Robert C. Knox

Surfactants for ground water remediation

Ground water contamination is a most intractable form of pollution. Spilled solvent or fuel liquids are trapped below the water table by colloidal forces. Surfactants may be used to dramatically improve contaminated aquifer remediation rates. Principal remediation mechanisms include micellar solubilization and mobilization of the trapped liquids by lowering of the oil/water interfacial tension. Surfactant selection is a key to the successful design of a remediation effort, and involves consideration of factors including Krafft Point, surfactant adsorption onto the aquifer solids, and the phase behavior of the oil/water/surfactant system. Successful field demonstrations have occurred in recent months and the technology is moving rapidly toward commercialization. Critical research issues remain including acceptable clean-up levels, surfactant/contaminant in situ biodegradation rates, and surfactant decontamination and reuse.

Integrated design of surfactant enhanced DNAPL remediation : Efficient supersolubilization and gradient systems

Abstract Widespread use of petroleum hydrocarbons and chlorinated solvents has resulted in contamination of soils and ground water supplies. This paper summarizes key technical and economic issues for surf ace act ive a ge nt (surfactant)-enhanced remediation of such contamination episodes. Laboratory and field results are cited illustrating each of these key issues. Using the design of an upcoming field study as an example, we illustrate the importance of system solubility enhancement, interfacial tension, viscosity and density in selecting a surfactant system. We also show how a site-specific capillary curve can be used to optimize contaminant solubility (super solubilization) while mitigating mobilization and vertical migration. Finally, we demonstrate the potential of a surfactant gradient system to progressively increase the super-solubilization potential without mobilizing trapped oil.

Prioritization of ground water contaminants and sources

The objective of this research was to identify chemical, physical, bacteriological, and viral contaminants, and their sources, which present the greatest health threat in public ground water supplies in the USA; and to classify (prioritize) such contaminants and relative to their health concerns. The developed contaminant prioritization methodology was based on frequency of occurrence and adverse health effects. Adverse health effects were based on carcinogenic potency, toxicity, hazardous chemical priorities and drinking water standards. Application of the methodology for wellhead protection areas, (WHPAs) revealed that approximately 200 different contaminants have been detected in the nations public ground water supplies. The seven chemical constituents with the highest priority were arsenic, chromium, cadmium, carbon tetrachloride, chloroform, 1, 1-dichloroethylene, and ethylene dibromide. Other contaminants of concern were trichloroethylene, nitrates, barium, 1,1,1-trichloroethane, benzene, tetrachloroethylene, selenium, lead, toluene, mercury, gross alpha radiation, methylene chloride, coliform bacteria, metolachlor, metribuzin, 1, 1, 2, 2-tetrachloroethane, dibromochloroethane, simazine, radium-266, and toxaphene. The contaminant source prioritization methodology was also based on frequency of occurrence. Over 30 categories of sources were evaluated, with the eight with highest priority including agricultural activities, hazardous waste sites, landfills, industrial operations, septic tank systems, oil and gas field activities, urban land use, and underground storage tanks.

Remediation of NAPL Source Zones: Lessons Learned from Field Studies at Hill and Dover AFB

Innovative remediation studies were conducted between 1994 and 2004 at sites contaminated by nonaqueous phase liquids (NAPLs) at Hill and Dover AFB, and included technologies that mobilize, solubilize, and volatilize NAPL: air sparging (AS), surfactant flushing, cosolvent flooding, and flushing with a complexing-sugar solution. The experiments proved that aggressive remedial efforts tailored to the contaminant can remove more than 90% of the NAPL-phase contaminant mass. Site-characterization methods were tested as part of these field efforts, including partitioning tracer tests, biotracer tests, and mass-flux measurements. A significant reduction in the groundwater contaminant mass flux was achieved despite incomplete removal of the source. The effectiveness of soil, groundwater, and tracer based characterization methods may be site and technology specific. Employing multiple methods can improve characterization. The studies elucidated the importance of small-scale heterogeneities on remediation effectiveness, and fomented research on enhanced-delivery methods. Most contaminant removal occurs in hydraulically accessible zones, and complete removal is limited by contaminant mass stored in inaccessible zones. These studies illustrated the importance of understanding the fluid dynamics and interfacial behavior of injected fluids on remediation design and implementation. The importance of understanding the dynamics of NAPL-mixture dissolution and removal was highlighted. The results from these studies helped researchers better understand what processes and scales are most important to include in mathematical models used for design and data analysis. Finally, the work at these sites emphasized the importance and feasibility of recycling and reusing chemical agents, and enabled the implementation and success of follow-on full-scale efforts.

Surfactant Effects on Residual Water and Oil Saturations in Porous Media

A series of soil column tests was performed to determine surfactant effects on residual water and oil saturations in porous media. In particular, these tests focused on the impact of submicellar surfactant solutions and the potential application of these low concentration systems to light nonaqueous phase liquid (LNAPL) contamination in the vadose zone. One set of tests involved surfactant flushing in soil-filled columns followed by drainage to residual water saturation and LNAPL injection to determine the subsequent residual LNAPL saturation. Another set of tests involved surfactant application to a soil-filled column already holding residual LNAPL saturation to promote the release of the previously trapped LNAPL. Test results showed surfactant systems could reduce both residual water and oil saturations by up to 50%. In addition, submicellar surfactant systems were equally effective as supramicellar solutions in reducing residual water saturations and potentially more effective at reducing residual oil saturations. Submicellar surfactant applications to a medium-grained (0.85–0.425 mm) soil containing residual LNAPL saturations were effective at releasing up to 50% of the previously trapped residual LNAPL. These applications were less successful in a fine-grained soil as full drainage of water and LNAPL was unachievable due to high capillary pressures. Overall, observations suggest low concentration surfactant solutions may have the ability to release significant amounts of previously trapped LNAPL in the vadose zone, potentially increasing free-product recovery rates and lowering LNAPL saturations to levels more favorable for biodegradation. The decrease in overall saturations (both water and oil) in a contaminated vadose zone could also present an increase in air permeability, thus enhancing other vadose zone treatment technologies such as bioventing or soil vapor extraction.

Surfactant-Enhanced NAPL Remediation: From the Laboratory to the Field

Pump-and-treat remediation has routinely been prescribed for subsurface nonaqueous phase liquid (NAPL) contamination. However, pump-and-treat systems have proven incapable of remediating contaminated aquifers in a timely and economical manner. Cost overruns of 80% and cleanup times as much as three time longer than original estimates are typically reported (Olsen and Kavanaugh 1993). Several factors have been identified that contribute to the inefficiency of pump-and-treat remediation, including: (1) diffusion limitations for contaminants from low conductivity zones to high conductivity zones; (2) hydrodynamic isolation, such as dead end zones; (3) rate-limited desorption of contaminants from solid surfaces; and (4) liquid-liquid dissolution of residual NAPLs (Bouwer et al. 1988; Keely 1989; Mackay and Cherry 1989; Haley et al. 1991; Schmelling et al. 1992; NRC 1994). When residual NAPL is present, subsurface contamination can be categorized into three zones: the source/residual zone, the concentrated plume (center of mass of the groundwater plume), and the dilute groundwater plume. Innovative technologies are necessary for residual phase materials as pump-and-treat alone will be extremely inefficient in this zone.

Protocol for selecting an in‐tank leak detection device

A protocol has been developed to rank in‐tank detection devices for underground storage tanks. Eleven leak detection devices were selected and evaluated relative to 12 decision factors. The importance of the factors differs with environmental, physical and economic conditions, therefore, four hypothetical operating situations were used for evaluation. The unranked paired‐comparison technique was used to weight the decision factors. The ranking approach for the in‐tank detection was devices simplified by a categorization scheme. The resultant decision matrix indicates that the selection of a leak detection device should be based upon the operating conditions and choices among devices that satisfy regulations and decrease the possibility of user liability.