Milwaukee's Green Stormwater Mandate

Wisconsin water officials passed a pollution permit requiring the Milwaukee area to develop one million gallons of green stormwater capacity annually for the next five years. The Milwaukee Metropolitan Sewerage District (MMSD) has been sponsoring the installation of area green roofs for nearly a decade, including this planting at the Aquatics Unlimited store in Greenfield, Wisconsin in December 2010.

The Milwaukee area will be the first in the nation to mandate ''green infrastructure'' to contain and manage stormwater.

The Wisconsin Department of Natural Resources (DNR) issued a new five-year wastewater discharge permit in January requiring the Milwaukee Metropolitan Sewerage District (MMSD) to establish one million gallons of green stormwater storage capacity each year. Sewer pipes, bedrock tunnels and concrete reservoirs cannot be used to meet the mandate.

The district will have to install a variety of stormwater management tools throughout the area to keep up with the rising mandate, offering potential work to area landscape designers and contractors. Green infrastructure can include plantings and soil, rain barrels, green roofs, rain gardens and bioswales, or permeable pavement. The district will also work to conserve and protect area wetlands.

Green infrastructure will reduce runoff to the sewer system, cutting potential overflows into waterways or basements, DNR and district officials said.

The district must work with municipalities and private property owners to achieve 250,000 gallons of other green storage each year. The mandate requires that no more than 75 percent of the one million gallons yearly total can come from new purchases of wetlands or floodplains under the permit.

A green roof or rain garden can capture up to 3 gallons of rain per square foot. One rain barrel holds 55 gallons.