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12172 N Hibbard Road Project No. 2021-00063 P a g e | 7 <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 <br />(Nc) * <br />(mg/L-N) <br />Acres <br />(A) <br />Average Daily Flow <br />(Q) <br />(gpd) <br />Effluent <br />Concen- <br />tration (Nw) <br />(mg/L-N) <br />Leachfield <br />Denitrifi- <br />cation (d) <br />Deep Percolation <br />of Rainfall (R) <br />(Plate 7) (in.) <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.