Monticello Mill Tailings Site, Operable Unit lll, Annual Groundwater Report, May 2015 Through April 2016
- USDOE Office of Legacy Management (LM), Washington, DC (United States)
- Navarro Research and Engineering, Oak Ridge, TN (United States)
This report provides the annual analysis of water quality restoration progress, cumulative through April 2016, for Operable Unit (OU) III, surface water and groundwater, of the U.S. Department of Energy (DOE) Office of Legacy Management (LM) Monticello Mill Tailings Site (MMTS). The MMTS is a Comprehensive Environmental Response, Compensation, and Liability Act National Priorities List site located in and near the city of Monticello, San Juan County, Utah. MMTS comprises the 110-acre site of a former uranium- and vanadium-ore-processing mill (mill site) and 1700 acres of surrounding private and municipal property. Milling operations generated 2.5 million cubic yards of waste (tailings) from 1942 to 1960. The tailings were impounded at four locations on the mill site. Inorganic constituents in the tailings drained from the impoundments to contaminate local surface water (Montezuma Creek) and groundwater in the underlying alluvial aquifer. Mill tailings dispersed by wind and water also contaminated properties surrounding and downstream of the mill site. Remedial actions to remove and isolate radiologically contaminated soil, sediment, and debris from the former mill site, Operable Unit I (OU I), and surrounding properties (OU II) were completed in 1999 with the encapsulation of the wastes in an engineered repository located on DOE property 1 mile south of the former mill site. This effectively removed the primary source of groundwater contamination; however, contamination of groundwater and surface water remains within OU III at levels that exceed water quality protection standards. Uranium is the primary contaminant of concern (COC). LM implemented monitored natural attenuation with institutional controls as the OU III remedy in 2004. Because groundwater restoration proceeded more slowly than expected and did not meet performance criteria established in the OU III Record of Decision (June 2004), LM implemented a contingency action in 2009 by an Explanation of Significant Difference to include a pump-and treat system using a single extraction well and treatment by zero-valent iron (ex situ treatment system). The contingency action was optimized in 2015 with the installation of8 extraction wells and 16 monitoring wells in a focused area of the aquifer, the area of attainment (AOA). Contaminated water is treated by solar evaporation at an existing facility at the LM repository.
- Research Organization:
- US Department of Energy (USDOE), Washington DC (United States). Office of Legacy Management (LM)
- Sponsoring Organization:
- USDOE Office of Legacy Management (LM), Office of Field Operations
- DOE Contract Number:
- LM0000421
- OSTI ID:
- 1348849
- Report Number(s):
- LMS/MNT/-S14233
- Country of Publication:
- United States
- Language:
- English
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