On April 20, 2010, an explosion on the offshore drilling platform Deepwater Horizon located in the Gulf of Mexico resulted in the largest oil spill in U.S. history. The subsequent use of massive amounts of chemical dispersants near the Gulf floor, an untested method, led to great controversy regarding the regulation, use, and toxicity of dispersants of the COREXIT family of products, as well as of dispersants in general. This study compares dispersant (COREXIT brand products in particular) regulation and use in the United States, Norway and the United Kingdom; the latter two countries are among the largest oil producers in the European Union. This study also applies Kingdons conceptual model of public policy development as a convergence of three independent streams in an attempt to gauge the outlook for increased regulation in the United States regarding COREXIT dispersants based on patterns of federal research funding, possible policy tool options, the existence of political will, and the perspective of the dispersant industry. The study found that with the exception of toxicity testing and approval mechanisms, the United States, Norway and the United Kingdom differ little in dispersant regulation and use. When research funding was examined, it was found that while initial funding levels increased, this may not be sustainable in the long term and therefore not a reliable indicator of the likelihood of policy change in the U.S.

Release of residual aviation gasoline saturation from field contaminated sandy aquifer material was investigated using six soil columns. Addition of a biodegradable non-ionic surfactant (5g/L) to the flushing solution produced an immediate increase in concentrations of methylated alkanes which declined over 20 pore volumes to below initial levels. 15g/L of surfactant produced higher effluent concentrations over 6 pore volumes. Adding 50% (v/v) 2-propanol caused a spike release of contaminants in less than 2 pore volumes. Methanol at 50% released contaminants at fairly low concentrations over 30 pore volumes. At 20% neither alcohol produced much increase in effluent concentrations. Combination of 20% 2-propanol and 5g/L Triton X-100 did not improve the performance of surfactant alone. Soil analysis showed more than 96% of the residual saturation was removed in all six columns. Solvophobic theory, including the effects of reduction in interfacial surface tension, predicted the relative results of both concentrations of alcohols.

Surface application offers an inexpensive, non-invasive alternative to injection wells and infiltration galleries for in situ bioremediation applications. The technology employs artificial recharge to create favorable hydraulic conditions for mixing and vertical transport of electron acceptor and nutrients. A field scale infiltration test and a conservative tracer test qualitatively indicated the feasibility of transporting solutes to the subsurface via recharging water. Modeling of the experiments provided quantitative estimates of site specific hydrogeologic and transport parameters. Results also indicated that dilution was a dominant BTEX attenuation mechanism during the experiment. Models calibrated to data from the infiltration experiment were scaled up for the design of nitrate delivery system for a pilot scale, bioremediation experiment to study enhanced in situ biodegradation of BTEX under denitrifying conditions. Modeling results suggest that dilution effects and stimulation of aerobic processes by oxygen in the recharging water may limit the effectiveness of the experiment.

The role of various particle size fractions in determining urban storm water quality (pH, suspended solids, total organic carbon, turbidity, metals, polyaromatic hydrocarbons and pesticide) has been evaluated in a series of field sampling efforts and laboratory experiments. Water quality during two storm events was monitored over time and changes in contaminant fractionation recorded. The potential for aggregation of suspended matter in the runoff stream and the importance of aggregation on partitioning of the polyaromatic hydrocarbon fluoranthene in various size fractions has been tested in laboratory experiments. Results confirmed the polluting nature of urban runoff and showed a considerable increase in the contaminants loading during storm events. Different pollutants reached their peak concentration during different stages of the storm. It was concluded that the rate and extent of aggregation processes are sufficient to significantly affect the apparent partitioning, fate and transport of associated contaminants.

This study was designed to characterize the quality of Houston area stormwater and its potential impact on receiving waters, including Galveston Bay. Stormwater samples were analyzed with regard to standard water quality parameters, as well as for metals. Large increases in the concentration of particles, suspended solids, organic carbon, iron, mercury and zinc were observed in storm runoff. Concentrations of barium and strontium, which occur naturally in area soils, decreased as result of a storm. Data suggested a link between increasing concentrations of smaller solids (0.45-20$\mu$m) and that of iron and mercury. Organic carbon showed evidence of being similarly related to zinc and larger solids ($>$20$\mu$m). Higher concentrations of these materials, in conjunction with increased runoff flows, resulted in storm loadings equivalent to months or even years of background flow. Particle size distributions measured in situ and laboratory simulations indicated significant aggregation in the runoff stream.

The use of surfactant and aqueous cosolvent soil washing for the restoration of contaminated aquifers was investigated by laboratory experimentation and literature review. The effect of surfactants on hydrocarbon biodegradation and the ability of aqueous cosolvents to mobilize residual gasoline from saturated porous media were addressed. Hydrocarbon degrading microorganisms were cultured in a flow-through sand column. Cultured organisms mineralized $\sp{14}$C-benzene and $\sp{14}$C-naphthalene, but not $\sp{14}$C-anthracene. Mineralization of radiolabeled substrates was inhibited by the presence of surfactant. Surfactants were at least partially biodegradable on the basis of oxygen utilization. Soil washing with surfactant solutions did not enhance removal of residual gasoline beyond that obtained with water. Aqueous ethanol solutions increased the desorption of gasoline components from aquifer material. Cosolvent soil washing should be further investigated. Surfactant soil washing may not be suitable for aquifer restoration because of oxygen demand, mobilization of soil fines, and increased fluid viscosity.

Microorganisms have been added to the subsurface in an attempt to enhance bioremediation. The transport, attachment and fate of these organisms as well as their possible contribution to remediation remain poorly understood. The effect of hydraulic conductivity and injection velocity on microbial transport through porous media was investigated. Glass chromatography columns were packed separately with clean quartz sand of two diameters (0.368 mm or 0.240 mm) and two hydraulic conductivities (1.37 $\times$ 10$\sp{-1}$ cm/sec and 3.65 $\times$ 10$\sp{-2}$ cm/sec respectively). Three injection velocities, 1.18 $\times$ 10$\sp{-3}$, 2.35 $\times$ 10$\sp{-3}$ and 4.73 $\times$ 10$\sp{-3}$ cm/sec were investigated. Microbial transport under the conditions tested was limited and could be predicted mathematically using a model based on filtration theory which incorporated particle trajectory analysis.

The common approach to investigating the extent of contamination at a hazardous waste site is to drill monitoring wells to obtain geotechnical and chemical information. A new technology is now being utilized at various hazardous waste sites in order to facilitate the hydrogeologic data collection process. The use of cone penetration testing has proven to be a relatively quick and inexpensive method for initial site investigations compared to current techniques. Cone penetrometer testing can quickly determine the stratigraphy of an area, the soil properties, and (by taking samples) the extent of contamination. The data are obtained immediately, which allows in-field evaluation and "on the spot" decisions, resulting in enhanced placement of monitoring wells and in some instances a substantial reduction in the number of wells needed. Fewer monitoring wells means a large cost savings. Applications of cone penetrometer testing are presented and recommendations for further research are discussed.

The rate of movement of contaminants in groundwater is a topic of environmental importance and public concern. Early work in contaminant transport showed that the ratio of the velocity of the water to the velocity of the contaminant (v$\sb{\rm w}$/v$\sb{\rm c}$ or retardation, R) in a flowing saturated soil column can be determined using known values of soil density, soil porosity, percent organic carbon in the soil, and the octanol-water partition coefficient of the contaminant. More recent studies indicate that the retardation of the contaminant in a soil may vary due to soil/contaminant isotherm non-linearity and non-equilibrium conditions in the column. In this research, the effect of velocity on the observed retardation of methylated benzenes is evaluated using three different soils (organic carbon range--0.008% to 0.27%) and a wide range of linear velocities (0.2 ft/day to 40 ft/day). Contaminant solutions of 10 mg/l benzene, toluene, p-xylene and mesitylene, 1 mg/l naphthalene, and 50 mg/l ethylbenzene were pumped through a 0.9 cm ID saturated soil column into a UV/Vis flow-through spectrophotometer for detection of contaminant breakthrough. Breakthrough and flush-out curves, in general, were found to be symmetric, regardless of velocity or contaminant used. Below a velocity of 3 ft/day, compounds with K$\sb{\rm ow}$ values of $>$10$\sp3$ showed an increase in retardation with decreasing velocity. Data were fitted to both an equilibrium and non-equilibrium model with one variable parameter. Results indicated that the data could not be modeled by the non-equilibrium model but did fit the equilibrium model with variable retardation.

The sorption and desorption behaviors of chlorinated hydrocarbons and naphthalene to and from Lake Charles sediments were studied. The sorption of 1,2- dichlorobenzene, 1,2,4-trichlorobenzene, and naphthalene was determined to be linear via hydrophobic effect, and the partition coefficients of these compounds were in the range of literature reported values. The desorption of chlorinated hydrocarbons and naphthalene were studied with two systems--a desorption with continuous removal of aqueous phase contaminants and a desorption by the repetitive water extraction. The desorption of both historically-existed and newly-added compounds showed great deviations from the equilibrium conditions. A biphasic desorption, with a labile phase and a resistant phase, has been observed to exist for both freshly- and aged-contaminated sediments. The desorption from the irreversible compartment reached a near-constant concentration, which was orders of magnitude lower than that predicted by equilibrium equations. The size of the resistant fractions seemed highly related to the initial solid phase concentration. Several factors, including pH, temperature, and competitive sorption, were found to significantly affect the release of historically-existed contaminants from the sediments. The laboratory observations in this study agreed well with other laboratory and field observations. The existence of the irreversible fraction may have a significant impact on regulatory, modeling and remediation activities.