Pinnacle Engineering was retained to perform supplemental site assessments on a portfolio of properties, mostly retail gas stations, a client had recently purchased in Minnesota, North Dakota and Montana. The goal of the work was to initiate an assessment where little or no previous environmental investigation had been completed and to provide further delineation at sites where contamination had been previously identified. Pinnacle’s role was to complete the assessments and perform remediation at high risk sites or where dictated by regulatory requirements.
Contaminants identified in the assessments included petroleum compounds (benzene, toluene, ethylbenzene, xylenes, and diesel range or gasoline range organics) that originated in historical releases from the operation of underground storage tanks and distribution systems. Other non-petroleum impacts (chlorinated solvents) were also identified at several sites, creating additional challenges due to the complexity and co-solvency of intermingled plumes.
Using historical investigation information and additional subsurface investigation, Pinnacle recommended subsurface bioremediation amendment injections across sites based on regulatory requirements or client risk reduction decisions. In some situations, bioremediation was completed in conjunction with other remedial approaches, such as multi-phase extraction. Based on bioremediation data from previous sites, Pinnacle recommended zoned doses relative to respective contamination plume concentrations.
Work activities, including investigation, injection, and preliminary monitoring required completion within less than two years from the date of authorization. Pinnacle successfully completed the first injection in sub-freezing temperatures in winter of 2016, and the first round of monitoring (82 days) indicates BTEX compound removal at between 75% and 95% and GRO compound removal at approximately 78%.