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. 1. Water Retention Ability Seepage beneath the dam will be through the shale/sandstone bed- rock of the Wasatch Formation. Due to the relatively low permeabil ity of this formation and the presence of the shear key, which acts as a seepage cutoff, only minimal seepage (less than 5 cfs) is expected beneath the dam. . Seepage through the abutments is of concern primarily at the south abutment. At the north abutment, a low-permeability bedrock is present at the pool elevation immediately adjacent to the dam. Only negligible seepage (less than 1 cfs) should occur through this abutment. At the south abutment, the exact lateral extent of the bedrock formation has not yet been determined. The bedrock could extend as far as 200 ft laterally (to the south) from the dam at crest level at the abutment. Seepage quantities through the sand, gravel, and boulder materials in the south abutment are est imated to be 25 to 30 cfs. If desired, this quantity could be reduced to negligible amounts relatively inexpensively by grouting during or after dam construction if seepage presents unforeseen problems. Seepage through the bOdy of the dam will be contro 11 ed by the detail of the construction joints of the dam. If joint techniques are not carefully developed and closely monitored at the particular dam site, difficulties with excessive seepage through the dam may be experienced. The appropriate techniques will be identified during final design. . Estimation of reservoir seepage losses was not within the scope of this investigation. However, based on the geology of the area, bedrock within the reservoir is most likely the same Wasatch Formation material found at the dam axis. Further investigations should confirm that the Wasatch Formation rises gently toward the east and should form an impervious bottom and sides for the entire reservoir. 3686-a/8 IV-5