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�..• �./ k'9 KLEINFELDER the north, a commercial/trailer sales facility to the south, Highway 99 to the west, and Frontage Road to the east. HISTORICAL GROUNDWATER DEPTH In accordance with groundwater reports published by the San Joaquin County Flood Control and Water Conservation District (Spring 1972 to Spring 1999), high groundwater in the project area has been recorded at depths in the range of about 15 to 20 below ground surface. FIELD EXPLORATIONS AND TESTING The subsurface conditions at the leach field were explored on July 31, 2001 by drilling one boring to a depth of about 30 feet below existing grade in the area of the proposed leach field and adjacent percolation test P-1. The boring was drilled using a Simco 2400 truck-mounted drill rig equipped with 4-inch O.D. solid-stem auger. During the same time period, two percolation borings (P-1 and P-2) were drilled to depths of about 3 and 3.4 feet, respectively, below site grade. The approximate percolation test locations are presented on the attached plate. Based on our findings, the subsurface soils encountered consisted predominately of fine to medium grained "clean" sands and slightly silty sands to the depths explored. Between depths of about 15 to 20 feet, a stratum of low plastic sandy silt was encountered. Groundwater was encountered at a depth of about 28 feet below site grade at the boring location. Groundwater was measured at a depth of about 24.8 feet in the well located near the north-central portion of the site. The percolation tests were performed in accordance with accepted guidelines using clear potable water. The procedure calls for first placing about 2 inches of fine gravel at the bottom of the bore hole, installing a perforated PVC casing, and then placing additional gravel. Approximately one inch of additional gravel was placed in P-2 and about 2.8 feet of additional gravel was placed in P-1. The holes were then pre-soaked with water at least 24 hours prior to performing the tests. The tests are performed by first adding about 6 inches (P-2) and 3 feet (P-1) of water to the hole. From a fixed reference point, the drop in water level was measured in approximately 10 minute intervals for 1 (P-2) and 2 hours (P-1), refilling as necessary to maintain the original head of water over the gravel. Under the observation of a sanitarian from the San Joaquin County Public Health Department, the last 10 minute reading of the monitoring period was recorded and used to calculate the percolation rate in minutes per inch and gallons per square foot per day (gfd). The estimated percolation rates at each test location are as summarized below. A copy of our field percolation test results is attached. st € I r'': .. Pero no Vie::: P� c� t.�a�1i il�e ... If .ld .. . ........................ . .. P-1 3.8 23.6 P-2 4.9 24.8 20-4630-O1.G01/2011R986 Page 2 of 5 Copyright 2001 Kleinfelder,Inc. August 16,2001