WINDHAM — Dinsmore Brook in Windham is one of four streams along Interstate 93 the New Hampshire Department of Environmental Services has determined to be impaired for chloride.
“The levels of chloride in the brook are higher than they should be,” said Pete Stamnas, the Department of Transportation I-93 project manager. “The use of salt in the winter is collecting in Dinsmore Brook over time.”
The other three streams include Policy-Porcupine Brook in Salem and Windham, North Tributary to Canobie Lake in Windham, and Beaver Brook in Derry and Londonderry.
Those areas now have Total Maximum Daily Loads, or what Theodore Diers of DES calls a cleanup plan to reduce chloride.
“A TMDL is a best guess at what you need to do to achieve water quality standards,” he said.
The streams have stalled the paving of the fourth lanes in the I-93 widening project. the expanded highway is built for eight lanes, but only six will be paved for travel until the water quality issues are resolved.
“They have to prove they can maintain that fourth lane without using any additional salt,” Windham highway agent Jack McCartney said. “They have to show they can reduce from Exit 1 all the way to Exit 5.”
For now, the DOT has built the footprint for four lanes in the areas, but will only finish three lanes.
“Until the impairment is removed, or a plan to remove the impairment is in place, we are only able to pave and operate three lanes in the Dinsmore Brook watershed,” Stamnas said.
Four lanes would keep I-93 uniform throughout the state and prevent bottlenecks, McCartney said.
Windham would see economic growth once the lanes are expanded, Town Administrator David Sullivan said.
“Any improvements from what we have today will be a benefit,” he said. “Going from two lanes to three lanes will be a benefit.”