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MKLEIN FELDER b. 5. SOIL PROFILE ., The subsurface conditions within then new leach field area were explored on January 28, 2004, by drilling one boring to a depth of approximately 25 feet below existing grade. The boring was drilled using a Simco 2400 truck-mounted drill rig equipped with 6-inch O.D. solid-stem auger. The approximate boring location and approximate dimensions from a reference point are presented on the site plan (Plate 1). Based on our findings, the subsurface soils encountered consisted of moderately- to highly- plastic silty clay to a depth of about 11 feet below existing site grade, followed by low-plastic sandy silt and sandy clay to a depth of about 16.5 feet. These soils were followed by silty sand / �- and sandy clay to a depth of about 18.5 feet, silty sand to a depth of about 24 feet, and sandy clay to a depth of about 25 feet, the maximum depth explored. A detailed description of the subsurface conditions encountered during our field investigation is presented on the attached Log of Boring(Plate 3). The Soil Survey of San Joaquin County, California published by the U.S. Department of Agriculture, Soil Conservation Service (1992) refers to the near-surface soil within the project area as belonging to the Hollenbeck and Stockton soil series (Map Symbols 173 and 250, Lrespectively). The soils are described as having slow permeability characteristics due to high clay content. Other attributes are given in the table below: s_ Map Available Water Capacity, Organic Symbol Soil Name inches/inch PH Content, percent 173 Hollenbeck 0.14 - 0.26 6.6 - 8.4 1 - 2 ` 250 Stockton 0.14 - 0.17 7.4 - 8.4 2 - 5 6. PERCOLATION TESTING Two 6-inch diameter percolation test holes were drilled directly adjacent to the soil profile boring to depths of about 3 and 21.8 feet below site grade on January 28. 2004. Following drilling, the sides of the holes were scored and significant loose material was removed from the bottom of the hole. The percolation tests were then prepared by first placing about 2 inches of fine gravel at the bottom of the holes and installing a 4-inch diameter, perforated PVC pipe. (6 io About 12 inches of water was then placed in the holes for pre-soaking. Since we could not arrange to perform the tests the followinda the holes were again pre-so ed with about 12 inches of waterefore9.00 AM on J 04. The percolation tests were started at 11: 05 AM under sunny and warm weather on January 30, 2004, in accordance with SJCEHD (4- accepted guidelines using clear potable water. None of the holes exhibited sloughing or caving. L The holes were empty of water prior to testing. From a fixed reference point (a marked location on the side of PVC pipe), the drop in water level was measured in approximate 30- minute intervals for a period of four hours, refilling as necessary to maintain the prescribed�L 5 amount of water over the gravel (SJCEHD Procedure #2). Under the observation of a representative from the SJCEHD, the last 30-minute reading of the four-hour period was 40141.G01/ST04R206 February 24,2004 ©2004 Kleinfelder,Inc. Page 4 of 7