Because iron-based materials that are used for the permeable reactive barrier systems come in various shapes, sizes, and with various surface properties depending on the manufacturing sources, their reductive powers vary in a wide spectrum. A new experimental procedure to evaluate the reductive power of iron material was developed in this study. Tri-iodide (I3(-)) was used as the representative oxidizing agent that reacts with zero-valent iron (ZVI). Three iron-based materials (two scraps, two powders) and four chlorinated chemicals [perchloroethene (PCE), trichloroethene (TCE), 1,1,1-trichloroethane (TCA), and pentachlorophenol (PCP)] were used in this study. Redox reactions were conducted in glass vials containing aqueous solutions of chlorinated compounds or tri-iodide with known masses of iron material. After a predetermined reaction time each vial was opened and the solution was analyzed for the concentration of reduced compound. The apparent rate contant (k(i)(obs)) of iodine reduction reaction with ZVIs was found to be proportional to that (k(c)(obs)) of chlorinated contaminant. The surface area-normalized reduction rate constants (k(c)(nor)) for contaminants and tri-iodide (k(i)(nor)) were also proportional to each other. The ratio of rate constants, K(nor) (= k(c)(nor)/k(i)(nor)) was estimated for each contaminant; 3.29 × 10(-7), 5.86 × 10(-7), 6.70 × 10(-7), and 7.87 × 10(-10) M, for PCE, TCE, TCA, and PCP, respectively. The results of this study suggest that the reductive power of ZVI materials can be standardized using tri-iodide, and thus, can provide a good reference for the quantitative assessment of the reactivity of metallic reducing agents of environmental interest including ZVIs.

An innovative surfactant-enhanced ozone sparging (SEOS) technique was developed in this study. The synergistic effect of simultaneous surfactant and ozone application on the removal of organic contaminants in an aquifer during air sparging was investigated. Using laboratory-scale one- and two-dimensional physical models packed with water-saturated sand, air sparging and ozone sparging were implemented either at high or low level surface tension of the groundwater. A water-dissolved chemical (fluorescein sodium salt) and a nonaqueous phase liquid (n-decane) were used as the representative contaminants. Sodium dodecylbenzene sulfonate was used for sparging experiments at low level surface tension. Ozone sparging at low surface tension (SEOS) was found to be the most efficient process for the removal of organic chemicals, among AS (air sparging at high surface tension), SEAS (surfactant-enhanced air sparging, air sparging at low surface tension), and OS (ozone sparging at high surface tension), based on the results from a one-dimensional column study. Two-dimensional model experiments also showed that SEOS is more efficient than conventional AS processes. The increased air saturation and sparging influence zone achieved by surfactant application, and the oxidative power of ozone are responsible for the enhanced removal of contaminants from the aquifer. Considering that the application of conventional AS is limited to volatile contaminants, and that OS has a very narrow influence zone, SEOS can be an useful option for the removal of contaminants of low vapor pressures from an expanded zone of influence.

Capillary fringe divides the groundwater and the vadose zone controlling the diffusive mass transfer of contaminants and gases. The thickness of capillary fringe is of great importance for the rate of contaminant mass transfer across the capillary fringe. Application of surface active chemicals including surfactants and alcohol-based products into the subsurface environment changes the surface tension of the aqueous phase, which in turn, affects the thickness of the capillary fringe. In this study, a bench-scale model was used to assess the quantitative relationship between the surface tension and the thickness of the capillary fringe. An anionic surfactant (Sodium dodecylbenzene sulfonate, SDBS) and an aqueous solution of ethanol were used to control the surface tension of the groundwater. It was found that the thickness of the capillary fringe is directly proportional to the surface tension. The air entry pressures measured by the Tempe Pressure Cell at different surface tensions using SDBS (200 mg/L) and ethanol (20%, v/v) solutions were in good agreement with the thicknesses of the capillary fringe measured by the model. A simple method to correct the conventional Brooks-Corey model for estimating the air entry pressure was also presented.