DEEP: DEEP Announces Temporary Repairs Will Be Made to Pachaug Pond Dam, Griswold

2017 Press Release
October 5, 2017
DEEP Announces Temporary Repairs Will Be Made to
Pachaug Pond Dam, Griswold

Drawdown of water to start Tuesday to allow for needed repairs

Connecticut’s Department of Energy and Environmental Protection (DEEP) announced today that immediate temporary repairs will be made to Pachaug Pond Dam, Griswold, to address increases in the rate of seepage of water through the masonry wall of the spillway. 

In order to undertake the necessary repairs, Pachaug Pond will be drawn down 3.5 feet beginning Tuesday (October 10).  DEEP plans to maintain the drawdown through the winter, and then begin to restore the water level at Pachaug Pond starting in late March or early April 2018.

Monitoring of seepage will occur over the winter.  If no significant changes are noted, the pond level will be allowed to return to normal levels and an inspection will be performed to monitor the results of the temporary repairs. If the temporary repair is determined to be satisfactory, the water will be allowed to flow again down the spillway.
Temporary Repairs
The proposed temporary repairs include drainage (pumping) of the stilling basin to create a safe working platform replacement (if possible/feasible) of missing masonry with on-site stone masonry and filling of any other visible voids with cementitious repair mortar. On the dam crest, grouting the voids behind and between existing capstones will be done to the extent possible.  A drawdown of 3.5 feet will be necessary to facilitate the temporary repair to the downstream face and spillway capstones.

Background Information

Pachaug Pond is an 817-acre pond retained by an earthen dam approximately 750 feet in length and 17 feet high. The spillway is a 121-foot long stone masonry broad crested weir, flanked by stone masonry training walls on either side. There is a gate house structure and sluice gate located along the right training wall of the spillway at the crest of the dam.

As a result of an inspection conducted during a maintenance drawdown last October, Macchi Engineers, LLC was hired to design repairs due to visible seepage through the downstream face of the dam.

A more recent inspection showed that conditions required some immediate, temporary repairs, because of increased seepage that was observed, prior to the start of the overall project.

The permanent work proposed for the fall of 2018 will be protected by a cofferdam and there is no plan, at this time, to draw down Pachaug Pond to accommodate this construction. The project will improve the spillway, training walls, toe drains, reinforce the upstream face of the earthen dam and update the dam to handle potential extreme precipitation events.