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Upper Buckley Water Quality Retrofit

Tacoma, Washington

Stormwater Treatment


City of Tacoma


Parametrix Bremerton


Northwest Cascade


April 2023

Technical Description:

  • CDS® Hydrodynamic Separator
  • Stormwater Management StormFilter® 
  • StormGate® High-Flow Bypass Structure

The Upper Buckley storm main replacement project replaced aging and failing storm drainage infrastructure running underneath private property in Tacoma, Washington. The project realigned the existing storm sewer system by abandoning pipe locations under private properties and replaced them with pipe in the public right of way.

“Development activities within the North Tacoma Watershed have been identified as a significant source of increased flows, excessive sediment load, and gravel scouring within the watershed and, therefore, within the Puget Sound,” said Kirk Myklestad, City of Tacoma Project Manager. “The overall goal of the Upper Buckley Water Quality Project is to help protect and restore water quality by reducing stormwater impacts from existing infrastructure and development. In partnership with the Washington State Department of Ecology, a regional stormwater treatment facility was constructed in the Upper Buckley sub-basin of the North Tacoma Watershed that will treat approximately 340 acres of the 484-acre sub-basin. The project will improve water quality by providing basic treatment for suspended solids and phosphorus.”

Site constraints included a tight construction schedule to limit road closures, a location in a dense residential area, and a limited site footprint to accommodate all structures while connecting to the existing 48” diameter sewer line.

To meet these regulations, the engineer and the city selected a StormFilter to remove nutrients, a CDS hydrodynamic separator as pretreatment, and a StormGate high-flow bypass structure.  The StormFilter was selected because of its ease of maintenance, long-term maintenance cycle, and the city’s experience using the technology of over 20 years.

Pretreating the StormFilter is a 33’ tall, 10’ diameter CDS hydrodynamic separator. A custom 6’ x 8’ StormGate high-flow bypass vault allows stormwater runoff flows up to the water quality design flow to enter the water quality facility and bypass or re-direct the flows greater than the design flow around the stormwater treatment facility.

The StormFilter vault is a 26’ deep, 22.5’ x 86’ vault that houses 454 cartridges filled with PhosphoSorb®, a lightweight media built from a Perlite base that removes total phosphorus (TP) by adsorbing dissolved-P and filtering particulate-P simultaneously. The vault is designed to treat 19 cfs of runoff. Contech provided complete cast-in-place vault design, structural analysis, field installation support and training for the contractor and City staff.

"Working with Contech on this project was a great compliment to our design team, said Mallory Wilde, PE, Senior Engineer, Parametrix."  Chris Hass and team provided technical expertise on the facility sizing and design that helped lead to the success of this complicated project. We especially benefitted from Contech’s experience with facility maintenance and constructability. Contech even went the extra mile during design and attended meetings with the City to help the Owner better understand the product that they were purchasing. We look forward to working with Contech again on the next project!

Technical Description:

  • CDS® Hydrodynamic Separator
  • Stormwater Management StormFilter® 
  • StormGate® High-Flow Bypass Structure

800-338-1122 |
Project #: 638,199


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