West Sitcum Stormwater Treatment

The Northwest Seaport Alliance currently leases out approximately 140 acres for container handling operations at the West Sitcum Terminal. Operations at this site are permitted under the NPDES General Permit for Industrial Activities by Ecology, where quarterly sampling by the terminal operator found stormwater discharges that exceeded permit benchmarks. Parametrix prepared a characterization of existing stormwater from this terminal and related industrial activities and developed a solution for attaining water quality benchmarks to meet NPDES permit requirements.

A risk-based approach guided the team to the preferred treatment solution, which was approved by the engineering and All Known and Reasonable Technologies (AKART) reports to Ecology. Parametrix subsequently prepared the plans, specifications, and estimates for the preferred alternative, modular wetlands with associated pumping and conveyance system. The scope included design of three new duplex submersible pumping stations, three pretreatment hydrodynamic separators, and 28 new media filtration units, targeting copper and zinc benchmarks, which were selected to provide the best opportunity to meet permit requirements throughout the design life.

West Sitcum Stormwater Treatment


Northwest Seaport Alliance

Tacoma, WA


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