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Field Demonstrations of Innovative Subsurface Remediation and Characterization Technologies: Introduction 1
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Mark L. Brusseau , John S. Gierke , and David A. Sabatini 1
Department of Soil, Water, and Environmental Science and Department of Hydrology and Water Resources, University of Arizona, Tucson,AZ85721 Department of Geological Engineering and Sciences, Michigan Technological University, Houghton,MI49931-1295 Department of Civil Engineering and Environmental Science, University of Oklahoma, Norman,OK73019
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Groundwater pollution has become one of our most pervasive environmental problems, and remediating sites with contaminated groundwater has proven to be a formidable challenge. Remediation efforts are often limited by the complexity of the subsurface environment, and by our lack of knowledge of that environment. Recent research has focused on enhancing our understanding of the complex subsurface environment and on developing innovative technologies capable of handling these complexities. An important step in the evolution of a new technology is going beyond well-controlled laboratory experiments to testing the technology at the field scale (i.e., real world). The purpose of this volume is to present evaluations of selected innovative technologies that have undergonefielddemonstration testing. This volume also reports on recent advances in subsurface characterization techniques that are critical to the proper design of all technologies, and that can help assess the performance of these technologies.
The Need for Innovative Technologies Initial efforts to remediate groundwater contamination focused on pump-and-treat approaches (flushing water through the formation and treating the extracted fluids). This approach has proven to be generally successful for preventing further spread of contamination (plume containment). Unfortunately, it has been generally ineffective for restoring systems to "pristine" conditions (l-~\ Numerous factors are responsible for the ineffectiveness of pump-and-treat remediation, with one of the most common being zones of high concentrations or large masses of contaminants (i.e., source zones). While pump and treat can effectively manage the dilute portion of the plume, contaminant mass removal from the source zones is usually limited by equilibrium (e.g., solubility) and kinetic (e.g., dissolution, desorption) related
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© 1999 American Chemical Society
Brusseau et al.; Innovative Subsurface Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
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3 constraints. For example, as noted in a recent National Research Council report (3), the presence of immiscible-liquid contamination in the subsurface is often the single most critical factor influencing site remediation. Successful remediation of many contaminated subsurface systems is dependent on the development and implementation of technologies that can control or remove source-zone contamination. If source zones are present, the associated groundwater contaminant plumes can not be remediated effectively unless the source zones are at least controlled. This can be accomplished in a number of ways. For example, physical barriers (e.g., slurry walls) can be used to isolate the source zone, thus shutting off the supply of contamination to the plume. Hydraulic controls can also be used, especially for deep or large source zones where physical barriers are impractical. Of course, the control system will need to be managed "in ρεφβηώγ", which in itself may be costly. A different approach to source control involves altering the chemical nature of the contaminant to reduce its mobility. This may be accomplished, for example, by injecting a reagent that promotes binding of the contaminant to the solid phase of the porous medium. A major technical and regulatory concern for this approach is the potential reversibility of the treatment. An alternative to source control is actually reducing the contaminant mass resident in the source zone. This can be accomplished by either increasing the mass removal rate associated with pump and treat, or by promoting in-situ chemical or biological transformation reactions. Many of the innovative technologies currently in development are focused on source-zone remediation. Introducing chemical amendments to enhance pump-and-treat removal of organic and inorganic compounds is discussed by Palmer and Fish (4). Chemical amendments include complexing agents, cosolvents, surfactants, oxidation-reduction agents, precipitation-dissolution reagents, and ionization reagents. The use of surfactants and cosolvents for enhanced removal of immiscible-liquid contamination has become a major focus of research, and is considered to hold promise for improving site remediation (5). Thus, these technologies are discussed in detail in this volume. Promoting in-situ biotransformation of contaminants is another approach receiving enormous attention. Methods based on this approach are covered extensively in other venues and are therefore not discussed herein. The promotion of in-situ chemical transformations has received much less attention. One example of a demonstration of this approach is covered in this volume. It is important to stress that many of these technologies are designed for implementation in source zones, which are generally much smaller in size compared to contaminant plumes. In addition, many of the technologies are based on the injection of amendments, which may involve a relatively large materials cost. As such, implementation of these technologies can not be viewed in the same manner as traditional technologies. For example, the large materials cost associated with a surfactant flush may be more than compensated by the cost savings associated with the elimination of many years of pump-and-treat operation. Thus, it is important to do a comprehensive cost-benefit analysis as part of the technology evaluation process. The heterogeneous nature of the subsurface is another major constraint to the successful cleanup of contaminated subsurface environments. Clearly, the selection, design, implementation, and evaluation of a remediation system can not be optimized
Brusseau et al.; Innovative Subsurface Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
Downloaded by 80.82.77.83 on May 26, 2018 | https://pubs.acs.org Publication Date: August 5, 1999 | doi: 10.1021/bk-1999-0725.ch001
4 without accurate and sufficient information on the physical, chemical, and biological properties of the subsurface. This includes characterizing (1) the magnitude and variability of important material properties (e.g., hydraulic conductivity, bacterial populations, pH), (2) the type, amount, and distribution of contaminants, and (3) the major contaminant transport and fate processes. Currently, most sites are not characterized sufficiently due to cost and time constraints. The development of new site-characterization technologies will enhance the effectiveness of current remediation technologies and provide the basis for implementation of new innovative technologies. Most current characterization methods are based on "point sampling": groundwater monitoring wells for aqueous samples and coring for solid-phase sampling. Newer technologies based on geoprobes are also point sampling methods. These methods have the potential to provide accurate and precise data for a small domain. This is an advantage for certain applications. However, point-sampling methods are also constrained by the size limitation. Specifically, because of the heterogeneity inherent to the subsurface, it is very difficult to accurately characterize a system without a cost- and time-prohibitive number of sampling points. In addition, the use of geostatistical methods for calculating representative values for the sampled domain is rarely straightforward. Thus, methods that provide measurements over much larger areas are being developed. One such group of technologies is based on the use of tracers. Several examples of "innovative tracer tests" are presented in this volume.
The Need for Field Demonstrations of Innovative Technologies Many groundwater hydrologists and environmental engineers initially thought that groundwater remediation would be relatively simple. Groundwater hydrologists were routinely analyzing well fields, while environmental engineers were adept at designing waste water treatment plants. It seemed that together these two disciplines should be able to design effective groundwater remediation systems. However, it quickly became evident that issues relatively unimportant to groundwater flow were critically important to contaminant transport, and that the subsurface environment is dramatically different from the "ideal" reactors used in industrial facilities. The complexity of the subsurface environment thus proved to have much more of an impact on remediation technology performance than either discipline anticipated. Subsurface complexities also pose a formidable challenge to the feasibility and effectiveness of innovative remediation technologies. As a result, many technologies that performed wonderfully in the laboratory may fail in the field. The key question for any innovative technology is, of course, will that technology perform at thefieldscale? Clearly then, "proof of performance" is central to the acceptance and use of any remediation technology. Unfortunately, however, proof of performance is lacking for many innovative technologies. There are three primary reasons why proof of performance may be lacking for a given technology: (1)field-scaleperformance tests have not been conducted, (2) the available performance data are poor due to poorly conducted tests, (3) the results of properly conducted tests are not disseminated to interested parties. Thefirsttwo factors can be addressed by conducting proper performance tests for the specific technology. A proper performance test should answer these two questions (6): (1) does the technology reduce the risks posed by the contamination (i.e., reduce mass, mobility, toxicity)?; (2) was the technology the cause of the risk
Brusseau et al.; Innovative Subsurface Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
Downloaded by 80.82.77.83 on May 26, 2018 | https://pubs.acs.org Publication Date: August 5, 1999 | doi: 10.1021/bk-1999-0725.ch001
5 reduction? The most important element of an effective performance assessment is a carefully controlled field test of the technology (6). This test should include a comprehensive site characterization and the development of a sound understanding of the factors controlling contaminant transport and fate (7,8). For the third constraint, dissemination of results, Dzombak (9) and Gierke and Powers (7) suggest that the publication venue is a critical component of acceptance. Comprehensive works appearing in refereed literature were found to be the most useful. Conversely, bibliographies, literature reviews and summaries, conference proceedings, newsletters, and database software appeared to be of limited value in selecting and designing innovative treatment systems. The studies presented in this volume were designed to provide an accurate and effective performance evaluation of their respective technologies. Thus, it is hoped that this information will be interesting and useful to those involved in subsurface remediation. Furthermore, we hope that this volume proves to be a successful method of disseminating this information.
References 1. 2. 3. 4. 5. 6. 7. 8. 9.
Keeley, J. 1989. Performance Evaluations of Pump and Treat Remediations. USEPA, EPA/540/4-89-005. 19 pp. Haley, J. L., Hanson, B., Enfield,C.,and Glass, J. Ground Water Monitoring Review. Winter 1991, 119-124. National Resource Council. Alternatives for Groundwater Cleanup; National Academy Press: Washington, D.C., 1994, 315 pp. Palmer, C. D. and Fish, W. Chemical Enhancements to Pump and Treat Remediation. USEPA, EPA/540/S-92/001, 1992, 20 pp. USEPA (U.S. Environmental Protection Agency). 1992. Dense Nonaqueous Phase Liquid-- A Workshop Summary. USEPA, EPA/600/R-92/030. National Research Council. Innovations in Ground Water and Soil Cleanup; National Academy Press: Washington, D.C., 1997, 292 pp. Gierke, J. S.; Powers, S. E. Water Environ. Res. 1997, 69, 196. Brusseau, M.L.; Rohrer, J.W.; Decker, T.M.; Nelson, N.T.;Linderfelt, W.R. 1998, in this volume. Dzombak, D.A. Water Environ. Res. 1994, 66, 187.
Brusseau et al.; Innovative Subsurface Remediation ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
