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2. SUBSURFACE SOIL HYDRAULIC CONDUCTIVITY As referenced on the Log of Boring,the subsurface soils consist predominately of a sandy silt/silty sand, except for the hardpan stratum. The hydraulic conductivity (K) of the vadose zone (the zone above the water table) determines the downward flow characteristics of septic effluent and surface waters (e.g., rainfall and domestic irrigation). To quantify this parameter, the Shallow-Well Pump-In Test Method (Soil Science Society of America) was employed. The test was conducted in the above-referenced deep boring and measures the hydraulic conductivity below the hardpan layer, which ultimately determines downward migration of nitrate. A constant level of water was supplied to the boring. The rate at which water flowed into the soil (Q) was determined to be 40,000 cc/hr. The equation to determine the hydraulic conductivity (K) in cm/hr under conditions where there is o restrictive layer, is as follows: K= [In (hr) + ((h=r)z-1)0.5-1 IQ 2 lI h2 Where: h= 8 ft (244 cm) r= 0.21 ft(6.4cm) Q =40,000 cc/hr T, = 16 ft(488 cm) Therefore, K= 0.5 cm/hr The test results indicate the hydraulic conductivity of the subsoil strata possess a rapid permeability due to the sand soil structure under the hardpan stratum. These test results indicate it would theoretically take a nitrate molecule approximately 975 hrs or 41 days to travel from under the hardpan stratum to the water table, -20 ft below grade. C. PERCOLATION TEST RESULTS Percolation tests were conducted on November 30 under U.S.E.P.A. and San Joaquin County Environmental Health guidelines. Each boring was drilled to 40 inches to represent typical leachline depths. In accordance with PHS-EHD regulations, a perc test was not conducted on the Designated Remainder. As indicated on the attached FIELD PERCOLATION TESTING REPORT, the perc rates for Parcels 1 and 2 were 5.9 and 5.0 minutes per inch (min/in), respectively. These rates can be considered rapid and illustrate the porosity of the sandy soil. The tests exhibited a slowing of the perc rate over time as soil saturation increased. Test results are summarized below: 4 Valley AB Research