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12172 N Hibbard Road Project No. 2021-00063 P a g e | 8 6.0 DISCUSSION OF NITRATE LOADING RESULTS 6.1 Total Nitrate Impact The nitrate maximum contaminant level (MCL) set by the US EPA is 45 mg/L-NO3 or 10 mg/L-N. The domestic well reported groundwater at the site was 2.0 mg/L-N. As discussed above, the depth to groundwater is approximately 130 feet below ground surface at the site. The background concentration of nitrate detected in the domestic well for the site is 2.0 mg/L-N. Based on the methods and assumptions described, the project will result in nitrate of 11.1 mg/L-N. However, the depth to groundwater for this site is approximately 130 feet below ground surface. Based on the very low background nitrate concentration detected, the low-density septic systems for the area, the slow percolating clay layers underneath the site, and the depth to groundwater, we believe the proposed project will not likely cause a build- up of nitrate in the ground water above the nitrate maximum contaminant level (MCL) set by the US EPA of 10 mg/L-N above the total nitrogen over the long term. Based on the methods and assumptions described, in addition to our professional judgement and geologic setting, we believe the proposed project is unlikely to cause a build-up of nitrate in the ground water above the USEPA maximum concentration level of total nitrogen 10 mg/L over the long term. 6.2 Nitrate Loading - Methods of Mitigation Based on the very low background nitrate concentration detected, the low-density septic systems for the area, and the depth to groundwater, we believe the proposed project will not likely cause a build-up of nitrate in the ground water above the nitrate maximum contaminant level (MCL) set by the US EPA of 10 mg/L-N above the total nitrogen over the long term. It is our professional opinion that mitigation measures are not warranted at this time. While our study has shown that nitrate concentrations within groundwater will not likely buildup to levels above background based on the onsite use, it should be recognized that San Joaquin County EHD may require long-term nitrate monitoring (in the form of annual well sampling) or a septic system capable of mitigating and reducing nitrate. 7.0 EXISTING AND PROPOSED SEPTIC TANK USAGE 7.1 Existing On-Site Septic Tank Usage, Permits and Repair History There is no permit available for review related specifically to the site septic system. Permit No. SU0006150, issued in 2006 is an application for a lot line adjustment. One septic system with a 1500- gallon septic tank is reported in the application. No repair permits were reported for the site. The lot line adjustment application is available for review in Appendix B.