Record of Decision System (RODS)
PUGET SOUND NAVAL SHIPYARD COMPLEX
|Site Name:||PUGET SOUND NAVAL SHIPYARD COMPLEX|
|City & State:||BREMERTON WA 98310|
|NPL Status:||Currently on the Final NPL|
|ROD Type:||Record of Decision|
Alt 3: Dredging with Excavated Confined Aquatic Disposal
Dredging sediment would be used to fill a lined monofill cell constructed in a ravine on BNC land. The cell would include a protective cap and leachate collection and treatment system. The monofill cell would be maintained and monitored.
Dredging with excavated confined aquatic disposal has been chosen as the selected remedy for the marine environment at OU B. The selected remedy includes the following subsections:
Dredging of sediments. Sediments with PCB concentrations greater than the remedial action level of 12 bg/kg OC will be removed by dredging. Sediments will also be dredged in area where mercury concentrations exceed 3 mg/kg and PCB concentrations exceed 6 mg/kg OC. An accumulation of sediments above the level of sill at the moth of Drydock 1 will also be dredged. While PCBs in this area are below 6 bg/kg OC, mercury has been found above 3 mg/kg nearby. Unless the accumulated sediments are removed future drydock usage is likely to resuspend the sediments and put them into circulation in the inlet.
The combined area of sediments to be dredged is approximately 32 acres. The remedial design will require that areas targeted for dredging be dredged to a minimum depth of 2 feet. With an allowance for overdredge depth and side slopes, the volume of impacted sediments to be dredged for environmental remediation is estimated at 200,000 in-place cubic yards. Dredging will be accomplished mechanically with a clamshell bucket or functional equivalent. The selection of specific equipment, such as the type(s) and size(s) of mechanical dredging buckets, and use of an environmental bucket, will be accomplished in the remedial design.
The conceptual dredge design may be modified during the remedial design as more information on logistical constraints becomes available. The intent of the remedial design will be to remove sediments with contaminant concentrations greater than the remedial action levels. However, practical constraints such as vessel moorage requirements, slope stability considerations, and safety issues will be taken into account during remedial design, and alternative FSSUs may be dredged to accomplish a similar reduction in area-weighted average contaminant concentrations. It is expected that there will be instances in which the FSSUs targeted for dredging do not exactly correspond to the areas exceeding the remedial action levels.
Debris or other solid waste may be encountered and removed during sediment dredging. Material that cannot be recycled will be sampled and characterized for off-site disposal. All off-site treatment, storage, and disposal of CERCLA waste will occur at facilities that are acceptable under the off-site rule (40 CFR 300.440) Because the short term risks to construction workers are considered to be greater than any long-term risk reduction accomplished by under-pier dredging, no under-pier sediments will be dredged.
Confined Aquatic Disposal CAD Cell Construction. CERCLA sediments and unsuitable navigational sediments will be disposed of in one or more excavated CAD cells constructed on Navy-owned submerged land. The excavated CAD cells will be constructed off the OU A shoreline in Sinclair Inlet. The CAD cells will consist of one or more pits excavated into the native sediments and occupying approximately 10 acres. The pits will be sized to hold the expected quantities of both CERCLA and navigational sediments, nominally estimated at 300,000 in-place
Estimated Capital Cost: $356,347,000
Estimated Annual O&M Costs: Not provided
Estimated Present Worth Costs: $399,361,000
Total O&M Costs: $ 237,724,000
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