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Prospect Pond Embankment Inspection <br />On September 16, 2008, 1 inspected the embankment of the Prospect Pond located in the <br />NW /4 of Section 14, T3N, R93W. As has been previously reported, this impoundment <br />experienced an overtopping event that resulted in sheet flow over the crest of the <br />embankment following a major thunderstorm event on August 9, 2008. <br />During the inspection, I found no evidence of cracks or scarps on either the crest or upstream <br />and downstream faces. The embankment appeared normal in all respects, except that <br />vegetation was clearly knocked over along most of the downstream face. Most of the existing <br />vegetation is expected to recover. <br />There was no evidence of bulging or sloughing. Only minor rilling is evident. No sign of <br />seepage or moisture is evident along the downstream toe. <br />Given the relatively low permeability of the material used to construct the compacted <br />embankment, it is unlikely that that the phreatic surface within the embankment would have <br />had time to rise appreciably during the short time the water surface was elevated above the <br />normal pool at the weep hole elevation. This is estimated to be about 24 hours. A rapid <br />impoundment drawdown with an elevated phreatic surface can result in slope instabilities on <br />the upstream and downstream embankment faces. No evidence of such failures was found, <br />and it can be assumed that the time elapsed since the event would result in the phreatic <br />surface returning to the normal pool elevation or less. <br />On the date of this inspection, the open channel emergency spillway was found to be partially <br />blocked due to a mass of matted vegetation debris, and small logs. This is a contributory <br />factor to the embankment overtopping. Photographs of the blockage were taken (see <br />attached) and the spillway was subsequently cleaned. The drop inlet spillway appeared to be <br />functioning normally. <br />During pond clean -out operation, the crest elevation of the embankment should be surveyed <br />and raised if necessary to meet the design elevation of 6755.0. <br />While this was a significant event, it is my conclusion that this incident had no effect on the <br />overall stability of the embankment. I am a Licensed Professional Engineer in the State of <br />Colorado and a representative of Environmental Solutions, Inc, P. O. Box 2996, Cheyenne, <br />Wyoming. <br />o�P�fl • L CF ,z1o� <br />32257 z <br />• 24' <br />ONAL <br />P.E. No. 32257 <br />�ql /5 /0 8 <br />