In Situ Bioremediation Operations and Maintenance

Trihydro developed and installed an in situ bioremediation system to treat various constituents and contain plume migration at a Department of Energy Pantex Plant.

The project site presented significant challenges. Various constituents, including trichloroethylene (TCE), high explosives, hexavalent chromium, and perchlorate (an emerging contaminant), were present at the site in a relatively deep saturated zone, about 300 feet below grade, where conventional ex situ technologies were not an option for remediation.

Installing an In Situ Bioremediation System

Trihydro installed an in situ bioremediation (ISB) system at multiple locations to remove constituents and contain the plume. The ISB system treats constituents at a depth of about 280 feet below grade, where the impacts are in a complex geologic setting of perched groundwater on top of a thin, fine-grained aquitard. This inhibits contaminant migration downward to the regional Ogallala Aquifer.

The project required phased work with field efforts related to well inspection and testing, well maintenance, and scheduled amendment injection. Before injection, we evaluated each well with a hydraulic injected water test. The team used the resulting data to calculate specific capacity values for each well and determine the effect of biofouling and overall well efficiency in maintaining injection operations.

The water used during well testing and for injection blending was obtained from the onsite pump-and-treat system. Using treated water provided a cost-effective, sustainable solution while achieving the overall site goal to decrease the amount of water in the perched zone.

Maintaining the In Situ Bioremediation System

We maintained the ISB system by injecting various carbon substrates, such as emulsified vegetable oil and molasses, into the subsurface. Our team revisited the conceptual site model every year to apply a new understanding of subsurface conditions observed in monitoring wells and modify the injection design accordingly.

The project also included a large-scale injection of deoxygenated water to facilitate the bioaugmentation of the natural biota with species-specific bacteria known to fully degrade TCE and its daughter products.

Data Analyses

Trihydro performed statistical analyses of the site data to optimize the system. Data analyses provided insight into where and when well injections could be discontinued or paused, leading to cost savings for the client.

Trihydro also leveraged data to evaluate innovative aspects of the technology, such as performing a carbon isotope study, molecular diagnostics, decision tree analysis, abiotic degradation, and biotic degradation modeling.

Following each injection, Trihydro prepared reports documenting results. These reports focused on changes observed in the system and recommended optimization actions. Through Trihydro’s continual system optimization process, the team maximized mass reduction, reduced treatment costs, and gained efficiencies while maintaining compliance with the Record of Decision.

Project Outcomes

The project resulted in the following outcomes:

• Established treatment zones and achieved treatment goals for high explosives, hexavalent chromium, and perchlorate, as well as TCE degradation into daughter products. Recent and ongoing system expansions are addressing constituents across a broader area of the site.
• Saved client over $1 million due to targeted injection locations and optimizing injection volumes.
• Delivered value-added system optimization by completing a pH study, flux zone analysis, and molecular diagnostics such as a carbon isotope study.
• Completed a decision tree study with cost-benefit for determination of future remediation scenarios.