Sunday, July 20, 2008 12:09 AM PDT
By Amy M.E. Fischer
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A new West Longview subdivision has the first privately built porous concrete street in Washington and has other environmentally friendly features that place it among the "greenest" residential projects to pop up recently on the Interstate 5 corridor, city officials say.
"It improves urban land instead of promoting sprawl, and it better mimics pre-existing conditions," said Longview Stormwater Manager Josh Johnson.
Containing 14 lots, Cascade Construction's final plat of "Homestead No. 4" at Ohio Street and 38th Avenue was designed to reduce water runoff that pollutes rivers with oils, brake dust, silt, pet droppings and other contaminants, Johnson said.
Instead of building stormwater detention ponds to trap run-off (and provide a breeding area for mosquitoes), Mark Questad and Joni Geier of Cascade Construction built a permeable street that allows water to seep through the concrete rather than wash across it.
The hard, durable surface, which is made using less fine sand particles and water than regular concrete, is supported by an open rock base that doubles as a water filtration field. The street slopes toward the middle instead of toward the curb so it can percolate through the pavement and into underground collection pipes.
Up close, its texture resembles wads of bubble gum mashed together with tiny gaps between them. It's more expensive to install and more delicate to work with than regular concrete, but it will last just as long, Public Works Director Jeff Cameron told the City Council earlier this month.
The concrete is fine for driving and walking, but "it might be a little rough to skateboard on," Cameron said.
In all, the development has 27 percent less impervious surfaces than a typical development. According to a city fact-sheet, "If all developments shed as little water as this one, then municipal and Diking District capital investments in stormwater infrastructure could be planned for farther into the future."
Permeable asphalt, which is similar, has been used in a handful of local commercial projects, including the parking lots at Quivers Restaurant, Don Connell Mini Storage, and the future
St. Vincent de Paul food and clothing warehouse on Baltimore Street, Johnson said.
The subdivision also ends in a "hammerhead" turnaround instead of a cul-de-sac. The T-shaped design requires less pavement and is easier for large emergency vehicles to maneuver. Another unique feature is that building lots were raised with fill to make homes less flood-prone.
Beneath the street and along the development's borders are 1,400 feet of 12-inch perforated pipe designed to catch, store and absorb runoff.
In natural areas, Johnson said, more than 99 percent of runoff flows through soils, forms little pools or is intercepted by trees. But contemporary development has disrupted this pattern, leading to pollution. Stormwater from farms, streets, rooftops and parking lots is the main reason almost half of U.S. waters are too contaminated for swimming or drinking, Johnson said, citing U.S. Environmental Protection Agency statistics.
By summer 2009, the state is requiring Longview, Kelso and other parts of the county to update stormwater runoff rules. One change is to encourage low-impact development practices that would reduce and treat runoff with filtration, landscaping, open space and site designs requiring less impervious surface.
According to Johnson, some of these techniques are challenging in the Longview-Kelso area because of poor soils, high water tables and steep slopes, but many developments are moving toward such practices.