An Investigation of Engineered Injection and Extraction as an in situ Remediation Technique for Uranium-Contaminated Groundwater

摘要

During in situ remediation of contaminated groundwater, a treatment chemical is injected into the contaminated groundwater to degrade a contaminant through chemical reaction that occurs in the subsurface. Reactions and subsequent contaminant degradation occur only where the treatment chemical contacts the contaminant long enough to complete degradation reactions. Traditional in situ groundwater remediation relies on background groundwater flow to spread an injected treatment chemical into a plume of contaminated groundwater.;Engineered Injection and Extraction (EIE), in which time-varying induced flow fields are used to actively spread the treatment chemical into the contaminant plume, has been developed to increase contact between the contaminant and treatment chemical, thereby enhancing contaminant degradation. EIE has been investigated for contaminants degrading through irreversible, bimolecular reaction with a treatment chemical, but has not been investigated for a contaminant governed by complex biogeochemical processes. Uranium fate and transport in subsurface environments is governed by adsorption, oxidation reduction, solution, and solid-phase interactions with naturally occurring solution species, microbial communities, minerals and aquifer media. Uranium primarily occurs in aqueous, mobile U(VI) complexes in the environment but can be reduced to sparingly soluble, immobile U(IV) solid-phase complexes by native dissimilatory metal reducing bacteria.;This work investigates the ability of EIE to promote subsurface delivery of an acetate-amended treatment solution throughout a plume of uranium-contaminated groundwater to promote in situ growth of native microbial communities to immobilize uranium. Simulations in this investigation are conducted using a semi-synthetic flow and reactive transport model based on physical and biogeochemical conditions from two uranium contaminated sites: the Naturita Uranium Mill Tailings Remedial Action (UMTRA) Project site in southwestern Colorado and the Old Rifle UMTRA Project site in western Colorado.