Butte, Montana

A diesel release due to defects in underground piping was discovered during removal of underground storage tanks (USTs) at the former Port of Montana Facility (Facility) in Butte, Montana. Since discovery of the release, multiple investigations and remedial actions have been implemented at the Facility to address subsurface contamination. WET has led investigations, evaluation of potential remedial alternatives, and implementation of these alternatives at the Port to address subsurface contamination. Investigations completed by WET included a laser-induced fluorescence (LIF) investigation which aided in delineating the magnitude and extent of contamination and determining subsurface hydraulic properties. To support the LIF investigation, a scope of work was developed for the subcontractor and contractor bids were reviewed for adherence to its requirements before issuing an award. WET developed a sampling grid for the placement of LIF borings and confirmation sample locations, provided Geoprobe direct push services to advance the LIF probe to desired depths, and technical oversight to complete the LIF investigation. Additional activities included collection of detailed field notes, data interpretation, and development of a report detailing the LIF findings. Geoprobe services were also used to collect confirmation samples to confirm the LIF results.

Results from the LIF investigation suggested that bioventing may be a feasible remediation option. To further evaluate this alternative, WET conducted a pilot test. The pilot test included drafting of the scope of work, installation of five soil vapor probes, conducting background respirometry testing on vapor points and wells near the extraction point, conducting a blower “step-test”, conducting post-shutdown respirometry testing, collecting detailed field notes, and data evaluation. Respirometry testing included monitoring oxygen, carbon dioxide, and volatile organic compound (VOC) concentrations in vapor points and monitoring wells. The blower “step-test” included incrementally increasing vacuum applied to the extraction well and respirometry testing following each vacuum increase. The blower was then operated at maximum vacuum for a period of 24 hours. Following blower shutdown, respirometry testing was conducted twice per day until concentrations returned to background conditions. Data from this pilot test indicated bioventing would be a suitable option for Facility remediation.

Remedial actions completed by WET include operation of a skimmer system to recover free product and design, installation, construction, operation, and monitoring of a bioventing system. WET drafted a scope of work detailing the number of necessary remediation wells and their construction, required blower size, and monitoring details for the proposed system. Once the scope of work and design was approved, WET supervised installation of five additional extraction wells and system construction, which included trenching lateral piping from each remediation well to a shed housing the blower, construction of a manifold for the individual wells, and connection of system components. Following installation, WET conducted system optimization to ensure maximum treatment in areas displaying greatest contamination as determined by VOC concentrations measured in the air stream. Currently, WET conducts routine system checks that include measurements of flow, vacuum, and VOC concentrations at various system locations. In addition to routine system checks, WET conducts semi-annual monitoring of the system effluent and Facility groundwater to track system effectiveness.