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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />foundation, possibly due to valley wall spreading, valley wall <br />slumping and/or uncontrolled blasting during installation of the <br />outlet tunnel. The sandstone foundation materials elsewhere in the <br />dam foundation are also highly fractured, but the joints are <br />believed to be considerably tighter, especially in the near-surface <br />materials. We believe that the tighter joint systems in combination <br />. with lower heads and/or lower hydraulic gradients are probably <br />responsible for the lack of reported sinkhole activity to date in <br />these areas. <br /> <br />The sinkholes discovered during 19B6 are believed in most <br />instances to be reactivations of earlier sinkholes which were <br />backfilled with soil and blanketed with a synthetic liner <br />sheet/soil bl anket system as they developed. Informati on obtained <br />from the files of the Colorado Office of the State Engineer <br />indicates that three sinkholes were reported in 1974, two in 1976, <br />and four in 197B. All nine of the "new" sinkholes were backfilled <br />with cement/water/sand grout by direct gravity inflow from the <br />ground surface during the emergency/repair program (Phase One) <br />completed during April 1987. This simple. foundation treatment has <br />proved to. be reasonably effective to date in reducing foundation <br />seepage along the right wall of Gurley Canyon as determined from <br />comparison of spring flow measurements downstream of the dam before <br />and after the grouting program. The grouting of voids around the <br />tunnel from inside of the outlet works, also completed during April <br />1987, may also have been a factor in reducing the measured <br />foundation seepage. Combined spring flows for equivalent reservoir <br />levels following the emergency repair grouting program are to date <br />approximately half of those measured prior to the program. <br /> <br />5.4 Embankment <br /> <br />The results of the subsurface exploration program, the <br />geophysical exploration and the laboratory testing program indicate <br />that the embankment consists of an apparently homogeneous mass of <br />medium stiff to stiff sandy low plasticity clay. The results of <br /> <br />-17- <br />