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• 4 2 TPH-D in Soil Table 3 presents the results of TPH-D analyses conducted on four soil samples collected during installation of monitoring wells DMW-6 and DMW-7 The two wells were intentionally placed in the locations of the former USTs where maximum TPH-D concentrations would be anticipated, based on previous studies Diesel was only reported in sample DMW-6 1 (18,000 mg/kg), which was collected from a depth of 25 feet bgs TPH-D was not reported in the other three samples, which were sampled at depths of 30, 35, and 40 feet bgs The reported concentration and sampling depth correspond to previous site assessments, which suggest that residual contamination is present at depths up to 26 feet bgs (Dames & Moore, 1995a) The groundwater level at the time of sampling was approximately 39 feet bgs, suggesting that an unsaturated zone approximately 13 feet thick separates the groundwater from impacted soil TPH-D was not reported in soil samples collected from depths of 40 feet to 30 feet bgs 4 3 TPH-D in Groundwater TPH-D groundwater results for samples collected between 1988 and 1998 are compiled in Table 4 TPH-D has not been reported in previous groundwater analyses TPH-D was reported at a concentration of 0 48 mg/L in one sample collected at DMW-6 on December 21, 1998 i Unknown hydrocarbon was reported for samples MW-7 (0 18 mg/L) and its duplicate MW- 0 (0 11 mg/L), collected at DMW-7 on December 21, 1998 The unknown hydrocarbon was reported to represent an unknown mixture in the range of n-C10 to n-C40, which did not match the diesel fuel reference Review of historical data indicates that unknown hydrocarbon has only been reported in one sample at a concentration of 0 18 mg/L in a sample collected at DMW-4 on May 13, 1994 Comparison of water level elevations with top of screen elevations (see Table 2, page 2) indicates that the monitoring well screens have been situated below the groundwater surface since at least May 1994 for DMW-1, DMW-2 and DMW-4 Well screens at DMW-3 and DMW-5 have been situated below the water table since at least May 1995 and January 1997, respectively However, a total of 25 groundwater samples were collected at dates when the well screen intersected the groundwater surface TPH-D was not reported in any of these 25 samples 6 11DM SACl\SYS1JOBWFPIREPORT1lgrpt doc