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Comment on “A Polymer Membrane Containing Fe0 as a Contaminant Barrier” Shimotori et al. (1) are commended for an interesting study regarding the use of polymers containing Fe0 to improve the performance of barrier systems used for waste containment. The development of reactive liners is an area of waste containment technology that is ripe for research. We were surprised, however, by the sweeping statements made to justify the study. In particular, the Introduction indicates that “leakage through the polymer barrier, however, occurs frequently, and such leakage is a common sediment and groundwater contamination source”. This statement is partly true; all liners leak to some degree, including those that contain a geomembrane (geomembrane is the engineering term generally used to describe polymeric liners). However, the inference that this leakage is a common source of groundwater contamination is patently false. Shimotori et al. (1) go on to indicate that “15% of the current National Priority List (NPL) sites” are landfills. What they fail to state, however, is that the landfills on the NPL generally are unlined dumps rather than modern engineered waste containment facilities with sophisticated barrier systems that include geomembranes. In fact, we challenge the authors to show how many of these NPL sites actually contain a modern liner with a geomembrane. Shimotori et al. (1) also cite two references (2, 3) to support their statements that leakage from geomembrane-lined sites is a common source of groundwater contamination. Review of these documents indicates that they do not support this assertion. Such statements are a disservice to geoenvironmental engineering and professionals practicing in solid waste engineering because they provide misleading information regarding the actual performance of modern barrier systems. Consider the state-of-the-practice review of modern waste containment systems published by the U.S. Environmental Protection Agency (4). This review illustrates that modern engineered landfills are a success story, at least in terms of minimizing the potential for groundwater contamination. Modern liners do leak, but they leak at very low rates and discharge contaminants in small quantities. This is a characteristic of nearly all successful pollution control technologies. Mass discharges are limited to rates sufficiently small so that they can be attenuated by the environment without detrimental impacts. Means to estimate these discharges can be found in refs 5 and 6. We are currently conducting a review of contaminant discharges from landfills in Wisconsin that contain a
10.1021/es049315v CCC: $27.50 Published on Web 08/28/2004
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geomembrane in the liner. Wisconsin is unique in that state regulations required installation of a large (typically 110 m2) pan lysimeter directly beneath the liner of each landfill cell to monitor the quantity and quality of water being discharged. Data from these lysimeters are being used for the analysis. To date, data from 91 landfill cells from 38 different landfills have been analyzed. Concentrations above maximum contaminant levels (MCLs) have been found in 90 out of 1200 samples (≈8%) from cells with liners containing geomembranes. These exceedances mainly have been for VOCs (primarily toluene, tetrahydrofuran, dichloromethane, benzene, and ethylbenzene) and have been modest (typically 10%). The effects of dilution, adsorption, and degradation likely will render concentrations of these contaminants below detectable levels by the time they reach a compliance point (e.g., perimeter monitoring well). The very low concentrations that we have observed suggest that liners in modern engineered landfills in Wisconsin have functioned very well, at least for our relatively short performance record (≈10-20 yr). The U.S. Environmental Protection Agency study (4) suggests that the same can be said for engineered landfills throughout the United States. However, we acknowledge that the performance record is relatively short and that final conclusions regarding the performance of modern waste containment systems can only be made when we have a truly long-term record available (7).
Literature Cited (1) Shimotori, T.; Nuxoll, E. E.; Cussler, E. L.; Arnold, W. A. Environ. Sci. Technol. 2004, 38 (7), 2264-2270. (2) National Research Council. Alternatives for Ground Water Cleanup; National Academy Press: Washington, DC, 1994. (3) Schwarzbauer, J.; Heim, S.; Brinker, S.; Littke, R. Water Res. 2002, 36 (9), 2275-2287. (4) Bonaparte, R.; Daniel, D.; Koerner, R. Assessment and Recommendations for Improving the Performance of Waste Containment Systems; EPA/600/R-02/099; U.S. Environmental Protection Agency: Cincinnati, 2002. (5) Foose, G.; Benson, C.; Edil, T. J. Geotech. Geoenviron. Eng. 2002, 128 (5), 391-403. (6) Foose, G.; Benson, C.; Edil, T. Geosynth. Int. 2001, 8 (6), 551575. (7) Edil, T. Waste Manage. 2003, 23 (7), 561-571.
Craig H. Benson* and Tuncer B. Edil Department of Civil and Environmental Engineering University of WisconsinsMadison Madison, Wisconsin 53706 ES049315V
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