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Alcosan project will leave sewage tunnels flush with cleanness

| Monday, Feb. 18, 2013, 12:13 a.m.
Tim Prevost, right, manager of Wet Weather Programs for ALCOSAN, decribes the process used by the Doetsch Company, which is cleaning out 1, 200 feet of sewer tunnel along the North Shore of Pittsburgh. Heidi Murrin Pittsburgh Tribune-Review

The rushing sound that more than a half-century's worth of grit makes as it's pumped from a 5-foot-wide sewage tunnel 80 feet below the Allegheny River brings a smile to Timothy Prevost's face.

“The guys like to say that's the sound of money,” said Prevost, manager of wet-weather programs for the Allegheny County Sanitary Authority.

It really is.

ALCOSAN is paying Detroit-based contractor Doetsch Environmental Services a $270 performance bonus for each ton of debris workers blast out of the line, using 60,000 gallons of highly pressurized river water each day.

Submersible pumps bring the grime to the surface, where it's shipped to a landfill in sealed, truck-size orange containers situated next to the Confluence Building and the Morgan at North Shore Apartments.

Prevost said workers shut down noisy generators and engines by 7 p.m. so they don't disturb residents. Neighbors said they aren't bothered by noise and haven't noticed an odor.

Doetsch built a long, plywood conduit to contain the pipes so the North Shore Riverfront Trail could remain open to pedestrians without the need for a detour.

In January, the firm extracted about 100 tons. Work on a 1,200-foot-long section of the sewage tunnel began in December and is expected to wrap up this week. Doetsch won a $712,000 contract to do the work last year.

Prevost, a civil engineer, is overseeing the progress. It's the first time since ALCOSAN was formed in 1946 that the high-density concrete tunnel is being cleaned. Workers encountered bricks and large rocks that slowed progress because they can't fit through the pumps.

“It's a very difficult operation, so it's not something that's typical,” Prevost said.

Sonar inspections of the deep tunnel indicated a significant amount of debris. He said some of the debris, grit and rocks flows into the system from a stream that runs through the Spring Garden neighborhood of the North Side and from drainage through the East Street corridor along the Parkway North.

“We knew what was in the line; we just needed to figure out how to get it out,” he said.

Removing the debris will increase the sewer line's capacity and help ALCOSAN comply with a Environmental Protection Agency consent decree to reduce the sewage overflows into waterways during storms. On a dry day, the line handles about 16 million gallons, but in wet weather, that amount can spike.

Construction costs to upgrade the system could top $2 billion, making it the largest public works project in Allegheny County history.

“We're required to address the situation of debris coming into the lines,” Prevost said. “If I have a pipe that's half full of something, that means I only have half of that pipe to have water and sewage flow through it. I'd rather have full capacity.”

Jeremy Boren is a staff writer for Trib Total Media. He can be reached at 412-320-7935 or jboren@tribweb.com.

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