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State of Oregon, Department of Environmental Quality (DEQ), 11 pp, 2018

This memo documents DEQ remedial decision-making on a portion of the Columbia Steel site in Portland to address dioxin contamination present in the site's Lowland Area. Remedial alternatives are constrained by seasonal (winter/spring) inundation of the Lowland Area. The proposed removal action consists of excavation and off-site landfill disposal of shallow soil from SU-13 (the most heavily contaminated area remaining on site) and in situ sequestration of dioxin contamination in remaining units (>520 pg/g PRG) using granular activated carbon (GAC). In and around SU-13 where the highest dioxin concentration (4,850 pg/g) was found, ~235 yd3 of contaminated surface soil will be removed to ~18" bgs, and GAC will be applied to the excavation "leave surface" as a measure of protection. In six of the remaining 12 Lowland Area SUs, which encompass a natural area >2 acres, soil removal is neither practical nor cost effective. Application of GAC as a contaminant sequestration agent is expected to result in a significant reduction (up to 90%) in dioxin bioavailability. Analysis indicates that sufficient GAC should be applied to represent a 3% concentration, by weight, within the top 6" of site soil, which is ~53 yd3 GAC on a dry weight basis. GAC would be hydrated prior to application as a weighting measure and applied as slurry during the dry season. See this Strategy Recommendation and other site documents at https://www.deq.state.or.us/Webdocs/Forms/Output/FPController.ashx?SourceIdType=11&SourceId=104&Screen=Load.

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