Evapotranspiration And Geochemical Controls On Groundwater Plumes At Arid Sites: Toward Innovative Alternate End-States For Uranium Processing And Tailings Facilities

Management of legacy tailings/waste and groundwater contamination are ongoing at the former uranium milling site in Tuba City AZ. The tailings have been consolidated and effectively isolated using an engineered cover system. For the existing groundwater plume, a system of recovery wells extracts contaminated groundwater for treatment using an advanced distillation process. The ten years of pump and treat (P&T) operations have had minimal impact on the contaminant plume – primarily due to geochemical and hydrological limits. A flow net analysis demonstrates that groundwater contamination beneath the former processing site flows in the uppermost portion of the aquifer and exits the groundwater as the plume transits into and beneath a lower terrace in the landscape. The evaluation indicates that contaminated water will not reach Moenkopi Wash, a locally important stream. Instead, shallow groundwater in arid settings such as Tuba City is transferred into the vadose zone and atmosphere via evaporation, transpiration and diffuse seepage. The dissolved constituents are projected to precipitate and accumulate as minerals such as calcite and gypsum in the deep vadose zone (near the capillary fringe), around the roots of phreatophyte plants, and near seeps. The natural hydrologic and geochemical controls common in arid environments such as Tuba City work together to limit the size of the groundwater plume, to naturally attenuate and detoxify groundwater contaminants, and to reduce risks to humans, livestock and the environment. The technical evaluation supports an alternative beneficial reuse (“brownfield”) scenario for Tuba City. This alternative approach would have low risks, similar to the current P&T scenario, but would eliminate the energy and expense associated with the active treatment and convert the former uranium processing site into a resource for future employment of local citizens and ongoing benefit to the Native American Nations

Sorption of cesium and strontium by arid region desert soil

Online access for this thesis was created in part with support from the Institute of Museum and Library Services (IMLS) administered by the Nevada State Library, Archives and Public Records through the Library Services and Technology Act (LSTA). To obtain a high quality image or document please contact the DeLaMare Library at https://unr.libanswers.com/ or call: 775-784-6945.The sorption and ion exchange properties of nonradioactive cesium and strontium were studied in this investigation. Ion exchange studies have shown that the studied soil sorbs cesium preferentially relative to strontium, and that charge for charge, the exchange-phase cations released from exchange sites exceed the cesium and strontium sorbed by the soil

Monitored Natural Attenuation of Groundwater: Is Past Performance an Indication of Future Results? -11222

ABSTRACT Monitored natural attenuation, or MNA, is a groundwater remediation strategy at 14 sites managed by the U.S. Department of Energy Office of Legacy Management (LM). Monitoring data for the MNA remedies are being interpreted on contaminant-specific and site-specific bases to assess the progress of groundwater cleanup. Results from the monitoring conducted thus far are mixed; some sites show notable decreases in contaminant concentration and others indicate little to no decreases. Temporal plots of concentration at wells designed for evaluating MNA progress occasionally match trends predicted by previously developed mathematical models, but water quality trends observed at most sites managed by LM tend to diverge from model projections. Departures between predicted and observed contaminant concentrations may pose concerns about the long-term effectiveness of MNA but do not raise immediate issues regarding human health impacts or environmental risk. Ongoing evaluations of the natural attenuation remedies, in which particular focus is given to identifying the key physical and chemical phenomena that influence contaminant levels on a sitewide scale, will largely determine whether modified groundwater remediation approaches are needed