Most areas in the City of Pittsburgh have combined sewers, which means that stormwater and sewage are carried in the same pipe. The average rain storm will cause this system to reach capacity and overflow, discharging a mix of stormwater and sewage into the rivers. This is known as a Combined Sewer Overflow (CSO).
What is a Sewershed?
A sewershed is the area of land where all the sewers flow to a single end point. As with watersheds, sewersheds can be large or small. Many smaller sewersheds lead to larger conveyance pipes, eventually leading to the ALCOSAN wastewater treatment plant. In Pittsburgh, there are many places where sewage can overflow into rivers or streams when stormwater fills up the pipes. We define the area that drains to each of these diversion points as a sewershed.
The above map delineates the different sewersheds in the area, the dark green are combined sewer areas and the light green are separated sewer areas. Type in your address in the search bar above to find out what sewershed you live in and how much your sewershed contributes to overflows into our rivers. To see what parts of the city generate the most overflow volume in a typical year, navigate to the legend on the top left corner of the map and check the "Priority Sewersheds" box.
Click on a sewershed to see details about it. The table contains information on whether the sewershed is combined or separated, the point of connection, the overflow volume in a Typical Year (TY) and other statistics. The Typical Year is based on historic trends and precipitation data from 2003. The sewershed listed as "Targeted for GI" are those where less than 85% of wet weather volume is conveyed to the wastewater treatment plant in a typical year. The table also includes statistics on average annual runoff for each sewershed. These estimates area based on modeling simulations that take into consideration the land use and topography of each sewershed.
You can make a difference and help reduce overflow volume!
Green Infrastructure allows rain to soak into the landscape and stay out of the sewer pipes.
Learn more about how you can incorporate green infrastructure on your property and in your community.
Conserving water when it rains can also reduce CSOs. If less water enters the sanitary sewer, flow coming from homes and businesses, the combined sewer system will have more capacity to manage stormwater.
Here are some ways you can reduce stress on the system during storm events:
Wait to do laundry
Take a shorter shower (or take one later)
Wait to flush the toilet
Here are some ways you can conserve water every day:
When doing laundry, always wash full loads.
The same applies when using a dishwasher—only run full loads.
If washing dishes by hand, fill up the sink instead of leaving the water running.
When it’s time to replace your washer unit or dish washer, choose a high efficiency washer with a low water factor.
Check water bills for high water use instances to identify leaks.
Use low-flow shower heads and faucet aerators to reduce water use.
Don’t leave the water running when you brush your teeth.
Use a broom to clean your driveway or sidewalks instead of hosing them down.
Set up a rain barrel to reuse water for irrigating your lawn and plants.
If you live in a separated area, you can help improve water quality!
Although the separate sewer system does not carry sewage to the river during wet weather events (as the combined sewer system does), pollution carried by stormwater does degrade the water quality of our rivers. Stormwater collected in these pipes is not treated before being discharged into our rivers. As stormwater runoff flows over roads, rooftops and other impervious surfaces, it collects debris, oils,animal waste, salts, eroded soils, and other bacteria and metals, polluting the water.
Learn more about what you can do to prevent this pollution.