Theme: 01. Remediation Technology Innovations

Topic Area: 01q. Electrical Resistance Heating: Best Practices and Lessons Learned

Formatted Title:

Fast Track to Closure: Remedy Selection

Background/Objectives:

The Site was a former dry-cleaner facility that operated from approximately 1949 through 2014 and used tetrachloroethene (PCE) and trichloroethene (TCE) in the dry-cleaning process. In 2011, approximately 7,900 pounds of waste PCE and TCE sludge and filters were transported offsite for disposal. In 2019, during a Phase I and Phase II Environmental Site Assessments on an adjacent property, PCE and TCE were detected in three soil vapor samples above vapor intrusion screening levels. As a result, the Idaho Department of Environmental Quality (DEQ) requested an initial site characterization at the former dry-cleaner Site. The 2019 site investigation included three soil borings and two soil vapor samples that detected PCE and TCE. In 2020, the EPA Environmental Response Team collected additional soil gas samples and subcontracted the installation and sampling of groundwater at and around the site. Five of the soil gas samples exceeded removal management levels for PCE. PCE also was detected in the groundwater samples, but at concentrations well below the maximum contaminant level (MCL).

Approach/Activities:

In 2022, an underground storage tank (UST) was discovered during the removal of a heating oil tank by the owner. This UST had apparently been used to store dry cleaning fluid. Tetra Tech removed the tank and fifteen 55-gallon drums of contaminated soil. Tetra Tech collected additional groundwater, soil and vapor samples in February/March 2023. Groundwater exhibited detectable concentrations of PCE that were less than the MCL. However, as long as residual PCE and TCE remain in the soil column, transport to groundwater is possible via infiltration and/or vapor transport. In addition, the highest soil impacts were generally located 15 feet below ground surface on top of a clay layer. Below the clay layer, the soil is generally sandy, and the concentration decreases significantly with depth. As a result, remediation efforts were focused on how to target the removal or treatment of the soil below the former tank and adjoining area. An alternative analysis eliminated excavation due to the proximity to the building.

In situ thermal remediation (ISTR) has been selected to remediate the remaining soil contamination and to achieve site closure. This method was selected over other remediation alternatives based on treatment time, cost, and space constraints at the site. Haemers Technologies, Inc. was selected as the technology provider and contracted in August 2023. Once the ISTR activities have been completed, contaminant concentrations will be reduced in site soils to below their respective RSLs. The ISTR remediation will begin in early 2024 and conclude late Spring 2024.

Results/Lessons Learned:

A draft Site Closure Plan has been developed by Tetra Tech and has been approved by the DEQ. It is currently under the mandatory public comment period. The closure schedule is anticipated to be completed in 180 days with the exception of waste removal and decontamination due to:

Uncertainty in the time required for the in-situ thermal remediation to reduce soil contamination levels below RSLs.
Co-location of the contaminated soil with site structures (buildings), which requires additional and more complex remediation setup and controls.

Site investigation data, with the remediation selection evaluation and process, and all results of the ISTR remediation will be presented.

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Maureen McGraw