Characterization and Remediation of Aquifers Contaminated by Nonaqueous Phase Liquids Using Partitioning Tracers and Surfactants

Abstract

The main objectives of this work were the development of the partitioning interwell tracer test for estimation of nonaqueous phase liquid (NAPL) saturation in saturated porous media, performance assessment of surfactant enhanced aquifer remediation using partitioning tracers and screening and selection of environmentally acceptable surfactant solutions for surfactant enhanced aquifer remediation (SEAR) of soils contaminated by NAPLs. The contaminants studied in this work were tetrachloroethylene (PCE), trichloroethylene (TCE), jet fuel (JP4) and contaminant from Hill Air Force Base, site Operational Unit 2 (Hill OU2 DNAPL) and contaminant from Hill Air Force Base, site Operational Unit 1 (Hill OUl LNAPL). The first step in screening partitioning tracers involved performing several batch experiments to determine partition coefficients of about 28 alcohols and 10 NAPLs. Partitioning tracer tests were performed to estimate NAPL saturation in soil packs with known amounts of NAPL. A close match between NAPL saturation estimates based on mass balance and partitioning tracers was obtained in column experiments with several NAPLs thus validating the partitioning interwell tracer test as an effective tool for estimating residual NAPL saturation. The next step involved the development of laboratory procedures for designing field partitioning tracer tests. Two field partitioning tracer tests were designed using these procedures. The first field test was a partitioning interwell tracer test (PITT) performed by The University of Florida and EPA at the Operational Unit 1 site at Hill Air Force Base, Utah and the second test was the PITT performed by INTERA Inc. at the Operational Unit 2 site at Hill Air Force Base, Utah. Surfactants were selected by performing phase behavior experiments with surfactant, NAPL, alcohol, electrolyte and water mixtures. The surfactants used were the anionic surfactants, sodium diamyl sulfosuccinate, sodium dihexyl sulfosuccinate and sodium dioctyl sulfosuccinate. Surfactant solutions with low viscosities and quick equilibration times were selected for use in soil column experiments. Alcohols such as isopropyl alcohol and secondary butyl alcohol were used to minimize gel/liquid crystal formation and emulsions and to lower equilibration times. These favorable characteristics were confirmed by measurement of low pressure losses (hydraulic gradients) across the soil packs during surfactant flooding in several column experiments. The effect of the addition of polymer to the surfactant solution on surfactant remediation was investigated by performing several surfactant remediation experiments with surfactant, alcohol and polymer solutions. Based on all the column experiments, a laboratory procedure for designing field surfactant enhanced aquifer remediation tests was developed. This was used to design a surfactant flood at Hill AFB, site Operational Unit 2. Both the laboratory and field results showed that with the proper surfactant selection, laboratory procedures and process design, more than 99% of the DNAPL can be removed from sandy/gravely soil of the type found in Hill AFB, Utah. This is a much more favorable result than previously reported and a strong indication that surfactant remediation is a viable alternative, perhaps the best alternative for these very difficult DNAPL sites. Partitioning tracers and other site characterization played a key role in this success and were an integral part of all this research. The main contributions of this work were the validation the PITT for estimation of NAPL saturations and performance assessment of surfactant remediation and development of laboratory procedures for selection of both partitioning tracers and surfactants for application in field PITT and SEAR operations.