City preparing to get bids for dredging South Fork
By Sean Tubbs
Wednesday, July 21, 2010
has asked city staff to begin writing a request for proposals for companies interested in dredging the
South Fork Rivanna Reservoir
to remove some of the sediment that has accumulated there over the past 43 years.
“What I want to do is to get our ducks in a row so that we’ll be prepared to issue the RFP if council decides officially that dredging should be part of the water-supply solution,” Norris said in an interview. He added that he expects that decision to be made within a couple of months.
Dredging was not included in the
community water supply plan
adopted in 2006 because it was deemed too expensive and because it failed to provide enough water storage capacity for the community’s anticipated needs in 50 years. Instead, the water plan specified a new dam be built at the
Ragged Mountain Reservoir
as well as a pipeline to supply it from South Fork.
Opponents of the plan, which carried an original price tag of more than $140 million, have urged the council to insist on updated studies, including a second look at dredging. As part of a series of studies, the
Rivanna Water & Sewer Authority
to conduct a dredging feasibility study and the council heard the report at its meeting Monday.
HDR identified a total of 1.4 million cubic yards that could be removed without affecting protected wetlands or the shoreline. Project Manager Carey Burch said one of the challenges to dredging is the requirement to find a site for the sediment to dry out.
“There’s not a lot of flat land near the reservoir that doesn’t have something on it,” Burch said. “There are a lot of rolling hills. Land in a conservation districts is out. Land that is in flood plain is out.”
HDR is recommending a multi-phase, one-time dredging project that would cost $34 million to $40 million and take about seven years. The first phase would cost between $8 million and $13 million to gain 58.6 million gallons of storage. The cost depends on whether sand contained in the sediment could be sold.
Burch said sand is particularly valuable, with a cost ranging from $52 and $62 per cubic yard.
The second phase would cost between $26 million and $27 million to restore 169 million gallons of storage. Burch said this phase would be more expensive because it would require the construction of basins to retain water during the dewatering process.
In response to a question from Councilor
, RWSA Executive Director
Thomas L. Frederick
Jr. said dredging alone would not provide enough water for the community’s future needs.
“The community water supply plan approved in 2006 identified a need for 1.7 billion gallons of additional storage [for the year 2055],” Frederick said. He said dredging as outlined by HDR would supply only 13 percent of that amount.
Supporters of dredging praised the HDR study but said the feasibility study’s approach constrained the dredging alternatives. For example, they said, HDR was told to identify only two potential dewatering sites.
Former City Councilor
said issuing an RFP for dredging would allow the private sector to come up with its own solutions and may produce lower bids.
“I think you’ll find that when it’s a real RFP and people are talking about real money and not just a study, you’ll get better proposals back and you’ll see parcels [of land] that were not [considered] in the study,” Lynch said.
Norris said he is leaning towards dredging but is not ready to decide his vote until additional studies are completed.
“I haven’t been convinced yet that we can’t meet our 50-year water supply needs through a combination of dredging and a slightly enlarged dam at Ragged Mountain,” he said.
In August, the firm Black and Veatch will complete the first phase of a study of whether it is feasible to build on top of the 102-year-old
Lower Ragged Mountain Dam
instead of building a new, larger earthen dam downstream. The RWSA board will also get a report in August related to a re-examination of the 2004 demand analysis that served as the basis for the community water supply plan.