FIELD STUDY OF THE PARTITIONING TRACER METHOD FOR DETECTION OF DENSE NONAQUEOUS PHASE LIQUID IN A TRICHLOROETHENE-CONTAMINATED AQUIFER

Abstract

Tracer experiments were conducted at a trichloroethene-contaminated Superfund site located in southern Arizona. Two tracers were used, SF6 (partitioning) and bromide (conservative). Because SF6 partitions into immiscible-liquid phases, it can be used to detect the possible presence of residual-phase (liquid) trichloroethene in the aquifer. Breakthrough curves for SF6 and bromide were obtained at several wells located within the hydraulic influence of an injection/extraction well couplet, which was used to generate flow through a 6 m thick semi-confined aquifer 42 m below ground surface. SF6 appears to have been used successfully as a partitioning tracer for potential detection of dense nonaqueous phase liquid (DNAPL) saturation in the aquifer. Moment analysis of breakthrough curves allowed mass recovery, retardation, and apparent DNAPL saturation to be calculated. Assuming that partitioning to DNAPL is the only mechanism for retention of SF6, the results indicate the presence of DNAPL saturation in some portions of the aquifer.