Formatted Title
In Situ Remediation of Chlorinated Solvents in Tight Matrix by Applying Low-Intensity Electric Fields
Background/Objectives
Background/Objectives. The Denver Basin is a formation along the Front Range (Colorado), which includes the Denver metropolitan area. Material overlaying formations such as the Denver and Arapahoe aquifers consist of sandstone, mudstone, claystone, and conglomerate. Saturated alluvial aquifers common to the area primarily consist of clay and silty sandy clay. Hydraulic conductivity and low groundwater flow velocity are indicative of the low permeability of the aquifer material; therefore, sites impacted with chlorinated volatile organic compounds (CVOCs) are difficult to remediate in situ. Remedial technologies requiring injections and dispersion are typically restricted in the Denver metropolitan area due to the low permeability of the clayey aquifer material. Electrochemical remediation technologies are an option for overcoming this challenge to achieve in situ treatment of groundwater in low-permeable aquifers. This presentation describes a low-intensity electric field technology that has been successfully applied in treating CVOC-impacted groundwater in the low-permeable aquifers.
Approach/Activities
Approach/Activities. This presentation will summarize case studies for two sites in the Denver metropolitan area where the low-intensity electric field technology has been implemented. From these and other case studies (as well as past research work) mechanisms were derived to explain how the technology works to overcome the challenges of low-permeable aquifer material. The first case study is a residential site downgradient from a former dry cleaner. The site consisted of three electrochemical systems with voltage gradients set at <10 V/m. The second case study is a Brownfields site, which consisted of five systems with voltage gradients also set <10 V/m. Both sites were successfully closed with “no action determination” from the Colorado Department of Public Health and Environment.
Results/Lessons Learned
Results/Lessons Learned. The first case study achieved a 75% reduction in PCE within 92 days. The second case study achieved a PCE reduction rate of 31 to 50 μg/L/day with no rebound after the system's decommission. The low-intensity electric field creates a “micro-capacitor” mechanism, in which perpetual charging and discharging of electrons form a reductive treatment zone, resulting in an abiotic dichlorination dominant pathway that can effectively destruct CVOCs and other constituents of concern (COC) that can be reductively degraded. The process also can trigger electrical repulsion and configuration shifts of the water cage at the solids-water interface, resulting in enhanced desorption of COC into water for mass removal and degradation. This presentation will include more detailed discussions of such mechanisms. Synergies of this technology with other technologies will also be discussed.