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D. CALCULATED IMPACT FROM NITRATE-NITROGEN LOADING <br /> The calculated (or estimated) nitrate impact to the soil and ultimately to the groundwater is extremely <br /> difficult to determine due to the number of variables involved. The following calculations are based <br /> on using a conventional or traditional type of septic system consisting of two septic tanks, leachfield <br /> and seepage pits. <br /> HANTZSCHE/FINNEMORE EQ UA TION FOR SEPTIC SYSTEM IMPA CT <br /> INw(1 =d)+RNb <br /> Nr= (1+R) <br /> Where: <br /> Nr= Resultant average concentration of nitrate-nitrogen in recharge water- (ppm NO3-N) <br /> 1 = Volume rate of wastewater entering the soil averaged over the gross developed area in ' <br /> inches per yr <br /> Nw= Total nitrogen concentration of wastewater in N mglL (66 mg N/L/day) <br /> d = Fraction (%) of nitrate-nitrogen loss due to denitrification in the soil <br /> R = Average recharge rate of rainfall - inches per yr(13) <br /> Ne= Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater <br /> influences (ppm NO,-N) <br /> Values and Assumptions - <br /> `� ' <br /> 68 gals/person/day x 4 people per household x 3 new houses+ 1 existin house17.32 Ac x 365 d/ =2.00 in/yr. <br /> 1= 43,560 cu ft/Ac ft x-7.48 gal/cu ft x (1 ft/12 in) <br /> Nw= 66 mg/L - 20%reduction from two septic tanks in.series = 53 mglL N <br /> d = 10% from biomat and 15% from saturated clay soil conditions under leachlines and seepage pits. <br /> Nb= Assumed to be 0.1 ppm NO3-N <br /> l 2.00 in ,r (53 mg N/L) 1 - 0.25 + 13.5 in/yr x 0.1 mg/L) <br /> Nr — (2.00 in/yr + 13.5 in/yr) <br />�4 t <br /> Nr = 5.2 ppm as NO3-N or 23.2 ppm as NO, <br /> 6,g <br /> 9 <br /> Che mey Consulting <br /> A <br />