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<br /> <br />EDNA MINE <br />MOFFAT AREA <br />PHREATIC SURFACE <br />In accordance with the Settlement Agreement dated November <br />19, 1987, a description of the predicted steady state water <br />conditions of the embankment below the proposed sediment pond are <br />described in this report. <br />With the addition in the sediment pond in the Moffat area, <br />the steady state seepage conditions will be altered in the <br />embankment from the existing conditions. The location of the <br />phreatic surface is determined by the water elevation of the pond <br />and the location of pond from the edge of the slope. The water <br />elevation of 6999.6 feet was used to determine the steady state <br />seepage within the embankment. This water elevation corresponds <br />to the elevation of the primary spillway of the proposed pond. <br />Although higher water levels could occur in the pond, the duration <br />would be short and steady state conditions at this higher water <br />elevation would not be reached. <br />The methods developed by Yanq H. Huang were used to predict <br />the theoretical phreatic surface of the embankment below the <br />proposed sediment pond. An explanation of Huanq's method is <br />included in Chapter 4 "Phreatic Surfaces" in the book, Stability <br />Analysis of Earth Sloaes. Huang has developed charts to determine <br />points on the predicted phreatic surface following procedures <br />developed by Casaqrande in 1937. These charts were used to <br />determine the exit point of the phreatic surface in the creek <br />bank. <br /> <br />A typical cross section of the topography of the slope in the <br />area of the proposed sediment pond is shown on Figure 1. This <br />configuration was used to determine the surface seepage elevation <br />in the embankment slope. As indicated by this drawing, the <br />further the pond is located away from the edge of the slope, the <br />lower the elevation of the surface seepage in the creek <br />embankment. Table 1 on the following page includes elevations for <br />surface seepage in the creek bank with varying values for the <br />distance X ae shown on Figure 1. The elevations shown on this <br />table were determined using the charts developed by Huang for <br />determining points on the theoretical phreatic surface. <br />1 <br />