Theme: 01. Remediation Technology Innovations

Topic Area: 01r. Thermal Conductive Heating: Best Practices and Lessons Learned

Formatted Title:

Pasco Sanitary Landfill NPL Site: Regulatory and Design Approach for Implementation of Thermal Conductive Heating

Background/Objectives:

The Industrial Waste Area Zone A at the Pasco Landfill National Priorities List (NPL) Site is currently undergoing in situ thermal remediation (ISTR) by thermal conduction heating (TCH) to treat approximately 27,000 cubic yards of soil with heterogenous patterns of chlorinated volatile organic compounds (cVOCs), total petroleum hydrocarbons (TPH), and other organic and non-organic analytes. The unique contamination profile originated from approximately 35,000 drums and containers containing hazardous industrial wastes that were placed unlined within Zone A in the 1970s. The site was added to the NPL in 1990, with vapor extraction interim actions over the years supported by PBS Engineering and Environmental. In July 2022 the multi-party group of potentially liable persons (PLPs) successfully completed the removal of all hazardous waste drums. ISTR and a final engineered cap will complete the final cleanup action. Floyd|Snider is the lead project coordinator, TRS Group, Inc. (TRS) is leading TCH implementation, and the work is being overseen by the Washington State Department of Ecology (Ecology).

Approach/Activities:

Following completion of the removal action, post-excavation soil characterization was completed to inform the development of remediation levels (RELs) and ISTR design. Additionally, samples were collected for a bench-scale treatment test. Volatile- and semi-volatile organic compounds and TPH were identified as the ISTR drivers and RELs were developed for cVOCs (trichloroethene, tetrachloroethene, and vinyl chloride), BTEX (benzene, toluene, ethylbenzene, and xylene), naphthalenes (naphthalene, 1-methylnaphthalene, and 2-methylnaphthalene), gasoline-range organics, and diesel-range organics. RELs were based on bench-scale testing results to determine technical feasibility and factoring in the final engineered cap over Zone A that will eliminate future stormwater infiltration. The Pasco site is ideal for application of TCH technology because of the dry soil conditions that will minimize the energy required for desiccation and expedite reaching the target treatment temperature identified by bench-scale testing. The thermal treatment area was divided into two phases of consecutive treatment to work within the limits of the existing on-site regenerative thermal oxidizer (RTO) used during the interim soil vapor extraction system and to sustainably reuse heater and vapor recovery components between phases. The existing air discharge permit for the RTO was also modified and reissued. Performance samples will be collected following both phases as system operation data indicates treatment is complete. A phase-tiered approach with multiple lines of evidence, including statistical evaluation of the 95% upper confidence level of the mean, was developed for performance sample evaluation. This approach was designed to account for the limited performance dataset following the first phase of treatment and shift toward statistical evaluation once the performance dataset is sufficient to ensure the final confirmation data set will achieve the RELs.

Results/Lessons Learned:

Early and ongoing coordination with Ecology was crucial to negotiating a customized approach to RELs within the State of Washington cleanup regulatory framework that addresses a range of non-continuous soil contaminants. A proactive transition between concluding the drum removal action and launching the thermal design process supported project efficiency and compliance with the Ecology enforcement order. Engaging TRS early during the drum removal created continuity during the site transition and took advantage of the general contractor’s presence when coordinating new power hookups, final site topography, utilization of existing vapor recovery lines, and bench-scale testing during post-excavation soil sampling. The range of experience brought by TRS, Floyd|Snider, the multi-group PLP members, and a third-party thermal expert reviewer was leveraged to thoroughly assess the thermal design at multiple stages and make intentional improvements such as adding additional deep vapor capture to reduce the risk of vapor migration to groundwater. ISTR installation and start-up is currently ongoing at Zone A, with the first phase of treatment expected to be complete by September 2024 and final completion in 2025.

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Layni Wachter

Biography