Presentation Title:
Choosing In Situ Stabilization and Solidification to Replace Dredge and Cap at the Gasco Sediments Site in the Portland Harbor Superfund Site

Background/Objectives:

This panel session will discuss how in situ stabilization and solidification (ISS) replaced more traditional dredge and cap technologies for sediment remediation at the Gasco Sediment Site in the Portland Harbor Superfund Site. ISS is a proven treatment technology identified in the National Contingency Plan. The decision to replace dredge and cap with ISS was made after EPA required that NW Natural re-evaluate an initially proposed dredge and cap remedy to address several site-specific concerns. This evaluation showed that the application of ISS to the full depth of contamination from the navigation channel to the top of the riverbank, coupled with an integrated deep ISS treatment barrier wall at the top of the riverbank managed by the Oregon Department of Environmental Quality, has the potential to more fully achieve all of EPA’s design objectives and better assure long-term protectiveness. The panel will discuss the complex and extensive set of factors and associated evaluations that led to this outcome.

Approach/Activities:

The session will open with a brief presentation that will describe the regulatory setting, explain the multiple lines of evidence and technical and source control basis for switching from a dredge and cap remedy to an ISS remedy, give a simple overview of the ISS treatability testing and lessons learned, and describe the field pilot study performed and lessons learned that optimized ISS construction means and methods and verified ISS sediment effectiveness at the Gasco Sediments Site. The presentation will be approximately 20 minutes leaving at least 80 minutes for the panel discussion.

Results/Lessons Learned:

The lessons learned from the full-scale pilot study and the previous treatability studies continue to show that switching the remedy from a traditional dredge and cap option to ISS is likely to more fully achieve all of EPA’s design objectives and better assures long-term protectiveness.

The panel would then be open to questions on a broad variety of topics, including:

Technology effectiveness and application (dredging and capping, ISS)
Management of NAPL and PTW
Treatability testing for grout mix selection (strength and permeability)
Treatability testing for leachability and chemical diffusion
Debris removal
ISS field implementation, including equipment, means, and methods
Water quality sampling and compliance
Swell management
Field laboratory and QA/QC testing methods
Regulatory decision making, including Tribal and other stakeholder factors
Public communications
And many others!

Taylor Crystal

Affiliation

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Choosing In Situ Stabilization and Solidification to Replace Dredge and Cap at the Gasco Sediments Site in the Portland Harbor Superfund Site