Another major combined-sewer-overflow storage tank is planned for our area, this time on the east edge of West Seattle, near the 1st Avenue South Bridge. This is the West Duwamish Combined Sewer Overflow (CSO) Control Project, and its aim is to comply with orders to reduce the number of overflows into the Duwamish River – specifically one outfall on SW Michigan Street that overflows an average of 4.6 times a year and one at Terminal 115 that overflows an average of 1.7 times a year. The new facility near 2nd SW/SW Michigan will be on 60,600 square feet of T-115, which is owned by the Port of Seattle, centered on a 1.25 million gallon underground tank – 140′ x 110′, 26′ deep – and related pipes. Here’s the King County Wastewater Treatment Division map:
For comparison, the storage capacity is 25 percent more than the big tank built across from Lowman Beach five-plus years ago, now known as the Murray Wet Weather Facility. The West Duwamish project will also include an above-ground 5,300-square-feet “facility building and outdoor odor control area” plus landscaping including a “stormwater bioretention facility.” The project also includes associated facilities such as a “diversion structure” near West Marginal Way and Highland Park Way SW.
Construction is not expected to start until 2025, but another key comment period is open now. Through February 14th, comments are being taken on the environmental checklist for the project – you can see it here. You can comment via email at WTDSEPA@kingcounty.gov. You’ll get a chance for a briefing and Q&A about the project at an upcoming HPAC meeting – watch hpacws.org for word of that.