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family residences over 158.8 acres, which represents the maximum concentration of homes on any of the three proposed parcels. Ne =AWN, (1-D) + (Nb) R AW+ R Where: NC = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation—mg/l, as N. A = Number of dwelling units per acre on septic tanks (unit/acre) = 0.01 (based on two a homes divided by 158.80 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.) Nµ, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 40 mg/I ((Hantzsche and Finnemore (1992)based on residential uses.) D = Percent dentrification of leachfield effluent = 0.2 percent (0.1 to 0.35 percent typical �. per Hantzsche and Finnemore (1992)). 0.2 selected given the interbedded clay strata and the depth to groundwater. R = Annual deep percolation of precipitation (inches) = 6.3 inches (representing 70 percent of the average annual rainfall of approximately 9 inches. The remaining 30 percent of rainfall is assumed to drain off-site into natural or manmade drainages or be lost to evapotranspiration.) Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = 0.5 mg/l (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico Urban Area,page 6, Dames and Moore, April 1996) Our calculation is as follows: Ne = 0.01(2)(40)(1 —0.2) +0.5(6.3) = 0.64 + 3.2 = 0.6 mg/1 as N 0.01(2) + 6.3 0.2 + 6.3 8. CONCLUSIONS ` The results of our percolation tests indicate that the near-surface soils exhibit suitable percolation characteristics. A suitable soil condition for a test between 3 and 3'/2 feet is defined as a stratum capable of percolating water at a rate of 60 min/inch or faster. L 48524.G0I/ST04R1163 September 3,2004 ©2004 Kleinfelder,Inc. Page 6 of 8 r