For example, Seattle and King County, with more than 120 combined sewer overflow outfalls, discharge an average of about one billion gallons per year of untreated sewage, stormwater and industrial wastewater. These overflows affect Lakes Washington and Union, the Duwamish River, the Ship Canal, and Puget Sound.
Combined sewer overflows (CSOs) are unlike the infrastructure in communities that have separate sanitary sewers and stormwater drainage systems. Combined systems deliver all of the water — both the sewage and the stormwater — to treatment plants. This combined treatment of stormwater is a good thing except that during and after large rainstorms, inadequate CSO systems send untreated sanitary and stormwater sewer overflows directly into our waters. Combined sewer areas with properly functioning CSO controls serve the important function of treating polluted stormwater runoff that would otherwise flow into lakes, rivers and Puget Sound.
Infrastructure investments are needed to address water pollution caused by both CSO and stormwater discharges. In areas served by combined systems, CSO projects provide solutions to both CSO and stormwater pollution.
The investments ratepayers make in their communities’ CSO programs protect public health and Washington’s waters, two principal missions of sewer and stormwater utilities. The success of these projects advances the goals of our state and federal laws to protect, clean up and preserve our waters for present and future generations.
Improving CSOs is especially important in heavily industrialized areas, such as the Duwamish River basin. Numerous industries discharge into a combined collection system, which overflows during some storms. By capturing these industrial flows (as well as sewage and stormwater) in controlled CSOs even during storms, many of the toxic pollutants associated with industrial discharges receive necessary treatment at a wastewater treatment plant and aren’t discharged into our state’s waterways and sediments.
Washington’s approach recognizes the potential costs local governments and ratepayers could face to put CSO controls in place. The state’s program incorporates two key strategies that help CSO communities manage this undertaking.
1. Washington’s rule allows an average of one combined sewer overflow per year per outfall. Storms and rainfall vary from year to year. By using an average of CSOs over several years, the overall discharge is decreased without the need to over-build for high-flow years. It means a city has the flexibility to design its CSO control program in a more affordable manner. The state has allowed Seattle and King County, for example, to spread the average over 20 years.
2. The state also has taken a flexible approach in the time allowed for communities to build their CSO control programs. Spreading project costs over time reduces the effect on utility rates. State law, adopted 24 years ago, requires CSO reduction “at the earliest possible date.” Seattle and King County have received approval to complete their CSO programs by 2025 and 2030, respectively, in order to minimize annual costs. Since adoption of the State law in 1987, King County and Seattle will have about 40 years to implement their CSO reduction programs.
Local governments have flexibility to pick the strategies that are the most cost-effective for them to meet the standards.
Washington’s strategy for those cities with combined-systems to treat and reduce their overflows is similar to EPA’s national policy. Our state’s CSO strategy targets high priority pollution sources and protects public health. It is a key to restoring Puget Sound.
Strategies for controlling CSOs include separation, storage or treatment of flows. More recently, cities have built green stormwater infrastructure – alone or in concert with other control strategies — as a cost effective approach for some CSO reduction projects.
A number of the 11 communities have completed their programs to control and reduce their CSOs. The others continue to make significant progress with their CSO programs.
CSOs present a real threat, and corrections are worthy investments. Delaying these investments would miss a chance to reduce a real water pollution problem.
For more information, please see: www.ecy.wa.gov/programs/wq/permits/cso.html.
EPA on CSO
Statement from Dennis McLerran, EPA Regional Administrator, regarding CSO/SSO Pollution in Seattle and King County
"Discharging large amounts of raw sewage to Puget Sound and Lake Washington is simply not acceptable. That's why EPA has worked closely with the state, King County and Seattle over many years to address sewage treatment and the ongoing problem of Combined Sewer Overflow
(CSO) pollution. With that work nearly completed, now is not the time to lose our resolve to finish the job visionary leaders in the Puget Sound region started some 40 years ago.
"Combined systems — and climates like Seattle’s — often conspire to produce huge sewage and storm water overflows during the wet winter months. It's our view that there are few better investments than protecting our citizens and waterways, especially Puget Sound, from millions of gallons of raw sewage. We understand the concern over major construction expense in these tough economic times, but we are convinced this is a critically important step in protecting the Sound and the citizens who rely on it. We also believe a prudent approach, one that includes phasing the construction, tackling the biggest challenges first and looking for other ways to economize, can help make it more affordable in the long run.
"Also central to this discussion is the very real and serious threats stormwater poses to the Sound. Make no mistake, we are equally as committed to stormwater control efforts as we are to controlling CSOs."
"We stand ready to work with Seattle and King County to do whatever it takes to reduce these threats and protect the people's health, the Puget Sound and our precious lakes and streams."