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<br />' the azgtunent presented in TR-26 is still valid, i.e., the water level in the West Pit should be <br /> lowered to an elevation just below the elevation of the water surface in the Rito Seco <br />' <br />~ adj <br />e <br />t t <br />th <br />ri <br />i <br />l <br />Th <br />h <br />f <br />i <br /> ac <br />n <br />g <br />o <br />e o <br />na <br />seep. <br />ere <br />ore, t <br />e most env <br />ronmentally protective modification <br />' that could be imposed on the hydrologic system in the West Pit would b.: to install the <br />d <br />l <br />ll <br />h <br />d <br />li <br />i <br />i <br />b <br /> propose <br />urry wa <br />s <br />as a <br />y <br />rau <br />c <br />arr <br />er, <br />n conjunction with lowering the water level in <br />' the West Pit by approximately 15 feet (as contemplated in TR-26). Installation of the slurry <br />ll <br />ld <br />id <br /> wa <br />wou <br />prov <br />e the interim mechanism to control the flow of groundwater between the <br />' West Pit and the Ri[o Seco alluvium. Whereas lowering the water level irr the West Pit <br />d <br />i <br /> woul <br />prov <br />de the long-term hydrologic assurance that there would not 5e outflow of <br />' groundwater from the West Pit. <br />' 3.2 Consequences <br /> The benefits of installing the slurry wall have been discussed in the previous pazagraphs. <br />' There is one potential hydrologic consequence of installing a slurry wall th.it is a natural <br /> consequence of modifying the flow of groundwater in the Rito Seco alluvium. <br />' The width of the Rito Seco alluvial aquifer upgradient of the West Pit is approximately 200 <br /> feet (Figure 1). Adjacent to the zone of West Pit outflow (the "window") and downgradient <br />' idth <br />f <br />i <br />if <br />h <br />id <br />h <br />f <br />h <br />ll <br />i <br />d <br />i <br />h <br />Ri <br />S <br />ll <br />l <br /> uv <br />e a <br />uv <br />ecreases t~~ a w <br />eco a <br />aqu <br />er, t <br />e w <br />t <br />o <br />t <br />um <br />o <br />n t <br />e <br />to <br />a <br /> approximately 60 feet. The action of [he slurry wall on the east side of the W:st Pit will be <br />' i <br />th <br />t <br />l <br />l <br />i <br />Ri <br />S <br />ll <br />l <br />if <br />h <br />h <br />di <br />h <br />fl <br />f <br />d <br />h <br /> ume <br />uv <br />a <br />aqu <br />er suc <br />e to <br />a <br />vo <br />e <br />ow o <br />groun <br />water <br />n t <br />e <br />to <br />eco a <br />t <br />at <br />to <br />vert t <br />' ' of groundwater currently migrating through the upgradient section of Rito Seco aquifer and <br />h <br />h <br />i <br />d <br />h <br />h <br />h <br />l <br /> on <br />west t <br />roug <br />e narrower sect <br />y be route <br />to t <br />e sout <br />t <br />into the West Pit would subsequent <br /> of the alluvium (approximately 60 feet). There aze two probable hydroloic responses <br /> resulting from the re-direction of groundwater flow through the narrower section of alluvium. <br />' First, the water levels in the Rito Seco alluvial aquifer upgradient of the W~:st Pit would <br /> likely increase, but probably not sufficiently to either intersect the land :surface or to <br />' influence the backfill of the East Pit. Secondly, a seepage face would probably form along <br /> the Rito Seco arroyo sidewall in the vicinity of the West Pit. That is, seeps would probably <br />' form along the Rito Seco upstream from the current surface expressions of the seepage front <br /> associated with the existing outflow of groundwater from the West Pit. However, these new <br /> <br /> Battle Mountain Resources, /nc. Sbepherd Miller. lnc. <br />' p:voa:e;u~n,.ryw.,mor~;e„r~p.-~sx 6 November 5, 1999 <br />