| Corey Clark, P.E., Chief Engineer at the Dam Bureau, NH DES, has this update on the situation at Dolloff Dam:
“The good news is that Pawtuckaway Lake is now full. The sinkhole at Dolloff Dam has not increased in size since it was first observed this spring and leakage through the dam has stabilized at the full lake elevation. However, we are still physically monitoring the site twice a week and several sensors are still providing real time data on the rate of leakage and the water level in several monitoring wells. We are still concerned that sediment is being transported with the leakage resulting in the continued loss of embankment material from the dam. While the volume of sediment is very low, it still needs to be monitored for changes or increases and ultimately needs to be remediated. Diving is scheduled to take place at the dam next week and we are currently working with our engineering consultant to schedule additional test borings at the dam. It is likely that these borings will take place later this summer and will allow us to better understand why the sink hole has developed and what can be done to remedy the situation. It is likely that any remedy will be temporary, and a much larger future rehabilitation of the dam will need to occur to mitigate this and other dam safety issues. Additionally, the removal of Burnhams Marsh Dike has been completed and the site of the former dam has now been restored to what we believe was the condition of the site prior to the installation of the dam. While I hope you find this email as good news, if we observe that the sinkhole is increasing in size or if the structural stability of the dam is questioned, then we will again start lowering the elevation of Pawtuckaway Lake to reduce the risk of an emergency situation from developing. Should that need arise I will notify everyone on this email as soon as possible. I will discuss the status of things when I speak at the Annual Pawtuckaway Lake Improvement Association Meeting on June 14th at 9:30am at the Pawtuckaway State Park Pavilion. Hope to see you there.” |