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Mr. Roger Schmidt <br /> March 15,2017 <br /> Page 7 <br /> made structure(s) located within two hundred (200) feet of the <br /> affected lands." <br /> For reasons outlined in the WWE letter report dated September 2, 2016, the Al mining <br /> operation was the reason the original alignment of the Boyd-Freeman Ditch was rerouted <br /> to its current configuration. The gravel mining operation created a pit that was susceptible <br /> to erosion and headcutting when exposed to flood flows in the mapped floodplain. Those <br /> flood flows resulted in erosion of the pit embankment and subsequent headcutting that <br /> caused damage to the pipeline in 2013 and 2014 and erosion in the agricultural field in <br /> 2014. <br /> Tetra Tech letter,p. 3, third paragraph: <br /> The origin of the 2013 erosion that led to the breach and damage to the pipeline could have been <br /> caused by three modes of failure: 1) Simple sheet flow down the reclamation slope, 2) Leaky <br /> joints in the 48-inch inverted siphon that resulted in settlement above the pipeline, or 3) the <br /> removal of the 15-inch CMP [i.e., corrugated metal pipe] that resulted in uncontrolled <br /> overtopping of the reclamation slope. " <br /> WWE comments: <br /> The three possible modes of failure identified in the Tetra Tech letter are each evaluated <br /> and discussed below: <br /> • Simple sheet flow down the reclamation slope <br /> WWE comment: <br /> Sheet flow down the reclamation slope is the only mode of failure that is <br /> supported with evidence based on the information we have reviewed. Photos of <br /> water flowing over the crest of the embankment, taken during the early stages of <br /> the 2014 flood event, show evenly distributed sheet flow as it reaches the crest of <br /> the pit's embankment. <br /> • Leaky joints in the 48-inch inverted siphon that resulted in settlement above the <br /> pipeline. <br /> WWE comment: <br /> No evidence of pipe leakage or settlement was observed by personnel from the <br /> City of Greeley who are responsible for pipeline operations and maintenance. The <br /> pipeline operations and maintenance personnel typically conduct at least two <br /> visits per day along the pipeline alignment when water is flowing. In addition, the <br />