Formatted Title
8 Million Cubic Feet of CVOC-Impacted Groundwater Treated Using Large-Scale ERD in a Fractured Bedrock Aquifer
Background/Objectives
Background/Objectives. A 200-acre industrial manufacturing facility operated from the early 1960s until 2000, using chlorinated solvents in its manufacturing process. Chlorinated solvents used in the manufacturing process resulted in the release of CVOCs into the subsurface, forming a plume extending over 1,000 feet downgradient and reaching depths of nearly 100 feet below ground surface (bgs) in the underlying bedrock. The primary CVOCs forming the plume included trichloroethene (TCE), trichloroethane (TCA), and their degradation products. CVOC concentrations exceeded 5,000 micrograms per liter (µg/L) in the plume core. The bedrock consists of Pennsylvanian-aged, interbedded sandstone, shale, and calcareous marine deposits. CVOCs migrated into and through the two uppermost water-bearing bedrock units. Remedial investigation and cleanup began soon after manufacturing activities ceased in 2000. Multiple remedial strategies have been implemented across the site, including shallow soil source area excavation, soil vapor extraction system to mitigate vapor intrusion of CVOCs into the building, in situ enhanced reductive dechlorination (ERD), and phytoremediation along the eastern property boundary to treat the shallow, contaminated groundwater.
Approach/Activities
Approach/Activities. In 2014, CEC conducted an ERD pilot test, utilizing an engineered three-stage electron donor, ferrous gluconate solution, and anaerobic dechlorinating microbes, successfully demonstrating reductive dechlorination of the CVOCs in groundwater. The pilot test’s success led to the use of the ERD approach for the full-scale remediation effort. The Pennsylvania Department of Environmental Protection formally approved the cleanup plan specifying the full-scale ERD approach in 2017.
The full-scale remedial application design consisted of 102 injection wells with most of the wells arranged in a series of staggered transects perpendicular to the primary direction of the plume migration. Following hydrogeologic characterization, wells in the transects were installed with open-hole sections in the bedrock. Each well’s open hole section corresponded to one of three bedrock units delineated by CEC. The maximum vertical extent of treatment in the bedrock ranged from 5 to 93 feet bgs. The total CVOC plume treatment volume considered for product dosing estimation was roughly 8,000,000 cubic feet, with a total volume of approximately 88,000 gallons of ERD amendments specified for the treatment. The injection of the remedial amendments was completed in less than 13 days, finishing the project on time and on budget in the Spring of 2020. Well-specific volumetric loadings were determined to provide distribution of the reagents across the transects. These loadings were based on the injection wells' spacing within each transect and unit and estimated porosities within these units.
Results/Lessons Learned
Results/Lessons Learned. The favorable results achieved across the site to date and the field application/approaches will be presented in detail. Design verification using hydrogeologic characterization and product distribution activities will be presented and discussed. Remedial injectant and implementation logistics will be discussed.