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L KLEINPELDER <br /> I <br /> L Where: <br /> Ne = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources <br /> L and precipitation—mg/l, as N. <br /> A = Number of dwelling units per acre on septic tanks (unit/acre) = 0.025 (estimated <br /> based on a maximum of 2 residences per parcel divided by 80 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 /> j N,,, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/l (Hantzsche and <br /> L Finnemore (1992)). Percent denitrification selected based on past discussions with <br /> Mr. Mike Huggins of SJCEHD. <br /> D = Percent dentrification of leachfield effluent = 0.35 percent (0.1 to 0.35 percent <br /> typical per Hantzsche and Finnemore (1992). 0.35 selected given the deep depth to <br /> groundwater and interbedded strata of low-permeable soils. <br /> L <br /> R = Annual deep percolation of precipitation (inches) = 13.6 inches (representing 80 <br /> percent of average annual rainfall of approximately 17 inches in project area. <br /> ` Remaining 20 percent of rainfall is assumed to drain off-site into natural or <br /> manmade drainages.) <br /> ` Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = <br /> 0.5 mg/1 (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 /> L <br /> N, = 0.025(2)(35)(1 —0.35) + 0.5(13.6) = 1.14 + 6.8 = 0.6 mg/l as N <br /> 0.025(2) + 13.6 0.05 + 13.6 <br /> 8. CONCLUSIONS <br /> 6.. <br /> As shown above, we calculate 0.6 mg/1 of nitrate-nitrogen (1) in groundwater resulting from the <br /> proposed leach fields, a result that is well below the state standard of 10 mg/l. Based on this <br /> L relatively low level of nitrate-nitrogen, we anticipate that the impact on surrounding wells will be <br /> minimal and no remediation will be necessary. Goose Creek and an unnamed reservoir are the <br /> nearest natural water bodies to the site and are located about 1/4 to 1/3 mile from the site, but are <br /> generally not down gradient. Based on this distance and the relatively low nitrate-nitrogen levels <br /> calculated, we anticipate that the impact to water bodies will be minimal and no remediation will <br /> be necessary. There also appear to be two unnamed creeks west of the site; however, these <br /> 6. appear to be predominantly dry creeks that will carry water only during storm events. <br /> 36600.G01/ST03RI537 October 16,2003 <br /> ©2003 Kleinfelder,Inc. Page 6 of 7 <br /> L <br />