Delridge GSI Retrofit for CSO Control

Herrera just wrapped up a 13 block green infrastructure (GSI) retrofit for the City of Seattle. This GSI retrofit was built in the right-of-way to reduce combined sewer overflows to Longfellow Creek and 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.

Check it out – 17th Avenue SW & SW Cloverdale Street, Seattle, WA

Image credit: Johnson and Southerland

Image credit: Johnson and Southerland