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7 Realizing Future Capabilities During the past two decades, advances in computing and microelectronics have stimulated the production of an impressive array of tools and techniques for noninvasive characterization of the shallow subsurface. These advances have made existing tools and techniques faster, cheaper, or more effective. However, there have been relatively few fundamental innovations with regard to the phe- nomena being observed or the sensing devices that convert those phenomena into electrical signals. Additional research and development (R&D) is needed to en- hance and extend current capabilities, to develop fundamentally new measure- ments, and to close the aforementioned gap between the state of the practice and the state of knowledge. Some of R&D areas are short-term (e.g., 3 to 5 years) opportunities for advances that can be achieved using existing knowledge and technologies in other words, enabling the state of the practice to be closer to the state of the art. These include the automation of tools and techniques and the development of methods for monitoring properties, processes, and temporal variations. Others are of a long-term (e.g., 10 to 20 years), high-risk nature, but they offer the potential to enhance significantly our ability to "see into the earth." The long-term needs deal primarily with the discovery of fundamentally new phenomena that can provide information about subsurface conditions and the development of new sensing tech- niques for making measurements at a distance. In this section, the recommenda- tions for R&D are presented in order from short term to long term. The resource industries (particularly oil) have invested heavily in R&D be- cause they are profit driven; breakthroughs in exploration can dramatically in- crease profits. In comparison to the gross expenditures on characterization ef- forts, the near-surface characterization industry invests relatively little in R&D. 120
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REALIZING FUTURE CAPABILITIES 121 The committee believes that lack of investment results because site characteriza- tion activities do not generate revenue for the client but are required in a wide range of environmental and engineering situations. In this situation, R&D is often a cost without commensurate short-term benefits. This is exacerbated by the "low-bid" nature of most specific site characterization efforts (Shuirman and Slosson, 1992), a situation not likely to change. As a result, the private sector usually defers needed R&D in favor of activities that produce more immediate benefits in the form of cost reduction. As such, the committee believes that it is in the interest of the nation to increase the federal government' s investment in R&D and to provide incentives and mechanisms for increased private sector invest- ment. Finally, because much of the research is based in universities and federal laboratories, it will be important to provide for effective communications be- tween researchers and industry to ensure that both short-term and long-term R&D products are of great value to the near-surface characterization industry. Government agencies should be encouraged to increase their in- vestment in near-surface characterization R&D in the areas appropri- ate to their mission. For example, this includes: . Agencies (e.g., the Department of Defense and the Department of En- ergy) that are required to deal with near-surface problems (hazardous waste, construction, etc.) at their own sites; · Agencies (e.g., the Environmental Protection Agency, the Department of the Interior, the Department of Transportation, and the U.S. Army Corps of Engineers) responsible for oversight of the environment, resource development, transportation, and infrastructure where near-surface characterization can be an integral part of their business; and · Agencies for which basic research either is their primary mission (e.g., the National Science Foundation) or is critical to their mission (e.g., the U.S. Geological Survey). In addition, research programs supported by federal agencies should take advantage of advisory boards to ensure that R&D expenditures are producing innovations that will be of value to the site characterization process. The federal government already supports some of the R&D that is needed to deal with proliferating societal issues ranging from land mines to hazardous waste to underground construction. A mechanism should be developed to stimu- late private sector investment in R&D in spite of the cost-driven nature of the industry and its size (usually small consulting firms) and application-specific nature.
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22 SEEING INTO THE EARTH Government and industry should cooperatively investigate mecha nisms for coordination and support of site characterization research. One possible mechanism is a quasi-governmental entity that could be em- powered to collect funds from site characterization contractors and clients. On the other hand, the site characterization industry may have special characteristics that demand an entirely new model. Initially it would be useful to define the needs and characteristics of the industry (particularly the economic structure) prior to designing a solution that optimally meets these needs. In addition to traditional forms of R&D support, universities and government labs should be encouraged to form more partnerships with industry to develop tools and techniques that will enhance everyday field applications. This will help effect the transition between the state of knowledge and the state of practice. To ensure rapid technical transfer from research to practice, research could be carried out by teams that include both practitioners (e.g., geobiologists, geo- chemists, geophysicists) and clients (e.g., environmental scientists, civil engi- neers). Such research teams should communicate their results to the scientific, engineering, and user communities in widely available venues and in forms suit- able for more immediate adoption. AUTOMATION OF TECHNIQUES Research and development efforts applied to automation of data acquisition, data processing, and decision making could produce rapid improvement in all aspects of near-surface characterization and should be given a high priority for research funding. Automation can be applied to data acquisition (e.g., robotics), data process- ing, and decision making (e.g., use of expert systems and other decision tools for survey planning and data interpretation). The benefits of automation include ease of use, consistency, quality assurance, and cost reduction. It also could enable more rapid technology transfer of the latest tools and techniques from the re- search lab to the field, thus enabling the state of the practice to be nearer to the state of the science. Finally, automation could help the site characterization in- dustry deal with periodic shortages of trained professionals in specialized fields. At present, for example, there is a potential shortage of individuals with advanced education in shallow-exploration geophysics. Low enrollments in uni- versity programs for the past decade, coupled with employment opportunities in the oil and mining industries, may make it difficult for site characterization companies to hire enough qualified professionals. However, computers can help design a site survey, automate data acquisition, check the quality of data, process the data, model the data, and provide a rough interpretation. For example, the Geophysics Advisor Expert System (Olhoeft, 1992) can help select appropriate
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REALIZING FUTURE CAPABILITIES 123 geophysical tools to apply to EPA Superfund site problems (and in the process, educate site managers and contractors). However, such systems are guides and will not replace the need for skilled professionals; the uniqueness of sites makes it difficult to include every possibility in such systems. Another example is a tunnel detection system (Olhoeft, 1993) that automatically tests data quality through 12 consistency tests (and, if necessary, indicates what might be wrong with the data and ways to correct them). The system also processes the data for the normal logistical, operational, and instrumental artifacts; manipulates and models the data; and provides a graphical output of the most likely location for detection of a tunnel. At each step, the program provides quantitative data pro- cessing, modeling, and interpretive (uncertainty and confidence) indicators. These types of automation and decision support systems can provide the expertise to complement the skills of practitioners and help alleviate personnel shortages. Automation also can make an important contribution to work in hazardous environments. Not only can robotic technology make it possible to avoid putting humans in dangerous situations, but expert systems and decision support tools can further enhance the quality of data by making real-time decisions about optimizing acquisition parameters. Ultimately, such systems could improve data quality, lower cost, and enhance safety. These are only a few examples of automation techniques that could provide expertise, guide the characterization process, and ensure quality control. The necessary capability to develop such techniques exists in universities and govern- ment laboratories, and the techniques could be rapidly embedded in systems for broad use. Impediments to broader development and use of these automated systems include the issue of deciding how such systems should be certified, who should be authorized to conduct the certification, and how the systems will be updated. Automation will not replace skilled practitioners; however, it can signifi- cantly increase the knowledge base that practitioners use to accomplish their jobs. By producing a better result, more rapidly and at lower cost, robotics and decision support systems could be the key to more and more effective use of site characterization methods. Therefore, automation of site characterization pro- cesses should be pursued on two broad fronts simultaneously. Experts in univer- sities and government laboratories should move aggressively to develop tech- niques and systems for automation of activities and decision-making processes. At the same time, the key regulatory bodies should develop certification policies and procedures using experts from the legal, technical, and political arenas. Re- search and development should include (but not be limited to) the following: . Expert systems to provide advice and guidance in designing characteriza- tion surveys, optimizing parameters, estimating probability of success, validating decisions, and justifying costs;
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24 SEEING INTO THE EARTH · Automated data acquisition instruments to ensure competent use, enable field processing and interpretation, and provide quality control; Expert systems, decision trees, and pattern recognition software to guide data processing sequences; · Decision support systems to assist in interpretation, incorporating effec- tive use of modeling and simulation to validate possible interpretations and pro- vide quantitative estimates of uncertainty; . . Policies and procedures for certifying the validity and effectiveness of automation tools; and · Guidelines for regulatory adoption of the appropriate and proper use of certified automation tools. MONITORING TEMPORAL VARIATIONS Many site characterization problems involve changes with time. Examples include monitoring engineered barriers to confirm containment of contaminants, analyzing changes in soil moisture to assess water fluxes, or surveying an envi- ronmental remediation site to characterize the reduction in the extent of subsur- face contamination. A single observation or survey at a characterization site may show the distribution of materials in question at that point in time, but it will not provide information about changes from earlier conditions or help predict future evolution. In many cases, properly designed multiple surveys can detect and monitor small changes in properties with higher resolution than is possible within a single survey. Significant advances can result from the development of exploration strategies (using existing tools) for acquiring, processing, and interpreting time- varying information. In the long term, research also is needed to develop mea- surement technology that will allow monitoring new processes such as in situ leaching or bioremediation. Uses for time-varying information include the following: · The ability to predict changes that may occur in response to human activ- ity (or lack thereof) is essential to design and defend remediation plans. · Baseline data and historical information often are needed to assess liabil- ity or responsibility. Where baseline information does not exist, data from re- peated measurements sometimes can be extrapolated backwards to provide in- sight into history. . Monitoring the remediation process might either verify that the plan is working or provide a quantitative basis for changing the plan to improve the chances of success. Observing contaminant transport in the subsurface has been done almost exclusively through the use of monitoring wells. However, certain situations may
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REALIZING FUTURE CAPABILITIES 125 preclude the use of monitoring wells. Even where wells are allowed, they often may not be the most-cost effective solution, and in many cases they provide limited areal coverage. Noninvasive methods could provide an economical means for large-scale, long-term monitoring and also reveal the dynamics of subsurface processes; for example: · Monitoring of the land surface by remote sensing techniques could pro- vide much information about the subsurface conditions in the top meter or so. · Changes in moisture conditions at the surface could indicate subsurface heterogeneity. Soil-gas surveys could monitor microbial activity or assess the success of remediation schemes. · Repeat geophysical surveys could indicate changes in the distribution of subsurface fluids, which is particularly useful in monitoring contaminant move- ment (e.g., DNAPL remobilization) during site remediation activities. Noninvasive monitoring for prolonged periods of time should be considered an integral part of site characterization, underground construction, and remedia- tion projects that require monitoring. Noninvasive techniques could augment traditional invasive monitoring and enhance our ability to test and develop an understanding of subsurface processes. In some cases, noninvasive methods are the only alternative. The following R&D efforts are needed for this to become common practice: · Geological noise and other factors limit the resolution of a survey method. If the noise does not change with time, then changes in key properties often can be detected with higher resolution than the properties themselves can be mapped. The development of processing and interpretation techniques that take advantage of differential measurements would allow existing tools and survey methods to be used effectively for monitoring. · As new remediation techniques are developed (in situ leaching, bio- remediation, etc.), monitoring properties indicative of the progress of a remedia- tive actions might be difficult using existing characterization tools and survey methods. Fundamentally new tools (such as magnetic resonance imaging and seismic-electric techniques) offer the promise of making measurements previ- ously thought impossible. Monitoring needs for the next decade could require a long-term, sustained program of fundamental research into "exotic" measure- ment technologies. PROPERTIES AND PROCESSES Site characterization historically has focused on mapping the subsurface geometry (e.g., location of anomalies, shapes of boundaries). Physical, chemical, and biological properties and processes (including coupling between processes)
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26 SEEING INTO THE EARTH are at least as important as geometry; however, there has been limited research into the noninvasive measurement of such properties and processes and their distribution. Developing the ability to observe these properties and processes noninvasively will require long-term research, from the perspective of both un- derstanding the phenomena and developing the methodology to measure and interpret these phenomena. Until recently, measurements of properties (e.g., the bearing strength of the foundation material at a construction site) usually have been done on samples obtained by drilling or other intrusive means. Today there is a growing demand for nonintrusive surveys that measure in situ properties (chemical and biological as well as mechanical). For example, no longer is it sufficient to find the top of the saturated zone; now it also is necessary to determine water quality or identify contaminants. In the future, solutions to environmental and engineering problems of the shallow subsurface also will depend on understanding and observing in situ chemical and biological processes and the interactions between them. Characterization methods used to find anomalies or map subsurface geom- etry actually are detecting variations in properties or mapping boundaries be- tween areas of different properties. However, quantitative relationships between the phenomena being observed and the values of the in situ properties usually are not well defined and often involve ambiguity. Therefore, although the location of the variations or boundaries can be mapped, relatively little information about the properties themselves (such as the specific contaminant being mapped) can be determined. The problem is worse if the target involves a chemical or biological process because, in many cases there is little knowledge about the relationship between the in situ process and the phenomena observable at the surface. An example would be the situation wherein a biological agent was introduced into a region containing a chemical pollutant. We know little about whether the biologi- cal process produces any effect that is potentially measurable, let alone how to measure it. As part of a basic research program, there needs to be a signifi cant effort directed toward quantification of physical and chemical realities of what is being sensed as well as possible interactions be tween in situ properties and processes. Some noninvasive methods for subsurface characterization are well under- stood. For instance, there is a good correlation between seismic measurements and the elastic properties of the material being sensed. This is not the case for many other measurements. Fundamental studies should be initiated and expanded to include the following: · Understand subsurface processes and the interactions between them, and
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REALIZING FUTURE CAPABILITIES 127 identify the measurable properties that might be associated with these processes or combinations of processes. Establish theoretical and phenomenological relationships between the properties and processes of interest and the phenomena that could be measured noninvasively at the surface. · Develop instruments and techniques that will allow these phenomena to be measured with useful resolution and adequate signal-to-noise ratio. . . Produce the interpretive tools and procedures to invert the surface mea- surements into an accurate description of the properties or processes at depth. Fundamental studies should be supplemented by variable-scale testing, rang- ing from laboratory examination of cores to full-scale integrated surveys of stan- dard test sites. The National Geotechnical Test Site Program, supported by the National Science Foundation and the Federal Highway Administration and man- aged by the National Council for Geo-Engineering and Construction, might serve as a useful model. Other test sites (e.g., those at the University of Arizona, Stanford University, and the Idaho National Environmental Engineering Labora- tory) have been established for specific research projects. These test sites can be used to develop new techniques and to validate models. OPPORTUNITIES FOR INNOVATIVE MEASUREMENTS Most existing technologies measure physical phenomena and are used to interpret physical properties and processes. Few methods exist to monitor the chemical or biological properties and processes that are becoming increasingly important, particularly in areas such as groundwater management and hazardous waste mitigation. The discovery of fundamentally new measurement technolo- gies, the ability to observe fundamentally new phenomena, and better interaction between disciplines are essential for nonintrusive site characterization to meet current and future needs. Nonintrusive characterization methods inherently rely on "action at a dis- tance." Furthermore, the action at a distance must occur rapidly compared to the time scale of the process in order for the measurement to reflect current conditions. For example, biological agents working on organic pollutants at depth might pro- duce a volatile by-product that can migrate to the surface where it could be mapped with a soil-gas survey. However, if the rate of propagation of the volatile product is slower than the action of the biological agent, the soil-gas survey could be describ- ing conditions that have changed by the time of the survey. The measurement of physical phenomena on the surface to infer physical properties at depth is relatively well developed. However, many of the challenges in site characterization for environmental applications involve interpreting sur- face measurements to infer chemical and biological properties and processes at depth. Methods for accomplishing the latter are not as well developed, and in
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28 SEEING INTO THE EARTH many cases, there are no quantitative measurements that can yield information about such properties or processes. Some physical phenomena can be interpreted to yield such information (for example, subtle features in a ground penetrating radar signal are linked to the chemistry of certain subsurface pollutants); however the relationships between the phenomena and the properties or processes generally are not well understood. There are a few geochemical measurements that also can provide information about in situ properties (the use of "sniffers" to sample gases emanating from the soil), but again the connection between the source and the observation is not always well understood. Furthermore, in many cases involving geochemical mea- surements, the time scale of the phenomenon is long relative to the process being monitored (e.g., the soil-gas survey mentioned above), in which case the mea- surements may be of little practical use. In the future, the committee expects subsurface biological activity to become a major issue; however, the ability to relate surface observations to biological properties and processes is even more limited. A few physical measurements indirectly involve biological agents (for example, spectral imaging can be used to interpret the health of plants that, in turn, can indicate depth to water table). However, there are few, if any, ways to infer biological agents or activity at depth directly from physical observations on the surface. It may be possible to use geochemical observations to infer geobiological properties or processes, but at the present time the capabilities of most of these methods are limited and their efficacy has not been demonstrated. Such measurements also are subject to the time-delay problems mentioned above. The committee believes that the lack of progress in these areas is the result of insufficient research directed to the connections between the physical phenomena and the chemical or biological property or process; part of this is probably a lack of understanding or appreciation of the importance of these problems. However, the problem may be more deeply rooted in the lack of communication between geophysicists, geochemists, and geobiologists. Fragmentation in the traditional earth sciences is well documented (there are 32 separate professional societies that are members of the American Geological Institute and even more that do not participate in this organization), but the gap between fields and geochemistry or (especially) geobiology is even greater. Therefore, any increase in support for research in mapping chemical or biological properties must be accompanied by a commitment to truly effective cross-disciplinary interaction. Long-term research to develop fundamentally new noninvasive tools and techniques should be given a high priority, with emphasis on research done by multidisciplinary teams. Among the challenges in site characterization technologies in the coming decades will be measurement, both direct and indirect, of geochemical and
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REALIZING FUTURE CAPABILITIES 129 geobiological properties and processes. Meeting this challenge will require long- term investment in high-nsk research leading to · A better understanding of the relationship between chemical and biologi- cal properties and processes and physical phenomena that can be measured with existing instruments; . The discovery of fundamentally new measurement technologies that can measure a physical phenomenon that has a causal relationship with subsurface chemistry or biology; make a direct chemical or biological measurement that is diagnostic of conditions at depth; and 3. the ability to observe fundamentally-new phenomena; and · Better data fusion and integrated processing, modeling, and visualization of data from all three specialties. Development of these innovative techniques and measurements will require the following: · Research to be done by multidisciplinary teams; · Cross-disciplinary education of specialists to enhance their ability to work effectively on multidisciplinary teams; . Facilities such as well-controlled test sites that support multidisciplinary development and validation of measurement, processing, interpretation, and mod- eling systems; and · More effective communication and interaction between the biological, chemical, and physical specialists within the site characterization community. Progress in promoting more effective use of existing tools for noninvasive characterization and improving and developing new techniques should lead to a greater understanding of the shallow subsurface and the applications that depend on this understanding. REFERENCES Olhoeft, G. R., 1992. Geophysics Advisor Expert System (version 2.0): U.S. Geological Survey Open-File Report 92-526, 21 pp. and floppy disk. Olhoeft, G. R., 1993. Velocity, attenuation, dispersion and diffraction hole-to-hole radar processing, in Proceedings of the Fourth Tunnel Detection Symposium on Subsurface Exploration Technol- ogy, Colorado School of Mines, Golden, Colorado, 26-29 April 1993, R. Miller, ea., U.S. Army Belvoir Research, Development and Engineering Center, pp. 309-322. Shuirman, G., and Slosson, J. E., 1992. Forensic Engineering, Environmental Case Histories for Civil Engineering and Geologists, Academic Press, Inc., San Diego, California, 296 pp.
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Representative terms from entire chapter: