Delridge GSI Retrofit for CSO Control

Herrera worked with the City of Seattle to design 13 blocks of green stormwater infrastructure (GSI) retrofits in the right-of-way to reduce combined sewer overflows to Longfellow Creek. This GSI retrofit was designed in partnership with a neighborhood greenway project in the Delridge neighborhood to enhance pedestrian mobility and increase traffic safety. A basin-wide retrofit planning process was conducted to select the project blocks that would offer the highest CSO control benefit and achieve informed consent from the public. Planning involved a desktop GIS analysis, windshield survey, and targeted field investigations. The project design includes bioretention facilities, intersection bioretention bulb-outs, permeable pavement sidewalks, and sidewalk and ramp reconfigurations for ADA compliance. The bioretention planters design includes underdrains that collect and convey treated stormwater to a simplified UIC well (“drilled drain”) for deep infiltration. To gain approval for this new GSI practice, Herrera worked with Seattle utility, transportation, and maintenance departments to develop a standard drilled drain detail, as well as programmatic guidance for commissioning, and operation and maintenance of these new facilities. Herrera supported community outreach in the diverse, multi-lingual community through a series of public meetings and project “walk-and-talks.” Construction was completed in late 2016. Herrera is currently working on a comprehensive operations and maintenance plan to ensure long-term performance of the GSI facilities.

Project Details