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tunnel conditions. His report (~ibit 4) concludes that any attempt to modify the Rampart Tunnel is not a reasonably feasible alternative to the construction of Conduit No. 26. He points out from personal knowledge that the U.S.B.R. assumption that the existing lining can be pressure grouted is wrong. " 2. Construction Problems !n ~ Tunnel Denver also sought the advice of an internationally recognized firm of consulting engineers on the construction problems associated with the modification of the tunnel inCluding the grouting prOblem. Parsons, Brinckerhoff, Quade and Douglas, Inc. reported (Exhibit 5) that "All factors considered, the construction of a new tunnel designed for the capacity and pressure conditions required represents the best and, in fact, '~ only prudent engineering solution." 3. Surge Chamber Required Slow closing valves proposed to avoid the high cost of an adequate surge chamber cannot provide the flexibility and reliability of service required for municipal water utility operations. A slow-closing valve of the type assumed by the United States Bureau of Reclamation to be adequate would pose a serious risk to the operation and in fact the in- tegrity of the filter plant. This is so because if it were to fail and close too quickly, the resulting water hammer would not only blowout the outlet works but would also expose the entire filter plant to risk of severe damage. Safety of operating personnel must also be considered. Responsible water utlities do not expose their systems or personnel to such hazards: instead, they provide for the dissipation of water hammer pressures by use of a surge chamber, a chamber whose function and need in this situation is well described in the letter report from the consulting engineering firm of CH2M Hill (Exhibit 6). In this case, the chamber would have to be an expensive vertical shaft from the top of the tunnel to the surface of the ground. To cut the cost of using the Rampart Tunnel alternative, the U.S.B.R. eliminated this vitally necessary safety component: the inevitable result is that the cost figures presented by the U.S.B.R. for that structure are unrealistically low. 4. Time Of Construction -- The Rampart Tunnel carries almost the entire water supply for the City of Aurora. The United States Bureau of Reclamation assumed that it could be taken out of operation for a series of five-month periods during winter seasons. This is wrong. Aurora has stated that it can permit an outage of not more than one month in the winter without an alternative source of supply. Actual construction would -9-