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Question: <br /> 9 . TP #4 deposition method empties tailing slurry into the <br /> trough between TP #4 toe and the state highway. <br /> Trenches cut into the bog immediately across the <br /> highway exhibit standing water, seemingly seeping from <br /> the ponded slurry across the road. This may create <br /> instability of highway foundation. This solution <br /> requires discharge with the other permitted discharge <br /> (NPDES) . Please sample this solution to determine if <br /> it is seepage from Pond #4 . If so, a method to seal <br /> the area receiving the slurry overflow may be required. <br /> Please discuss. <br /> Response: <br /> The area in question is that of the peat stockpiles. <br /> Samples have been obtained of these waters to compare <br /> with existing data on tailings waters . Results will be <br /> forwarded to the Division upon their review at SGC. <br /> The organic rich environment of the peat stockpiles <br /> could reduce and alter the chemistry of any standing <br /> water within these stockpiles, and there is every <br /> reason to expect that surface water quality within the <br /> peat area will not resemble that in the TP no. 4 pump <br /> back pond. <br /> To provide historical perspective on seepage in this <br /> area, a set of black and white aerial photographs taken <br /> on June 4, 1976 were reviewed. They clearly show the <br /> drainage ditches actively being cut into the peaty <br /> material underlying the current stockpiles before <br /> construction of TP no. 4 and relocation of Colorado <br /> State Highway 110. It would be very difficult to <br /> believe that the Colorado State Highway Department was <br /> not aware of a shallow water table problem at this site <br /> before road relocation began, and that it was not <br /> compensated for in the road foundation design. Indeed, <br /> digging the drainage ditches may well have been an <br /> integral part of the highway design. Considering that <br /> the pre-pond no. 4 shallow groundwater situation must <br /> have been apparent to the designers and builders of the <br /> highway 110 relocation, SGC considers highway 110 to be <br /> stable under the conditions of seepage which are <br /> currently visible in the peat stockpile drainage <br /> ditches . <br />