The site includes an underlying limestone bedrock aquifer. Water-bearing fractures exist at depths of 40 to 55 feet below ground surface. A highly conductive anomaly oriented in the direction of groundwater flow was identified near a leaking aboveground storage tank.
Targeted Environmental Media:
 Fractured Bedrock
The references abstract did not identify plume characteristics however it is known that 75-gallons of 1,1,1-trichloroethane (TCA) were released from an aboveground storage tank and contaminated groundwater in the underlying limestone bedrock aquifer.
Major Contaminants and Maximum Concentrations:
- 1,1,1-Trichloroethane (20,000 µg/L)
- 1,1-Dichloroethane (0 µg/L)
- 1,1-Dichloroethene (0 µg/L)
- Chloroethane (0 µg/L)
- Coring
- Other (Electrical resistivity (ER) survey)
Comments:
Bedrock cores were taken to indicate the presence and depth of water-bearing bedrock fractures. The depth and location of bedrock fractures was confirmed through an ER survey.
- Fracturing
- Other (Zero-valent iron (ZVI))
Comments:
Prior to ZVI delivery, fracturing was performed under gas pressures of up to 650 pounds per square inch (psi). During June and September 2006, 13,100 pounds of ZVI was injected in conjunction with Pneumatic Fracturing to position a commercially available sponge ZVI (H-200). ZVI was introduced into a 15-foot thick bedrock zone in 3 to 3.5-foot sections and isolated by high-pressure packers. The ZVI was delivered under pressures that ranged between 60 to 280 psi with a maximum of 550 psi. Approximately 50% of the treatment zone did not have ZVI injected because the bedrock was competent.
Pressure monitoring took place during injection. As far as 200 feet from the injection area, pressure was observed. The pattern of pressure propagation was highly variable, probably determined by the existing fracture orientation.
None provided
Over 12 months, TCA, 1,1-DCA, and 1,1-DCE concentrations within the source zone were decreased by 90%. Downgradient well concentrations of TCA and 1,1-DCE have decreased by 85% and 75% respectively, though 1,1-DCA concentrations increased.
References:
Chen, Steve, David Sarr, and Kay Powell. Successful Treatment of 1,1,1-TCA in Bedrock by Pneumatic Fracturing and Zero-Valent Iron Injection, Poster Session E1 . Presented at the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, CA. May 19-22, 2008.
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