CYCLODEXTRIN ENHANCED REMOVAL OF DNAPL IN THE FIELD UNDER UNCONSTRAINT CONDITIONS

Cyclodextrins are a group of nontoxic, cyclic sugars that have been used successfully to remove toxic compounds such trichloroethylene (TCE) from contaminated aquifers. Previous cyclodextrin field tests were either conducted under well controlled conditions, i.e. sheet piles surrounded the treatment zone, or were limited to point treatment using a vertical circulation well. We are currently conducting a full-scale cyclodextrin enhanced DNAPL remediation project at the Little Creek Naval Amphibious Base in Virginia. The test site is characterized by a shallow water table in a sandy aquifer. TCE concentrations in the groundwater are several hundred ppm, indicating the presence of DNAPL. Approximately 22 ft below surface, a thick clay layer (approx. 50 ft) retards the downward movement of DNAPL at the site. Technical grade cyclodextrin (as hydroxyl-beta-cyclodextrin) was injected at 20% (wt/wt) solution into one injection well. Four to five extraction wells surrounding the injection well are being pumped to retrieve the cyclodextrin-TCE complex. The injection rate was aimed at treating on pore volume source zone per day. Both, extraction an injection wells were screened over the bottom 5 ft only. This injection scheme was selected to force the cyclodextrin solution delivery into the most contaminated zone at the bottom of the aquifer. Clean water was injected upgradient to maintain hydraulic control of the flow field. The TCE in the extracted cyclodextrin solution was removed using conventional air stripping equipment. The waste water discharge objective was 5 ppb. Because of dilution in the subsurface, the cyclodextrin concentration needed to be reconcentrated before reinjection. The reconcentration was achieved by an ultrafiltration (UF) system specifically designed for this test. After passage through the UF system, the cyclodextrin solution was reinjected into the contaminated aquifer. This presentation summarizes preliminary test data and evaluates how effective the unconstraint treatment system was for handling the TCE contamination and for reconcentrating the cyclodextrin solution.