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i �p k4 K L E I N F E L D E R Impacts, Hantzsche and Finnemore (1992)), which is presented below with an explanation for each factor and the value used in our study. The selection of parameters was based on previous studies and investigations performed by our firm and others, San Joaquin County Sewage Standards, and information provided in a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by Mr. Hantzsche for a development in the Stockton area. + _ N,—AWN W (1-D (Nb) R AW+ R Where: N, — 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) = 0.625_(estimated based on an estimated water usage of 90 gal./day, a typical water usage for 6 employees at 15 gal/employee per the SJC PHS/EHD Sewage Standards divided b 150 gal./day to obtain an equivalent number of homes, divided by 0.96 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) N,,, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/l typical (Hantzsche and Finnemore (1992)) D = Percent dentrification of leachfield effluent = 0.25 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore ([1992]). R = Annual deep percolation of precipitation (inches) = 7.6 inches (representing 80 percent of average annual rainfall of 9.5 inches in project area. Remaining 20 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 = 0.5 mg/1 (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico Urban Area, page 6, Dames and Moore, April 1996) Our calculation is as foll� D NG = 0.625(2)(35)(1 —0.25) +0.5(7.6) — 32.8 + 3.8 = 4.1 mg/l as N 0.625(2)+7.6 1.25 +7.6 g gr CONCLUSIONS Based on the above evaluation, we conclude that wastewater produced by the proposed leach field should not have a nitrate as nitrogen (N) concentration at the groundwater level greater than 10 mg/1. Furthermore, the results of our percolation tests indicate that a conventional leach trench 12573/200212320 April 16,2002 _ ©2002 Kleinfelder,Inc. Page 3 of 4 r