Remedial Investigation / Feasibility Study Matthiessen & Hegeler Zinc Company Site
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Project Objective

The Carus Chemical Company owns a chemical manufacturing plant and adjacent land that includes a slag pile from a former zinc smelting operation. The slag pile and the adjacent Little Vermilion River (LVR) are part of Operable Unit 1 (OU1) of the Matthiessen & Hegeler Zinc Company Superfund Site. With the understanding that removal of all slag material from the LVR and its banks would be prohibitively costly and result in severe ecological disturbance, a key objective of the project was to fully evaluate baseline risks to LVR receptors and to design mitigation measures to cost-effectively maximize long-term risk reduction.

Geosyntec’s Scope of Services

Geosyntec has provided a variety of consulting services and performed a number of site investigation and assessment efforts, including preparation of the CERCLA Remedial Investigation (RI) and Feasibility Study (FS). A key feature of the Site’s OU1 is a large slag pile that is approximately 100 ft high by 3,000 ft long and has a 1 to 1 slope in some areas. The RI included a comprehensive assessment of whether the Site (slag pile) was adversely impacting receptors associated with the LVR. Geosyntec used a multiple-lines-of-evidence approach to evaluate risk to LVR receptors, including:

  • Statistical evaluation of sediment and surface water chemistry data and comparisons to risk-based benchmarks.
  • Tissue sampling for food web modeling and evaluation of ecological and human health risks.
  • Toxicity testing for to assess the growth and survival of macroinvertebrates exposed to Site sediments.
  • Macroinvertebrate and fish field surveys to evaluate the structure and health of communities.

The multiple lines of evidence supported a conclusion that the Site is not having a significant adverse effect on the overall health of the ecological community of the river. Geosyntec presented these and other findings in a comprehensive RI Report that included a Human Health Risk Assessment and Baseline Ecological Risk Assessment. Based on these findings, the USEPA accepted an FS alternative that involves stabilizing the slag pile through sloping and benching to minimize future erosion to the river and installing a clay cover and institutional controls to minimize direct contact. Additionally, USEPA agreed that slag already in the river did not require removal. Demonstrating the risk reduction afforded by this approach and its feasibility relied on Geosyntec’s geotechnical capabilities to develop a detailed conceptual design of how the slag pile will be regraded into a stable configuration and support installation of a cover system. The FS was accepted by USEPA and memorialized in a Record of Decision. USEPA is awaiting acceptance of the ROD by IEPA and then will direct conducting remedial design for the Site.

Notable Accomplishments

The client faced the prospect of potentially having to remove several hundred thousand cubic yards of zinc slag from the banks of the LVR and from within the river itself. Geosyntec’s biological assessment provided a “weight-of-evidence” component to the risk assessment supporting a conclusion that the status of the aquatic and benthic communities in the river were comparable to areas of the river unaffected by Site activities. This outcome provided a compelling argument for remedial alternatives that avoid large scale removal of the zinc slag, thus substantially lowering the cost of cleanup for the client. The FS-recommended remedy of stabilizing the slope and covering is not a traditional remedial approach and demonstrates Geosyntec’s capabilities in both traditional environmental RI/FS work and our capabilities in geotechnical/geoenvironmental engineering. Additionally, this work involved extensive interface with USEPA Region 5 as the Agency conducted the work for OU2 and Geosyntec was charged with combining both OUs into single RI and FS reports.

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Project Summary

  • Location: LaSalle, IL
  • Client: Carus Chemical Corporation
  • Project Practice Areas: Environmental Management
  • Type of Facility: Transmission
  • Services Provided: Remedial Investigation, Feasibility Study, Human health and ecological risk assessments, Multiple line of evidence assessment of impact to the Little Vermilion River, Extensive interaction with USEPA Region 5
  • Type of Work: Bioassessment
  • Governing Regulation: State and local