According to a recent study performed by the U.S. Geological Survey (USGS), the removal of the concrete Good Hope Mill Dam in Conodoguinet Creek, Cumberland County, PA, did not harm the environment, as some citizens had feared.
The dam was removed to mitigate safety concerns and promote the free passage of native fish, most notably, the American Shad. Specific concerns about the effects of the dam removal included large fish kills, toxic sediment release, and fear over the Creek drying up.
In September 2001, the Pennsylvania Department of Environmental Protection (DEP) accepted bids for the removal of the dam.
“This orphan dam with no owner of record has deteriorated to the point that it now is a safety hazard to stream users during high water conditions,” said Bureau of Waterways Engineering Director Michael Conway in 2001. “Since there is no owner, we must take steps to remove the dam to protect public safety.”
The dam was built around 1918. The structure was 240 ft. (73.1 m) long and approximately 5.5 to 6 ft. (1.7 m to 1.8 m) high. It consisted of a combination of rock-filled wooden timber, stone masonry, and concrete (a total of approximately 310 cu. yds. [237 cu m] of material).
“It was considered an attractive nuisance, a public safety hazard, an obstruction to the natural flow of the river, and thus an obstruction to fish migration. No persons or organizations could be found to take ownership. Ownership of the structure would have involved repairs, maintenance, installation of safety signs, periodic patrolling, and the acceptance of the liability that would be associated with the dam,” said Jake Kernoschak, project coordinator of the DEP Bureau of Waterways Engineering.
“As with any dam removal, there were a few local objections,” said Kernoschak.
“These generally come from the people living upstream of the dam who have always enjoyed the ponded water effect and have used it for recreation such as fishing, canoeing, and swimming. At Good Hope, there were some individual objections and loosely organized group concerns regarding the removal, but the broadly organized effort to stop removal never really materialized once they realized the costs and responsibilities they would be assuming if they took ownership of the dam.”
On Sept. 24, 2001, the DEP awarded the demolition contract to John W. Gleim Jr. Inc. of Carlisle, PA, for its low bid of $32,200. Work began Nov. 2, 2001 and was completed Nov. 8, 2001. Funds for removal were provided through American Rivers and the U.S. Fish & Wildlife Service.
To accomplish the work, the contractor utilized a track-mounted Case 9040B backhoe with an opposable thumb, a slightly smaller track-mounted Cat excavator fitted at various times with either a jack hammer or a backhoe bucket. Gleim also used a front-end loader on tires and numerous tri-axle dump trucks for hauling the material away to an approved spoil site.
“The project went off without a hitch. The work was completed several weeks in advance of the completion date that the DEP had set for Gleim,” said Kernoschak.
“Optimal weather and low-flow creek conditions made it possible for us to finish the job ahead of schedule,” explained Dale Bentz, manager of Gleim Environment Group, a department of John W. Gleim, Inc.
“We also were within eight miles of the disposal site; the Pennsy Supply Quarry at Silver Springs,” continued Bentz. Gleim Environmental Group specializes in watershed restoration projects including stream restoration, dam removals and wetland construction.
“Worst-case concerns on how the Creek and aquatic organisms would respond to removal of the dam did not materialize,” said Jeff Chaplin, USGS hydrologist and report coauthor.
In fact, the major finding of the report, which examined how the shape of the stream channel, water quality, fish and aquatic organisms, sediments, and aquatic habitat responded, is that there were few effects from removal of the dam.
Scientists attribute the lack of significant changes in part to the absence of fine sediment, which dams often trap in large quantities along with toxins. The shape of the channel and habitat that supports aquatic life did not change much also because of the low supply of sediment.
“The outcome of a dam removal is very site specific,” said John Nantz, information specialist of USGS. “Our agency tests the hydrologic and chemical properties in the water pre- and post-demolition. Many of the dams in this area were built in the late 1800s and early 1900s, so there has often been years of industrial waste such as arsenic, lead and PCBs dumped into the water. The Good Hope Mill Dam had low sediment build-up, making it a good candidate for demolition.”
When a dam is being considered for removal and the environmental tests detect large amounts of sediment and/or toxins, the dam may be dredged prior to removal. Dredging is often costly, however, and treatment/disposal of the waste can pose a problem.
The Pennsylvania Fish and Boat Commission is currently deciding the fate of the Glenburn Pond Dam in Lackawanna County. Environmental tests performed at the dam showed high levels of sediment and toxins, eliminating dam removal as an option until the toxins are properly removed.
“The owners of the dam no longer want to deal with the upkeep and financial responsibilities associated with the dam,” said Dave Kristine, fisheries biologist of the Commission. “They knew that the contaminant issues needed to be addressed as well, so they’ve turned it over to the Commission in order to restore the stream to free-flowing condition and improve the water quality.”
While no action has been taken yet, the Commission is working on securing funds for the engineering design and removal of the dam.
“We will probably use a combination of dredging and drawing the impoundment down to allow vegetation to re-establish in order to stabilize the exposed sediment before the dam is breached,” said Kristine.
Fortunately, removal of the Good Hope Mill Dam was not hindered by these types of obstacles. With respect to water quality, the dam removal changed how some constituents vary throughout the day, but it did not affect the daily maximum or minimum concentrations.
Scientists noted a short-term (weeks) change in the community of aquatic organisms living in the vicinity of the dam. Within a year, the community composition became similar to other communities outside the influence of the dam. Changes observed in the fish community were within the scope of natural fluctuations and could not be attributed to removal of the dam. CEG