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12958/12970 E Jahant Road Project No. 2022-00037 Page 17 For the site, the total daily toilet use contributing wastewater quantity, considering the existing and planned residential dwellings is 750 gallons per day. The average total nitrogen concentration of domestic wastewater is normally considered to be 20-85 mg/L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). Based on EHD request with previous studies, it is estimated that residential domestic wastewater concentration will be approximately 35 mg/L-N. 5.4.2 Denitrification Estimate Denitrification is an important process which occurs within the leach field whereby certain bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, and organic material denitrify by about 35 percent, and soils with high sand content and fast percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. Although there was clay and hardpan observed at the shallow percolation test layer, a sandy loam layer was observed from approximately 8 feet to 12.25 feet below ground surface. Based on the fine sandy loam soil type for the subject property, denitrification is estimated to be 25 percent. 5.5 Nitrate Loading A nitrate loading scenario was performed to determine the impact from the proposed project. The scenario utilizes the variables discussed previously which represent the estimated conditions and uses associated with this project. The following table presents a summary of the nitrate loading calculation for the parcel. Table 4. Srnmmnry of Nitrate MaCC Ralance Analvsis_ 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 8.4 4.59 750 35.00 25% 5.29 * Maximum contaminant level (MCL) for nitrate in drinking water is 10 mg/L-N. 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. Based on the methods and assumptions described, the project will result in nitrate 8.4 mg/L-N. The depth to groundwater for this site is approximately 155 to 160 feet below ground surface. Based on the mass balance analysis results, in addition to our professional judgement, low septic tank density, and geologic setting showing the deep groundwater table underlying the Site, we believe the proposed project will not likely cause a build-up of nitrate in the ground water above the background concentration of total Petralogix Engineering, Inc. 26675 Bruella Road, Galt, Ca 95632 (209)-400-5729 www.petraloglx.com