Laserfiche WebLink
U <br />dam, encountered a lens of coarse, clayey sand at a depth of <br />approximately 20 to 25 ft. Testhole 5, also drilled by Lincoln- <br />DeVore on the crest of the dam, encountered a gravel lens in a <br />clayey sand, at a depth of 24 to 30 ft. The Dames F, Moore Boring <br />N1, drilled from the crest of the dam after construction encoun- <br />tered a lens of brown silty to fine medium sand with a trace of <br />coarse sand and some fine to coarse gravels at a depth of approx- <br />imately 20 ft. beneath the original land surface, or 75 ft. <br />beneath the dam crest. These data indicate the heterogeneous <br />nature of the material overlying the bedrock, and the potential <br />for channelization of seepage along old stream channels. The <br />dam cut-off wall was not designed to form a cut-off to bedrock <br />or an impervious layer, but rather was used to lengthen the <br />flowpath of seepage under the dam. <br />SITE OBSERVATIONS <br />Homestake Mining Company has previously been discharging <br />tailings along the face of the dam, in an effort to build a <br />slime beach to reduce the amount of seepage. In addition, ar- <br />rangements have been made for a single 2 -inch line to discharge <br />tails into the upper portion of the pond. This single -point <br />discharge has built a tailings delta along a single spot on the <br />east side of the dam. Provisions are under way for discharge <br />of the tailings slimes around the periphery of the tailings ba- <br />sin, to reduce the permeability of the basin bottom. It was <br />noted that the tailings basin bottom remote from the points of <br />tailings discharge was essentially free of tails, and would <br />-3- <br />