What is a Combined Sewer Overflow (CSO)?
In St. Joseph, like many older cities, sewer pipes carry both wastewater (used water and sewage that goes down the drain in homes and businesses) and stormwater (rain or snow that washes off streets and parking lots) to a sewage treatment plant. In many parts of St. Joseph, the mixed wastewater and stormwater flow together in a single pipe. This is called a Combined Sewer System.

During a heavy rain the pipes may get too full and start to overflow into the Missouri River. When this happens, it's called a Combined Sewer Overflow (CSO). This provides a "safety valve" that prevents back-ups of untreated wastewater into homes and businesses, flooding in city streets, or bursting underground pipes.

The Combined Sewer System was built as St. Joseph grew during the early 1970's, as an economical way to handle wastewater and stormwater. One advantage of this system is that most of the time, when rainfall is low to moderate, both the stormwater and wastewater go to the treatment plant.

Are CSOs a new problem?
No. When the Combined Sewer System was designed over thirty years ago, it was less expensive than building two entirely separate systems of pipes and tunnels to carry stormwater and wastewater. Before the sewage treatment plants were built, all sewage and stormwater was discharged into the nearest body of water.

The CSO locations were left in place when the present sewer system was updated to act as safety valves when the pipes get too full to handle the high volume of water during heavy rains. The advantage of a combined sewer system is that both stormwater and wastewater are treated most of the time. The disadvantage is that during heavy rains, untreated stormwater and wastewater may be discharged at CSO locations. In fact, there are far fewer overflows now than in the past due to construction projects to control the overflows.

What can I do to keep local water safe and clean?
Remember that what goes down drains may go into the Missouri River. We can all help keep the water clean by:

• Keeping paints, oils, and pesticides out of storm drains.
• Fixing leaks from vehicles.
• Planting a rain garden with native plants.
• Taking cars to a commercial car wash where the water is often recycled before going to the treatment plant.

• Wash it with a biodegradable soap over grass or gravel.
• Use a bucket and a hose nozzle to limit the amount of soap and water used.
• Wash only the outside of the car, not the engine.

How much rain does it take for a CSO discharge to occur?
It varies between CSO locations, depending on how the system has been designed and built. Some locations will have CSO discharges during a moderate summer storm, while other locations will only overflow during the worst storms.

Can CSOs be eliminated?
Yes, they can be eliminated, however, the cost is too much of a hardship.

One way to eliminate CSOs would be to add a separate system of pipes to drain stormwater directly to the rivers. Again, this would be very expensive and would also release untreated stormwater in all storms, which would add chemicals from surface runoff to the water bodies.