The RSWG formed in September of 2005 to reevaluate costs and benefits, if any, to regional governance of stormwater discharge required under a proposed NPDES Phase II permit from the Washington Department of Ecology. With funding provided by an Ecology grant, the RSWG contracted for a Value Engineering report to examine the proposed permit requirements and estimate the cost for each municipality to comply with the minimum requirements of the permit. A followup report (PDF) examined regional savings that could be realized and any extra costs of running a regional program.
Based on favorable findings in these reports, an intergovernmental local agreement (ILA) was signed in July of 2007, providing a basis for the County to provide regional permit compliance services through 2010 to the Cities of Yakima, Union Gap, and Sunnyside. In 2014 the ILA was amended due to the City of Yakima withdrawing from the ILA, and the City of Selah joining.