By Bob Barth
Rainfall-poor areas of the nation and world have long viewed stormwater reuse as critical to their water management efforts. To Minnesotans living in the rainfall-rich upper Midwest, the practice may seem innovative, but it is becoming more of a necessity.
The Minnesota Department of Natural Resources has published recent reports about the state’s over-allocated groundwater. These reports suggest that Minnesota may be entering an era of restricted groundwater use. Can we continue depleting fossil groundwater to irrigate our lawns? If Minnesota answers no, then stormwater reuse will become as common as the stormwater pond.
What is stormwater reuse?
The use of stormwater runoff to supplement or replace groundwater already occurs on a grand scale throughout the United States. For example, the large dams on the Colorado River store spring melt from the Colorado Rockies for use as drinking and irrigation water in Los Angeles.
When we capture and store runoff water for later use, we can call that stormwater reuse, regardless of the scale. Minnesotans often think of stormwater reuse as a means to protect our wet¬lands, lakes, streams, and rivers. However, we should expand our view to include groundwater preservation.
Most Minnesota reuse projects collect runoff to irrigate turf grass. Twin Cities area municipalities use two to four times more water in summer than winter, and most of this water ends up on our lawns. Stormwater can supplement the use of city water for lawn irrigation and, in some instances, can replace the city water entirely.
With the advent of small treatment facilities, stand-alone water systems also become more feasible. This means that rainfall from a building roof can be harvested, stored, and treated for toilet and sink water, drinking water, and industrial water. Capturing roof water for drinking water occurs frequently in parts of the world where municipal water supply is unreliable or nonexistent.
Stormwater reuse is partly a response to regulation and partly a response to the obvious waste of using fossil water to irrigate turf grass. The regulation takes form through the National Pollutant Discharge Elimination System (NPDES) permit, both the Municipal Separate Storm Sewer System (MS4) and construction permits, which require some level of runoff volume control from the urban landscape. From the regulatory perspective, capturing stormwater runoff for later reuse is equivalent to infiltrating this runoff.
Reuse projects in the Twin Cities
There are several examples of reuse projects in the Twin Cities area. Probably the most high-profile project is the Target Field Rainwater Recycle System. Rain hitting the seven-acre field percolates into an underground collection system that delivers the water to a 12-foot diameter cistern under the field. After passing through a filtration system, the water is used to irrigate the ball field and wash the stadium decks. The recycled runoff reduces use of city water at Target Field by about 50 percent, according to the Minnesota Twins organization.
Another example is the City of St. Anthony’s water reuse facility, which it built as part of its goal to become a more sustainable city. The 500,000-gallon underground facility collects runoff from City Hall, an adjacent school, local streets, and Silver Lake Road. The city’s water treatment plant also discharges backwash water into the facility.
The recycled water irrigates ball fields in Central Park, reducing the volume of city water used for this purpose by 5 million gallons per year. The project has also reduced downstream pollutant loads by 95 percent, exceeding watershed permit requirements.
Simple policy changes can also promote stormwater reuse. The City of Medina prohibits larger new developments from connecting a private irrigation system to city water. Developers can adapt easily to this requirement without drilling private wells by using storm pond water and installing pump and filtration systems to deliver this water to irrigable areas. In fact, taking irrigation water from stormwater ponds is the cheapest way to implement a reuse system.
Stormwater regulation currently drives the need for reuse projects. An emerging issue of groundwater depletion in Minnesota will add urgency. As the cost of urban land rises and water resource regulations become more restrictive, water reuse facilities will become a cost-effective means to manage stormwater runoff and protect our groundwater resources.
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