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1 Mr. Thomas M. Robertson 5 June 17, 1981 The pond water level has been increasing at a fairly steady rate with only minor fluctuations. No quantitative information is available at this time about pumping rates which would enable correlation of inflow and outflow rates with the change in pond level. The increase in pond level with time is shown in Figure 3; a nearly linear increase in pond level with time. Although such increases in pond level would be expected to cause increases in seepage rates, the increases in seepage rates would not be as dramatic as those which have recently been observed. The difference between the rate of increase in seepage and the increase in pond level indicates that other factors may be controlling the seepage (rate more directly. l• Seepage rates are directly affected by the area which water can seep through. The pond surface area as a function of time is shown in Figure 3. The surface area of the pond increases linearly with time as compared to the non—linear increase in seepage rate. Again, the increase in pond area is insufficient by itself to account for the observed increases in seepage rates. It appears that changes in seepage rate which have been observed over the past few years cannot be explained solely by increases in pond level land/or pond area. However, there are indications that changes in the inundated area of alluvial deposits along the stream channel may be an important factor. The area of alluvial deposit inundated with time is shown in Figure 3. Because of the configuration of the alluvial deposit, the area inundated by the tailings pond increased sharply between 1979 and 1981. The deposit was completely submerged by 1981 and the inundated ' alluvial area will remain constant. The rate of increase of alluvial area submerged corresponds conceptually with the rate of increase of seepage from the pond. This indicates that these alluvial deposits may be a prime contributing factor to pond seepage. 2.3 PIEZOMETRIC SURFACE The water levels in the piezometers and wells (as a reflection of seepage pressure) were examined in order to define the directions of flow and the zones of material through which seepage is occurring. Water level measurements in the pond and in the piezometers and wells were used to I' construct the piezometric surface map shown in Figure 4. The majority of the piezometric information is confined to the area below the Lower Tailings dam near the stream channel; only a few points of measured piezometer information are available through the dam crest and the abutments. 1 Other information concerning the piezometric surface is found in the observed exit points of seepage in downstream areas. Figure 4 shows the location of seeps and wet areas. Outbreak of seepage at the ground surface is concentrated downstream from the east abutment where two small ravines incise the alluvium in this area. Seepage is emerging primarily llJ®—a ID ll ADNiI 2]