2018-07-02_PERMIT FILE - M2017013

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Earth Engineering Consultants.LLC EEC Project No. 1122096 Signal Resen oir Improvements August 5.2015 Page I Based on the design documents provided us, we understand the proposed final embankment will be constructed as shown in Figure 2 and described as follows. The embankment will be constructed with upstream and downstream slopes of 3:1 (horizontal to vertical). We understand the embankment will be constructed with a maximum height (from toe to crest) of approximately 15 feet. The toe drain will be located near downstream toe as per the civil details provided by the design consultant, as highlighted on the various slope-stability diagrams included in Appendix D of this report. Based on the sections, elevations, and subsurface conditions, the embankment will generally consist of apparent lean clay fills, overlying native lean clay, overlying bedrock. We understand any new fill or backfill materials would be similar (hydraulic conductivity and friction angle) to the existing embankment lean clay subsoils. Based on the information outlined in our Suhsuirface Exploration Report and the provided embankment geometry, seepage and stability analyses were carried out by EEC. Those analyses assumes a high water elevation at the "normal maintained water level" elevation of 5145. Seepage was analyzed at steady-state flow. The stability analyses were carried out using Bishop's method of slices with pore pressures integrated from the seepage analysis for high water elevations, or from a predicted piezometric surface for end of construction and rapid drawdown scenarios. Soil parameters used in the analyses were included below in Table 1. Summary of Soil Parameters Used in Seepage and Stability Analyses Wet Unit Coefficient of Effective Effective Undrained Soil Zone Soil Description Weight Permeability Friction Cohesion, Shear Angle, C' Strength,S„ Fill Sandi Lean Clav 123 pcf 10 s10 cm/sec 250 250 800 psf Native Sande Lean Clay 126 pcf 1.0 X10`cm/sec 200 200 800 psf Dram Sand 130 pcf 3 30x 10-4 cm/sec 320 0 0 psf Bedrock Claystone.Siltstone 123 pcf 1 0 X10 cm/sec Impenetrable Impenetrable Impenetrable Note that the soil parameters in the above table and used in the design, may vary from those encountered in the construction phase, yet reflect conservative conditions in design or were estimated based on our experience with similar materials and/or available literature. Such variations/assumptions used in the design include: • Sandy lean clay: chosen friction angle was less than determined in laboratory testing. Material was assumed to be a relatively homogeneous, isotropic material.