Olympia, WA Environmental Rules: Stormwater Management (2026)

OMC 13.16.030 bars anyone in the City of Olympia from discharging, or causing the discharge of, any materials into the MS4 other than stormwater, clean groundwater and clean city potable water with chlorine concentrations less than 0.1 ppm. Thirteen exceptions follow. They cover water from emergency firefighting, discharges under an NPDES permit when the discharger is in full compliance, air conditioning condensation, springs, uncontaminated crawl space and basement pump water, uncontaminated pumped groundwater, and lawn watering or irrigation runoff, except water from the City's supply that was wasted in violation of OMC 13.04.080. Street and sidewalk wash water is allowed only when the surfaces are swept first, detergents are not used and water use is minimized. External building wash water must also be detergent free with minimized water use, and dust control water must be minimized. Pool, spa and hot tub water must be dechlorinated to a total residual chlorine concentration of 0.1 ppm or less, pH-adjusted and reoxygenated if necessary, and volume, velocity and temperature controlled. Pool cleaning wastewater and filter backwash cannot go to the MS4 at all. A final exception covers other discharges that follow a pollution prevention plan approved by the Director.

The rest of Chapter 13.16 builds around that rule. Under OMC 13.16.020, before stormwater is discharged to any part of the storm drainage system, the parcel owner applies to the Community Planning and Development Department for an engineering permit, with terms set by the Drainage Design and Erosion Control Manual. OMC 13.16.040 requires Public Works to inspect stormwater facilities before final approval or occupancy and prohibits illicit connections to the MS4, including connections that were lawful when made. If an owner does not abate an illicit connection after notice and opportunity to cure under OMC 4.44.030, the City can abate it and bill the owner, and delinquent payments become a lien on the parcel. OMC 13.16.045 requires anyone storing or using contaminant materials to apply the source control best management practices in the Manual.