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`. KLEINFELDER LNe=AWN, (1-D) + (Nb R AW+R Where: L Ne = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources L — and precipitation—mg/1, as N. A Number of dwelling units per acre on septic tanks (unit/acre) = 0.37 (estimated based on two homes on each of the ten lots divided by 54.7 acres.) L 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.) 6. Nw = Nitrate concentration of nitrified leachfield effluent (mg/1) =35 mg/1 (Hantzsche and Finnemore (1992)). Percent denitrification selected based on depth to groundwater and presence of interbedded low-percable soil strata. 6 D = Percent dentrification of leachfield effluent = 0.35 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore (1992). 0.35 selected given the large depth to groundwater(90+ feet). 6. R = Annual deep percolation of precipitation (inches) = 8.4 inches (representing 70 percent of average annual rainfall of approximately 12 inches in project area. Remaining 30 percent of rainfall is assumed to drain off-site into natural or L 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 L Chico Urban Area, page 6, Dames and Moore, April 1996) Our calculation is as follows: L Ne = 0.37(2)(35)(l -0.35) +0.5(8.4) = 16.84+4.2 = 2.3 mg/l asN 0.37(2)+8.4 0.74 +8.4 L CONCLUSIONS As shown above, we calculate 2.3 mg/1 of nitrate-nitrogen (1) in groundwater resulting from the ` proposed leach fields, a result that is below the state standard of 10 mg/l. Based on this relatively low level of nitrate-nitrogen, we anticipate that the impact from the proposed construction on surrounding wells will be minimal. Little Johns Creek is the nearest natural L water body to the site and is located approximately 0.7 miles down gradient from the site. Based on this distance and the relatively low nitrate-nitrogen levels calculated, we anticipate that the impact to water bodies will be minimal The results of our percolation tests for Lots 1, 8, and 26 indicate that the near surface soils (at a depth of about 3 to 3'/2 feet) exhibit suitable percolation characteristics. A suitable soil condition for a test at this depth is defined as a stratum capable of percolating water at a rate of 60 min/inch or faster. A conventional septic tank/leach trench sewage disposal system designed per SJCEHD Lcriteria should adequately serve the proposed residences. L L32585.G01/ST03R1168 November 26,2003 L ©2003 Kleinfelder,Inc. Page 5 of 6