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1246 N Fine Road Project No. 2021-00025 Page 18 5.6 Impact of Nitrate Loading to Nearby Water Sources 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 15 mg/L-N. As discussed above, the depth to groundwater is approximately 165 to 170 feet below ground surface at the site. Although the soil is a fine sandy loam, the San Joaquin soil reported for the area is known to have layers of clay and indurated layer from approximately 20 to 60 inches below ground surface; based on a review of the well completion log for the site confirming several layers of clay soil and a deep water table, the site likely has several layers of clayey soil which would further protect the groundwater. The background concentration of nitrate detected in the domestic well for the site is 0.92 mg/L-N. Based on the methods and assumptions described, the project will result in nitrate of 13.2 mg/L-N. However, the depth to groundwater for this site is approximately 165 to 170 feet below ground surface. Based on the very low background nitrate concentration detected, the low density septic systems for the area, verified layers of clay from the onsite well log, 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 relatively flat topography of the site, we do not foresee percolating effluent affecting any surface water resources. 6.0 DISCUSSION OF NITRATE LOADING RESULTS 6.1 Total Nitrate Impact 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, verified layers of clay from the onsite well log, 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. Petralogix Engineering, Inc. 26675 Bruelia Road, Galt, Ca 95632 (209)-400-5729 www.petralogix.com •