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12172 N Hibbard Road Project No.2021-00063 Page 17 <br /> For the site, the total daily toilet use contributing wastewater quantity, considering the <br /> existing and planned residential dwellings is 450 gallons per day. The average total nitrogen <br /> concentration of domestic wastewater is normally considered to be 20-85 mg/L-N with 35 <br /> to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). Based on EHD request with <br /> previous studies, it is estimated that residential domestic wastewater concentration will be <br /> approximately 35 mg/L-N. <br /> 5.4.2 Denitrification Estimate <br /> Denitrification is an important process which occurs within the leach field whereby certain <br /> bacteria utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N2) to the <br /> atmosphere. Denitrification is expressed as a percentage, and the normally accepted range <br /> is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, <br /> and organic material denitrify by about 35 percent, and soils with high sand content and fast <br /> percolation rates are estimated to denitrify at a lower rate, about 10 percent to 15 percent. <br /> Based on the clay soil types for the subject property, denitrification is estimated to be 35 <br /> percent. <br /> 5.5 Nitrate Loading <br /> A nitrate loading scenario was performed to determine the impact from the proposed <br /> project. The scenario utilizes the variables discussed previously which represent the <br /> estimated conditions and uses associated with this project. The following table presents a <br /> summary of the nitrate loading calculation for the parcel. <br /> Table 4. <br /> Summary of Nitrate Mass Balance Analysis. <br /> Parcel Result Acres Average Daily Flow Effluent Leachfield Deep Percolation <br /> (Nc)* (A) (Q) Concen- Denitrifi- of Rainfall(R) <br /> (mg/L-N) (gpd) tration(Nw) cation(d) (Plate 7) (in.) <br /> (mg/L-N) <br /> 1 11.1 1.18 400 35.00 35% 5.29 <br /> * Maximum contaminant level (MCL) for nitrate in drinking water is 10 mg/L-N. <br /> 5.6 Impact of Nitrate Loading to Nearby Water Sources <br /> Based on the relatively flat topography of the site, we do not foresee percolating effluent <br /> affecting any surface water resources. <br /> Petralogix Engineering,Inc. <br /> 26675 BruelIa Road,Galt,Ca 95632 <br /> (209)-40o-5729 <br /> www.petralogix.com <br />