History
Large volumes of process waste have been deposited at this IFRC site. Nuclear fuels fabrication wastes were disposed to the 300 Area North and South Process Ponds from 1943 to 1975, and later to the 300 Area process trenches (e.g., 316-5; 1975-1994). The important waste streams were low pH copper/uranyl nitrate solutions and high pH sodium aluminate solutions. The disposed chemical inventory includes U (33,566-58,967 kg), Cu(241,311 kg), aluminum (113,398 kg), fluorine (117,026 kg), nitrate (2,060,670 kg), and large volumes of acid (HNO3) and base (NaOH).
Shallow contaminated sediments were excavated from the process ponds and trenches between 1995-2004 as a source control measure to minimize additional groundwater contamination. Vadose zone and aquifer sediments were sampled beneath the process ponds after excavation to determine U and Cu distribution and chemical speciation through the vadose zone and into groundwater. The excavated process ponds and cribs were backfilled and the land surface regraded to a natural state.
A groundwater U plume has existed beneath the 300 Area since the early operations of the process ponds, with the highest U concentrations observed from the early 1950s to the late 1980s. These concentrations decreased rapidly after disposal activities ceased in the early 1990s, and groundwater U concentrations have slowly decreased since then. The plume resulted from liquid process waste infiltrating through the 4- to 10-m-thick vadose zone beneath the disposal facilities. Despite source term removal and elimination of other leak sources, the general shape of the groundwater plume has not changed significantly for ten years, with the core of the plume exceeding the drinking water standard (DWS, 30 µg/L). The plume occasionally experienced sizable water table fluctuations during pre-dam Columbia River flooding and, to a lesser extent, during present day, dam-controlled, river stage fluctuation that redistributed dissolved U into uncontaminated capillary fringe and deep vadose zone sediments.
Wells have been installed in the 300 Area since the early 1940s for subsurface characterization and contaminant monitoring. This monitoring network has been sequentially expanded in response to the growing size and concerns regarding the U(VI) plume, and attendant RCRA and CERCLA investigations (Lindberg and Bond 1979; Schalla et al. 1988; Swanson et al. 1992). Pump testing and numerous other hydrologic investigations have been performed. This monitoring program and the resulting data-base, and decisions have been recently and comprehensively summarized by Peterson et al. (2005).
In 1996 a CERCLA interim remedy of monitored natural attenuation (MNA) was selected for the 300 Area U plume based on equilibrium, Kd-based reactive transport modeling. The modeling analysis implied that natural processes of groundwater flushing and desorption would decrease U concentrations below the DWS within ten years. Subsequent monitoring has documented that groundwater U concentrations are not decreasing as projected, and remain above the DWS throughout much of the area. As a result of the ineffectiveness of MNA and regulatory mandates, DOE-RL initiated a Phase III Feasibility Study (FS) for 300-FF-5 in 2005. The FS includes a limited field investigation (LFI; DOE 2005) to define the depth distribution of U in the aquifer and capillary fringe, and to further characterize the hydrogeologic properties of the unconfined aquifer and the topography and hydrogeology of the Hanford-Ringold contact. Sonic drilling has been used to recover continuous and intact large-diameter sediment core from four LFI boreholes in 2006. Depth-discrete groundwater sampling and aquifer testing was performed to delineate the distribution of uranium contamination and hydrologic flow parameters throughout the unconfined aquifer.
In response to the success of the LFI, a DOE EM-22-funded project used one or more of the new LFI wells to perform a field-scale feasibility experiment to induce the precipitation of autunite [Ca(UO2PO4)2·8H2O] by polyphosphate injection to lower groundwater U(VI) concentrations.
DOE EM-30 is highly supportive of the use of the 300 Area U Plume Site for basic field studies of coupled processes controlling long term fate of contaminant U effective remedial actions. DOE has agreed to make the 300 Area Site and the archive sample database available to an ERSD IFRC for the requested period of 7 years.
ReferencesLindberg JW and FW Bond. 1979. Geohydrology and Ground-Water Quality Beneath the 300 Area, Hanford Site, Washington. PNL-2949, Pacific Northwest Laboratory, Richland, Washington.
Peterson RE (Editor), EJ Freeman, CJ Murray, PD Thorne,MJ Truex. VR Vermeul, MD Williams, SB Yabusaki, JM Zachara, JL Lindberg, and JP McDonald. 2005. Contaminants of Potential Concern in the 300-FF-5 Operable Unit: Expanded Annual Groundwater Report for Fiscal Year 2004. PNNL-15127, Pacific Northwest National Laboratory, Richland, Washington.
Schalla R, RW Wallace, RL Aaberg, SP Airhart, DJ Bates, JVM Carlile, CS Cline, DI Dennison, MD Freshley, PR Heller, EJ Jensen, KB Olsen, RG Parkhurst, JT Rieger, and EJ Westergard. 1988. Interim Characterization Report for the 300 Area Process Trenches. PNL-6716, Pacific Northwest Laboratory, Richland, Washington.
Swanson LC, GG Kelty, KA Lindsey, KR Simpson, RK Price, and SD Consort. 1992. Phase 1 Hydrogeologic Summary of the 300-FF-5 Operable Unit, 300 Area. WHC-SD-EN-TI-052, Rev. 0, Westinghouse Hanford Company, Richland, Washington.