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a. The materials to be disposed of ore relatively homogeneous; i.e., cases where the overburden removed from one level is not materially different from that removed from any other level, and b. A foundation sufficiently competent to eliminate the possibility of future subsidence is available or can be attained by reasonable measures, and c. There is a likelihood that disposal of spoil in the valley or head-of- hollow fills could in effect create a dam which might at times function as a water impoundment, or d. Precipitation is very high and the fill could possibly become saturated. In brief, apart from their generality (which no doubt was purposeful), the Regulations imply construction of embankments to a standard that would normally be followed in constructing a conventional dam or other structure intended to impound water and to be safe under such conditions, For such situations, the Regulations are appropriate. In the case of the spoil fill in Streeter Canyon, however, none of the con- ditions cited previously obtain. Firstly, the Streeter Gulch fill cannot create a water impoundment. Secondly, and perhaps of greatest importance is the fact that the materials to be disposed of will vary over a wide range from time to time and from place to place which would make it almost impossible to avoid producing a "layered" fill composed of materials having wide{y different characteristics if compacted in lifts of limited depth. At one point in time, the material coming out of the pit might be composed of relatively hard durable sandstone or shale, and at another time materials that might be geologically similar would under compaction break down into afine- grained granular mass calling for different modes of compaction. Unlike the conven- tional water-retaining dam where different kinds of materials are selected in the quantities 9