Vapor Intrusion/Groundwater Investigation/Regulatory Support
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Project Objective

Release of chlorinated solvents and hexavalent chromium (site COCs) in the 1980s led to a facility listing under the Ohio Environmental Protection Agency (OEPA) Resource Conservation and Recovery Act (RCRA) Corrective Action Program.

In the late 1990s, pump and treat (P&T) systems were constructed by a prior contractor as an interim measure to provide hydraulic containment of impacted groundwater. The P&T systems operated at an annual cost of approximately $100,000 with minimal decrease in contaminant mass and required ongoing maintenance. Geosyntec aimed to delineate the groundwater plumes, investigate and address vapor intrusion concerns, and develop a pathway to site closure.

Geosyntec’s Scope of Services

A RCRA Facility Investigation (RFI) was completed and included investigation of groundwater and soil gas impacts downgradient of the site. Components of the RFI included:

  • Installing thirty additional monitoring wells to delineate shallow and deep groundwater plumes;
  • Installing twenty five soil gas probes to guide vapor intrusion (VI) investigation areas;
  • Completing residential VI assessment at more than ninety properties;
  • Mitigating residential VI pathways at thirty two homes with indoor air exceedances of site COCs; and
  • Efficient investigation and mitigation the indoor air exposure pathway at the Site using High Volume Sampling.
  • Beginning in 2015, enhanced in situ bioremediation (EISB) of chlorinated solvent and in situ chemical reduction (ISCR) of hexavalent chromium using calcium polysulfide were explored as an alternative remedial measures that could reduce contaminant mass, prevent off-site migration, and decrease long-term costs. Results of a bench-scale biotreatability study were used to design the pilot and full-scale field implementation. The full-scale EISB injections completed in 2018 consisted of injecting amendments and bioaugmentation culture through 30 direct push temporary injection points. ISCR injections were sucessfully completed inside the facility in a 48-hour window of non-operation and performance monitoring indicated achievement of groundwater cleanup standards within three months. Positive performance monitoring allowed these remedies to replace the P&T system and allowed for its decommissioning.

    Additionally, Geosyntec completed an Ohio Corrective Action Plan (CAP) Corrective Measures Study which OEPA is currently using to develop their Statement of Basis for selection of the replacement interim measures as key components of the selected remedy for public review. Upon Corrective Measure Implementation, the site will approach closure under CAP guidelines.

    Notable Accomplishments

    Geosyntec sucessfully replaced interim remedial measures for groundwater impacts and identified and mitigated the VI exposure pathway at both commercial and residential locations. Throughout the process, Geosyntec has maintained excellent relations with OEPA regulators and affected homeowners, allowing the project to progress quickly.

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Project Summary

  • Location: Southwest Ohio
  • Client: The Ohio Environmental Protection Agency (OEPA) and Resource Conservation and Recovery Act (RCRA) Corrective Action Program
  • Project Practice Areas: Water & Wastewater
  • Type of Facility: Vapor Intrusion
  • Services Provided: Groundwater plume delineation, Vapor intrusion evaluation, Commercial and residential vapor intrusion mitigation, Groundwater monitoring and modeling, Pump a treat system replacement with enhanced in-situ bioremediation, Regulatory negotiation
  • Type of Work: Groundwater Remediation
  • Governing Regulation: State and local