Salt/Nutrient Management Plan for the Paso Robles Groundwater Basin MAY 2015 Salt/Nutrient Management Plan for the Paso Robles Groundwater Basin Final Report Prepared by: May 2015 Paso Robles Salt / Nutrient Management Plan Table of Contents This page intentionally left blank. May 2015 Paso Robles Salt / Nutrient Management Plan Table of Contents Table of Contents Executive Summary .............................................................................................................. ES-1 ES-1 Introduction ........................................................................................................ ES-1 ES-2 Outreach ............................................................................................................. ES-2 ES-3 Basin Characterization ...................................................................................... ES-3 ES-4 Existing and Foreseeable Salt and Nutrient Sources ..................................... ES-6 ES-5 Assimilative Capacity and Anti-Degradation Analysis ................................. ES-11 ES-6 Implementation Measures, Goals & Objectives ............................................ ES-13 ES-7 Salt and Nutrient Groundwater Quality Monitoring Program ....................... ES-16 Chapter 1 Introduction ........................................................................................................... 1-1 1.1 Regulatory Framework ............................................................................................ 1-1 1.2 Purpose of the SNMP ............................................................................................. 1-2 1.3 Preparation and Participation .................................................................................. 1-2 Chapter 2 Outreach ................................................................................................................ 2-1 2.1 Outreach and the SNMP Process ........................................................................... 2-1 2.2 Stakeholders ........................................................................................................... 2-1 2.3 Outreach Mechanisms ............................................................................................ 2-2 Chapter 3 Basin Characteristics ........................................................................................... 3-1 3.1 Setting ..................................................................................................................... 3-1 3.2 Landuse .................................................................................................................. 3-3 3.3 Climate and Hydrology ............................................................................................ 3-7 3.4 Geology and Hydrogeology ................................................................................... 3-11 3.5 Water Quality ........................................................................................................ 3-25 3.6 Water Balance Estimation ..................................................................................... 3-44 3.7 Summary ............................................................................................................... 3-54 Chapter 4 Loading Analysis .................................................................................................. 4-1 4.1 Selection of Baseline and Future Planning Period .................................................. 4-1 4.2 Identification of Salt and Nutrient Indicator Constituents ........................................ 4-2 4.3 Loading Analysis Tools ......................................................................................... 4-27 4.4 Identification and Quantification of Salt and Nutrient Sources .............................. 4-28 4.5 Septic and Wastewater Systems .......................................................................... 4-39 4.6 Summary ............................................................................................................... 4-45 Chapter 5 Assimilative Capacity and Anti-Degradation Analysis ...................................... 5-1 5.1 Basin Conceptual Model ......................................................................................... 5-1 5.2 Fate and Transport in Groundwater Basin .............................................................. 5-1 5.3 Existing Groundwater Quality .................................................................................. 5-3 5.4 Surface Loading Model ........................................................................................... 5-5 5.5 Groundwater Quality Trend Analysis .................................................................... 5-12 5.6 Antidegradation Assessment ................................................................................ 5-22 Chapter 6 SNMP Goals and Objectives ................................................................................ 6-1 6.1 Basin Management Goals and Objectives .............................................................. 6-1 Chapter 7 Implementation Measures .................................................................................... 7-1 7.1 Management Strategies .......................................................................................... 7-1 Chapter 8 Groundwater Quality Monitoring ......................................................................... 8-1 8.1 Background ............................................................................................................. 8-1 8.2 Summary of SNMP Groundwater Quality Monitoring Program ............................. 8-11 May 2015 Paso Robles Salt / Nutrient Management Plan Table of Contents 8.3 Conclusions and Recommendations ..................................................................... 8-12 Chapter 9 References ............................................................................................................. 9-1 9.1 Chapter 3 - Basin Characteristics ........................................................................... 9-1 9.2 Chapter 4 - Loading Analysis .................................................................................. 9-1 9.3 Chapter 5 - Assimilative Capacity and Anti-Degradation Analysis .......................... 9-3 9.4 Chapter 7 - Implementation Measures .................................................................... 9-4 9.5 Chapter 8 - Groundwater Quality Monitoring .......................................................... 9-4 List of Tables Table 2-1: Paso Robles SNMP Stakeholder Workshops ........................................................... 2-3 Table 3-1: Major Land Use Group ............................................................................................. 3-4 Table 3-2: Average Monthly Precipitation at Weather Stations ................................................. 3-9 Table 3-3: Average Monthly Reference Evapotranspiration ...................................................... 3-9 Table 3-4: Measured Streamflow for Major Rivers and Creeks ............................................... 3-10 Table 3-5: Average Aquifer Properties and Well Information from Historic Field Data ............ 3-21 Table 3-6: Average Alluvium Properties Computed from Basin Groundwater Model .............. 3-21 Table 3-7: Average Confined Aquifer Properties Computed from Basin Groundwater Model ............................................................................................................................... 3-22 Table 3-8: Median Surface Water Quality Objectives .............................................................. 3-26 Table 3-9: Median Groundwater Quality Objectives ................................................................ 3-26 Table 3-10: Nitrate (as N) Water Quality Objectives for Municipal and Domestic Supply, and Agricultural Water Use ..................................................................................................... 3-26 Table 3-11: Title 22 Drinking Water Standards for TDS, Nitrate (as N), and Chloride ............. 3-26 Table 3-12: Measured and Average Water Quality Constituent Concentrations for Study Areas ..................................................................................................................... 3-31 Table 3-13: Average Annual Groundwater Recharge in the Unconfined Aquifer..................... 3-49 Table 3-14: Average Annual Groundwater Recharge in the Confined Aquifer ........................ 3-50 Table 3-15: Average Annual Net Horizontal Subsurface Inflows in the Unconfined Aquifer between Study Areas ....................................................................................................... 3-50 Table 3-16: Average Annual Net Horizontal Subsurface Inflows in the Confined Aquifer between Study Areas ...................................................................................................................... 3-51 Table 3-17: Average Annual Net Vertical Groundwater Flow from Unconfined to Confined Aquifer .............................................................................................................................. 3-52 Table 3-18: Average Annual Groundwater Discharge in the Unconfined Aquifer .................... 3-53 Table 3-19: Average Annual Groundwater Discharge in the Confined Aquifer ........................ 3-54 Table 4-1: Evaluation of Potential Indicator Constituents .......................................................... 4-3 Table 4-2: Average