Formatted Title
Combined Colloidal Carbon and Colloidal ZVI Optimized HRDO Remedy for PCE/TCE Source Area
Background/Objectives
A former dry-cleaning facility operated at a commercial shopping center through 2000. A release of chlorinated solvents to the subsurface was subsequently discovered to have occurred through an impaired sewer line beneath a supermarket in the commercial shopping center several hundred feet away from the dry-cleaning facility during an assessment in 2012. The sewer line was replaced, but access to the release area has been difficult. The supermarket retail space was recently vacated, allowing for the opportunity to access the source area. Dissolved phase source area concentrations were over 10 mg/L for PCE.
Approach/Activities
Prior to in situ remediation a high resolution design optimization (HRDO) was performed with MiHPT to better define the injection area and vertical intervals for targeting of contaminants.
Based on contaminant mass distribution and lithology, Cascade and Terracon collaborated and selected a combined remedy of injectable colloidal ZVI, activated carbon and a bioaugmentation culture to quickly reduce contaminant concentrations to progress the release toward a no further action determination. Prior to injection, MiHPT was performed at 16 locations around the source area monitoring well. These results were used to finalize the injection approach and chemical dosing.
Results/Lessons Learned
MiHPT results and groundwater monitoring results available prior to this conference will be presented. The MiHPT identified that the majority of chlorinated contaminant occurrence was in a thin layer within course-grained soil atop a depression in the underlaying claystone. Post remediation monitoring has identified a 99.9% reduction in dissolved phase PCE concentrations through the first four months (October 2023), with other water chemistry parameters indicating continued biological treatment of cis-1,2-DCE and VC. Lessons learned over the life of the project will also be presented.