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' testing of the SF-2 well indicates a permeability of 0.006 gallons per day leer square foot (0.00079 feet per day). Tests of monitoring wells screened in the Santa Fe Formation yielded ' an average hydraulic conductivity of 0.0016 feet per day. 2.4 Rito Seco Alluvium The Rito Seco alluvium is a medium to light gray and light brown unconsolidated silty conglomerate. Angular and sub-round clasts of several rock types including granite, gneiss, ' and quartzite are present in the alluvium. The Rito Seco alluvium appeazs to tlucken towards the axis of the Rito Seco, and thins to the north and south of the valley. ' Along the alignment of the proposed slurry wall, the Rito Seco alluvium is composed of two distinct units that can be correlated using the geologic logs from the monitoring wells. The ' upper alluvial unit is a brown sand and gravel. Beneath the brown alluvial unit, the sand and gravel is gray. The thickness of each unit varies between monitoring well borings. The gray ' alluvial unit is absent in monitoring wells SF-2 and M-20 as shown on Figure 2. The geologic log for monitoring well M-30 describes a 30-foot screened interval of ltito Seco ' alluvium. Hydraulic testing of that well indicates a permeability of 27 gallons per day per squaze foot (3.6 feet per day). Tests of monitoring wells screened in the Rito Seco alluvium gave an average hydraulic conductivity of 5.06 feet per day. ' 3.0 HYDRAULIC BARRIER DESIGN ' The intent of the hydraulic barrier is to provide a 1x106 cm/s or less hydraulic creak between the West Pit and the Rito Seco. The trench for the bamer will be excavated tnd backfilled ' with the slurry mixture in an ongoing conswction process, progressing along the proposed alignment. ' Irnmediately following trench excavation, bentonite clay slurry will be mixed with available on-site screened material or off-site borrow material. These materials will Ise required to ' provide an effective soil/slurry mixture. Material specifications for the soil/:slurry mixture will be a minimum of 30% passing a No. 200 sieve with a maximum not to exceed 50% passing a No. 200 sieve. The trench width will be approximately 2 to 3 fe a, and trench depths may range from 10 to 60 feet, with an average depth of approximately 50 feet. With ' Battle Mountain Resources. lnc. .Shepherd Miller, lnc. P.I/0°]L'LSlurryWdliOesigvrpwr.~br 4 November 5, /999 1