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KLEINFELDER ,i, A = Number of dwelling units per acre on septic tanks (unit/acre) = 4.0 (estimated rased on two homes divided by 0.5 acres) W = Annual wastewater loading per dwelling unit per acre (inches) =2.0 inches (per year per dwelling unit assuming a flow of 150 gal./day/dwelling unit) NW = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/1 typical (Hantzsche and Finnemore (1992)) Percent denitrification selected based on depth to groundwater and presence of interbedded low-percable soil strata. D = Percent denitrification of leachfield effluent = 0.35 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore (1992). 0.35 selected given the large depth to groundwater(>75 feet)) R = Annual deep percolation of precipitation (inches) = 12.33 inches (representing 85 percent of average annual rainfall of 14.5 inches in project area. Remaining 15 percent of rainfall is assumed to drain off-site into natural or manmade drainages) Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = 1.0 mg/l (typically ranges from 0.5 to 1.0 mg/1 per abstract titled "Predicting Ground-water Nitrate Nitrogen Impacts"by Hantzsche and Finnemore (1993)) Our calculation is as follows: N, = 4 2 35 1 —0.35 + 12.33(l.0) = 182 + 12.33 = 9.60 mg/1 as N 4(2)+12.33 8 + 12.33 CONCLUSIONS Based on the above evaluation, we conclude that wastewater produced by the maximum possible number of leach fields allowed combined or individually should not cause the nitrate levels in groundwater below the site to rise above the state standards. Furthermore, the results of our percolation tests indicate that a conventional septic tank/leach trench sewage disposal system draining to seepage pits should adequately serve the proposed residence. As an alternative to seepage pits, disposal trenches could be cut deep to intercept the percolating sand stratum. LIMITATIONS The conclusions of this report are based on the information provided regarding the existing and proposed development and on the site conditions. It was assumed that the percolation test results are representative of the subsurface conditions in the general area. M i 20-4684-01.GO1/ST02R73[ November 5,2002 O 2002 Kleinfelder,Inc. Page 4 of 5