Formatted Title

Interim RA at Hamilton Labree Superfund Site

Background/Objectives

On behalf of U.S. EPA (lead agency), the Washington Department of Ecology, and the USACE Seattle District, AECOM (as affiliate company, URS) implemented an interim RA at the Hamilton/Labree Roads Groundwater Contamination Superfund Site, OU 1, which spreads across roughly 10 acres. The source of contamination within OU1 is thought to be the result of a spill or direct release of liquid PCE into Berwick Creek. The contaminants of concern (COCs) in OU1 include PCE and its degradation products TCE, cis-1,2-DCE, and vinyl chloride. Tetrahydrofuran and methylene chloride are also COCs.

The purpose of the RA was to implement an interim remedy which consists of a combination remedial approach using in situ thermal remediation (ISTR) and enhanced anaerobic bioremediation (EAB) to achieve a 90 percent reduction in contaminant mass discharge from the OU1 source area. The interim remedy for OU1 includes the following RA components:

• Management of surface water to enable ISTR and other remedial measures to be implemented in the vicinity of Berwick Creek;
• ISTR of soil with PCE concentrations greater than 10 mg/kg;
• Excavation and off-site disposal of creek bed surface soil and sediment with PCE concentrations greater than 0.468 mg/kg;
• EAB treatment of any remaining subsurface soil with PCE concentrations greater than 10 mg/kg;
• EAB treatment of groundwater with PCE concentrations greater than 4,000 µg/L; and
• Site reclamation and creek restoration following remedial activities.

Approach/Activities

URS/AECOM with teaming partners TerraTherm, Inc. and Brice Environmental, prepared the ISTR, EAB, and Berwick Creek remedial/ engineering design, management, quality, and safety documentation as part of a design-build remediation system, commensurate with the bulleted steps delineated above. ISTR was implemented as a combination of electrical resistive heating (ERH) targeting the tighter alluvium and till stratigraphies and steam enhanced extraction (SEE) to treat the highly permeable glacial outwash sands. A total of 49 steam injection wells and 49 electrodes were installed to heat and maintain the thermal treatment zone (TTZ) at the boiling point of water. The ISTR system was also equipped with 21 horizontal vapor extraction wells to aid in mass recovery and pneumatic control near the surface, as well as 15 multi-phase extraction wells to assist with deep mass removal, pneumatic control, and the TTZ water balance. Approximately 550 standard cubic feet per minute (scfm) of non-condensable vapors and steam and approximately 14.1 gpm of liquids were extracted during ISTR operation to maintain inward vapor and hydraulic gradients (i.e., pneumatic and hydraulic control). The total operational duration for the thermal remedy was 154 days. EAB injections were attempted at 148 direct push injection points, four injection wells, 12 steam wells, and three multiphase extraction wells. A combination abiotic/biotic reducing amendment (ferrous iron gluconate and ABC^®) and reductive dechlorinating bacteria were injected to promote anaerobic dechlorination of the COCs. Prior to implementing the interim RA, a baseline mass discharge measurement was performed. This measurement consisted of the collection of groundwater samples and slug tests from monitoring wells located along the established mass discharge transect and water level measurements from monitoring wells located within OU1. As remediation progressed, performance monitoring data were collected and evaluated to aid in optimization of the remediation during operation and determining when the interim RA was complete.  Following completion of the interim RA, a post-RA mass discharge measurement was performed and compared to the baseline mass discharge measurement to evaluate the overall efficacy of the interim RA for OU1. 

Results/Lessons Learned

The ISTR system removed 7,813 lbs of PCE from the subsurface; over 123 million cubic feet of vapor was removed and treated; and over 4.5 million gallons of water was removed and treated. Post-treatment soil sampling results from all 15 boring samples collected from within the TTZ were below the 10 mg/kg cleanup goal for PCE. The remediation goal for groundwater at the Site is to achieve 90 percent reduction in PCE and TCE contaminant mass discharge from the source area through the defined mass discharge transect. An interim mass discharge measurement was completed in January 2023 to evaluate progress towards the 90 percent reduction goal. The results indicated that the RA has achieved an approximate 94 percent reduction in PCE and TCE contaminant mass discharge from the transect, when compared to the baseline mass discharge measurement. Although the mass discharge goal has been met, pockets of residual contamination remained upgradient of the transect, where PCE concentrations exceeded the 4,000 µg/L goal. Therefore, additional strategic EAB injections were completed in August 2023 in those areas to further reduce concentrations to below 4,000 µg/L. Additional groundwater monitoring was completed in October 2023 and another is scheduled for March 2024. The results of these events will be used to confirm the RA objectives have been met.