Laboratory Evaluation of Partitioning Tracers

by
Jeffrey Randall Edgar, MSE

University of Texas at Austin, 1997
Supervisor: Gary A. Pope

The main objectives of this work were to experimentally investigate suitable partitioning tracers for estimating the volume and/or saturation of dense nonaqueous phase liquid (DNAPL) in saturated aquifers before and after surfactant remediation, and to quantify the adsorption of partitioning tracers on soil from the aquifers. The contaminants studied were trichloroethylene (TCE) and a DNAPL from Hill Air Force Base, site Operable Unit 2. The Hill DNAPL is a mixture of TCE and lesser amounts of other chlorinated solvents and grease. Adsorption of several hydrophobic organic chemicals (various alcohols used at low concentration as partitioning tracers) by three field soils ranging in fractional organic carbon (f_oc) from 0.07% to 0.20% was measured using column experiments.

Partitioning tracer experiments were performed to identify suitable tracers with high partition coefficients that could be used to estimate low residual TCE saturations. Good agreement between the residual TCE saturation estimated based on mass balance and partitioning tracers was obtained in column experiments. The first step in screening candidates for partitioning tracers involved performing a batch experiment to determine the static partition coefficient between the DNAPL and water. This tracer was then tested in a column experiment to further evaluate its suitability.

At low residual NAPL saturation, there is a potential for interference due to adsorption of the alcohol tracers to sedimentary organic carbon (SOC) and/or mineral surfaces. Adsorption of the partitioning tracers to aquifers increases the retardation of the partitioning tracers. Many of the tracers with high partition coefficients have low aqueous solubilities, which makes them more likely to adsorb to SOC. Column experiments to measure alcohol tracer adsorption of 1-octanol and 1-heptanol were conducted with three types of field soils with a range of SOC content to determine when and to what extent adsorption represents a significant contribution to the measurement error of partitioning interwell tracer tests.

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