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.. K L E I N F E L D E R EXPECT MORE` _ Average calculated nitrate-nitrogen in groundwater resulting from leach field N` source and precipitation — mg/l, as N. Volume rate of waste water entering the soil averaged over the gross developed I = area = 3.82 inches per year (calculated as follows: ([30,730 gal/week x 52 weeks/year x 0.1337 cubic fugal]/[15.4 acres x 43,560 sq ft/acre]) x 12 inches/ft) Nitrate concentration of nitrified leach-field effluent (mg/1) = 45 MMI (The HantzsGhe NW = and Finnemore (1992) technical paper indicates that the average total nitrogen concentration in septic tank effluent ranges from 35 to 45 mg/l. This range was also reported in the 1996 Dames and Moore technical memorandum.) Fraction of nitrate-nitrogen loss due to dentrification of leach field effluent = 0.30 percent (Per Hantzsche and Finnemore (1992), 0.10 to 0.35 is typical). The 0.30 D = value was selected given that groundwater in the project area is relatively deep and the subsurface soils are interbedded with fine-grained soils that would inhibit or slow infiltration of effluent to the groundwater Average recharge rate of rainfall = 9.6 inches per year (representing 80 percent of R = the average annual rainfall of approximately 12.0 inches. The remaining 20 percent ., of rainfall is assumed to drain off-site into natural or manmade drainages or be lost to evapotranspiration.) Background nitrate nitrogen concentration of rainfall recharge at the water table = Nb = 0.5 mg/I (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 = 3.82(45)(1-0.30) + 9.6(0.5) = 9.33 mg/I as N (3.82 + 9.6) Given the above factors, we estimate that the proposed Pilot Travel Center would require an average waste/sewage flow of 34,090 gallons per week in order to exceed the state drinking water standard for nitrogen (N) of 10 mg/I in groundwater. 10. CONCLUSIONS The results of our percolation tests indicate that a suitable soil percolation stratum does exist at the percolation test location at the SJCEHD observed depths tested of about 3, 4, 6'/2, and 9 feet below existing site grade. A suitable soil condition is defined as a stratum capable of percolating water at a rate of 60 min/inch or faster at shallow depths and 30 min/inch for deep tests. 82946.G01/ST07R401/siw:1y/Ir May 30,2007 0 2007 Kleinfelder Page 6 of 8