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03/06/2006 13:33 FAX 0 040/041 <br /> + SH KLEINFELDER <br /> I - Volume rate of waste water entering the soil averaged over the gross <br /> developed area = 4.02 inches per year calculated as follows: (63,000 <br /> gaVweek (assuming 4,200 gal/week/lot) x 52 weeks/year x 0.133' cubic <br /> ft/gal)/(30 acres x 43,560 sq ft/acre)x 12 inches/ft) <br /> Nw = Nitrate concentration of nitrified leach field effluent (mg/1) = 35 mg/I typical <br /> (Hantzsche and Finnemore (1992)) <br /> D = Percent dentrification of leach field effluent = 0.25 percent (0.1 to 0.25 <br /> percent typical per Hantzsche and Finnemore (1992). 0.25 selected given <br /> the large depth to groundwater and the presence of interbedded low <br /> permeable clay layers.) <br /> R = Annual deep percolation of precipitation (inches) = 9.8 inches (representing <br /> 70 percent of the average annual rainfall of 14 inches in project area. <br /> Remaining 30 percent of rainfall is assumed to drain off-ste into natural or <br /> manmade drainages) <br /> Nb = Background nitrate concentration of the deep percolating precipitation - mg/I <br /> = 0.5 mg/I (per Technical Memorandum, Hydrologic and Soil Investigation <br /> for the Chico Urban Area, page 6, Dames and Moore, April 1996) <br /> Our calculation that includes both the proposed subdivision is as follows: <br /> N� = 4.02(35)(1-0.25) + (9,8)(0.5) = 7.99 mgR as N <br /> (4.02 + 9.8) <br /> Given the above factors, we estimate that the subdivision would require an average <br /> waste/sewage flow of almost 90,000 gal,/week in order to exceed the state drinking <br /> water standard for nitrogen (N) of 10 mg/I in groundwater. <br /> Conclusion <br /> Based on the above evaluation, we conclude that at the estimated groundwater level, <br /> the nitrate concentration of the wastewater produced by the maximum possible number <br /> of leach fields allowed should not exceed the state standards. <br /> Closing <br /> We have prepared this letter in substantial accordance with the generally accepted <br /> geotechnical engineering practice as it exists in the site area at the time of our study. <br /> No warranty is expressed or implied. <br /> 23197.GOVSTOL77-, March 6,2006 <br /> Copyright 2006 K OInfelder,Inc Page 3 of 4 <br />