Formatted Title
Solvent Remediation Using Hydraulic Control with Biodegradation Amendment Injections and Source Thermal Soil Mixing with ZVI Injections Using LDA
Background/Objectives
Historical operations on the property included draining/emptying/disassembly of electrical equipment, steam cleaning, vapor degreasing, sandblasting components, varnishing and oven-curing finished components, small motor repair, electrical testing, and motor winding. The initial assessment indicated the presence of chromium and volatile organic compounds (VOCs) in groundwater, including chlorinated solvents and polychlorinated biphenyls (PCBs) in the soil. Constituents exceeding Groundwater Cleanup Target Levels (GCTLs) were primarily VOCs (benzene, chlorobenzene, trichloroethene [TCE], 1,3-dichlorobenzene [1,3-DCB], 1,4-dichlorobenzene [1,4-DCB], 1,2,4-trichlorobenzene), and PCBs. The PCBs were addressed by a shallow source removal back in 2010.
Groundwater remediation has been addressed using three different remedies; hydraulic control system for the downgradient end of the plume (2018), followed by thermal soil mixing at the source and carbon amendment along the 1,600-foot-long plume (2020).
Approach/Activities
Site assessment activities reported chlorinated solvent contamination in soil and groundwater to a depth of approximately 65 feet below ground surface (bgs). WSP designed and installed the hydraulic control system and injected carbon amendments at three transects along the 1,600-foot plume while contracting with Geo-Solutions Chlorinated Source Contamination Removal Technology to remove adsorbed, soluble, and dense non-aqueous phase liquid contaminant mass from the source area. This technology used large diameter auger (LDA) soil mixing equipment to deliver a mixture of high-pressure steam and hot air to volatilize the majority of the contaminant mass, followed by an injection of a zero-valent iron (ZVI) slurry into the thermally-treated soil column to act as a long-term polishing agent for continued treatment of residual chlorinated solvent contamination. A key advantage of this technology is that it combines several well-established treatment processes into a single operation to achieve a rapid cleanup at a competitive cost at the source.
Results/Lessons Learned
The hydraulic control system was effective in preventing further migration of the plume. The thermal treatment along with bioaugmentation injections along the plume has been effective in allowing the shutting down of the groundwater control system and bisecting the groundwater along the 1,600-foot plume. WSP used the technology’s innovative real-time data monitoring system to optimize the remedial process by evaluating trends in contaminant location, depth, and concentration. As a result, WSP was able to effectively delineate the horizontal and vertical extent of the source area and quantitatively assess the effectiveness of the treatment. WSP treated 36 LDA soil columns to a depth of approximately 65 feet over a 2,146 square-foot area. Based on the system operational data and the physical and chemical properties of the contaminants, WSP estimates that approximately 370 pounds of contaminants were removed during treatment. Thermal treatment and ZVI costs were approximately $200 per treated cubic yard.