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West Elk Mine In the event that a surface crack opens and stays open, surface and spring flows that • encounter relatively permeable zones in the overburden will move downgradient and reemerge as springs with subsequent dischazge into either the Dry Fork or the North Fork. WWE and Messrs. Rold and Dunrud have determined that there is virtually no potential for a surface crack in the permit area to be deep enough to connect with a mine fracture zone. In the extremely unlikely scenario in which this occurs, however, the implications would be minor. If this scenario were to happen to the south of the drainage divide (in the Dry Fork basin} the surface andlor spring flows would be discharged into the mine workings. Waters collected within the mine workings would be treated, if necessary, to comply with the National Pollution Dischazge Elimination System (NPDES) pemrit requirements and pumped through a drill hole back into the Dry Fork basin, as specified in the water augmentation plan (Exhibit 52). Losses within the mine are minor -less than 5 percent of the total inflow which could be experienced. The decreed augmentation plan for the Dry Fork basin conservatively provides replacement water for 100 percent of the yield of the basin. The magnimde of replacement water provided by MCC in the Dry Fork/Minnesota Creek basin is orders of magnitude more than will be required, based upon the subsidence evaluation conducted by W WE with Messrs. Rold and Dunrud. • There is a very small risk (WWE has calculated the risk to be less than one percent that one or more of the stock ponds in the Apache Rocks permit revision area could be adversely affected via surface cracks. This risk calculation also holds for the Box Canyon permit revision azea. Pond water could be diverted into locally permeable zones within the overburden where it could: (1) migrate down-dip toward the North Fork or Dry Fork to become part of the tributary alluvial/colluvial contribution of baseflow to the stream system, (2) reappear as an eghemeral seep or spring, or (3) become trapped as storage in an isolated zone within the overburden. If any of these circumstances were to occur, they would render the affected stock pond temporarily useless for retaining surface water. However, the lost water would eventually return to the Dry Fork and/or North Fork. The stock pond embankments could conceivably be effected by surface cracking; although, the probability of this occurring is insignificant. It is important to note that the overburden materials in the permit area contain numerous shale and claystones layers and lenses which tend to undergo plastic deformation under compression, thereby sealing fractures which develop. In addition, the sediment load within surface flows (especially during spring runoffl will tend to fill surface cracks which may develop, thus further reducing the potential to transmit water downward. i 2.~$-1 ~8 RevisedJun. 1995 PR06; !/96RN03: Revised May 1999 TR89; Revised Jan. 1998 PR08