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KL EINFEL DER On June 5, 2002, a representative with our firm obtained a sample of groundwater using clean procedures from a spigot near the on-site well. The well was located approximately 300 feet east and 40 feet north of that parcel's southwest corner. The same day, the water sample was submitted to Sequoia Analytical using chain-of-custody procedures for DBCP and nitrate testing. The results of our tests and a copy of the chain-of-custody are attached. Basin Percolation Test One percolation test was performed during our investigation at a depth of about 10 feet below the existing ground surface. Normally, San Joaquin County requires a 5-foot separation between groundwater and the bottom of storm drainage basins. The approximate location of the test hole is shown on Plate 1. No free groundwater was encountered. The percolation test was performed in accordance with accepted guidelines using clear potable water. The procedure calls for maintaining a head of water approximately 3 feet above the bottom of the test hole. The water level in the test hole is recorded and reestablished in approximate 30-minute intervals for a period of at least 4 hours. The last 60-minute reading is then used to calculate the percolation rate in gallons per square foot per day (gfd). The estimated percolation rate is as follows: Test Number De th, t. Percolation Rate ( d) Soil Type P-1 10 19 Silty Sand There are many factors that influence storm water disposal. Clear water was used in our test, whereas oil residue, silt, organic matter, and other deleterious material will likely be included in the actual storm water. Variations in soil conditions within the basin will also likely affect percolation characteristics. For use in design, a factor of safety on the order of 1.5 to 2 should be applied to the percolation rate estimated. The above values apply to drainage trenches or drywells installed in the basin and possibly to the sides of the basin. Depending on the depth of the basin, the design percolation rates for the basin sides should be further reviewed. Over time, very little percolation should be assumed through the basin bottom due to silting and organic build-up unless a vigorous program is followed to maintain the basins by frequent cleaning and disking to reduce silt build-up. Subsurface drain trenches and/or drywells should be equipped with filtered intakes. Our representative should be allowed to observe the soils exposed during construction of the basin and subsurface trenches or drywells in order to confirm that the design rates used are appropriate for the actual soils encountered. NITRATE LOADING CALCULATIONS Per SJCPHS/EHD requirements, the following summarizes our nitrate loading calculations for the proposed leach field. The State drinking water standard for nitrate is 45 milligrams per liter (NO3) and 10 mg/l as Nitrogen (1) in groundwater. In our evaluation of nitrate loading, we have 17357.G011ST02R327 August 8,2002 0 2002 Kleinfelder,Inc. Page 3 of 5