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A view of a final clarifier on Monday at the Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.
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Massive, $2 billion overhaul of area's sewer system revs up with $30 million contract

Steph Chambers/Post-Gazette

Massive, $2 billion overhaul of area's sewer system revs up with $30 million contract

Every flush in Pittsburgh and 82 nearby municipalities is supposed to end up at Alcosan's plant along the Ohio River, but for decades it's been clear that the complex of pumps and tanks is overwhelmed when rain pours into the sewers.

Thursday afternoon, the Allegheny County Sanitary Authority's board of directors took a step toward addressing that, by voting to hire Downtown-based engineering firm Michael Baker International to oversee the decade-long job of expanding the plant. That $300 million-plus project is part of an overall sewer system upgrade that will take twice as long and cost at least $2 billion.

Alcosan plans to double the plant's capacity for treating wastewater and stormwater, and Michael Baker will be paid an estimated $30 million to enforce the schedule, keep costs under control, stay within a cramped 59-acre site and satisfy a host of regulators.

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“If nothing else, this is telegraphing to the world that this is real. We’re moving,” said Alcosan executive director Arletta Scott Williams.

When it’s over — likely in 2027 — the plant expansion is expected to reduce by 3 billion gallons the amount of wastewater that flows, untreated, into rivers and streams each year.

“This is just one piece of the big clean-water plan,” said David Borneman, director of engineering and construction at Alcosan.

“This is the biggest piece in terms of immediate benefit,” added Jeanne Clark, Alcosan’s communications director.

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Solving one-third of the problem

Right now, when it rains, much of what pours into the sewers mixes with human wastewater and overflows into the rivers. In an average year, 9 billion gallons overflows into the rivers, often accompanied by localized floods and basement backups.

The U.S. Environmental Protection Agency and U.S. Department of Justice have been pushing for decades for a dramatic reduction in the overflows, and a pending amended consent decree should set strict timelines.

During and after the plant expansion, Alcosan will be working on other measures for reducing the overflows, including improving the sewer trunk lines, funding “green” landscaping projects that would absorb stormwater, and possibly digging giant underground holding tunnels. All of that is expected to take until at least 2037.

In an effort to start paying for it, Alcosan’s board in November voted on a four-year series of rate hikes that will boost the average household’s monthly sewerage charge from around $32.50 to $42.75 by 2021. Alcosan serves around 823,600 people.

The board voted Thursday to approve a bond borrowing of around $166 million to start paying for the plant expansion and other improvements.

The plant expansion is going to be one of the trickiest parts of the project.

“The plant has to remain in service,” said Douglas Jackson, director of operations and maintenance at Alcosan, even as it undergoes “significant additions within the plant as well as modifications of existing processes.”

Adjusting the flow

Today, all of the water that flows into the plant goes into a giant, round “wet well” 40 feet in diameter and 100 feet deep. The wet well and its pumps can handle 480 million gallons per day. The water is then pumped through screening machines that remove things like basketballs, bottles and rags. The flow then goes through sedimentation tanks as long as football fields, where fats, oils and grease are scraped from the top, and human waste removed from the bottom.

The water then flows through eight outdoor aeration tanks, where microorganisms break down much of the remaining waste.

To get the capacity to 600 million gallons per day, Alcosan is going to have to add another pumping station, new screening machines, and two more aeration tanks. The authority will have to demolish two buildings to make room for the tanks.

The biggest bottleneck is in the next stage of processing, in which the water sits in circular tanks called final clarifiers, stirred by massive arms. Alcosan will increase the number of final clarifiers from 16 to 18, but there’s so little space on the site that they’ll have to build out into the Ohio River channel. (On Thursday, the board voted to hire design firm Arcadis, based in the Netherlands, for $298,924, to study the effects on fish, mussels and other river life.)

Even with the new final clarifiers, that portion of the plant will only be able to handle 295 million gallons per day. So in heavy rains, some of the wastewater will skip that step. More on that later.

Today, water that has gone through the final clarifiers flows back toward the middle of the plant, where it is disinfected with several thousand gallons per day of highly concentrated bleach, then treated with sodium bisulfite to take the bleach out. Then it pours into the Ohio River, adding around 1 percent to the river’s volume. The whole process, from wet well to outflow, takes around 9 to 12 hours.

The expansion will create a new disinfection station and outflow chute, on the facility’s northern end. That new station will handle normal wastewater flows.

When the flows are higher than 295 million gallons per day, the excess will skip the aeration tanks and the final clarifiers and flow straight to the current disinfection station and then into the river.

Alcosan will also build four to six new centrifuges to thicken waste into a sludge. That will be dried and either incinerated or sold as fertilizer for crops used to feed animals.

‘The best team’

The massive job will be broken into phases, all to be managed by Michael Baker.

The process of choosing the manager started in January. Four firms indicated their interest, and three were invited to make full proposals. Alcosan staff and the board’s professional services committee chose from those.

According to Mr. Borneman, the firms were weighed based on their proposed approaches to the project, similar work they had done elsewhere, their experience with Alcosan, their ability to handle the workload and the personnel they planned to assign, their willingness to have an office in Allegheny County and their plans to use subcontractors owned by minorities, women or service disabled veterans.

Michael Baker “had the best team, the best depiction of how that team was going to work together, and how team members have worked together in the past,” Ms. Williams said.

“They need to think in terms of cost and schedule all the time,” Mr. Borneman said. “They are charged with really bringing it in.”

Planning starts promptly, with construction likely to start in 2020.

Store the water, or reduce it?

In the meantime, Alcosan’s board and the federal regulators are wrestling over the measures needed to handle the roughly 6 billion gallons of wastewater that would still flow into the rivers even after a plant expansion.

In some neighborhoods, wastewater and stormwater flow into separate sewers. In others, they flow into combined sewers. Those local sewers are owned by the municipalities.

Converting the region’s combined sewers to separated systems would greatly reduce the flow to Alcosan. The local sewers, though, are owned by the municipalities, not Alcosan. The authority has helped to fund some conversions of combined sewers into separated sewers, but has estimated that the cost of separating out all of the stormwater would be many billions of dollars, according to Ms. Clark.

“There’s going to be a need for likely some form of gray infrastructure, which is this tunneling component,” Mr. Borneman said. Water would accumulate in the tunnel, to be pumped out for treatment over a few days after a rainstorm.

Environmental groups have been arguing that tunneling makes less sense than above-ground landscaping improvements that would keep a lot of the stormwater from entering the sewers.

They’re touting the Pittsburgh Water and Sewer Authority’s citywide efforts “to get the sewage out of the river, reduce flooding, reduce basement backups and give benefits back to the community,” said Tom Hoffman, conservation programs coordinator for the Sierra Club Pennsylvania Chapter.

Expanding the plant is appropriate, but that should be followed by “green infrastructure,” Mr. Hoffman said.

“The tunnels would certainly get the sewage out of our rivers,” he said. “But we feel the green solutions would do that, also, plus bring a lot of other benefits back to neighborhoods.”

Rich Lord: rlord@post-gazette.com or 412-263-1542. Twitter @richelord

First Published: May 17, 2018, 11:55 p.m.

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A view of a final clarifier on Monday at the Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
A view of chlorine contact tanks on Monday, May 14, 2018, at Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
A view of a bar screen on Monday, May 14, 2018, at Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
A view of a wet well on Monday, May 14, 2018, at Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
David Borneman, director of engineering and construction for Alcosan, shows aeration basins on Monday, May 14, 2018, at the Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
A worker walks past aeration basins on Monday, May 14, 2018, Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
A view of the final effluent discharge of purified water going into the Ohio River on Monday, May 14, 2018, at Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
A view of an empty final clarifier on Monday, May 14, 2018, at Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
Director of Operations and Maintenance Douglas Jackson, P.E. shows the chlorine contact tanks on Monday, May 14, 2018, Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
Director of Operations and Maintenance Douglas Jackson, P.E. walks through the Allegheny County Sanitary Authority plant on Monday, May 14, 2018, under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
Director of Operations and Maintenance Douglas Jackson holds a container of dewatered biosoil mixed with limestone on Monday, May 14, 2018, at Allegheny County Sanitary Authority plant under the McKees Rocks Bridge.  (Steph Chambers/Post-Gazette)
Steph Chambers/Post-Gazette
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