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$660,000 DOT Antipollution Project Nears Completion on Rtes. 95, 295

Posted on: Tuesday, 30 August 2005, 18:00 CDT

WARWICK - Cardi Construction Corp. has nearly completed a $660,000 state project to clean the polluted stormwater runoff from the Warwick sections of Routes 95 and 295.

Under a Department of Transportation contract, the company has built artificial ponds and wetlands at four stormwater outfalls along the highways.

The work is part of a statewide effort to remove chemical and particle pollutants from highway runoff, to help protect resources ranging from freshwater aquifers to the shellfish beds in Narragansett Bay.

In recent weeks, travelers on Route 95 saw a construction crew working in wetlands off the southbound lanes of the interstate, just north of the Warwick Sewer Authority's treatment plant. The work area in wetlands runs about 500 feet along the highway and varies in depth from 50 to 100 feet.

The other work sites are off the southbound lanes of Route 95 at the Airport Connector; in the Route 95 median strip just south of Route 113; and in the Route 295 median strip at the Providence Street overpass on the West Warwick line.

Some earthmoving remains to be done at that last site, Stephen A. Cardi, the firm's treasurer, said yesterday. Later, all four will be hydroseeded and landscaped with trees and shrubs.

The polluted stormwater collected at the sites will no longer be dumped straight into the Bay via the Pawtuxet River, carrying with it oil, brake fluid, coolant, and dust given off by brakes and tires. Instead, the runoff will be collected in the artificial ponds so it can seep into the ground through sand filters.

The DOT will inspect the ponds annually and test for the volume of pollutants in them. When necessary, crews will dig out the sand and replace it.

Trees and shrubs will absorb some kinds of pollutants through their roots instead of letting them move through the environment.

Cardi said the contract calls for species of trees and shrubs suited to that purpose, among them inkberry, blueberry, red maple, summer sweet, Norway spruce, green ash, eastern red cedar, white swamp oak, red oak and black hawk viburnum.

"There's a lot of landscaping enhancement in this contract," he said, "and that should be done this fall, after we finish the underlying work."

J. Michael Bennett, deputy chief engineer at the DOT, said the federal Clean Water Act requires all states and municipalities to clean up their stormwater. The effort dates to 1991, Bennett said, when the late U.S. Sen. John H. Chafee obtained $16 million in federal grants to start documenting all of Rhode Island's stormwater drains and rank the quality of the streams and rivers that carry the stormwater into the Bay.

"We spend $2 million to $3 million a year designing and building these systems," Bennett said.

The ponds off Route 95 and Route 295 are big enough to hold the "first flush" of a heavy storm, he said, the water that washes most of the pollutants off the highway. In heavy rains, any excess water will spill over the top of the pond on the downstream end and flow into the river.

There are several ways to capture and treat polluted stormwater, but for the drains on Routes 95 and 295 in Warwick the state Department of Environmental Management approved building artificial ponds and wetlands.

Some cities and towns install "swirl chambers" to capture the first flush of stormwater and divert it into a concrete chamber where solids can precipitate out. (Some call a swirl chamber a Vortex, but that is a brand name for just one manufacturer.)

Swirl chambers were not the best solution on Routes 95 and 295, Bennett said.

"You can get very effective pollution control without big concrete structures," he said. The ponds "will take out a good deal of the pollutant constituents that even some of the swirl chamber units won't treat."

"The key is to slow the water down, let the solids settle out, and get vegetation growing around these artificial wetland environments," he said.

Some pollutants break down when exposed to air and sunlight in the pond, and others are taken up by the vegetation.

"It's a natural treatment that is very effective," Bennett said.

Source: Providence Journal

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