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• ~ of about 12 inches in diameter). About 1 foot or less of new fill had been placed uphill of the pipe. The marshy area uphill of the embankment was nearly level for some distance and had standing water and fern plants extending across the embankment length and at least 50 feet to the east. The downhill slope of the embankment exhibited evidence of slope instability, including mudflow features, tension cracks and hummocky appearance (Figs. 8-10), The most serious evidence of slope instability was within the middle third of the embankment length, which is the relatively highest section. No vegetation was established on the slope, with an average inclination of about 1.4H:1 V and height up to about 60 vertical feet in the central portion of the embankment. The soils exposed on the downstream slope consisted of scattered sand and gravel in a matrix of dark brown silty clay. Organic matter, consisting of leafy material, branches and wood was common in the fill, which also contained scattered plastic pipe scraps and asphalt chunks. The ground surface below the embankment sloped about 4.5H:1V. Evidence of mudflow from the 1997 failure was apparent by slight vegetative cover where it was not covered by recent mudflows. The spring reported by the inspector for DMG was measured by our representative and found to be flowing 3 gallons per minute. The spring was south of and slightly downhill of the toe of the new embankment material. The penstock was observed through one of four portals constructed of meta! culvert pipe. The top of the penstock was about 30 inches below surrounding ground grade. The top of the pipe was covered with rubber belting which had a small hole cut into it revealing an "x" mark, presumably used for surveying (Fig. 7). The site geology consists of eroded terrace deposits of glacial drift. Predominant layers of coarse gravel are separated by thin layers of fine to medium grained silty sands, generally with little, if any appreciable clay. Both road cuts north and south of the embankment expose these gravelly materials (Fig. 5). The conditions exposed at the road cuts and the materials exposed on the uphill slope of the embankment led us to assume the original embankment may be comprised of sand and gravel materials similar to the natural soils. No ground water seepage was noted in either cut. Field evidence and plans furnished to us indicate the penstock lies about 15 to 17 feet inside the uphill (east) edge of the embankment as it crosses the drainage. The penstock crosses the access roadway north of the embankment, near the present location of some temporary office trailers for Lafarge. Slone Analysis Based on field condtions which indicate the critical section of the embankment to be the highest portion, we plotted the geometry of our assumptions of the existing slope configuration as shown on Figs. 11 through 14. Several factors need to be considered in PUBLIC SERVICE COMPANY OF COLORADO AMES HYDRO PENSTOCK CTL? 31,848 4