In Situ Bioremediation System Design and Remediation Program
Trihydro reduced tetrachloroethene (PCE) concentrations by up to 99% at a Resource Conservation and Recovery Act (RCRA) site in Texas. With successful remediation and containment plans in place, the project has transitioned from corrective action to long-term monitoring.
The active Texas RCRA facility selected Trihydro to provide engineering services to address impacts from an on-site solid waste management unit. Subsurface impacts consist of volatile organic compounds and are primarily chlorinated solvents.
Trihydro has focused on assessing soil and groundwater impacts linked to past activities at the facility. Although the site is just 25 acres, the investigation expanded to over 100 acres due to the complex geology and plume data collected from more than 100 soil borings and 28 groundwater monitoring wells.
Trihydro assessed various remediation technologies and determined that a combination of in situ bioremediation (ISB) and institutional controls—including a Plume Management Zone where no water wells could be installed—would be the best approach to manage groundwater impacts at the site.
The team conducted a pilot test to gather data for a full-scale ISB system, which achieved a 95–99% reduction in PCE concentrations within five months. Monitoring showed that the treatment zone expanded downgradient, indicating that treatment from injections focused on a smaller zone was effective over a larger area.
Trihydro then launched a full-scale ISB program informed by pilot test data. The design involved source area and biobarrier treatment using emulsified vegetable oil delivered through injection wells. These wells were arranged in a grid in areas with the highest PCE concentrations. Biobarriers featured three linear arrays aligned perpendicular to groundwater flow with a reactive treatment zone for PCE-impacted groundwater in each biobarrier.
The initial emulsified vegetable oil injection resulted in an 80–99% reduction in PCE and other chlorinated compounds. Reinjection was performed at two-year intervals to achieve further reductions and maintain the biological treatment zones.
Trihydro’s work at the site has transitioned the project from corrective action to long-term monitoring. As a result, monitoring has been reduced from quarterly to annual.
