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• i 45@4. Federal Register/Vol. 6E, No. 11 /tA~ednesday,~~January 1?, 2001/Rubs and Regn!ations discussion regarding the discharge of pollutants. These scientists contended that mechanized excavation and drainage activities in wetlands, rivers and streams almost always cause the discharge of pollutants into waters of the U.S., and frequently result in severely harmful environmental effects. They noted that it is well-established in the peer-reviewed scientific literature that wetlands and many parts of river and stream beds act as natural sinks, collecting sediment, nutrients, heavy metals (e.g. lead, mercury, cadmium, zinc) toxic organic compounds (e.g., polycyclic aromatic hydrocarbons- PAHs, polychlorinated biphenyls-PCBs) and other pollutants which enter wetlands through polluted runoff, direct discharges, and aunospheric deposition. Moreover, they provided citations which describe other characteristics of wetlands and water bottoms that also play an important role in storing precipitated metals and other pollutants. For instance, over time, fresh layers of sediment added to wetland and river and stream beds can gradually bury and sequester trace metals and toxics. Vegetation also helps soils immobilize toxins and heavy metals by attenuating flow of surface waters and stabilizing the substrate, allowing metal- contaminated suspended particles to settle into sediment. Furthermore, these commenters cited scientific literature which illustrates that wetland soils and river and stream beds immobilize toxins and heavy metals and other pollutants. BrieFly summarized, these indicate that anaerobic conditions occur when wetland, river, and stream soils are saturated by water for a sufficient length of time; microbial decomposition of organic matter in the sediment produces anaerobic conditions. The anaerobic soil environment, with the accompanying neutral pH levels and presence of organic matter in the sediment, triggers different chemical and microbial processes in the soils. These characteristic conditions of wetland, river, and stream soils result in the precipitation of trace and toxic metals as inorganic compounds, or complexed with large molecular-weight organic material-effectively immobilizing these compounds. These commenters maintained, and provided citations illustrating, that when a wetland is ditched or drained. or a riverbed excavated, channelized or dredged, mechanized activities dislodge some of the sediments and resuspend them in [he water column from both the bottom and the sides of the ditch or other waterbody. Watet draining from ditched or excavated wetlands carries suspended sediments down ditches to receiving waters; similar resuspension and downstream movement occur when river and stream bottoms are channelized. They furthermore provided supporting literature from scientific journals documenting that when wetlands are ditched or drained or rivers and streams excavated, some pollutants move into the water column. As described, when wetlands soils are exposed to air, the anaerobic, neutral pH conditions that promoted toxins and heavy metals to precipitate-out can shift to aerobic conditions, and the soil chemistry is transformed by the oxidizing environment and possible shik in pH. The mobility of metals bound in sediment is generally determined by pH, oxidation-reduction conditions, and organic complexation- thus, precipitates may begin to dissolve and become available for transport when soils are exposed to air. Contaminated sediment resuspension does not usually result in a pH change in rivers; but there, as in wetlands, microbial action can release such pollutants as trace elements during the reoxidation of anoxic sediments that subsequently flow into drainage ditches and into receiving waters. Finally, commenters from the science commtmity pointed out that turbulence prolongs the suspension of sediment and contaminants in the water column, so moving water (e.g., drainage ditches) retains suspended materials longer than standing water. In general, organic chemicals and toxic metals are more likely to be attached to smaller, lighter particles, which also are more likely to remain suspended in the water column. The commenters noted that smaller particles may also give up organic chemicals more efficiently than lazger particles. Thus, they assert, exposing contaminated sediment to the water column causes some dissolution of pollutants, while the direct discharge of sediment into the water during dredging accelerates the release of contaminants. The agencies thank these commenters for their detailed discussion of current scientific literature, which we have included in the administrative record. We agree that the evidence presented points to the harmful environmental effects that can be associated with redeposits of dredged material incidental to excavation activity within a particular water of the United States. even those redposits occurring inclose proximity the point of initial removal. To the extent commenters believe that we should determine the scope of our jurisdiction based on such environmental effects, however, we decline to do so. As stated previously, today's rule does not adopt an effect- based test to determining whether a redeposit is regulated, but instead defines jurisdiction based on the definition of "discharge of a pollutant" in the Act and relevant caselaw. We have chosen to define our jurisdiction based not on the effects of the discharge. but on its physical characteristics-i.e., whether the amount and location of the redeposit renders it incidental fallback or a regulated discharge. Nonetheless. the evidence reviewed in these comments points to serious environmental concerns that can be associated with redeposits other than incidental fallback (which are regulated under today's rule), and support the agencies' view that it would not be appropriate, as suggested by some commenters, to establish quantitative volume or other "significance" thresholds before asserting jurisdiction over such redeposits. One technical commenter contended that the likelihood of toxicant release and mobility is many times greater for navigational dredging than it is for most other excavation activities, especially in wetlands. This commenter asserted that the primary reason for this is that the vast majority of excavation projects that would be subject to the proposed rule do not have toxic substances in toxic amounts present in the natural soils, but many navigational dredging projects in commercial ports do. The commenter stated that while it is true that some contaminants maybe more mobile in an oxidized than reduced state, the conclusion that contaminants will be released from normal excavation project activities is without technical merit. The commenter further recommended that since the effects of navigational dredging were determined tc be acceptable, the results of those same studies should be used to establish what is more than incidental fallback. As noted in today's preamble, the potential for release and distribution of pollutants contained in dredged material is a factor that would be considered in determining if a regulable discharge of dredged material beyond the place of initial removal results. We do not agree with the apparent suggestion that wetlands soils are necessarily in a pristine or natural state. As discussed in the proposed rule's preamble, wetlands can act as sinks for pollutants, and sequester contaminants. In addition, we note that the 404 pcogram applies to waters of the U.S., which include not just wetlands, but rivers, lakes, harbors and the like as well. Finally, we do not agree that the environmental effects of harbor dredging should somehow be