Clean Water for the Three Rivers

Speeding up solutions to sewage and runoff pollution in Allegheny County

Building green infrastructure and protecting forests can reduce the amount of stormwater that overwhelms Allegheny County's sewage system and pollutes the region’s waterways.

Matt Antonino |

The Three Rivers are a defining feature of southwestern Pennsylvania. They have shaped the region’s history and provide recreation opportunities and drinking water to the region’s residents today. The rivers and all of the region’s waterways should be safe for swimming and fishing, as intended by the federal Clean Water Act adopted 50 years ago.

Today, the region’s rivers and streams are far from clean, in part because of frequent overflows of raw sewage from the region’s wastewater system – a system stressed as never before by intense rainfall and expanding pavement and rooftops from new development. As a result, untreated wastewater frequently overflows directly into the Three Rivers and their tributaries, polluting the water with raw sewage.

The Allegheny County Sanitary Authority (ALCOSAN) and the municipalities it serves have developed plans that will begin to address the problem of sewage overflows. However, it will take many years to implement these plans and, even when fully implemented, they will not end the problem of sewage overflows.

The region should reduce stormwater runoff and improve quality of life by investing in more green infrastructure and seeking to accelerate fixes to the region’s sewer system. The availability of new federal funding for clean water and the adoption of additional local policies should be used to accelerate the cleanup of Allegheny County’s waterways.

The problem: Currently, across Allegheny County, rain runs off impervious surfaces such as roads, parking lots and rooftops and into the wastewater system, where it mixes with raw sewage. This influx of stormwater, coupled with an aging sewer system, results in untreated sewage being frequently released into the region’s streams and rivers and sometimes backing up into basements and city streets.

  • In a typical year, overflows from the ALCOSAN system spill more than 9 billion gallons of sewage and stormwater into rivers and creeks.
  • Sewage overflows happen from dozens of locations across the county, and in some locations, those releases are frequent occurrences. Roughly 115 locations in the county release sewage- contaminated water to waterways 49 or more times per year.

Unless changes are made, these pollution problems will only get worse in the years ahead. Continuation of current suburban development patterns will increase the amount of stormwater runoff, even from areas with new separate stormwater and sewer systems. This problem will be further exacerbated by increased precipitation as a result of climate change.

  • Annual precipitation has already increased in Pennsylvania due to climate change. Annual precipitation totals from 2000 to 2020 were nearly 5 inches higher than during the 1971 to 2000 period, and annual rainfall could increase by 8% by midcentury. Researchers at the RAND Corporation estimated that the additional climate-related precipitation will cause a greater volume of sewage overflows.
  • Despite a declining population over the first decade of this century, Allegheny County added 20 square miles of developed area, including 9 square miles of impervious surfaces from 2001 to 2011. Most of this development replaced forest, which can absorb tremendous volumes of precipitation, with impervious surfaces, which cause rainwater to flow directly into sewers and streams. With Allegheny County’s population expected to increase by as much as 16% by 2046, continued development in formerly forested areas of the county could add even more impervious surfaces generating even greater flows of stormwater.

ALCOSAN settled a water pollution lawsuit filed by the U.S. Environmental Protection Agency by signing a legally binding consent decree in 2008 to address sewage pollution in Allegheny County’s waterways. By 2020, ALCOSAN developed and received approval for a plan to reduce sewage overflows. The plan will reduce, but not eliminate, sewage overflows: Even after the plan has been implemented by 2036, ALCOSAN projects 2.7 billion gallons of sewage will still flow into the region’s waterways annually.

The Three Rivers – and the other waterways of southwest Pennsylvania – deserve better. Fortunately, there are policy solutions and new funding available for ALCOSAN and its member municipalities to take additional action toward ending sewage overflows as soon as possible. In particular, the region should strive to reduce pollution further by adding more “green infrastructure,” which allows stormwater to
soak into the ground or to flow into streams over time. Recent increases in federal funding provide the opportunity to accelerate progress toward clean water.

  • Pennsylvania allocated more than $200 million to the Water and Sewer program within the H2O PA Program and several million to stormwater management grants through the Department of Environmental Protection. H2O PA’s Water and Sewer program provides grants to help fund the
    construction of storm sewer, sanitary sewer and drinking water infrastructure.
  • The federal Infrastructure Investment and Jobs Act, also known as the Bipartisan Infrastructure Law, will provide supplemental funds to the Clean Water State Revolving Fund (CWSRF) general
    program. From 2018 through 2021, Pennsylvania received approximately $63 million in capitalization funds annually for its CWSRF, allowing it to lend more money each year. This amount could double in coming years as more federal funds are made available.

Municipalities should also accelerate rapid expansion of green infrastructure by creating or improving stormwater management fees. Under these policies, property owners would either adopt measures to stop runoff pollution from their own land or pay to fund stormwater infrastructure projects elsewhere.

  • The Pittsburgh Water & Sewer Authority began collecting a stormwater fee in 2022 that will generate an estimated $21 million annually for infrastructure upgrades. At least eight other communities in Allegheny County and served by ALCOSAN have adopted stormwater management fees.
  • The benefit of stormwater fees would be more far-reaching if municipalities offered rebates and advice to help owners of private property reduce runoff pollution, using rain barrels, rain gardens, permeable surfaces and other techniques.

Allegheny County and its municipalities should also change land use practices to reduce the volume of stormwater runoff polluting the region’s rivers, creeks and streams.

  • Land use and zoning policies should also be changed to prevent runoff pollution. Limiting the loss of forests and focusing development in a more compact manner or in already developed areas can reduce the amount of stormwater generated.
  • The impact of regulations to curb stormwater runoff is partially dependent on how well they are enforced. Municipalities may need to strengthen enforcement to obtain the full benefit of new land use and zoning rules.
Map methodology

Combined and sanitary sewer overflow annual frequencies, durations, volumes and planning basin name were obtained from the ALCOSAN 2019 Clean Water Plan (Allegheny County Sanitary Authority, ALCOSAN’s Clean Water Plan: Section 4, September 2019, Table 4-4 through Table 4-28). Outfalls were sorted by annual overflow volume as determined from a typical year model simulation performed by ALCOSAN, and the 20 outfalls with the greatest annual volume of contaminated water were selected. The corresponding geographic coordinate data, location name, municipality and receiving waterway for the top 20 locations were obtained from the ALCOSAN 2020 consent decree, based on the outfall ID (U.S. District Court for the Western District of Pennsylvania, Modified Consent Decree, 15 May 2020, available at The identifiers for each outfall were not exact matches. For any outfall ID in the format XX-##-OF, the last three characters were removed. Other outliers were adjusted as follows: M-59-DT-IRO was mapped to M-59; C-13A-IRO was mapped to C-13A; and O-14-00-EAST-OF was mapped to O-14E. The points were sized respective to the annual volume of overflows.


Elizabeth Ridlington

Associate Director and Senior Policy Analyst, Frontier Group

Elizabeth Ridlington is associate director and senior policy analyst with Frontier Group. She focuses primarily on global warming, toxics, health care and clean vehicles, and has written dozens of reports on these and other subjects. Elizabeth graduated with honors from Harvard with a degree in government. She joined Frontier Group in 2002. She lives in Northern California with her son.

John Rumpler

Clean Water Director and Senior Attorney, Environment America

John directs Environment America's efforts to protect our rivers, lakes, streams and drinking water. John’s areas of expertise include lead and other toxic threats to drinking water, factory farms and agribusiness pollution, algal blooms, fracking and the federal Clean Water Act. He previously worked as a staff attorney for Alternatives for Community & Environment and Tobacco Control Resource Center. John lives in Brookline, Mass., with his family, where he enjoys cooking, running, playing tennis, chess and building sandcastles on the beach.

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