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Ur_� ' ___� �' SAN JOAQUIN Environmental Health DepartmentJ�gi .;- —C O U N T Y---- Linda Turkatte REHS Director Greatness rows Dere. 9 Kasey Foley,REHS,Assistant Director PROGRAM COORDINATORS Robert McClellon,REHS Jeff Carruesco,REHS, RDI Willy Ng,REHS Muniappa Naidu,REHS Michael Kith,REHS February 5, 2019 Rick Marrun 38152 Hastings Court Fremont CA 94536 RE: Nitrate Loading Study for 11851 W. Valpico Rd., Tracy Service Request SR0079948 The San Joaquin County Environmental Health Department (EHD) has reviewed the Nitrate Loading Study, dated September 6, 2018, prepared by Live Oak Geo Environmental, Inc. In addition, on December 13, 2018, the EHD received your email, originally dated December 5, 2018, regarding the information you obtained from EHD staff relating to the installation of an onsite wastewater treatment system (OWTS) at the above noted property for a second unit dwelling. The Nitrate Loading Study and several other factors that influence nitrate loading to groundwater were evaluated as part of your request for EHD approval of a new onsite wastewater treatment system (OWTS) to serve a proposed second unit dwelling at the above noted location. Based on a review of the entirety of the information, a new OWTS to serve a second unit dwelling on this parcel cannot be approved without sufficient supplemental treatment to mitigate nitrate, as required pursuant to the San Joaquin County Local Agency Management Plan (LAMP), Page 31, and the OWTS Standards, Section 3.1. In addition, the parcel does not appear to have sufficient area to accommodate the existing and proposed OWTS, including future replacement areas, as required pursuant to the OWTS Standards, Section 1.11.2. The EHD cannot take action in conflict with the LAMP or OWTS Standards which may impair groundwater or threaten the water quality of your and your neighbor's water wells. The information considered for this determination is listed below. • The parcel size of 0.5 acres does not meet the minimum density requirement of two acres per dwelling. In addition, the parcel is in an area with a high density of existing OWTS and domestic water wells on small acreage, all potentially contributing nitrate to groundwater. • The nitrate loading study calculation was based on the gallons per day generated from one five- bedroom dwelling unit, and did not consider the cumulative nitrate contribution from each separate dwelling unit, including the kitchen/laundry areas. This method may not accurately represent the full potential nitrate loading conditions from two distinct dwelling units and provides a significantly lower average concentration of nitrate-nitrogen in the percolating wastewater. In any case, the results show it is highly likely that nitrogen from the existing and proposed OWTS will impact groundwater underlying the parcel at levels significantly above the 10 mg/I State maximum contaminant level (MCL) established for safe drinking water and the water quality objective established in the Basin Plan for the Central Valley Region to protect the beneficial uses of groundwater. • Sample data from the onsite domestic well shows a Nitrate Nitrogen result of 8.5 mg/I. The drinking water MCL and the water quality objective per the Basin Plan is 10 mg/I. These data show the onsite domestic water well is already impacted by nitrate and is at risk of exceeding these health protective target levels with additional nitrate loading to groundwater. 1868 E. Hazelton Avenue I Stockton, California 95205 1 T 209 468-3420 1 F 209 464-0138 1 www.sjcehd.com