PROJECT

MGP Site Remediation

Our team provided remediation services including a high-resolution comprehensive site characterization for a property that had been the site of a manufactured gas plant (MGP) for 50 years before ending operations in 1942. Owned by an electric utility, the property is now in an area primarily active with commercial and industrial uses.

Subsurface site investigation had begun in the 1990s and continued in 2020 as the utility learned that an adjacent property was to be developed for an elementary school. Site exploration was expanded to support expedited analysis and remediation of the adjacent parcel on behalf of the community.

The project team was able to meet the overall development timeline for the property, including the receipt of a No Further Remediation (NFR) letter. The combined remedy is estimated to have delivered savings of at least $4 million for the utility, when compared with alternatives.

The project team and contractor minimized field downtime by leveraging on-site earthwork capabilities. Simultaneous design and execution of separate remediation approaches targeted for different parcels also saved time. A pilot study provided actionable data for full-scale design refinement, including site-specific mobile porosity calculations, delivery methodologies and daylighting mitigation considerations.

Client

Confidential

Location

Central Illinois

Region

Midwest

Services

Environmental

Remediation

Manufactured Gas Plant (MGP) Site Remediation

Industry

Environmental

Case Study

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Multifaceted Treatment Approach Speeds Site Cleanup for Community

Solution Development

On the main site and adjacent properties north of the school property, including the public rights-of-way, we conducted high-resolution site characterization, using environmental sequence stratigraphy (ESS) and other techniques, combined with conventional soil and groundwater sampling. Most impacts were present in more permeable glacial outwash sands located approximately 20 to 35 feet below the ground surface.

We conducted a pilot study to evaluate the effectiveness of in situ remedies, an alternative that would be less disruptive to the community. The approach combined surfactant enhanced product recovery (SEPR) and in situ chemical oxidation (ISCO). Soil, groundwater and soil gas data were collected for several months after the pilot study to assess effectiveness.

Expanding Investigations

While the pilot study activities were ongoing, the project team began rapid investigation of the adjacent school property to evaluate potential soil, groundwater and vapor intrusion risks. The utility was able to issue a request for proposal for the excavation and engineered barrier installation to meet residential remediation objectives. The remedies applied to the school property were expedited. Our team prepared design documents, assisted in bidder selection, conducted air monitoring and served as owner’s engineer.

Remediation on the main site used a combination of in situ treatment and excavation and off-site disposal. Full-scale remedy implementation included 34 injection/extraction wells. The SEPR phase and the ISCO injection phase, which delivered aqueous-phase surfactant followed by iron-activated sodium persulfate via more than 200 direct-push injection locations, overlapped to meet the project deadline. The overlap was coordinated using a variety of factors, including property-specific schedule considerations and mass-flux recovery criteria updated using daily collected performance monitoring data.

Delivering Results

The high-resolution site characterization applied with support from the advanced geosciences group required more upfront investment, but the trust between the utility and the consultant saved considerable time on the back end by providing clear understanding of subsurface conditions, and focusing efforts and resources on the most impacted portions of the site. That enabled the team to mitigate issues from the start, rather than dealing with potential problems as they might have arisen later.