Porous pavement gets another tryout in Maryland

The concrete oozed rather than poured out of the mixer truck, almost as if reluctant to cover the ground partly because it won't, entirely.

Laborers shoveled pebbly gobs around to form a new sidewalk at a park-and-ride lot in Waysons Corner, one of two where the State Highway Administration is laying "pervious" concrete this summer as a test of its environmental friendliness.

Porous paving surfaces have been around for decades, but they're expensive and often didn't work well. Interest in such surfaces among governments and developers is on the rebound, though, in response to new state regulations aimed at curbing stormwater pollution from pavement smothering the Chesapeake Bay watershed.

"There has been a resurgence in permeable pavement in the state and across the bay watershed in recent years," said Tom Schueler, head of the Chesapeake Stormwater Network, an organization that trains engineers and others how to deal with runoff.

Stormwater runoff is the fastest-growing type of pollution in the region, according to the U.S. Environmental Protection Agency, accounting for one-sixth of all the nitrogen and phosphorus and one-fourth of the sediment fouling the Chesapeake.

Rooftops, roads and other pavement are the conduits, as rainfall washes off their hard surfaces, eroding stream banks and carrying accumulated dirt, oil and other pollutants. The amount of ground covered by pavement and buildings has grown nearly twice as fast as the population, the EPA figures.

Maryland and the other states in the Chesapeake's watershed are under pressure from the EPA to do more to curb polluted runoff.

The pervious concrete being poured in Waysons Corner is a lightly cemented batch of pea gravel with air pockets between the stones intended to let rainfall soak through into the ground rather than run off into storm drains and streams.

Water-absorbing pavement can help mitigate the impact of new development, and it's one of the few ways of curbing runoff in inner-city neighborhoods, where there's little or no open ground.

The use of permeable pavement and pavers has spread gradually in commercial and residential developments, starting in the South, according to Colin Lobo, senior vice president for the National Ready Mixed Concrete Association.

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Porous pavement gets another tryout in Maryland