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Larry Perino <br />Page 2 October 1, 2000 <br />The miners had done an excellent job of removing loose rock <br />from the tunnel roof, walls and floor. I could not find any loose <br />rock. There was no dust, mud or alteration products present on any <br />of the rock exposed in the tunnel. The upstream cofferdam has <br />intersected all the water previously flowing through the bulkhead <br />tunnel section. <br />The thrust collar and two water stops are installed on the <br />6 -in bypass pipe. Trim bars were tied into each rebar cage where <br />the bypass pipe passes through the rebar. <br />I was impressed by the care with which the second Terry Tunnel <br />Bulkhead was constructed. <br />I was informed that Type V cement was not available for the <br />concrete mix. I concur with the decision to substitute Type II <br />cement for this bulkhead. The inner Terry Tunnel bulkhead <br />effectively prevents the higher sulfate (2850 ppm) mine pool water <br />from entering the outer 3800 feet of the Terry Tunnel. The outer <br />Terry Tunnel bulkhead will only be subject to the approximately 600 <br />ppm sulfate groundwater entering between stations 15 +54 and 3 +03. <br />The American Concrete Institute classes this as "Moderate" <br />(150 -1500 ppm) sulfate exposure and recommends Type II cement <br />without pozzolan. The addition of pozzolan to the mix will further <br />increase the sulfate resistance of the bulkhead concrete. <br />Sincerely, <br />« <br />John F. Abel, Jr. <br />Colorado P.E. 5642 <br />