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k` ■ KLEINFELDER very little information is available on this subject. In the Chico area study, the California Regional Water Quality Control Board (CRWQCB) used a value of 2.2 mg/I reflecting primarily the fact that rainwater is considered relatively clean. Although the other parameters have essentially no effect on the equation, in their selection we have made use of previous studies by our firm as well as the report dated March 19, 1997 by Questa Engineering Corporation and authored by Mr. Norman Hantzsche. Mr. Hantzsche prepared a report for a subdivision in Stockton that had fine-grained silt and clay soils. The site in Escalon is more coarse-grained or sandy, however, the rainfall is similar. For these reasons, we have chosen to use the same or more conservative values considered appropriate by Mr. Hantzsche for the project in Stockton. An exception is D, which we have reduced to .15 to reflect the lack of clay soils in the area. The equation is as follows: N,AW x N,,,± -D)+(N_bZr AW+ r Where: N, = calculated nitrate concentration in groundwater resulting from domestic sources and precipitation—mg/I, as N A = number of dwelling units per acres on septic tanks(unit/acre)= .007 W = annual wastewater loading per dwelling unit per acre (inches) _ .5 inches (very conservative, based on 40 gpd/for the single employee restroom) N,,, = nitrate concentration of nitrified leachfield effluent (mg/1) = 60 mg/I as N (conservative assumption according to the Questa report) D = percent dentrification of leachfield effluent=0.15 r = annual deep percolation of precipitation (inches)= 5.0 inches(increase over the 3 inches used by Mr. Hantzsche in the Stockton area to reflect the more sandy soil conditions) Nb = background nitrate concentration of the deep percolating precipitation—mg/I =2.2 mg/l as N Our calculation is as follows: Low Estimate Nc _ .007 (.5) (60) (1 - .15) +2.2 (5) _ .178 + 11 = 2.2 mg/1 as N .007 (5) +5 .035 +5 As noted, N. of 2.2 is identical to Nb- When combined with our estimate for nitrogen in groundwater of between 6 to 7, it is our opinion that the single employee bathroom will not cause a rise in the nitrate levels above the state standard of 10 mg/1. LIMITATIONS The conclusions of this report are based on the information provided regarding the existing and proposed development and on the site conditions. It was assumed that the percolation test result is representative of the subsurface conditions in the general area. 20-1210-99/2019R1086 Page 3 of 4 Copyright 1999 Kleinfelder,Inc. December 14, 1999