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

Abstract

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.

222Rn as a Partitioning Tracer To Detect Diesel Fuel Contamination in Aquifers: Laboratory Study and Field Observations

“…Processes that govern the transport of partitioning tracers other than 222 Rn injected into aquifers have been mathematically described elsewhere (2,16). These equations do not apply to 222 Rn since 222 Rn emanates continuously from mineral surfaces and is subject to radioactive decay.…”

“…However, laboratory experiments and theoretical considerations have revealed that the volume of core samples is often too small to yield a representative average NAPL saturation (1). Partitioning tracer methods may be more accurate because they involve much larger volumes of aquifers (2). Furthermore, the same monitoring well can be used for repeated determinations of the NAPL saturation since the methods rely on the quantification of dissolved species and need only water samples.…”

“…Recently, the methods have been adapted to locate and quantify NAPL contamination (2,5,6). These methods usually consist of the simultaneous injection of a conservative nonpartitioning tracer along with one or several specific partitioning tracers.…”

“…The calculation relies on the assumption that a partitioning equilibrium is established between the NAPL and the water phase [local equilibrium assumption (5)]. So far, SF 6 (5,6) and various alcohols (2) have been used as partitioning tracers to detect NAPL contamination. The aim of our study was to investigate the feasibility of the use of 222 Rn, a naturally occurring radioactive isotope, to detect and quantify NAPL contamination in aquifers.…”

Peer Reviewed: Remediating Chlorinated Solvent Source Zones

“…Locating and delineating DNAPLs are difficult because of their complex spatial distributions as they migrate through the subsurface. Geophysical methods have not proven useful for locating DNAPLs at meaningful resolutions (29), despite advances in this area, such as partitioning interwell tracer tests (30) and natural radon abundance (31). Source delineation still typically relies on point-scale techniques, such as wells or borings that are often costly and subject to error.…”