TRAVERSE CITY — An email sent to a state official describes an engineering design modification to the Brown Bridge Dam removal project two days before a breach flooded dozens of Boardman River residential properties.
The Record-Eagle obtained the emails this week. They document an exchange between Sandra Sroonian, an engineer who supervises the Brown Bridge Dam removal project, and Lucas A. Trumble of the Michigan Department of Environmental Quality's Hydrologic Studies and Dam Safety Unit.
Sroonian wrote to Trumble on Oct. 3 and requested a design change to the dam removal project. The change was necessary because construction workers unexpectedly encountered a “prior/historic structure” buried deep underground at the dam site, she said.
The discovery was made as workers built a channel-like device adjacent to the dam known as a dewatering structure, which was supposed to allow for a slow, gradual draw-down of Brown Bridge pond through an earthern embankment adjacent to the dam.
Sroonian told Trumble that as workers built the dewatering device in the embankment they drove sheet piling into the ground and struck a buried “historic structure” at the spot where the dewatering device was supposed to go.
“While driving sheet piling in the vicinity of the drawdown structure, resistance was unexpectedly high, requiring use of heavier equipment than anticipated,” Sroonian wrote to Trumble. “During subsequent excavation of the area at the dam where the drawdown discharge channel will be constructed, the cause of the high resistance was visibly observed.”
Sroonian said she and others saw parts of the buried historic structure sticking up from the bottom of the planned channel. She described what she saw as “cobbles/boulders embedded in stiff clay along with foundation materials, including steel sheet pile from a prior/historic structure.”
The discovery prompted Sroonian to ask for permission to make a change to the project design. She requested and received permission from Trumble to raise the elevation of a proposed concrete slab below the dewatering device by two feet, without having to modify a project permit issued by the DEQ.