TRC

Enhanced Reductive Dechlorination

TRC's approach rapidly reduced the concentration of TCE in the source area by 99 percent, and at a much lower cost than other alternatives.

Industries

Client

Badger Meter, Inc.

Project Location

Wisconsin

Historical practices at Badger Meter’s facility near Milwaukee had resulted in trichloroethene (TCE) impacts to the bedrock, soil, and groundwater. Prior remediation activities had included the excavation of impacted soil and the installation of a groundwater pump‐and‐treat system to remediate the source area. After 2 ½ years of operation, however, significant concentrations of TCE (40,000 ppb) remained, suggesting that the pump‐and‐treat system was no longer effective. The client needed a new remedial approach to address the high concentrations of TCE that remained in the fractured dolomite bedrock aquifer.

The client hired TRC to review the existing data and develop a new approach to solve the problem.

Assessment for New Approach
TRC reviewed the existing groundwater data and completed additional sampling, which indicated that reductive dechlorination of TCE was occurring at the site. Enhancement of the naturally occurring remediation appeared to be a viable approach to solving the client’s stubborn problem.

Pilot Test for Remedial Approach
TRC developed a remedial approach that would enhance the reductive dechlorination in situ by injecting a lactate solution into the bedrock aquifer. To test the approach, TRC conducted a pilot test that delivered lactate solution over 2 ½ days to an injection well that was placed in the source area. Following the injection, groundwater sampling demonstrated that the lactate injection was successful in enhancing the reductive dechlorination. The technology was subsequently approved by the Wisconsin Department of Natural Resources (WDNR) as a full‐scale remedial option for the site.

Full‐Scale Remediation
TRC completed the full‐scale injection at the site, including a second injection, which significantly enhanced reductive dechlorination in the source area. Ongoing monitoring demonstrated that a 99 percent reduction in TCE concentrations has been achieved in the source area.

Site Closure
Before the site could be closed, TRC needed to first demonstrate that the source‐area remedy would be permanent and that concentrations of TCE and breakdown products would attenuate. TRC used the spatial and temporal groundwater quality to develop a contaminant transport model to demonstrate that the remedy would be protective.

Second, TRC needed to assess the vapor intrusion risk associated with residual TCE impacts. Because the Badger Meter facility has a thick, well‐maintained concrete floor, and well ventilated interior spaces, prescribed default attenuation assumptions and standard sub-slab point sampling approaches would have been overly conservative.

  • High volume sampling to appropriately average vapor concentrations and mitigate the effect of small‐scale hot spots, and
  • Measurement of site‐specific attenuation using a natural tracer, which typically demonstrates greater attenuation than default values

TRC recognized that naturally occurring reductive dechlorination at the impacted site could be enhanced with the help of our patented technology, lactate injection. The successful treatment process moved the site from its previously ineffective pump‐and-treat system to nearly complete remediation. Implementation of this “low‐tech,” yet highly effective, approach rapidly reduced the concentration of TCE in the source area from 40 ppm to 0.35 ppm, and at a much lower cost than the other alternatives, chemical oxidation or continued pump‐and‐treat. Two injections of lactate solution solved the problem in less than 2 years and saved the client an estimated 80 percent over alternative remediation methods.

TRC performed innovative sampling and analysis to evaluate vapor intrusion at this facility. This innovative approach demonstrated that the quality of the building construction, combined with the normal operation of the facility HVAC system, was protective of potential vapor intrusion, and additional vapor mitigation controls were not required.

The site has satisfied the regulatory requirements and has been granted closure from the WDNR.

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