ARCHIVED REPORTS XR0012865 - Laserfiche WebLink

Home Browse Search

►.. 4.4 Groundwater Analytical Results The grab groundwater sample collected from boring SB3 had non-detectable levels of TPHg,TPHd, BTEX and MTBE. The sample collected from SB4 had non-detectable concentrations of BTEX; however, TPHg, TPHd, t-butanol (TBA)and MTBE were detected at 380, 16,000, 260 and 1,900 parts per billion, respectively. It should be noted that the TPHg chromatogram did not match the typical gasoline pattem. Analytical results of groundwater samples are summarized in Table 2. Laboratory reports and chain of custody documentation are included in Attachment B. 5.0 CONCLUSIONS AND RECOAIMM DATIONS 5.1 Conclusions Although it is evident that the site has been impacted,only the samples collected from borings SB4 and SB4A, which are located in the vicinity of the western portion of the former dispenser island, gave evidence of petroleum hydrocarbon contamination. According to the analytical results, contamination in this area does not appear to extend beneath a depth of approximately 20 feet bgs. The data from this investigation combined with data previously obtained have defined the extent of soil contamination. Soil contamination of any significance appears to be present only beneath the southeast comer of the UST pit and beneath the former dispenser island. The estimated area of soil �✓ contamination is shown on Figure 2. Groundwater beneath the affected soil has been impacted by petroleum hydrocarbons and the oxygenated fuel additives MTBE and TBA. The extent of groundwater contamination has not been fully defined however no groundwater contamination was present in the sample collected from boring S133, northeast of the UST pit and north of the dispenser island. Groundwater flow is expected to be generally northeasterly. It is likely that only a limited volume of groundwater has been affected. 5.2 Recommendations Based upon the localized contamination and its(current)accessibility Ground Zero recommends the implementation of interim remedial actions consisting of excavation and limited groundwater extraction. 6.0 WORKPLAN FOR INTERIM REMEDIATION We propose using an excavator to remove residual soil contamination from the approximate area depicted on Figure 2. Excavation will continue laterally until field evidence indicates that the majority of contaminated soil has been removed. Excavation will proceed vertically to an estimated depth of approximately 18-20 feet or until groundwater is encountered. It is estimated that 200— ' Woolscychattcrlrcportst�+unarary.doe 5