Ohio scraps filtration system for rainwater runoff

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COLUMBUS, Ohio (AP) -- Filters on Ohio roadsides used to reduce pollution from the rainwater runoff don't work and won't be used anymore, transportation officials said.

The state has used exfiltration trenches since 2005 as a pollution-control feature in new and expanded highways.

They were supposed to replace the concrete rain channels that separate curbs from asphalt. Instead of flowing straight to a storm drain, rainwater is supposed to soak through layers of porous concrete and gravel to filter pollutants.

Now they've been scratched after researchers at Ohio University determined they are prone to clogs, The Columbus Dispatch reported Monday (http://bit.ly/1gxhCe2 ).

"A lot of debris settles on top and around it and it decreases its effectiveness," transportation spokeswoman Melissa Ayers said.

The finding undercuts the state's efforts to meet state pollution standards that are supposed to protect streams and aquatic wildlife from storm runoff.

It's not clear how many exfiltration trenches have been installed since 2005. Since 2006, the Ohio Environmental Protection Agency has required pollution-cutting measures for all new roads and any road repair projects that pave over at least 1 acre of soil.

Researchers found that debris that collected on top of the trenches increasingly kept water from soaking into the porous concrete. Sand and other debris diverted as much as 80 percent of rainwater from soaking into the filters even after they were cleaned.

Fish and aquatic insect species deemed sensitive to pollution are at risk when as little as 4 percent of a stream's drainage area is paved.

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Information from: The Columbus Dispatch, http://www.dispatch.com