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December 1999 As noted in Section 2 3, re-extraction occurred out of holding time, and the reported weathered diesel concentrations are considered estimated TPH as unknown hydrocarbons was also reported in the December 1999 sample collected at well DMW-3 (90 /rg/1) The peak patterns observed in this sample did not match the laboratory diesel standard, and do not match the weathered diesel observed in samples from DMW-6 and DMW-7 Results from this analysis suggest that the unknown hydrocarbon reported in this sample represents an unidentified petroleum product which does not correspond to fresh or weathered diesel Review of historical TPH-D data indicates that the maximum TPH concentration reported since 1987 was from the previous sampling event conducted in September 1999 Prior to the installation of DMW-6 and DMW-7 in December 1998, the only other reported TPH concentration was 180,ug/I at DMW-4 The weathered diesel has been consistently detected during the five sampling events conducted at DMW-6 and DMW-7 since December 1998 These wells are constructed so that representative water samples can be collected directly at the groundwater surface, M where a surficial TPH-film would be expected, if present DMW-6 and DMW-7 were installed near the centers of the two zones of residual TPH soil impacts associated with the former USTs Therefore, the concentrations detected at these two wells should be representative of the worst-case scenario for TPH-D concentrations in groundwater at the Site From December 1998 to December 1999, the reported concentrations ranged from 380 pg/I to 780 Ng/I in samples collected at DMW-6, and 82 ugll to 660 ,ug/I in samples collected at DMW-7 The weathered diesel observed at DMW-6 and DMW-7 does not I appear to be present in samples collected from wells DMW-1 through DMW-5, based on the review of chromatograms DAMES&MOORE 5 \\DM_5ACIWOL_21JOS1AFPIREPORTIQ4-1999 DOC