C153514 Feasibility Study

• Contract/PO #: C153514
• Contractor Name: Farmers Water Development Company
• Contract Type: Loan
• Water District: 60
• County: San Miguel
• Bill Number: SB 87-15
• Loan Projects - Doc Type: Feasibility Study

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6.3 Foundation Restoration

Based on the results of the field exploration program
indicating relatively high foundation permeability and probability
that this factor is a major contributor to the formation of
sinkholes, restoration of the dam foundation in the area of
historical sinkhole development has been determined to be
necessary. A foundation grouting program has been selected to
reduce seepage through the foundation and thereby reduce the
potential for continued sinkhole development in this area which
could eventually damage the. foundation and embankment sufficiently
to imperil dam safety. An effective grout curtain should reduce
seepage flows and lengthen seepage paths sufficiently in this
portion of the foundation to significantly reduce the opportunity
of reactivation of old sinkholes or development of new sinkholes.
The overall potential for sinkhole development in the area of
historical sinkhole activity which could impact dam safety should
be significantly reduced by the combined effects of a foundation
grouting program in conjunction with an outlet .conduit
rehabiliation program.

The remainder of the potential high seepage areas in the dam
foundation which were identified. during the field exploration
program will not be addressed in the proposed foundation
restoration program. These areas have no recorded history of
sinkhole development and may not be susceptible to this activity
for a wide range of possible reasons including tighter or less
continuous bedrock jOint patterns, lower hydraulic heads, less
erodible foundation and embankment materials and lower overall
hydraulic gradients. Although we feel that the present condition of
these areas does not warrant restoration work at this time, we
believe that it would be prudent to monitor these areas regularly
in the future to provide an accurate data base for long-term
performance compari sons and to mi nimi ze the potenti a 1 for
unexpected developments which could potentially impact dam safety.

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