ARCHIVED REPORTS XR0006446 - Laserfiche WebLink

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The most recent groundwater quarterly sampling occurred on September 23, 1997 Monitor wells MW1, MW2, MW3, MW8, MW10 and MW12 were sampled, see Appendix B Table 1 represents groundwater chemical results MW1, MW8 and MW10 showed slight decreases in gasoline range hydrocarbons MW3 was unchanged MW2 showed decreases in TPHg and Toluene with increases in Benzene and Ethylbenzene and MW12 showed decreases in Benzene and Ethylbenzene with increases in TPHg and Toluene, see Figure 5 for TPHg plume extent Charts have been developed for MWI, MW2, MW3, MWS, MW10 and MW12 and show the continued decline in concentrations of TPHg in the groundwater and the continued rise of the groundwater elevation since 1991 These charts are located with Table 1 A linear trend line has been computer generated for each chart and demonstrates the decline of gasoline range hydrocarbons in the groundwater for all wells with the exception of MW12, which is currently showing a slight upward trend For the most part the primary MCLs for Benzene, Toluene, Ethylbenzene and Xylenes have not been exceeded for drinking water standards for the State of Calf ronia And the perimeter wells have tested below laboratory lower detection limits for TPHg, BTEX and MTBE showing, plume stability with the exception of MW 12 Compound Primary MCL Secondary MCL Benzene 1 0 ug/L none Toluene 150 ug/L 42 ug/L Ethylbenzene 700 ug/L 29 ug/L Xylenes 1750 ug/L 17 ug/L MTBE none ?45 ug/L Of the wells that do test positive for gasoline range hydrocarbons (MW 1, MW2, MW3, MWS, and MW 10 MW 12) the following MCLS have not been exceeded MW1, which contained free product until August 1992 has not exceeded the primary and secondary MCLs since December 1993 MW2 is situated in a clayey facies of the silty sand aquifer beneath this site and has low transmissivity has not exceeded the primary MCLs for Ethylbenzene since December 1996 MW3 which contained free product until November 1992 has not exceeded the primary MCLs for Toluene, Ethylbenzene and Xylenes since March 1993 and the secondary MCLs for Toluene since September 1993 and for Ethylbenzene since September 1995 MW8, which is downgradient and offsite, has not exceeded the primary MCLs for Toluene during this Latest sampling It has never exceeded the primary MCLs for Ethylbenzene and has been below the primary MCLs for Xylenes since June 1994 MW10, which contained free product until November 1992, has not exceeded the primary MCLs for Benzene since December 1996, for Toluene since March 1994, for Ethylbenzene since March 1993 2