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,, Mr. Jim Mattem July 6, 2006 Page 3 borrow material from East Flume impoundment area. The borrow material used for Deal Gulch embankment is expected to be similar. Compaction test resuhs for this material aze shown in Figure 3. The assumed properties for the boaow material and dam foundation soils aze shown in Table 2. These values are based on examination of the she and interpolation from the previous laboratory tests. The local alluvial materials are expected to be sufficiem as compacted dam material, ahhough they might consist of slightly lower clay content. Table 2. Assumed Soil Characterization Representative for Desl Gulch Impoundment Classifica8on Content Weight Ratio Gravity (%) (Def) Compacted Partially SM 13.8 117.9 0.64 2.64 Saturated Dam Material Compacted Saturated Dam SM 100 200 0.64 2.64 Material Sub-grade Foundation SM 6 95 0.80 2.59 Partially Saturated Material Sub-grade Foundatim SM 100 180 0.80 2.59 Saturated Material The low dam height will provide only low confinemem to the soils. At low confinement, the initial Young's modulus aze typically in the range of about 188-313 kipps per square foot (ksf), increasing with repeated load cycles depending on in situ density and amount of fines. Poisson's ratio in sandy, sih soils aze typically in the range of 0.18-0.24. The strength of these soils will be governed primarily by the angulazity of the sand and silt grains. The angle of repose in such non-plastic sandy silt is about 26°-30°. The denser the soil, the greater it's strength. For medium dense sandy silts, the frictional resistance at peak strength is about 28°-32°, increasing to 30°-34° at higher densities. Once sheazed beyond peak, its residual frictional resistance drops to about 26°-30°? The assumed mechanical properties used in the stability analysis are summazized in Table 3. STABILITY ANALYSIS Stability of the Deal Gulch dam embankment was analyzed using the 2D numerical modeling program, FLAC. The FLAC program is an explicit, finhe difference program that solves the equilibrium force equations for a discretized material. It can simulate the deformation of the embankment given the strength of the material using effective stress principles and can account for buoyancy differences due to water seepage. r Mitchell, J.K. (1976), Fundamentals of Soil Behavior, John Wiley & Sons, inc. New York, New Yak, 422 p. Agapito Associates, Inc.