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May 21, 2010

Earthen dam proposed for water plan

Reader comments (0) DailyProgress By Brian Wheeler
Charlottesville Tomorrow
Friday, May 21, 2010

More than a year and a half after consultant Gannett Fleming was dismissed from work on the design of a new dam for the Ragged Mountain Reservoir, the Rivanna Water & Sewer Authority has unveiled a new approach that is expected to cost tens of millions of dollars less.

Schnabel Engineering, based in Glen Allen, has recommended that the RWSA build a massive earthen dam just downstream from the Lower Ragged Mountain dam. The new dam would raise the water level by 45 feet, allowing for storage of more than three times the amount of water held in the reservoir today.

RWSA Executive Director Thomas L. Frederick Jr. said the new dam would cost between $28.5 million and $36.6 million, which includes final design and engineering work, an environmental mitigation plan, and protection of the Interstate 64 embankment the larger reservoir would reach.

20100521-earthen-dam“When we hired Schnabel we were persistent in pushing for attaining the goals of the community, which is a fine line balance between a very safe and secure dam that provides that long-term water supply, and one at the best cost we can get,” Frederick said. “I think Schnabel has been successful at getting us there, and I commend their performance.”

Chris Webster, Schnabel’s Charlottesville project administrator, said construction costs for the major components of the dam are about $22.5 million. The RWSA says that is about $50 million cheaper than the last construction estimate by Gannett Fleming.

“We have given a range for the construction costs of about $20 [million] to $27 million,” Webster said. “The final design phase and engineering during construction would cost an additional $3.7 to $4 million.”

“We believe this is a conservative estimate and it is very possible the construction costs will come out at the low end of the range, or possibly even below that,” he said.

20100521-dam-costs-table One part of the plan

The new dam is one component of the 50-year community water supply plan that would serve Charlottesville and the urban areas of Albemarle County. Additional water storage capacity is needed to accommodate population growth and prepare for future droughts.

The 2006 plan called for a new, taller dam at Ragged Mountain and a new pipeline that would transfer water from the South Fork Rivanna Reservoir to fill the expanded reservoir. That plan has come under fire by opponents who favor dredging South Fork and a new study of the community’s long-term water needs.

Dede Smith, a representative of the group Citizens for a Sustainable Water Plan, which favors dredging, shared her initial reactions after seeing a copy of the executive summary provided to the RWSA board Thursday.

“I can’t comment on what this means without seeing a more detailed report,” Smith said. “It is difficult to compare this to earlier estimates because it is not detailed enough. … I am concerned about the sheer size of the dam. This is 135 feet tall versus 112 feet tall, so it is 23 feet taller and has a bigger footprint.”

Charlottesville Mayor Dave Norris has also advocated for an alternative approach that relies on dredging, increased conservation and a smaller dam at Ragged Mountain.

“Assuming these numbers are accurate, it is strong validation for the decision by the key parties to take a step back from the original plan and recommendations,” Norris said. “I am heartened to hear that, if we do build a new dam, it would not cost nearly as much as we had feared. However, I would like to continue pushing the envelope when it comes to evaluating other options that may save us even more money.”

Design evolution

Download RWSA Executive Summary
DownloadSchnabel Cover Letter
DownloadSchnabel Summary
DownloadDesign - Overall View
DownloadDesign - Dam sections
DownloadDesign - Borrow area detail
When the RWSA questioned Gannett Fleming’s 2008 design for the new Ragged Mountain Dam, and its $70 million-$99 million price tag, Schnabel Engineering was asked to provide a second opinion. At the time, Schnabel said a modified concrete design could be built for about $56.6 million.

With the two divergent proposals, Frederick convened in 2009 an independent panel of dam experts to determine how best to proceed. With the panel’s feedback, Schnabel replaced Gannett Fleming on the project in September 2009, when it was awarded a $1.3 million contract to redesign the dam.

According to Frederick, the idea for an earthen dam was first suggested by Schnabel. Following a review of that recommendation by the panel of dam experts, the RWSA announced in March that Schnabel would assess the option for an earthen dam after underground borings revealed the presence of much less rock and more soil.

WATCH THIS VIDEO: 3D views of the Ragged Mountain Reservoir earthen dam
Support for these visualizations comes from our generous donors, the Oakwood Foundation, and the Virginia Environmental Endowment.

Schnabel’s proposal has three major elements: the earthen dam; an inlet/outlet tower and tunnel through rock that houses the pipeline and spillway drain; and an emergency spillway carved out of nearby rock and designed to handle a 500-year flood event. The earthen dam is more cost effective because it relies on material available on site.

“Based on our calculations, we determined there is a need for 850,000 cubic yards of soil to construct the earthen dam,” Webster said. “There is at least 1 million cubic yards of material available on site.”

Other studies

Charlottesville officials have said in previous meetings that no decision would be made about the dam construction until the city gathers additional information on the costs of dredging, the feasibility and costs of building on top of the existing 1908 dam, and a validation of the water demand analysis that was the basis for the 2006 plan.

“This [report on the dam] is the first piece of info we were waiting for,” Smith said. “It will be difficult to assess what the feasible options will be until we get the results from all the other studies.”

The city is selecting its own engineering firm to investigate whether the 1908 Ragged Mountain Dam can be repaired or raised by 13 feet instead of building a new dam. Five companies responded to a recent request for proposals.

“We’re in the final negotiations phase with our selected firm, and hope to finish that in the next day and so,” said Judy Mueller, the city’s public works director. She said she hopes to reveal the firm’s name and the cost estimate for the study next week.

20100601-get-involved Gary O’Connell, Charlottesville’s former city manager, is the new head of the Albemarle County Service Authority, which provides public water and sewer to county residents. After reviewing the report, he suggested the timing was good for another joint meeting of the RWSA and ACSA boards, along with the City Council and the Albemarle County Board of Supervisors.

“Hopefully by the end of June we will have a lot of these questions addressed,” O’Connell said. “It seems like it would be a good opportunity to have the four boards come together and discuss the next steps.”

“I am encouraged by the [dam report],” O’Connell said. “We made the right decision to stop on the concrete dam approach and rethink it completely and have come back with a more cost effective approach that puts us back in the ball park of the original cost estimates.”

The earthen dam design will be presented to the RWSA board at its meeting Tuesday. A public information session has been scheduled for 6 p.m. June 1 in CitySpace at the Market Street Parking Garage.


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