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I <br />5-1 <br />5.0 CONCLUSIONS AND RECOMMENDATIONS <br />Construction activities consisting of a slurry wall cutoff and pump -back <br />system, dam grouting, and monitoring well installation have been successfully <br />completed in the lower tailings dam. Based upon observations to date, the <br />remedial measures have been at least partially effective in solving the <br />seepage problems of the dam. Based '.on' -'the ,drop of the ground water- table <br />downstream from. the slurry wall cutoff, the cutoff has stopped..a significant- <br />amount of subsurface seepage from passing downstream. Observation of pump - <br />back rates, weir flow rates, and ground water quality tend to support this <br />conclusion, however, insufficient time has passed since construction to reach <br />definitive conclusions from these data. <br />Assessment of the effectiveness of dam grouting is difficult at this time <br />because of the recent drop in the lower tailings pond level. Observed drops <br />in dam piezometer levels may be due to the grouting or the drop in pond level; <br />this is presently unclear. A _better assessment can be made when the pond <br />Y' <br />rises above its former level. In addition to a possible reduction in seepage <br />rates due to the grouting, some benefit to the integrity of the dam has been <br />gained by the filling of voids in coarse gravel and cobbles which appear to <br />exist immediately downstream from the dam cutoff trench. <br />It is recommended that continued monitoring of pond levels, piezometer water <br />levels,weir flow rates, pump -back rates, and g oun'I+va er" yanide on ent a- ~ <br />tions. occur ona regular basis for at'le'ast one"full year.- These data should <br />allow an accurate assessment of system performance to be made, from which a <br />decision concerning the neccessity of further medial activities for the dam <br />can be made. <br />1110AIPPOIAOINIA <br />