Determination of Chlorinated Solvent Sorption by Porous Material-Application to Trichloroethene Vapor on Cement Mortar

Experiments have been performed to investigate the sorption of trichloroethene (TCE) vapor by concrete material or, more specifically, the cement mortar component. Gas-flow experiments were conducted using columns packed with small pieces of cement mortar obtained from the grinding of typical concrete material. Transport and retardation of TCE at high vapor concentrations (500 mg L−1) was compared to that of a non-reactive gas tracer (Sulfur Hexafluoride, SF6). The results show a large magnitude of retardation (retardation factor = 23) and sorption (sorption coefficient = 10.6 cm3 g−1) for TCE, compared to negligible sorption for SF6. This magnitude of sorption obtained with pollutant vapor is much bigger than the one obtained for aqueous-flow experiments conducted for water-saturated systems. The considerable sorption exhibited for TCE under vapor-flow conditions is attributed to some combination of accumulation at the air-water interface and vapor-phase adsorption, both of which are anticipated to be significant for this system given the large surface area associated with the cement mortar. Transport of both SF6 and TCE was simulated successfully with a two-region physical non-equilibrium model, consistent with the dual-medium structure of the crushed cement mortar. This work emphasizes the importance of taking into account sorption phenomena when modeling transport of volatile organic compounds through concrete material, especially in regard to assessing vapor intrusion

Effects of rhamnolipid biosurfactants on removal of phenanthrene from soil

Solubilizing agents may enhance remediation of-soils contaminated with hydrophobic organic contaminants by diminishing sorption of the contaminants or increasing desorption rates. The effectiveness of rhamnolipid biosurfactants to enhance the removal of sorbed contaminants from soil was determined using column studies. Soil columns were contaminated with phenanthrene and subsequently eluted with electrolyte solution or with electrolyte solution containing 500 mg/L rhamnolipid. For the four soils studied, removal of 50% of the phenanthrene from the soil columns was accomplished in a 2-5-fold shorter time period, and the time required for 90% removal was reduced up to 3.5-fold when elution was performed with the rhamnolipid-containing solution as compared to the treatment without rhamnolipid. The effect of rhamnolipid on the removal of phenanthrene was satisfactorily simulated using independently obtained parameters with a two-component advective-dispersive model accounting for micellar solubilization and admicellar sorption. A more detailed analysis of the system showed that desorption rates of phenanthrene in the presence of 500 mg/L rhamnolipid were higher than predicted on the basis of desorption rate constants of phenanthrene determined in the absence of rhamnolipid. It is concluded that rhamnolipid enhanced the removal of phenanthrene mainly by micellar solubilization and also by influencing sorption kinetics

Transport of Co2+ in a Physically and Chemically Heterogeneous Porous Medium

The fate of radionuclides in the subsurface is of critical importance to the planning, siting, and evaluation of repositories for radioactive wastes. Mathematical models are an integral component of this process. An accurate understanding of radionuclide transport is required to successfully formulate and use these models. It is well-known that the subsurface is both physically and chemically heterogeneous. Recent research has shown that the resultant spatial variability of hydraulic conductivity and of sorption capacity can significantly affect solute transport in the subsurface. The impact of hydraulic conductivity variability and sorption capacity variability on the transport of radionuclides is, therefore, of great interest. Very few well-controlled, experimentally based laboratory investigations of the transport of radionuclides in physically and chemically heterogeneous porous media have been reported in the literature. The purpose of this paper is to report the preliminary results of such an investigation. We present results obtained for transport of Co2+ in a column packed with two media of differing hydraulic conductivities and sorption capacities. In addition to being influenced by these heterogeneities, transport of the Co2+ is also influenced by rate-limited diffusive mass transfer and non-equilibrium sorption

Influence of chain length on field-measured distributions of PFAS in soil and soil porewater

Soil and porewater concentrations measured for multiple PFAS were compiled from three field studies. The soil:porewater concentration ratios were shown to be functions of molar volume for all three data sets. Remarkable consistency was observed between the three sets of field-based measurements, indicating that PFAS distributions in the three soil systems exhibited similar magnitudes of overall retention. The relative contributions of solid-phase sorption and air-water interfacial adsorption to total retention were examined. The contribution of air-water interfacial adsorption was greater than that of solid-phase sorption for the longer-chain PFAS, whereas it was less than that of solid-phase sorption for the shorter-chain PFAS. These results show that the relative contributions of the two processes can vary as a function of the particular PFAS when the solid-phase sorption functionality deviates from that of air-water interfacial adsorption. This might occur for example when sorption is influenced by addition mechanisms beyond hydrophobic interaction, or when sorption and/or adsorption are nonlinear. Based on the results from all three data sets, soil concentrations are likely to be smaller than porewater concentrations for the shortest-chain PFAS. Conversely, soil concentrations will generally be significantly greater than porewater concentrations for longer-chain PFAS. The results from this study have implications for characterizing and evaluating PFAS distributions in vadose-zone soils

Partitioning Tracers for In-Situ Measurement of Nonaqueous Phase Liquids in the Subsurface - Final Report - 09/15/1996 - 09/14/2000

The overall goal of the proposed project is to explore the use of partitioning tracers to characterize dense nonaqueous phase liquids (DNAPLs) in aquifer systems. Bulk-phase partitioning tracers will be investigated to detect and determine DNAPL saturation, while interface partitioning tracers will be investigated to measure the area of the DNAPL-water interface. The specific objectives that will be addressed to accomplish this goal are: (1) Investigate the use of partitioning tracers to detect and determine both the saturation and interfacial area of DNAPLs in saturated porous media. (2) Investigate the effect of rate-limited mass transfer on the transport behavior of partitioning tracers. (3) Investigate the effect of porous-media heterogeneity on the transport behavior of partitioning tracers. (4) Develop and evaluate mathematical models capable of simulating the transport of partitioning tracers in complex systems. This proposal outlines an integrated approach for the development and testing of a unique method for detecting and measuring DNAPL in aquifer systems. The approach combines one-dimensional laboratory experiments, three-dimensional intermediate-scale flow cell experiments, physical methods for DNAPL description (including dual-energy gamma radiation), and advanced modeling techniques. This approach will allow a new, promising technique for characterizing DNAPL in aquifer systems to be verified by established laboratory and numerical methods. The effect of heterogeneity will be examined by the use of a flow-cell packed with layers of variable permeability and containing multiple sample ports. The effect of rate-limited liquid-liquid mass transfer will be investigated by examining the impact of pore-water velocity and DNAPL form on transport of the partitioning tracers. Effective risk assessment and remediation of DNAPL contaminated sites is constrained by the limitations of current site characterization techniques. A major weakness of the current methods is that they provide data at discrete points, such that the probability of sampling a zone of localized DNAPL is quite small. The results of the research will lead to improved techniques for characterizing DNAPL contaminated sites and will enhance our understanding of the distribution of DNAPLs in the subsurface risk assessments and remediation planning

Partitioning Tracers for In Situ Detection and Quantification of Dense Nonaqueous Phase Liquids in Groundwater Systems

The overall goal of the project is to explore the use of an innovative in-situ method (partitioning tracer tests) for detection and quantification of dense nonaqueous phase liquids (DNAPLs) in subsurface systems. DNAPLs occur in the subsurface at numerous contaminated sites and can act as long-term sources of groundwater contamination. Both effective risk assessment and remediation of DNAPL-contaminated sites is limited by current site characterization techniques. A major limitation of the current methods is that they provide data at discrete points, such that the probability of sampling a zone of localized DNAPL is quite small. The results of this research will lead to an improved method for characterizing DNAPL-contaminated sites and will enhance our understanding of the distribution of immiscible liquids in the subsurface. The use of this method will help reduce the uncertainty associated with risk assessments and remediation planning

Solubilization and removal of residual trichloroethene from porous media: Comparison of several solubilization agents

The development of improved methods for remediation of contaminated subsurface systems has emerged as a significant environmental priority. One technology that appears to have considerable promise involves the use of solubilization-enhancing agents, such as surfactants, cosolvents, dissolved organic matter (DOM), and complexing agents, to promote removal of immiscible-liquid and sorbed phase organic contaminants. We examined the use of six flushing agents, i.e., two anionic surfactants, two complexing agents (cyclodextrins), a humic acid, and an alcohol, for solubilizing and removing residual-phase immiscible liquid from porous media. The results of batch experiments conducted to measure the degree of trichloroethene (TCE) solubilization induced by these agents show that the solubility of TCE was enhanced between 3 and 57 times depending on the flushing agent. Column experiments were conducted to compare water and agent-enhanced flushing of Borden sand containing residual saturations of TCE. As expected, the total flushing volume necessary to remove the residual saturation was reduced substantially in the presence of all applied agents. The relative effectiveness of the agents varied based on the method of evaluation. On a mass-efficiency basis, SDS outperformed all other agents, whereas DOM provided the best performance on a molar-efficiency basis. Copyright (C) 2000 Elsevier Science B.V