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decrease the flow, thereby reducing the potential <br />for piping under the dam. However, it is recognized <br />that tailings slimes do have a finite permeability, <br />and there will continue to be an infiltration of <br />contaminated water to the subsurface. <br />(3) Homestake Mining Company should arrange for the in- <br />stallation of nested piezometers, as shown in the <br />attached figure, at three sites; on the crest of the <br />dam, at the toe of the dam, and at the area of the <br />existing seepage. The deepest of the nested pie- <br />zometers should be drilled well into bedrock, with <br />the other piezometer points selected subsequent to <br />the deep drilling, to provide data on the vertical <br />ground -water gradient, which exists at each of the <br />three points. A decreasing ground water head with <br />depth indicates a zone of ground -water recharge and <br />potential movement of contaminated ground water into <br />the subsurface, while an area of increasing ground- <br />water head with depth indicates a zone of ground- <br />water discharge, and the presence of potential uplift <br />forces contributing to instability. These piezometers <br />should be installed by use of a hollow -stem auger, with <br />the piezometer screen, consisting of a Johnson Hydro- <br />sphere or equivalent screen, isolated from the sur- <br />rounding material by back -filling with bentonite beads. <br />Ground -water elevations should be monitored no less <br />frequently than monthly by use of an electric sounding <br />am <br />