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.. y _ � _.-. .,._::�. ,�� ..,�.��,:,..,, ...,�..�,,��,-nom• r . k Harding Lawson Associates t -� the dry well. Ground-water samples from monitoring wells that initially had hydrocarbon concentrations above detection limits have shown steady declines in such concentrations. This phenom- ena has been observed in MW-A, MW-B ' (now MW-7) , MW-1 and MW-8. MW-A and MW-B were 41-inch wells installed by Southland to warn of gasoline leaks in the tank backfill. In December, 1986,, approximately two gallons of floating product were bailed from these wells. Since then, no freepro duct has been observed. Because no construction details or lithologic iogs were available +( for MW-A or XW-B, these wells were never formally sampled, merely I i checked for free product. In December 3987, MW-B was redrilled P: n and converted to MW-7, andis now part of the active site moni- L taring program. 4' MW-1 initially had detectable concentrations of total . . xylenes (76 ppb) and TPH (4 ppm) in December,. 1986 (Table 3) . } : - These concentrations are believed to have resulted from surface r- � gasoline spills that were washed or. carried by rain -water runoff { into the dry well immediately southeast. (downgradient) of MW-1. t F - - - - - -LJ = -Since the installation- of 'MW-1 `in november 1986, concentrations ?' of these constituents have fallen below detection limits. This w+ t. result indicates that the presence of- hydrocarbons were from a i transient source'. Since their installation in December 1987, MW-7 and NW- � �.� ' 8 also initially. showed hydrocarbon concentrations above levels of detection (Tables 3 and 4) .. BTEX concentrations have decreased dramatically, f as shown in the tables. Where initial - 15 _ MIS