Discretely fractured metagabbro overlain by saprolite makes up the bedrock environment at the site. The top portion of the metagabbro, less than 80 feet below ground surface (bgs), contains smaller, less conductive fractures that are hydraulically connected to the saprolite [well yields range from <5 to 15 gallons per minute (gpm)]. Approximately 140 to 160 bgs, a large, deep horizontal fracture system originates (well yields >40 gpm). Primary pathway of contamination originates in the top portion of the metagabbro with a second pathway in the 140-160 bgs section.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
Major Contaminants and Maximum Concentrations:
- Tetrachloroethene (0 µg/L)
- Borehole Geophysics
- Other (Unknown downhole geophysics)
- Fluid Loggings
- Flow
- Electromagnetic Flowmeter
- Pumping Tests
- Coring
- Other (Pressure pulse interference testing)
Comments:
A two phase process was used to perform hydraulic and chemical characterization of the groundwater system. The first phase consisted of two parts: 1) hydraulic characterization of in-borehole flow including electromagnetic borehole flowmeter (EBF), down-hole geophysics, and depth-discrete sampling; and 2) an assessment of the fracture connectivity which was achieved using short-duration pump testing and pressure-pulse interference testing. The second phase consisted of the installation of monitoring and injection/extraction wells and EBF characterization pump testing and sampling to confirm fracture connectivity, well yields, and capture zones.
- Chemical Oxidation (In Situ)
- Bioremediation (In Situ)
Comments:
Bench-scale testing was performed to evaluate the effectiveness of bioremediation and in situ chemical oxidation (ISCO). ISCO was selected for the pilot-scale testing which consisted of sodium permanganate up to 2 grams per liter for 3 weeks followed by groundwater recirculation with no oxidant addition for 4 weeks. Full-scale implementation consisted of ISCO injection and recirculation on a cycled rotation targeting the source area and the deep fracture pathway that presented the greatest risk for off-site migration. Permanganate amendment will continue for 3 years with monitored natural attenuation as a finishing treatment.
None provided
The full-scale remedial system was designed through preliminary technology assessment followed by a systematic evaluation of design factors.
References:
Konzuk, Julie, Leah MacKinnon, Suzanne OHara, Eric Hood, and Evan Cox. Testing and Design of a Full-Scale Chemical Oxidation System in Fractured Bedrock, Platform Abstract Session A4. Presented at the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA. May 19-22, 2008.
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