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111!% 5.0 Conclusions and Recommendations Two monitoring wells were installed and sampled at the Site during December 1998 Soil and groundwater samples were collected and analyzed for TPH-D The wells were installed at locations corresponding to where former USTS resulted in the maximum TPH-D impacts Water level measurements were collected to assess the depth to groundwater, and the groundwater flow direction Water level measurements indicate that the groundwater at the Site is continuing to show an upward trend, which has been occurring since 1991, when the depth to groundwater was approximately 69 feet bgs The current water level is approximately 38 feet bgs The screened zones at monitoring wells DMW-1 through DMW-5 have been below the groundwater surface since January 1997 or earlier, depending on the well construction TPH-D was reported in one soil sample at a concentration of 18,000 mg/kg, which corresponds to previous assessments indicating residual TPH-D-impacted soil at depths up to 26 feet bgs TPH-D was not reported in samples collected in the unsaturated zone between the 30 feet at the groundwater at approximately 38 feet bgs This suggests that the rising groundwater is not in contact with soil impacted with TPH-D TPH-D was reported at a concentration of 0 48 mg/L (DMW-6) in one sample This result is the first and only reported TPH-D detection since sampling was initiated at the Site in 1987 Unknown hydrocarbon which does not correspond to the laboratory diesel fuel standard was reported in a December 1998 sample from well DMW-7 (0 18 mg/L), and a May 1995 sample from DMW-4 (0 18 mg/L) The recently installed wel Is were constructed so that the screens intersect the current water level However, review of historical data indicates that TPH-D was not detected in 25 samples collected at periods when the well screen intersected the water levels Additional sampling would be necessary to better assess the potential TPH-D groundwater impact Additional groundwater samples will be collected and analyzed for TPH-D during 1999 Three additional sampling events are scheduled for February, May, and September 1999 In accordance with the Work Plan, monitoring wells DMW-6 and DMW-7 will be sampled, and water levels will be measured at all seven monitoring wells Quarterly reports will be issued following each sampling event DAMES&MOORE 7 R\sac\044misc\9902_03 doc