Post-Remedy Evaluation of In Situ Stabilization Used to Treat Seven Compound Classes in a Remnant Industrial Lake

摘要

Background/Objectives. Constituents of interest (COIs) from seven constituent classes(volatile organic compounds, semi-volatile organic compounds, metals, chlorinated herbicides,organochlorine insecticides, dioxins/furans, and polychlorinated biphenyls) werepresent at elevated concentrations in the sediments of a shallow, approximately 1-acrelake remnant that received industrial wastes and stormwater over a period of approximately40 years. In situ solidification/stabilization (ISS) of lake sediments was approvedby the state regulatory agency as a remedial measure to both eliminate direct contact exposurepathways for human and ecological receptors, and to minimize COI mobility andleaching. This selection was based on the results of a six-stage treatability study, geotechnicalinvestigation, and engineering evaluation/cost analysis. The bench-scalelaboratory treatability study (TS) program and results were presented at the Battelle SeventhInternational Conference on Remediation of Chlorinated and Recalcitrant Compoundsin 2010.Approach/Activities. ISS was implemented at full-scale in 2010 using an amendment ofPortland cement (20% weight/weight [w/w]), bentonite (5% w/w), organophilic clay (5%w/w) and granular activated carbon (5% w/w). The post-ISS effectiveness evaluation includedanalytical testing of six representative samples of stabilized and solidifiedsediment prepared using the United States Army Corp of Engineers Sequential BatchLeachate Test (SBLT) procedure, and comparison of the results to the approved evaluationcriteria. The evaluation criteria approved by the agency were the 95% upperconfidence limit (UCL) of the Phase 6 TS results, and the most conservative ecologicalscreening level value published in the EPA/Oregon DEQ Joint Source Control Strategydocument for the Portland Harbor Superfund Site. The post-ISS effectiveness evaluationalso includes a 2-year semi-annual groundwater monitoring program at eleven nearbyshallow monitoring wells. Groundwater elevations and analytical results were comparedto historical data sets to evaluate if shallow groundwater conditions had changed followingimplementation of ISS.Results/Lessons Learned. Post-remedy SBLT and groundwater monitoring resultsdemonstrate that the ISS remedy effectively reduced or eliminated mobility and leachingof the constituents of interest. Results of the post remedy monitoring are consistent withthe results of the treatability study for all seven constituent classes evaluated. These resultsdemonstrate that the ISS remedy successfully achieved the remedial action objectivesfor which it was designed.