Grantee Research Project Results
Final Report: Simulation of the Kinetic Sorption and Desorption of Trichloroethene (TCE) and Surfactant in Ground Water at Picatinny Arsenal, New Jersey
EPA Grant Number: R824365Title: Simulation of the Kinetic Sorption and Desorption of Trichloroethene (TCE) and Surfactant in Ground Water at Picatinny Arsenal, New Jersey
Investigators: Smith, James A. , Imbrigiotta, Thomas E.
Institution: University of Virginia , United States Geological Survey
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1995 through April 1, 1997
Project Amount: $79,000
RFA: Exploratory Research - Engineering (1995) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
The objective of this research project was to determine if chemical modification of groundwater by the addition of surfactants or by pH changes could increase the rate of pollutant desorption from long-term contaminated field soil and thereby improve the performance of a pump-and-treat remediation system. Secondary, more specific objectives included gaining insight into the sorption and transport of the nonionic surfactant, Triton X-100, in a natural groundwater system, and developing models to accurately simulate the kinetic sorption and desorption of both surfactant and TCE in the subsurface.Summary/Accomplishments (Outputs/Outcomes):
The early experimental work in the laboratory focused on identifying a surfactant that had the following properties: (1) weak to moderate sorption to soil; (2) no adverse affect on the hydraulic conductivity of the field soil; (3) the ability to increase the rate of TCE desorption from laboratory-contaminated soil from the field site. After tests of both anionic and nonionic surfactants, we concluded that Triton X-100, a heterogeneous nonionic polyethoxylate surfactant manufactured by Union Carbide, met all of our criteria. We then proceeded with detailed desorption experiments using a continuous-flow stirred tank reactor (CFSTR) methodology. The results of these experiments were presented by Deitsch and Smith (1995), who demonstrated that Triton X-100, at concentrations as low as 30 mg/L, effectively increases the desorption mass-transfer coefficient and hence increases the rate of TCE desorption from the laboratory-contaminated soil. This result had never been reported previously in the scientific literature and validated the fundamental hypothesis of the project. Deitsch and Smith (1995) also determined that rates of desorption decrease with longer periods of soil exposure to the contamination (time periods ranging from 1 to 4 weeks were studied). Also, information on Triton X-100 sorption to the field soil was presented.One problem we encountered early in our experiments was the absence of a two-parameter kinetic sorption model to adequately describe our experimental data. However, in the second year of the project, researchers at Cornell University published a paper outlining a new two-parameter kinetic sorption model that assumes the soil has an infinite number of compartments and that each compartment has a unique mass-transfer coefficient. The distribution of mass-transfer coefficients can be described by a two-parameter gamma distribution. The Cornell model was designed for use in interpreting batch experiments with purging of the aqueous phase (e.g., maximizing the concentration gradient for desorption). Because our experiments at that time included batch, CFSTR, and column tests, we needed a more robust model to describe and interpret our data. To this end, we joined forces with Dr. Teresa Culver in the Civil Engineering Department at the University of Virginia and developed a numerical model incorporating the conceptual approach of the researchers at Cornell. We tested this model successfully using our batch, CFSTR, and column data and against other, more traditional models such as the two-site model (Culver, et al., 1997). Based on our successes, we have adapted SUTRA, the U.S. Geological Survey two-dimensional flow and solute transport model, to include the gamma kinetic sorption model. We are using this model for final analyses of our field data.
Following our CFSTR experiments, we moved to batch and column experiments using actual field-contaminated soil (in the past, our experiments used field soil that had the contamination removed; the soil was then recontaminated in the laboratory). We also extended our study to investigate the effect of pH increases on TCE desorption in addition to the effect of Triton X-100. For the case of Triton X-100, our results again showed that this surfactant, even at sub-CMC concentrations, could increase the rate of TCE desorption from the long-term contaminated field soil at Picatinny Arsenal. We also observed that pH increase had a similar effect. This latter result will be reported for the first time in the scientific literature in about 4 months in Environmental Science and Technology (Sahoo and Smith, 1997). In this paper, the gamma kinetic sorption model is successfully used to model and interpret the experimental data.
As the final step of the project, we moved to the most complex experimental system: the TCE-contaminated water-table aquifer at Picatinny Arsenal. We conducted a 9-month field test of this new surfactant technology. To start the test, we injected clean water into the center of the contaminant plume for a 30-day period. We followed this with injection of water containing Triton X-100 at a concentration of 400 mg/L for the next 30-day period. Finally, for the final 7-month period, we once again injected clean water into the aquifer. Downgradient, we monitored TCE and surfactant concentrations in a network of wells. We also conducted a bromide-ion tracer test to characterize the groundwater velocities and dispersivities. The results of these field studies currently are being documented in two papers (Smith, et al., 1997; Sahoo, et al., 1997). The primary results can be summarized as follows:
- The sorption of Triton X-100 through the aquifer cannot be described using a local sorption equilibrium assumption. A kinetic sorption model must be employed to adequately predict surfactant transport in the aquifer. The kinetic sorption is caused by some combination of subsurface flow-field heterogeneities and by rate-limited mass transfer between the soil particles and water.
- Triton X-100 sorbs nonlinearly to natural soil, with the greatest isotherm nonlinearity occurring at equilibrium aqueous surfactant concentration around critical micelle concentration (CMC).
- The desorption of TCE from the contaminated field soil is strongly kinetic and severely limits remediation of the site. A local sorption equilibrium cannot be assumed in any model that attempts to predict remediation times.
- Triton X-100 appears to increase the rate of TCE desorption from the field soil, as evidenced by sudden increases in the aqueous-phase TCE concentration in wells as the surfactant arrives at the well.
- The "jumps" in TCE concentration can only be modeled by incorporating sudden increases in the desorption mass transfer coefficient into the model, suggesting further that Triton X-100 increases the desorption mass-transfer coefficient.
In total, the results of all these studies point to a similar conclusion: Triton X-100, even at relatively low concentrations, can increase the desorption mass-transfer coefficient and thereby improve the time scale for remediation of long-term contaminated field soils. This observation is supported by laboratory experiments using laboratory-contaminated soil, laboratory experiments using field-contaminated soil, and a pilot-scale field test of the technology at Picatinny Arsenal. It is our hope that this research will be the first step in the development of technologies to improve the remediation rates of contaminated groundwater sites using surfactants or pH changes.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
Other project views: | All 7 publications | 5 publications in selected types | All 5 journal articles |
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Type | Citation | ||
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Culver TB, Hallisey SP, Sahoo D, Deitsch JJ, Smith JA. Modeling the desorption of organic contaminants from long-term contaminated soil using distributed mass transfer rates. Environmental Science & Technology 1997;31(6):1581-1588. |
R824365 (Final) |
not available |
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Deitsch JJ, Smith JA. Effect of Triton-X-100 on the rate of trichloroethene desorption from soil to water. Environmental Science & Technology 1995;29(4):1069-1080. |
R824365 (Final) |
not available |
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Sahoo D, Smith JA. Enhanced trichloroethene desorption from long term contaminated soil using Triton X-100 and pH increases. Environmental Science & Technology 1997;31(7):1910-1915. |
R824365 (Final) |
not available |
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Sahoo D, Smith JA, McLellan HM, Imbrigiotta TE. Surfactant-enhanced remediation of a trichloroethene-contaminated aquifer. 2. Transport of TCE. Environmental Science & Technology 1998;32(11):1686-1693. |
R824365 (Final) |
not available |
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Smith JA, McLellan HM, Sahoo D, Imbrigiotta TE. Surfactant-enhanced remediation of a trichloroethene-contaminated aquifer. 1. Transport of Triton X-100. Environmental Science & Technology 1997;31(12):3565-3572. |
R824365 (Final) |
not available |
Supplemental Keywords:
water, groundwater, pump-and-treat remediation, TCE desorption, surfactant effect, remediation efficiency., Scientific Discipline, Geographic Area, Water, Waste, Environmental Chemistry, Mathematics, Remediation, State, Engineering, Chemistry, & Physics, Environmental Engineering, Groundwater remediation, contaminant transport, New Jersey (NJ), chemical transport modeling, aquifer remediation design, chemical kinetics, kinetic models, transport models, groundwater contamination, contaminated aquifers, mathematical formulations, rate-limited sorption model, TCEProgress 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.