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Mr. Thomas M. Robertson 5 June 17, 1981 <br /> <br /> <br />1_ <br />f. <br />f. <br />C` <br />The pond water level has been increasing at a fairly steady rate with <br />only minor fluctuations. No quantitative information is available at <br />[his time about pumping rates which would enable correlation of inflow <br />and outflow rates with the change in pond level. The increase in pond <br />level with time is shown in Figure 3; a nearly linear increase in pond <br />level with time. Although such increases in pond level would be expected <br />to cause increases in seepage rates, the increases in seepage rates would <br />not be as dramatic as those which have recently been observed. The <br />difference between the rate of increase in seepage and the increase in <br />pond level indicates that other factors may be controlling the seepage <br />rate more directly. <br />Seepage rates are directly affected by the area which water can seep <br />through. The pond surface area as a function of time is shown in Figure <br />3. The surface area of the pond increases linearly with time as compared <br />to the non-linear increase in seepage rate. Again, the increase in pond <br />area is insufficient by itself to account for the observed increases in <br />seepage rates. <br />I[ appears that changes in seepage rate which have been observed over the <br />past few years cannot be explained solely by increases in pond level <br />and/or pond area. However, there are indications that changes in the <br />inundated area of alluvial deposits along the stream channel may be an <br />important factor. The area of alluvial deposit inundated with time is <br />shown in Figure 3. Because of the configuration of the alluvial deposit, <br />the area inundated by the tailings pond increased sharply between 1979 <br />and 1981. The deposit was completely submerged by 1981 and the inundated <br />alluvial area will remain constant. The rate of increase of alluvial <br />area submerged corresponds conceptually with the rate of increase of <br />seepage from the pond. This indicates that these alluvial deposits may <br />be a prime contributing factor to pond seepage. <br />2.3 PIEZOMETRIC SURFACE <br />The water levels in the piezometers and wells (as a reflection of seepage <br />pressure) were examined in order to define the directions of flow and the <br />zones of material through which seepage is occurring. Water level <br />measurements in the pond and in the piezometera and wells were used to <br />construct the piezometric surface map shown in Figure 4. The majority of <br />the piezometric information is confined to the area below the Lower <br />Tailings dam near the stream channel; only a few points of measured <br />piezometer information are available through the dam crest and the <br />abutments. <br />Other information concerning the piezometric surface is found in the <br />~ observed exit points of seepage in downstream areas. Figure 4 shows the <br />location of seeps and wet areas. Outbreak of seepage at the ground <br />surface is concentrated downstream from the east abutment where two small <br />ravines incise [he alluvium in this area. Seepage is emergin¢ primarily <br />c~l~ l~ ~l_1~%ll.erf171`~ IL~ <br />