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.~ <br />Mr. Thomas M. Robertson 6 June 17, 1981 <br />from [he north or pond side of the east-west trending ravine and both <br />sides of the north-south trending ravine. There is also seepage on the <br />flatter ground surface immediately upstream from the ravines. There is a <br />small "pipe" located on the north side of one ravine (sample point no. <br />C 12) which is flowing at a rate of approximately 4 gpm, indicating rela- <br />tively high seepage pressures in this area. <br />C The piezometric map in Figure 4 is based on piezometric readings from <br />both the rock and the soil (see table in figure for location of screened <br />interval in piezometers and wells.) The piezometers downstream of the <br />dam (sampling point 15S and 15N) indicate a higher pressure in the top of <br />rock as compared to the overlying soil. This indicates that water is <br />seeping upward through the rock and into the soil, and there are signi- <br />ficant uplift pressures within the east abutment. A similar flow condi- <br />tion is found at the toe of the dam, where pressures in the rock are <br />( higher than those in the soil (see sample point No. 3 and No. 16). These <br />two conditions indicate that the rock is providing a significant path for <br />seepage in the downstream toe area. It is also noted that the piezometric <br />head of the piezometers a[ the toe of the dam is the same as that measured <br />in Wells 6 and 7, which are further downstream and [o the east. The fact <br />that there is no pressure gradient between these wells may indicate that <br />the major flow path is not along the stream channel, but rather that the <br />_ major flow paths are through [he abutments, primarily the east abutment. <br />Along the crest of the dam, there is only one piezometer, which is sealed <br />in the rock. Thus, Ch ere is no information about pressures in the <br />~- natural soil and in the dam fill along the dam crest. Since the pressures <br />within the natural soil and the dam fill may be different than those in <br />[he rock, piezometric information along the crest is very limited, and <br />the piezometric contours which are drawn on Figure 4 in the area may not <br />be representative of [he general flow conditions under the dam. <br />The flow paths as shown in Figure 4 can be delineated only in a general <br />sense from the piezometric surface contours and observed exit flow <br />conditions. The piezometric pressures indicate that flow is occurring <br />beneath the entire length of the dam, although the relative quantities of <br />flow at different locations are no[ known. Exit conditions and [he [rend <br />toward higher pressures to [he east at the toe of the dam indicate the <br />C potential of greater flows beneath the east abutment. <br />2.4 WATER QUALITY ANALYSIS <br />C Water quality can often be used as an effective tracer in assessing the <br />source of seepage as well as help delineate the paths of seepage. Water <br />was sampled in the tailings pond and a[ 12 points downstream of [he Lower <br />Tailings Dam during the period of March 9, 1981 to May 11, 1981. <br />The parameters measured were temperature, pN, total copper, total <br />zinc and free cyanide. Figure 5 shows the average pH and free cyanide <br />concentrations monitored over the two month period. These two parameters <br />are the best indicators for identifying seepage from [he pond. <br />1~•~~1ale'~LJJl`V Zlr-i1 <br />