Resolution 2879 - Laserfiche WebLink

All three alternatives require a containment dike structure with revetments, other extensive site preparations prior to the start of disposal operations, and a cap of clean sediments. None would have the capacity to contain the entire amount of uncontaminated material to be dredged from the East Waterway. An alternative disposal site, probably at the RADCAD site or at an approved PSDDA site, would have to be utilized for the excess material. Approximately 436,000 cubic yards of material would have to be removed from the Smith Island site and deposited elsewhere to provide for the necessary capacity for the excavated alternative. Section 10.1 of Section 404(b)( 1) Evaluation of the Corps ROD provides a discussion of the practicability of the RADCAD and various Smith Island alternatives. Costs, technology, logistics, and potential environmental impacts are compared. The Smith Island and RADCAD alternatives are logistically possible and existing technology can be utilized to perform the work. There are environmental risks associated with each of the alternatives. Losses of suspended contaminated material associated with RADCAD dredging and disposal activities will have short-term impacts on organisms in the water column and adjacent to the disposal site. A short-term loss of 380 acres of deep benthic habitat is expected to result. Some bioaccumulation and transfer of contaminants to higher order food web organisms could occur for a short time following disposal operations. Such impacts are not considered significant. Loss of the existing benthic habitat and associated benthic fauna is expected to be compensated for the long term by colonization of the RADCAD site by juveniles and adults of adjacent communities. While important populations of Dungeness crabs, shrimp, and flatfish are located nearby the disposal site, these organisms are not expected to be significantly impacted by the proposed CAD disposal technique. The RADCAD process will be extensively monitored during and after the disposal to determine the effectiveness of the technique and if adverse impacts are occurring to the species and whether remedial action is necessary. Smith Island alternatives could result in environmental impacts on the surrounding aquatic environment and wetlands habitat from effluent discharge into the Snohomish River, leaching of contaminants from the site into the groundwater or into Snohomish estuary system, or from dispersion of contaminants by flooding and/or seismic events. Materials once in a saturated condition would then be exposed and metals could be released from the spoils in the change from anaerobic to aerobic state. The use of solidification and/or stabilization techniques could also present problems. Although it looks promising, it does not have any long range monitoring to back up its effectiveness. The longest monitoring period has been only about seven years and there has been some indication of mechanical breakdown of the product. There is also a concern about the sheer weight of the solidified material and whether the underlying substrate can support it. Conclusion: Given proper design and controls, RADCAD is feasible and could effectively isolate the contaminants to be dredged from the East Waterway. There would be a breakdown of the spoils when placed in an upland area and the change from anaerobic to aerobic could release metals and other substances into the leachate. Solidification methodologies have no long-range track record, and the weight of the end product could be too heavy for the underlying material on the site. Additionally, the wood waste presently on the site must be removed -10-