Grantee Research Project Results
Final Report: Partitioning Tracers for In-Situ Detection and Measurement of Nonaqueous Phase Liquids in Porous Media
EPA Grant Number: R825407Title: Partitioning Tracers for In-Situ Detection and Measurement of Nonaqueous Phase Liquids in Porous Media
Investigators: Brusseau, Mark
Institution: University of Arizona
EPA Project Officer: Hahn, Intaek
Project Period: November 1, 1996 through October 31, 1999
Project Amount: $246,339
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Objective:
Nonaqueous phase liquids (NAPLs) occur in the subsurface at numerous contaminated sites and can act as long-term sources of both vapor-phase and groundwater contamination. NAPL often is distributed non-uniformly as pooled and residual saturation, which makes direct observation in soil or water samples difficult. When LNAPL (light nonaqueous phase liquid) contamination encounters the saturated zone, it spreads laterally, forming a lens-shaped pool floating at the top of the water table. If the water table changes due to seasonal fluctuations or pumping, the zone of LNAPL contamination can be smeared vertically, complicating characterization. Effective risk assessment and remediation of NAPL-contaminated sites is limited by current site-characterization techniques, which include aqueous-solution sampling, soil-gas sampling, core sampling, cone penetrometer testing, well measurements, and geophysical logging. A major weakness of these methods is that they provide data at discrete points, such that the probability of sampling a zone of localized NAPL is quite small.The overall goal of the proposed project is to explore the use of an innovative in situ method for the detection, description, and mass estimation of LNAPLs in saturated media. The specific objectives that will be addressed to accomplish this goal are:
1. Investigate the use of partitioning tracers to detect and determine the residual saturation of LNAPLs in porous media.
2. Investigate the effect of mass transfer rate limitations on the transport behavior of partitioning tracers.
3. Investigate the effect of porous-media heterogeneity on the transport behavior of partitioning tracers.
Summary/Accomplishments (Outputs/Outcomes):
We have achieved accomplishments along several fronts, as outlined below.1. Analysis of the influence of biodegradation, heterogeneity, and mass transfer on efficacy of the partitioning tracer method.
We have performed detailed analyses of partitioning-tracer tests conducted at intermediate and field scales to examine the performance of the method under more realistic conditions. As part of this research, we have examined the impact of porous-media heterogeneity, liquid-liquid mass transfer, and biodegradation on the performance of the method.
? For example, we previously conducted several partitioning-tracer tests within enclosed (3 meters x 5 meters) test cells in a LNAPL-contaminated aquifer at Hill AFB, UT. Analysis of the results showed that the magnitudes of the NAPL saturation estimates obtained from the partitioning-tracer tests were similar to values obtained from analysis of core data. This indicates that the partitioning-tracer tests were successful in providing representative estimates of the NAPL saturation. We also examined the impact of tracer biodegradation on the performance of the partitioning-tracer method. In this method, NAPL saturation is obtained by calculating a retardation factor for a partitioning tracer used in conjunction with a nonreactive tracer. The retardation factor for a partitioning tracer is usually determined by calculating the quotient of the travel times measured for the partitioning and nonpartitioning tracers. Our results show that biodegradation of the partitioning tracer can reduce the magnitude of its calculated travel time, which results in an underestimation of the retardation factor, and thus of NAPL saturation. This work has resulted in one published manuscript (see below), one currently in review, and one in preparation.
? For another example, we recently have completed a set of intermediate-scale experiments designed to examine the efficacy of the partitioning tracer method for measuring NAPL saturation associated with "pool" systems. The hypothesis tested for this work is that the preferential (non-uniform) flow caused by the presence of the pool limits mass transfer of tracers between the aqueous solution and the NAPL comprising the pool. This mass-transfer constraint may possibly result in the partitioning-tracer method producing an under-measurement of the NAPL volume. We currently are preparing a manuscript describing these results.
2. Development of mathematical models.
We have developed mathematical models to describe the transport of reactive (e.g., partitioning) tracers in heterogeneous systems. The models explicitly incorporate multiple mass transfer processes and allow for heterogeneity at multiple scales. We have shown that such an approach, wherein the heterogeneity inherent to each process is explicitly accounted for, is important for providing accurate descriptions of reactive tracer transport in heterogeneous systems. We currently are using the models to analyze the results obtained from our intermediate-scale partitioning-tracer experiments. This work has resulted in one published manuscript (see below) and two in preparation.
3. Gas-phase partitioning tracer tests.
The research discussed above involves aqueous-phase tracer tests conducted in water-saturated systems. We also are evaluating the use of gas-phase partitioning tracer tests for measuring NAPL saturation in the vadose zone. We have conducted a series of pilot-scale tracer tests at a hydrocarbon-contaminated site in Tucson that is being treated with a soil vapor extraction (SVE) system. A reduction in immiscible-liquid saturation of 47 percent is estimated based on the results of the tracer tests, conducted 8 months apart. Thus, the tracer tests exhibited a response to the reduction in immiscible-liquid mass caused by the SVE system. The reduction in immiscible-liquid saturation is used to calculate an equivalent volume of immiscible liquid removed from the zone of influence of the SVE extraction well, which is compared to the volume of immiscible liquid removed as calculated from effluent contaminant concentration data obtained from the SVE system for the time period between the two tracer tests. Analysis of the partitioning tracer test results yields values of 13 and 52 m3 of immiscible liquid removed. The latter value, which incorporates a scaled immiscible-liquid saturation that accounts for data truncation that occurred in the first test, is relatively close to the value of 62 m3 obtained from the SVE effluent data. Based on these results, the gas-phase partitioning tracer test appeared to provide reasonable estimates of NAPL saturation. Two manuscripts have been produced based on this research, one currently is in review and one is in preparation.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
| Other project views: | All 7 publications | 3 publications in selected types | All 3 journal articles |
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Cain RB, Johnson GR, McCray JE, Blanford WJ, Brusseau ML. Partitioning tracer tests for evaluating remediation performance. Ground Water 2000;38(5):752-761. |
R825407 (1998) R825407 (1999) R825407 (Final) |
not available |
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Li Z, Brusseau ML. Nonideal transport of reactive solutes in heterogeneous porous media 6. Microscopic and macroscopic approaches for incorporating heterogeneous rate-limited mass transfer. Water Resources Research 2000;36(10):2853-2867. |
R825407 (1998) R825407 (1999) R825407 (Final) |
not available |
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Nelson NT, Oostrom M, Wietsma TW, Brusseau ML. Partitioning tracer method for the In Situ measurement of DNAPL saturation: influence of heterogeneity and sampling method. Environmental Science & Technology 1999;33(22):4046-4053. |
R825407 (1998) R825407 (1999) R825407 (Final) |
Exit Exit |
Supplemental Keywords:
groundwater, soil, chemical transport, risk assessment, chemicals, solvents, NAPL, remediation, cleanup, hydrology, measurement methods., RFA, Scientific Discipline, Waste, Ecosystem Protection/Environmental Exposure & Risk, Health Risk Assessment, Environmental Chemistry, Remediation, Chemistry, Fate & Transport, Hazardous Waste, Hazardous, hazardous waste treatment, fate and transport, oils spills, fate and transport , NAPL, contaminant transport, risk characterization, chemical speciation, transport contaminants, partitioning tracers, adverse human health affects, chemical contaminants, ecological impacts, hazardous chemicals, porous media, contaminant transport models, restoration planningProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.