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Fj <br /> March 28, 2007 <br /> NOA Project Number: E06122A <br /> residential use. It is estimatec_tha the average concentration for total nitrogen in waste water for <br /> the project is approximately 85 mg/L-N ov r the long term. <br /> 3.4.2 DenitriScation Estimate <br /> Denitrification is an important process which occurs within the leach field whereby certain bacteria <br /> 0 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 /> Fdenitrify 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 /> A typical denitrification factor of 35 percent was selected for the site because of the fine grained 6 .0 <br /> soils that exist at the site. <br /> 3.5 Nitrate Loading Scenario <br /> A nitrate loading scenario was performed to determine the impact from the proposed project. The <br /> Fj 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 the parcel. <br /> F1 Table 2. <br /> Fi�� Summa of Nitrate Mass Balance Anal sis. <br /> Parcel Result Acres Average Daily Effluent Leachfield Deep p <br /> F _ (Nc)* (A) Flow(Q) Concen- Denitrifi- Percolation of <br /> (mg/UN) (Table 3) tration(Nw) cation(d) Rainfall(R) <br /> F (gpd) (mg/L-N) (Plate 9) (in.) <br /> 1 23.1 4.97 1,186 85 35% 4.67 <br /> * Maximum contaminant level(MCI.)for nitrate in drinking water is 10 mg/I—N. <br /> Fad / <br /> 3.6 Impact of Nitrate Loading to Nearby Water Sources <br /> 7i Based on the method and assumptions described,in addition to the geologic setting,we believe the <br /> proposed project could cause a build up of nitrate in the ground water above 10 mg/L-N over the <br /> long term. <br /> Since the Site is relatively flat,we do not foresee percolating effluent affecting any surface water <br /> resources. <br /> F! <br /> 6 <br /> FJ <br /> { <br />