1.3 LID & the Eastern Washington NPDES Municipal Stormwater Permit

On August 1, 2012 (with an effective date of August 1, 2014), Ecology reissued the Eastern Washington Phase II NPDES Municipal Stormwater General Permit (Permit). The Permit takes incremental steps toward broad implementation of LID practices. LID is defined within the Permit as a “stormwater and land use management strategy that strives to mimic pre-disturbance hydrologic processes of infiltration, filtration, storage, evaporation and transpiration by emphasizing conservation, use of on-site natural features, site planning, and distributed stormwater management practices that are integrated into a project design” (Ecology, 2012a).

In eastern Washington, permittees have considerable experience with LID-based BMPs described in the 2004 SWMMEW, such as bio-infiltration swales and vegetated filter strips. This Manual is intended to provide additional information about LID planning, design, BMPs, maintenance, plant lists, and related topics in eastern Washington.

The Permit identifies a schedule for local governments to amend codes and ordinances to “allow” LID and to meet the proposed 10-year, 24-hour storm event onsite retention standard. The Permit deadline for local governments to amend codes and ordinances to allow LID is December 31, 2017. This Manual is an important tool to provide local jurisdictions with design guidance to facilitate the LID projects that will be allowed under the Permit (Ecology, 2012a).

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