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Novel Pavement Means Cleaner Runoff Near Mall

July 15, 2009 - SOUTH PORTLAND — Motorists fuming at tie-ups caused by work on the Maine Mall Road this summer can take solace in the fact that the street will be greener come fall.

The state is tearing up nearly half a mile of the road in front of the mall to put down a layer of sand, gravel and porous pavement that should result in cleaner runoff heading into nearby Long Creek.

"It's the first step in terms of trying to address the issues raised on water quality in the watershed," said Erik Carson, South Portland's assistant city manager.

Peter Newkirk, project manager for the Maine Department of Transportation, said work will begin Monday. The contract calls for paving to be done by Oct. 1 and all work to be completed by Nov. 7. At least two lanes should stay open throughout.

The stretch being worked on starts near the mall entrance near the On the Border restaurant and runs almost to the intersection with Gorham Road.

The goal is to reduce the amount of pollutants flowing into Long Creek, which runs southeast of the mall. Runoff from acres of roads and parking lots carry oil and gasoline, heavy metals and other pollutants into the water.

Newkirk said the porous pavement approach has been used to reduce runoff in Europe and some southern states, but is still relatively new in the Northeast. The state plans an extensive monitoring program afterward to see how well it works.

The approach involves digging down about 30 inches and installing a series of perforated pipes that will tie in with existing drainage systems. A layer of sand goes on top of the pipes, and a bed of coarse gravel goes on top of that. The gravel is topped with porous pavement that allows rainwater to drain down to the filtration layer.

The pavement, Newkirk said, "looks like rice cakes as far as consistency."

In addition to filtering the water, the system also allows the water to cool before it flows into the creek. Water that sits on top of hot pavement before running off is too warm for the creek to support much life, he said.

There's also a safety benefit to the porous pavement because water drains down instead of pooling on top and causing cars to hydroplane, Newkirk said.

Because of the layers and digging, the project will cost about $1.5 million, roughly three times what it would cost to repave the stretch with regular pavement, he said. The porous pavement is expected to have the same lifespan, he said, about seven to 10 years.

Newkirk said MDOT isn't sure the system will work in the Northeast. One problem, he said, is sand, which tends to clog the pores in the pavement.

South Portland doesn't use sand on its streets in the winter, he said, but some neighboring landowners do. MDOT plans to work with them to try to minimize the amount of sand that gets carried onto Maine Mall Road.

"There's lots of questions we want answered," Newkirk said, but if the pavement works well in Maine, there are other areas where reducing runoff can have a significant environmental benefit. The pavement also produces less road noise, he said, so if it works on Maine Mall Road, it could also be used in places where the state wants to minimize noise, such as some highway off-ramps.

"DOT is not going to do this everywhere because it's more expensive, but we'll get benefits out of it and information," he said.

Carson said city and MDOT officials will hold a meeting to discuss the road work with residents and business owners from 5 p.m. to 7 p.m. Thursday at the Wyndham Portland Airport Hotel on Maine Mall Road.

By EDWARD D. MURPHY, Staff Writer, Portland Press Herald, July 15, 2009


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