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North Fork Clover Creek WQ Retrofit

Parkland, Washington

Stormwater Treatment


Pierce County 


Pierce County 


September 2020

Technical Description:

  • Filterra Bioscape® Bioretention System
  • StormGate™ High Flow Bypass Structure

Pierce County Washington’s Storm Drainage and Surface Water Management Plan identified stormwater issues and recommended capital improvements for each major drainage basin in the County. This included an existing stormwater system that outfalls directly to Clover Creek without water quality treatment. Using grant money from the Washington State Department of Ecology, Engineers from Pierce County sought a retrofit solution to provide sediment treatment and reduce fecal loads to Clover Creek.

The project was designed by Pierce County and reviewed by the Washington Department of Ecology. The design used a traditional bioretention facility and a Filterra Bioscape high-flow- bioretention system to intercept and treat existing impervious areas to improve water quality in Clover Creek.

With a contributing basin of 37 acres, the Filterra Bioscape was selected based on its small footprint and ability to achieve TSS and fecal load reductions. Prior collaboration between Contech and Piece County on other projects and the recently constructed Point Defiance Bioscape system in Tacoma also helped pave the way to using a Filterra Bioscape option. 

The small footprint and unique hydraulic design were challenging elements of this project. The Pierce County engineer designed a 570-square-foot cast-in-place Filterra Bioscape with staggered wall heights and multiple up-flow bubbler pipes throughout the cell to distribute inflows to the system and protect it from high water levels in the creek during winter.

Installation of the Filterra Bioscape began in September 2020. A Contech Field Consultant and Sales Engineer coordinated with the contractor on material delivery to the small job site.

“It was a pleasure to work with you and your design staff on this very unique “up-welling bubbler” design, said Jeffrey Davidson of Pierce County. “All of you at Contech were extremely helpful and knowledgeable every step of the way to make this project a success.”

Technical Description:

  • Filterra Bioscape® Bioretention System
  • StormGate™ High Flow Bypass Structure

800-338-1122 |
Project #: 561915


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