Varadarajan Dwarakanath

Partitioning Tracer Test for Detection, Estimation, and Remediation Performance Assessment of Subsurface Nonaqueous Phase Liquids

In this paper we present a partitioning interwell tracer test (PITT) technique for the detection, estimation, and remediation performance assessment of the subsurface contaminated by nonaqueous phase liquids (NAPLs). We demonstrate the effectiveness of this technique by examples of experimental and simulation results. The experimental results are from partitioning tracer experiments in columns packed with Ottawa sand. Both the method of moments and inverse modeling techniques for estimating NAPL saturation in the sand packs are demonstrated. In the simulation examples we use UTCHEM, a comprehensive three-dimensional, chemical flood compositional simulator developed at the University of Texas, to simulate a hypothetical two-dimensional aquifer with properties similar to the Borden site contaminated by tetrachloroethylene (PCE), and we show how partitioning interwell tracer tests can be used to estimate the amount of PCE contaminant before remedial action and as the remediation process proceeds. Tracer tests results from different stages of remediation are compared to determine the quantity of PCE removed and the amount remaining. Both the experimental (small-scale) and simulation (large-scale) results demonstrate that PITT can be used as an innovative and effective technique to detect and estimate the amount of residual NAPL and for remediation performance assessment in subsurface formations.

Partition coefficients for alcohol tracers between nonaqueous-phase liquids and water from UNIFAC-solubility method

Abstract In this work, we have applied a group-contribution activity-coefficient model, UNIFAC, and the solubility of alcohols in water to estimate partition coefficients for alcohol tracers between water and nonaqueous-phase liquids (NAPLs). The effects of temperature and mutual solubility between NAPL and aqueous phases on the estimation of partition coefficients were also investigated. By comparing the estimated results with experimental partition coefficients for 30 alcohol tracers between 10 NAPLs and water, we found that: i) the UNIFAC-solubility method, in which the UNIFAC model in its infinite-dilution form is applied to the NAPL phase and the solubility of tracers in water is used for estimation of the activity coefficient in the aqueous phase, works better than the UNIFAC model; ii) a linear relation between the logarithm of partition coefficients and the logarithm of tracer solubility in water is observed for those tracers having a similar chemical structure (i.e. the same number of branched methyl groups). This can serve as a useful tool for quick selection of the tracers that exhibit the desired partition coefficients; iii) the effect of mutual solubility between NAPL and aqueous phases can be neglected because such miscibility is very small, usually of the order of 10 −3 mole/mole unit; and iv) temperature variation between 15° and 25°C does not significantly affect partition coefficients.

Surfactants: Surfactant Enhanced Aquifer Remediation

The use of surfactants to remediate groundwater contaminated by nonaqueous phase liquids has been under investigation and field testing since at least the 1980s. Surfactant enhanced aquifer remediation (SEAR) is especially important for dense nonaqueous phase liquids such as chlorinated solvents because they are difficult to remediate and because there are few good alternatives to SEAR to remove these contaminants from groundwater. The technology has continued to improve and recent field demonstrations at superfund sites have shown that under certain conditions very favorable results can be obtained with SEAR. Some of these advances can be attributed to the adaptation of technology developed for surfactant enhanced oil recovery over the past 30 years. The emphasis on phase behavior for screening and evaluating surfactants is especially noteworthy and important. In this chapter, we first briefly review the phase behavior of surfactants when mixed with organic liquids of interest, and then give a detailed example of a study done at the University of Texas to further evaluate surfactant candidates in soil column tests in the laboratory. Introduction The contamination of groundwater by nonaqueous phase liquids (NAPLs) is a cause for concern throughout the world. NAPLs can be classified by their density as those lighter than water (LNAPLs) and denser than water (DNAPLs). NAPLs migrate into aquifers because of gravity and capillary forces and may be trapped in the form of immobile blobs or ganglia or when present in sufficient volume DNAPLs may form pools above aquitards.