Watershed Sanitary Survey Final Modesto Irrigation District and Stanislaus Regional Water Authority September 30, 2020 Watershed Sanitary Survey Modesto Irrigation District and Stanislaus Regional Water Authority Contents List of Acronyms ........................................................................................................................................................viii Watershed Sanitary Survey Executive Summary .......................................................................................................xiii Background ......................................................................................................................................................xiii Water Supply Systems .....................................................................................................................................xiii Upstream Watersheds ...................................................................................................................................... xiv Significant Potential Contaminant Sources and Source Water Quality Recommendations .............................. xv Don Pedro Reservoir .............................................................................................................................. xv Modesto Reservoir ............................................................................................................................... xvii Lower Tuolumne River Watershed .....................................................................................................xviii Invasive Species .................................................................................................................................... xix Conclusions and Recommendations ................................................................................................................. xx 1 Introduction ......................................................................................................................................................1-1 1.1 Background ...........................................................................................................................................1-1 1.2 Objectives .............................................................................................................................................1-2 1.3 Conduct of the Study ............................................................................................................................1-2 1.4 Report Content and Organization .........................................................................................................1-2 2 Watershed Study Areas and Water Supply Systems ........................................................................................2-1 2.1 Watershed Sanitary Survey Study Area Descriptions ...........................................................................2-1 2.1.1 Don Pedro Reservoir Subwatershed Study Area Description .................................................2-2 2.1.2 Modesto Reservoir and Upper Main Canal Watershed Description .......................................2-6 2.1.3 Lower Tuolumne River Subwatershed Description ..............................................................2-13 2.2 Watershed Sanitary Survey Summaries ..............................................................................................2-20 2.2.1 SFPUC Hetch Hetchy Reservoir Watershed Sanitary Survey ..............................................2-20 2.2.2 Don Pedro Recreation Agency Don Pedro Reservoir Watershed Sanitary Survey ..............2-25 2.2.3 TID Lower Tuolumne River and Turlock Lake Watershed Sanitary Survey .......................2-25 2.2.4 MID 2014 Modesto Reservoir Watershed Sanitary Survey ..................................................2-26 2.3 MID Water System .............................................................................................................................2-27 2.3.1 System Facilities ...................................................................................................................2-27 2.4 SRWA Water System .........................................................................................................................2-31 2.4.1 System Facilities ...................................................................................................................2-31 2.4.2 Emergency Plans ..................................................................................................................2-32 3 Potential Contaminant Sources ........................................................................................................................3-1 3.1 Wastewater............................................................................................................................................3-1 3.1.1 Potential Contaminant Sources ...............................................................................................3-1 3.1.2 Water Quality Concerns .......................................................................................................3-10 3.1.3 Watershed Management .......................................................................................................3-10 3.2 Septic Tank Systems ...........................................................................................................................3-11 3.2.1 Potential Contaminant Sources .............................................................................................3-12 3.2.2 Water Quality Concerns .......................................................................................................3-14 3.2.3 Watershed Management .......................................................................................................3-14 3.3 Urban Runoff ......................................................................................................................................3-15 3.3.1 Potential Contaminant Sources .............................................................................................3-15 3.3.2 Water Quality Concerns .......................................................................................................3-17 3.3.3 Watershed Management .......................................................................................................3-18 September 30, 2020 i Watershed Sanitary Survey Modesto Irrigation District and Stanislaus Regional Water Authority 3.4 Recreational Use .................................................................................................................................3-18 3.4.1 Potential Contaminant Sources .............................................................................................3-18 3.4.2 Water Quality Concerns .......................................................................................................3-26 3.4.3 Watershed Management .......................................................................................................3-27 3.5 Agricultural Crop Land Use ................................................................................................................3-30 3.5.1 Potential Contaminant Sources .............................................................................................3-30 3.5.2 Water Quality Concerns .......................................................................................................3-34 3.5.3 Watershed Management .......................................................................................................3-35 3.6 Grazing Animals and Confined Animal Facilities ..............................................................................3-35 3.6.1 Potential Contaminant Sources .............................................................................................3-36 3.6.2 Water Quality Concerns .......................................................................................................3-37 3.6.3 Watershed Management .......................................................................................................3-38 3.7 Wild Animals ......................................................................................................................................3-38 3.7.1 Potential Contaminant Sources .............................................................................................3-38 3.7.2 Water Quality Concerns .......................................................................................................3-39 3.7.3 Watershed Management .......................................................................................................3-39 3.8 Solid and Hazardous Waste Disposal Facilities ..................................................................................3-39 3.8.1 Potential Contaminant Sources .............................................................................................3-40 3.8.2 Water Quality Concerns .......................................................................................................3-42 3.8.3 Watershed Management .......................................................................................................3-42 3.9 Hazardous Materials Storage ..............................................................................................................3-42 3.9.1 Potential Contaminant Sources .............................................................................................3-42 3.9.2 Water Quality