BOLTON - The state's recent reclassification of Edgecomb Pond Dam as a "high-hazard"structure has triggered a requirement of the town of Bolton to conduct an engineering analysis, undertake safety upgrades, and prepare an emergency action plan in the case of a dam breech.
Edgecomb Pond Dam has been holding back drinking water without incident in Bolton since 1979. Following the failure of the Hadlock Pond Dam in 2005, the state Department of Environmental Conservation instituted tighter regulations for all dams, and the process prompted the re-classification. Responding to the state mandate, the town of Bolton hired C.T. Male Associates of Latham to conduct an engineering analysis and recommend upgrades.
Richard Wakeman, vice president of C.T. Male, said Monday that during a 2010 inspection of the dam by DEC, the structure was found to have a spillway design flaw so it didn't conform to New York State dam guidelines and it needed to be reconfigured.
A DEC survey determined that the Edgecomb Pond Dam fit the "high hazard" category because failure of the dam would likely result in widespread damage to homes, highways, infrastructure and loss of human life and cause substantial economic loss. Estimates cite that three minutes after dam failure, citizens downstream would face the onrush of water.
Although chances of such a severe storm occurring are minimal, extreme rainfall could threaten the lives and property of downstream residents, Wakeman said.
"There will have to be some revisions made to allow the event to pass without over-topping the dam," Wakeman said. "An auxiliary spillway to the south will need to be put in place."
Wakeman told town board members earlier this year that regardless of the change in the classification, the DEC requires that the spillway has to withstand water flow associated with a 100-year storm event, or one-half of a probable maximum flow of 33.6 inches of rainfall over 72 hours.
Such a storm event might send water five feet deep over the spillway, causing the embankments to collapse and the dam to fail.
The DEC requires all dams to have an emergency action plan in case of an extreme storm event. This plan was submitted to DEC before an Aug.19 deadline, Wakeman said Monday. In the unlikely event of an emergency, he added, the plan allows citizens and officials to be notified "ahead of time, not after."