Formatted Title
Rapid Abiotic Dechlorination of Chlorinated Solvents by Remediation Emplacement of Zero Valent Iron (ZVI)
Background/Objectives
In 2019, Wasatch Environmental performed a Phase II Limited subsurface investigation at a former dry cleaning site operating since 1987. This investigation determined that the tetrachloroethene (PCE) degradation products were above Environmental Protection Agency (EPA) Maximum Contaminant Levels (MCL) guidelines in the groundwater (GW) and detected PCE and trichloroethene (TCE) in the sub-slab soil gas at the location.
The GW plume and soil contamination were fully delineated, and the Corrective Action Plan (CAP) was submitted in March 2021 and approved by the Division of Waste and Radiation Control. The plan was to remediate a lateral treatment area covering 4,600 ft2 with ZVI. The site geology is gravely sand underlain by sand and silt layers.
Approach/Activities
Wasatch provided the borehole locations, vertical treatment zone, and emplacement interval (EI). C.E.R.E.S. Corporation provided the design support and product supply for the ZVI mass required to treat the contaminants of concern. A local contractor conducted the soil mixing of ZVI into the upper vadose zone between 0-8 ft bgs. Geo Tactical Remediation Ltd. performed the fracture injection emplacement of the EI volume into the deeper GW plume zones between 8-24 ft bgs.
The project emplaced a total mass of 68,420 lbs of ZVI by fracture injection. Geo Tactical’s work encompassed 27 emplaced boreholes with 110 discrete fracture intervals to ensure appropriate overlap and interconnectivity of fractures to allow for best contaminant contact. ZVI is beneficial because it creates a highly reductive environment and is persistent (treats potential rebound). ZVI abiotically reduces the chlorinated solvents to ethene.
Results/Lessons Learned
One injection event was commenced and completed in August 2021. The final GW monitoring results were collected in March of 2022 (seven months). The GW chlorinated solvent plume was treated to EPA MCL criteria. The volatile organic compounds: PCE, TCE, cis-1,2-dicholorethene and trans-1,2-dichloroethene levels all dropped below either detection limits or below MCLs.
The site currently meets the requirements for unrestricted property use. The site owner requested the facility be granted regulatory closure with a status of Corrective Action Plan with Controls to expedite the process.