Groundwater in a fractured shale/limestone bedrock aquifer is contaminated. A crystalline limestone formation serves as an aquitard that separates the shallow bedrock and deep bedrock aquifer systems.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Major Contaminants and Maximum Concentrations:
- Trichloroethene (71,000 µg/L)
- Other (Column Treatability Testing)
Comments:
Column treatability testing was performed by introducing groundwater from the source area monitoring wells packed with Peerless and Connelly granular iron. The permeable reactive barrier (PRB) technical design specifications were finalized with assistance from the patent holders for using PRBs comprised of granular iron to treat CAH in groundwater.
- Other (Permeable Reactive Barrier)
Comments:
A funnel and granular iron gate PRB was installed between October 2003 and February 2004 in a shallow bedrock aquifer along the western boundary of the site. The PRB is designed to mitigate the potential for off-site migration of CAH. The PRB system includes a trench with 650 feet of impermeable slurry "funnel" sections on opposite sides of a 300-foot-long granular iron "gate" section. The PRB trench is 30 feet deep by 18 inches wide and is installed along the downgradient edge of the plume, along with a 50-foot long PRB performance section near the CAH source area. The performance section was designed to provide expedited monitoring data as well as a reduction in concentrations in the source area. The PRB was keyed into the crystalline limestone aquitard beneath the shallow bedrock aquifer.
The remediation program is implemented as part of the closure strategy designed to achieve a "Certification of Completion" determination under the Missouri Department of Natural Resources (MDNR) Cleanup Levels for Missouri (CALM) Voluntary Cleanup Program. The Tier 2 risk assessment and use of institutional and engineering controls form the basis for requesting the "Certification of Completion" letter. Tier 2 also is the premise for demonstrating that there is no significant on-site risk of exposure to constituents of concern (COC) via the soil and groundwater exposure pathways.
Performance monitoring wells were installed along the main PRB gate and performance trench sections. Starting in April 2004, performance groundwater monitoring for volatile organic compounds and natural attenuation parameters (redox potential, dissolved oxygen, methane, iron/manganese, and related parameters) has been conducted to confirm the effectiveness of the PRB. Monitoring was conducted monthly for the first 3 months and semi-annually thereafter.
Reference:
Adams, Timothy V.; Dennis J. Sopcich; Scott Tarmann. 2004. PRB installation for TCE remediation in a bedrock aquifer. The Fourth International Remediation of Chlorinated and Recalcitrant Compounds Conference, Monterey, California. May 24-27.
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