How One City May Put an Alien Species to Good Work

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On the shores of the Puget Sound, Olympia, Washington's capital city, gets an average of 51 inches (130 centimeters) of rain each year, causing the city's streams to swell during a storm.

Rain that hits city streets and sidewalks runs off in a torrent known as storm water. The same roads that cars and people use become conduits for rainwater during a storm. Storm water engulfs local creeks and streams.

Olympia is growing rapidly, and with more development comes more pavement. Water running off the paved areas of the city is funneled directly into streams, often causing floods. Waterways are often contaminated by pollutants washing off the roads.

Storm-water drainage may be the biggest environmental problem the city faces, said Emmett Dobey, a program manager at the city's Department of Public Works.

This is where the slipper limpet can come to the rescue.

The scoop-shaped shell of the snail could help slow storm water. Currently the city uses rock and gravel beneath sidewalks to stabilize the concrete. City officials want to try using snail shells instead.

Water Traps

Millions of snail shells could act as tiny traps for storm water, releasing it slowly to retard the flow to the city's streams and storm-water holding ponds, Dobey said.

Dobey and others have tested the shells under sample sidewalk. They found that the shells held the water back for much longer than sidewalks' traditional underlay—enough time, Dobey said, to significantly slow the flow from street to stream.

The process also seemed to reduce the amount of pollutants that typically come along for the ride, he said.

Streets and sidewalks aren't the only paces that may benefit from shell underlays.

Olympia is trying to encourage its growing population to get out of their cars. It is using bike paths and sidewalks to make the city more friendly for walkers and cyclists.

One project would connect a series of parks via new paths, and this is where Dobey wants to put in shell-lined surfaces. An EPA grant would be used to make the new sidewalks. But even if the city doesn't get EPA funding for the project this year, it will begin construction on a few sidewalks this spring and summer, Dobey said. "We're starting to design them right now."

The project could be a bonanza for oyster harvesters. Right now the snail shells they scoop up while harvesting oysters are a nuisance. But what if they could get some economic benefit from the bycatch?

The city is "thinking outside the box, and that's great," said Tim McMillin, the president of Olympia Oyster, a Shelton, Washington, company that has harvested Puget Sound's oysters since 1878. If the project goes ahead, McMillin said, "I could sell these pest snails, make a little money, and clear out the ground for more oysters."

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