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• 1. Confirmation of gravity sorting of high lift, end dumped spoil piles. The • degree of sorting was characterized with respect to height of lift and particle size distribution at different heights within the lift. 2. The gradation characteristics of the test drain section were determined and the test section was examined to determine if end dumping over the drain • caused contamination of the drain. 3. The flow capacity of the drain system and associated highly permeable base layer of the spoil lift were evaluated. 4. The gradational characteristics of the spoil and drain were evaluated to ~ determine if filter criteria and non-contamination requirements can be satisfied without a separate designed filter layer(s) based upon both observations at the test section and evaluation of typical spoil piles across the site. The following sections describe results of the investigation. • 1. Gravity Sorting The effect of gravity sorting of end-dumped, high lift spoil has been discussed in • previous reports by CTU'fhompson, Inc. (Reference 3). These effects have been further documented and analyzed during this investigation. Photos 1 through 4 (Figs. 1 and 2) illustrate the sorting which occurs with high lifts at the Colowyo Mine. The spoil piles shown were typical and the effects shown are observed to some degree on all spoil piles at the mine site. The effects of gravity results • in sorting of the spoil with larger particles reaching the base of the lift with progressively i smaller particles distributed towards the top of the lift. We found that lift thickness has an important effect on the degree of sorting. As lift thickness decreases (or as distance from the top of each lift decreases) the percentage of smaller particles and fines becomes significant and less complete sorting occurs (top 1/3 of 1/2 of lift in Photo 1). • Observations indicate the degree of sorting increases substantially when lift thickness exceeds 30 feet and approaches 50 feet. However, for all the spoil piles we observed, ranging in height from 30 to 60 feet, the lowest portion of the lift was very effectively sorted (i.e. very uniform) and contained no appreciable percentage of fines. Based upon our observations the thickness of this highly sorted layer varies from 2 to 3 feet thick for lifts 10 to 30 feet in height (approximately 10°,6 of lift height); to approximately 20 to 30 • feet thick for higher lifts on the order of 40 to 60 feet (approximately 50% of lift thickness). This is illustrated and confirmed in Photos 1 through 4. The rapid increase in thickness of the highly sorted layer with larger lift thickness is important due to the fact the test section was constructed at a lift thickness of 30 feet compared to planned 50 foot lifts in the actual fill. • 2 •