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k" KL E I N F E L D E R <br /> Where: <br /> N, = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources <br /> and precipitation—mg/l, as N <br /> A = Number of dwelling units per acre on septic tanks (unit/acre) = 1.10 (estimated <br /> based on 10 residences, 2 per parcel, divided by 9.1 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 /> Nw = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/l typical <br /> (communication with Mr. Mike Huggins with SJC/EHD) <br /> D = Percent denitrification of leachfield effluent = 0.25 percent (0.1 to 0.35 percent <br /> typical per Hantzsche and Finnemore ([1992]). Percent denitrification selected <br /> based on depth of groundwater and presence of interbedded low percable soil strata <br /> R = Annual deep percolation of precipitation (inches) = 13.6 inches (representing 80 <br /> percent of average annual rainfall of 17 inches in project area. Remaining 20 <br /> percent of rainfall is assumed to drain off-site into natural or manmade drainages) <br /> Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = <br /> 0.5 mg/l (per Technical Memorandum, Hydrologic and Soil Investigation for the <br /> Chico Urban Area, page 6, Dames and Moore, April 1996) <br /> Our calculation is as follows: <br /> Nc = 1 10(2)35)(1 —0.25) +0.5(13.6) = 57.8 + 6.8 = 4.09 mg/1 as N <br /> 1.10(2)+13.6 2.2 +13.6 <br /> CONCLUSIONS <br /> Based on the above evaluation, we conclude that wastewater produced by the proposed leach <br /> fields, combined or individually, should not have a nitrate as nitrogen (N) concentration at the <br /> groundwater level greater than 10 mg/l. The results of our percolation tests indicate that a <br /> suitable soil percolation stratum exists at a depth of about 3.5 feet at the locations tested in <br /> Parcels 1 (retest) and 4. For Parcels 2, 3 and 5, the results of our percolation tests indicate that a <br /> conventional septic tank/leach trench sewage disposal system with seepage pits should <br /> adequately serve the proposed development. The seepage pits should extend to the sandy soils <br /> underlying the site that were encountered at depths ranging from about 9 to 12 feet below site <br /> grade. <br /> 22276.G01/ST02R677 November 5,2002 <br /> ©2002 Kleinfelder,Inc. Page 4 of 5 <br />