Background/Objectives: Electrical resistance heating (ERH) is a well-established technology for contaminant mass removal particularly in source areas. Traditional In Situ Thermal Remediation (ISTR) operating temperatures (100°C or higher) limit microbial activity in the source area. However, thermal treatment can be performed with a concerted heat enhanced bioremediation strategy in the dissolved plume. Moderate heating (i.e. 35°C) accelerates dissolution/desorption and enhances biotic degradation. Anaerobic dehalorespiration reactions responsible for the in situ degradation of chlorinated solvents can approximately double with every 10°C increase in groundwater temperature. As such, recirculating post-ISTR heat energy from the ISTR source zone area along with biostimulation amendments throughout the larger dissolved phase plume can provide an efficient remedy for chlorinated Sites featuring a distinct source area and large dissolved plume.

Approach/Activities: This presentation will chronicle the overall performance of the Bothell Service Center Simon and Sons BSCSS project in Bothell, WA. The BSCSS site is a former dry cleaning/service station facility impacted by tetrachlorethene (PCE), trichloroethene (TCE), and their daughter products. This Site is situated in the middle of downtown Bothell, and is at the heart of the City of Bothell’s redevelopment efforts. Kane Environmental led the efforts for the combined remedy project as the principle consultant on the Site, with collaborative input from Cascade Thermal, ETEC, and Mr. Brian Timmons. The overall project team developed a high resolution site characterization (HRSC) strategy to further delineate the source zone, size an ERH treatment system for source zone mass removal, and design a biostimulation/warm-water recirculation system to utilize residual heat energy from the ERH project to enhanced dehalorespiration rates in the larger dissolved phase plume. The overall combined remediation strategy tied the two technologies and project phases together spatially and temporally, in order to improve projects costs, timeline, and efficiency while optimizing the downgradient impacts of ERH treatment on bioremediation efforts.

The ERH system consisted of 38 electrodes installed to depths of up to 55 feet below ground surface (bgs). The wellfield layout and treatment depths were selected for source zone contaminant mass removal based on 3-D EVS modelling of the HRSC efforts. Following a 100⁰C thermal treatment approach over the course of a 167-day run-time, the source zone was remediated from an average concentration of PCE in soil of 3,504-ppm to a post-ERH average concentration of 0.0379-ppm. Following the 99.9989% mass removal in the source zone, the biostimulation/biorecirculation system was started in order to remediate the downgradient dissolved phase plume. The recirculation system placed numerous injection and extraction points within the ERH treatment area and throughout the larger dissolved phase plume, allowing post-ERH heat and Carbstrate amendment injections to be homogeneously dispersed throughout the plume. Periodic monitoring of chlorinated compounds, geochemical parameters (ORP, TOC, DO), and related microbial populations (qPCR - quantarray chlor) are being used to quantitatively evaluate the degree of biodegradation occurring throughout the plume.

Results/Lessons Learned: The BSCSS ERH/bioremediation project presents a successful example of when and how in situ thermal remediation (ISTR) technologies can be seamlessly integrated with a bioremediation strategy to meet site cleanup goals expeditiously while minimizing overall project costs. The discussion will center on the economic drivers surrounding the remedial efforts, technology selection, combined remediation system design considerations, and the overall results of both the ERH and bio-recirculation components of the overall project approximately one year post thermal. Quantitative biodegration data will be presented to show the overall efficacy of this approach, and inferences will be made surrounding overall impacts to the RORI for this legacy Site.