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the Canterbury Tunnel. Therefore, the Canterbury Tunnel remains an important source <br />of supply because of the heat content. <br />4.2. DESCRIPTION OF THE PROBLEM <br />Despite the excellent chemical quality of the source, the physical quality and rate of flow <br />of water from the Canterbury Tunnel deteriorated to the point where it was no longer a <br />viable source of supply. Specifically, turbidity spikes occurred on an increasing basis, <br />forcing the District to take the supply off-line in the summer of 2003. As well, the flow <br />rate is now less than 200 gpm. The suspected source of the problem is the deteriorating <br />tunnel structure. It is believed that the tunnel was constructed through glacial till material <br />with timber cribbing as wall reinforcements for at least the first 1,200 feet of its length. <br />The remainder of the tunnel was driven into hard rock that did not require continuous <br />structural support. Over time, the timber cribbing deteriorated to the point where <br />portions of the tunnel are slowly collapsing. Surface manifestations of the collapsed <br />tunnel are visible as an intermittent surface scar above the first 700 feet of the tunnel's <br />length and District personnel have noted the continued extension of the surface scar <br />above the tunnel. There is reportedly a very old pipeline within this portion of the tunnel, <br />presumably preventing its complete collapse. The tunnel portal is sealed, preventing a <br />visual inspection of its condition. <br />4.3. IMPORTANCE OF THE CANTERBURY TUNNEL <br />Continued use of the Canterbury Tunnel is important to the District for several reasons. <br />First, the tunnel provides an extremely reliable source of water in terms of yield and <br />water rights. Prior to the collapse of the initial portion of the tunnel, flow measurements <br />indicated its yield is unaffected by wet or dry climatic conditions, at approximately 625 <br />gpm in all months of the year. The availability is further secured under the Stevens & <br />Leiter direct flow water right, which Parkville transferred to the tunnel many years ago. <br />The right has an appropriation date of September 1, 1873 for 3.0 cfs. Because of this <br />senior status, the Stevens & Leiter right is almost completely dependable. This reliable <br />water source is of particular value to the District during periods of high municipal <br />�! W. W. Ulhaeler and Assocfatas, Ine 5/19/2010 Final <br />- 1 Wotar Resouress Enginasrs Page 12 <br />