Performance Monitoring to Assess Environmental System Behavior I
Presiding: T J Nicholson, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission; L Gray, IICER/CISTEMS, Florida State University
H42B-01 INVITED 10:30h
A Structural Approach to Performance Monitoring of Waste Sites: Obtaining Actionable Information
Both government and non-government agencies are faced with the challenge of long-term monitoring of waste sites and landfills. Such monitoring should provide actionable information on how these sites are evolving, including (but not limited to) information on the success of remedial treatment methods (either active or passive), compliance with regulatory standards, and evolution of system behavior associated with these sites. Current monitoring efforts suffer from the lack of integration between data collection, data management, information extraction and information use. An alternative to such efforts is the use of a structural approach to performance monitoring developed at Idaho National Laboratory (INL). This approach has the following characteristics (1) tight integration between monitoring objectives and data collection efforts (2) well structured storage of all relevant monitoring data (3) establishment of transparent, reproducible procedures for translation of data to information (including coupling of data to models) (4) development of a web based interface to the monitoring system, providing easy access to data and results by multiple stakeholders. We will discuss several examples of the implementation of the INL monitoring system, including an EPA superfund site and several landfill sites.
H42B-02 10:50h
Performance Monitoring of MNA Remedies for VOCs in Ground Water: A Framework
Effective monitoring of natural attenuation processes requires a clear understanding of hydrogeologic controls on ground-water flow, a three-dimensional approach to monitoring network design, and clearly defined performance criteria based on site-specific remedial action objectives. Objectives for the monitoring program generally will be met through routine evaluations of institutional controls and measurements of contaminant, geochemical, and hydrologic parameters. These data are used to evaluate changes in three-dimensional plume boundaries, changes in contaminant mass and concentration, and hydrological and geochemical changes that may indicate changes in remedy performance. Data interpretation focuses on detection of spatial and temporal changes, and assessment of their impacts on the achievement of site-specific goals. Particular changes of interest include: - Progress toward contaminant removal objectives, - Contaminant detections indicative of additional releases and detections at the plume boundaries that may indicate plume expansion, - Geochemical changes (e.g., oxidation-reduction conditions) indicative of possible changes in contaminant transformation processes and rates, - Changes in ground-water flow rates or directions such that contaminants may move into uncontaminated areas or threaten possible receptors, and - Changes in land and resource uses that threaten the effectiveness of institutional controls. Decisions regarding remedy effectiveness and the adequacy of the monitoring program will generally result in either continuation of the program, program modification, modification of the remedy, or termination of the performance monitoring program. Such decisions are appropriately based on specific, quantitative performance criteria defined in a monitoring plan.
H42B-03 INVITED 11:05h
The Advanced Monitoring Systems Initiative--Performance Monitoring for DOE Environmental Remediation and Contaminant Containment
The Advanced Monitoring System Initiative (AMSI) is a new approach to accelerate the development and application of advanced sensors and monitoring systems in support of Department of Energy needs in monitoring the performance of environmental remediation and contaminant containment activities. The Nevada Site Office of the National Nuclear Security Administration (NNSA) and Bechtel Nevada manage AMSI, with funding provided by the DOE Office of Environmental Management (DOE EM). AMSI has easy access to unique facilities and capabilities available at the Nevada Test Site (NTS), including the Hazardous Materials (HazMat) Spill Center, a one-of-a-kind facility built and permitted for releases of hazardous materials for training purposes, field-test detection, plume dispersion experimentation, and equipment and materials testing under controlled conditions. AMSI also has easy access to the facilities and considerable capabilities of the DOE and NNSA National Laboratories, the Special Technologies Laboratory, Remote Sensing Laboratory, Desert Research Institute, and Nevada Universities. AMSI provides rapid prototyping, systems integration, and field-testing, including assistance during initial site deployment. The emphasis is on application. Important features of the AMSI approach are: (1) customer investment, involvement and commitment to use - including definition of needs, desired mode of operation, and performance requirements; and (2) employment of a complete systems engineering approach, which allows the developer to focus maximum attention on the essential new sensing element or elements while AMSI assumes principal responsibility for infrastructure support elements such as power, packaging, and general data acquisition, control, communication, visualization and analysis software for support of decisions. This presentation describes: (1) the needs for sensors and performance monitoring for environmental systems as seen by the DOE Long Term Stewardship Science and Technology Roadmap and the Long Term Monitoring Sensors and Analytical Methods Workshop, and (2) AMSI operating characteristics and progress in addressing those needs. Topics addressed will include: vadose zone and groundwater tritium monitoring, a wireless moisture monitoring system, Cr(VI) and CCl4 monitoring using a commercially available "universal sensor platform", strontium-90 and technetium-99 monitoring, and area chemical monitoring using an array of multi-chemical sensors.
H42B-04 11:25h
Techniques for Assessing the Performance of In Situ Bioreduction and Immobilization of Metals and Radionuclides in Contaminated Subsurface Environments
Department of Energy (DOE) facilities within the weapons complex face a daunting challenge of remediating huge below inventories of legacy radioactive and toxic metal waste. More often than not, the scope of the problem is massive, particularly in the high recharge, humid regions east of the Mississippi river, where the off-site migration of contaminants continues to plague soil water, groundwater, and surface water sources. As of 2002, contaminated sites are closing rapidly and many remediation strategies have chosen to leave contaminants in-place. In situ barriers, surface caps, and bioremediation are often the remedial strategies of chose. By choosing to leave contaminants in-place, we must accept the fact that the contaminants will continue to interact with subsurface and surface media. Contaminant interactions with the geosphere are complex and investigating long term changes and interactive processes is imperative to verifying risks. We must be able to understand the consequences of our action or inaction. The focus of this presentation is to describe recent technical developments for assessing the performance of in situ bioremediation and immobilization of subsurface metals and radionuclides. Research within DOE's NABIR and EMSP programs has been investigating the possibility of using subsurface microorganisms to convert redox sensitive toxic metals and radionuclides (e.g. Cr, U, Tc, Co) into a less soluble, less mobile forms. Much of the research is motivated by the likelihood that subsurface metal-reducing bacteria can be stimulated to effectively alter the redox state of metals and radionuclides so that they are immobilized in situ for long time periods. The approach is difficult, however, since subsurface media and waste constituents are complex with competing electron acceptors and hydrogeological conditions making biostimulation a challenge. Performance assessment of in situ biostimulation strategies is also difficult and typically requires detailed monitoring of coupled hydrological, geochemical/geophysical, and microbial processes. In the following presentation we will (1) discuss contaminant fate and transport problems in humid regimes, (2) efforts to immobilize metals and radionuclides in situ via bioremediation, and (3) state-of -the-art techniques for assessing the performance of in situ bioreduction and immobilization of metals and radionuclides. These included (a) in situ solution and solid phase monitoring, (b) in situ and laboratory microbial community analysis, (c) noninvasive geophysical methods, and (d) solid phase speciation via high resolution spectroscopy.
H42B-05 11:40h
Surrogate Indicators of Radionuclide Migration at the Amargosa Desert Research Site, Nye County, Nevada
Contaminant-transport processes are being investigated at the U.S. Geological Survey's Amargosa Desert Research Site (ADRS), adjacent to the Nation's first commercial disposal facility for low-level radioactive waste. Gases containing tritium and radiocarbon are migrating through a 110-m thick unsaturated zone from unlined trenches that received waste from 1962 to 1992. Information on plume dynamics comes from an array of shallow (<2 m) and two vertical arrays of deep (5-109 m) gas-sampling ports, plus ground-water monitoring wells. Migration is dominated by lateral transport in the upper 50 m of sediments. Radiological analyses require ex-situ wet-chemical techniques, because in-situ sensors for the radionuclides of interest do not exist. As at other LLRW-disposal facilities, radionuclides at the ADRS are mixed with varying amounts of volatile organic compounds (VOCs) and other substances. Halogenated-methanes, -ethanes, and -ethenes dominate the complex mixture of VOCs migrating from the disposal area. These compounds and their degradates provide a distinctive "fingerprint" of contamination originating from low-level radioactive waste. Carbon-dioxide and VOC anomalies provide indicator proxies for radionuclide contamination. Spatial and temporal patterns of co-disposed and byproduct constituents provide field-scale information about physical and biochemical processes involved in transport. Processes include reduction and biorespiration within trenches, and largely non-reactive, barometrically dispersed diffusion away from trenches.
H42B-06 INVITED 11:55h
Plant-Based Plume-Scale Monitoring Reveals the Extents and Pathways of Tritium Transport
Cost-effective methods are needed to detect contamination near radioactive-waste and other contaminated sites. Such methods should be capable of providing an early warning of contaminant releases and be accurate and robust enough for monitoring the long-term performance of waste-isolation facilities and remediation measures. Plant-based methods were developed adjacent to a closed low-level radioactive waste (LLRW) facility in the Amargosa Desert, Nevada. Objectives were to (i) characterize and map the spatial variability of plant-water tritium, (ii) develop empirical relations to predict subsurface tritium contamination from plant-water concentrations, and (iii) gain insight into transport pathways and processes. Tritium was selected because it is a common radionuclide disposed at radioactive waste sites and it is a good tracer of water movement. Solar-distillation and solid-phase-extraction were used to collect and prepare plant (creosote bush, Larrea tridentata) foliage water for direct-scintillation counting. The maximum plant-water tritium concentration was 4,890 Bq/L; background values averaged 2.5 Bq/L. Geostatistical analysis showed that plant concentrations were spatially correlated to a distance of 380 m. Simple-contour and kriged maps of plant concentrations identified "hot spots" that were verified by soil-water-vapor measurements. Empirical linear relations between plant water and soil-water-vapor concentrations measured at the 0.5- and 1.5-m sampling depths were used to map the spatial distributions of root-zone and sub-root-zone tritium, respectively. Results showed that tritium migration away from the waste source primarily occurs in the gas phase with preferential transport through a dry, gravelly layer beneath the root zone, from which it moves upward and is subsequently released to the surface environment. Shallow and deep geologic units controlling preferential transport through the unsaturated zone were mapped by direct-current electrical resistivity imaging. Our study is apparently the first to document such extensive (> 300 m) subsurface gas-phase transport of tritium away from a disposal area. Sampling plant water for tritium requires one-fifth the time of soil-gas samples, reduces equipment costs, and provides a volume-integrated (versus point) sample that reflects the soil volume exploited by the plant's roots. The plant-sampling approach is likely to be transferable to additional species and environments; site-specific testing can be used to develop and evaluate the accuracy of predictive relations between plant and subsurface tritium concentrations. Plant-based plume mapping revealed the extents and pathways of tritium transport at the Amargosa Desert site. Process-based numerical models have failed to reproduce this observed transport by as much as one order of magnitude. Better process understanding is needed to support long-term monitoring of contaminated sites.
http://nevada.usgs.gov/adrs/