Stormwater two

Municipal stormwater: Medium and large separated storm sewer systems (MS4) – Phase I

In the early 1990s, in response to a lawsuit, U.S. EPA developed the stormwater program requirements for urban areas with population greater than 100,000. Because it was the first step to address stormwater runoff, it has been called “Phase I.”

This program applied primarily to major cities across the United States. However, these permits have often included smaller communities within an urbanized area, the county government surrounding the city proper, and state and municipal departments of transportation as co-permittees. In some places, the permit is held by a stormwater utility whose jurisdiction covers multiple municipalities. These individual permits require development of management plans and ordinances to control pollution in stormwater runoff from the urbanized area.

Stormwater management plans and programs must meet the statutory requirement of “reducing pollutants to the maximum extent practicable” (MEP) (CWA, Section 402(p)(3)(B)(iii)). Specifically, the medium and large municipal separated storm sewer systems areas need to identify and control major stormwater discharges to rivers, lakes and streams, non-stormwater discharges to the stormwater system, pollutants coming from industrial, commercial and residential areas, and discharges from construction (at least one acre in size) within the urbanized area. They also must carry out inspections and monitoring necessary to determine compliance (40CFR122.26(d)(2)(i)). With each renewal, permittees, states and citizens have the chance to evaluate the effectiveness of the previous permit.