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S A N J Q A Q U I N Environmental Health Department —COU N T Y--- Linda Turkatte, REHS, Director Greatness grows here. Kasey Foley,REHS,Assistant Director PROGRAM COORDINATORS Robert McClellon,REHS Jeff Carruesco,REHS, RDI April 2, 2019 Willy Ng,REHS Muniappa Naidu, REHS Don Chesney Michael Kith, REHS Chesney Consulting P O Box 3794 Turlock, CA 95381 RE: Nitrate Loading Mitigation Report 26451 North Sacramento Blvd, Thornton ,CPN 001-200-83, Service Request SR0080103 The San Joaquin County Environmental Health Department(EHD) has received the Nitrate Loading Mitigation Report, dated January 18, 2019, for the above noted location and has the following comments for your consideration. The Nitrate Loading Mitigation Report was prepared to provide an engineered onsite wastewater treatment system (OWTS) designed to mitigate nitrates from the wastewater generated from a proposed 4-bedroom single family dwelling on 0.37 acres, based on the results of the Nitrate Loading Study, dated July 25, 2018, prepared by Live Oak GeoEnviron mental, Inc. that indicated a potential impact to groundwater. The OWTS design in the Nitrate Loading Mitigation Report proposed a septic tank capacity of 2000 gallons, 400 gallons over the minimum required, the use of rock-less chambers in four leach lines exceeding 100 feet in length, and the use of sawdust or other organic material placed on the floor of the leach lines. Pursuant to Section 7.1 of the San Joaquin County Sewage Standards (Sewage Standards), these features would be considered an alternative treatment system, defined as a standard system with additional enhancements above the required minimum to augment the treatment capabilities of the system, including additional septic tank capacity, additional length of leach lines, or the addition of organic material under the leach line. Please be advised that per Section 9.4.4 of the Sewage Standards, the maximum length of an individual leach line is 100 feet and additional leach line over this length is not allowed. Because the Hantzche and Finnemore calculation that is used to estimate potential nitrate impact to groundwater provides a conservative (worst case), first approximation of groundwater nitrate concentration and ignores dispersion, lateral flow, and mixing with groundwater flow from upgradient areas, the EHD considered several other factors in evaluating the overall potential impact of the proposed OWTS and to determine if supplemental treatment would be necessary to protect the beneficial uses of groundwater. In conducting this evaluation, the following additional factors were considered: • The lot is an existing historical parcel, nonconforming for OWTS usage due to size. The parcel was recently merged with an adjacent parcel resulting in a total parcel size of 0.37 acres. The parcel size does not meet the current minimum density requirement for OWTS usage and requires a variance. • The parcel and surrounding homes do not utilize individual water wells but are served by a public water system, County Service Area 12–Thornton. The California Drinking Water Watch website information shows this system has 292 service connections serving a population of approximately 957 persons. Recent sample results from the two water wells serving this water system indicate these wells are not impacted by nitrate. 1868 E. Hazelton Avenue I Stockton, California 95205 1 T 209 468-3420 1 F 209 464-0138 1 www.sjcehd.com