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I I I I I I I I I I I I I I I I Specific details for each alternative are shown in Table 3. Item Top of Dam Elevation -Spill~aJ{Ifle~atI;n------------- ------------------------------- Dam Height ------------------------------- Dam Length ------------------------------- Reservoir Surface Area TABLE 3 - Dam Alternatives Alternative 1 17.1 acres Alternative 2 5367 feet ------------------------------- 5360 feet ------------------------------- 47 feet ------------------------------- 1156 feet ------------------------------- 16.9 acres ------------------------------- 300 ac-ft e sIte may gIVe 5375 feet ------------------------------- 5368 feet ------------------------------- 45 feet ------------------------------- 1040 feet ------------------------------- ------------------------------- Normal Storage Capacity 300 ac-ft These v ues are approxunatlOns ase slightly different values. PLAN OF DEVELOPMENT General. To be able to evaluate the physical needs and subsequent costs for each dam site, a geotechnical evaluation of each site was conducted. This included subsurface investigations, laboratory testing of the soils form the site, a geotechnical evaluation of stability and seepage, and a hydrologic and hydraulic evaluation of the required spillway and outlet works. A summary of these evaluations follows. Geotechnical Investigations. The geotechnical investigations conducted on the proposed reservoir site are described in Appendix B of this report. These investigations were conducted in June of200l by Smith Geotechnical. The investigation included drilling four borings at the north dam site, two borings at the south dam site, four borings in the borrow are within the reservoir, and laboratory testing on selected samples. The plan of development is based on this data and additional drilling, sampling, and testing will have to be conducted prior to final design after the final location for the dam is determined. Soil and Rock Description. 1. Overburden Soils. The overburden soils at the dam sites consist of overburden sandy clays, clayey sands, silty sands, and sandy silts. These soils range from nonplastic to low plastic with t'1e plastic soils having a plasticity index (PI) or approximately 15. These soils should be acceptable for use to construct the dam core whereas the nonplastic soils should not be utilized to construct the core but can be used in the dam shell. The soils were found to be relatively uniform across the site with the more plastic soils being found on the east side of the drainage and the low to nonplastic soils being encountered on the west side of the drainage. We would recommend only the soils on the east side of the drainage be used for core material. 2. Bedrock. Underlying the overburden soil is the Lyons sandstone. The bedrock was found at depths ranging from ten (10) feet to thirty (30) feet below grade. The bedrock is relatively hard, fractured, and is thinly bedded. A quarry operation north of the site provides a good location to view this formation. The Lyons sandstone is a sedimentary rock of the Triassic and Permian ages and is fine grained with weak to strong cementation. This rock may be susceptible to solutioning in a partially saturated environment and may be susceptible to erosion where the cementation is weak. The shear strength and hardness of the rock is acceptable for a dam foundation of the height proposed. The only weakness is the seepage potential due to the fractured nature of the rock. 3. Borrow/Materials. The primary source of borrow materials is expected to come from Stone Canyon Dam Feasibility Page 8