Chlorinated volatile organic compounds (cVOCs) continue to be the primary contaminants of concern for the Department of Defense (DoD), even though many suitable treatment technologies have been developed and verified. Potential clean-up costs are in the billions of dollars. One of the greatest challenges remaining for remediating these contaminants at DoD sites and protecting downgradient receptors is the treatment and/or control of large dilute plumes. Remedial costs are particularly high at sites where contamination is extensive but concentrations are low, and there are few in situ technologies to cost-effectively enhance plume attenuation rates under these conditions. Current approaches to address large plumes, such as pump-and-treat, are typically long-term and have high capital and operations and maintenance (O&M) costs, including energy usage. On the other end of the spectrum, relying solely on monitored natural attenuation for treatment of large dilute cVOC plumes may require hundreds of years to achieve cleanup goals, which prolongs DoD liabilities, adds significant uncertainty when projecting life cycle costs, and is often faced with resistance from regulatory agencies.

The overall objective of this project is to demonstrate effective treatment of large, dilute cVOC plumes using a cometabolic approach that is both passive and sustainable. The approach utilizes gas pressure and solar power for remediation. Specific objectives include: (1) evaluating horizontal and vertical distribution of gaseous amendments within and downgradient of the target treatment zone; (2) quantification of oxygen and alkane gas degradation rates within the target treatment zone to optimize gaseous amendment delivery mass and frequencies; (3) quantification of changes in concentrations of target cVOCs and degradation rates within and downgradient of the treatment zone; and (4) determining the efficiency and reliability of passive techniques to provide sufficient amendments to promote cVOC degradation on a large scale.

This project entails cometabolic biosparging using horizontal wells installed perpendicular to groundwater flow across the width of a large, dilute cVOC plume. Contaminated groundwater will be treated as it flows through a biologically active zone (i.e., bio-curtain) created by biosparging oxygen and an alkane gas (propane, methane, or ethane). The gases will be pulsed into the aquifer using one of several different delivery systems including a traditional compressor, a solar-powered compressor, or via gas pressure alone. For this project, the team plans to use a passive delivery system that works entirely based on gas pressures with liquid oxygen and alkane gas. Control and monitoring equipment will be powered by solar energy, thus making this a completely off-the-grid biosparging system that requires minimal O&M.

This project will demonstrate a cost-effective, sustainable approach for enhancing bioremediation of large, dilute cVOC plumes. The biosparging approach will not require traditional grid power. Rather, gas pressure and/or solar energy will be used to distribute amendments and for system control, making this approach applicable even in remote locations. With dilute cVOC plumes being one of the key current issues for the DoD, this approach is anticipated to have broad applicability for the military and commercial entities. This approach is mature, cost effective, and can be safely applied in a number of different configurations based on site conditions. (Project Completion - 2022).