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d = Fraction(%)of nitrate-nitrogen loss due to denitrification in the soil <br /> R = Average recharge rate of rainfall- inches per yr <br /> Nb= Background nitrate-nitrogen concentration of rainfall recharge,exclusive of wastewater influences <br /> (ppm NO3-N) <br /> Values and Assumptions <br /> I= 2400 gpd x 365 d/yr=876,000 gals=total WW/yr= 117,112 cu ft = 1.61 in. <br /> 20 Ac x 43,560 sq ft/Ac x(1 ft/12 in.) <br /> Nw = 113 mg N/L:20%N reduction occurring in the septic tank and 10%in biomat=(1-0.3)113=79 mg N/L <br /> d = Assume 25%due to the native clay soil and therefore high denitrification potential. <br /> R = 10.5 in/yr. <br /> Nb= Assumed to be 0.1 ppm NO3-N <br /> 1.61 in/yr(79 mg N/L) 0 -.25)+(10.5 in/6r x 0.1 mg/L) <br /> Nr = (1.61 in/yr+ 10.5 vetyr) <br /> Nr 8.0 ppm as nitrate-nitrogen(NO3-N)or 35.8 ppm as nitrate <br /> To determine the nitrogen concentration emanating from the recharge effluent on a"pounds per acre per <br /> year,the Crites/Tchobanoglous Formula is used below and discussed further in the Conclusions Section. <br /> Crites/Tchobanoglous Formula <br /> LN = Lw CNF <br /> Where: <br /> LN = nitrate-nitrogen loading in lbs/ac-day <br /> LW = wastewater loading in gals/ac-day=2,400 gals/day-20 ac= 120 gals/ac-day <br /> Cr, = nitrogen concentration:average determined to be 79 mg N/L <br /> F= conversion factor: 8.341bs/[10'gal-(mg/L)] <br /> LN= 120 gats/ac-day x 79 mg N/L x (8.34)(10')=0.0791 lbs N/ac•day x 365 days/yr= <br /> 28.9 lbs N/ac/yr. <br /> The disposal area will be approximately 215 ft x 70 ft= 15,050 sf,or 0.35 acres. <br /> 0.35 acres x 28.9 lbs N/ac/yr = 10 lbs N/Disposal Area/yr <br /> 10 <br />