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Title: Refining the site conceptual model at a former uranium mill site in Riverton, Wyoming, USA

Milling activities at a former uranium mill site near Riverton, Wyoming, USA, contaminated the shallow groundwater beneath and downgradient of the site. Although the mill operated for <6 years (1958-1963), its impact remains an environmental liability. Groundwater modeling predicted that contaminant concentrations were declining steadily, which confirmed the conceptual site model (CSM). However, local flooding in 2010 mobilized contaminants that migrated downgradient from the Riverton site and resulted in a dramatic increase in groundwater contaminant concentrations. This observation indicated that the original CSM was inadequate to explain site conditions and needed to be refined. In response to the new observations after the flood, a collaborative investigation to better understand site conditions and processes commenced. This investigation included installing 103 boreholes to collect soil and groundwater samples, sampling and analysis of evaporite minerals along the bank of the Little Wind River, an analysis of evaportranspiration in the shallow aquifer, and sampling naturally organic-rich sediments near groundwater discharge areas. The enhanced characterization revealed that the existing CSM did not account for high uranium concentrations in groundwater remaining on the former mill site and groundwater plume stagnation near the Little Wind River. Observations from the flood and subsequent investigations indicate that additional characterizationmore » is still needed to continue refining the CSM and determine the viability of the natural flushing compliance strategy. Additional sampling, analysis, and testing of soil and groundwater are necessary to investigate secondary contaminant sources, mobilization of contaminants during floods, geochemical processes, contaminant plume stagnation, distribution of evaporite minerals and organic-rich sediments, and mechanisms and rates of contaminant transfer from soil to groundwater. Future data collection will be used to continually revise the CSM and evaluate the compliance strategy at the site.« less
 [1] ;  [2] ;  [2] ;  [3] ;  [3] ;  [3] ;  [4]
  1. Dept. of Energy (DOE), Washington DC (United States)
  2. Stoller Newport News Nuclear, Inc., Newport News, VA (United States)
  3. Savannah River Site (SRS), Aiken, SC (United States). Savannah River Ecology Lab. (SREL)
  4. Shoshone and Arapaho Tribes, Lander, WY (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Environmental Earth Sciences
Additional Journal Information:
Journal Volume: 74; Journal Issue: 10; Journal ID: ISSN 1866-6280
Research Org:
US Department of Energy/Office of Legacy Management
Sponsoring Org:
USDOE Office of Legacy Management (LM), Office of Site Operations (LM-20)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES conceptual site models, uranium, unsaturated zone, groundwater contamination, river flooding, evaporite mineral deposits