Municipal Stormwater Permits

Municipal Stormwater Permit jurisdiction areas for Phase I and Phase II permits, issued by the Washington State Department of Ecology. The Phase I permit regulates discharges from municipal separate storm sewers owned or operated by Clark, King, Pierce and Snohomish Counties, and the cities of Seattle and Tacoma. The Phase II Municipal Stormwater Permit rule extends the coverage of the National Pollutant Discharge Elimination System (NPDES) program to certain "small" municipal separate stormwater sewer systems (MS4s). These permit areas incorporate 2019 updates to incorporated City boundaries and unincorporated Urban Growth Areas (UGA) as defined by the Growth Management Act, as well as 2010 Census extents for urbanized areas adjacent to permitted cities and UGAs. This dataset was last updated in 2026. The current permit is effective Aug. 1, 2024, and expires on July 31, 2029.本数据集为华盛顿州生态部（Washington State Department of Ecology）颁发的第一阶段与第二阶段市政雨水许可管辖区域。第一阶段许可监管克拉克县、金县、皮尔斯县、斯诺霍米什县以及西雅图市、塔科马市所拥有或运营的市政独立雨水下水道的排放活动。第二阶段市政雨水许可规则将国家污染物排放消除系统（NPDES）项目的覆盖范围拓展至特定“小型”市政独立雨水排水系统（MS4s）。本许可区域纳入了2019年更新的已建制城市边界，以及按《增长管理法案》（Growth Management Act）划定的非建制城市增长区（UGA），同时纳入了毗邻许可城市与UGA的城市化区域的2010年人口普查范围。本数据集末次更新时间为2026年。当前许可于2024年8月1日生效，有效期至2029年7月31日。