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PWSA ramps up its green-infrastructure program

Projects around the city will reduce sewage overflow

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Artist’s rendering of the completed green-infrastructure project at Centre and Herron avenues, in the Hill District
  • Artist’s rendering of the completed green-infrastructure project at Centre and Herron avenues, in the Hill District

In a lot at the corner of Centre and Herron avenues, in the Hill District, a few feet below the surface sits one fix for the bad stuff that happens to Pittsburgh’s rivers when it rains.

Buried here is an array of R-Tanks, black-plastic boxes resembling oversized milk crates. Once in place, they hold the earth apart to create storage space for rainwater until it is either taken up by the plants above or seeps into the water table. The tanks are part of a “cascading bioswale” that runs up Centre’s steep hill. The bioswale will re-direct and sequester rainwater that formerly poured into storm sewers — flushing garbage, motor oil, even untreated sewage a mile south, into the Monongahela River near the Birmingham Bridge.

Most of that water and debris will soon stay put thanks to this project, one of three pilot Pittsburgh Water and Sewer Authority (PWSA) efforts in an ambitious “Green First” program to reduce both local flooding and wet-weather sewer overflows. A federal consent decree requires the Allegheny County Sanitary Authority to protect the rivers from billions of gallons of untreated sewer water, and Pittsburgh is one of 83 municipalities ALCOSAN serves.

Discussion of green infrastructure blossomed a few years back. ALCOSAN had proposed dealing with combined-sewer overflows (CSOs) overwhelmingly with “gray infrastructure”: bigger sewer pipes and larger processing facilities. The U.S. Environmental Protection Agency rejected that plan, and recent local efforts have concentrated on “green” projects that would keep rainwater where it falls, and out of the sewers. Many cities face similar problems, and green-infrastructure advocates say such solutions are ultimately cheaper and more effective, as well as more environmentally friendly. Green infrastructure mimics nature, engineering ways to manage rainwater that hark to when the land was forest and field. Techniques include green roofs, permeable paving and rain gardens. Green stormwater control is gaining popularity with private developers, too. “You see everyone doing it,” says Vivien Li, president and CEO of Pittsburgh-based nonprofit advocacy group Riverlife.

The city-owned Centre/Herron lots sit just downhill from some University of Pittsburgh athletic fields. “I’ve been out here in storms,” says PWSA assistant project manager Megan Zeigler. “It’s a lot of water rushing to this site.” Starting in August, contractors dug out a couple of Western Pennsylvania Conservancy gardens and a curbside strip running a few hundred yards uphill along Centre (1.27 acres, in all). Old catchbasins will be disconnected from the sewer system; rainwater that once fed them will now run onto stone pavers, laid unevenly to slow its flow. Some rainwater will run into the adjacent bioswale, planted with vegetation that can withstand both drought and soggy conditions. Whatever escapes the bioswale heads for those R-Tanks, buried under soil and pea gravel, and swathed in a filtering layer of geotextile.

For unusually heavy storms, there’s also an overflow pipe that does connect to the sewer. Still, says spokesperson Rebecca Zito, PWSA expects that once it’s online, in December, this single project will reduce CSO by 750,000 gallons a year. A similar but more extensive “stormwater park” under construction on two vacant lots high on Garfield’s Hillcrest Street will cut CSO by 800,000 gallons, and reduce flooding in nearby communities. “This will help Shadyside flooding, this will help Polish Hill,” says Zeigler. “This is at the top of the watershed.” A stormwater-sensitive street renovation and raingarden on Melwood Avenue, in Polish Hill, will divert 800,000 gallons. In total, the three projects will cost an estimated $3.3 million, partially offset by funding from ALCOSAN’s Green Revitalization of our Waterways program. 

Given that Pittsburgh now produces 3.07 billion gallons of CSO a year, the 2.47 million gallons these three projects will handle is just a start. But PWSA has earmarked $147.8 million of its 2018-22 capital budget for future green-infrastructure projects citywide. The authority anticipates that green solutions will ultimately handle 32 percent of Pittsburgh’s total CSO problem, says Zito, minimizing the expansion of gray infrastructure. As Zeigler puts it, “These projects aren’t going away.”


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