The Natural & Logical Drains of Pittsburgh

On a rainy day in Pittsburgh, raw sewage spills out into the river. A marina employee hangs up an orange flag to warn boaters to avoid touching the water while a rowing team splashes past.

There are a lot of rainy days in Pittsburgh.

Moon Over Pitt

(I guess this wasn’t one of them) “Moon Over Pitt” by Flickr user Brook Ward

Typically, around 60 to 70 rainstorms per year cause a combination of sewage and stormwater to overflow at hundreds of points along Pittsburgh’s three rivers. These overflows disrupt the aquatic environment and contaminate the water with potentially disease-causing bacteria and viruses. Officials from the local sewage treatment authority say that fixing the problem will require the most expensive public works project the region has ever undertaken. Community activists say we could do it more economically by using “green” solutions. But whichever methods we choose, the Environmental Protection Agency (EPA) has made it clear: to continue to pollute our rivers is against federal law.

Pittsburgh is not the only city struggling with this problem. Joel Tarr, a professor of history at Carnegie Mellon University, says that large cities all over the Northeast inherited nineteenth century sewer designs that use the same pipes to carry both stormwater and household wastewater. These combined sewer systems were more economical to build than two separate systems and engineers of the time believed that running water purified itself. In 1912 the superintendent of the Pittsburgh Bureau of Construction even declared that “rivers are the natural and logical drains and are formed for the purpose of carrying the wastes to the sea.”

Four years before the superintendent made this statement, the City of Pittsburgh started filtering its water supply. In those four years, Pittsburgh’s typhoid rates — which had been the worst in the nation — dropped dramatically. In 1907, the year before filtration started, there were 4,283 typhoid cases in Pittsburgh. In 1912, there were only 188 cases. By treating the polluted water before people consumed it, Pittsburgh reduced its public health crisis, but that also meant it could continue discharging waste into the rivers. “Of course the downstream cities were not so happy about it,” Tarr says. Eventually, the Commonwealth of Pennsylvania enacted laws to regulate water quality in the rivers.

In 1959, after a protracted debate about the best way to satisfy these laws, the Allegheny County Sanitary Authority (Alcosan) finally opened what was then the largest sewage treatment plant in the nation. It was to treat sewage collected from more than 80 sewer systems, each owned and operated by a different municipality.

Until then, individual municipal sewer systems had discharged directly into the rivers at hundreds of outflow points. To divert these outflows into the treatment plant, Alcosan built an enormous collection system more than 100 feet under the river.

But the engineers were worried about Pittsburgh’s infamous wet weather. Every time it rains heavily, the volume of water in a combined system increases. Although Alcosan’s treatment plant could easily handle the amount of raw sewage entering on a dry day, it just did not have the capacity to treat all the water from a large storm. So they protected the system with hundreds of “escape valves.”

At each point where a municipal sewer reached the river, Alcosan built a shaft that directed the sewage down into the Alcosan system, and at each of these points where the two systems meet, they installed a regulator structure that could divert flow away from the collector system during storms. “Most of them are just big, flat plates,” says Arthur Tamilia, deputy executive director of Alcosan and its director of environmental compliance. “When a lot of water hits them, they tilt so that the majority of the water is directed into the river.” In the language of the EPA, this is a Combined Sewer Overflow (CSO) structure.

Tamilia says that the engineers who designed the CSOs assumed the dilution provided by stormwater would make the overflows less harmful and that the current would carry quickly away any pollutants.

Attitudes are different now. Every time sewage overflows into the rivers, the Allegheny County Health Authority issues an advisory that warns boaters and swimmers to “minimize direct contact” with the water, adding that anyone with a weakened immune system or open cuts is “especially vulnerable to infection from exposure to these contaminated waters.” Marinas and river access points hang out orange flags bearing “CSO” in black letters. On average, these flags fly for about half of the recreational boating season.

In addition to the overflow structures that were deliberately built into the combined sewer system, there are also unplanned overflows from the so-called sanitary sewers that serve the outer municipalities of Alcosan’s treatment area. Sanitary sewers are intended to carry only wastewater and are not connected to stormwater drains. However, stormwater frequently enters these systems anyway, both because aging pipes allow groundwater to leak into the system and because homeowners illegally connect their downspouts to the sanitary sewer system. This means that wet weather can cause overflows of concentrated sewage into nearby streams and eventually into the main rivers.

Sewer overflows of all types are now strictly regulated by the EPA. In 2008, Alcosan signed a legally binding agreement with the EPA that obliges it to eliminate sanitary sewer overflows and to limit combined sewer overflows to no more than 15% of the total wet weather volume of the combined sewer system.

Alcosan’s plan to meet this obligation is to expand their infrastructure. The biggest projects will be to increase the capacity of the treatment plant by around 60% and to build an enormous underground tunnel system to divert and store combined sewage overflows. They propose around 10 miles of 12-14 ft wide tunnels running underneath their existing collecting sewers, which would give the system an additional capacity of 62 million gallons of combined sewage. They estimate the cost at $2.8 billion dollars, which will be paid for by a doubling of homeowners’ sewage bills.

However, the plan still falls short of the EPA’s minimum requirements because 21% of the wet weather volume of the combined sewers would still reach the rivers. The requirement to eliminate sanitary overflows would also not be met, though the volume of sanitary overflows would be reduced by around 90%.

In their submission to the EPA, Alcosan argued that to satisfy their legal obligations by 2026 would require rate increases significantly above the EPA’s own affordability guideline of 2% of median household income. The EPA has yet to approve the modified plan, which was submitted in January, but many ratepayers still consider the plan too expensive.

“It’s the largest public works investment in the history of Allegheny County,” says Jennifer Kennedy, the campaign director for local advocacy group the Clean Rivers Campaign. “It’s going to cost more than Heinz Field, PNC Park, the Convention Center and the North Shore Connector combined.”

The problem, charges the Clean Rivers Campaign, is that Alcosan has focused exclusively on expensive “grey infrastructure” when it should have been pursuing the benefits of “green infrastructure.”

The Clean Rivers Campaign argues that the incorporation of green infrastructure into Alcosan’s Plan would not only be significantly cheaper than the current plan, it would relieve many other problems faced by the region, like flooding, poor air quality and urban blight.

While the goal of grey infrastructure projects is to increase the capacity of the sewer system, the goal of green infrastructure projects is to reduce the amount of rainwater entering sewers in the first place. One approach is to replace impermeable surfaces like concrete with porous paving designs that allow rainwater to soak into the soil and join the groundwater table.

Plants play a crucial role in many of these projects, since they absorb water and then release that water back into the atmosphere as vapor. For example, “green roofs” are partially covered with vegetation and “rain gardens” feature flood-resistant plants in a shallow depression that absorbs runoff. “Even a simple thing like a tree can soak up water and help it go into the air instead of going into our sewer system,” says Kennedy.

In addition to reducing the volume of water in the sewers, these strategies decrease the speed and intensity of runoff during storms, reducing flooding and erosion. Supporters claim the techniques improve air quality, reduce urban temperatures in the summers, provide habitat for wildlife, and even improve property values.

Above all, green infrastructure projects are small-scale and flexible. Matthew Jones, an engineer at a firm that specializes in green infrastructure projects, told the audience at a Clean Rivers Campaign event that one of the key benefits of the approach is that it can be rolled out incrementally and reach areas that might be inaccessible to very large construction projects.

However, this small scale also means that green approaches alone could probably not achieve the reduction in sewage overflows that is mandated by the EPA. What’s more, because the success of these projects is so heavily dependent on local conditions like soil type and weather, it’s difficult to estimate how effective they would be in Pittsburgh without an in-depth site evaluation.

Several non-profit organizations, including the Pittsburgh United coalition, are in the process of trying to quantify the potential of green infrastructure in Pittsburgh. But Tamilia says that the Alcosan plan had to be designed using existing evidence. “The information wasn’t available that would prove to the regulator’s satisfaction that it [green infrastructure] would make a significant difference.”

Kennedy says that the EPA actively encourages communities to embrace green infrastructure. She also says the activists’ dispute with Alcosan is about their failure to address any green approaches at all. “Instead of building giant tunnels first and then adding on green infrastructure later, we think it would be better to see how much water we can capture first, to see how big the tunnels should be” says Kennedy. “In Cincinnati, for instance, they’ve eliminated an entire tunnel system by being able to capture that water and keep it out of the system.”

Tamilia says Alcosan doesn’t have any objections to green infrastructure in principle, but they don’t have the legal power to implement it. The shared sewer authority can’t make urban planning decisions — like mandating green infrastructure standards for new developments — on behalf of its 83 constituent municipalities. “Every community still owns their own sewer system,” says Tamilia. “Right now we’re only able to control what we receive from those communities.”

Kennedy agrees that it’s a challenging issue, but says there are incentive strategies that Alcosan has the legal power to use.

But Alcosan is not the only organization under scrutiny. The municipalities are also being compelled to address the sewer overflow problem by the Allegheny County Health Department and the Pennsylvania Department of Environmental Protection. Although individual municipalities may be in a better position to implement green infrastructure strategies, their feasibility studies are not due until July of this year. This means Alcosan could not take the municipal plans into account in their stormwater plan that was due to the EPA in January. They built the plan around the assumption that municipalities would not reduce the amount of sewage they produce in the future.

When Alcosan released their stormwater plan for public comment last July, there was widespread community outcry about the cost and focus on grey approaches. In response, Alcosan requested an 18 month extension from the EPA to allow them to conduct its own feasibility study for green infrastructure.

Until the EPA reviews the stormwater plan, no one knows whether it will grant the extension. If there is an extension, it’s not clear whether Alcosan will judge green infrastructure approaches to be feasible or useful. Nor do we know whether Alcosan and its constituent municipalities will be able to work efficiently together or consolidate some of their infrastructure, as recommended by the Sewer Regionalization Review Panel, a committee of local stakeholders.

But one thing we do know is that grey infrastructure will be the backbone of Alcosan’s plan. “You will not be able to rely completely on green technology to cure these problems,” says Tamilia. “We’re looking at a combination of green and grey.” And since the proposed construction won’t be finished until at least 2026, Pittsburgh residents should continue to watch for orange flags flying along their rivers.

Picture of row crew in Pittsburgh

“Crew” by Flickr user Matthew Niemi

Where to learn more:

3 Rivers Wet Weather: 3RWW is a non-profit environmental organization that is helping Allegheny County municipalities work together to address sewer system problems. Their website has lots of educational information and resources.

And that concludes my little series of class assignments!


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