The subject site is a former retail petroleum station in Decatur, Alabama. Following the removal of nine USTs in 2010, two phases of site investigation were performed to delineate the extent of petroleum hydrocarbon impacts in soil and groundwater. BTEX constituents and MtBE were detected in groundwater at concentrations exceeding Site Specific Target Levels (SSTLs). A Corrective Action Plan consisting of excavation and groundwater remediation by natural attenuation was implemented in June 2013. Due to a significant increase of benzene in a groundwater sample collected in June 2017, an alternate form of remediation was determined to be necessary. The selected technology was a BOS 200® injection within a 1,600 sq ft treatment area. Four post-injection progress analysis sampling events were performed following the completion of the injection. Based on the findings that no wells produced groundwater samples that exceeded SSTLs during the progress analysis sampling events, ADEM issued a No Further Action (NFA) letter in July 2019.
The primary challenges were injection at the relatively shallow depth of 6 feet bgs without daylighting and attaining groundwater remedial goals within one month of injection in the remedial progress monitoring well (MW-19).
The BOS 200® injection design was developed based on existing site data with the goal to achieve cleanup standards less than 4 weeks from the time of injection. A total of 480 injections were completed within 64 points on 5-foot centers in June 2018. The treatment area was approximately 1,600 square feet in area, with a targeted treatment interval of 6 to 20 feet bgs. A total of 4,800 pounds of BOS 200® was mixed with injected over a period of four days. A total of 1,450 pounds of BOS 200® was mixed with 4,320 gallons of water and injected as a slurry.
Following three post-injection groundwater sampling events demonstrating that cleanup goals had been achieved, the ADEM closed the site and issued a No Further Action With Conditions letter to the responsible party on July 17, 2019.