Geo2 TM Remediation Ltd. carried out the remediation of a former service station following historic contamination from leaking underground storage tanks (USTs). Concentrations were significant near the source area and migrated downgradient towards the edge of the property. The initial remedial strategy included the removal of the leaking USTs and excavation of the impacted soils. A Dual-Phase Vacuum Extraction (DPVE) system was installed to recover residual light non-aqueous phase liquid (LNAPL) and reduce the total petroleum hydrocarbon (TPH) concentration in groundwater. After one year of operation, the DPVE system had reduced contaminant concentrations across the site, but had reached asymptotic levels commonly observed in physical abstraction-based systems. The DPVE system was shut down to allow for rebound monitoring, which showed the successful removal of free-phase contamination. However, the dissolved-phase TPH concentration had not been reduced to below the site specific target levels (SSTLs) issued by the regulatory authorities.
The next phase of remediation included an in-situ chemical oxidation (ISCO) application using RegenOx™ to augment the DPVE system and improve the contaminant abstraction efficiency. This approach was novel (never attempted previously) and was based on features of the RegenOx product designed for other purposes. RegenOx was applied via direct-push technology to the residual dissolved-phase contaminant plume. The DPVE system was re-structured to treat the soil above the water table in order to provide on-going soil vapor extraction. RegenOx fully oxidized some of the TPH but also produced more soluble intermediate products by partial oxidation and temporarily increased the desorption of TPH sorbed to the soil matrix (Figure 2). As a result, 2 weeks after the RegenOx injection, the DPVE system was lowered into the groundwater once more to remove the partially oxidized contaminants and the desorbed fraction produced by the RegenOx application. The extraction efficiency of the DPVE system was enhanced due to the application of RegenOx.
This remedial technique was completed again as a second RegenOx application was applied. As a result, regulatory closure was granted - on time and on budget – and the development of the site proceeded on schedule.