Formatted Title
In Situ Remediation of Chlorinated Solvents and Chlorofluorocarbons in Groundwater Using Aerobic Cometabolism and a Liquid Primary Substrate
Background/Objectives
The site is a legacy chemical manufacturing plant contaminated with a variety of chloromethanes, chlorinated ethanes, chlorinated ethenes, trichlorofluoromethane, and degradation products. A biosparging system was installed to treat the downgradient edge of a contaminated groundwater plume to control migration. The objective of the system is to reduce groundwater concentrations below applicable criteria before groundwater migrates off site and either enters another property or a water body.
The site is located in the central Appalachians, on the Appalachian plateau, in a temperate, moist environment. The ancient plateau is highly eroded, hilly, and heavily forested. The site is located on alluvium near the water body. Chemical manufacturing activities at the site date back to before World War II.
Approach/Activities
The biosparge system installed at the site includes 38 biosparge wells installed in two rows on 25-foot centers, with the rows located 70 feet apart and placed to cross the plume roughly perpendicular to flow. Compressed air is fed to the system at an average flow of 4 scfm per well. The primary substrate (SoyGold® 5000) is injected into each biosparge well periodically (about every 9 months) and the sparge process is used to distribute the substrate into the aquifer. There are three transects of three monitoring wells across the biosparge system providing data from up-gradient of the system, between the biosparge rows and down-gradient of the system. In addition, a row of monitoring wells is located at the property line. Monitoring includes the COCs, geochemical parameters, field parameters, total organic carbon, and functional genes. Functional genes include short chain alkane monooxygenase (SCAM), propane monooxygenase (PPO), soluble methane monooxygenase (SMO), toluene monooxygenases (RDEG and RMO) and DCM reductase. It is assumed that any increase observed in the presence of enzymes is a result of the addition of SoyGold® 5000 and aeration of the aquifer.
Results/Lessons Learned
Current results indicate a downward trend across several of the transects. The system appears to have increased the presence of RDEG and RMO throughout the treatment system and the decline in concentration is attributable to generation of these enzymes, which are known degraders of chlorinated compounds. Temporary increases in soluble methane monooxygenase (sMMO) have also been observed, suggesting temporary and localized development of anaerobic activity. The system does not appear to have increased the presence of more general degraders like SCAM and PPO, with degradation apparently specific to halogenated compounds.