EFFECT OF POST-REMEDIATION CYCLODEXTRIN CONCENTRATIONS ON NAPL-WATER PARTITION COEFFICIENTS

Field partitioning tracer tests (PTTs) are an innovative method for detecting and characterizing the volume and distribution of nonaqueous phase liquids (NAPLs). PTTs have several useful purposes: locating subsurface NAPL zones, estimating NAPL saturation or volume within these contaminated zones, and providing a quantitative and qualitative means of assessing remediation performance. PTT theory is based on the chromatographic separation of a tracer pulse consisting of suites of partitioning and nonpartitioning tracers that travel with the advecting groundwater. The NAPL saturation can be calculated from the retardation of the partitioning tracer compared the nonpartitioning tracer and the laboratory-measured NAPL-phase partitioning coefficient (Knw). The Knw provides a quantitative measure of the tracer’s tendency to partition to the NAPL phase. Enhanced dissolution of NAPL contaminants has been verified during several field investigations using the complexing agent hydroxy-propyl beta cyclodextrin (HPCD). An HPCD remediation effort is currently underway to remediate a trichloroethene (TCE)-NAPL source zone at the Little Creek Amphibious Base in Virginia Beach. Residual HPCD remains in the subsurface for some time after remediation efforts are concluded, particularly during the short-term period when PTTs are conducted. Knw values are generally measured prior to site remediation in laboratory batch experiments using clean groundwater. However, laboratory results indicate that aqueous HPCD concentrations of 2000 mg/L cause Knw values to be reduced by as much as 32%. The effect lessens as the original Knw value of a tracer decreases. No effect was observed for any tracer at HPCD concentrations below 200 mg/L. Between 200 mg/L and 2000 mg/L HPCD concentrations, the reduction in Knw was nearly linear. Thus, use of Knw values measured in HPCD-free groundwater. Thus, use of Knw values measured in HPCD-free groundwater result in erroneous estimations of residual NAPL saturations and NAPL volumes after remediation, and therefore provide an imprecise evaluation of remedial success. Several common alcohol partitioning tracers were used in the experiments, with TCE as the NAPL phase. This research is also relevant for other remediation agents, such as surfactants, alcohols, and chemical oxidation agents.