Chlorinated solvents like tetrachloroethene (PCE) and trichloroethene (TCE) are man-made chemicals typically used in industrial applications, such as metal de-greasing or dry cleaning. When introduced to the environment through historical or current activities (e.g., waste management practices, manufacturing processes, spills, etc.), chlorinated solvents can lead to persistent contamination of soil and groundwater. Unlike other contaminants, chlorinated solvents do not degrade effectively under aerobic conditions. As such, addressing chlorinated solvent impacts typically requires costly investigation and remediation efforts. Site-specific remedial strategies are developed based on site characterization data, logistics, and regulatory requirements. There are a number of proven technologies that can be combined to comprise an effective suite of remedies to reduce contaminant concentrations and risks to human health and the environment.
One of the most effective remedial options, assuming available access, is to physically remove the source area through excavation of contaminated soils. Waste characterization data and approved waste profiles are required for proper disposal of excavated materials in accordance with all applicable federal, state, and local laws and regulations. Depending on the age of chlorinated solvent contamination, source area removal can stop or entirely prevent contaminants from further leaching into groundwater. Additional remedial technologies may be necessary to treat remaining soil and groundwater impacts, particularly if the release is historical in nature.
Thermal remediation through electrical resistive heating can effectively degrade and remove chlorinated solvent impacts in both soil and groundwater over a relatively short period of time. Using a grid of buried electrodes, subsurface soil and groundwater are heated to a critical temperature to thermally degrade and/or volatilize chlorinated solvents. Volatilized solvents are captured through a vapor recovery system and condensed into liquid form for off-site disposal. These systems have significant capital expense but are capable of more rapid source area cleanup.
For treatment of groundwater impacts, ex-situ treatment technologies, such as pump and treat were the most common remedial technologies. However, over the last 20 years, most remedial treatment technologies utilize in-situ methods. Currently, a primary method of remediation of chlorinated solvents in groundwater is in-situ chemical reduction (ISCR). ISCR facilitates reductive dechlorination through biotic and abiotic processes, using a mixture zero-valent iron (ZVI), a carbon nutrient source, and Dehalococcoides (DHC) microbial culture. Applications of ISCR reagents are implemented through subsurface injections and are active for a period of up to 2-3 years, depending on subsurface conditions and chlorinated solvent concentrations. Multiple rounds of ISCR injections may be necessary to decrease chlorinated solvent and daughter product concentrations below remediation goals. Longer-lasting ISCR reagents can be injected to create a permeable reactive barrier (PRB) that remediates impacted groundwater as it flows through. PRBs are generally utilized to prevent off-site migration of impacted groundwater or as “polishing” steps to treat residual concentrations at a contaminant plume boundary.
Sites with significant chlorinated solvent contamination may have a long tail for continued monitoring and evaluating compliance after remedy implementation. Institutional controls (ICs) are key components that should be evaluated as part of a suite of remedial options to ensure ongoing protection of human health and the environment. Site-specific ICs may include environmental covenants that restrict property usage (e.g. industrial usage only or no potable wells) and/or soil management plans to protect site workers from hazards associated with residual impacts.
The technologies and methods described above are only some of the options available to address chlorinated solvent contamination at a property. August Mack Environmental continues to partner with new and established clients to develop innovative strategies to navigate chlorinated solvent contamination with respect to client goals, regulatory program requirements, and environmental best practices. Register now for our upcoming webinar to learn more about a pilot study for remediating chlorinated solvents in a fractured bedrock aquifer in northern Ohio.