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11655 S UNION ROAD Project No. 2020-00095 Page 18 <br />Based on the methods and assumptions described, the project will result in nitrate of 18.4 <br />mg/L-N. The background concentration of nitrate detected in the domestic well for the site <br />is 15 mg/L-N. The depth to groundwater for this site is approximately 35 feet below ground <br />surface. Based on the mass balance analysis results, background concentration detected, low <br />density septic systems for the area, and the hardpan layer associated with the Veritas soil, <br />we believe the proposed project will not likely cause a build-up of nitrate in the ground water <br />above the background concentration of total nitrogen above 15 mg/L over the long term. <br />Based on the relatively flat topography of the site, we do not foresee percolating effluent <br />affecting any surface water resources. <br /> <br />6.0 DISCUSSION OF NITRATE LOADING RESULTS <br /> <br />6.1 Total Nitrate Impact <br />Based on the methods and assumptions described, in addition to our professional judgement <br />and geologic setting, we believe the proposed project is unlikely to cause a build-up of nitrate <br />in the ground water above background concentration level of total nitrogen 15 mg/L over <br />the long term. <br /> <br />6.2 Nitrate Loading - Methods of Mitigation <br />Based on the mass balance analysis results, in addition to our professional judgement, low <br />septic tank density, hardpan within the Veritas soil type, and geologic setting showing the <br />depth of the groundwater table underlying the Site, we believe the proposed project will not <br />likely cause a build-up of nitrate in the ground water above the background concentration of <br />total nitrogen above 15 mg/L over the long term. It is our professional opinion that <br />mitigation measures are not warranted at this time. <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 /> <br />7.0 EXISTING AND PROPOSED SEPTIC TANK USAGE <br /> <br />7.1 Existing On-Site Septic Tank Usage, Permits and Repair History <br />There is one septic permit available for review related to the site septic system. Permit No. 10296, <br />issued in 1958 is for the installation of a concrete septic tank and disposal field for one 3-bedroom <br />1-bath residence. No repair permits were reported for the site. <br />The permit is available for review in Appendix B. <br />Petralogix Engineering, Inc. <br />26675 Bruella Road, Galt, Ca 95632 <br />(209)-400-5729 <br />www.petralogix.com