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WHO SAYS YOU CAN’T PUSH HDPE? - CRESCENT CITY WATER POLLUTION CONTROL FACILITIES OUTFALL PROJECT
Author: Robert L. Allen and Bill Faisst , Brad Hamad, Ward Stover (Stover Engineering); Jim Barnts (Crescent City Public Works, Crescent City)
Date: 3/206
No Dig 2006 Conference

The City of Crescent City currently discharges treated effluent to the Pacific Ocean on the south side of Lighthouse Island, at a depth of about 15 feet in the surf zone. The City first used this discharge location in the late 1950's. Most of the pipeline from the City's water pollution control facility (WPCF) is 12-inch-diameter ductile iron pipe with very limited hydraulic capacity. Pumping is required to convey existing flows with a maximum capacity of about 8 million gallons per day (mgd). Brown and Caldwell designed a new parallel pipeline from the WPCF to the existing discharge location to increase gravity discharge to 17 mgd. The new 23-inch-diameter pipeline is about 1,500 feet long installed by directional drilling, selected to minimize construction impacts to Lighthouse Island and the intertidal zone. The pilot hole entry pit located near the WPCF and the pilot hole was constructed from the land side of the horizontal directionally drilled (HDD) installation toward the Island. Generally, the reamer is attached to the drill string on the bank opposite the drilling rig and pulled back into the pilot hole. However, in this project, two reamers were pushed into the pilot hole to enlarge the hole. By pushing the pipe into place, no heavy equipment was mobilized on the Island nor was a pulling barge used offshore. Given the option of using press-fit connected steel pipe or high density polyethylene (HDPE) pipe, the contractor selected HDPE pipe. The cost for construction of the outfall was $2.1 million; the total project cost, about $2.5 million. The City of Crescent City currently discharges treated effluent to the Pacific Ocean on the south side of Lighthouse Island, at a depth of about 15 feet in the surf zone. The City first used this discharge location in the late 1950's. Most of the pipeline from the City's water pollution control facility (WPCF) is 12-inch-diameter ductile iron pipe with very limited hydraulic capacity. Pumping is required to convey existing flows with a maximum capacity of about 8 million gallons per day (mgd). Brown and Caldwell designed a new parallel pipeline from the WPCF to the existing discharge location to increase gravity discharge to 17 mgd. The new 23-inch-diameter pipeline is about 1,500 feet long installed by directional drilling, selected to minimize construction impacts to Lighthouse Island and the intertidal zone. The pilot hole entry pit located near the WPCF and the pilot hole was constructed from the land side of the horizontal directionally drilled (HDD) installation toward the Island. Generally, the reamer is attached to the drill string on the bank opposite the drilling rig and pulled back into the pilot hole. However, in this project, two reamers were pushed into the pilot hole to enlarge the hole. By pushing the pipe into place, no heavy equipment was mobilized on the Island nor was a pulling barge used offshore. Given the option of using press-fit connected steel pipe or high density polyethylene (HDPE) pipe, the contractor selected HDPE pipe. The cost for construction of the outfall was $2.1 million; the total project cost, about $2.5 million.

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