03.02.2015  |  News

Revised Washington Municipal (MS4) Stormwater Phase I and Phase II Permits



The Washington Department of Ecology has released revised versions of Phase I and Western Washington Phase II Municipal Stormwater (MS4) Permits (Permits), effective January 16, 2015.  These changes were initiated as the result of the disposition of appeals of the Permits that were issued in 2012.

Stormwater Suburban Runoff

The most significant change to both Permits relates to watershed-scale stormwater planning. Both revised Permits outline the scope of the watershed-scale plan, documentation for the planning process, coordination between Permittees, and milestones that must be met. The revised Phase I Permit identifies the watersheds for which watershed-scale stormwater plans will be prepared.

In both Permits, the deadline to start conducting the Status and Trends Monitoring Option #2 – conducting water quality, benthos, habitat, and sediment chemistry monitoring – was delayed from July 31, 2014 to October 31, 2014. Ecology also defined the term “discharge point” in both Permits as a location where stormwater from the municipal separate storm sewer system (MS4) leaves the system by way of an infiltration BMP or facility. This allows further clarification on how Low Impact Development (LID) can be incorporated into the MS4 and allows the Permits to capture a larger range of waters leaving the MS4. “Conveyance system”, which was not previously defined in either Permit, is now defined in both as the portion of the MS4 that conveys or is designed to convey stormwater. Also, both “outfalls” and “receiving waters” are redefined in the Permits to clarify that only discharges to naturally occurring and/or reconstructed surface water bodies and groundwater are considered; discharges to constructed stormwater facilities (e.g. stormwater ponds) are not included under these definitions.

A couple small changes were also made to each Permit individually. The Phase I Permit included an updated link to Ecology’s WQWebPortal website. The Phase II Western Washington Permit included clarification on the required number of designated monitoring locations for Status and Trends Monitoring Option #2. Updates to the Phase II Permit also included a deadline of February 2, 2018 for updating MS4 maps to identify and eliminate illicit discharges, as well as a requirement for the maps to identify all connections with MS4’s owned or operated by other municipalities or public entities.

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