The dam is more than 100 years old and many of the stones are missing from the downstream face, with water flowing through the masonry at random locations, the consultants' report says.
Advantages of repairing the dam include maintaining the current look of the park and existing stream characteristics, while disadvantages include the need for a fish ladder and associated maintenance, and the fact that the type of repair recommended would detract from the historic nature of the dam, consultant John Keenan told the commissioners.
The recommended repair method is to encase the dam in concrete to fill in any holes and improve its stability.
A historically accurate restoration would require demolishing and rebuilding the dam with skilled stonemasons and would cost about three times the cost of the concrete encasement, the report says.
Removing the dam would allow the stream to return to a more natural condition, benefiting fish, but it would require extensive stream bank restoration and change the look of Devil's Backbone Park dramatically, Keenan said.
Upstream of the dam site, the water level would drop about nine feet, leaving steep banks, he said. Also, the stream velocity would increase dramatically, requiring measures to prevent additional erosion and transport of sediment downstream, the report says.
Keenan said a partial removal would be the "worst of both worlds," requiring both concrete work and stream stabilization.
Commissioner William J. Wivell said the report seemed "skewed toward dam repair" and said the cost estimates contradicted information presented by dam-removal advocates, who said removal is almost always more cost efficient in the long run.
Dave Biser, President of the Antietam Creek Watershed Alliance, asked the commissioners for more time to research grants for dam removal and consult with dam-removal experts for their feedback on the report.
Commissioner Kristin B. Aleshire said he favored the repair option, provided access to the repaired dam would not be restricted, a fish ladder would not degrade the appearance and the Maryland Historical Trust would agree to it.
Wivell said he thought it was unlikely MHT would agree to the concrete encasement plan and said he was leaning toward the partial removal option.
Commissioner Terry Baker said he was encouraged by the lowered estimate for repairs, but wanted to know if grants for dam removal would help bring the removal option more in line.
"I'm still torn as to what decision I want to make," he said.