Air sparging with trenches had failed to remove groundwater and soil contamination at an industrial Superfund site in Piedmont soils in South Carolina. The major contaminants of concern were cis 1,2-dichloroethene (DCE) and trichloroethene (TCE) ranging from 0.5 to 2.0 mg/L. The treatment area was approximately 15,000 square feet.
Ozone sparging was chosen as preferred remediation alternative for several reasons. Ozone rapidly reduces common organic contaminants such as chlorinated VOCs and BTEX. A costing of alternatives showed that life cycle costs of using microbubble ozone would be the lowest cost choice when compared with groundwater pump and treat, air sparging, and liquid oxidation (permanganate). Ozone sparging also provided operational flexibility with its capacity to vary injection patterns and multi-pass treatment.
A field pilot test was performed in spring 2001 to verify expected contaminant removal rate and injection well radius of influence. Initial testing for 12 weeks on two ozone sparging wells showed over 50% removal. During 2001-2002, full-scale design and construction was completed utilizing nine ozone microbubble sparging wells with recirculation capability. The air/ozone mix was supplied at 2 to 3 cfm per well and 300 to 500 ppm ozone. In October 2002, the system was started.
After 12 months of treatment, all monitoring wells but one were at recommended EPA drinking water MCLs (minimum concentration limits). Seven of the 9 ozone sparge wells were turned off. After 18 months of treatment, the remaining monitoring point achieved cleanup goals. With all monitoring wells meeting closure requirements, the system was turned off. Continued monitoring showed no rebound.
*Presented at the 21st Annual Conference on Soils, Sediments & Water, University of Massachusetts, Amherst, MA, October 18, 2005.