The McNary Dam Juvenile Bypass System Outfall Pipe Relocation was a fast paced project to remove and replace an existing juvenile bypass system outfall pipe. The project included the installation of 3,000 feet of new outfall pipeline, with 1,200 feet placed in the Columbia River.
The outfall portion of the project included the installation of 24 total steel cased drill shafts placed in the river. AAC constructed a special barge to facilitate the over water drilling. Special anchoring devices were developed to hold both the barge and drilling casing in place against the fast moving current. The 48-inch diameter shafts had an additional 60-inch diameter cap pour to support the pipe saddles.
The upland work included 900 feet of 42-inch buried HDPE pipe that spanned between the steel pipe to the 36-inch u-shaped corrugated metal flume section. Work to the existing fish facility included an 18-inch secondary bypass line, 30-inch raceway drain pipe addition and demolition of the existing 36-inch CMP outfall.