ARCHIVED REPORTS_XR0007498 CASE 1

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Mr Wade Broughton General Mills, Inc January 26, 1995 Page 4 Soil samples were submitted to Calitornia Laboratory Services, a state-certified laboratory, for analysis of BTEX and TPH as diesel Laboratory analytical results reported TPH as diesel was detected in the 15 and 17 5-toot samples trom soil boring SB-1, and the 4-toot sample from soil boring SB-2, at concentrations of 990, 27, and 410 ppm, respectively Ethylbenzene was detected in the 15-foot sample obtained trom SB-1 at a concentration of 0 01 ppm All other soil samples and analytes were not detected at or above the laboratory's reporting limits Cumulative soil sample analytical results trom soil borings are presented in Table 2 Copies of the soil sample laboratory analytical reports have been included to Enclosure C Semi-Annual Ground Water Monitoring and Sampling Results Second-Half 1994 Depth to ground water measurements were collected trom the three on-site monitoring wells on November 30, 1994 Depth to ground water in the vicinity of the tormer tank locations ranged from 40 44 to 40 86 feet below the tops of the well casings (approximately 40 94 to 41 46 feet bsg) This is a decrease of approximately 1-toot trom the previous measurements obtained on June 23, 1994 Cumulative ground water table measurements are included in Table 3 The ground water table measurements collected on November 30, 1994, were used to construct the water table contour map shown in Figure 5 The interred direction of ground water flow is toward the southwest with a hydraulic gradient of approximately 0 004 This direction and gradient is consistent with previous measurements at the site since monitoring began Ground water samples were collected trom monitoring wells MW-1, MW-2, and MW-3 on November 30, 1994 A representative of the County was present to observe the monitoring and sampling activities The ground water samples were submitted to Calitornia Laboratory Services, in Rancho Cordova, California, for analysis of BTEX and TPH as diesel Concentrations of BTEX and TPH as diesel were not detected at or above the laboratory's reporting limit Cumulative analytical results from the ground water samples are compiled in Table 4 The methods used to monitor and sample the wells is described in Enclosure A Sampling information sheets and laboratory reports for the November 1994 sampling event are included in Enclosures D and E, respectively Discussion Laboratory results from additional soil borings SB-1, SB-2, and SB-3 installed on July 26, 1994, reported TPH as diesel concentrations in two soil samples collected from soil boring SB-1 (at 15 and 17 5 feet bsg) and one soil sample from soil boring SB-2 (at 4 feet bsg) Laboratory reports indicated no soil sample collected below 17 5 teet from any of the three borings reported hydrocarbon concentrations TPH as diesel was reported in soil boring SB-1 at 15 feet bsg at a concentration of 990 ppm The soil sample analyzed trom the same boring at 17 5 bsg reported 27 ppm TPH as diesel Analytical results trom soil samples collected at similar depths trom SB-2 and SB-3 were not detected at or above the laboratory's reporting limits Based on these results, it appears that the hydrocarbon containing soil remaining in place tollowing the excavation and removal of the USTs is limited to the area between 15 and 17 5 teet bsg