In 2017, Trihydro began environmental work at a facility with petroleum contamination. Investigations identified areas for active remediation, facilitated the closure of four documented releases, and prioritized remaining areas for remediation.

A Helena, Montana, operating facility with two petroleum terminals and a pump station faced petroleum contamination in its soil and groundwater. Resource Environmental, LLC (RELLC) hired Trihydro to manage the characterization and remediation at the site. Successful project management required overcoming project-specific challenges.

First, the facility's operation since the 1950s and historical spills resulted in co-mingled contamination plumes. The site's geology also presented challenges due to multiple water-bearing zones with varying pressure conditions. Furthermore, potential risks associated with impacted soil and groundwater vapor necessitated considering both on-site and off-site receptors. Finally, successful project management required close coordination between various stakeholders, including multiple responsible parties, the Montana DEQ, and adjacent property owners.

Trihydro began work at the facility in 2017. The initial focus involved performing multiple soil and groundwater investigations to identify the areas of interest (AOIs) that could potentially 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 employed laser-induced fluorescence (LIF) techniques to pinpoint areas with residual light non-aqueous phase liquid (LNAPL).

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. The data collected also enabled the prioritization of remaining areas for active remediation. The Montana DEQ subsequently approved a detailed plan outlining specific actions for each area (Remedial Alternatives Analysis). The most contaminated areas were addressed first in 2022 by expanding existing vapor removal systems (air sparge and SVE) and implementing entirely new systems for SVE and oxygen injection.

Trihydro continues to operate and maintain the remediation systems. The team analyzes system data and regularly collects additional groundwater samples to track progress. These efforts resulted in significant reductions in contaminant concentrations, as demonstrated by the routine groundwater sampling data evaluation. To mitigate potential vapor intrusion concerns at an on-site occupied structure, Trihydro also maintains sub-slab depressurization system. Furthermore, Trihydro is collaborating with project stakeholders to optimize the monitoring programs for both groundwater and the remediation systems. Ultimately, the goal is to facilitate the closure of the remaining documented releases stemming from the site's historical operations.

"Trihydro has done an excellent work on this complex project. Their company has been instrumental in navigating a complex regulatory and technical environment. Trihydro has been professional, timely, and efficient. I would definitely recommend them for any similar type projects."

Greg A. Vogelpohl, Vice President, Resource Environmental LLC

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