2008-05-06 - Laserfiche WebLink

Home Browse Search

2 year plan, though they encourage a 50 year plan. He said that theoretically dredging the South Fork Reservoir could get us close to meeting the demand and we would only need to raise the Ragged Mountain dam to 30’, with a gravity fed pipeline to the Mechums. He said dredging was eliminated as an option because we were told that it would be too expensive. He said he thinks it could be done for substantially less than estimated, and that would eliminate the need for a pipeline to Ragged Mountain which would save $60 million. Mr. Chris Gibson of Gahagan and Bryant, said his firm is a dredging engineering firm, not a water supply engineering firm. He said he was asked by a group of citizens to look at whether dredging the South Fork Reservoir is a feasible option. He said a feasibility study could be done. He said there is a different way and cost to moving different materials. He said what is done with the dirt is the most important question regarding cost. He said there are different dredging methods. He said the possibility of a pipeline to the airport was looked at, but the distance is too long and the topography is not conducive to having slurry material, so that does not seem feasible. He said the dirt needs to be put where the water goes back to where you want it. He said a physical and geotechnical site investigation would need to be done as well as a dredging feasibility study and dredging material management plan. He said his firm has a good history of cost estimation, and they have been within 10% of bids. Dr. Brown said that he met with the representatives of Gahagan and Bryant earlier in the day, and he wanted to confirm what he had learned from them. Dr. Brown listed what he understood from the meeting, and Mr. Gibson confirmed that he was correct: the permitting process takes between 12 and 18 months for dredging; the dirt that is easier to dredge is harder to dispose of, and conversely the dirt that is harder to dredge is easier to dispose of; the previous dredging cost estimates given to Rivanna Water and Sewer Authority sound reasonable though the handling cost after dredging seemed a bit high; the volume estimated to be dredged seemed reasonable but the timing seemed not to take advantage of the economy of scale since it was harder to find a site; the cost varies due to the material and where it is located; the pile needs to be stirred to get dry; a one step process would only work for a small amount; and noise is not a big issue (Mr. Gibson clarified that noise abatement is done, but dredging takes place 18 hours a day); there are ways to prevent the Reservoir from silting, but mechanical ways are problematic from a regulatory point of view. Mr. Taliaferro asked if odor is a problem, and Mr. Gibson said that if there are a lot of decaying leaves there would be some odor. Ms. Edwards asked what happens if contaminated material is discovered while dredging. Mr. Gibson said there are regulations dealing with that. He said he does not think there are huge possibilities that the Reservoir has contaminated materials. Responding to a question from Mr. Huja about the study costs, Mr. Gibson said site investigations would cost $100,000 and a feasibility study and development of a long term plan would cost $175,000. Mr. Norris asked if potential dewatering sites were identified. Mr. Gibson said that several feasible sites were identified, but they may not be politically feasible. He said that would be part of the feasibility study. Mr. Aaron Keno of Gannett Fleming, reviewed the engineering work that the firm has done for Rivanna Water and Sewer Authority for the past five years. He said it is estimated that 100,000 cubic yards of silt a year for 50 years would need to be removed from the South Fork Reservoir. He said the work done by Gannett Fleming was at the conceptual level and was not a feasibility study. He said there is a limited market in the Charlottesville area for use of the material, and no one in the South Fork Reservoir area was interested in accepting the material. He said if dredging is done it would produce a safe yield of only 14.3 mgd.