ARCHIVED REPORTS_XR0002097 - Laserfiche WebLink

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lti i . GROUNDWATER SAMPLING AND ANALYSIS Monitoring wells MW1, MW2, MW3, MW4, MW5, MW6, and MW8 were purged and sampled on July 27, 1995 Well MW7 was Inaccessible due to a damaged well box All purge water was contained on site In labelled drums approved by the Department of Transportation (DOT) Well purge logs are Included in Attachment B Groundwater samples were submitted to Argon Laboratories (DHS Cert #1873) for analysis of TPHG and BTEX utilizing EPA methods 8015 mod and 8020, respectively Laboratory analyses detected gasoline hydrocarbon constituents in samples collected from wells MW1, MW3, MW4, and MW5 The gasoline constituents detected in well MW4, however, were relatively low benzene at 3 1 parts per billion (ppb) and TPHG at 87 ppb No hydrocarbons were detected in samples collected from wells MW2, MW6, or MW8 No sample was collected from well MW7 Analytical results for the reporting period are summarized in Table 2 Laboratory data sheets and chain of custody documentation are included in Attachment C Historical analytical results are included in Attachment A CONCLUSIONS The unusually wet winter/spring conditions had an indeterminate effect on dissolved contaminant concentrations Relative to laboratory results from September 1994, contaminant concentrations decreased in wells MW1 and MW2, increased in wells MW4 and MW5, and remained unchanged in well MW8 No samples were collected from wells MW3, MW6, or MW7 in September 1994, but contaminant concentrations in decreased in well MW3 since April 1994 and remained unchanged in well MW6 No sample was collected from well MW7 in July 1995 Contaminant concentrations detected in July 1995 are well within historic ranges for the respective wells Based upon analytical results of groundwater samples, It appears that the rise of the water table Into the zone of residual soil contamination (approximately 35 to 50 feet below ground surface) has had no mayor effect on groundwater contaminant concentrations i RECOMMENDATIONS Based upon historical analytical results of groundwater samples collected at the site, Ground Zero recommends the following modifications to the groundwater sampling program 1) Remove well MW7 from the sampling program MW7 is upgradient from the contaminant source and petroleum hydrocarbons in samples collected from the well have been consistently at or below the laboratory detection limit No gasoline constituents have been detected in samples collected from the well since December 1992, 2) Remove well MW6 from the sampling program MW6 is cross-gradient (southwest) of the contaminant source and has been consistently non-detect for petroleum hydrocarbons No gasoline constituents have been detected in samples collected from the well since December 1990, groun Oknowles haml3gmr1995 Ipl 2