Wet Weather and its Effects
Sewage is polluting one of the region’s greatest resources—our waterways—and
threatening public health and the environment. Wet weather is defined as rain or snow
melt. Excess water gets into the sewage collection system and overflows.
The Pittsburgh region’s frequent rainfall brings an underground, out-of-sight problem
into clear view. As little as one-tenth of an inch of rain—an average Pittsburgh rainfall is
one-quarter inch—can cause raw sewage to overflow into our rivers and streams.
Melting snow can cause the same effect. During dry weather, the sewage collection
system, which transports wastewater from thousands of homes to the wastewater
treatment plant generally operates effectively. However, during wet weather, extra storm
water gets into the sewage collection system through direct connections or through leaky,
cracked pipes. This extra volume of water overloads the sewage collection system pipes
and raw sewage overflows from manholes or floods homeowners’ basements before it
reaches the treatment plant.
Wet Weather and Public Health
The effects of wet weather can last for days after rain falls or snow melts. These
overflows contaminate our waterways with bacteria and viruses.
Wet weather causes our sewer system to overflow. Due to sewage overflows, our
waterways are contaminated and present a health risk to the public. Physical contact with
the water while boating or swimming can expose an individual to disease-causing
organisms. While this exposure may not be fatal for a healthy adult, it can be deadly for
those with weaker immune systems, the elderly and small children.
In addition, Pittsburgh’s three rivers serve as the main source of drinking water for 90%
of Allegheny County residents. While the public water systems do an excellent job of
purifying the water before sending it to homes, source protection is the cheapest and most
effective way to ensure drinking water quality.
What Is a Sewage Overflow?
Sewage overflows occur during wet weather (rainfall or snow melt). The excess water
gets into the sewer system and overflows into rivers and streams before reaching the
treatment plant. Hundreds of overflows, which violate the Clean Water Act, occur across
Allegheny County during each rainstorm. The Clean Water Act prohibits any person or
entity from discharging pollutants (such as sewage) into waterways without a permit.
The Act requires that communities eliminate all overflows from separate sanitary systems
and significantly reduce overflows in combined sewer systems.
Why Do Sewer Overflows Occur?
Untreated sewage overflows from the sewer system during wet weather because the
century-old collection system cannot handle the extra storm water that seeps into the
pipes. Storm water enters the system through improperly connected rainspouts and
driveway drains and cracked, and deteriorated sewer pipes.
Knowing your Sewer System
Types of Sewers
Sanitary Sewer System (SSS) - Carries sewage only. Overflows from these systems,
called sanitary sewer overflows (SSOs), are illegal and include overflowing manholes
and basement back-ups.
Combined Sewer System (CSS) - Carries both sewage and storm water. Overflows from
these systems, called combined sewer overflows (CSOs), must be reduced from about 60
occurrences a year to no more than four. While CSOs occur primarily from large
overflow pipes along rivers and streams, they also include overflowing manholes and
basement back-ups.
What Can You Do To Help Reduce Sewage Overflows?
Redirect your downspouts so that the rain is absorbed into your yard or garden, rather
than running down the driveway or into the street.
Install a rain barrel to help capture and store rainwater that can be used on your lawn and
garden. It helps to reduce the amount of storm water that flows into the sewer system,
keeps water out of your foundation drain and provides a source of soft water at the right
temperature for your garden or lawn.
Plant trees and other vegetation to help reduce storm water run-off by allowing rainwater
to soak into the ground.
More Helpful Ways to Reduce Sewage Overflows
Use only toxic-free home and garden products. When it rains, pesticides and other
chemicals are washed into the stormwater system and deposited directly into the rivers.
If possible, wash your car at a commercial self-car wash that recycles wash water. If you
do wash your car at home, wash it on your lawn so the water is soaked up by the ground,
use environmentally safe products and don’t leave the hose running continuously.
Water your lawn and garden in the morning when less water is lost to evaporation and
limit it to one hour a week. Healthy grass only needs about 1 inch of water a week. Keep
the grass cut at about 2.5-3 inches so it doesn’t dry out as quickly.