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24 types of materials should be evaluated by a professional dam engineer. The above discussion describes only a small selection of foundation problems to be considered in the evaluation and repair of existing dams and the design and construction of new dams. Projects located in varied geologic settings can benefit from the participation of professional geologists, engineering geologists, and/or geological engineers. Case Histories QUAIL CREEK DAM AND RESERVOIR Quail Creek Reservoir is located in the southwestern part of Utah near Saint George. The reservoir is formed by a main dam and dike. On January 1, 1989, the 78- foot-tall dike failed and released 25,000 acre-feet of water causing approximately 12 million dollars in damage (Carlson, D.D. and Meyer, D.F. 1989). The foundation of the dike was formed by sedimentary rocks deposited in a marine tidal flat environment and consisted of alternating, thin beds of gypsiferous siltstone, sandstone, gypsum, and dolomite (Robert James, J. et al. 1989). The geology was complex, and the rock was described as very weathered, highly fractured, faulted, and folded. Figure 15 is an aerial photograph after the failure of the dike that scoured soils away exposing the underlying bedrock. Figure 15 - Quail Creek Dike Upon first filling of the reservoir, seepage began to flow immediately through the foundation. The response to the seepage was a grouting program and installation of an unfiltered rock toe drain. Three different phases of grouting were done between 1986 and 1988. On December 31, 1988, brown, discolored seepage was observed flowing at about 200 to 300 gallons per minute. A filter was constructed over the seepage area, but ultimately the flow was too great and a backwards piping erosion failure mode caused portions of the embankment to collapse, causing a catastrophic failure. After the failure occurred, an investigation revealed that although the complexity of the foundation geology was known ahead of time, proper treatment of foundation defects, such as openings and voids along bedding planes, was not used during construction. Figure 16 shows an example of some of the openings along bedding at Quail Creek Dike. In addition to the nature of the foundation defects, the orientation of bedding played important role in the failure. As shown above in Figure 15, the orientation of bedding is perpendicular to the axis of the dike which allowed continuous, downstream pathways for foundation seepage. Figure 16 - Openings along Bedding Planes Perhaps the most significant deficiency that led to breach of the dike was the failure to provide adequate filters to protect the core of the dam from internal erosion and piping into and along the foundation. The investigation of the failure concluded that several adverse conditions existed that contributed to breach of the dike. The conditions included:  Open joints along bedding planes were not treated during construction and allowed an unfiltered seepage path with a direct connection with the reservoir.