The Lowell Case Study involved the remediation of a site located in Lowell, Massachusetts, where Gas Thermal Remediation (GTRTM) was employed to remove trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), and their degradation products from the soil and groundwater. The site covered a target treatment zone of 14,100 square feet, extending from the surface to 78 feet below ground surface (bgs). This zone was characterized by varying lithology, including historical fill, fine to coarse sand, silty sand, clayey silt, and dense silt with clay lenses overlying the bedrock. The groundwater was encountered at 21 ft bgs(Lowell, Massachusetts).
The remediation process was conducted using Thermal Conductive Heating (TCH) technology to heat the subsurface to a target temperature of 100°C. The heating period lasted for 160 days, during which 126 heater wells were used to elevate the temperature of the soil from near the ground surface down to bedrock. 67 Soil Vapor Extraction (SVE) wells and 52 Multiphase Extraction (MPE) wells were strategically located across the treatment zone to effectively extract contaminants and vapors(Lowell, Massachusetts).
Remediation Objectives and Approach: The primary objective of this project was to significantly reduce the mass of TCE and TCA in the soil and groundwater. Active heating at 100°C ensured that contaminants were volatilized and removed efficiently. The SVE and MPE wells operated throughout the target treatment zone to extract both non-aqueous phase liquids (NAPLs) and contaminated groundwater. The extracted off-gas was treated with C3 Technology and a granular activated carbon (GAC) system, while the condensed water was processed through a wastewater treatment system(Lowell, Massachusetts).
Remediation Results:
The average contaminant reduction across the site was 96%, with every chemical of concern (COC) reduced by more than 80%, surpassing the original remediation goals.
Specifically, the project achieved a 91.7% reduction in TCE mass and an impressive 99.99% reduction in TCA mass, indicating the efficacy of the thermal remediation approach in addressing both primary contaminants and their degradation compounds(Lowell, Massachusetts).
Site Features and Technology:
Heated Depth: The thermal treatment depth ranged from 0 to 81 ft bgs, ensuring thorough heating from the surface to the top of bedrock.
Extraction Wells: The use of 67 SVE wells allowed for effective vapor and steam extraction, while the 52 MPE wells were instrumental in extracting contaminated liquids, vapors, and groundwater.
Lithology: The site's lithology consisted of fine to coarse sand, silty sand, and clayey silt up to 69 ft bgs, with a dense silt layer and clay lenses encountered just above the bedrock.
Summary: The Lowell remediation project demonstrates the successful application of in-situ thermal remediation (ISTR) using TCH technology to reduce the concentration of complex contaminants. The integration of thermal conductive heating, SVE/MPE wells, and advanced treatment technologies like C3 and GAC systems contributed to the achievement of high contaminant mass removal rates. The project underscores the effectiveness of thermal remediation in reducing VOC and SVOC levels in challenging subsurface environments, ultimately meeting and exceeding the site-specific cleanup goals within a 160-day heating period.
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