ARCHIVED REPORTS XR0006513 - Laserfiche WebLink

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' collected from all monitoring wells associated with this site (MW1 MW2 MW3 MW4 MWS MW6, MW7, MW8, MW9, MW10, MWI 1, MW12 and MW13) These samples were analyzed for TPH-g, benzene, toluene, ethylbenzene, xylenes (BTEX), and Methyl tertiary Butyl Ether (N4BTE) using EPA methods 8015 modified and 8060 Figure 11 represents the groundwater gradient obtained on May 28, 1998 and shows a groundwater low with a depression at MW 10 and a groundwater high at MW2 with a general site gradient that flows to the east Figure 12 is a Lithologuc Fence Diagram and shows the historic high and low groundwater levels for this site Top of screened interval has been above the top of groundwater for the following wells MW I,MW2, MW3, MW4,MWS, MW6, MW7, MW8, and MW9 since mud 1998 In monitor wells MW-10, MW I 1 and MW 12, the top of groundwater has been above the top of the screened interval since 1995 Charts have been developed for MW I, MW2 MW3 MW9, MW I O and MWI2 that show the continued decline in concentrations of TPH-g in the groundwater These charts are presented in Appendix C A computer generated regression Jure demonstrates the decline of gasoline range hydrocarbons in the groundwater for all wells except for MW12, which is currently showing a I stable trend All perimeter wells, except MW 12, have tested below or at laboratory lower detection limits for TPH-g, BTEX and MTBE, showing phime stability Of the wells that tested positive for gasoline range hydrocarbons (MW I, MW2, MW3, MW8, MW 10 MW 12 and MW13), the following MCLs have not been exceeded with the exception of the December 1997 sampling which contained elevated levels for BTEX due to residuals in the pump Yearly average benzene and TPH-g concentrations from monitoring well MW1, which contained free product until August 1992, have not exceeded the primary and secondary MCLs since December 1993 I 6 I