Combined sewer systems are designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe. Most of the time, combined sewer systems transport all of their wastewater to a sewage treatment plant, where it is treated and then discharged to a water body. During periods of heavy rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other water bodies.
These overflows, called combined sewer overflows (CSOs), contain not only storm water but also untreated human and industrial waste, toxic materials, and debris. They are a major water pollution concern for over 700 cities and towns in the U.S. that have combined sewer systems.
What can we do? 10 things you can do to help prevent storm water runoff pollution.
Use fertilizers sparingly and sweep up driveways, sidewalks, and roads.
Never dump anything down storm drains.
Vegetate bare spots in your yard.
Compost your yard waste.
Avoid pesticides; learn about Integrated Pest Management (IPM).
Direct downspouts away from paved surfaces.
Take your car to the car wash instead of washing it in the driveway.
Check car for leaks, and recycle motor oil.
Pickup after your pet.
Have your septic tank pumped regularly.