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� KLEINFELDER X. PERCOLATION TESTING AND NITRATE LOADING CALCULATIONS . Based on our experience and discussions with the San Joaquin County Environmental Health Department (EHD), deep percolation tests were performed in anticipation of the need of seepage pits. In other words, the surface and near-surface clay soils do not percolate well causing the standard 3 foot deep percolation tests to fail. The test borings drilled for this investigation were purposely extended to depths where more permeable sand and silt soils were encountered. Several inches of gravel were placed in the bottom of the hole and a perforated plastic pipe was placed in each boring to prevent caving. Each percolation hole was partially filled with water on January 14, 1999 (the day the holes were drilled), and the actual percolation tests were performed the following day. The percolation tests were performed over a time period of approximately 4 hours in accordance with guidelines established by San Joaquin County. The last 30 to 60 minutes of each test was witnessed by a representative of San Joaquin County. The signed field test forms for each percolation test are presented on Plates A-11 through Al 6. The percolation results varied from 8.6 minutes per inch to 60 minutes per inch with the average of the 6 tests being 30 minutes per inch. We were also requested by Mr. Mike Huggins of the EHD to calculate the nitrate loading for the proposed leach field. As you are aware, the drinking water standards for nitrate is 45 milligrams per liter (NO,) and 10 mg/I as Nitrogen (l). In our evaluation of nitrate loading, we have used the Hantzsche mass balance equation which is presented below with an explanation for each factor and the value used in our study. NcfAW x NK 1-D)+ b) AW+r Where: Nc = calculated nitrate concentration in groundwater resulting from domestic sources and precipitation—mg/l,as N A = number of dwelling units per acres on septic tanks (unit/acre)=0.1 W = annual wastewater loading per dwelling unit per acre (inches) = 2.0 inches (based on 150 gpd/residence) Nw = nitrate concentration of nitrified leachfield effluent(mg/1)=40 mg/l to 60 mg/l as N D = percent dentrification of leachfreld effluent=0.25 to 0.10 = annual deep percolation of precipitation (inches) = 3.0 inches (based on 13.5 inches precipitation,2 inches runoff and 8.5 inches ET) Nb = background nitrate concentration of the deep percolating precipitation—mg/l=2.2 mg/1 as N In our selection of parameters for this equation, we have made use of previous studies by our firm, as well as a report dated March 19, 1997, by Questa Engineering Corporation and authored by Mr. Norman Hantzsche. Mr. Hantzsche prepared a report for a subdivision in the Morada area which has similar fine grained silt and clay soils as encountered at the Lone Tree Subdivision site. Since several of the parameters could vary significantly, we have prepared, following Mr. Hantzsche's example, a low and high estimate of nitrate loading. Because of the 20-4280-OI.G01/20I9RI50 Page 9 of 12 Copyright 1999 Kleinfelder,Inc. April 14, 1999