Title
Support approval of an Agreement for Professional Services with AECOM Technical Services, Inc. for engineering services for Nacimiento Dam and San Antonio Dam; and authorize the General Manager to execute the Agreement.
Report
RECOMMENDATION:
It is recommended that the Monterey County Water Resources Agency Finance Committee:
Support approval of an Agreement for Professional Services with AECOM Technical Services, Inc. for engineering services for Nacimiento Dam and San Antonio Dam; and Authorize the General Manager to execute the Agreement.
SUMMARY/DISCUSSION:
The Federal Energy Regulatory Commission (FERC) and California Department of Water Resources, Division of Safety of Dams (DSOD) regulate matters regarding dam safety for Nacimiento Dam. Prudent practice and FERC and DSOD require seismic stability analysis of dams within their jurisdiction. The latest seismic stability analysis of Nacimiento Dam was performed in 2005. The best estimate of seismically induced vertical deformation is about 10 feet (GEI, 2005), considerably less than the 25 feet of normal operating freeboard at full reservoir elevation of 800 feet. The 2005 seismic stability analysis had to rely on certain assumed embankment and foundation soil properties and assumed water surface location within the dam embankment because complete information is not available from original construction records (from the mid-1950's), there are no means for determining the water surface location within the dam embankment, and no samples from the embankment or foundation have been collected since construction. Soil property assumptions made in the 2005 analysis are considered conservative, but the estimated performance of the dam embankment during a major earthquake is not fully known due to the assumptions described. Drilling into the embankment and into the streambed sands and gravels under the embankment and soil sample collection is needed to provide reliable soil property information and wate...
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