But where it flows could make all the difference between a healthy environment and a contaminated one. In natural areas, about half of rainwater and snowmelt is quickly absorbed by the ground and plants; 10% runs off into nearby waterways. The rest just evaporates. It’s Mother Nature’s perfectly designed way of managing water.
It’s quite another story when that water moves across surfaces Mother Nature never intended — paved driveways and parking lots, sprawling urban and suburban developments, commercial and industrial facilities, and ever-present construction sites. Then, water becomes “stormwater” that picks up contaminants as it flows downstream. By the time stormwater drains into a storm sewer or nearby waterway, it can contain a nasty mix of debris, sediment, metals, oil, grease and bacteria, causing major water quality problems locally — and surprisingly — even globally.
Stormwater is a leading cause of water pollution
Every roof, roadway and redevelopment project adds yet another impervious surface and a new contamination transportation system. The increased pressure (and an increased amount of pollutants in runoff from high-density land use) has immediate and long-term effects on the water bodies and the people, animals and aquatic communities that depend on them. Stormwater frequently overwhelms streams and rivers, scours streambanks and river bottoms, and harms fish and other aquatic life.
Nationally, stormwater is a leading source of water pollution. About 13% of our rivers, 18% of lakes, and 32% of estuaries are classified as impaired, or considered unsafe for swimming or fishing, due to stormwater. It also contributes to the degradation of many more waterways.
The surest way to improve water quality in Minnesota is to better manage stormwater.
Sources of contamination
Sediment. Sources include construction activities, gardening, erosion along riverbanks and shorelines. The problem? Tiny soil particles containing pollutants can cover stream and lake bottoms, smother habitat, create murky conditions that block light, and can clog drinking water intake pipes.
Nutrients. Common sources include grass clippings, leaves, fertilizer and animal waste. The problem? Increased likelihood of algal blooms and plants that can kill fish and other animals.
Bacteria. Often resulting from improper disposal of animal wastes, failing septic systems and sewage spills. The problem? People and animals can get sick from contaminated water. See www.mnbeaches.org for a list of Minnesota swimming beaches that are monitored for E. coli bacteria during the summer months.
Toxic chemicals, metals and airborne deposition. These enter our waterways from improper use, spills, disposal or emissions (solvents, pesticides, oil, paints and stains, deicing salt, metals, lead, mercury, zinc) and can severely harm, or kill, aquatic life.
MPCA's stormwater program
To better manage stormwater across the state, the MPCA administers the requirements of the federal Clean Water Act, in addition to its own State Disposal System requirements. At the MPCA, the Stormwater Program includes three general stormwater permits: the Municipal Separate Storm Sewer Permit, the Construction Stormwater Permit and the Industrial Stormwater Permit. Each program administers a general permit (and in some cases, individual permits) that incorporates federal and state requirements for Minnesota stormwater management.
Many of the everyday activities at industrial facilities can contribute pollutants to receiving waters, ranging from minimal amounts to toxic levels in the discharge. This is possible because anything that is applied to the land or released from storage piles, waste management systems, fertilizer or pesticide applications, smokestack vents, or a vehicle’s tailpipe or tires can be deposited on, and washed off, impervious surfaces.
Even though an industrial facility may contribute minimal pollution to the state’s water resources, the cumulative impact of thousands of facilities’ stormwater discharges can account for significant water quality problems. To address the variety of potential industrial stormwater discharges, the Multi-Sector General Permit can be complied with through a number of management options. These range from choosing and installing a variety of best management practices that meet the permit to a variety of options for sampling and monitoring.
Planning can help
Because stormwater is recognized as a leading cause of our nation’s water pollution, in the 1990s, the U.S. Environmental Protection Agency modified the Clean Water Act to require permits for industrial and municipal stormwater discharges. Minnesota and other states then created management requirements and best management practices for these sources as well as construction activity — primary dischargers with the potential to affect our water quality.
Experts say careful planning of developments, homes and buildings can alleviate much of the contamination from urban runoff. A non-regulatory alternative, the MPCA’s stormwater management toolkit, offers thoughtful best management practices that mimic the natural landscape and tackle stormwater in an environmentally beneficial way.
A growing number of Minnesota city managers, builders and developers are voluntarily incorporating low impact development and green infrastructure techniques, such as rain-capture systems and vegetation strips adjacent to paved surfaces into their plans. Not only can these practices enhance the property’s value, they may reduce runoff by as much as 50% and often lower stormwater management costs, too.