Petroleum Contamination Site Characterization and Remediation
Trihydro’s ongoing efforts at a Montana site with complex petroleum contamination have significantly reduced contaminant levels, supporting the client’s goal of eventual site closure.
Petroleum contamination in the soil and groundwater has impacted the Helena, Montana, operating facility, including two petroleum terminals and a pump station. A confidential client hired Trihydro to manage this site’s characterization and remediation efforts.
Addressing Site Challenges
Successful project management required overcoming several site-specific challenges. First, the facility’s operation since the 1950s and historical spills resulted in co-mingled contamination plumes. Second, the site had multiple water-bearing zones with varying pressure conditions. Third, potential risks associated with impacted soil and groundwater vapor required us to consider both on-site and off-site receptors. Finally, successful project management necessitated close coordination between various stakeholders, including multiple responsible parties, the Montana Department of Environmental Quality (DEQ), and adjacent property owners.
Performing Soil and Groundwater Investigations
Trihydro first performed multiple soil and groundwater investigations to identify areas of interest that might require active remediation. This included drilling over 25 monitoring wells to characterize groundwater flow and installing 14 soil borings to assess soil quality. Additionally, Trihydro used laser-induced fluorescence techniques to pinpoint areas with residual light non-aqueous phase liquid.
Data collected during the investigations led to the closure of four historically documented releases, receiving “No Further Corrective Action Required” approvals from the Montana DEQ. It also helped prioritize remaining areas for active remediation. The Montana DEQ subsequently approved a detailed plan outlining specific actions for each area. The most contaminated areas were addressed first in 2022 by expanding existing air sparge and soil vapor extraction (SVE) remediation systems and implementing new systems for SVE and oxygen injection.
Operating and Maintaining Remediation Systems
Trihydro continues to operate and maintain the remediation systems. Our team analyzes system data and regularly collects additional groundwater samples to track progress. These efforts have significantly reduced contaminant concentrations, as demonstrated by the routine groundwater sampling data evaluation. We also maintain a sub-slab depressurization system to mitigate potential vapor intrusion concerns at an on-site occupied structure.
Trihydro is collaborating with project stakeholders to optimize these remediation and groundwater monitoring programs. Ultimately, our goal is to facilitate the closure of the remaining documented releases stemming from the site’s historical operations.
