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Perfomna Inc. May 7,2003 Page 6 Table 3. Summary of percolation tests results. Test Time Period of Test,Date Test Depth Percolation Rate* P-1 One(1)hour,March 25, 2003 3.0 feet less than 1.6 minutes/inch P-2 One (1)hour,March 25, 2003 3.0 feet less than 1.6 minutes/inch *Acceptable percolation rate is less than or equal to 60 min/in during the I ast measurement. A satisfactory percolation rate was achieved in both shallow percolation test holes in accordance with the requirements of the San Joaquin County Environmental Health. A percolation rate of less than 1.6 minutes per inch is a rapid percolation rate. Soils with rapid percolation rates combined with shallow ground water are sensitive to nitrate impacts. Dairies, agriculture, and septic systems are common causes of high nitrate levels in ground water in shallow aquifers. 5.0 HYDROGEOLOGY 5.1 Regional Setting The subject property is located on an alluvial fan near the flood plain deposits of the San Joaquin ' River Delta. The surface soils the area are loose sand and silt deposits, chiefly fluvial in origin of the Pleistocene age Modesto Formation(Atwater, 1982). An isocontour map of the area indicates the the upper 50 feet of sediment at the site has between ten and twenty feet of sand ' thickness (DWR, 1967). According to DWR(1967), the base of fresh water in the area is between 400 and 600 feet below mean sea level. The base of which is defined by water quality standards. As mentioned previously, the soil at boring B-1 was found to be a brown, moist, medium to fine sand with silt to a depth of three feet. Underlaying the surface material between three to six feet depth was a light brown moist sand with silt. From a depth of six to thirteen feet, a greyish, light brown, clean, fine sand was encountered. From a depth of thirteen feet to 25 feet, a silty clay soil ' was encountered. Ground water was encountered at a depth of 20 feet 4 inches. Not a great deal of published information or formal studies were available regarding the extent of nitrate contamination in the shallow aquifer in the area between Manteca and French Camp. Our office spoke with Ms. Linda Turket of the EHD. Ms. Turkel has mapped nitrate levels in San Joaquin County from well records and water quality tests,however, the data that Ms. Turket has ' gathered, was not for the shallowest ground water. In fact, sometimes the water analyzed was from as deep as 500 feet. Dr. Gary Litton,Environmental Engineer of University of Pacific ?yERfO N S 'r Q A