REMEDIATION SERVICES - Gasoline Service Stations

Historical/Current Use: Two gasoline stations and auto repair facilities

Contaminants of Concern: Petroleum compounds including benzene and methyl tertiary butyl ether

Summary of Impact/Sensitive Receptors: Gasoline migrated to the basement of a residence, a brook,  and the Sebago Lake southern basin.  The Town of Standish and Portland Water District public water supply intakes were located in this area

Campbell Environmental Group staff investigated and evaluated remedial alternatives for a petroleum release that occurred at two gasoline service stations which were located within 100 yards of each other.  The release at the facilities threatened the quality of public water supplies for the Town of Standish and, more remotely, the Portland Water District.  The release at one of the stations also impacted air quality within a private residence.

The objectives were to design a remedial system that prevented vapors from adversely impacting human health in the residence, to reduce the concentrations of gasoline in the soil and groundwater, and to minimize the migration of gasoline to the threatened surface water bodies. CEG evaluated soil and groundwater conditions by conducting pump and remedial pilot tests for the design of two air sparge, soil vapor extraction, and groundwater treatment systems.  The air sparge system at one of the stations used angled drilling

Indoor air quality within the residence was monitored using a photoionization detector and a gas chromatograph.  The results of the analyses were compared to the Department's Interim Ambient Air Guidelines.  Following activation of the remedial systems, it was determined that indoor air quality did not pose an adverse health risk.ethods to remediate gasoline below a building.

Plot of remediation systems at service station

The remediation system at the first station successfully reduced gasoline in the subsurface from liquid-phase thicknesses on the groundwater and petroleum saturated soil to within the Maximum Exposure Guidelines of the Maine Department of Human Services for drinking water within two years.  The site was subsequently closed from the Department's top 10 Priority List.  The second site is still active.  Approximately 95 percent of the impacted area has been remediated to the Department's closure standards.  One recalcitrant area still contains gasoline concentrations that require remediation.  CEG has recently conducted new pilot testing using oxidation injection and designed a helium air sparge evaluation test to determine if the air from the system was impacting the desired area.  The oxidation injection system was determined to be ineffective, but the helium testing results indicated that excessive negative pressure generated from the soil vapor extraction system was inhibiting airflow to the area.  The vapor extraction system was adjusted to enhance airflow and allow the remediation system to be more effective.  Despite this one area, no significant impacts have been observed in the surface water and the public water supply intakes are no longer threatened by the releases from these stations.

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Campbell Environmental Group

173 Gray Road

Falmouth, ME 04105

(207) 253-1990 f(207) 253-1988