A proposal to relocate a portion of Colvin Run in Great Falls as part of the Route 7 widening project has raised the eyebrows of some residents, but federal, state and Fairfax County officials say they are taking proper environmental precautions to protect the waterway and the historic mill across the road.
The Virginia Department of Transportation (VDOT) is widening a nearly 7-mile-long stretch of Route 7 between Reston Avenue and Jarrett Valley Drive just north of Tysons. The design/build project will be executed by Shirley Contracting Co. LLC and Dewberry.
Fairfax County Park Authority officials began working with VDOT in 2012 to ensure the circa-1811 Colvin Run Mill would not be harmed by the project, said Park Authority spokesman Judy Pedersen. Doing so will necessitate shifting Route 7 southward near the mill site and relocating a degraded section of Colvin Run, she said.
Colvin Run flows on the south side of Route 7 from slightly west of Carpers Farm Way to Difficult Run, located roughly 1,200 linear feet east of Carpers Farm Way, said VDOT spokesman Jenni McCord.
Park Authority officials asked VDOT to consider a natural-channel design for the Colvin Run relocation so as to protect surrounding forested wetlands, Pedersen said.
VDOT submitted 10 designs to the U.S. Army Corps of Engineers and the Virginia Department of Environmental Quality. The latter two entities reviewed the proposal, but indicated they only would approve a design that met all of their specifications, include reduced impacts to those wetlands, Pedersen said.
The Army Corps of Engineers indicated a trapezoid-shaped, straight-line channel would have the least impact to the wetlands, McCord said.
VDOT prepared a channelized stream-relocation design that met the regulatory agencies’ requirements and included a Gerry Connolly Cross County Trail pedestrian-and-equestrian connection beneath the Route 7 overpass at Difficult Run, Pedersen said.
The stream-relocation proposal chosen by the Army Corps of Engineers, dubbed Option 10C, would cost an estimated $3.75 million and convey 1,660 linear feet of Colvin Run through a straight channel lined with riprap or an equivalent material. The channel would not meander and there would be no floodplain. Workers would build a retaining wall on south side of Route 7 and provide a box culvert under Carpers Farm Way that would be angled to direct the stream closer to Route 7.
Under this option, Route 7 would be shifted 20 feet to north, a bridle trail would be built between Route 7 and Colvin Run and a pump-station access road would come from the north under Difficult Run bridge.
The proposed stream-location channel would be lined with articulated concrete block, which would allow grass to grow up through it, McCord said.
“There will be no impacts to historic Colvin Mill,” she said. “The existing waterway that powers the mill on the north side of Route 7 will not be impacted by the project.”
The Great Falls Citizens Association (GFCA) favored the first three options of the 10 available, all of which would have employed a natural-channel design. Option 1 would have had a wide meander, a wide constructed floodplain and a Cross County Trail/bridle trail between Route 7 and Colvin Run. Option 2 would have been similar, but with a narrow meander, step pools, rock vanes and narrow floodplain. Option 3 was identical to Option 2, but offered no floodplain.
Officials rejected all three of those options because of high wetlands impacts.
In a May 23 letter to Robert Berg of the U.S. Army Corps of Engineers, GFCA president William Canis wrote that Option 10C “is not a best practice” and “seems like a throwback to an earlier era that resulted in downstream degradation and erosion.”
“The unintended consequences of channelizing this stream will have to be addressed in the future, at great cost to the commonwealth or the Fairfax County Park Authority,” Canis wrote.
GFCA leaders have distributed a message asking group members to register their objections to the proposal with the Virginia Marine Resources Commission.
State Sen. Barbara Favola (D-31st) and Del. Kathleen Murphy (D-34th) also wrote a letter to Berg at the U.S. Army Corps of Engineers to express their support for the natural-channel options favored by GFCA.
Under proposed Option 10C, “the stream will become an unattractive sluiceway through which the abundant rainfall that seems to be the new normal will speed downstream and pour into Difficult Run, worsening the scouring and erosion that characterize too many local streams today,” the legislators wrote.
Several environmental permits are required for the project, including ones from the Marine Resources Commission, Virginia Department of Environmental Quality and U.S. Army Corps of Engineers, McCord said.
Those three agencies “may request more information from an applicant based on input related to the permit that they receive during the comment period,” she said.
Improvements being made under the Route 7 widening project also will include an extra travel lane in each direction; intersection improvements, including a soon-to-be-implemented triple-left-turn lane from westbound Route 7 to southbound Baron Cameron; a replaced and raised bridge over Difficult Run; a pedestrian underpass for access to Colvin Run Mill Park; and shared-use paths on either side of Route 7.
Construction on the project’s western end began in May, and work in the Colvin Run area will begin late this year and last until the project ends in July 2024, McCord said.