With so much concern about water scarcity around the world, it seems a no-brainer that rain is a good thing. But nothing’s perfect. Even something as beneficial as precipitation can have its downsides. One problem, of course, is flooding. Another problem you may not have thought of comes with stormwater runoff in urban settings. What’s the problem?
In cities, buildings and pavement prevent water from being quickly absorbed into the ground. Freely flowing water picks up pollutants as it courses through parking lots and streets, and into storm drains.
There often is confusion about where stormwater goes next. Does it go to the sewage treatment plant? Usually that’s not the case. It’s most often diverted into pipes, ditches, or other infrastructure and delivered, untreated, directly to the nearest waterway.
Contaminants are a problem and a challenge for urban planners. The Center for Watershed Management explains:
Stormwater runoff also picks up and carries with it many different pollutants that are found on paved surfaces such as sediment, nitrogen, phosphorus, bacteria, oil and grease, trash, pesticides and metals. It comes as no surprise then that stormwater runoff is the number one cause of stream impairment in urban areas.
Many of the contaminants in urban stormwater runoff originate from vehicles. Roadways pick up motor oil, antifreeze, hydraulic fluids, dust from tire wear, and other substances. Road salts can be an issue in areas that use it for deicing.
In 1987, the United States Environmental Protection Agency started requiring cities to get permits for stormwater runoff as part of the Clean Water Act.
This meant municipal governments had to devise ways for developers and large corporations to help with compliance. For instance, an organization could be required to capture stormwater and divert it to a wastewater treatment plant. Stormwater management often requires the imposition of fees or taxes to help governments with compliance.
Reusing Stormwater Runoff
What about water reuse? Relatively little attention has been devoted to reuse because of the range of contaminants that are found in runoff, including all sorts of sediments and particulates, as well as nitrogen, phosphorous, organic compounds, and microbes.
But growing water scarcity and the increasing cost of water distribution are making stormwater collection and treatment an attractive option, according to Water World.
For example, General Motors was able to save $140,000 in a year with stormwater capture and reuse at its Detroit-Hamtramck assembly plant. The facility had been paying stormwater discharge fees to the city of Detroit based on site acreage. By capturing stormwater and treating it with simple sand filtration for reuse in its cooling towers, the company saved more than 20 percent of the plant’s water consumption. It expects eventually to save $2 million a year.
To retain water, the plant uses two 10-million-gallon ponds and a 25-million-gallon pond.
Todd Williams, senior project engineer for water and wastewater treatment at General Motors, explained to Environmental Leader:
We thought, we can make high purity water for ourselves. After going through the multimedia filter, we run it through carbon filters to prepare it for reverse osmosis. [In 2016], we reused about 50 million gallons of stormwater in our cooling towers and our paint process. This year we hope to reuse between 100 million and 200 million gallons.
Regional and municipal governments are working to develop creative solutions. Florida’s Tampa Bay region is a coastal area with more than 3 million residents. It needed ways to cope with flooding and sea-level increases resulting from climate change.
Some developers there are designing mixed-use projects with stormwater retention and reuse, in addition to redevelopment projects with open space and parks that help address some of the challenges.
As mentioned above, stormwater capture is an increasingly important aspect of water reuse (also known as water recycling). The practice being gradually embraced worldwide to increase water sources.
Melissa Meeker, executive director of WateReuse, explained:
To grow the economy, we need to invest in infrastructure — that means better roads, safer bridges and a sustainable supply of clean water. […] Investing in water recycling will not only create jobs now but also ensure a reliable supply of clean water for sustained economic growth.