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33503 S Koster Road Project No.2021-00073 Page 18 Table 4. Summary of Nitrate Mass Balance Analysis. Parcel Result Acres Average Daily Flow Effluent Leachfield Deep Percolation (Nc)* (A) (Q) Concen- Denitrifi- of Rainfall(R) (mg/L-N) (gpd) tration(Nw) cation(d) (Plate 7) (in.) (mg/L-N) 1 18.5 1.26 350 1 35.00 1 30% 1 1.28 * Maximum contaminant level (MCL) for nitrate in drinking water is 10 mg/L-N. 5.6 Impact of Nitrate Loading to Nearby Water Sources 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 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 4.3 mg/L-N. As discussed above, the depth to groundwater is approximately 70 to 80 feet below ground surface at the site. The background concentration of nitrate detected in the domestic well for the site is 4.3 mg/L-N. Based on the methods and assumptions described, the project will result in nitrate of 18.5 mg/L-N. However, the depth to groundwater for this site is approximately 70 to 80 feet below ground surface. Based on the very low background nitrate concentration detected, the low-density septic systems for the area, the moderate percolating clayey loam 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 such as an engineered septic are not warranted at this time, however, a standard septic system with an oversize Petralogix Engineering,InC. - 26675 BruelIa Road,Galt,Ca 95632 "` (209)-40o-5729 www.petralogix.com