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476 N Patton Avenue Project No. 2021-00084 Page 19 <br /> 6.2 Nitrate Loading- Methods of Mitigation <br /> Based on the depth to groundwater and low to moderate percolation rates of the clay and <br /> clayey loam soils on site, we believe the proposed project will not likely cause a build-up of <br /> nitrate in the ground water above the background concentration of 12 mg/L-N over the long <br /> term. It is our professional opinion that mitigation measures such as an engineered septic <br /> are not warranted at this time, however, a standard septic system with an oversized septic <br /> tank to mitigate potential buildup of nitrate by increasing retention and digestion time <br /> within the tank to improve leach field conditions is recommended. <br /> While our study has shown that nitrate concentrations within groundwater will not likely <br /> buildup to levels above background based on the onsite use,it should be recognized that San <br /> Joaquin County EHD may require long-term nitrate monitoring (in the form of annual well <br /> sampling) or a septic system capable of mitigating and reducing nitrate. <br /> 7.0 EXISTING AND PROPOSED SEPTIC TANK USAGE <br /> 7.1 Existing On-Site Septic Tank Usage, Permits and Repair History <br /> One repair/addition permit was available for review related specifically to the site septic <br /> system. Permit No. SR0080558, issued in 2018 is an application for the installation of one <br /> new leach line to the existing septic system. <br /> The permit is available for review in Appendix B. <br /> 7.2 Expected Maximum Septic Tank Usage for Site <br /> Expected maximum septic tank usage for the Site is to accommodate the current <br /> three-bedroom, single-family residence, and the proposed three-bedroom, two-bath, <br /> accessory dwelling-unit. <br /> 7.3 General Area Septic Tank Usage,Permit,and Repair History <br /> In an attempt to determine the septic system density for the vicinity of the site, our office <br /> reviewed a recent aerial photograph available from GoogleEarthTM.We counted the clusters <br /> within approximately one square mile of the Site,with the assumption each building cluster <br /> has one septic system.Using this method,we determined there are approximately 200 septic <br /> systems per square mile in the immediate vicinity of the Site. This is a moderate number of <br /> septic systems, with the majority of these systems located within the immediate <br /> neighborhood which is condensed and surrounded by large tracts of agricultural land. <br /> Petralogix Engineering,Inc. <br /> 26675 BruelIa Road,Galt,Ca 95632 <br /> (209)-40o-5729 <br /> www.petralogix.com <br />