Urban storm water is the rain and snow melt that isn’t absorbed by the ground and plants but instead flows into storm drains (“street sewers”) and then into rivers or lakes – or runs directly into water bodies. Impervious surfaces (roads, parking lots, sidewalks, rooftops) carry polluted stormwater to storm drains, instead of allowing the water to percolate through soil. Most municipal storm sewer systems discharge stormwater, untreated, to streams, rivers and lakes.

This stormwater runoff contains:

·         Gasoline, motor oil, heavy metals, trash, polycyclic aromatic hydrocarbons (combustion byproducts of gasoline and other fuels) and the heavy metals nickel, copper, zinc, cadmium, and lead from roadways and parking lots;

·         Fertilizers, pesticides, nitrates and phosphorus from lawns, golf courses and parks; and

·         Synthetic organic compounds and zinc (from galvanized gutters) from roofs.

The diagrams below illustrates the different pathways of precipitation falling on an area with natural cover versus falling on impervious surfaces.

(Courtesy of EPA via Wikipedia Commons)

All of this can be damaging, and even deadly, to fish and other aquatic life. In Minnesota, urban stormwater runoff is the leading cause of phosphorus impairment in lakes with urbanized watersheds.

Urban stormwater from over 200 cities in Minnesota is governed by a general Clean Water Act permit. This is referred to as a Municipal Separate Storm Sewer System (MS4) permit. MCEA challenged several aspects of the initial 2002 MS4 permit, including the lack of public notice, potential degradation of water, requirements to meet antidegradation requirements, and monitoring requirements. The Minnesota Court of Appeals held that the process used by MPCA denied the public of its notice and comment rights, did not meet all antidegradation requirements, and did not include certain federally-required language. As a result of the lawsuit, MPCA revised the permit and undertook a different public notice process that better incorporated the local stormwater plans.

One problem in preparing water restoration plans (called TMDLs or Total Maximum Daily Loads) is that the Minnesota Pollution Control Agency is assigning an aggregated, lump pollution reduction goal to multiple MS4 cities draining to the same waterbody impaired by urban stormwater.  Yet these lump allocations are not being broken into individual municipal goals that are incorporated into each city’s permit.  US EPA has proposed guidance to address this problem which recommends that TMDL plans assign pollution loads to each MS4 permit holder separately. This would insure that each MS4 permittee knows its pollution limits and can incorporate the required reductions into its stormwater plan. MCEA submitted comments supporting the guidance and pointing out that some cleanup plans in Minnesota already do this.

Court of Appeals decision

MS4 information from US EPA

US EPA Guidance on MS4s and TMDLs

MCEA comments on Minnesota MS4 general permit 

MCEA Comments on US EPA Guidance

MPCA webpage for 2011 MS4 general permit