Characterization of a TCE DNAPL zone in alluvium by partitioning tracers

Partitioning interwell tracer tests (PITT) were used to determine the spati al distribution and volume of residual trichloroethene (TCE) present in all uvium beneath the Portsmouth Gaseous Diffusion Plant in southern Ohio. Its first use at this site was in support of the design of a surfactant flood t o remove the residual DNAPL (dense nonaqueous phase liquids) from the alluv ial aquifer. The second application assessed the performance of the surfact ant flood. The average DNAPL saturation in the first PITT was 0.1 to 0.2% i n a swept pore volume of 4500 gallons (17,000 L). A second PITT was underta ken following the surfactant flood and yielded an average residual saturati on of 0.06% in a swept pore volume of 3400 gallons (13,000 L), the reductio n in pore volume being due to the confinement of the tracers to the lower s and and gravel unit of the alluvium. The design, operation, and analysis of the two PITTs provided strong evidence of a buried channel that controls t he spatial distribution of the residual TCE DNAPL in the basal sand and gra vel aquifer and must be considered in the eventual full remediation of this aquifer.