It was a good idea at the time. In the mid-1800s, Pennsylvania’s cities and towns wanted to end the stench and slippery surfaces caused by open sewers on streets. Their solution was to get both human waste and rainwater out of sight by shunting them together through buried terra cotta, iron and wooden pipes to the nearest stream or river.

Ruth Hocker, stormwater manager for Lancaster, PA

Ruth Hocker, stormwater program manager for Lancaster, PA, stands by an outfall point where combined overflows of stormwater and sewage empty into the Conestoga River.

This now outdated form of engineering is called a combined sewer system. It is still very common in many older localities throughout the Chesapeake Bay region. In contrast, modern sewer systems in the United States are built with separate pipes to carry sewage and stormwater.

Pennsylvania, because of the age of its communities, has many combined sewer systems. And during rainy days and sudden snowmelts, as water surges through the pipes, that relic from a bygone era overwhelms dozens of sewage plants within the Bay drainage portion of the state.

To keep sewage plants from being inundated — and prevent sewage backups into basements and streets — the pipes are designed to divert overflows of stormwater and raw sewage directly into streams and rivers during heavy rainfalls.

The watery soup can contain a range of contaminants: viruses, coliform bacteria, microbial pathogens and parasitic worms that can be harmful to humans, along with feces, urine, oils and grease and chemicals that harm the environment.

This pollution is called a combined sewer overflow, or CSO.

Across the United States, CSOs have degraded water quality and contaminated drinking water sources. They have also led communities to close beaches, ban swimming and declare shellfish unsafe to eat.

Pennsylvania has the unwanted distinction of having the most CSOs in the nation, accounting for about 17% of the total. Its overflows make up almost two-thirds of all CSO discharges in the Chesapeake region, an area that includes parts of six states and the District of Columbia.

In 2019, according to state records examined by the Bay Journal, 28 Pennsylvania municipal sewer systems released more than 3 billion gallons of stormwater mixed with raw sewage into streams that flow into the Susquehanna River and eventually the Bay.

Many communities contain dozens of individual overflow pipes that discharge into streams. Some of those overflows were caused by as little as 0.08 of an inch of rain. At the Greater Hazleton wastewater treatment plant, 16 different outfalls had overflows an average of 48 days last year. The Ashland Borough Wastewater Treatment Plant had 134 days in which rain triggered a CSO.

Water bursting from manhole cover

Water gushes out of a manhole cover as a surge of rainfall overwhelms underground drainage pipes. In older systems, overflows like these can contain a mix of both stormwater and raw sewage.

A 2019 report by the Environmental Integrity Project found that 58 CSO outfalls in Harrisburg released almost 1.4 billion gallons of combined stormwater-sewage in 2018. One of the 58 Harrisburg CSOs identified in the report came from the governor’s residence. Testing of the Susquehanna River along the city’s popular waterfront park after overflows found unhealthy levels of E. coli bacteria up to 10 times the level deemed safe for swimming. City officials reject such findings, though, saying pollutants coming downriver already make the water unsafe.

Indeed, the state Department of Environmental Protection said it has no record of a CSO being identified as the sole reason for a stream to be listed as impaired.

But some think that may reflect a gap in sampling. Susquehanna River-keeper Ted Evgendiadis said the citizens group is planning to expand testing in Pennsylvania’s other CSO communities.

 A costly and growing problem

Fixing CSO problems is expensive and often requires working around utilities and pipes already buried under streets. Many communities in Bay states struggle to meet cleanup mandates, but some have attacked the problem and seen water quality vastly improve.

For example, the District of Columbia, which was sued because of CSOs, is building miles of massive underground storage tunnels to hold stormwater, then send it to a sewage plant for treatment. The project’s overall price tag — $2.7 billion — illustrates the primary challenge of controlling CSO discharges. But it illustrates its benefits as well. After the first stretch of tunnels went online in 2018, they captured almost 90% of stormwater that normally would go into the Anacostia River — 4.48 billion gallons.

Later that year, the river received its first passing grade in more than a decade from a regional environmental group.

But most communities struggle with the cost of CSO solutions, while the problems are on the rise. Many saw their overflow discharges soar in the last two years, driven by record-setting rainfall. The Mid-Cameron Sewer Authority, which has eliminated its combined sewer system, nevertheless saw its first overflows in years in 2019. 

And a changing climate is likely to make that more common. Scientists say precipitation from extremely heavy rainstorms has increased 70% in Northeastern states, including Pennsylvania, since 1958. Harrisburg saw a 13% increase in rain events of a half-inch to an inch.

Lower Susquehanna Riverkeeper Ted Evgeniadis

Lower Susquehanna Riverkeeper Ted Evgeniadis samples the Susquehanna River in Harrisburg. The Environmental Integrity Project said in a 2019 report that sewage released during combined sewer overflows made a riverside beach unsafe for swimming. (Tom Pelton / Environmental Integrity Project)

The increase in intense rainfall worries regulators in their quest to decrease CSOs.

“There are places where improvements have been made that are getting unmade, due to rainfall,” said James Shallenberger, manager of the monitoring and protection program for the Susquehanna River Basin Commission.

Federal and state agencies have been trying to arrest this pollution since 1994 with varying success.

The U.S. Environmental Protection Agency has fined and obtained consent decrees (legal agreements that set terms for improvements) from 10 of the 28 Pennsylvania communities with CSOs.

The goal is not to completely eliminate all CSOs — the EPA acknowledges that’s economically unfeasible in most cases — though a few communities have done it. Rather, the aim is to reduce the discharges so that they don’t violate water quality standards under the federal Clean Water Act.

Often, that comes down to capturing 85% of stormwater overflows. It’s a daunting and hugely expensive task.

What’s the harm?

How much are ongoing releases of raw sewage harming people, local waterways and the Chesapeake Bay?

In terms of impact to the Bay, it appears not much.

Stormwater delivered by CSOs carries the nutrients nitrogen and phosphorus, the main form of pollution in the Bay and the source of its oxygen-starved “dead zone.” But nutrients from agriculture, sewage plants and other sources dwarf CSO input.

The 927,495 pounds of nitrogen and 112,983 pounds of phosphorus estimated by Bay Program computer models to have reached the Bay from Pennsylvania CSOs in 2018 is less than 1% of the state’s total nitrogen load for that year. They also contributed just 3% of the phosphorous load and 0.3% of the sediment.

Still, that was nearly double the total nutrient contributions from CSOs in the rest of the Bay watershed.

Even if funding materialized for the billions of dollars required to eliminate CSOs from the Bay drainage portion of Pennsylvania, “That money would not show up as a cleaner Bay if that is all we did,” Shallenberger said.

Impacts on local water quality are a greater concern.

Although state laws forbid municipalities from degrading streams, studies about the impacts of CSO pollution on local waterways and drinking water are scarce.

Combined sewer overflow graphic

(Lucidity Information Design)

Most Pennsylvania municipalities with CSOs in the Bay watershed downplay harm and point to the vast dilution effect of relatively clean rainfall mixing with the sewage. As much as 85% of the mix is rainwater, they say. In addition, officials say the “first flush” of stormwater that carries the bulk of pollutants washed off roads, parking lots and lawns does go to a treatment plant before the system begins to generate overflows.

“Of course we impact water quality. Every CSO does,” said Charlotte Katzenmoyer, chief executive officer of Capital Region Water, which maintains Harrisburg’s much-criticized 1880s era sewage system. “But whether we are impacting the Susquehanna with a huge dilution rate and with other pollution loadings coming down, I would be shocked that we would not be able to meet water-quality standards.”

Lancaster city, which sent 514 million gallons of overflows into the Conestoga River in 2019, maintains the releases don’t violate water quality standards except for fecal coliform bacteria. And they plan testing with EPA oversight to prove it. Tests already have proven that no water intakes are affected downriver, said Ruth Hocker, the city’s stormwater program manager.

“The loads are higher coming from upstream problems like failing septic systems,” she said. “If we were to remove all our CSOs, there would still be water-quality problems.”

All cities with consent decrees, including Lancaster, have to post warning signs on streams and rivers where there are CSO outfalls and known swimming areas. Lancaster city’s say,” Warning: Combined Sewage Outfall. Avoid contact with discharge.”

But CSOs are not good for the health of streams, at least in the area of discharges.

Pumping sewage into streams or rivers is never good, said SRBC’s Shallenberger. “Any release of unregulated sewage is something to be very concerned about.”

Greg Scott, who has written about Pennsylvania CSOs for the American Society of Civil Engineers, agreed. “Anything you are doing to put organics into a river is going to have a detrimental impact on the water quality and fish and Chesapeake Bay,” he said.

An EPA official, who asked not to be named, said, “Untreated waters just don’t belong in the water we swim in and drink from. Its time has long since passed.”

Varied solutions

If money was no object, the most direct way to reduce or eliminate CSOs would be to separate the pipes: one system to carry sewage and industrial waste directly to the treatment plant and another to capture stormwater and send it either to the plant or into a stream during severe storms.

But separating a combined sewer system, long-buried under streets and buildings, is complicated and expensive.

Lancaster and Harrisburg are attempting to capture stormwater before it enters the underground system by investing tens of millions of dollars in “green infrastructure,” such as rain gardens, porous pavement and tree plantings. By holding rain on the ground longer, and encouraging it to sink it, they hope to prevent overflows from happening.

Other strategies include enlarging pumping stations to increase stormwater storage and reduce flows by removing illegal connections from sump pumps and rain gutters into sewer.

PA combined sewage overflow map

(Lucidity Information Design)

Some communities are building new treatment plants capable of handling more stormwater, though CSO prevention is rarely the motivation. Williamsport, Altoona and Scranton have built large storage tanks to temporarily store stormwater until treatment plants can again handle the overflow.

All CSO communities must have what the EPA calls Nine Minimum Controls to reduce related problems. They include such things as making sure plastic bottles, litter, plastic bags, cigarette butts and other floatables are captured by screens during overflows, and sweeping streets to minimize the amount of sediment and debris that can be swept into stormwater.

But while CSOs still number in the billions of gallons annually in the 28 Pennsylvania communities that drain into the Bay, some progress has been made.

From 2009–19, nitrogen reaching the Bay from Pennsylvania CSOs declined by 17% and phosphorus by 11%, according to modeling data from the Bay Program.

Twelve combined sewage systems have been completely removed. And five communities have satisfied the terms of their consent decrees. Each of the 28 communities has an approved Long Term Control Plan with time frames to bring down CSOs.

Mark Glenn, the Altoona Water Authority’s engineer, likes to point out that because of CSO reductions and sewage plant upgrades over the last 30 years, two local streams now support trout.

“DEP believes there is a long-term downward trend in the mass of pollutants discharged from CSOs,” the agency said. But it added, “DEP acknowledges that there has also been an upward trend in annual precipitation across the state.”

“There’s more awareness now,” said Scott of the American Society of Engineers. “You don’t see people dumping grass down [stormwater] basins anymore. They’re still working hard at it. But we’re not in a position now to throw money at a problem. If you want it done tomorrow, there is not a program to fund it.” 

Unfunded mandate?

The cost to bring Pennsylvania CSOs into compliance is massive. EPA estimated it at $2.8 billion in 2012.

Harrisburg has launched a $600 million project to correct its many CSO problems. Pennsylvania American Water has committed $140 million to fixing Scranton’s longstanding CSO ills. Lancaster’s next phase will cost $25 million.

Rain garden in Lancaster, PA

A rain garden installed along the Lancaster Brewing Company in Lancaster, PA, is designed to reduce the amount of water traveling through underground pipes by capturing and absorbing some of the stormwater runoff before it enters the system. 

But most of the CSOs in Pennsylvania come from small, depressed communities that cannot afford massive infrastructure overhauls.

“We’re a small beat-up town in the middle of coal country with a pretty elderly population,” said Matt Lawrence, plant manager for the Mahanoy City Sewer Authority, where the average value of a home is just $44,000.  “We just do what we can.”

The sewage system serves a population of not even 4,000 people, and its receiving stream is yellow, a legacy from acid mine drainage. Yet an initial estimate to separate the town’s combined sewers and modify the treatment plant came in at $270 million. The plan was rejected.

In many communities, the overflows are compounded by leaky sewer pipes, which allow groundwater to seep into the system, as well as illegal connections and problems involving pipes clogged with congealed cooking oil.

Sewer authority officials complain of a lack of state and federal funding to help make expensive changes needed to bring down overflow discharges. Instead, most CSO efforts come on the backs of ratepayers.

“All the big shots in Harrisburg don’t understand what it’s like up here in a town with 1,200 people,” said Tony Adami, president of the Galeton Borough Authority. “We’re trying. We’re making progress every year, but it’s not getting done overnight.”

The Williamsport Sanitary Authority, which serves about 51,000 people, has handed out four rate increases of 25% each to deal with its CSOs and sewer plant upgrades to the tune of $130 million so far. Authority board member Wendy Walter complains that the same amount of focus is not placed on a much bigger source of nutrients — agriculture.

“It’s not that we don’t want to. We just want to get the bigger bang for the buck for nutrients,” she said.

The Shamokin Coal Two Joint Sewer Authority, levied with a consent decree in 2012, originally drew up a plan to separate its combined sewer system but abandoned it because of “stark financial realities.”

“We’re $50 million in debt. We’re all for cleaning up CSOs, but [the government has] got to drop some change, too,” said Paul Petrovich, the authority’s general manager.

Many people are still unaware of CSOs and their impact, including some public officials. When Roger Hadsall became manager of Tunkhannock Borough’s Municipal Authority, he was surprised to find out that raw sewage was flowing into a local stream. “I said, ‘What? We let sewage overflow into the creek? We have to stop this.’”

Shallenberger said that reaction is common.

“It is a shock to the senses to hear that sewage is being discharged to our waterways. Lay people don’t expect that.”

Ad Crable is a Bay Journal staff writer based in Pennsylvania. Contact him at 717-341-7270 or

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