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Biodegradation experiments have revealed that mixtures of polycyclic aromatic hydrocarbons in the micelle are directly bioavailable in the multicomponent systems. In addition, the bioavailability of naphthalene, phenanthrene and pyrene in the micellar phase decreased with increasing surfactant concentration. Results also reveal that a compound demonstrate similar bioavailability either as a single solute or in different binary or ternary mixtures.

Ideal solubility theory, which says that a nonaqueous phase liquid (NAPL) will turn into a homogeneous solution if each constituent's mole fraction is less than the solid-liquid reference fugacity ratio at the system temperature, is useful in determining the phase stability of polycyclic aromatic hydrocarbons (PAHs) and NAPL. Doubts concerning the melting temperature and entropy of fusion, however, may make the determination of PAH-NAPL phase stability difficult.

A study aimed at evaluating the parameters that govern the rates of the mass transfer of the individual components of four synthetic dense non-aqueous phase liquid (DNAPL) mixtures into the aqueous phase is presented. Toluene and eight other polynuclear aromatic hydrocarbons (PAHs) are the DNAPL mixtures that were utilized as models for coal tars and creosotes. The reactor used allowed a normally stable interface between internally mixed but separated aqueous and DNAPL phases.

The phase equilibria of a coal tar-solvent-water mixture was characterized as a ternary system using an excess free energy equation. The thermodynamic modeling, which treated the coal tar as a pseudocomponent, decreased the required data for describing ternary liquid-liquid equilibria. In addition, it also demonstrated the viability of using binary water vapor-liquid equilibria, binary mutual solubility data and three tie lines for modeling the ternary system.

Several former manufactured gas plant sites (MGP) are plagued with soil and groundwater contamination problems due to past process operations and residuals management practices. Remediation costs for individual MGP sites amount to tens of millions of dollars. Gas Research Institute estimates show that almost 70% of the costs incurred were due to the management of soils and sediments that have been contaminated with tar.

The presence of coal tar has been noted in former manufactured gas plant sites. Water-miscible solvent extraction has been proposed as a remediation technology for sites contaminated with coal tar, which is classified as a nonaqueous phase liquid, a group of sursurface contaminants that are immiscible in water. The solvent extraction remediation method requires thorough knowledge of the influence of water-miscible solvents on coal tar's solubility.

This study was designed to examine the role of molecular structure in determining the biodegradation rates of polycyclic aromatic hydrocarbons (PAHs). Laboratory experiments were performed in aqueous systems, and data were analyzed in a manner that allowed determination of first-order biodegradation rates independent of bioavailability limitations from physical-chemical processes. An aerobic mixed culture was used, which had been enriched on a broad range of PAHs. The 22 PAHs included in this study ranged in size from two to four rings and included compounds with 5-carbon rings and alkyl substituents. The range of observed biodegradation rates was only 1 order of magnitude, which is much less than that which is typically observed in the field. This supports the findings of other types of studies, which conclude that most of the observed variation in environmental PAH biodegradation rates comes from processes controlling the bioavailability of the compounds and not processes controlling uptake or biotransformation. Rate differences that were observed were attributable either to the presence of a 5-carbon ring or an alkyl substituent in an a position. Various molecular descriptors that might be expected to correlate with rate-limiting steps in the biodegradation process were used in an attempt to develop a quantitative structure-activity relationship for the PAH biodegradation rates. No significant correlations were found, but rate limitation from interactions with the relevant enzymes remains a possibility. [ABSTRACT FROM AUTHOR]

Examines factors governing human health risk assessment for nonaqueous phase liquids (NAPL) containing polycyclic aromatic hydrocarbons. Effect in aqueous solubilities on NAPL composition; Solidification of the less soluble NAPL constituents; Estimation on the carcinogenic risk due to ingestion of contaminated groundwater.

We developed the Leakage Risk Monetization Model (LRiMM) which integrates simulation of CO2 leakage from geologic CO2 storage reservoirs with estimation of monetized leakage risk (MLR). Using geospatial data, LRiMM quantifies financial responsibility if leaked CO2 or brine interferes with subsurface resources, and estimates the MLR reduction achievable by remediating leaks. We demonstrate LRiMM with simulations of 30 years of injection into the Mt. Simon sandstone at two locations that differ primarily in their proximity to existing wells that could be leakage pathways. The peak MLR for the site nearest the leakage pathways ($7.5/tCO2) was 190x larger than for the farther injection site, illustrating how careful siting would minimize MLR in heavily used sedimentary basins. Our MLR projections are at least an order of magnitude below overall CO2 storage costs at well-sited locations, but some stakeholders may incur substantial costs. Reliable methods to detect and remediate leaks could further minimize MLR. For both sites, the risk of CO2 migrating to potable aquifers or reaching the atmosphere was negligible due to secondary trapping, whereby multiple impervious sedimentary layers trap CO2 that has leaked through the primary seal of the storage formation.

Fractures in geological formations may enable migration of environmentally relevant fluids, as in leakage of CO2 through caprocks in geologic carbon sequestration. We investigated geochemically induced alterations of fracture geometry in Indiana Limestone specimens. Experiments were the first of their kind, with periodic high-resolution imaging using X-ray computed tomography (xCT) scanning while maintaining high pore pressure (100 bar). We studied two CO2-acidified brines having the same pH (3.3) and comparable thermodynamic disequilibrium but different equilibrated pressures of CO2 (PCO2 values of 12 and 77 bar). High-PCO2 brine has a faster calcite dissolution kinetic rate because of the accelerating effect of carbonic acid. Contrary to expectations, dissolution extents were comparable in the two experiments. However, progressive xCT images revealed extensive channelization for high PCO2, explained by strong positive feedback between ongoing flow and reaction. The pronounced channel increasingly directed flow to a small region of the fracture, which explains why the overall dissolution was lower than expected. Despite this, flow simulations revealed large increases in permeability in the high-PCO2 experiment. This study shows that the permeability evolution of dissolving fractures will be larger for faster-reacting fluids. The overall mechanism is not because more rock dissolves, as would be commonly assumed, but because of accelerated fracture channelization.

Reactions of CO2 with magnesium silicate minerals to precipitate magnesium carbonates can result in stable carbon sequestration. This process can be employed in ex situ reactors or during geologic carbon sequestration in magnesium-rich formations. The reaction of aqueous CO2 with the magnesium silicate mineral forsterite was studied in systems with transport controlled by diffusion. The approach integrated bench-scale experiments, an in situ spectroscopic technique, and reactive transport modeling. Experiments were performed using a tube packed with forsterite and open at one end to a CO2-rich solution. The location and amounts of carbonate minerals that formed were determined by postexperiment characterization of the solids. Complementing this ex situ characterization, (13)C NMR spectroscopy tracked the inorganic carbon transport and speciation in situ. The data were compared with the output of reactive transport simulations that accounted for diffusive transport processes, aqueous speciation, and the forsterite dissolution rate. All three approaches found that the onset of magnesium carbonate precipitation was spatially localized about 1 cm from the opening of the forsterite bed. Magnesite was the dominant reaction product. Geochemical gradients that developed in the diffusion-limited zones led to locally supersaturated conditions at specific locations even while the volume-averaged properties of the system remained undersaturated.

Sulfur dioxide is a possible co-injectant with carbon dioxide in the context of geologic sequestration. Because of the potential of SO2 to acidify formation brines, the extent of SO2 dissolution from the CO2 phase will determine the viability of co-injection. Pressure-, temperature-, and salinity-adjusted values of the SO2 Henry's Law constant and fugacity coefficient were determined. They are predicted to decrease with depth, such that the solubility of SO2 is a factor of 0.04 smaller than would be predicted without these adjustments. To explore the potential effects of transport limitations, a nonsteady-state model of SO2 diffusion through a stationary cone-shaped plume of supercritical CO2 was developed. This model represents an end-member scenario of diffusion-controlled dissolution of SO2, to contrast with models of complete phase equilibrium. Simulations for conditions corresponding to storage depths of 0.8-2.4 km revealed that after 1000 years, 65-75% of the SO2 remains in the CO2 phase. This slow release of SO2 would largely mitigate its impact on brine pH. Furthermore, small amounts of SO2 are predicted to have a negligible effect on the critical point of CO2 but will increase phase density by as much as 12% for mixtures containing 5% SO2.