Feb. 1, 2021: KC Coal Creek Sewer Upgrade Project. The King County Wastewater Treatment Division proposes to replace the north segment of the existing Coal Creek Trunk sewer pipe with a new pipe, in order to meet existing and future capacity needs. The new pipe will be installed below ground using trenchless methods where feasible, and open-cut methods where ground conditions or other site constraints are unsuitable. To continue collecting local flows, the County also proposes to provide a combination of new local connections and appropriately resized existing connections. Project elements also include decommissioning the existing pipe and physical removal where feasible, environmental mitigation actions within the Coal Creek Natural Area, and improvements for trail users in the Natural Area. Construction is anticipated from 2022 through 2027. The Project will have unavoidable impacts to Coal Creek in two locations and one of its tributaries. Five wetlands will also have unavoidable impacts. The project will include mitigation for wetland and stream impacts within the Coal Creek basin as much as feasible, including: wetlands enhancement and creation that will connect fragmented and degraded habitats adjacent to Coal Creek; creation of additional aquatic habitat complexity in Coal Creek and removal of a fish passage barrier on a tributary to Coal Creek; physical removal of decommissioned sewer infrastructure where feasible; and other mitigation actions as required by regulatory agencies.
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