By Brian Wheeler
Charlottesville Tomorrow
Wednesday, June 23, 2010
A month after reviewing a proposal to build an earthen dam at Ragged Mountain, the
Rivanna Water and Sewer Authority’s
board on Tuesday discussed updated cost estimates for dredging sediment from the
South Fork Rivanna Reservoir
.
Even with a clearer picture of the costs of both approaches, a decision by local leaders about what should be the central element of the community’s 50-year water supply plan — a new dam or dredging — is at least several months away.
“I feel like we are making very good progress in coming to a decision,” Charlottesville Mayor
Dave Norris
said after the meeting. “I can see the light at the end of the tunnel now.”
Norris said the city was still waiting for other studies on the water supply demand analysis and expansion of the existing
Lower Ragged Mountain Dam
, which was built in 1908. City officials said Tuesday that information will be available on both studies in August.
“We are waiting for the data to come in, one of the chief questions being how much water do we need,” Norris said. “Are there alternatives to meeting those long-term water needs that are cheaper and have less environmental impact than the current plan?”
 Carey Burch, Project Manager, HDR Engineering |
Carey Burch, a project manager with
HDR Engineering
, was at the meeting to provide an update on the costs and feasibility of dredging the South Fork. His firm has recommended to the RWSA a multi-phase, one-time dredging project that would cost about $34 million to $40 million and take about seven years.
HDR identified 1.4 million cubic yards of total material that it said could be realistically dredged. Burch said some materials removed from the reservoir, such as sand, could be sold potentially in the local market and thereby reduce dredging costs by about $5 million to $9.5 million.
“We were able to get to about 79 percent of that maximum dredging target,” Burch said.
“If you did [both phases of dredging], it would restore all of your usable water supply volume in the reservoir.”
Past studies of dredging from consultant Gannett Fleming included the costs of dredging continuously for the 50-year period of the water supply plan and totaled as much as $223 million. HDR’s proposal, however, does not include any maintenance dredging and Burch said subsequent dredging projects would be more expensive because fewer disposal sites would exist.
Burch said an ideal disposal site for hydraulic dredging would be a flat, 100-acre parcel with a berm 15- to 16-feet-high that would be filled to a height of 11 feet with dredging spoils, allowing for dewatering to occur. The berms have to be initially issued permits as dams and then, after the water is removed, the landscape is filled in with the dredged material.
Topography around the reservoir required HDR to identify multiple locations at Panorama Farms and on the “Llewellyn Parcel” that would have a combined capacity as suitable disposal sites in the second phase of the dredging project.
The RWSA board was told that the quarry near the South Fork dam, which
was recently acquired by Roanoke-based Rockydale Quarries
, was not an attractive disposal site for sediment even if it had not been sold. Burch said material was not available at the quarry site to build an appropriate berm and that other nearby parcels owned by Dr. Charles Hurt were also determined to be unsuitable.
“Early on in this whole process, that was presented to us as a tantalizing option,” Norris said. “I am glad now we have had the chance to bring in a third party and take an objective look at that, and it sounds like it is not nearly as viable an option.”
With the dredging costs finalized, RWSA Executive Director Thomas L. Frederick Jr. recommended to the board in his staff report that a new earthen dam at Ragged Mountain continue to be pursued as the best approach for securing long-term water storage capacity. In May,
Frederick said the earthen dam could be built at a cost of between $28.5 million and $36.6 million
and create a much greater amount of permanent water storage capacity as compared with one-time dredging.
“I would say the cost projections on the earthen dam are a game changer in many ways,” Norris said. “Originally, it was easy to say there was an alternative that would be more cost effective than a giant concrete dam which would cost upwards of $60 million. Now that we think it might cost half of that, it potentially changes the whole equation.”
After discussing the dredging study, the RWSA board discussed whether to commit about $1.2 million for
Schnabel Engineering
to complete the final design of the earthen dam. The board decided to allocate only $325,000 to support continued geotechnical work that will continue to analyze the locations of clay and to evaluate sub-surface rock conditions for the dam’s two spillways. A decision on other planning for the earthen dam will be put on hold until the city has completed its remaining water supply studies.
No final decisions were made at Tuesday’s meeting on the dredging projects. A public information session on the dredging report has been scheduled for 6 p.m. June 30 at CitySpace in the Market Street Parking Garage.
