From Gray Skies to Green Solutions: Effectively Managing Stormwater Runoff in Parking Lots

by Michele Ostrove — Not so long ago, a parking lot was viewed as simply that—an area designated by a layer of impermeable pavement, designed as a convenience for businesses and customers, a property value enhancer, and, ideally, a source of income.

For generations, little thought was given to a parking lot’s effects on the environment. Yet each time it rained, antifreeze, oil, hydrocarbons, metals from wearing brake linings, rubber particles from tires, and nitrous oxide from car exhaust washed off the lot into nearby storm inlets, where they made their way into lakes, rivers and streams. Unlike natural, undeveloped areas, parking lots not only lacked the soil and vegetation that normally intercepts 90 to 95 percent of rainfall, but also contributed pollutants, disturbed stream ecosystems, and increased erosion by redistributing rain flow.

Fortunately, parking lots are viewed much differently today, thanks to the industry’s fundamental shift in thinking and focus on sustainability.

A Framework on Sustainability for Parking Design, Management, and Operations, published by the International Parking Institute (IPI), outlines industry-wide goals and action plans that contribute to sustainability through environmentally-conscious parking design, management and operations.

One parking lot owner took a comprehensive approach to stormwater runoff management, implementing a series of Best Management Practices, or BMPs, all along water’s path before it left their site. Designers at the Johnson County Community College in Kansas took a comprehensive approach to stormwater runoff management, implementing a series of BMPs to slow and filter the water before it entered a bioswale of native vegetation, creating a critical habitat for a variety of wildlife as well as an outdoor laboratory for students.

More parking facilities are using vegetation and filter media or soil to treat water, which is a significant departure from the ineffective systems of the 1990s, when urban stormwater management first became nationally regulated, notes Seth Brown, stormwater program and policy manager at the Water Environment Federation (WEF). Those early attempts to convey stormwater into manmade ponds or basins helped some, but recent studies show that “streams in urban areas are still seriously eroded, and lakes still have reduced biotic integrity,” he says.

“New technologies and approaches to manage stormwater runoff generated from parking areas may be able to address excessive runoff more cost-effectively than traditional approaches, and provide many other benefits beyond water quality,” according to Brown. As an added bonus, he says, these new approaches may even be profitable.

For example, Elmhurst College in Illinois found a solution that was both green and economical: a 400-car, permeable, interlocking concrete pavement parking lot. According to Mark Wright, principal of Mark Wright Communications and a regular contributor to the Parking Matters Blog, the facility used layers of aggregate material beneath concrete pavers to allow stormwater to trickle down while filtering pollutants out. It saved both money and space by negating the need for a separate water-detention facility.

Looking at stormwater solutions can often be done on a small, but effective scale with big impact outcomes, says Rachel Yoka, LEED AP BD+C, CPSM, vice president, planning and sustainability, Timothy Haahs & Associates. She recommends looking at pervious pavement as a starting point. Yoka points to a community center in urban Philadelphia that integrated pervious pavement to allow water to naturally filter into the groundwater system as an example. “Combined with the nearby compact bioswales, this was simple and elegant solution that many parking authorities, campuses, and property owners can implement,” she says.

With nearly one million acres of land expected to be developed annually over the next three decades, the need for change is apparent, and one reason the parking industry has made sustainability a key priority. “Parking professionals play an integral role in helping communities meet stormwater management requirements and overall sustainability goals,” says IPI Chair Casey Jones, CAPP. “Development is inevitable, but parking and transportation solutions should always balance consideration of environmental effects with public health and welfare and economic feasibility.”

Michele Ostrove is a Santa Fe, New Mexico-based freelance writer who frequently writes about parking, transportation, and sustainability.

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