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Thrifty Oil Company Job No: 13-6782-026-00-00 <br /> January 7, 1988 Log No: HTC-7-1398 <br /> Page 3 <br /> 1 <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 lithologic 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 any 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 /> ' feet below ground surface . <br /> ' 3.0 INVESTIGATIVE PROCEDURES <br /> 3 . 1 General <br /> The investigation was conducted according to the <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 of concrete patch . All <br /> boring cuttings were placed into 55-gallon drums for <br /> future disposal in accordance with laboratory findings . <br />