Resolution 2879 - Laserfiche WebLink

particles, gradually building up the cap, no displacement of contaminated material due to impact is expected to occur during the capping process. The quantity of contaminated sediments released is not expected to occur or to significantly affect nearby biota. The RADCAD dredging and disposal operations will be monitored closely during and after Phases I and II and over the long term to determine if adverse impacts are occurring and whether any remedial action would be required in the event that the CAD technique does not perform as anticipated. 2. Smith Island It should be noted that the three upland alternatives, considered here, have not been submitted for shoreline permit approval. If an upland disposal site is considered, a shoreline permit for that particular site must be submitted for approval. This specific application proposes confined aquatic disposal and alternatives are included for the purpose of comparison. There are three alternative methodologies for upland disposal discussed in the U.S. Army Corps of Engineers Record of Decision: excavated saturated disposal, elevated disposal, and elevated/stabilized disposal. The alternatives would be performed on approximately 110 acres located about 4 miles north of the Homeport site (north edge of Smith Island, west of Highway 99). The alternatives are: a. Excavated/Saturated Disposal The excavated alternative would involve excavating a cell below the existing groundwater level which would be backfilled with contaminated sediments. These sediments would remain saturated and anaerobic over the long term. Saturation of the spoils keeps metals and other substances bonded to the material. If the dredge spoils are dried and are exposed to oxygen, there is a risk of release of toxic substances to the environment. b. Elevated Disposal The elevated version would involve placing the contaminated sediments above existing ground and the water table within a constructed perimeter dike. Because the contaminated sediments would eventually dry and oxidize, liners would have to be included in this alternative to contain potential leachate associated with the aerobic condition. A leachate collection system and a treatment facility to process any leachate collected would have to be included in the elevated design. c. Elevated/Stabilized Disposal The elevated/stabilized disposal version utilizes fly ash, gypsum or some other chemical stabilizer that is used for solidification of the contaminated material. This also involves placing the contaminated sediments above existing ground water and the water table. The solidifier is mixed with the stabilizer as it is placed on the site and allowed to harden to a cement-like consistency. -9-