Background/Objective: The Solvents Recovery Service of New England (SRSNE) Superfund Site is located in Southington, Connecticut (EPA Region 1). SRSNE processed more than 100 million gallons of solvents between 1955 and 1991. Disposal to lagoons and other releases produced a non-aqueous phase liquid (NAPL) source zone in overburden and fractured bedrock. The PRP Group formed in 1993, and performed two Non-Time-Critical Removal Actions to hydraulically contain impacted groundwater, completed the Remedial Investigation / Feasibility Study (RI/FS), and in 2015 completed in-situ thermal remediation (ISTR) of overburden NAPL, as specified in the 2005 Record of Decision (ROD).
Approach/Activities: The ROD required ISTR to address an overburden NAPL zone delineated during the FS. This resulted in a target area/volume of 2,800 m2 / 36,000 m3 estimated to contain 230,000 to 910,000 kg of VOC mass, depending on the NAPL distribution and assumed bulk retention capacity. The ROD expected ISTR to remove 95% to 99% of the NAPL mass. The 2008 RD/RA Statement of Work (SOW) provided numeric clean up levels for soil, stating: “VOC contamination shall be reduced to levels that are not indicative of the presence of pooled or residual NAPL”. Sensitivity analysis of aquifer and NAPL characteristics defined soil concentrations exceeding 42 to 222 mg/kg for selected individual VOCs as indicative of NAPL presence; these values became the required clean up levels in the SOW. Key aspects of the design process focused on drilling methods to minimize the potential for further downward migration of NAPL during installation of the 607 heater wells, and a robust vapor treatment system. The heated volume increased to 43,300 m3 during drilling, due to NAPL found beyond the target area, and installation of heaters through weathered rock into the upper meter of competent bedrock. During ISTR, VOC mass removal rate peaked at 4,500 kg/day, with a higher-than-expected fraction of combustible aromatics, resulting in modifications to the vapor treatment system. Meeting required soil concentrations necessitated field modifications to the heater and insulation system. Final soil sampling occurred in February 2015. As VOC mass removal rates dropped below 45 kg/ day (and continued to decrease to <10 kg / day), vapor treatment changed from thermal oxidation to GAC adsorption, for both cost effectiveness and public relations.
Results/Lessons Learned: ISTR at a high VOC mass site requires a robust design, and an experienced team to address the project issues. Drilling techniques to minimize downward NAPL migration were cost-effectively implemented. Discovery of NAPL beyond the planned treatment zone required adaptive system redesign during construction. The mix of chlorinated, aromatic, and ketone compounds required unique monitoring approaches to safely operate the oxidizer and track incremental and cumulative VOC mass removal. Air permit equivalency limits were met throughout ISTR. The soil clean-up levels were met in all samples (50 locations, 2-3 samples vertically per location), with 99.7% VOC removal from soils. Although not a performance metric per the SOW, total VOCs were monitored in groundwater and found to decrease significantly during and following the thermal treatment process. The highest pre-treatment groundwater TVOC concentration was 598 mg/L, which increased to 645 mg/L shortly after heating began. Post-treatment (2/2015), this well dropped to 34 mg/L TVOC. Groundwater concentrations continue to decrease, with a TVOC concentration of 0.577 mg/L at this well in July 2016. 225,000 kg VOCs were removed with ISTR, which combined with an estimated 170,000 kg removed from the ISTR zone through biodegradation during the time between NAPL delineation and ISTR, reasonably compares with the pre-treatment mass estimate.
Bruce R. Thompson
de maximis, inc.
Mr. Thompson serves on the Board of Directors for de maximis, inc., with responsibility for New England operations. He has more than 25 years of experience in complex site investigation and remediation, and currently serves as the Project Coordinator for RI/FS, RD/RA, and/or NTCRA work at the SRSNE, Nuclear Metals, Inc., Industri-plex OU2, and York Oil OU1 & OU2 CERCLA sites, and for a single party RCRA RFI/CMS. He is a 1985 graduate of the United States Naval Academy.
Jeffrey S. Holden, PE, LSP, LEP
ARCADIS U.S., Inc.
Mr. Holden is a Vice President and Principal Engineer with Arcadis located in the Manchester, CT office. He has over 24 years of experience in the investigation and remediation of industrial sites under various regulatory programs including Superfund, RCRA, TSCA, and the Massachusetts Contingency Plan. He is a registered Professional Engineer in CT and MA, a Licensed Site Professional in MA, and a Licensed Environmental Professional in CT. He holds degrees in Mechanical/Aeronautical and Civil/Environmental Engineering from Clarkson University.
James Galligan, P.E.
Jim Galligan is Senior Vice President of Operations at TerraTherm. He has over 25 years of experience designing and implementing a variety of remediation technologies. Jim joined TerraTherm when it was founded in 2000, serving in a variety of technical and management roles, implementing in-situ thermal remediation technologies at sites across the US and at a number of international sites. He holds a B.S. in Mechanical Engineering from Boston University and an MBA from Northeastern University. Jim provided engineering support and management oversight for the SRSNE project dating back to 2008 when TerraTherm first began working on the project.