Assessing Chlorinated Solvent Mass Flux Change and Treatment Performance in Three Adjoining In Situ Pilot Studies
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Background/Objectives. Geosyntec Consultants identified and delineated a chlorinated solvent (trichloroethene [TCE]) groundwater plume (1,500 feet in length and encompassing 25 acres) at a site in North Florida.

The site historically operated as an electronic vacuum tube manufacturing facility that allegedly used TCE as a degreasing agent. Assessment work also identified a potential source area containing TCE as a residual dense non-aqueous phase liquid (DNAPL). Regulatory approval was obtained to conduct pilot studies in a portion of the general source area prior to preparation of a formal remedial design. The objective of the pilot studies was to assess the performance of three identified viable remedial approaches with regard to effectiveness, implementability, cost, and anticipated short- and long-term impact on site cleanup. To support the effectiveness evaluation process, a novel approach using passive flux meters (PFMs) was incorporated into the pre- and post-pilot study performance monitoring program as an additional remedial metric. Approach/Activities. In the fall of 2010, Geosyntec implemented three pilot studies that included: (1) in situ chemical oxidation (ISCO) with groundwater recirculation, (2) enhanced reductive dechlorination (ERD) via biostimulation, and (3) ERD via biostimulation and bioaugmentation. The ISCO pilot study consisted of direct-push technology (DPT) injection of oxidant (sodium permanganate) throughout the target treatment zone, followed by operation of a closed-loop extraction and re-injection system to maximize contact and distribution of oxidant within the test plot. Both ERD pilot studies used a passive approach that consisted of DPT injection of aquifer buffering agent, electron donor (emulsified soybean oil), and a microbial culture (KB-1; bioaugmentation test plot only). Baseline conditions before pilot study implementation were assessed by groundwater performance monitoring well sampling within the test plots and installation and retrieval of PFMs to assess baseline mass flux. Baseline results revealed TCE concentrations ranging up to 33,000 micrograms per liter and a measured mass flux up to 533 milligrams per meter squared per day (mg/m2-day). The pilot studies began operation in October 2010 and will continue for approximately one year with groundwater performance monitoring conducted during implementation. Following completion (fall 2011), PFMs will be re-installed throughout the test plots to facilitate an evaluation of the post-pilot study changes in chlorinated solvent flux (by location and discrete depth). Results/Lessons Learned. This presentation will provide a summary of results associated with three implemented pilot studies based upon groundwater performance monitoring well sampling and pre- and post-pilot study PFM data. The presentation will also evaluate the implications of PFM data and the applicability of PFMs as a remediation performance metric for pilot studies of in-situ treatment of chlorinated solvents in groundwater and potential full-scale remedial technology flux evaluation and remedial technology selection.

Publication Summary

  • Geosyntec Authors: Jim Langenbach, Paul Brookner, Neal Durant
  • All Authors: Jim Langenbach, Paul Brookner, Neal Durant, Mike Annable, Martin Howe
  • Title: Assessing Chlorinated Solvent Mass Flux Change and Treatment Performance in Three Adjoining In Situ Pilot Studies
  • Event or Publication: Battelle Eight International Conference on the Remediation of Chlorinated and Recalcitrant Compounds
  • Practice Areas: Groundwater Assessment and Remediation, Site Investigation and Remediation
  • Date: 2012
  • Location: Monterey, California