Stormwater management is an inescapable fact of life for landscape architects and designers. But permeable interlocking concrete pavers are proving to be an attractive solution that also is friendly to the environment.

To reduce pollution discharged to lakes, rivers, streams and estuaries from paved surfaces, federal stormwater management rules under the federal Clean Water Act were upgraded in 1999 to include:
Regulated small municipal separate storm sewer systems not covered under earlier regulations. Most of these are in urban areas of at least 50,000 population and overall population density of 1,000 people per square mile, or in areas near particularly sensitive waters or that otherwise require more stringent safeguards.
Construction activity disturbing between 1 to 5 acres of land.

Rules Deadline Looms

Permitting under the new rules began in December 2002. Operators of regulated small municipal sewer systems have until December 2007 to fully implement their Stormwater Management Plans. The regulations specify certain "best management practices," including permeable pavers, to achieve the goals of reducing runoff volume and pollution.

"Permeable pavers have been used in a variety of applications in which stormwater runoff was a concern," Jay Krech, national sales manager for Willow Creek Concrete Products in Kimball, Minn., said. Willow Creek (willowcreekpavingstones.com) is a manufacturer of Aqua-Loc Permeable Concrete Paving Stones in the Upper Midwest. "City streets, sidewalks, parking areas, driveways — any area that requires a pavement surface can be designed with permeable pavers. Aqua-Loc permeable pavers have been particularly effective in areas near lakes, rivers and streams."

Research has shown that permeable concrete interlocking paver surfaces can reduce runoff volume by 90 percent or more. Permeable paver surfaces significantly reduce the runoff loads of such contaminants as nitrite, nitrate, phosphate, phosphorus, metals, BOD and ammonium at higher levels than even permeable asphalt or concrete surfaces. In addition, permeable concrete pavers reduce the temperature of runoff water by several degrees more than asphalt surfaces, which benefits fish such as trout and other aquatic life sensitive to temperature fluctuations.

A permeable paver system permits stormwater to drain through voids between the pavers into subsurface aggregate detention areas. From there, it's directed through a series of natural filtration processes before gradually exiting the system. By creating subsurface detaining and filtration areas, the need for space-wasting detention ponds is dramatically reduced or even eliminated.

Because of flexible surfaces, permeable pavers tolerate movement from freeze/thaw cycles without damage, making them especially well-suited to harsh northern climates. Permeable paving stones also may be removed and replaced for easy, virtually invisible repairs to underground utilities.

Commercial Project

In a recent installation, Willow Creek Aqua-Loc permeable pavers allowed a business owner in Afton, Minn. to expand without removing a paved driveway. Afton's building requirements limited the amount of impervious surface on individual properties to 20 percent maximum site coverage in the downtown area, which lies in the floodplain of the St. Croix National Scenic Riverway.

"He exceeded the limit with the traditional driveway he had," Mitch Berg, Afton city administrator, said. "We came up with an agreement that said he could expand and continue to exceed that if he put in a pervious pavement."

Berg says he sees the potential for more permeable pavers in Afton.

"We've got many buildings that are already at or above the 20 percent threshold. If they want to do any expansion or remodeling or renovation, they'll have to address that."

Jay Riggs, district manager for the Washington Conservation District, oversaw the Afton Aqua-Loc project. He agrees that permeable pavements increasingly will be used to resolve stormwater runoff issues.

"Residential streets, commercial parking lots, residential driveways — I see them having application in all those areas. It all depends on the sensitivity of the receiving waters of the stormwater," Riggs said. CM