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'�✓ KLEINFELDER 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.) NW = Nitrate concentration of nitrified leachfield effluent (mg/1) = 40 mg/1 ((Hantzsche and Finnemore (1992)based on residential uses.) D = Percent dentrification of leachfield effluent=0.3 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore (1992)). 0.3 selected given the interbedded clay strata and the depth to groundwater. R = Annual deep percolation of precipitation (inches) = 12.4 inches (representing 75 percent of the average annual rainfall of approximately 16.5 inches. The remaining 25 percent of rainfall is assumed to drain off-site into natural or manmade drainages or be lost to evapotranspiration.) Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = 0.5 mg/l (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico Urban Area, page 6, Dames and Moore, April 1996) Our calculation is as follows: ` Nc = 0.4(2)(40)(1 —0.3) + 0.5(12.4) = 22.4 + 6.2 = 2.2 mg/l as N 0.4(2)+ 12.4 0.8 + 12.4 boo 8. CONCLUSIONS The results of our percolation tests indicate that a suitable soil percolation stratum exists at the percolation test location at the depth tested of about 22 feet below existing site grade. A suitable soil condition for tests deeper than 3%Z feet is defined as a stratum capable of percolating water at a rate of 30 min/inch or faster. Based on these results, it is our professional opinion that a conventional septic tank/leach trench sewage disposal system with seepage pits designed per SJCEHD criteria should adequately serve the proposed residence, and there is no need for an engineered system to be installed at the site. The seepage pits should extend into the more sandy soils that were encountered from a depth of about 20 feet below the existing site grade to the maximum depth explored of about 25 feet below the existing site grade. As previously discussed, we calculate 2.2 mg/1 of nitrate-nitrogen (N) in groundwater resulting from the proposed leach fields, a result that is below the state drinking water standard of 10 ` mg/l. Based on this level of nitrate-nitrogen, we anticipate that the impact on surrounding wells will be low. Coyote Creek is the nearest water body to the site and is located approximately 3/4 mile north of the property. Due to the distance to Coyote Creek, the depth to groundwater (greater than 100 feet), and the shallow nature of the creek, we anticipate that the impact to surface water will be low. 51727.G01/ST04R1700 December 17,2004 ©2004 Kleinfelder,Inc. Page 5 of 6 r..