South Fork Task Force drills dredging expert with questions
First of three stories
Dede Smith represents the group Citizens for a Sustainable Water Plan on the South Fork Reservoir Stewardship Task Force. Smith was formerly the director of the Ivy Creek Foundation which is dedicated to the protection of the Ivy Creek and Ragged Mountain natural areas. She is opposed to the construction of a new dam at Ragged Mountain and has recommended that the South Fork Rivanna Reservoir be dredged to restore its original capacity as the first step in the community’s long term goal to increase its water supply. Smith has repeatedly asked for the task force to spend some time with a representative of dredging firm
Gahagan and Bryant
to get clearer answers on what dredging would entail. She got her wish at the task force’s meeting on November 13, 2008. Chris Gibson spent over an hour answering questions about the cost of dredging, how the permitting process might unfold, and other logistical issues.
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Gibson said that his firm has not further studied the reservoir since
coming to visit in May 2008
, and was waiting to see what the outcome of the task force would be. At that time, Gibson had suggested that the community first establish reasons why it would be dredging the reservoir before seeking permits and bids.
The task force’s charge is in part to answer that question
Much of the discussion focused on the cost of dredging. Gibson said it would be hard to give an estimate without clearly knowing what is on the bottom of the reservoir. If tree stumps are left over from when the reservoir was flooded, Gibson said that would mean a different kind of dredge would need to be used. He also said it would be hard to come up with an estimate of how much on-going maintenance dredging would cost without having more information on what kind of material is on the reservoir floor.
“Figuring out what the logistics are, the type of material you’re dealing with and what you can do with that material, once you have those, you can get a pretty firm grasp on what it’s going to cost,” Gibson said.
Gibson said it would be hard to guarantee a cost estimate given that 30% of the cost of dredging is related to the cost of fuel. While oil prices may currently be down, it is impossible to predict what the cost of diesel fuel might be when dredging begins.
Gibson did lay out some constraints under which his firm would dredge. They would only dredge up to Reas Ford Bridge because it would be difficult to get equipment past that point. Equipment and fuel would need to be stored on a site that is at least 200 feet by 200 feet. A road capable of handling at least 35,000 pound loads would be necessary to get to that staging area. A crane would need to move the dredging boat onto the reservoir.
Wren Olivier, who is representing the Piedmont Group of the Sierra Club, asked Gibson if the South Fork Reservoir is similar to any of his other projects.
“The biggest difference you’ve got with what we do and what I do day to day is the topography around the site,” Gibson said. He said the reservoir is down in a deep valley, and dredged material would need to pumped at least 60 or 70 feet uphill to a dewatering site. Gibson said that was not impossible but would involve complex engineering. He said if the nearby quarry were chosen as a disposal site, many of those logistical challenges would “go away” but “a good bit of lift” would be required to transfer the dredged material to the site.
Thomas asked how the cost of the project would be affected if only selected portions of the reservoir would be dredged. Gibson said there might be financial advantages to a smaller project, but it would depend on where the site was selected and how many booster pumps would be required to transfer material to the dewatering and disposal site. He said the noise of the pumps would be “somewhere between a Dodge pick-up and a Mack truck” and he did not think it would be an issue. The cost of obtaining an environmental impact study would range from $50,000 to $200,000 and would not be included in the feasibility study.
“The feasibility study gets you to the point where… there’s enough information to make an educated and reasonable decision on whether to move forward or to stop,” Gibson said. Data collected would include geotechnical investigations to determine the make-up of the material, geological surveys of potential disposal sites, a side-scan which would use sonar to determine what lies above the sediment, as well as a bathymetric study. Comparing both the side-scan with the bathymetric study would create a more detailed picture of the bottom of the reservoir.
Karen Joyner of the Ivy Creek Foundation asked Gibson if Gahagan and Bryant’s feasibility study would cover all of the possible options. Gibson responded they would look at up to five of potential dredging scenarios.
August 2008 tour of the South Fork Rivanna Reservoir
Gaffney said that when the task force took a tour of the reservoir, they noticed many new islands that have been created since the reservoir was formed in 1966 that might be protected by the federal government as wetlands. Did Gibson think this would pose an obstacle to receiving a permit to dredge?
Gibson said he did not know what the U.S. Army Corps of Engineer’s stance would be on that, but did say that he knows the mitigation ratio for wetlands could be as high as four to one. That means that every acre of wetlands destroyed would require the creation of four somewhere else. The required mitigation for the permitted dam and pipeline project is two to one, and involves the use of land the RWSA purchased at Buck Mountain Creek. Gibson recommended trying to avoid dredging any of these new islands to keep project costs lower, although he acknowledged that would reduce the amount of storage capacity that would be restored.
Gibson said it would take at least 18 months to conduct the feasibility study, conduct the environmental assessments, and obtain a permit from the DEQ and the U.S. Army Corps of Engineers. Only after a permit was in hand could an RFP be issued to dredging firms.
Wren Olivier asked how long it would take to fully dredge the South Fork Reservoir back to its original capacity. The working estimates assume that 2 million cubic yards of sediment would need to be initially removed, as well as the periodic removal of 5 million more cubic yards over the life of the 50 year water plan. Gibson said it would take as much as a year, but he could not guarantee that given that he does not know enough information about the reservoir to determine if icy conditions would require dredging to cease during the winter.
As the questioning wound down, Gibson summarized his philosophy on how he as a contractor approaches projects such as this.
“Give those people that are elected to the make the choices, give them all the information they need to make the best choices they can, but when you start making the choices for people, you’re getting out of the engineering world, and into the political world, and I like staying in the background and dealing in the facts,” Gibson said.
The November 13 meeting of the South Fork Reservoir Stewardship Task Force also featured expert testimony from two other speakers. Barbara Hutchison, Executive Director of the Charlottesville Airport Authority, spoke of the limitations of using dredged material as fill for the planned runway expansion project. Bob Wichser, the RWSA’s Operations Director, described how the chemistry of the reservoir would change when its bottom is disturbed by dredging.
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