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.- <br />Mr. Thomas M. Robertson 8 June 17, 1981 <br />C <br />In order to define the chemical reactions of the tailings water and <br />soils, an assessment of the major ions and cations in the tailings water <br />and a determination of the major mineral species and the cation exchange <br />capacity of the soil would be required. Such an evaluation is not <br />considered necessary at the present time. <br />3.0 SUMMARY AND RECOMMENDATIONS <br />1_ <br />t <br />Detailed study of the available information at the Lower Tailings dam <br />has shown that there is insufficient information to clearly define the <br />seepage path(s) a[ the present time; however, the results of Phase I do <br />indicate that seepage is concentrated in the east abutment and in the <br />rock. Additional data are needed to confirm or modify these preliminary <br />conclusions and develop realistic remedial measures. <br />The results of Phase I indicate that the probable source of seepage is <br />tailings water seeping into the alluvial deposit in the north end of the <br />pond. The alluvial deposit provides a downstream seepage path under <br />the beached tailings, The cutoff trench which intersects the alluvial <br />deposit restricts further flow of the water downstream through the <br />deposit. The seepage is able to move laterally into the abutments, <br />passing under the cutoff trench there before flowing downstream. It <br />appears that the major seepage is through the east abutment. The lateral <br />extent across the dam and the depth to which water is flowing through the <br />abutments is not defined at this time. Additional information about <br />seepage conditions along the crest of the dam and at the toe of the dam <br />is required in order to clearly define the seepage path(s). The required <br />additional information can be obtained by the subsurface investigation <br />program described below. <br />Subsurface Investigation <br />In order to define the seepage path(s), the primary zones of seepage must <br />be identified by measuring permeabilities and piezometric heads within <br />and beneath the dam. The areas where such information is needed and <br />r lacking are beneath the crest of the dam and in the downstream abutments. <br />IL A subsurface investigation program has been developed which focuses on <br />these areas. The purposes of these investigations will be to: <br />(~ • Identify pervious zones which could be trans- <br />k witting significant quantities of seepage. <br />• Measure piezometric pressures in order to define <br />directions of seepage flow. <br />• Provide water quality sampling points to "trace" <br />seepage from the pond. <br />This will be accomplished by sampling [he material encountered, perform- <br />ing hydraulic testing in the boring, and installing piezometers to be <br />used for water level measurement and obtaining water quality samples. <br />~c-~2f l~ V.l/~lt`1 i1t31 <br />