In 2006, Antea Group assumed project responsibility for an active retail petroleum service station with an open LUST (Leaking Underground Storage Tank) incident. The site had been managed by other consultants since 1989. Groundwater monitoring revealed off-site contamination seemingly associated with the dissolved phase petroleum hydrocarbon plume at the site. For this reason, the state required that Antea Group run the existing remediation system consisting of a soil vapor extraction/groundwater pump and treat system (SVE/P&T).
Antea Group completed safety and efficiency related upgrades to the SVE/P&T and began operation to control plume migration while determining a more effective approach to close the open incident. Analytical results reported from the monitoring well network of the subject site did not suggest that the on-site petroleum hydrocarbon plume was migrating off-site, yet a hydraulically down-gradient off-site monitoring well reported elevated petroleum hydrocarbon concentrations.
Antea Group began reviewing historical Sanborn maps and property-use records of the adjacent properties surrounding the subject site, specifically the property with the impacted off-site monitoring well. During this research, Antea Group discovered that the off-site property which contained the impacted monitoring well had previously been used as a retail petroleum service station. This discovery identified the previous property use as the likely source of the petroleum hydrocarbon concentrations observed from the off-site monitoring well.
The historical off-site property use and storage tank location information had never been presented to the state before. Upon Antea Group’s presentation of the off-site property use information to the state case manager, the state agreed with Antea Group’s conclusions that the off-site impact was not caused by the subject site and that the remediation system could be immediately shut-down. Antea Group was granted incident closure in 2007 after two consecutive quarters of groundwater monitoring following the shut-down of the remediation system.