Hydrologic resources management program and underground test area FY 1999 progress report

This report highlights the results of FY 2000 technical studies conducted by the Analytical and Nuclear Chemistry Division (ANCD) at Lawrence Livermore National Laboratory (LLNL) in support of the Hydrology and Radionuclide Migration Program (HRMP) and Underground Test Area (UGTA) Project. This is the latest in a series of annual reports published by LLNL-ANCD to document recent investigations of radionuclide migration and transport processes at the Nevada Test Site (NTS). The HRMP is sponsored by Defense Programs (DP) at the U.S. Department of Energy, Nevada Operations Office (DOENV), and supports DP operations at the NTS through studies of radiochemical and hydrologic processes that are relevant to the DP mission. Other organizations that support the HRMP include Los Alamos National Laboratory (LANL), the U.S. Geological Survey (USGS), the Desert Research Institute (DRI) of the University of Nevada, the U.S. Environmental Protection Agency (EPS), and Bechtel Nevada (BN). The UGTA Project is sponsored by the Environmental Management (EM) program at DOENV; its goal is to determine the extent of radionuclide contamination in groundwater resulting from underground nuclear testing at the NTS. The project strategy follows guidelines set forth in a Federal Facilities Agreement and Consent Order between the U.S. Department of Energy, the U.S. Department of Defense, and the State of Nevada. Participating contractors include LLNL (both ANCD and the Energy and Environmental Sciences Directorate), LANL, USGS, DRI, BN, and IT Corporation (with subcontract support from Geotrans Inc.).

New gravity and magnetic data collected in the vicinity of Massachusetts Mountain and CP basin (Nevada Test Site, NV) provides a more complex view of the structural relationships present in the vicinity of CP basin than previous geologic models, helps define the position and extent of structures in southern Yucca Flat and CP basin, and better constrains the configuration of the basement structure separating CP basin and Frenchman Flat. The density and gravity modeling indicates that CP basin is a shallow, oval-shaped basin which trends north-northeast and contains ~800 m of basin-filling rocks and sediment at its deepest point in the northeast. CP basin is separated from the deeper Frenchman Flat basin by a subsurface ridge that may represent a Tertiary erosion surface at the top of the Paleozoic strata. The magnetic modeling indicates that the Cane Spring fault appears to merge with faults in northwest Massachusetts Mountain, rather than cut through to Yucca Flat basin and that the basin is downed-dropped relative to Massachusetts Mountain. The magnetic modeling indicates volcanic units within Yucca Flat basin are down-dropped on the west and supports the interpretations of Phelps and KcKee (1999). The magnetic data indicate that the only faults that appear to be through-going from Yucca Flat into either Frenchman Flat or CP basin are the faults that bound the CP hogback. In general, the north-trending faults present along the length of Yucca Flat bend, merge, and disappear before reaching CP hogback and Massachusetts Mountain or French Peak.

The Phase II Frenchman Flat groundwater flow model is a key element in the ''Federal Facility Agreement and Consent Order'' (FFACO) (1996) corrective action strategy for the Underground Test Area (UGTA) Frenchman Flat corrective action unit (CAU). The objective of this integrated process is to provide an estimate of the vertical and horizontal extent of contaminant migration for each CAU to predict contaminant boundaries. A contaminant boundary is the model-predicted perimeter that defines the extent of radionuclide-contaminated groundwater from underground testing above background conditions exceeding the ''Safe Drinking Water Act'' (SDWA) standards. The contaminant boundary will be composed of both a perimeter boundary and a lower hydrostratigraphic unit (HSU) boundary. The computer model will predict the location of this boundary within 1,000 years and must do so at a 95 percent level of confidence. Additional results showing contaminant concentrations and the location of the contaminant boundary at selected times will also be presented. These times may include the verification period, the end of the five-year proof-of-concept period, as well as other times that are of specific interest. This report documents the development and implementation of the groundwater flow model for the Frenchman Flat CAU. Specific objectives of the Phase II Frenchman Flat flow model are to: (1) Incorporate pertinent information and lessons learned from the Phase I Frenchman Flat CAU models. (2) Develop a three-dimensional (3-D), mathematical flow model that incorporates the important physical features of the flow system and honors CAU-specific data and information. (3) Simulate the steady-state groundwater flow system to determine the direction and magnitude of groundwater fluxes based on calibration to Frenchman Flat hydrogeologic data. (4) Quantify the uncertainty in the direction and magnitude of groundwater flow due to uncertainty in parameter values and alternative component conceptual models (e.g., geology, boundary flux, and recharge).

The Lawrence Livermore National Laboratory (LLNL) Nuclear Forensics Summer Program is designed to give both undergraduate and graduate students an opportunity to come to LLNL for 8–10 weeks for a hands-on research experience. Students conduct research under the supervision of a staff scientist, attend a weekly lecture series, interact with other students, and present their work in poster format at the end of the program. Students also have the opportunity to meet staff scientists one-on-one, participate in LLNL facility tours (e.g., the National Ignition Facility and Center for Accelerator Mass Spectrometry) to gain a better understanding of the multi-disciplinary, on going science at LLNL. Currently called the Nuclear Forensics Summer Program, this program began 13 years ago as the Actinide Sciences Summer Program. The program is run within the Glenn T. Seaborg Institute in the Physical and Life Sciences Directorate at LLNL. The goal of the Nuclear Forensics Summer Program is to facilitate the training of the next generation of nuclear scientists and engineers to solve critical national security problems in the field of nuclear forensics and have the student experience conducting research at the Lab. We select students who are majoring in physics, chemistry, geology, mathematics, nuclear engineering, chemical engineering and environmental sciences. Students engage in research projects in the disciplines of actinide chemistry, radiochemistry, isotopic analysis, computational analysis, radiation detection, and nuclear engineering in order to strengthen the “pipeline” for future scientific disciplines critical to DHS (DNDO), NNSA.

The Department of Energy (DOE) and the National Nuclear Security Administration (NNSA) at their Nevada Site Office are addressing groundwater contamination resulting from historical underground nuclear testing through the Environmental Management program and, in particular, the Underground Test Area project. One issue of concern is the nature of the somewhat poorly constrained pre Tertiary geology and its effects on ground-water flow in the area adjacent to a nuclear test. Ground water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey, supported by the DOE and NNSA-NSO, collected and processed data from 51 magnetotelluric (MT) and audio-magnetotelluric (AMT) stations at the Nevada Test Site in and near Yucca Flat to assist in characterizing the pre-Tertiary geology in that area. The primary purpose was to refine the character, thickness, and lateral extent of pre Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (late Devonian - Mississippian-age siliciclastic rocks assigned to the Eleana Formation and Chainman Shale) in the Yucca Flat area. The MT and AMT data have been released in separate USGS Open File Reports. The Nevada Test Site magnetotelluric data interpretation presented in this report includes the results of detailed two-dimensional (2 D) resistivity modeling for each profile (including alternative interpretations) and gross inferences on the three dimensional (3 D) character of the geology beneath each station. The character, thickness, and lateral extent of the Chainman Shale and Eleana Formation that comprise the Upper Clastic Confining Unit are generally well determined in the upper 5 km. Inferences can be made regarding the presence of the Lower Clastic Confining Unit at depths below 5 km. Large fault structures such as the CP Thrust fault, the Carpetbag fault, and the Yucca fault that cross Yucca Flat are also discernable as are other smaller faults. The subsurface electrical resistivity distribution and inferred geologic structures determined by this investigation should help constrain the hydrostratigraphic framework model that is under development.

The Nevada Test Site (NTS), located in southern Nevada, was the site of 928 underground nuclear tests conducted between 1951 and 1992. The tests were performed as part of the Atomic Energy Commission and U.S. Department of Energy (DOE) nuclear weapons testing program. The NTS is managed by the DOE Nevada Operations Office (DOE/NV). Of the 928 tests conducted below ground surface at the NTS, approximately 200 were detonated below the water table. As an unavoidable consequence of these testing activities, radionuclides have been introduced into the subsurface environment, impacting groundwater. In the few instances of groundwater sampling, radionuclides have been detected in the groundwater; however, only a very limited investigation of the underground test sites and associated shot cavities has been conducted to date. The Underground Test Area (UGTA) Subproject was established to fill this void and to characterize the risk posed to human health and the environment as a result of underground nuclear testing activities at the NTS. One of its primary objectives is to gather data to characterize the deep aquifer underlying the NTS.

Certification of a new series of gravimetrically prepared synthetic reference materials for n(236U)/n(238U) isotope ratio measurements

The Nuclear Chemistry Division (NCD) at the Lawrence Livermore National Laboratory (LLNL) has a long history of using its resources to enhance the scientific literacy of students at virtually all educational levels, as well as providing for the continued scholarly development of its own staff. The Division has shown a particularly deep concern for motivating young scientific talent, and has a strong record of commitment toward educating and increasing the scientific skills of minorities and women. These activities are carried out by individual, group, or Division initiative and range from simple community involvement and classroom teaching to highly structured and specialized technical training. This report collects and describes the official and unofficial educational activities that have been conducted in the Nuclear Chemistry Division at LLNL during the recent past. These activities serve as a model of what a few dedicated individuals and an enlightened management can contribute to the education of a new generation of scientists and engineers.

During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

The potential for the contamination of ground water beneath the Nevada Test Site (NTS) by nuclear testing has long been recognized. The United States has conducted underground nuclear weapons testing at NTS since 1957, and a considerable amount of radioactive material has been deposited in the subsurface by this work. As a part of the U.S. Department of Energy Nevada Operations Office’s Underground Test Area Operable Unit (UGTA OP), the Lawrence Livermore National Laboratory (LLNL) has compiled an inventory of radionuclides produced by underground LLNL weapons tests from 1957 through 1992.

This report extends verification and validation testing of the NUFT package of codes (Nitao 2000a,b) to the US1P module of code designed for simulation of single-phase mixed or “coupled” saturated and unsaturated (or “variably saturated”) groundwater flow. Importantly, the verification and validation testing of US1P in this report includes performance evaluation of a modified numerical algorithm that was not included in prior quality assurance (QA) of the NUFT package by Carle et al. (2014) for Underground Test Area (UGTA) project activities, which are directed at assessment of radionuclide contamination in groundwater sourced from underground nuclear test locations at the Nevada National Security Site (NNSS). An immediate purpose of this report is to provide QA for ongoing large-scale, three-dimensional (3-D) groundwater flow modeling of transient water levels associated with longterm water supply pumping and underground nuclear testing at the NNSS (Jackson and Fenelon, 2018; Jackson et al., 2021). For UGTA activities, the QA refers to the standards of ASTM (1996) for verification and validation testing of groundwater modeling codes.

Characterizing and managing groundwater contamination associated with the 828 underground nuclear tests conducted at the Nevada Test Site are among the most challenging environmental remediation issues faced by the U.S. Department of Energy. Although significant long-term stewardship and risk management issues are associated with underground nuclear tests on the Nevada Test Site, of possible equal concern are a smaller number of underground nuclear tests conducted by the United States, 12 total, at eight sites located off the Nevada Test Site. In comparison to the Nevada Test Site, the U.S. Department of Energy has minimal institutional controls at these “offsite test areas” (Offsites) to serve as risk barriers. The corrective action and closure strategy under development for the Central Nevada Test Area and proposed recommendations [1] concerning long-term stewardship for this and the other Offsites illustrate long-term stewardship and risk management strategies applicable to underground nuclear test areas in the United States. The groundwater flow and transport model for the Central Nevada Test Area, site of the 1968 Faultless underground nuclear test, is the first model accepted by a U.S. state regulator (the Nevada Division of Environmental Protection) for an underground nuclear test area. Recommendations for the Central Nevada Test Area and other Offsites include developing decision support models to evaluate the impacts of future changes of land and water uses on previous decisions involving groundwater-use restrictions. Particularly for the Offsites in arid states such as Nevada, New Mexico, and Colorado, it is difficult to envision all future demands on subsurface resources. Rather than trying to maintain complex flow and transport models to evaluate future resource-use scenarios, decision support models coupled with original contaminant flow and transport models could be used as scoping tools to evaluate the sensitivity of previously established resource-use boundaries. This evaluation will determine if the previously established boundaries are still adequate for proposed new land and resource uses or if additional data collection or modeling will be necessary to make technically sound decisions. In addition, previously developed Data Decision Analyses, used to quantitatively evaluate the costs and benefits of different data collection activities conducted during the site characterization phase, could be maintained as a long-term stewardship tool to identify new data collection efforts, if necessary as indicated by a decision support model.

The ER-6-1 multiple-well aquifer test-tracer test (MWAT-TT) investigated groundwater flow and transport processes relevant to the transport of radionuclides from sources on the Nevada Test Site (NTS) through the lower carbonate aquifer (LCA) hydrostratigraphic unit (HSU). The LCA, which is present beneath much of the NTS, is the principal aquifer for much of southern Nevada. This aquifer consists mostly of limestone and dolomite, and is pervasively fractured. Groundwater flow in this aquifer is primarily in the fractures, and the hydraulic properties are primarily related to fracture frequency and fracture characteristics (e.g., mineral coatings, aperture, connectivity). The objective of the multiple-well aquifer test (MWAT) was to determine flow and hydraulic characteristics for the LCA in Yucca Flat. The data were used to derive representative flow model and parameter values for the LCA. The items of specific interest are: Hydraulic conductivity; Storage parameters; Dual-porosity behavior; and Fracture flow characteristics. The objective of the tracer transport experiment was to evaluate the transport properties and processes of the LCA and to derive representative transport parameter values for the LCA. The properties of specific interest are: Effective porosity; Matrix diffusion; Longitudinal dispersivity; Adsorption characteristics; and Colloid transport characteristics. These properties substantially control the rate of transport of contaminants in the groundwater system and concentration distributions. To best support modeling at the scale of the corrective action unit (CAU), these properties must be investigated at the field scale. The processes represented by these parameters are affected by in-situ factors that are either difficult to investigate at the laboratory scale or operate at a much larger scale than can be reproduced in the laboratory. Measurements at the field scale provide a better understanding of the effective average parameter values. The scale of this tracer test is still small compared to the scale of a CAU, but is of sufficient scale to be generally representative of the processes that affect in-situ transport. The scale of the tracer test undertaken is limited by the rate of transport in the formation and the resultant time frame required for completing such a test. The measurements at the field scale will provide information for relating laboratory measurements for transport processes to the larger scale. This report describes the analysis of the tracer test data and development of a conceptual model of transport in the LCA in Yucca Flat.

This report details the work of Chemistry Division personnel from Los Alamos National Laboratory in FY 2001 for the U. S. Department of Energy National Nuclear Security Administration Nevada Operations Office (NNSA/NV) under its Defense Programs and Environmental Restoration divisions. Los Alamos is one of a number of agencies collaborating in an effort to describe the present and future movement of radionuclides in the underground environment of the Nevada Test Site. This fiscal year we collected and analyzed water samples from a number of expended test locations at the Nevada Test Site. We give the results of these analyses and summarize the information gained over the quarter century that we have been studying several of these sites. We find that by far most of the radioactive residues from a nuclear test are contained in the melt glass in the cavity. Those radionuclides that are mobile in water can be transported if the groundwater is moving due to hydraulic or thermal gradients. The extent to which they move is a function of their chemical speciation, with neutral or anionic materials traveling freely relative to cationic materials that tend to sorb on rock surfaces. However, radionuclides sorbed on colloids may be transported if the colloids are moving. Local conditions strongly influence the distribution and movement of radionuclides, and we continue to study sites such as Almendro, which is thermally quite hot, and Nash and Bourbon, where radionuclides had not been measured for 8 years. We collected samples from three characterization wells in Frenchman Flat to obtain baseline radiochemistry data for each well, and we analyzed eight wells containing radioactivity for {sup 237}Np, using our highly sensitive ICP/MS. We have again used our field probe that allows us to measure important groundwater properties in situ. We conclude our report by noting document reviews and publications produced in support of this program.

One of the original drivers behind the development of pulsed power was the need for short-pulse (flash) x-ray sources for hydrodynamic tests. These systems continue to be an important diagnostic for the evaluation of hydrodynamic phenomena. In the United States, three primary facilities provide this function: Flash X-Ray (FXR) at Lawrence Livermore National Laboratory (LLNL); the Dual Axis Radiographic Hydrodynamic Test (DARHT) Facility at Los Alamos National Laboratory (LANL); and Cygnus at the Nevada National Security Site (NNSS). FXR and DARHT provide highly penetrating radiographic capabilities but are limited in the types of hydrodynamic experiments that can be performed, while Cygnus can support a larger range of experiments, but does not provide the same penetrating capability. To fill this gap in hydrodynamic experimental capability, the National Nuclear Security Agency (NNSA) has recently issued a set of high-level requirements describing a radiographic capability similar to that of DARHT, but located in a facility similar to Cygnus. In response to these requirements, a project called Scorpius has been developed as a joint partnership between LANL, LLNL, Sandia National Laboratory (SnL), and the NNSS. A key requirement is the delivery of multiple (2 or more) radiographic images along a single axis in a short time scale. This requirement effectively limits the possible system choices to a linear induction accelerator (LIA). However, there are several families of multi-pulse LIA architectures from which to choose. This paper describes the high-level system requirements for Scorpius as well as the evaluation of technologies and systems that might meet those requirements. In addition, the current preferred option and the initial conceptual designs are discussed.