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News

Forebay Dam design nears completion

By From page A3 | March 08, 2013

Design work to raise Forebay Dam in Pollock Pines is 90 percent complete, but additional state and federal requirements caused the El Dorado Irrigation District board to amend the contract with its consultant.

The amendment, approved 5-0 last month, will cost EID $299,000.

The additional requirements include a three-stage consultation with the Federal Energy Regulatory Commission and directives from the state Division of Safety of Dams covering 60 percent of the design.

Between capitalized engineering and staff work and the consultant, the total estimated expenses for design are $1.4 million. Since 2011 and as of the Feb. 11 meeting GEI Consultants have accounted for $1.39 million of that. GEI Consultants is headed by a former employee of the state Division of Safety of Dams.

EID staff  “negotiated cost-effective means of resolving these safety concerns” with DSOD and FERC, according to a staff report. The reduction in “cost impacts” amounted to $1 million, according to a staff report by EID engineer Jake Eymann.

The 10-foot dam-raising project is estimated to cost $16.8 million with the design level at 90 percent, up from $15 million estimated in February 2012 when design was at 60 percent and $8.7 million estimated in February 2011, and will have a payback period of two-three years, according to Eymann’s report, by providing more water for hydropower. Additional design requirements by FERC and DSOD account for most of the increase in cost estimates.

Western States Power Co., which built Forebay Dam, had originally planned to raise it 23 feet and add another generator to the powerhouse. EID has not talked about adding another generator.

Western States Gas & Electric Co. bought the canal in 1916, enlarged Medley Lakes, which are now called Lake Aloha, added Caples Lake and began hydrogeneration in 1924. Four years later Western States sold Project 184 to PG&E. EID acquired Project 184 in 1999 for $1, plus PG&E gave the district $15,000 when it transferred.

Forebay holds 400 acre-feet, but siltation has cut that down to 290 acre-feet. Forebay is the terminus of the 22 miles of flumes, canals and tunnels that bring water from a diversion dam near Kyburz, providing EID 15,080 acre-feet of water, plus an additional 17,000 acre-feet of water rights recently granted by the state. Raising the dam 10 feet will increase the supply of water for Treatment Plant 1 in Camino from eight hours to six days. It will also increase the acre-feet of water to 550.

Forebay also feeds water into 14,443 feet of penstock that runs the Pelton water wheels turning two generators producing 21 megawatts of electricity. That currently provides an average of $8 million of income annually for EID. The gain from the additional water produced by raising the dam 10 feet will be $300,000 annually, Eymann told the board.

A 70-acre area below the dam was acquired by Western States as a borrow area to get dirt to add to the dam. Eymann told the board after stripping off the organic material there would be 4-5 feet of useable material and a 100-foot buffer. The district would file a timber harvest plan.

“The amount of fill is 100 feet deep, the size of a football field,” Eymann told the board Feb. 11, adding that most of the work will be done by offroad vehicles.

The move to raise the dam was a result of the state Division of Safety of Dams raising concerns about the compacted dirt dam’s stability in 2003. GEI was hired in 2004 to conduct geotechnical and stability analysis.

An analysis of the inundation area in the event of a dam failure shows there are no homes in the inundation area, Eymann said.

Public outreach to the neighborhood and other meetings will take place this month. The project schedule shows environmental documentation being completed by September 2014, bidding in January 2015 and construction taking place April 2015-November 2016.

EID General Manager Jim Abercrombie said he expected to fund this project and $20 million worth of flume replacement over the next five years with a $30 million to $60 million bond issue, though he may phase them in, he told the Mountain Democrat. Bonds will be repaid 53 percent from hookup fees and 47 percent from water rates.

Abercrombie additionally indicated he would have water and wastewater master plans on the agenda for May. Those would be followed by studies for Facility Capacity Charges (hookup fees), which were last updated in 2008.

Michael Raffety

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