HYDROGEOLOGY AND NUMERICAL MODELING OF THE FLAMBEAU MINE SITE, RUSK COUNTY, WISCONSIN

In 1968 Kennecott Minerals Company discovered a copper/zinc sulfide body near Ladysmith, northwest Wisconsin, which it proposes to mine through surface and deep methods. The chief objective of this study was to devise numerical models of the ground-water flow systems at the mine site and at an associated tailings-disposal area to assist in hydrologic-impact evaluation. After defining the flow systems using field and laboratory data, the Pleistocene glacial deposits and a Cambrian sandstone at each site were modeled as single-layer unconfined aquifers overlying the Precambrian surface.;Simulations of the mine site were performed for a 55-acre open pit and a smaller direct-ship pit to determine the effects of (1) interior seepage collection and (2) enclosing the pits by an impervious slurry wall. Simulations of the first case showed the diversion of flow from the Flambeau River to the pits and the creation of cones of depression around them. Predicted steady-state rates of seepage into the pits ranged from 25 to 45 gpm. Simulations of the encircling slurry wall indicated ground-water mounding on its up-gradient (east) side and head losses northwest of the mine due to the obstruction of subsurface flow and the loss of recharge through the area occupied by the excavation. The use of dewatering wells to control seepage into the direct-ship pit was also simulated. The optimal dewatering scheme consisted of 10 wells with a combined discharge of less than 17 gpm. The low pumping rate suggests that dewatering methods more suited for low-transmissivity soils would be more effective.;In simulations of the waste-disposal impoundment, seepage losses from the structure were represented by increases in areal recharge. Simulations assuming that tailings and waste rock would be placed directly on the natural land surface inside the structure predicted maximum steady-state water-loss rates of 72 and 140 gpm for waste accumulations of 25 and 50 feet, respectively. Both simulations indicated some ground-water mounding beneath the structure and suggested that surface seepage could occur along all sides of the site. Simulating the effects of lining the impoundment with compacted clay saprolite to reduce seepage was unsatisfactory due to the prominent role of unsaturated flow under these conditions. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.