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n <br /> September 30, 2007 <br /> _= NOA Project Number: E07146A <br /> e'averageltotal nitrogen concentration of domestic waste water is normally considered to be <br /> 20-Sig--/'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 estimated--ffi-a theave age 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 Dc iviFcation 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 /> F1 estimated to denitrify at a lower rate, about 10 percent to 15 percent. <br /> A denitrification factor of 25 percent was selected for the site due to the silty nature of the soils. <br /> 14.5 Nitrate Loading Scenario <br /> A nitrate loading scenario was performed to determine the impact from the proposed pro)ect. The <br /> scenario utilizes the variables discussed previously which represent the estimated conditions and <br /> uses associated with this project. The following table presents a summary of the nitrate loading <br /> calculation for each parcel. <br /> Table 2. <br /> / Summa of Nitrate Mass Balance Analysis. <br /> �/ <br /> Result Average Daily Effluent Leachfield Deep <br /> Acres Flow(Q) Concen- Percolation of <br /> Plate (Nc)* (A) (Table 3) tration(Nw) anon(d Rainfall(R) <br /> (m ) (gpd) (mg/L-N) cation(d) 9 (in.) <br /> j Subject 5.4 1.5 126 80 25% 14.06 <br /> 1 <br /> Property <br /> * Maximum contaminant level(MCL) for nitrate in drinking water is 10 mg/L-N. <br /> F4.6 Impact of Nitrate Loading to Nearby Water Sources <br /> Based on the method and assumptions described, the result of the nitrate loading balance indicates <br /> F! 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 /> li <br /> 5 <br /> R <br />