Story and photos by Keri DeTore
Reporting for West Seattle Blog

Seattle Public Utilities brought its CSO (Combined Sewer Overflow) Planning crew to Youngstown Cultural Arts Center tonight for a community open house to share information and to get public comments related to overflow-reduction projects around the city.

A CSO is what happens when heavy rainfall overloads the capacity of existing tanks at treatment plants. Excess water is deposited directly into Puget Sound, Lake Washington and other streams and creeks without being treated — putting oil, toxins, and raw sewage directly into our waterways.

You may have heard about CSOs here before over the past two years – but that was about the plans for county facilities; now, it’s the city’s turn.

According to Ed Mirabella, long-term control plan manager, SPU has been monitoring rainfall throughout the city for the past three years. The results were entered into a computer model that simulates long-term sewage-infrastructure needs. This information, along with new laws limiting the amount of CSO allowed in cities, led SPU to plan for millions of gallons’ worth of new capacity to handle storm events. These tanks will hold the water until it can be released in a metered way to the treatment facilities.

In West Seattle, there are currently two underground stormwater storage tanks along Delridge: one at Orchard and one at Barton. Each of these tanks holds 1.6 million gallons. The anticipated need for stormwater storage in West Seattle by the year 2025 will be 5.4 million gallons, necessitating the building of two smaller storage facilities, or one large one. These alternatives are part of what’s being looked at by SPU as they consider the best way to mitigate the amount of water entering the sewer systems during storms.

The planning stage now is “at a very high level,” according to Andrew Lee, CSO program manager for SPU. He stresses that they are not yet at a stage of choosing sites for any of the potential options; they’re merely looking at a variety of solutions to improve the existing system and asking the public for comments as they move forward in the process. For example, some comments from past events have questioned the impact on transportation during construction, or the impact on cultural sites, such as an Olmsted-designed park (if that were chosen as an underground storage facility site). Siting will not begin until 2016.

Large paper tablets were set up on easels to allow public comment during this event; cost seemed to be the major concern of the dozen-plus who attended. For more information and to view Long-Term Control Plan information online, go here. Comments are being accepted until November 7.

(Combined Sewer Overflows happen during major rainstorms – next time we get that kind of rain, if you want to see whether overflows are happening, you can check real-time information online here.)