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<br />6.0 SUBSIDENCE IMPACTS <br />6.1 LAND USE <br />As shown on Plate 9, most of the area of the future <br />lease has been classified as rangeland/wildlife habitat - <br />recreation. It cannot be expected that the predicted <br />subsidence will alter this classification. Subsidence cracks <br />that are expected to occur within the zone of the greatest <br />subsidence impact can comprise danger for the cattle and the <br />wildlife; observations of the existing cracks above the <br />Orchard Valley Mine indicate that the cracks may stay open <br />for a period of several years. The cracks will stay open <br />specifically on mountainous ridges while they may heal and <br />close in depressions where occasional runoff will tend to <br />fill them with soil. <br />Land use could be changed by the subsidence within <br />zones of grazing pasture and hay producing areas if the <br />surface and/or ground grater regime is altered by the <br />subsidence and the springs are disrupted. Such potential <br />disruptions are discussed in Sections 6.2 and 6. 3. As <br />discussed in previous sections of this report, disruptions <br />of surface and shallow ground water regimes can be expected <br />only in tt~e area of relatively low overburden and are thus <br />• limited to Stevens Gulch alluvium (C'AI well field), limited <br />parts of East Roatcap Creek and to the area of grazing and <br />stock ponds in the southwest part of Section 8 (T135, R91W). <br />6.2 SURFACE WATER <br />Subsidence can impact surface streams or impoundments <br />in several ways: <br />o vertical settlement of the surface <br />o local changes in surface slopes <br />o vertical or subvertical subsidence cracks caused by <br />tensile strain <br />• <br />Vertical settlement of identical magnitude over large <br />areas has frequently a negligible effect on surface water <br />bodies. TYie changes of stream gradient are very minor (if <br />any) and the vertical displacement has very little effect on <br />the impoundments such as stock ponds in the area. <br />4? - <br />