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R. J. Irish Consulting Engineering Geologist, Inc. The intergrenuler permeability of the granitic rock at this demsite should be essentially zero, but ground water is likely to course through joints end fractures. The permeability of the rock mass due to those discontinuities may permit unacceptably high volumes of underseepage. This is indicated by the results of pecker tests run in 2 of the 4 borings drilled near the planned damsite (Fig. 3). for example, water "takes" fora 37- foot long section of rock penetrated by boring DH- M-2 , a boring angled at 45 degrees from the horizontal, from 55 feet to 92 feet ranged from 7 to 13 to 29 gpm at pressures of 25, 50, and 100 psi, respectively. Consequently, curtain grouti ng may 6e advisable. A single line of grout holes spaced on 5-foot centers and terminated at a depth of about 35 feet should be adequate. Grout "takes" ere estimated to 6e on the order ofone-half sack per foot of grout hole in the top 20 feet of the rack on the average, end about 1 sack per foot of grout hole from 20 feet to 35 feet in the rock. A few open joints capable of taking 4 to S sacks of grout could be intercepted. The grout holes should be angled about 45 degrees from the horizontal so thatthey would interceptthe predominentlynaar-vertically dipping main joints or possibly thin, near-vertically dipping sheer zones. If the dam is to be founded on the alluvial soils their engineering performance character- istics need to be established by laboratory testing of a suite of those soils. In particular, their bearing capacity and permeability need io be determined . Almost certainly, the permeability of those sandy soils would need to be reduced bygrouting--probably chemical grouting, because the silt content of the soils appears to be too high to permit cement grouting. The alluvial fan at the mouth of the gorge about aquarter-mile downstream from the demsite is formed primarily of fine to coarse grained sands. We understand the engineering performance characteristics of those sands have been determined by laboratory testing,end those results indicate that the sands should be useable as fine concrete aggregate. The soils downstream from the dam need io be protected from scour otherwise inherent to spillway discharge. This protection could be provided by a concrete mat or a rock rip-rapped channel. Rock suitable for that purpose could be quarried from the granodiorite either immediately upstream or downstream from the damsite. Potential flood flow volumes should be assessed by an hydrologist experiencedin that work. The reservoir area essentially is enopen-ended basin of granitic rock locally mantled by disconnected bodies of slopewash and residual soils across the valley slopes and by alluvial soils across the valley floor. The alluvial soils appear to be ground water saturated to within a few inches of the surface of the floor. Bank storage should be minimal. The bedrock typically is massively jointed, and soil-blanketed slopes rarely ere steep. As e 6