Full-scale Permanganate Remediation of a Solvent DNAPL Source Zone, Ft. Lauderdale, Florida

Full-scale permanganate remediation was conducted in a sand aquifer in southern Florida at a small industrial site with TCE and 1,1,1-TCA contamination from the water table zone at 3 ft down to 70 ft bgs. Near-saturation concentrations of permanganate solution were injected into the DNAPL source zone (30 ft diameter in plan view) where a small mass of residual TCE DNAPL caused this zone to have TCE concentrations exceeding 10,000 ug/L, with small zones approaching TCE saturation. The first remediation phase, which took place in 2000, comprised three injection episodes, each occurring over several days during which small volumes of KMnO₄ solution were injected at depths between 5 and 65 ft bgs in each of 6-8 direct push holes. During the 2-3 months after each injection episode, the large initial density contrast caused the permanganate to spread out laterally and move downward while fingering and dispersion occurred. The combination of these migration and mixing processes caused complete KMnO₄ coverage of the source zone, even though the coverage immediately after each episode was only 1-8% of the total pore volume of this zone. By keeping the initial injection volumes small relative to the total aquifer pore space within the targeted treatment zone, displacement of TCE mass outward from the source zone was avoided. The post-treatment monitoring conducted two years after the last injection showed that the combined effect of the three permanganate injection episodes was a 99% reduction in the aquifer volume where TCE in groundwater was initially above 100 ug/L. The injections caused the maximum TCE concentration in groundwater to drop from 635,000 ug/L, measured just before the first injection episode, to 1,500 ug/L, with this latter value occurring only in a very small zone. The 1,1,1-TCA concentrations were reduced from a maximum value of 9,900 ug/L down to 135 ug/L, which is below the MCL. These results indicate that all of the DNAPL has been destroyed, and hence, post-treatment monitoring showed no rebound. These encouraging results are based on monitoring an exceptionally detailed three-dimensional network of depth-discrete, multilevel, groundwater samplers. A fourth and final injection episode was conducted in early October, 2002, with the expectation that this will reduce the VOC concentrations below MCLs at all or nearly all sampling locations and below 100 ug/L everwhere.