Let It Drain
While it’s true that retailers and developers are by and large embracing environmentally friendly programs and processes, the associated development costs aren’t so popular or easy to absorb. Developers in St. Louis have been grappling with significant cost increases stemming from environmental regulations and stringent standards that are part of the new Environmental Protection Agency (EPA) Phase II Storm Water Regulations (see sidebar). On a local level, under the St. Louis County Phase II Storm Water Management Plan, the Metropolitan St. Louis Sewer District (MSD) is requiring commercial developers to install better filtration devices to contain unwanted contaminants, such as fuel and oil, before storm water is flushed into the sewer system.
In some cases, that has required the installation of sand filters, underground detention and rain gardens, systems that can account for more than 55% of the cost of a typical parking lot.
A new product—porous asphalt—may offer a solution by reducing storm water runoff and potential flooding. Developed by St. Louis-based Pace Construction Co., the asphalt is currently being tested for the first time in the region by local commercial paving contractor Byrne & Jones Construction Co.
“Porous asphalt allows water to drain through it,” explained Brian Goggins, president of Maryland Heights, Mo.-based Byrne & Jones. Once the water seeps through the surface, it is held in a sub-base of clean rock and filter fabric before infiltrating the soil below or gradually draining from the site through an underground drain.
“It could save up to 30% of construction costs compared to typical sand filtration or rain garden systems,” Goggins added. Just as important, the porous asphalt meets the EPA’s requirements for storm water management.
The porous asphalt is currently being tested in a 130-ft., newly paved alley in metro St. Louis; it uses a higher grade of oil that has a better adhesive quality to maintain the integrity of the aggregate while allowing for 18% to 20% voids in the surface so water can soak through. The St. Louis Board of Public Service authorized the test paving on Cardinal Alley, at Cardinal and Park Avenues. Before the installation, MSD tested water quantity and quality in sewers just downstream from the test site, and will monitor water quantity and quality again next spring to measure the porous asphalt’s effectiveness in containing and filtering runoff.
Byrne & Jones laid the porous asphalt on top of 18 inches of rock with approximately 40% voids to allow water to filter freely. A porous geo-textile fabric beneath the sub-rock gives the pavement enhanced stability. In a recent demonstration, Byrne & Jones soaked the pavement with a fire hose to test its ability to shed rainwater. Over the next several months, the company will observe wear and tear on the surface.
“We’re expecting the wear-and-tear results to show porous asphalt wears similarly to conventional asphalt,” Goggins said. If testing is favorable, porous asphalt parking-lot installations could spell the end of curb cuts, which tend to contain the water to the site.