1998-01-10_REVISION - M1988112 - Laserfiche WebLink

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' BATTLE MOUNTAIN RE50URCES, SAN LUIS PROJECT CMLRD ADEQUACY LETTER RESPONSES Page 8 of 28 14. Please determine and describe the percent moisture content within the tails which would constitute a saturated condition and compare this figure to the anticipated moisture within the desiccated tails. Wi11 the amount of water entrained within the tails vary vertically? If so, describe how this would affect the long-term, post reclamation stability of the facility. RESPONSE: The results of the laboratory testing of the tailings indicates that upon consolidation, the tailings will exhibit a void ratio of 0.7 to 0.75. If 100 percent saturated the moisture content will be approximately 26 to 27.5 percent. If completely desiccated, the moisture content of the tailings will approach 15 to 20 percent (based on the tailings box depositional modelling, see Appendix E of the amendment). Deposition of the tailings will initially result in a zone of saturated tailings due to their high rate of rise. These tailings will be in contact with the drainage layer and will consolidate and ' drain. Subsequent deposition will take place using the thin layer deposition technique described in the amendment application (see D.6.1). This deposition will create beached tailing and will allow the desiccation to occur. The desiccation process will' reduce the moisture content of the surface layer to less than saturation. Subsequent layers of deposition will wet the top of the previously desiccated layer, however, the low permeability of the tailings will limit infiltration of this water. As the new layer is desiccated an equilibration of the moisture within the two layer will take place. Although some increase in the moisture within the lower layer will result, the amount of increase is not anticipated to resaturate the tailings. Saturated conditions will occur beneath the area of the free water pond during operation. Vertical changes in the degree of saturation will, therefore, vary across the impoundment. Some distance upstream of the embankment unsaturated tailings will extend down to the zone of initial ' ~ deposition which will itself drain over time. Within the center of the facility saturated conditions will occur beneath the pond. Under long-term, post reclamation conditions, the moisture content of the tailings will decrease with time through drainage. Drainage will be essentially complete adjacent to the embankment prior to the reclamation of the facility. Drainage of the remainder of the tailings following reclamation will continue, however, equilibrium conditions will result in extremely low drainage sites. The stability of the facility is primarily effected by the conditions at and adjacent to the embankment. The tailings in this area do not present concerns as to stability during operations and following reclamation, will tend to increase in stability over time. 1