NPDES & MS4 History
The Stormwater NPDES program has been implemented in two phases. Phase I was designed for medium and large Municipal Separate Storm Sewer Systems (MS4s) and industry, and Phase II is designed to focus on stormwater discharges from small MS4s. Locally, the DOE facilities fell under the Phase I requirements and currently maintain a single NPDES permit which includes stormwater discharges.