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n n <br /> { September 30, 2007 <br /> NOA Project Number: E07146A <br /> e average total nitrogen concentration of domestic waste water is normally considered to be <br /> 20-8"/'L-N with 35 to 45 mg/L-N being typical (Crites and Tchobanoglous, 1998). It is <br /> estimated that commercial use will have higher concentrations of total nitrogen when compared to <br /> residential use. It is estimatedZt-a-t-thea�rage concentration for total nitrogen in waste water for <br /> the project is approximately 60 mg/L-N o er the long term. <br /> 4.4.2 Denitrification Estimate <br /> i. <br /> Denitrification is an important process which occurs within the leach field whereby certain bacteria <br /> utilize the oxygen in the nitrate (NO3) and release nitrogen gas (N� to the atmosphere. <br /> Denitrification is expressed as a percentage,and the normally accepted range is 10 percent to 35 <br /> percent. Soils with higher clay content, moist soil conditions, high pH, and organic material <br /> denitrify by about 35 percent, and soils with high sand content and fast percolation rates are <br /> estimated to denitrify at a lower rate, about 10 percent to 15 percent. <br /> �j A denitrification factor of 25 percent was selected for the site due to the silty nature of the soils. <br /> f SI 1/4.5 Nitrate Loading Scenario <br /> A nitrate loading scenario was performed to determine the impact from the proposed project. The <br /> ` scenario utilizes the variables discussed previously which represent the estimated conditions and <br /> 1 uses associated with this project. The following table presents a summaty of the nitrate loading <br /> {�! calculation for each parcel. <br /> Table 2. <br /> / <br /> S mmary of Nitrate Mass Balance alysis. <br /> 1/ Result Average Daily Effluent Deep <br /> F1 <br /> Ixachfield <br /> 1 1 Plate (Nc)* Acres Flow(Q) Concen- Denitrifi- Percolation of <br /> t t ( (A) (Table 3) tration(Nw) cation(d) Rainfall(R) <br /> (gpd) (mg/L-N) <br /> Subject 5.4 1.5 126 80 25% 14.06 <br /> ( Pro er <br /> j * Maximum contaminant level(MCL) for nitrate in drinking water is 10 mg/I'N. <br /> I <br /> `1 l 7 4.6 Impact of Nitrate Loading to Nearby Water Sources <br /> I <br /> FI Based on the method and assumptions described, the result of the nitrate loading balance indicates <br /> that the proposed development on the proposed parcels should not cause a build up of nitrates in <br /> the aquifer above 10 mg/L-N. <br /> Since the site is relatively flat,we do not predict that percolating effluent will affect any surface <br /> water resources. <br /> 5 <br /> i ! 1 <br />