WESTFIELD – The Massachusetts Department of Transportation is seeking to install a detention basin alongside Route 20 to improve the quality of stormwater being discharged into the Westfield River.
DOT engineer Alex Murray and consulting engineer Benjamin Lundsted of Comprehensive Environmental Inc. of Merrimack, N.H. presented details of the project to construct a detention basin at the end of an existing drainage swale created during construction of the Army and Air Force National Guard bridges to the Conservation Commission last night .
Murray said the current drainage system collects stormwater for four acres of pavement, or impervious surface, at the intersection of East Main Street (Route 20) and Little River Road (Route 187) and the entrance to the Home Depot store.
That water is currently discharged from a 36-inch pipe and runs through the swale into the Westfield River. Murray said the state has a program to improve water quality throughout the Commonwealth and that the DOT is focusing on stormwater issues with the goal of improving the quality of stormwater being discharged into rivers and ponds.
The state is proposing to create the detention basin with baffles at the end of the swale to slow the velocity of stormwater, which will allow sediment to settle out of the water before it is discharged into the river. The detention basin would have several “chambers” to collect sediment and an overflow pipe terminating at the river.
Murray said the work would occur in the state’s right of way and in an area of “previously disturbed soils.”
“The Westfield River is impaired,” Murray said. “This project is designed to mitigate the effects of (stormwater) runoff into the river.”
A primary target is to reduce turbidity of the river water by removing solids and nutrients such as “phosphorous and nitrogen that can be associated with highway runoff,” Murray said. “The idea is to hold back the water and release it slowly to allow solids to settle out.”
Lundsted said the detention basin is designed to hold 30,000 cubic feet of stormwater.
“That is equivalent to two inches of rain falling on the impervious area being drained by this system,” Lundsted said. “This is a retrofit to an existing (drainage) system.”
The commission supported the idea of improving the quality of stormwater being discharged into the Westfield River, but also expressed reservations with the plan as presented. The primary issue of concern voiced last night is compensatory storage, floodwater that will be displaced by construction of the detention basin structure.
The commission voted to continue the hearing to its Aug. 13 session to allow further refinement of the project to address the concerns raised last night.
