Aerosol Delivery for Amendment Distribution in Contaminated Vadose Zones

Remediation of contaminated vadose zones is often hindered by an inability to effectively distribute amendments. Many amendment-based approaches have been successful in saturated formations, however, have not been widely pursued when treating contaminated unsaturated materials due to amendment distribution limitations. Aerosol delivery is a promising new approach for distributing amendments in contaminated vadose zones. Amendments are aerosolized and injected through well screens. During injection the aerosol particles are transported with the gas and deposited on the surfaces of soil grains. Resulting distributions are radially and vertically broad, which could not be achieved by injecting pure liquid-phase solutions. The objectives of this work were A) to characterize transport and deposition behaviors of aerosols; and B) to develop capabilities for predicting results of aerosol injection scenarios. Aerosol transport and deposition processes were investigated by conducting lab-scale injection experiments. These experiments involved injection of aerosols through a 2m radius, sand-filled wedge. A particle analyzer was used to measure aerosol particle distributions with time, and sand samples were taken for amendment content analysis. Predictive capabilities were obtained by constructing a numerical model capable of simulating aerosol transport and deposition in porous media. Results from tests involving vegetable oil aerosol injection show that liquid contents appropriate for remedial applications could be readily achieved throughout the sand-filled wedge. Lab-scale tests conducted with aqueous aerosols show that liquid accumulation only occurs near the point of injection. Tests were also conducted using 200 g/L salt water as the aerosolized liquid. Liquid accumulations observed during salt water tests were minimal and similar to aqueous aerosol results. However, particles were measured, and salt deposited distal to the point of injection. Differences between aqueous and oil deposition are assumed to occur due to surface interactions, and susceptibility to evaporation of aqueous aerosols. Distal salt accumulation during salt water aerosol tests suggests that solid salt forms as salt water aerosols evaporate. The solid salt aerosols are less likely to deposit, so they travel further than aqueous aerosols. A numerical model was calibrated using results from lab-scale tests. The calibrated model was then used to simulate field-scale aerosol injection. Results from field-scale simulations suggest that effective radii of influence on the scale of 8-10 meters could be achieved in partially saturated sand. The aerosol delivery process appears to be capable distributing oil amendments over considerable volumes of formation at concentrations appropriate for remediation purposes. Thus far, evaporation has limited liquid accumulation observed when distributing aqueous aerosols, however, results from salt water experiments suggest that injection of solid phase aerosols can effectively distribute water soluble amendments (electron donor, pH buffer, oxidants, etc.). Utilization of aerosol delivery could considerably expand treatment options for contaminated vadose zones at a wide variety of sites.