By DAVID SMITH/ecoRI News contributor
A contract to remove the 112-foot-wide concrete White Rock Dam on the Pawcatuck River was awarded to SumCo Eco-Contracting LLC of Salem, Mass., on April 23 for $710,869, according to Scott Comings, associate director of the Rhode Island Chapter of The Nature Conservancy.
The dam is on the border of Westerly, R.I., and Stonington, Conn. The contractor will have access to the dam on both sides of the river, but the main staging area will be from a piece of property on the Westerly side owned by Cherenzia & Associates.
The contractor is expected to begin bringing in equipment and supplies to the property adjacent to the dam in June. According to regulations, work on the river can’t begin until July 1.
“They know what they are doing,” Comings said about SumCo. “They have done a lot of these (dam removals).”
SumCo removed the Kenyon Mill Dam in Charlestown in 2013, the last dam project on the Pawcatuck River.
Comings said the first work will be to build a bridge across a sluiceway and work on sculpting the river bed below the dam. The Nature Conservancy is working to maintain the level of the river below the dam so that it doesn’t change the potential for flooding.
When that work is complete, a cofferdam will be built upstream of the dam to dewater it and aid in its removal.
There will be signs on the river notifying boaters of the construction project and to direct them to a path for safe portaging while the project continues into October. The granite wall sluiceway, which has been a favorite for kayakers and canoeists, will not be removed. A barrier will be built in front of it on the upriver side and water will only flow into it during high water, Comings said.
“It will be neat to see the river run free for the first time since we became a country,” Comings said.
The first dam at the site was built in 1770. It was rebuilt several times over the centuries. When the dam was washed away in the 1938 Hurricane it was again rebuilt using concrete.
Comings said that if excavation reveals parts of the original rock and wooden dam, work will be halted for a few days so that it can be recorded. He said it is possible that when it was rebuilt workers used the same stone foundation.
Nils Wiberg, an associate with Fuss & O’Neill Engineering of Providence, has said that because the level of the river is so flat in that area, the water levels will drop from 2.5 to 3 feet at the dam, from 1.5 to 3 feet upstream at the Boom Bridge Road Bridge and up to a half-foot at Potter Hill Dam, more than a mile upstream.
Wiberg said tests on the sediment behind the dam show the usual levels of volatile organic compounds and metals expected to be found in a river system dotted with mills, but that the levels are all below exposure levels established by the Environmental Protection Agency (EPA). That means the sediment will stay on site and be used to form the new river channel or distributed in the old canal and capped with rock.
White Rock would be the third dam on the Pawcatuck River earmarked either for removal or modification. The effort is designed to improve fish passage on the 20-plus-mile waterway that stretches from Worden’s Pond in South Kingstown to Little Narragansett Bay in Westerly. The work is also expected to reduce flooding above the site.
About 15 miles upstream, the Kenyon Dam and Lower Shannock Falls Dam have been removed, while a fish ladder was built at the historic Horseshoe Falls.
A total of $1.9 million in federal Sandy funds is available for the White Rock project, according to Comings.
Comings said that the engineering contract for the White Rock project is $313,793, and will cover all three phases of the dam removal and the first phase of study regarding Bradford Dam, about 6 miles upstream.
Fuss & O’Neill has done the work on the two dam removal projects and the building of the fish ladder at Horseshoe Falls Dam.