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SUBSIDENCE HANDBOOK ~~ INTRODUCTION Geo-Hydro Q~nsul ting, Inc. "Subsidence Study" ampleted in June, 1983, con- cludes: 8.2 PREDICTED IMPACTS CN RESOURCES, STRC~TURES AND FACILITIES P7ost of the land under which mining will occur is currently used for relatively low intensity agricul hiral purposes such as forest land, rangeland and grazing, with limited local hay production. These activities should not be sensitive to the effects of subsi- dence and are unlikely to be adversely affected directly, How- ever, to the extent that these activities depend on water, there will be a negative impact on then if necessary water sources are disrupted. Subsidence cracks, while open, would pose a danger m the cattle or wildlife before they are filled and healed by natu- ral processes. Surface water resources consist of stock ponds and surface streams. These should be unaffected by changes in surface grad- ients or total subsidence resulting from development of a subsi- dence profile. 'Ihe ponds could be damaged and drained by a subsi- dencf_~crack that would occur directly below the pond, 4he proba- bil ity of such an event is very low and the pond could be easily repaired. 4he streams could be disrupted by the subsidence cracks; such disruption wuld occur at any of the Barth Fork trib- utaries. Obviously, East Ibatcap Creek and Stevens Gulch are the tro important drainages that are endangered by such a possibil- ity. C~ound water within the P~saverde Formation has been found m be of 1 invited extent, occurring only as isolated perched we ter bear- ing acmes. these tunes are not currently exploited and, because of their limited extent, have no potential for future development. Disruption of local, perched water bearing zones may occur due to mining where they lie in the immediate vicinity of the mine roof, although, because of the nature of this ground water, this will not constitute an impact on the area's resources. The most significant ground water resource identified consists of the alluvial deposits of Stevens (inch, which supplies us ter tt~ Ct9I and other users. 'there is the potential that subsidence cracks due to mining could drain this aquifer; its protection would probably require adequate changes in mining methods below the area. Colluvial deposits are the source for local springs within the proposed long-term lease area. 'these are generally located where there is sufficient overburden thickness that the risk of the development of surface subsidence cracks is low. n