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�y�//'A/��� 1 iCLE/NFELOER <br /> Bright People.Right Solutions. <br /> NC <br /> Average calculated nitrate-nitrogen in groundwater resulting from leach field source <br /> = <br /> and precipitation — mg/I, as N. <br /> Volume rate of waste water entering the soil averaged over the gross developed area <br /> I = = 3.95 Inches per year (calculated as follows: ((35,000 gal/week x 52 weeks/year x <br /> 0.1337 cubic ft/gal)/(16.95 acres x 43,560 sq ft/acre)) x 12 inches/ft) <br /> Nitrate concentration of nitrified leach-field effluent (mg/1) = 40 mg/I (The Hantzsche <br /> Nw _ and Finnemore (1992) technical paper indicates that the average total nitrogen <br /> concentration in septic tank effluent ranges from 35 to 45 mg/I. This range was also <br /> reported in the 1996 Dames and Moore technical memorandum.) <br /> Fraction of nitrate-nitrogen loss due to dentrification of leach field effluent = 0.25 <br /> D = percent (Per Hantzsche and Finnemore (1992), 0.10 to 0.35 is typical). The 0.25 <br /> value was selected given the relatively deep depth of groundwater. <br /> Average recharge rate of rainfall = 9.0 inches per year (representing 90 percent of <br /> R _ the average annual rainfall of approximately 10.0 inches. The remaining 10 percent <br /> of rainfall is assumed to drain off-site into natural or manmade drainages or be lost <br /> to evapotranspiration.) <br /> Background nitrate nitrogen concentration of rainfall recharge at the water table = 0.5 <br /> Nb = mg/l (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico <br /> Urban Area, page 6, Dames and Moore, April 1996) <br /> Our calculation is as follows: <br /> NC _ 3.95(40)(1-0.25) + 9.0(0.5) = 9.5 mg/I as N <br /> (3.95 + 9.0) <br /> Given the above factors, we estimate that the proposed septic system would require an average <br /> waste/sewage flow of over 37,800 gal./week in order to exceed the state drinking water standard <br /> for nitrogen (N) of 10 mg/I in groundwater. <br /> 4.4 CONCLUSIONS <br /> The concentration of Nitrate found in the groundwater (5.3 mg/L) was below the drinking standard <br /> (10 mg/L). Even though the estimated waste/septic flow and nitrate concentration of the leach <br /> 20200144.001 A/ST019R95450 Page 8 of 12 May 8, 2019 <br /> 0 2019 Kleinfelder www.kleinfelder.com <br />