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Nature of the Exoerimental Practice <br />• Colowyo is presently constructing a permanent fill in Streeter <br />Draw. The spoil placed in these fills will not be required to <br />achieve approximate original contour as shown on the Post-mining <br />Topography Map (Map 19) and the Fill Design - Experimental Practice <br />Map (Map 30). <br />Colowyo has undertaken geotechnical engineering studies to <br />demonstrate that spoil pile fills in this area can be constructed <br />with 100 foot lifts, and no durable rock underdrains and still meet <br />or exceed the public safety and environmental protection standards <br />intended by regulation. See Exhibit 12, Experimental Practice <br />Information. <br />Use of the Exverimental Practice <br />The alternative method of excess spoil pile construction at the <br />Colowyo operation provides an opportunity to advance technologies <br />of mine fill construction beyond the stringency of existing design <br />criteria to assist in the formulation of a systematic approach to <br />• tailor the design standards found in regulations for specific <br />conditions found in the arid West. The proven effectiveness of the <br />practice will be an economical savings not only to Colowyo, but <br />ultimately to the consumer. <br />Environmental Protection <br />The location of the excess spoil pile in Streeter Draw is shown on <br />the Existing Structures - South Map (Map 22). <br />The fill structure has been designed so that drainage will not be <br />directed over the outslope and all surface water runoff from the <br />area above the fill will be diverted into designated diversion <br />structures as shown on the Hydrology Map - South (Map 12) and the <br />Fill Design - Experimental Practice Map (Map 30). <br />Runoff will be directed to the sedimentation pond located at the <br />base of the fill. The remaining fill to be placed in Streeter Fill <br />will be placed in lifts not to exceed 100 feet. Detailed geotech- <br />nical work has been performed on the Streeter Fill to evaluate and <br />• <br />2.06-6 <br />