Theme: 01. Remediation Technology Innovations

Topic Area: 01d. Combined Remedies and Treatment Train Technologies

Formatted Title:

20 Years of Cleanup: A Tale of Six Remedies

Background/Objectives:

The site consists of a former aggregate quarry where industrial waste was used to backfill areas following cessation of quarrying operations in the 1970s. Contamination at the site includes volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), metals, and polychlorinated biphenyls (PCBs) within a layered, multi-aquifer system of alternating sand and clay. It was named to the National Priorities List (NPL) in the 1980s and has undergone multiple phases of investigation and remediation since the initial NPL listing, and even before. Since 2005, the site has undergone a series of remedial efforts designed to systematically address principal threat and low-level threat contamination in soil and groundwater, and also to protect on-site sediment and surface water. The site has experienced changing regulatory environments, revisions to cleanup levels/maximum contaminant levels, advances in remedial technologies, changes in understanding of the conceptual site model, and more recently the addition of the emerging contaminant 1,4-dioxane as a contaminant of concern. As a result, the remedial strategy for the site has evolved over the last 20 years, requiring re-evaluation of site data, development of phased remedial designs, and most importantly on-going communications with regulatory and project stakeholders to ensure that the remedial action objectives are being met in accordance with the Record of Decision (ROD).

Approach/Activities:

This presentation will provide a summary of each remedial phase of the site over the last 20 years, as well as a brief summary of activities performed prior to 2005. Remedial activities since 2005 have included (1) excavation of principal threat soil (VOCs) and ex situ thermal desorption of the soil for site re-use, (2) excavation of special materials (PCBs/metals) not able to be treated thermally and off-site disposal of that soil, (3) bioventing of vadose zone soil with lower concentrations of VOCs, (4) site dewatering to facilitate excavation and bioventing and treatment of captured groundwater, (5) in situ chemical oxidation (ISCO) to address VOCs that are not readily degradable aerobically (1,4-dioxane, chlorobenzene, etc.) and higher VOC mass areas, and (6) enhanced in situ bioremediation (EISB) to address lower concentrations of VOCs. A perimeter groundwater capture and treatment system has remained operational since the 1990s and will remain in place until overall cleanup criteria are met for the site. For each phase of remediation, a remedial design was prepared, the remedy was implemented, and post-remediation sampling/monitoring was performed to evaluate the performance of the remedy and plan for the next phase of treatment. The primary adjustment to the the remediation strategy was due to the inclusion of 1,4-dioxane into the site contaminant list, as well as identification of higher contaminant mass in groundwater than originally expected following the excavation and bioventing remedies. This remedial curveball warranted an interim step of ISCO prior to the ROD-prescribed EISB phase. To remain in compliance with the ROD, while addressing those contaminants and mass not readily treated by EISB, an ISCO reagent with a bioremediation supporting back-end was selected and implemented.

Results/Lessons Learned:

In addition to presenting the overall remedial strategy and a summary of results of each remedial phase, the presentation will also provide some lessons learned throughout the 20 years of site cleanup. The lessons learned will focus on the need to adapt to changes, development of mitigation strategies, and out of the box thinking to address site contamination, remain in compliance with a ROD, and ultimately achieve site goals. Additionally, the presentation will provide a summary of the key stakeholder communications aspects of the project, which were critical for getting regulatory buy-in and continuing to move the project forward.

Angela McGinty

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20 Years of Cleanup: A Tale of 6 Remedies