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<br />Chapter IV - Formulation of Alternatives <br /> <br />Several alternatives were considered during the development of the CWCB memorandum <br />dated September 18, 2002. The alternatives included the following: <br /> <br />1. Removal and replacement ofthe existing 24-inch outlet. The altemative would also include <br />the removal of a secondary 18- inch CMP and the replacement of the toe drain system. <br /> <br />2. Cured-in-place pipe (CIPP) lining ofa p0l1ion of the 24-inch outlet combined with open cut <br />replacement of the damaged portion of the 24-inch outlet and toe drain. <br /> <br />3. CIPP lining of the secondary 18-inch CMP conduit and rehabilitating its intake and outlet <br />structure. Concrete grouting and abandonment-in-place of the existing 24-inch CMP outlet. <br />The toe drain system would be replaced. <br /> <br />4. No-Action alternative. <br /> <br />Field inspection ofthe sinkhole by Boyle revealed that the 24-inch CMP had failed along the <br />crown of the pipe and then crushed due to the embankment loading along the failed section. <br />Sleeving or plugging the pipe, or using a CIPP, are not viable alternatives since the existing pipe's <br />structural integrality has been compromised. Therefore, Alternatives 2 and 3 are eliminated. Two <br />alternatives were evaluated for the rehabilitation of Lake Arrowhead Dam and they include outlet <br />pipe replacement and the no action alternative. <br /> <br />Figure IV -1 shows the general configuration of the existing dam with respect to the reservoir. <br />The existing outlet works consist of a concrete inlet tower, a 24-inch CMP outlet pipe, and a riprap <br />discharge basin. The figure shows the location of the sinkhole that was caused by the failed outlet <br />works. The boreholes that were drilled for the project are also located on the drawing. Weld County <br />has a road located along the crest of the dam, which has been closed due to the failure of the <br />downstream embankment. The County will reconstruct the asphalt road after the Company has <br />rehabilitated the dam. Several irrigation lines owned and operated by the Company are located along <br />the crest of the dam along with a City of Evans waterline. The Company's irrigation lines will be <br />removed and replaced to accommodate the excavation of the outlet pipe. The City's waterline will <br />be abandon as part of this project. The waterline will be abandon following the City's design <br /> <br />Lake Arrowhead Dam Rehabilitation Feasibility Study <br /> <br />6 <br /> <br />13DVLE <br />