Northside Master Planned Community Stormwater Management System

Oct. 28, 2022

Northside is a 280-site, multi-phase, master-planned community located on the border of Washougal and Camas, Washington. The 100-acre site will be constructed in 6 phases over several years.

The project was required to meet the Washington State Department of Ecology’s standards for runoff reduction and phosphorus treatment, as the site drains to Lacamas Lake, which is protected with a phosphorus TMDL. Engineers from Hayward Uskoski & Associates designed a stormwater management system using Contech’s Filterra Bioscape and the Stormwater Management StormFilter for treatment and a large pond for detention.

Due to steep slopes on the site, traditional bioretention was infeasible, as it would have required encasing all the bioretention cells with difficult to design and expensive to install cast-in-place vaults. Having worked with Contech on previous designs, the engineer worked with Contech early in the design to identify an alternative solution.

Filterra Bioscape, a high-flow bioretention system, was identified as the best treatment option to treat a majority of the site based on its small footprint and cost-effectiveness. Two Filterra Bioscape systems were placed strategically within the site. A 42' x 15' system was used to treat a contributing basin of 32.8 acres, and a 7' x 30' system was used to treat a contributing basin of 13.5 acres. The Each Filterra system is pretreated with a CDS hydrodynamic separator to remove sediment and trash and extend the time between maintenance events. Four Stormwater Management StormFilter Catch Basin's and one StormFilter Manhole were used to treat portions of the site that could not be routed to the Filterra systems. The four StormFilter catch basins required custom sloped risers to be fabricated to match the road grade.

Contech provided sizing calculations and technical details to the engineer throughout the permitting process. Installation of the Bioscape systems began in December 2021 and continued through the late spring of 2022 with the planting and activation of the Filterra systems. The local Contech Field Consultant and Sales Engineer were onsite for pre-construction meetings and to provide installation supervision for the contractor.

The Filterra Bioscape allowed Contech to provide the engineer with a customized treatment plan with engineering and installation support on a topographically challenging site that could be easily inspected by the jurisdiction and maintained by the HOA.

"The Filterra Bioscape allowed us to provide a customized treatment plan on a topographically challenging site with limited means of treatment that could be easily inspected by the jurisdiction and maintained by the HOA," said Valerie Uskoski, PE at Hayward Uskoski & Associates. "This customizable option was very cost effective and easy to install."