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4 <br /> ,f Thrifty Oil. Company Job No: 13-6782-026--00-00 <br /> January 7., 1988 Log No: HTC-7-1398 <br /> Page 3 <br /> 2 .2. Local Subsurface Conditions <br /> Engineered fill composed of gray medium-grained sand was <br /> encountered. to a depth of three feet in Boring B-3 . <br /> Native sediments observed to a depth of 20 feet in all <br /> borings, consisted of very stiff 'to hard clayey silt <br /> and silty clay. A gray fine-grained silty sand was <br /> encountered at a depth of approximately 19 feet in <br /> Borings B-2 and B-3 . Detailed -lithalogic descriptions <br /> of each boring are included in Appendix B, Figures B-3 <br /> through B-6. <br /> 2. 3 Hydrogeology <br /> Groundwater was not encountered in ariy :boring to a <br /> depth of 20 feet. According to hydrogeologic maps (see <br /> references ) , shallowest groundwater beneath the site is <br /> expected to be present at a depth of approximately 30 . <br /> Ifeet below ground surface . <br /> 3.0 INVESTIGATIVE PROCEDURES <br /> 3 . 1 General <br /> IThe investigation was conducted according to the <br /> ,F <br /> planned scope of work. Four vertical borings were <br /> excavated around the tank cluster to. a depth of 20 <br /> feet. Sampling of soil was performed at five-foot <br /> depth intervals. Each borehole was backfilled with <br /> bentonite grout under the observation of an Inspector <br /> from the County of San Joaquin . Each boring was capped <br /> with approximately six inches ofconcrete patch. All <br /> boring cuttings were placed into 55-gallon drums for <br /> future disposal in accordance with laboratory findings. <br />