Title: RADIOACTIVITY IN WATER. CENTRAL NEVADA TEST AREA.

Water table maps, water table gradient maps, and depth-to-water maps have been constructed for the Nevada Test Site and the Central Nevada Test Area by empirical simulation using a digital computer. Although the digital computer program has been developed specifically for the areas mapped, it is directly applicable to any hydrologic province where ground-water recharge areas occur between the discharge areas such as humid regions and the arid Great Basin of the Western United States. This report presents maps constructed during May 1975, a listing of the water level control points, and a brief description of the empirical mapping technique.

This Corrective Action Decision Document (CADD) identifies and rationalizes the U.S. Department of Energy, Nevada Operations Office's selection of a recommended corrective action alternative (CAA) appropriate to facilitate the closure of Corrective Action Unit (CAU) 417: Central Nevada Test Area Surface, Nevada, under the Federal Facility Agreement and Consent Order. Located in Hot Creek Valley in Nye County, Nevada, and consisting of three separate land withdrawal areas (UC-1, UC-3, and UC-4), CAU 417 is comprised of 34 corrective action sites (CASs) including 2 underground storage tanks, 5 septic systems, 8 shaker pad/cuttings disposal areas, 1 decontamination facility pit, 1 burnmore » area, 1 scrap/trash dump, 1 outlier area, 8 housekeeping sites, and 16 mud pits. Four field events were conducted between September 1996 and June 1998 to complete a corrective action investigation indicating that the only contaminant of concern was total petroleum hydrocarbon (TPH) which was found in 18 of the CASs. A total of 1,028 samples were analyzed. During this investigation, a statistical approach was used to determine which depth intervals or layers inside individual mud pits and shaker pad areas were above the State action levels for the TPH. Other related field sampling activities (i.e., expedited site characterization methods, surface geophysical surveys, direct-push geophysical surveys, direct-push soil sampling, and rotosonic drilling located septic leachfields) were conducted in this four-phase investigation; however, no further contaminants of concern (COCs) were identified. During and after the investigation activities, several of the sites which had surface debris but no COCs were cleaned up as housekeeping sites, two septic tanks were closed in place, and two underground storage tanks were removed. The focus of this CADD was to identify CAAs which would promote the prevention or mitigation of human exposure to surface and subsurface soils with contaminant concentrations above preliminary action levels. Based on the potential exposure pathways, several risk-based CAAs were developed and evaluated against the individual CAS requirements. It was determined that a combination of the CAAs would be recommended to meet all applicable state and federal regulations for closure of these sites and to eliminate potential future exposure pathways to the TPH-contaminated soils.« less

This Corrective Action Decision Document/Corrective Action Plan (CADD/CAP) has been prepared for the subsurface at the Central Nevada Test Area (CNTA) Corrective Action Unit (CAU) 443, CNTA - Subsurface, Nevada, in accordance with the ''Federal Facility Agreement and Consent Order'' (FFACO) (1996). CAU 443 is located in Hot Creek Valley in Nye County, Nevada, north of U.S. Highway 6, about 48 kilometers north of Warm Springs, Nevada. The CADD/CAP combines the decision document (CADD) with the corrective action plan (CAP) and provides or references the specific information necessary to recommend corrective actions for the UC-1 Cavity (Corrective Action Site 58-57-001)more » at CAU 443, as provided in the FFACO. The purpose of the CADD portion of the document (Section 1.0 to Section 4.0) is to identify and provide a rationale for the selection of a recommended corrective action alternative for the subsurface at CNTA. To achieve this, the following tasks were required: (1) Develop corrective action objectives; (2) Identify corrective action alternative screening criteria; (3) Develop corrective action alternatives; (4) Perform detailed and comparative evaluations of the corrective action alternatives in relation to the corrective action objectives and screening criteria; and (5) Recommend a preferred corrective action alternative for the subsurface at CNTA. A Corrective Action Investigation (CAI) was performed in several stages from 1999 to 2003, as set forth in the ''Corrective Action Investigation Plan for the Central Nevada Test Area Subsurface Sites (Corrective Action Unit No. 443)'' (DOE/NV, 1999). Groundwater modeling was the primary activity of the CAI. Three phases of modeling were conducted for the Faultless underground nuclear test. The first involved the gathering and interpretation of geologic and hydrogeologic data into a three-dimensional numerical model of groundwater flow, and use of the output of the flow model for a transport model of radionuclide release and migration behavior (Pohlmann et al., 2000). The second modeling phase (known as a Data Decision Analysis [DDA]) occurred after the Nevada Division of Environmental Protection reviewed the first model and was designed to respond to concerns regarding model uncertainty (Pohll and Mihevc, 2000). The third modeling phase updated the original flow and transport model to incorporate the uncertainty identified in the DDA, and focused the model domain on the region of interest to the transport predictions. This third phase culminated in the calculation of contaminant boundaries for the site (Pohll et al., 2003).« less

The environmental remediation closure process for the nuclear test at the Central Nevada Test Area (CNTA) has progressed from the approved Corrective Action Decision Document/Corrective Action Plan (CADD/CAP) to this addendum. The closure process required the installation of three monitoring/validation (MV) wells and validation analysis of the flow and transport model. The model validation analysis led to the conclusion that the hydraulic heads simulated by the flow model did not adequately predict observed heads at the MV-1, MV-2, and MV-3 validation points (wells and piezometers). The observed heads from screened intervals near the test horizon were higher than the modelmore » predicted and are believed to be the result of detonation-related effects that have persisted since the nuclear test. These effects, which include elevated heads out from the detonation zone and lower heads in the immediate vicinity of the detonation, are seen at other nuclear tests and typically dissipate within a few years. These effects were not included in the initial head distribution of the model. The head variations at CNTA are believed to have persisted due to the very low permeability of the material at the detonation level.« less

This report documents data collection, results, and interpretation of the expedited site characterization (ESC) pilot project conducted from September 1996 to June 1997 at the Central Nevada Test Area (CNTA), Nye County, Nevada. Characterization activities were limited to surface sites associated with deep well drilling and ancillary operations at or near three emplacement well areas. Environmental issues related to the underground nuclear detonation (Project Faultless) and hydrologic monitoring wells were not addressed as a part of this project. The CNTA was divided into four functional areas for the purpose of this investigation and report. These areas include the vicinity ofmore » three emplacement wells (UC-1, UC-3, and UC-4) and one mud waste drilling mud collection location (Central Mud Pit; CMP). Each of these areas contain multiple, potentially contaminated features, identified either from historic information, on-site inspections, or existing data. These individual features are referred to hereafter as ``sites.`` The project scope of work involved site reconnaissance, establishment of local grid systems, site mapping and surveying, geophysical measurements, and collection and chemical analysis of soil and drilling mud samples. Section 2.0 through Section 4.0 of this report provide essential background information about the site, project, and details of how the ESC method was applied at CNTA. Detailed discussion of the scope of work is provided in Section 5.0, including procedures used and locations and quantities of measurements obtained. Results and interpretations for each of the four functional areas are discussed separately in Sections 6.0, 7.0, 8.0, and 9.0. These sections provide a chronological presentation of data collected and results obtained, followed by interpretation on a site-by-site basis. Key data is presented in the individual sections. The comprehensive set of data is contained in appendices.« less