Issaquah, WA Environmental Rules: Stormwater Management (2026)

IMC 13.28.025(A) says no person shall throw, drain, or otherwise discharge, or allow others under their control to do so, into the municipal storm drainage facility or surface and groundwaters any materials other than stormwater. The list of examples runs to 31 items, from trash, petroleum products, paints, pesticides, soaps and detergents to swimming pool or spa cleaning wastewater, domestic animal wastes, lawn clippings, leaves or branches, and silt, sediment, concrete, cement or gravel. Subsection D bans the construction, use, maintenance, or continued existence of illicit connections, expressly including connections made in the past that were lawful when built, and treats a line carrying sewage to the MS4 as a violation.

Subsection B lists allowable discharges such as foundation drains, footing drains, springs, uncontaminated pumped groundwater, and emergency firefighting flows, unless the Director determines they are causing or likely to cause pollution. Dye testing needs verbal notification to the Director at least 1 day before the test. Subsection C makes some discharges conditional. Fire hydrant flushing and hydrostatic test water must be dechlorinated to 0.1 ppm total residual chlorine or less, and street sweeping must come before washing at active construction sites.

Development drainage design falls under IMC 13.28.030, which sends all clearing, grading, and stormwater management work to Chapter 16.26 IMC. Under IMC 13.28.130 the owners of private stormwater facilities are responsible for operation, maintenance, repair, and replacement, and the City requires annual inspections. The City must give written notice at least 90 days before the inspection deadline, and an owner can hire a qualified third party to certify the inspection or let the City do it on 7 days' written notice. IMC 13.28.090 keeps the title holder and the applicant responsible for facilities the City has not accepted, and IMC 13.28.100 requires removal of debris, sediment and vegetation.