The vadose zone roadmap (DOE 2001) developed a set of vadose zone research and

Transcription

1 Developing a Long-Term National Vadose Zone Research Agenda By Stephen J. Kowall, Ph.D. 1 Abstract The vadose zone roadmap (DOE 2001) developed a set of vadose zone research and infrastructure priorities for the next quarter-century in four areas: Invasive Characterization, Non- Invasive Characterization, Physical Processes, and Simulation and Modeling. The resulting roadmap document describes the research and application activities needed to achieve a reasonable scientific understanding of how contaminants of all forms move in the vadose zone of the principal geological environments. If successful, the research undertaken in this effort will dramatically improve characterization, monitoring, and modeling capabilities, thereby providing a firmer scientific foundation upon which regulators and site managers can make confident decisions and predictions when dealing with contamination in the vadose zone. Additional work to refine, extend, and update this roadmap will require continued dialogue within the vadose zone research community, with other U.S. government and state and local agencies, and with affected stakeholders. Introduction During the time that the field of vadose zone hydrology has been evolving, a host of environmental regulations have been imposed at the national level. In particular, the public and water quality regulators have demanded that our nation s groundwater be protected from contaminants. Because the percolating water and the chemicals entrained therein pass through 1 Idaho National Engineering and Environmental Laboratory, , kowasj@inel.gov 1

2 the vadose zone before becoming groundwater recharge, developing a comprehensive understanding of the physical, chemical, and biological processes active in the vadose zone, as well as reliable monitoring and prediction of water and chemical migration, are of paramount importance to protecting our aquifers. While there has been a national mandate to prevent groundwater pollution, there has surprisingly been no national research agenda to develop a comprehensive understanding of the vadose zone, in particular how to characterize, monitor, and simulate its behavior over large space and time scales. Recent evidence indicates that hazardous and radioactive chemicals have migrated unexpectedly through the deep vadose zone at multiple DOE facilities. For example: At the Hanford 200 West Area Tank Farm, cesium-137 appears to have migrated roughly 80 feet vertically through highly sorptive material that should have prevented such migration. At Los Alamos National Laboratory, plutonium and americium were discovered 100 feet beneath a liquid waste impoundment where nuclide transport was believed to be dominated by sorption and thus should have been very limited. At Sandia National Laboratories, trichloroethane from a landfill was discovered at depths of 500 feet in an area of very dry soil and low recharge. Near the prospective site for a high-level radioactive waste disposal repository in the dry desert climate of Yucca Mountain, tracer substances such as bomb pulse chlorine-36 and tritium were found in fractured tuff at depths of as much as 1200 feet. These data imply unexpectedly rapid recharge along preferential pathways. 2

3 At the same time that such unanticipated contaminant migration was being recognized, the DOE had embarked on a long-term stewardship strategy; a program to address its contaminated sites after active remediation was completed (DOE, 1999). The long-term stewardship process may include such strategies as constructing an engineered cover, monitoring the subsurface, and controlling site access. Of the 144 DOE sites in the U.S., most are expected to be remediated and in a long-term stewardship mode by However, the available science and technology regarding the vadose zone was believed to be insufficient to satisfy DOE, regulators, and the public that the long-term stewardship strategy would be completely successful (NRC, 2000). The timeline for remediating DOE sites and placing them in long-term stewardship necessitated a more aggressive, accelerated program to better understand vadose zone processes and properties, to develop better tools and techniques to characterize and monitor contaminant migration, and to develop predictive models to address and access performance and long-term stewardship needs. Out of the need to solve this problem of national significance, an innovative approach was applied to identify the key science information and technology gaps and ways to close those gaps. What is the Roadmap? The vadose zone roadmap is a means of achieving, to the best of our current knowledge, a reasonable scientific understanding of how contaminants of all forms move in the vadose zone of the principal geological environments. The roadmap is intended to reduce the present uncertainties in predicting contaminant movement, which in turn will reduce the uncertainties in remediation decisions. The roadmap is much like a business plan, with a clear vision, specific goals to be achieved, an approach to achieve the goals, and a timetable. The roadmap does not assign a value to the information needed, nor does it express in quantitative terms how much would be saved were the information in hand. It does not discuss 3

4 tradeoffs in remediation techniques or the political and economic factors involved, nor does it explore the use of decision analyses to determine the "best" means of remediating a site. Rather, the information obtained from the research proposed will help determine the best course of action at the most recalcitrant sites of subsurface contamination in the U.S. and abroad. Achieving this ultimate objective will take some time, as fundamental knowledge is needed. However, significant value will be gained almost immediately from these undertakings. As a starting point, personnel from the DOE national laboratories who are familiar with end user needs and vadose zone issues (including several key collaborators who developed the compendium Vadose Zone Science and Technology Solutions [Looney and Falta, 2000]) prepared a summary of current deficiencies and capability gaps in vadose zone characterization, monitoring, and modeling within the DOE complex. A preliminary draft of the roadmap was completed on September 25, During the last six months of the effort, the scope of the roadmap was broadened from a focus on DOE problems and needs to a national perspective on vadose zone contamination as a threat to our invaluable groundwater resources. In addition, the DOE solicited feedback from stakeholders at 17 meetings held across the country. These efforts culminated in Rev. 0.0 of the roadmap, completed on September 1, Vision of Research If successful, the research described in the vadose zone roadmap will achieve its vision in advancing the state of the art in vadose zone characterization, monitoring, and modeling science and technology. To support the complex-wide needs of DOE, as well as the needs of other owners of vadose zone contamination problems and the regulators and stakeholders to whom they answer, these advances in the state of the art must make their way into practice. The work groups that developed this roadmap have emphasized pathways for this critical transformation of research results into practical results. 4

5 Creating a better scientific foundation for making both near-term remediation and waste handling decisions and long-term stewardship decisions regarding the management of contaminated vadose zone sites will require (1) an enhanced understanding of basic subsurface processes, (2) adequate data on the properties of fluids and media that affect flow and transport in the vadose zone, the extent and character of existing contamination, and the ability to monitor it effectively, and (3) the ability to translate this understanding and data into new predictive models that can reduce the technical uncertainty in environmental management decisions. The roadmap describes the research and application activities to improve the understanding of basic physical, chemical, and biological processes and properties, as well as to improve the modeling, measuring, and monitoring of fluid flow and contaminant transport. The roadmap identifies and discusses activities, tasks, and status points for cross-cutting issues, such as coupled processes, scaling, measurement and reduction of uncertainty, and the integration and validation of characterization, monitoring, and assessment tools at the system (site-wide) level. Anticipated Results Many of the near-term results expected for both the research and infrastructure activities share a common theme: moving the state of the art to the state of practice. This means putting the current knowledge and capabilities already existing in the research communities into operational use at the nation's priority sites of vadose zone contamination. One benefit is that these tasks provide quick returns because much of the research investment has already been made. A less obvious benefit is that a concerted effort to put new knowledge and technical capability into practice will bring researchers and solution-oriented problem owners into continuing and close interaction. For the mid-term, the roadmap outcomes of greatest significance are likely to be the cumulative advances in monitoring systems for vadose zone sites. A sound and efficient monitoring program 5

6 is critical at major sites both during environmental cleanup and afterward, throughout any period of stewardship required by residual contamination at the site. The state of practice has been to monitor the groundwater at and around the site rather than monitoring the vadose zone. However, for many sites where contaminants are at some distance from the water table, waiting for contaminants to appear in the groundwater represents lost opportunity. If remediation can remove or isolate source terms and halt plumes while they are still in the vadose zone, groundwater contamination can be prevented. In addition, the effectiveness of the remediation is often greatly enhanced and the cost significantly reduced compared to groundwater remediation alternatives. Many of the long-term results anticipated from the roadmap activities will provide better tools for supporting site-wide assessments and decisions on environmental cleanup and stewardship. Models and data gathering will undoubtedly improve incrementally in the near- and mid-term. However, after a decade or so of pursuing the roadmap's activities, a qualitative leap forward is expected in the ability to quickly and accurately visualize the current and projected future states of site-wide vadose zone systems. These projections, which will carry levels of certainty and sensitivity unattainable at present, should suffice to win the confidence of regulators and the public. Conclusion The status of the National Vadose Zone Roadmap is in limbo at present. The administration at DOE changed prior to completing the roadmap and, at least in the short-term, other matters had greater priority; therefore, funding for research and development at DOE has been limited. Nevertheless, this roadmap likely represents the first effort to organize vadose zone research needs and marshal a plan to implement the necessary research and technology development within a prescribed timeframe. Working within the broad problem defined by DOE, an 6

7 interdisciplinary team of scientists, rather than research program administrators, worked together to develop a long-term research agenda from the bottom up. With this roadmap, it can be clearly seen how contributions by individual researchers or teams of researchers fit together. An implementation plan for this roadmap would likely cut across many federal agencies, with the benefit of reducing unnecessary duplication of research effort, thereby achieving more value for the available research funds. 7

8 References Looney and Falta, Eds Vadose Zone Science and Technology Solutions. Battelle Press, Columbus, Ohio. National Research Council (NRC) Research Needs in Subsurface Science. National Academy Press, Washington, D.C. National Research Council (NRC) Conceptual Models of Flow and Transport in the Fractured Vadose Zone. National Academy Press, Washington, D.C. U.S. Department of Energy From cleanup to stewardship, A companion report to Accelerating cleanup: Paths to closure and Background information to support the scoping process required for the 1998 PEIS settlement study. DOE/EM Office of Environmental Management. October Available at < U.S. Department of Energy A national roadmap for vadose zone science & technology Understanding, monitoring, and predicting contaminant fate and transport in the unsaturated zone. Revision 0.0. Available at < August Related web sites INEEL National Vadose Zone Project: A National Roadmap for Vadose Zone Science and Technology, Long-Term Stewardship National Science and Technology Roadmap Program, 8