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Estimation of groundwater velocities from Yucca Flat to the Amargosa Desert using geochemistry and environmental isotopes

Description: Geochemical and isotopic data from groundwater sampling locations can be used to estimate groundwater flow velocities for independent comparison to velocities calculated by other methods. The objective of this study was to calculate groundwater flow velocities using geochemistry and environmental isotopes from the southern end of Yucca Flat to the Amargosa Desert, considering mixing of different groundwater inputs from sources each and southeast of the Nevada Test Site (NTS). The approach used to accomplish the objective of this study consisted of five steps: (1) reviewing and selecting locations where carbon isotopic groundwater analyses, reliable ionic analysis, and well completion information are available; (2) calculating chemical speciation with the computer code WATEQ4F (Ball and Nordstrom, 1991) to determine the saturation state of mineral phases for each ground water location; (3) grouping wells into reasonable flowpaths and mixing scenarios from different groundwater sources; (4) using the computer code NETPATH (Plummer et al., 1991) to simulate mixing and the possible chemical reactions along the flowpath, and to calculate the changes in carbon-13/carbon-12 isotopic ratios ({delta}{sup 13}C) as a result of these reactions; and (5) using carbon-14 ({sup 14}C) data to calculate velocity.
Date: June 1, 1997
Creator: Hershey, R.L. & Acheampong, S.Y.
Partner: UNT Libraries Government Documents Department

Continued investigations of the occurrence of water in Pahute Mesa emplacement holes

Description: Periodically, water has been observed in emplacement boreholes drilled for underground testing of nuclear weapons at Pahute Mesa, Nevada Test Site, and is often at levels elevated above the predicted local water table. Water which may provide a means to transport residual radionuclides away from weapon tests may originate as fluids introduced during drilling, from naturally perched groundwater draining into the borehole, or from penetration of the local groundwater table. Lithium-bromide (Li-Br) tracer is being used to evaluate both the origin and movement of these borehole waters. The drilling fluid used to drill the final 100 meters of borehole U-19bh was chemically labeled with LiBr tracer. Lack of significant increase in borehole Br inventory over time indicates that standing water in U-9bh is not returned drilling fluid. Possible sources for the standing water are drilling fluid infiltrated above the bottom 100 in or natural water from a perched or shallower-than-expected saturated zone. The minimum detectable Darcy velocity of water passing through U-19bh is 0.3 m/yr. Borehole U-19bk has a water level approximately 50 in above the predicted pre-drilling water level. Initial water samples were collected from U-19bk to characterize the borehole water quality prior to adding the tracer. The major-ion analytical results of U-19bk along with historical water quality analyses of Water Well 20 and water well UE-19c show that all three waters are similar in character and therefore the water in U-19bk may be either residual drilling fluids originating from Water Well 20 and UE-19c or naturally occurring Pahute Mesa groundwater. LiBr tracer was added to the U-19bk borehole and samples for tracer analysis were collected one month later. For the one month period, no detectable loss of Br was observed. Over this short time period, the minimum detectable Darcy velocity is 10.6 m/yr.
Date: April 1, 1995
Creator: Hershey, R.L. & Brikowski, T.H.
Partner: UNT Libraries Government Documents Department

Groundwater chemistry at the Nevada Test Site: Data and preliminary interpretations

Description: The interpretation of chemical analyses of groundwater collected at and near the Nevada Test Site (NTS) has been vital in developing conceptual models of groundwater flow in the area. These conceptual models are tested using recent chemical data generated by the Desert Research Institute, as well as historic analyses from the US Geological Survey. A total of 81 wells are represented by analyses from 1957 to 1990, with generally excellent agreement between repeat samples from the same location. As identified by previous workers, three hydrochemical facies are represented by the samples: Ca-Mg-HCO{sub 3} water in carbonate rocks or alluvium derived from carbonates, Na-K-HCO{sub 3} water in volcanic rocks and alluvium derived from volcanic rocks, and a mixed fades found in many carbonate and alluvium water samples, and some volcanic waters. There is a general lack of lateral continuity in chemical characteristics along presumed flowpaths within each hydrologic unit (alluvium, carbonate, and volcanic). Though a lack of continuity between basins on the east side of the NTS was expected for water in alluvial and volcanic units due to the absence of interbasin flow, chemical differences observed within individual basins suggest a dominance of vertical over lateral flow. Groundwater in volcanic materials on the east side of Yucca and Frenchman Flats and on the west side of Pahute Mesa and Yucca Mountain has a nearly pure Na-K-HCO{sub 3} signature that reflects contact with primarily volcanic material. Groundwater in volcanic units in the middle of the NTS and on the east side of Pahute Mesa contains a higher proportion of Ca, Mg, Cl, and SO{sub 4} than the other volcanic waters and indicates the contribution of water from the upper carbonate aquifer and/or hydrothermally altered regions.
Date: March 1, 1993
Creator: Chapman, J.B. & Lyles, B.F.
Partner: UNT Libraries Government Documents Department

Hydrogeologic characterization of wells HTH-1, UE18r, UE6e, and HTH-3, Nevada Test Site

Description: Monitoring for the migration of contaminants in groundwater or for the proper design of nuclear test emplacement holes at the Nevada Test Site (NTS) requires proper placement and completion of monitoring wells. This is only possible if the hydrogeologic system is understood in a regional and local context, necessitating data from existing wells and boreholes. Though the NTS Groundwater Characterization Project will be drilling wells, their great expense limits the number of new wells. However, there are many existing boreholes and wells on the NTS which have not been completely evaluated hydrologically. Some of these are incorporated in the Long Term Hydrologic Monitoring Program (LTHMP) of the US Environmental Protection Agency (EPA), others are related to the testing programs. In all cases, additional site investigation in necessary to properly interpret the hydrogeologic data from these wells. Monitoring wells on the NTS are poorly characterized with regard to aquifers penetrated, vertical hydraulic gradients, and vertical variations in water quality. One of the goals of the well validation program was to gain a thorough understanding of the parameters needed to interpret the source and fate potential hazardous and radioactive substances that may be detected in these wells in the future. One of the most critical parameters for monitoring is the knowledge of what aquifer or geologic unit is being sampled when a water sample is collected. Pumped water samples are weighted most heavily to the water quality of the most productive (highest transmissivity) aquifer penetrated by the well.
Date: June 1, 1991
Creator: Lyles, B.F.; McKay, W.A.; Chapman, J.B. & Tyler, S.W.
Partner: UNT Libraries Government Documents Department

Community Radiation Monitoring Program; Annual report, October 1, 1990--September 30, 1991

Description: The Community Radiation Monitoring Program is a cooperative effort between the US Department of Energy (DOE), the US Environmental Protection Agency (EPA), the Desert Research Institute (DRI), a division of the University and Community College System of Nevada, and the Nuclear Engineering Laboratory of the University of Utah (U of U). This eleventh year of the program began in the summer of 1991 and the work continues as an integral part of the DOE-sponsored long-term offsite radiological monitoring effort that has been conducted by EPA and its predecessors since the inception of nuclear testing at the Nevada Test Site (NTS). The primary objectives of this program are still to increase the understanding by the people who live in the area surrounding the NTS of the activities for which the DOE is responsible, to enhance the performance of radiological sampling and monitoring, and to inform all concerned of the results of those efforts. One of the primary methods used to improve the communication link with the potentially impacted area has been the hiring and training of local citizens as Managers and program representatives in 19 communities adjacent to and downwind from the NTS. These Managers, active science teachers wherever possible, have succeeded, through their training, experience, community standing, and effort, in becoming a very visible, able and valuable asset in this link.
Date: June 1, 1992
Creator: Cooper, E.N. & McArthur, R.D.
Partner: UNT Libraries Government Documents Department

Estimates of potential radionuclide migration at the Bullion site

Description: The Bullion site in Area 20 of the Nevada Test Site has been selected for an intensive study of the hydrologic consequences of underground testing, including subsequent radionuclide migration. The bulk of the chimney and cavity lie in zeolitized tuffs of low hydraulic conductivity, while the base of the cavity may extend downward into more conductive rhyolite flows. A mathematical analog to the Bullion setting is used here to estimate expected radionuclide migration rates and concentrations. Because of a lack of hydrologic data at the site, two contrasting scenarios are considered. The first is downward-transport, in which downward hydraulic gradients flush chimney contents into the conductive underlying units, enhancing migration. The other is upward-transport, in which upward gradients tend to drive chimney contents into the low-conductivity zeolitized tuffs, discouraging migration. In the downward-transport scenario, radionuclide travel times and concentrations are predicted to be similar to those encountered at Cheshire, requiring approximately 10 years to reach a proposed well 300 m downgradient. The upward transport scenario yields predicted travel times on the order of 2,000 years to the downgradient well. The most likely scenario is a combination of these results, with vertical movement playing a limited role. Radionuclides injected directly into the rhyolites should migrate laterally very quickly, with travel times as in the downward-transport scenario. Those in the zeolitized tuff-walled portion of the chimney should migrate extremely slowly, as in the upward-transport scenario.
Date: April 1, 1992
Creator: Brikowski, T.H.
Partner: UNT Libraries Government Documents Department

Summary of wells validated during fiscal years 1991 to 1992

Description: The Well Validation Project was initiated in fiscal year 1990, with the intended purpose to evaluate wells on the Nevada Test Site. During fiscal years 1991 and 1992, a temperature/electrical conductivity logging tool was redesigned and a thermal-pulse flowmeter logging tool was developed. Seven wells were evaluated during this time period: USGS HTH {number_sign}1, UE-18r, UE-14b, HTH {open_quotes}E{close_quotes}, USGS Test Well B Ex., UE-1q, and UE-5n. The validation techniques used at each site varied depending on the site-specific objectives. Thermal-pulse flowmeter surveys were carried out in several of the wells with limited success. The thermal-pulse flowmeter was designed for boreholes 2 to 6 inches in diameter, most wells at the Nevada Test Site are generally much larger in diameter, 10 to 24 inches. Therefore, the thermal-pulse flowmeter was outfitted with an inflatable rubber packer, which constricts borehole flow through the thermal-pulse flowmeter, increasing the resolution. The thermal-pulse flowmeter can be outfitted with various-sized packers depending on the borehole diameter to be evaluated; these packers are commercially available. The packers are inflated with borehole fluid via a small submersible pump which was designed, built, and tested as part of this study.
Date: June 1, 1993
Creator: Lyles, B. F.
Partner: UNT Libraries Government Documents Department

Hydrologic database user`s manual

Description: The Hydrologic Database is an electronic filing cabinet containing water-related data for the Nevada Test Site (NTS). The purpose of the database is to enhance research on hydrologic issues at the NTS by providing efficient access to information gathered by a variety of scientists. Data are often generated for specific projects and are reported to DOE in the context of specific project goals. The originators of the database recognized that much of this information has a general value that transcends project-specific requirements. Allowing researchers access to information generated by a wide variety of projects can prevent needless duplication of data-gathering efforts and can augment new data collection and interpretation. In addition, collecting this information in the database ensures that the results are not lost at the end of discrete projects as long as the database is actively maintained. This document is a guide to using the database.
Date: September 1, 1993
Creator: Champman, J. B.; Gray, K. J. & Thompson, C. B.
Partner: UNT Libraries Government Documents Department

Predicted fate of tritium residuum from groundwater tracer experiments in the Amargosa Desert, southern Nevada

Description: Analytic solutions are used in this study to evaluate potential groundwater transport of tritium used in goundwater tracer tests southwest of the Nevada Test Site. Possible transport from this site is of interest because initial radionuclide concentrations were high and the site is close to goundwater discharge points (12 km). Anecdotal evidence indicates that 90 percent of these tracers were removed by pumping at the completion of the tests; this study examines the probable transport of the tracers with and without the removal. Classical dispersive transport analytic solutions are used, treating the tracer test as a point slug injection. Input parameters for the solutions were measured at the site, and consideration of parameter uncertainty is incorporated in the results. With removal of the tracer, the maximum expected region with above-Safe Drinking Water Act (40 CFR 121) concentrations of tritium extends 5 km from the injection point, and does not reach any sites of public access. Detectable tritium from the tests is likely to have reached the Ash Meadows fault zone, but flow along the fault probably diluted the tracer to below detection limits before arrival at springs along the fault. Arrival at the springs would have occurred 20 to 25 years after the tests. Without removal of the tracer, the solutions indicate that tritium concentrations just above Safe Drinking Water Act standards would have reached the Ash Meadows fault zone. In this case, detectable tritium might have been found in Devil`s Hole or Longstreet Spring, the nearest points of possible public exposure.
Date: July 1, 1993
Creator: Brikowski, T.
Partner: UNT Libraries Government Documents Department

Geochemical and hydrologic characterization of the effluent draining from U12e, U12n, and U12t tunnels, area 12, Nevada Test Site

Description: The objective of the Tunnel Effluent Characterization Project at the Nevada Test Site was to characterize the tunnel effluents in terms of rate of discharge, pH, temperature, specific conductivity, turbidity, and aqueous chemistry. The parameters were monitored for one year to identify hazardous constituents within the effluent and to characterize temporal variations.
Date: May 1, 1993
Creator: Russell, C. E.; Gillespie, L. & Gillespie, D.
Partner: UNT Libraries Government Documents Department

Potential hydrologic characterization wells in Amargosa Valley

Description: More than 500 domestic, agricultural, and monitoring wells were identified in the Amargosa Valley. From this list, 80 wells were identified as potential hydrologic characterization wells, in support of the US Department of Energy (DOE) Underground Test Area/Remedial Investigation and Feasibility Study (UGTA/RIFS). Previous hydrogeologic studies have shown that groundwater flow in the basin is complex and that aquifers may have little lateral continuity. Wells located more than 10 km or so from the Nevada Test Site (NTS) boundary may yield data that are difficult to correlate to sources from the NTS. Also, monitoring well locations should be chosen within the guidelines of a hydrologic conceptual model and monitoring plan. Since these do not exist at this time, recompletion recommendations will be restricted to wells relatively close (approximately 20 km) to the NTS boundary. Recompletion recommendations were made for two abandoned agricultural irrigation wells near the town of Amargosa Valley (previously Lathrop Wells), for two abandoned wildcat oil wells about 10 km southwest of Amargosa Valley, and for Test Well 5 (TW-5), about 10 km east of Amargosa Valley.
Date: September 1, 1994
Creator: Lyles, B. & Mihevc, T.
Partner: UNT Libraries Government Documents Department

The relationship of the Yucca Mountain repository block to the regional ground-water system: A geochemical model

Description: Yucca Mountain, in southern Nevada, is being studied by the Department of Energy and the State of Nevada as the site of a high-level nuclear waste repository. Geochemical and isotopic modeling were used in this study to define the relationship of the volcanic tuff aquifers and aquitards to the underlying regional carbonate ground-water system. The chemical evolution of a ground water as it passes through a hypothetical tuffaceous aquifer was developed using computer models PHREEQE, WATEQDR and BALANCE. The tuffaceous system was divided into five parts, with specific mineralogies, reaction steps and temperatures. The initial solution was an analysis of a soil water from Rainier Mesa. The ending solution in each part became the initial solution in the next part. Minerals consisted of zeolites, smectites, authigenic feldspars and quartz polymorphs from described diagentic mineral zones. Reaction steps were ion exchange with zeolites. The solution from the final zone, Part V, was chosen as most representative, in terms of pH, element molalities and mineral solubilities, of tuffaceous water. This hypothetical volcanic water from Part V was mixed with water from the regional carbonate aquifer, and the results compared to analyses of Yucca Mountain wells. Mixing and modeling attempts were conducted on wells in which studies indicated upward flow.
Date: August 1, 1989
Creator: Matuska, N.A. & Hess, J.W.
Partner: UNT Libraries Government Documents Department

A conceptual model and preliminary estimate of potential tritium migration from the Benham (U-20c) site, Pahute Mesa, Nevada Test Site

Description: U-20c is the site of a large below-water-table nuclear test near the Nevada Test Site boundary. A conceptual model of potential groundwater migration of tritium from U-20c is constructed and quantitatively evaluated in this report. The lower portion of the collapse chimney at Benham is expected to intersect 200 m of permeable rhyolite lava, overlain by similar thicknesses of low-permeability zeolitized bedded tuff, then permeable welded tuff. Vertical groundwater flow through the chimney is predicted to be minimal, horizontal transport should be controlled by the regional groundwater flow. Analytic solutions treating only advective transport indicate 1 to 2 km of tritium movement (95% confidence interval 0.7--2.5 km) within 5 years after test-related pressure-temperature transients have dissipated. This point lies at the axis of a potentiometric surface trough along the west edge of Area 20, Nevada Test Site. Within 25 years, movement is predicted to extend to 3 km (95% confidence interval 2--5 km) approximately to the intersection of the trough and the Nevada Test Site boundary. Considering the effects of radioactive decay, but not dispersion, plume concentration would fall below Safe Drinking Water Act standards by 204 years, at a predicted distance of 11 km (95% confidence interval 7--31 km). This point is located in the eastern portion of the Timber Mountain Caldera moat within the Nellis Air Force Range (military bombing range).
Date: August 1, 1993
Creator: Brikowski, T. & Mahin, G.
Partner: UNT Libraries Government Documents Department