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I9 November 1992 <br /> (GeoAudit CV 42E1-1. 8) <br /> Page 3 of 6 <br /> 2 .2 Abandonment <br />' The three soil borings were grouted with Portland cement from total <br /> depth to surface. Four 94-1b sacks of cement were mixed with water <br /> in a 55-gallon drum. A total of 26 sacks of cement were used. The <br />' fourth boring was completed as a vapor extraction well. <br /> 3. 0 VAPOR EXTRACTION WELL <br /> During drilling, it became apparent that contamination was present <br /> in boring B-1 at depths greater than 30 feet, and this boring was <br /> continued. However, groundwater was not reached at the expected <br /> depth of 50 feet, and the boring was halted on 19 October at a <br /> depth of 60 feet so that additional augers could be obtained. The <br /> I augers were removed and borings B2 and B3 were drilled. Drilling <br /> was resumed on B1 the following day. Groundwater was encountered at <br /> 67 feet and the boring was terminated at 70 feet. Based on the <br /> results of mobile laboratory analysis, Ms. Hinson authorized the <br /> completion of the boring as a vapor extraction well in the depth <br /> range of 55-25 feet. The well design is illustrated in Figure 3 . <br /> 4. 0 GROUNDWATER INVESTIGATION <br /> 4.1 Depth to Groundwater <br /> When the original workplan was submitted in 1991, the depth to <br /> I groundwater was estimated by Mr. Dennis Corcoran of San Joaquin <br /> County Department of Public Works to be 80-85 feet. Prior to <br /> drilling, the estimate was revised to 40 to 60 feet, based on the <br /> Fall, 1990, depth to groundwater map prepared by the Flood Control <br /> ISection of the San Joaquin County Department of Public Works. Based <br /> on this estimate, the revised workplan called for 60-foot <br /> monitoring wells. <br /> Durina drillina. first groundwater was encountered at a depth of <br /> between 30 and -35 feet. This zone is believed to be a thin zone of <br /> perched water within the most permeable portion of layer 2 . <br /> A more substantial flow of water was encountered at the top of the <br /> lower sand bed, at a depth of about 67 feet. This depth agrees well <br /> with the depth measured at nearby sites, according to information <br /> provided by Ms. Hinson. <br />