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A simulation and decision analysis approach to locating DNAPL in subsurface sediments

Description: This report presents a strategy for delineating the location of residual dense non-aqueous phase liquids (DNAPL) that combines probabilistic simulations of DNAPL spill location and volume, geologic texture constraining migration pathways, migration physics through percolation modeling, and a decision analysis model to pick optimal locations for sampling wells. The authors` strategy is an iterative process of simulating the residual DNAPL location, selecting new locations for data collection, gathering data, and then using the data to condition further simulations of DNAPL migration. As they iterate through this process, data worth analysis is used to determine an appropriate stopping point. The authors present the results from a preliminary version of their model, showing how the process was used to delineate hypothetical DNAPL spills.
Date: September 1, 1997
Creator: Borchers, B.; Conrad, S.H. & Webb, E.K.
Partner: UNT Libraries Government Documents Department

A Probabilistic environmental decision support framework for managing risk and resources

Description: The ability to make cost effective, timely decisions associated with waste management and environmental remediation problems has been the subject of considerable debate in recent years. On one hand, environmental decision makers do not have unlimited resources that they can apply to come to resolution on outstanding and uncertain technical issues. On the other hand, because of the possible impending consequences associated with these types of systems, avoiding making a decision is usually not an alternative either. Therefore, a structured, quantitative process is necessary that will facilitate technically defensible decision making in light of both uncertainty and resource constraints. An environmental decision support framework has been developed to provide a logical structure that defines a cost-effective, traceable, and defensible path to closure on decision regarding compliance and resource allocation. The methodology has been applied effectively to waste disposal problems and is being adapted and implemented in subsurface environmental remediation problems.
Date: March 1, 1996
Creator: Gallegos, D.P.; Webb, E.K.; Davis, P.A. & Conrad, S.H.
Partner: UNT Libraries Government Documents Department

Using performance assessment for radioactive waste disposal decision making -- implementation of the methodology into the third performance assessment iteration of the Greater Confinement Disposal site

Description: The US Department of Energy is responsible for the disposal of a variety of radioactive wastes. Some of these wastes are prohibited from shallow land burial and also do not meet the waste acceptance criteria for proposed waste repositories at the Waste Isolation Pilot Plant (WIPP) and Yucca Mountain. These have been termed ``special-case`` waste and require an alternative disposal method. From 1984 to 1989, the Department of Energy disposed of a small quantity of special-case transuranic wastes at the Greater Confinement Disposal (GCD) site at the Nevada Test Site. In this paper, an iterative performance assessment is demonstrated as a useful decision making tool in the overall compliance assessment process for waste disposal. The GCD site has been used as the real-site implementation and test of the performance assessment approach. Through the first two performance assessment iterations for the GCD site, and the transition into the third, we demonstrate how the performance assessment methodology uses probabilistic risk concepts to guide affective decisions about site characterization activities and how it can be used as a powerful tool in bringing compliance decisions to closure.
Date: December 31, 1993
Creator: Gallegos, D.P.; Conrad, S.H. & Baer, T.A.
Partner: UNT Libraries Government Documents Department

The disposal of orphan wastes using the greater confinement disposal concept

Description: In the United States, radioactive wastes are conventionally classified as high-level wastes, transuranic wastes, or low-level wastes. Each of these types of wastes, by law, has a ``home`` for their final disposal; i.e., high-level wastes are destined for disposal at the proposed repository at Yucca Mountain, transuranic waste for the proposed Waste Isolation Pilot Plant, and low-level waste for shallow-land disposal sites. However, there are some radioactive wastes within the United States Department of Energy (DOE) complex that do not meet the criteria established for disposal of either high-level waste, transuranic waste, or low-level waste. The former are called ``special-case`` or ``orphan`` wastes. This paper describes an ongoing project sponsored by the DOE`s Nevada Operations Office for the disposal of orphan wastes at the Radioactive Waste Management Site at Area 5 of the Nevada Test Site using the greater confinement disposal (GCD) concept. The objectives of the GCD project are to evaluate the safety of the site for disposal of orphan wastes by assessing compliance with pertinent regulations through performance assessment, and to examine the feasibility of this disposal concept as a cost-effective, safe alternative for management of orphan wastes within the DOE complex. Decisions on the use of GCD or other alternate disposal concepts for orphan wastes can be expected to be addressed in a Programmatic Environmental Impact Statement being prepared by DOE. The ultimate decision to use GCD will require a Record of Decision through the National Environmental Policy Act (NEPA) process. 20 refs., 3 figs., 2 tabs.
Date: February 1, 1991
Creator: Bonano, E.J.; Chu, M.S.Y.; Price, L.L.; Conrad, S.H. & Dickman, P.T.
Partner: UNT Libraries Government Documents Department

Understanding the dynamics of water availability and use in China

Description: This report presents the preliminary results of an analysis of China`s water resources, part of an effort undertaken by the National Intelligence Council Medea scientists to improve the understanding of future food production and consumption in the People`s Republic of China. A dynamic water model was developed to simulate the hydrological budgetary processes in five river drainage basins located in northeastern, central, and southern China: the Chang Jiang (Yangtse River), Huanghe (Yellow River), Haihe, Huaihe, and Liaohe. The model was designed to assess the effects of changes in urban, industrial, and agricultural water use requirements on the availability of water in each basin and to develop estimates of the water surpluses and/or deficits in China through the year 2025. The model imposes a sustainable yield constraint, that is, groundwater extraction is not allowed to exceed the sustainable yield; if the available water does not meet the total water use requirements, a deficit results. An agronomic model was also developed to generate projections of the water required to service China`s agricultural sector and compare China`s projected grain production with projected grain consumption requirements to estimate any grain surplus and/or deficit. In future refinements, the agronomic model will interface directly with the water model to provide for the exchange of information on projected water use requirements and available water. The preliminary results indicate that the Chang Jiang basin will have a substantial surplus of water through 2025 and that the Haihe basin is in an ongoing situation. The agricultural water use requirements based on grain production indicate that an agricultural water deficit in the Haihe basin begins before the onset of the modeling period (1980) and steadily worsens through 2025. This assumption is confirmed by reports that groundwater mining is already under way in the most intensely cultivated and populated areas of ...
Date: July 1, 1997
Creator: Thomas, R.P.; Conrad, S.H.; Jeppesen, D.M. & Engi, E.
Partner: UNT Libraries Government Documents Department

An interative, probabilistic environmental decision analysis approach

Description: The framework is versatile and the generalized approach has worked well for a suite of evaluations or as a foundation for evaluation tools including developing the SEDSS computer software system for evaluating site safety for EPA Superfund problems, NRC Low-Level Nuclear Waste facility siting, and UMTRA site remediation decisions; iteration through the performance assessment of the Greater Confinement Disposal Facility; and optimizing data collection for DNAPL problems. In particular, the SEDSS computer system makes a portion of these tools accessible for broad scale application. Development of both details of the process and computer tools to support individual steps continues.
Date: March 1, 1996
Creator: Webb, E.K.; Conrad, S.H. & Brown, T.J.
Partner: UNT Libraries Government Documents Department

Preliminary evaluation of the use of the greater confinement disposal concept for the disposal of Fernald 11e(2) byproduct material at the Nevada Test Site

Description: This report documents a preliminary evaluation of the ability of the greater confinement disposal boreholes at the Nevada Test Site to provide long-term isolation of radionuclides from the disposal of vitrified byproduct material. The byproduct material is essentially concentrated residue from processing uranium ore that contains a complex mixture of radionuclides, many of which are long-lived and present in concentrations greater than 100,000 picoCuries per gram. This material has been stored in three silos at the fernald Environmental Management Project since the early 1950s and will be vitrified into 6,000 yd{sup 3} (4,580 m{sup 3}) of glass gems prior to disposal. This report documents Sandia National Laboratories` preliminary evaluation for disposal of the byproduct material and includes: the selection of quantitative performance objectives; a conceptual model of the disposal system and the waste; results of the modeling; identified issues, and activities necessary to complete a full performance assessment.
Date: September 1, 1997
Creator: Cochran, J.R.; Brown, T.J.; Stockman, H.W.; Gallegos, D.P.; Conrad, S.H.; Price, L.L. et al.
Partner: UNT Libraries Government Documents Department

Modeling the infrastructure dynamics of China -- Water, agriculture, energy, and greenhouse gases

Description: A comprehensive critical infrastructure analysis of the People`s Republic of China was performed to address questions about China`s ability to meet its long-term grain requirements and energy needs and to estimate greenhouse gas emissions in China likely to result from increased agricultural production and energy use. Four dynamic computer simulation models of China`s infrastructures--water, agriculture, energy and greenhouse gas--were developed to simulate, respectively, the hydrologic budgetary processes, grain production and consumption, energy demand, and greenhouse gas emissions in China through 2025. The four models were integrated into a state-of-the-art comprehensive critical infrastructure model for all of China. This integrated model simulates diverse flows of commodities, such as water and greenhouse gas, between the separate models to capture the overall dynamics of the integrated system. The model was used to generate projections of China`s available water resources and expected water use for 10 river drainage regions representing 100% of China`s mean annual runoff and comprising 37 major river basins. These projections were used to develop estimates of the water surpluses and/or deficits in the three end-use sectors--urban, industrial, and agricultural--through the year 2025. Projections of the all-China demand for the three major grains (corn, wheat, and rice), meat, and other (other grains and fruits and vegetables) were also generated. Each geographic region`s share of the all-China grain demand (allocated on the basis of each region`s share of historic grain production) was calculated in order to assess the land and water resources in each region required to meet that demand. Growth in energy use in six historically significant sectors and growth in greenhouse gas loading were projected for all of China.
Date: August 1, 1998
Creator: Conrad, S.H.; Drennen, T.E.; Engi, D.; Harris, D.L.; Jeppesen, D.M. & Thomas, R.P.
Partner: UNT Libraries Government Documents Department

Stochastic Parameter Development for PORFLOW Simulations of the Hanford AX Tank Farm

Description: Parameters have been identified that can be modeled stochastically using PORFLOW and Latin Hypercube Sampling (LHS). These parameters include hydrologic and transport properties in the vadose and saturated zones, as well as source-term parameters and infiltration rates. A number of resources were used to define the parameter distributions, primarily those provided in the Retrieval Performance Evaluation Report (Jacobs, 1998). A linear rank regression was performed on the vadose-zone hydrologic parameters given in Khaleel and Freeman (1995) to determine if correlations existed between pairs of parameters. No strong correlations were found among the vadose-zone hydrologic parameters, and it was recommended that these parameters be sampled independently until future data or analyses reveal a strong correlation or functional relationship between parameters. Other distributions for source-term parameters, infiltration rates, and saturated-zone parameters that are required to stochastically analyze the performance of the AX Tank Farm using LHS/PORFLOW were adapted from distributions and values reported in Jacobs (1998) and other literature sources. Discussions pertaining to the geologic conceptualization, vadose-zone modeling, and saturated-zone modeling of the AX Tank Farm are also presented.
Date: January 1, 1999
Creator: Ho, C.K.; Baca, R.G.; Conrad, S.H.; Smith, G.A.; Shyr, L. & Wheeler, T.A.
Partner: UNT Libraries Government Documents Department