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On October 26, 1963, the U. S. Department of Defense (DoD) and Atomic Energy Commission (AEC), now known as the U. S. Department of Energy (DOE), detonated a nuclear device with a total yield of 12 kilotons at a depth of 1,204 feet below ground surface in solid granite at the Project Shoal Area (PSA) - (Home). Radiological contamination of groundwater resulted from the test. Today, scientists and engineers, contracted by DOE, are working to identify the risks where radiological contamination exists in groundwater, predict the movement of the contaminated groundwater, and define the extent of migration of the radionuclides released during testing. 
The Federal Facility Agreement and Consent Order (FFACO), outlines a process to insure that the DOE and/or the DoD, under the regulatory authority and oversight of the Nevada Division of Environmental Protection, Bureau of Federal Facilities (NDEP), identify sites of potential historic contamination, thoroughly investigate these sites, and implement corrective actions based on public health and environmental considerations. For purposes of investigation and corrective action implementation, the Project Shoal Area (PSA) and the Central Nevada Test Area (CNTA) are grouped as the Nevada Off-Sites. Each of these two sites is considered a separate Corrective Action Unit (CAU) based on geographic location. This website has been developed by NDEP to improve public access to regulatory and programmatic information at the PSA. The PSA is located approximately 28 miles southeast of Fallon, in the Sand Springs Range of Churchill County, Nevada. Access is via U. S. Highway 50, Nevada Highway 839, and an improved gravel road into the site. The Vela Uniform program began in 1959 and was part of a Department of Defense (DoD) research and development program intended to improve the capability of detecting, monitoring, and identifying underground and high-altitude nuclear detonations. Project SHOAL was an underground nuclear test conducted jointly by the DoD and the Atomic Energy Commission (AEC). Part of the Vela Uniform program, it was designed to investigate the behavior and characteristics of seismic signals generated by a nuclear detonation in a granite rock formation and to differentiate them from seismic signals generated by naturally occurring earthquakes. The device was emplaced at a depth of 1,205 feet below ground surface and at the end of a 1050-foot drift - (Diagram) mined east from the vertical shaft was detonated on October 26, 1963. The nuclear test created a cavity with an approximate diameter of 171 feet which subsequently collapsed and formed a rubble-filled chimney 356 feet high. The chimney did not propagate to the land surface and no surface crater was formed. Radioactive contamination of the deep granitic rock around the shot cavity exists today. Groundwater is the most likely transport medium for this contamination, however, because of the depth of the contamination (approximately 1,204 feet) and the remoteness of the site, exposure to humans is unlikely. The environmental restoration strategy is to characterize groundwater flow and areas of contamination, assess risk to human health and the environment, and model contaminant movement away from the shot cavity. This characterization of the groundwater contamination at the PSA is being conducted by the DOE and its contractors.
Groundwater occurs at approximately 985 feet below ground surface. Decreasing hydraulic potentials with depth were noted during site characterization. The conceptual model is an underlying model of the phenomena it investigates. For the PSA, the conceptual flow model includes the description of hydrogeologic features such as primary groundwater flow direction, boundary conditions, sources and sinks, groundwater flow divides, and fracture locations. The strategy for the subsurface is to characterize groundwater flow and contamination transport through numerical modeling utilizing site-specific hydrologic data. The contaminant of focus is tritium, because, based on presently available data, it is the most conservative (i.e., remains in solution) and therefore the most mobile of the potential radiological contaminants. Initial subsurface characterization was performed using geologic and hydrologic data collected during site characterization activities in the early 1960s. DOE determined that additional information was necessary to properly characterize the groundwater flow system and in 1996 installed four new groundwater monitoring wells - (Diagram) (HC-1, HC-2, HC-3 and HC-4) across the site. Data from these new wells and the earlier hydrogeologic studies in the area were then used to construct a groundwater flow and transport computer model to predict the movement of radionuclides in groundwater away from the shot cavity. In order to further refine model predictions and reduce uncertainty, specific additional hydrogeologic data were needed which prompted the installation and testing of four additional groundwater monitoring wells - (Diagram) (HC-5, HC-6, HC-7, and HC-8) during the summer of 1999. Subsequent work performed in 2000 included completion of a long-term aquifer tracer test and in-depth analysis of recently-acquired hydrological parameter data. The primary objectives of the tracer test were: determine the effective porosity of the Shoal granite aquifer, determine hydraulic properties of the aquifer, quantify the dispersion coefficient at the 30-m scale, quantify the field-scale sorption coefficients for weakly sorbing solutes, determine the significance of matrix diffusion, and determine the hydraulic properties of the fractures. The new data from these wells and tests were used to up-date the groundwater flow and transport model and generate computer simulations to predict the migration of radionuclides away from the site during the next 1000 years. The modeling results predict a contaminant boundary that defines the area in which the radionuclides are expected to remain. Once the contaminant boundary is determined with a 95% confidence level, NDEP and DOE will establish a compliance boundary beyond which radionuclides may not migrate without further corrective action. It is anticipated that after boundaries have been established a determination can be made that monitoring alone will be acceptable and some form of active contaminant containment system will not be necessary. NDEP expects this work to result in a proposal for a network of carefully-positioned groundwater monitoring wells. This network of wells will be located relatively close to the detonation point and will be used to monitor any movement of tritium and other radionuclides away from the blast cavity. Tritium, a radioactive isotope of hydrogen, is considered a reliable indicator of radionuclide contamination. The monitoring well network will be used to verify that radionuclides remain within the compliance boundary. Work Currently in Progress: DOE completed the second iteration of groundwater flow and contaminant transport modeling. NDEP reviewed the work and provided comments back to DOE. It is incumbent on DOE to determine if sufficient data has been gathered to characterize the nature, extent, and potential rate of migration of radionuclides and provide sufficient confidence in the numeric model to allow the determination of contaminant and compliance boundaries. In order to continue on with the FFACO process (e.g., to a Corrective Action Decision Document and a Corrective Action Plan), investigative work must be complete and confidence levels met. If further data are necessary, the FFACO process will require that DOE prepare a Corrective Action Investigation Plan Addendum that details the field activities to be conducted and information that is to be collected (See also FFACO Appendix VI - Corrective Action Strategy, Section 3). |