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What is a combined sewer overflow? Combined sewers collect wastewater and storm water flow in a single system of pipes and transport it to a wastewater treatment plant. Wastewater is water and sewage that goes down the drains in homes and businesses. Storm water is water from rain or snow that washes off streets and parking lots. One advantage of the combined system is that both wastewater and storm water from small storms are treated before they are discharged to area waterways. However, during heavy rains, the storm water flow increases. When the pipes get too full, the combined sewer overflows into area waterways. These constructed overflows prevent street flooding and backups into homes and businesses. However, the untreated water that overflows into area waterways may contain impurities that could adversely impact water quality. No, combined sewer systems date back to the 19th century. It was less expensive to build one system of pipes to carry storm water and wastewater to rivers and streams. When treatment plants were built, the combined flow was treated at the plant, except during periods of heavy rain. Then, the combined sewer overflows acted as a safety valve that protected property by discharging the wet weather flows to area rivers. Early in St. Louis history, CSOs discharged at many points. Today there are fewer overflows than in the past because MSD projects have reduced the overflows. How many CSOs are there in the St. Louis area? There are 208 locations where CSOs can occur in MSD’s service area. The CSOs discharge to the Mississippi River, River Des Peres and their tributaries. How much rain does it take to create a CSO discharge? It varies among the CSO locations, depending on the system’s design. Overflows can occur at various times of the year. Some locations will have discharges during moderate rain. Others will overflow only during heavy storms. What is the impact on the water in our rivers and streams? Again, it varies by CSO location. In St. Louis, our most common CSO water quality problem is “visual pollution” from trash that is swept into our waterways. Generally, any pollutants in the discharge have higher concentrations during the first 15 minutes of an overflow event. Many of our CSO solutions are designed to contain this initial water flow, limiting the impact of CSOs. Do CSO’s threaten our water supply? No, the only water treatment plant located on the Mississippi River is the Chain of Rocks Plant operated by the City of St. Louis Water Department. St. Louis CSOs have no impact on this plant. Why is it important to learn about CSOs? MSD is committed to providing information about CSOs, their environmental impact, and action steps for residents and businesses. We have brochures available and representatives who will speak to local groups. As part of our public information program, MSD is posting signs near CSO locations. The signs warn people to stay out of the water during and after a heavy rain. What do the CSO warning signs mean? MSD CSO signs provide a warning of possible impurities in the water during and after a heavy rain. The signs warn people to stay away from the water. The signs also provide a phone number (314-768-6260) so residents can notify MSD of any dry-weather CSOs. Normally CSOs only occur during wet weather, so water flowing out of a CSO outfall pipe during dry weather may indicate a system problem that needs repair. What is MSD doing now to control CSOs? MSD is committed to making the best use of current infrastructure to minimize the impact of CSOs on local waterways, including:
MSD has monitored CSO locations to measure overflow frequency and water quality. The information is being used to develop specific plans to reduce the environmental impact of CSOs on local waterways. These are just some of the steps MSD is taking as part of a comprehensive CSO management plan. What are MSD’s plans for the future? Long-term CSO control requires constructed improvements to the combined sewer system. During the last 6 years, MSD has spent $168.4 on CSO control projects in our combined sewer area. Some are designed to add a separate system to transport storm water to area rivers. However most projects store the storm water during rainy periods and then release it to the treatment plant as capacity in the pipe becomes available. Current and future CSO projects will reduce the impacts of CSOs on our area. | |
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