Cos Cob drivers heading east on Old Post Road #6 will need a new route starting Monday, Oct. 5.

The Greenwich Board of Selectmen voted unanimously at their Thursday, Sept. 24 meeting to let the Department of Public Works (DPW) temporarily close the eastbound lane between Stanwich Road and Valleywood Road. Crews will install catch basins and a 20-foot-deep manhole that will intercept stormwater runoff before it floods Valleywood Road backyards.

DPW Deputy Commissioner Gabriella Circosta-Cohee told selectmen the project will capture water that now pours off Stanwich Road and pools in a low-lying stretch of Valleywood Road. "We're picking up the runoff that typically comes down Stanwich Road and makes a turn and turns into Valleywood Rd and into everyone's back yards into a bowl," she said at the meeting, as first reported by Greenwich Free Press.

The new catch basins will divert stormwater to an existing Connecticut Department of Transportation (CTDOT) structure beneath Route 1. The manhole's four-foot sump will trap sediment and debris before they cause downstream backups. Installing the manhole at that depth requires a crane on Route 1 and will temporarily close the driveway of a nearby medical office building. An alternate driveway will remain open.

The department announced the project on X on Sept. 23, saying it would begin in late September and last about two months. The board's approval sets Monday, Oct. 5 as the construction start.

The eastbound lane closure will not begin immediately. DPW estimates it will start roughly two weeks into construction, once excavation nears the Old Post Road #6 and Valleywood Road intersection, and last approximately two to three weeks.

The westbound lane will stay open throughout. During the eastbound closure, drivers will detour via Field Road to reach Valleywood Road. Signage at Chestnut Island will alert eastbound traffic on East Putnam Avenue.

At a separate point in the project, the westbound section of Stanwich Road will also close temporarily, with traffic routed up Field Road to Valleywood Road.

Construction hours are Monday through Friday, 6 a.m. to 7 p.m., and Saturday, 9 a.m. to 5 p.m. DPW does not plan nighttime work. Police and traffic-control personnel will be on site during active construction.

The work is Phase 1 of a three-phase drainage improvement effort. FGB Construction is the general contractor. DPW had originally announced a spring start in April, but the project was delayed because the custom 20-foot manhole took longer than expected to manufacture.

Circosta-Cohee asked the board to waive its standard second reading so the vote could proceed at the same meeting, and selectmen agreed. No timeline for Phase 2 or Phase 3 has been announced.