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Nov. 20. 2001 11 : 53AN 14L I q r SIONET STL Project No. 0010771 �Ia� Appendix n Page n.2 There is a 20 percent removal of nitrogen in the septic tank before discharge to the leach field (Kaplan., O. Benjamin, Septic Systems Handbook, page 148, 1988, Lewis Publishers). Denitrification is the process by which nitrogen gas is released into the environment as bacteria consumes tate oxygen available from nitrate in the affluent. Denitrification is expressed as a percent of the original concentration of nitrogen in the matrix. Soils with high organic contents, high pH, and high moisture contents, typically clays denitrify about 35 percent on the high end. Sandy Soils with a high percolation rate denitrify at a much lower rate, on the order of 10 to 15 percent, We have assumed a denitrification factor of 15 percent. The average precipitation in the region is around 17 inches per year. We have estimated that the deep percolation of rain is on the order of 8 inches per year, which is consistent with Department of Water Resources published data. The background concentration of rainwater was estimated at 0.17 mg/L N, based on the values provided by Hantzsche and Finnemore, 1991. Waste Loading Calculation: 1=(19gal/day)(icf/7.48gaIX16.Spersons/4acres)(lacre/43,560sfxl2in/ft)(365day/year) I = 1.0 inch/year Nw= (15g/dayperson)(1,000mg/g)(0.8—200/0 reduction in tank)(80gpd)(1gaU3.78L) Nu—40mg/L as N Combined Loading Cakulation' Nc= [(1-0 in/year)(40mg/L as Nx1-0.15)+ (8 Wyear)(.l7mglL-N)j/(Iin/yr + 8 inlyr) Ne= 4 mg/L as N (less than MCL = 10 mg/L as N) The results of the analysis indicate that a conventional septic system should be sufficient to handle the anticipated effluent without signtfteant risk of the development of methemoglobinemia. This conclusion is based solely upon the degree of accuracy for the method of determination and the assumptions utilized therein.