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,• <br />.~ <br />2 <br />and the 1971 USGS Hayden, Colorado, topographic quadrangle map. By comparing <br />terrain features on the various maps, I concluded that the dam axis crosses an <br />unnamed tributary of Hubberson Gulch in the NW114, NW1/4, 522, T5N, R88W. The <br />point is more accurately described as coordinates 40° 22' 50' north latitude - 107° 15' 21" <br />west longitude. The creek elevation at this location is approximately 7057 and the <br />creek gradient is about 0.04 ft/ft. Assuming a dam section with the crest at 7080, a <br />crest width of 35 feet, 3:1 (H to V) upstream slope, and a skewed dam footprint of 80 <br />feet along the creek from the axis to the heal, the original upstream toe should be about <br />elevation 7060. <br />The above conclusion is reinforced through examination of drawing EXHIBIT 7-13C by <br />Peabody Coal Co, dated 2-25-91. Although it is usually not proper to scale drawings, <br />the lowest foundation elevation appears to be 7058.5 along the dam axis as represented <br />by SECTION A-A'. Assuming the same stream gradient as above, the heal elevation <br />should be about 7062. On the same drawing, SECTION B-B' depicts original and <br />existing topographic expression along the principal spillway and into the ]eft valley <br />wall. This section illustrates classical dam geometry in a transform mode; however, it <br />is to the left of the valley thalweg and misleading. <br />Another procedure utilized was to superimpose the dam Footprint on topographic <br />drawings S10 and EXHIBIT 7-13C1 developed by AERO-GRAPHICS, Inc., Salt Lake <br />City, Utah. Both drawings exhibit photo date 7-1-89 with the latter showing a drawing <br />date of 2-15-91. Drawing S10 was drawn at a scale of 1 inch = 100 feet, whereas, <br />EXHIBIT 7-13CI is 1 inch = 50 feet. The photo date is important in that the Colorado <br />permit to build, Permit C-82-057, is dated July 17, 1989, and it is known that the dam <br />was not constructed until late 1989. The dam axis was not provided on S10 but was <br />shown on EXHIBIT 7.13C1. The two procedures yielded upstream toe elevations of <br />7063 and 7062 respectively. Drawing T10, an easterly continuation of S10 permitted <br />evaluation of various topographic expressions and could be used to examine the <br />watershed. <br />I, therefore, conclude that the virgin upstream toe elevation is between 7060 and 7063 <br />and that the storage volume is between 23 and 27 acre-feet. As such, the dam falls <br />under MSHA jurisdiction simply because the dam is more than five feet high and <br />contains more than 20 acre-feet of potential storage. <br />Items not addressed in this evaluation included spillway adequacy regrading hydrologic <br />aspects, such as, the inflow hydrograph or theoretical hydraulic calculations. <br />Furthermore, geotechnical considerations have not been examined. A cursory <br />examination of the submitted documentation does, however, generate a few questions <br />that should be addressed if formal plan approval is required. <br />1. It appears that the open channel emergency spillway has been placed through <br />deposited soil. Failure of a spillway which leads to failure of the embankment cannot <br />be tolerated. As such, channels of this type must be adequately protected. Engineering <br />