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3 SOILASSESSMErU <br /> To assess the vertical extent of patroleum hydrocarbon migration beneath the former 500- <br /> gallon UST one soil boring (B-7) was drilled adjacent to B-5. A second boring (B-8) was <br /> drilled approximately 45 feet to the northeast to assess background concentrations of <br /> chromium and zinc. <br /> 3.1 DRILLING AND SAMPLING PROCEDURES <br /> On August 10, 1989,soil borings B-7 and B-8 were drilled near the former 500-gallon UST. <br /> Boring B-7 was drilled adjacent to and on the north side of B-5. Poring B-8 was drilled <br /> approximately 45 feet northeast of boring B•7, approximately 30 feet south of the <br /> California Water Service Municipal Water Well. The locations of soil borings and the <br /> former USTs are shown on the Soil Baring Location Map,Plate 3. <br /> Soil samples were collected at 5-foot intervals from the ground surface to the termination <br /> depth of each boring. Boring B-7 was drilled to a depth of 51.5 feet below the ground <br /> -� surface, while B-8 was drilled to a depth of 11.5 feet below the ground surface. During <br /> sample collection, an experienced environmental geologist classified the subsurface soil <br /> and Iogged the boreholes. A copy of the Unified Soil Classification System used to classify <br /> the soil is included in Appendix A (Elate A-1). Descriptions of the soil encountered in <br /> each boring and the identificationof the sampling intervals are presented on the Log of <br /> Borings,Plate A-2 and A-3 (Appendix A). <br /> The soil encountered in the borings consisted primarily of clayey silt with some silty sand, <br /> sand and clayey sand. In general, clayey silt was encountered from 0 to 20 feet and silty <br /> sand, sand and clayey sand was encountered between 20 and 51.5 feet in B-7. Sand, silt, <br /> and clayey sand was encountered from 0 to 11.5 feet in B-8. Soil samples were generally <br /> moist and ground water was not encountered. <br /> At each boring location, a truck mounted drill rig equipped with 6-inch hollow stem augers <br /> was used to reach the desired sampling depths. Samples were collected by advancing the <br /> --------- boring-to-a-point-immediately-above-the-desired_sampling_depth_and_then-driving <br /> Modified California Sampler lined with three brass tubes into the undisturbed soil. The <br /> sampler was removed from the bottom of the boring, and the bottom tube was sealed with <br /> F13-90-60 4 <br />