Shore Avenue Stormwater Outfall Improvements
Developing a Stable Stormwater Outfall
The City of Everett’s Shore Avenue stormwater outfall was situated in an area of reoccurring slope failures above BNSF railroad tracks and along Puget Sound. Following a slide in 1998, an emergency repair had been made to the outfall serving a 70 acre portion of the Bay Bluffs drainage basin. Despite the repair, a permanent solution was still needed.
Initially, an extensive alternative analysis and design concept was completed, which relocated the outfall pipeline to a less slide prone area of the bluff and utilized an existing railroad culvert as the new outfall. Additionally, by installing a new, deep storm drainage system along Shore Avenue, the new outfall would also be able to serve the adjacent 30 acre Sound Avenue drainage sub-basin, thereby consolidating two outfalls into one.
The City engaged KPG to complete final design plans, permits, and provide support to the City’s pipeline license negotiation with BNSF. The final design includes 1,750 LF of new 18 inch to 36 inch storm drains with depths of up to 20 feet, including a 48 inch steel casing and HDPE bluff surface pipeline. We chose to slip-line an existing railroad culvert to protect the budget and schedule and added two hydrodynamic separators. These separators are known for their ability to capture floatable pollutants, like oil and fuel.
Environmental permitting included the State Environmental Policy Act (SEPA), Shoreline Substantial Development Permit and Hydraulic Project Approval from the Washington Department of Fish and Wildlife. In addition, a Section 401 Water Quality Certification and Section 404 permit from the Corps of Engineers were both also required.