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7Nw— Total nitrogen concentration of wastewater at 56 mg N/L based on average of three effluent samples. Does not account for loss of nitrogen in septic tanks (15%)car through biomat(10%+). d = Fraction (%) of nitrate-nitrogen loss due to denitrif cation in the soil R = Average recharge rate of rainfall - 17 inches per yr Nb = Background nitrate-nitrogen concentration of rainfall recharge, exclusive of wastewater influences (ppm NO3-N) Values and Assumptions 1= 1,971,000 gals = total WW/yr=263,502 cu ft/yr= 3.43 in/yr 21.19 Ac x 43,560 sq ft/Ac x (1 ft/12 in) Nw='56 mg N/L d = Assume 15% due to a fine-grained silt soil at soil/effluent interface. R = 17 in/yr. N, = Assumed to be 0.1 ppm NO3-N 3..43 in/yr(56 mg N/L)_R-_0.15) + (17 in/yr x 0.1 mg/L) Nr = (3.43 in/yr+ 17 in/yr) Nr = 8.1 ppm as nitrate-nitrogen (NO3-N) or 36.1 ppm as nitrate (NO3) Nr under the Maximum Contaminant Level (MCL) for nitrate-nitrogen at 10ppm. 2. Kaplan Parallele i ed Method Assumptions: 1.) The entire concentration of Total Nitrogen (56 ppm) is completely nitrified and percolates to the water table, 2.) Water table depth of five feet (mixing layer) is used, 3.)' Porosity is 37%, 4.) The entire length(N-S) of the project is used, 5.)No nitrogen input from on-site landscape fertilization, 6.) Water table Darcy velocity is assumed to be 2.3 ft/day as calculated on Page 9, 7.) Groundwater flow direction is west, as projected by the 1999 Lines of Equal Elevation. Volume of dilution: 1,200 ft length x 5 ft depth mixing layer x 2.3 foot/day x 365 days/yr x 1 m3/35.3 ft' = 142,690 in = 142,691,220 kg water/yr x 37%porosity= 52,795,750 kg water/yr- Amount of Nitrate: Taking the average of the lbs N/yr as determined, based on 6 kg N/person/yr= 792 lbs N/yr x 0.4536 (conversion factor) =359 kg N/yr ' Increase in Mixing Layer Concentration: 359 kg N_ 52.796 million kg water= 6.8 ppm NO3-N (30.3 ppm,NO3). The increase in mixing layer nitrate concentration as predicted by the Kaplan Method is 16% less than the Hantzsche/Finnemore Equation determination(6.8 ppm NO3-N vs. 8.1 ppm NO3-N). Page -13- Chesney Consulting