The city of Escondido is to receive a consultant’s report in July outlining mitigation options to prevent liquefaction of Lake Wohlford Dam in the event of a major earthquake at the city’s 1.7-MW Escondido hydroelectric project.
The City Council authorized a $195,800 contract in January for GEI Consultants Inc, of Carlsbad, Calif., to study ways to mitigate potential liquefaction of the dam’s hydraulic fill. GEI previously examined the potential for liquefaction under contracts totaling $258,400.
The studies and field and laboratory testing conducted by GEI determined the hydraulic fill in the upstream slope of the dam has the potential to liquefy during a maximum credible earthquake of 7.5 magnitude on the Elsinore fault. The rockfill portion of the dam was determined to be able to withstand an earthquake of that magnitude.
The Escondido project (No. 176) includes the 1.7-MW Bear Valley power plant, on San Luis Rey River and Escondido Creek in San Diego County. Lake Wohlford Dam was built of rock in 1895, reaching a height of 76 feet. In 1924, authorities used silt and sand to add 24 feet to its height. However, the city said the silt and sand materials were not evenly mixed.
In a filing with the Federal Energy Regulatory Commission, the city sets out design and construction activities to remediate the dam. The city plans to submit a draft design report by Nov. 30, 2008, and plans and specifications by Dec. 31, 2009. Once plans and specifications are approved, the project will be advertised for bids, the city said.
The city said it intends to start remediation work by July 29, 2010, and finish construction by July 28, 2011.
While remediation is investigated, the city said it would continue to operate the reservoir below the elevation of 1,460 feet — 20 feet below the spillway crest.