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33503 S Koster Road Project No.2021-00073 Page 19 <br /> septic 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 /> Two permits available for review related specifically to the site septic system. Permit No. <br /> 87-2400, issued in 1987 is an application for the installation of a new 1200-gallon capacity <br /> septic tank and 2 leach lines with seepage pits to 12 feet below ground surface. One <br /> repair/addition permit (Permit No. SR0026157) reported for the site in 2001 indicates a <br /> total of 12 infiltrators were installed in the leach field system. <br /> The permits are 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 three- <br /> bedroom, single-family residence, and the proposed two-bedroom, two-bath, accessory <br /> 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 50 septic <br /> systems per square mile in the immediate vicinity of the site. This is a low number of septic <br /> systems, with the majority of these systems located scattered within large tracts of <br /> agricultural land. <br /> The EHD septic permit files were obtained from the San Joaquin Environmental Health <br /> Department(EHD) Online EHD Program Records6 in an effort to obtain copies of permits for <br /> any septic tanks located within the general area of the subject property. <br /> Copies of the septic search permits for surrounding parcels have been included in Appendix <br /> D of this report. The records are summarized in the following table: <br /> 6 https://tfweb.sjgov.org/WebLink/Browse.aspx?dbid=1&tcr=1 accessed September 9, 2019 <br /> Petralogix Engineering,InC. <br /> 26675 BruelIa Road,Galt,Ca 95632 <br /> (209)-40o-5729 <br /> www.petralogix.com <br />