A new pipeline along Crabtree Creek could help keep sewage from spilling into rivers and streams during significant rain events like the one on Saturday night.
Crews are drilling tunnels and installing a 54-inch pipe adjacent to two existing 36- to 60-inch pipes that follow the creek, on each side. The two lines run near capacity at peak times, hauling about 20 million gallons to the city’s wastewater treatment plant – nearly half the volume arriving at the plant on an average day. During heavy rains, runoff and groundwater can flood into the pipes and cause them to overflow.
During Saturday night’s storms – more than 6 inches of rain fell in some parts of the Triangle, causing creeks and streams to jump their banks – and the already-full pipes couldn’t accommodate the extra water.
“There’s just too much water, and the pipes aren’t big enough to contain it,” said Eileen Navarrete, a construction projects administrator for the City of Raleigh.
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Raleigh crews reported sewage spills in seven places late Saturday, dumping more than 150,000 gallons of a slurry of sewage, rainwater and paper debris into Walnut, Crabtree and Big Branch creeks. About 130,000 gallons reached Crabtree Creek, Navarrete said.
The debris that accompanied the sewer water has been cleaned up in all but one area, which was too wet to access yet, said T.J. Lynch, assistant director of the City of Raleigh Public Utilities Department.
The Crabtree Creek drainage basin includes about 93,000 acres in Wake and Durham counties. In the area that runs along Crabtree Creek, the city’s utility crews conduct regular maintenance with smoke to find places that have broken or are missing covers, and could allow water to flow into the system, Lynch said.
During heavy storms, gaps that crews may have missed, manhole covers and breaks or gaps in underground pipe sections can allow water to spill in the system and cause it to overflow, he said. Planners think that adding the new 54-inch pipe should make sewer overflows in the area a thing of the past.
The new roughly $35 million pipeline is slated for completion in late 2018. It will run between 20 and 30 feet below ground for about four miles along Crabtree Creek, from just outside the Beltline near Glenwood Avenue to just east of Capital Boulevard.
Pipe has been laid in five of eight planned tunnels that will carry the pipe under roads and a rail line, she said. When the tunnels are completed, another contractor will connect them with pipe laid in open trenches.
The boring process is similar to what is used to build road tunnels and is slow-going. Typically, a crew can bore 50 to 60 feet a day in soft ground, but if they hit rock, progress can slow to as few as 6 feet, Navarrete said.
The weekend storms and creek overflows also caused trouble for Bradshaw Construction Corporation, the company digging the tunnels. The contractor had dug two deep pits and was ready to begin drilling a tunnel under a Yadkin Drive bridge passing over the Crabtree Creek and Greenway Trail.
On Monday, crews were busy shoring up the pits with gravel, and draining out silt and muddy water, but the setback will likely not cause major delays, she said.
The pipeline is part of a larger, roughly $80 million project known as the Crabtree Basin Wastewater System Conveyance Improvements.
The city is simply calling it the “Crabtree Pipeline” in its public information campaign, which includes a website, crabtreepipeline.com, as well as a phone number and email. Residents within 1,500 feet of the project are also notified with mailers.
The city already has completed two parts of the project: repairs to the existing pipeline and 21,000 feet of new pipeline running from Capital Boulevard to where it meets the U.S. 64/264 bypass ramp and the Beltline.
The project’s final portion calls for improvements and expansions of the Crabtree lift station, which is at the intersection of the U.S. 64/264 bypass ramp and the Beltline.
Chris Cioffi: 919-829-4802, @ReporterCioffi