NE 90th Street Stormwater Pond Retrofit

Image showing 90th Street Pond location

Project Overview

The existing NE 90th St stormwater pond treats the runoff from the 90th St stormwater basin before it drains into the Sammamish River. It was constructed in 2000 and currently provides about two thirds of the water quality treatment required by today’s regulations. The pond is also located within the Critical Aquifer Recharge Area and needs to meet recently adopted standards for protecting the City’s drinking water (Groundwater/Wellhead Protection).

The purpose of this project is to construct pond improvements that will:

  • protect the groundwater aquifer from untreated stormwater, 
  • improve the water quality of stormwater discharging to the Sammamish River, and 
  • reduce maintenance requirements.

To meet the recently adopted groundwater protection code, the project will be repairing the pond liner in 2022. This will minimize the risk of untreated stormwater infiltrating into the aquifer, while increasing water quality treatment at the pond.

The project is also designing a Filterra Bioscape system that will remove oils and grease, sediment, and dissolved metals. Once constructed, this system will treat the entire 90th St. basin to meet Department of Ecology water quality treatment standards. The Filterra Bioscape design is partially funded with a water quality grant from the Department of Ecology, and is planned for future construction as part of a larger 90th St basin plan.