ....................................................................................................................... x EXECUTIVE SUMMARY ............................................................................................................ 1 CHAPTER 1: INTRODUCTION AND BACKGROUND .............................................................. 5 1.1 Introduction ............................................................................................................... 5 1.2 State Water Resources Control Board 2009 Recycled Water Policy ......................... 5 1.3 Stakeholder Participation .......................................................................................... 7 1.4 Related Plans and Policies ....................................................................................... 8 1.4.1 Anti-Degradation Policy....................................................................................... 8 1.4.2 Regional Water Quality Control Plan ................................................................... 8 1.4.2.1 Beneficial Uses ............................................................................................. 8 1.4.2.2 Water Quality Objectives ............................................................................... 8 1.4.3 Integrated Regional Water Management Plan Objectives ................................... 9 1.4.4 District Board Ends Policies ...............................................................................10 1.4.5 Groundwater Management Plan Basin Management Objectives ........................10 1.5 Regulatory Framework ............................................................................................11 1.5.1 Waste Discharge Permitting Program ................................................................11 1.5.2 Total Maximum Daily Loads ...............................................................................13 1.5.3 Local Regulations ..............................................................................................13 1.5.4 Goals and Objectives for Recycled Water and Stormwater ................................14 CHAPTER 2: GROUNDWATER SUBBASIN CHARACTERIZATION ..................................... 15 2.1 Groundwater Basin ..................................................................................................16 2.1.1 Santa Clara Plain Hydrogeology ........................................................................16 2.1.2 Santa Clara Plain Pumping and Recharge .........................................................17 2.1.3 Santa Clara Plain Groundwater Elevation Trends ..............................................24 2.1.4 Santa Clara Plain Storage Capacity ...................................................................24 2.1.5 Santa Clara Plain Water Budget ........................................................................24 2.1.6 Santa Clara Plain Groundwater Quality ..............................................................25 2.2 Coyote Valley Hydrogeology ....................................................................................27 2.2.1 Coyote Valley Pumping ......................................................................................28 2.2.2 Coyote Valley Groundwater Pumping Trends ....................................................28 2.2.3 Coyote Valley Storage Capacity .........................................................................29 2.2.4 Coyote Valley Water Budget ..............................................................................29 Santa Clara Subbasin Salt and Nutrient Management Plan i TABLE OF CONTENTS Page 2.2.5 Coyote Valley Groundwater Elevation Trends ....................................................30 2.2.6 Coyote Valley Groundwater Quality ...................................................................31 2.3 Sources of Supply....................................................................................................31 2.4 Santa Clara Groundwater Subbasin Water Budget ..................................................31 2.5 Groundwater Quality – Salts and Nutrients ..............................................................33 2.5.1 Total Dissolved Solids ........................................................................................33 2.5.2 Nitrate ................................................................................................................34 2.5.3 Trends in TDS and Nitrate .................................................................................35 2.5.4 TDS Trends in Monitoring Wells, for 1998–2012 ................................................36 2.5.5 Nitrate Trends in Monitoring Wells, for 1998–2012 .............................................36 CHAPTER 3: ESTIMATING CURRENT AND FUTURE SALT AND NUTRIENT LOADING AND ASSIMILATIVE CAPACITY ................................................................ 39 3.1 Sources of Salts and Nutrients.................................................................................39 3.2 Fate and Transport of Salts and Nutrients ...............................................................40 3.3 Methodology for Estimating Salt and Nutrient Loading and Removal .......................42 3.3.1 Wet Loading Categories.....................................................................................43 3.3.1.1 Rainfall Recharge .........................................................................................43 3.3.1.2 Mountain-front Recharge ..............................................................................44 3.3.1.3 Basin Inflow and Saline Intrusion .................................................................46 3.3.1.4 Managed Recharge in Streams ....................................................................49 3.3.1.5 Managed Recharge in Percolation Ponds ....................................................50 3.3.1.6 Agricultural Irrigation ....................................................................................50 3.3.1.7 Landscape Irrigation – Municipal and Domestic Water Sources ...................51 3.3.1.8 Landscape Irrigation – Recycled Water ........................................................53 3.3.1.9 Conveyance Losses .....................................................................................54 3.3.1.10 Drainage Losses ..........................................................................................55 3.3.2 Dry Loading .......................................................................................................57 3.3.2.1 Agricultural Fertilizer and Lawn Fertilizer ......................................................57 3.3.2.2 Atmospheric Deposition ...............................................................................59 3.3.3 Salt and Nutrient Removal .................................................................................60 3.3.3.1 Groundwater Pumping .................................................................................60 3.3.3.2 Basin Outflow ...............................................................................................61 3.3.3.3 Gaining Reaches of Streams........................................................................61 3.3.3.4 Groundwater Infiltration into Sewer Lines and Storm Drains ........................61 Santa Clara Subbasin Salt and Nutrient Management Plan ii TABLE OF CONTENTS Page 3.3.3.5 Storm Drain Infiltration..................................................................................61 3.3.4 Overall Salt and Nitrate Balance ........................................................................62 3.4 Assimilative Capacity ...............................................................................................64 3.4.1 Ambient Groundwater Quality ............................................................................64 3.4.2 Volume-Weighted Average Basin Concentrations ..............................................67 3.4.3 Estimated Basin Assimilative Capacity ...............................................................68 3.4.4 Projecting Future Assimilative Capacity .............................................................68 3.4.4.1 Assumptions for Future Loading ...................................................................68 3.4.4.2 Methodology and Assumptions for Mixing Calculation ..................................71