Paving plan is full of holes, but may help with sprawl

In the Chicago area’s topsy-turvy climate, where floods and droughts areknown to take turns causing headaches, a pavement that could help ease bothhas begun to seep into planners’ thoughts.
Used in Europe for decades, so-called permeable pavement allows rainwaterto pass through instead of running off into rivers or lakes. Made of eitherporous asphalt and concrete or paving stones shaped to leave gaps at thecorners, the surfaces are just starting to catch on in the area as part of themovement toward “green building,” which seeks to lessen the environmentalimpact of development.
Its potential has the paving industry speaking in near-religious terms,said Chuck Taylor, general manager of Advanced Pavement Technology in Oswego.
“Any horizontal surface that is being paved now could theoretically bepaved with permeable pavement,” Taylor said. “We could immediately reduce theamount of runoff, capture the first-flush pollutants … [and] promotegroundwater recharge so we can replenish our drinking water.”
Chicago has used permeable pavement as part of a “green alleys” program andplans to use it in streets in the next year or two, said Department ofTransportation spokesman Brian Steele.
“It works especially well in alleys, where drainage is a problem,” Steelesaid, because most are not hooked into storm sewers and are lined withdecidedly non-absorbent garages.
There are two main types of surfaces.
Porous asphalt and concrete are mixed as usual but without sand or othersmall particulates.
The resulting substance, which has been described as like a Rice KrispiesTreat, allows water to pass straight through to a gravel base.
The other system uses paving stones shaped to leave gaps at the corners,filled with fine gravel or dirt and grass, that act as miniature drains.
Many of their uses are interchangeable, but there are differences in thematerials, experts say. Porous asphalt and concrete drain better and arebetter for high-speed roads, more than 40 m.p.h., where pavers can be noisyand tires can suck the gravel out of the joints.
Pavers are more attractive and more durable than porous asphalt, which hasto be laid down much thicker than regular asphalt to handle heavy traffic.
Some questions remain about whether the pavement will become clogged overtime and how well it will stand up to northern freezes, but environmentalistsare generally enthusiastic.
“It’s one of the more exciting and buzzworthy technologies these days,”said Max Zahniser of the non-profit U.S. Green Building Council, whichpromotes environmentally friendly building.
In the last few years dozens of surfaces have been paved with thematerials, from the Morton Arboretum in Lisle to the Villa Park police stationto a subdivision in Highland Park. They are also in use across the country,especially in the Southeast and Pacific Northwest. Various studies are tryingto compare surfaces to see which drain and filter water the best.
“With all the building going on, [green construction] is going to be moreand more needed. We should do a lot more of it,” said Susan Hall, a landscapearchitect for the Lake County Forest Preserve District, which installed a testsurface of permeable asphalt at the Ryerson Woods Conservation Area’s WelcomeCenter, which opened last summer.
Other than a sign warning heavy vehicles to keep off, Ryerson’s looks likeyour average asphalt parking lot except the blacktop is unsealed and hasnoticeable spaces between the rocks.
Underneath is 3 feet of loose gravel that traps water until it can soakinto the ground. As it does, naturally occurring microbes attack pollutantssuch as oil and antifreeze, helping break them down before the waterreaches–and recharges–aquifers that supply well water.
A clean-water grant from the Illinois Environmental Protection Agencypicked up 60 percent of the tab, Hall said.
The Lake County Stormwater Management Commission signed up early to see howthe system works and whether it might be useful, especially in a county stillrapidly developing in parts, adding more water-dependent humans while pavingover more land, causing wells to suffer.
The agency does have doubts, including how well storm water will beabsorbed by the clay soil of Lake County and whether the gravel retention basewill fill up with silt, reducing the volume of water detention.
“We don’t have much experience with it, and we wanted to see how it works,”said Bob Gardiner, an engineer for the agency.
The surfaces can cost up to twice as much but last much longer, said TomPrice, an engineer with Conservation Design Forum, a consulting firm inElmhurst.
An analysis for a new lot at the Morton Arboretum found that after 20years, the porous-paver construction will be more cost-effective, Price said.
Others in the industry say that taking into account less need for drainageinfrastructure, the work can be done for about the same cost.
“As we’re trying to control sprawl, and there are concerns about theefficient use of land, I think it’s great for urban planning,” Price said. “Ithas the opportunity to really address many issues.”
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dgibbard@tribune.com