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I <br /> " - M KLEINFEFDER <br /> 1 <br /> A — Number of dwelling units per acre on septic tanks (unit/acre) = 4.0 (estimated based <br /> on two homes divided by 0.5 acres) <br /> W = Annual wastewater loading per dwelling unit per acre (inches) =2.0 inches (per'year <br /> per dwelling unit assuming a flow of 150 gal./day/dwelling unit) <br /> Nom, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/I typical <br /> f (Hantzsche and Finnemore (1992)) Percent denitrification selected based on depth <br /> to groundwater and presence of interbedded Iow-percable soil strata. <br /> w <br /> D — Percent denitrification of leachfield effluent = 0.35 percent (0.1 to 0.35 percent <br /> typical per Hantzsche and Finnemore (1992). 0.35 selected given the large depth to <br /> groundwater(>75 feet)) <br /> R = Annual deep percolation of precipitation (inches) = 12.33 inchesre resentin <br /> { p g 85 <br /> percent of average annual rainfall of 14.5 inches in project area. Remaining' 15 <br /> percent of rainfall is assumed to drain off-site into natural or manmade drainages) <br /> g ) <br /> Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = <br /> 1.0 mg/I (typically ranges from 0.5 to 1.0 mg/1 per abstract titled "Predicting <br /> Ground-water Nitrate Nitrogen Impacts"by Hantzsche and Finnemore (1993)) j <br /> Our calculation is as follows: <br /> N, = 4 2 35 1 —0.35 + 12.33(l.0.) = 182 + 12.33. = 9.60 mg/1 as N <br /> 4(2)+12.33 8 + 12.33 <br /> CONCLUSIONS <br /> Based on the above evaluation, we conclude that wastewater produced by the maximum possible <br /> number of leach fields allowed combined or individually should not cause the nitrate levels in <br /> groundwater below the site to rise above the state standards. Furthermore, the results of.',our <br /> percolation tests indicate that a conventional septic tank/leach trench sewage disposal system <br /> draining to seepage pits should adequately serve the proposed residence. As an alternative to <br /> seepage pits, disposal trenches could be cut deep to intercept the percolating sand stratum. <br /> LIMITATIONS <br /> The conclusions of this report are based on the information provided regarding the existing and <br /> proposed development and on the site conditions. It was assumed that the percolation test results <br /> are representative of the subsurface conditions in the general area. <br /> I' <br /> I <br /> 20-4684-0 I.GO 1/ST02R731 <br /> November 5,2002 <br /> ©2002 Kleinfe[der,Inc. Page 4 of 5 <br />