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Table 3 Summary of Permeability Values Used in Dam Seepage Analysis <br /> Permeability Permeability <br />Material ftls cm/s <br /> Existin Materials <br />Embankment Material 4.85x10"9 1.48x10"' <br />Soft Sediment 2.30x10"6 7.02x10"5 <br />colluvium 6.02x10"9 1.83x10"' <br />Weathered Bedrock 3.28x10"' to 3.28x10"5 1.00x10"5 to 1.00x10"3 <br />Pro osed Materials <br />Buttress 4.85x10"9 1.48x10"' <br />Downstream Draina a Blanket 3.28x10"s 1.OOx10'~ <br />U stream Cla Blanket 4.85x10"9 1.48x10"' <br />Trench Drain 4.00x10"' 1.22x10"5 <br />Permeability values for the materials that comprise the existing dam were selected based on <br />laboratory values and model calibration to match installed piezometers as closely as possible. The <br />permeability values associated with the embankment material and soft sediment were based on model <br />calibration, but measured laboratory values were used as a gauge. The permeability of the colluvium <br />was based solely on measured laboratory values (Armstrong and Associates, 1983). Weathered <br />bedrock permeability values were estimated using seepage model calibration to match the total heads <br />reported in the piezometers under full reservoir conditions. These values are different at the two <br />analyzed cross-sections through the dam, with 1.0x10"3 cm/s at Cross-Section B and 1.0x10"5 cm/s at <br />Cross-Section C. The seepage model calibration is described in detail in Section 8.1.3.2. <br />Permeability values for proposed materials, or those that are associated with the improvements to <br />Monument Dam, were based on a combination of measured values, typical values, and model <br />calibration. The buttress and upstream blanket materials were assumed to be the same as the <br />embankment material, which is compacted colluvium. The value used in the analysis was considered <br />a rough average of the measured permeability of two compacted colluvium samples tested by <br />Lambert and Associates (2006) and it matched the embankment material permeability from model <br />calibration. The drainage blanket permeability was considered a typical value for clean sand. Finally, <br />the trench drain permeability used in the analysis was an equivalent permeability used in the model <br />to obtain the amount of drawdown predicted from drain spacing design as discussed in Section 8.3. <br />8.1.3 Modeling <br />Modeling of the seepage was conducted using SEEP/W, acomputer-modeling program developed by <br />GEO-SLOPE International, Ltd. SEEP/W uses the fmite-element analysis technique to model flow <br />and porewater pressure distribution within porous materials such as soil. This method was chosen <br />because comprehensive formulation makes it possible to analyze both simple and highly complex <br />P:\Mpls\06 CO\26\0626067\WorkFiles\DesignReport\FINAL\DesignReportFlNAL.doc 20 <br />