ARCHIVED REPORTS XR0001126 - Laserfiche WebLink

Home Browse Search

- - - 04 October,1996 r, AGE-NC Project No 95-0121 Page 3-of 4 MW-2) MTBE was detected in' samples from MW-2, MW-5 and MW-7 at concentrations up to 230 Ppb r I F ' w The analytical results for ground water samples are summarized in Table 2 -Analytical Results of Ground Water Samples' The laboratory report (CAL Laboratory Batch No 860) and chain-of- custody farms are included in Appendix B {f , 4.0. CONCLUSIONS & RECOMMENDATIONS -4 1 CONCLUSIONS 1 , Based upon data collected: during the August 1996 monitoring, AGE has,the following conclusions • 1 , Ground water flow direction has remwned relatively constant at the site over the past two ' years Monitoring wells MW-6 and MW-9 continue to be up-gradient of the former UST area, wells MW-8 and MW-5 continue to be down-gradient ` zConcehtrations of some dissolved petroleum hydrocarbon constituents increased in six of nine wells at the site Concentrations of all dissolved kiydrocarbons decreased only-in wells-MSV-4, 4b- MW-7 and 'MW-9, which are northeast, northwest and southwest of the former UST ' excavation, respectively The greatest concentrations of dissolved petroleum hydrocarbons continues to be in the area of wells MW-I through MW-4, near the "core" of hydrocarbon-impacted soil • TPH-d in MW-I,through MW-4'and'MW-6 through MW-9 were reported to have a non- diesel chromatographic pattern Further review of laboratory chromatographs suggested that the non-diesel patterns were tho result of gasoline interference _ • ' Concentrations"of benzene detected in MW-1 through MW-4,-MW-7 and MW-8,were above,' the State of California Maximum'Contaminant Levels (MCLS) for drinking water of 1 0 pgn', Concentrations of toluene, ethylbenzene and xylenes also exceeded the MCL or Action Limit v h (AL) in many wells at the site x •a Concentrations of MTBE in MW'2 and MW-7, are above,the State of California Dnnking Water AL of 35 ppb - r _ ' x � r { • The overall increase of detectable hydrocarbons concentrations at the site may be related to ' the rise and fall of ground water elevations causing washing of impacted soil withm'the _M r'r capillary fringe or lower vadose zone - • The ground water surface was between one and ten feet above the top of screen intervals in , • r ;monitoring wells MW-1 through MW-9 Because screened intervals are below ground water , r r ' � x a