A 1987 amendment to the Federal Clean Water Act required implementation of a two-phase comprehensive national program to address polluted stormwater runoff. Since the early 1990s, Phase I regulated large construction sites, 10 categories of industrial facilities and cities with a population over 100,000.
On March 10, 2003, Phase II was implemented to include runoff from construction sites disturbing one acre or more. Metropolitan communities, the City of Blaine included, were required to obtain permits for the management of stormwater sewer systems. It also required running stormwater and sanitary sewer through separate pipe systems, thus the term Municipal Separate Storm Sewer System and the acronym MS4.
Minnesota Pollution Control Agency
The United States Environmental Protection Agency (EPA) delegated permitting authority of the national program to the Minnesota Pollution Control Agency (MPCA). The Minnesota Pollution Control Agency's stormwater program was developed to reduce the pollution and damage caused by runoff from construction sites, industrial facilities, and urbanized areas Municipal Separate Storm Sewer Systems (MS4s).
Additional information is available through the Minnesota Pollution Control Agency (PDF).