Municipal Storm Water Phase I Facilities

The Municipal Storm Water Permits regulate storm water discharges from municipal separate storm sewer systems (MS4s). Under Phase I, which began in 1990, the Regional Water Boards have issued NPDES MS4 permits to permittees serving populations greater than 100,000 people. Many of these permits are issued to a group of co-permittees encompassing an entire metropolitan area. These permits are reissued as the permits expire.