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• current mining plan could be used to reduce the subsidence <br />and strains to which these structures will be subjected. <br />No other structures or facilities which lie within <br />these zones are considered to be susceptible to damage from <br />the expected subsidence and strains. <br />7.3 ZONES OF GREATEST SUBSIDENCE <br />Zones of greatest subsidence impact are shown on Plate <br />17 as those zones having less than 800 feet of overburden <br />cover. Large subsidence magnitudes and strains are predicted <br />within these zones, even from the mining of individual <br />panels. This subsidence could result in potentially severe <br />damage to any structures located within these zones. There <br />is a high to moderate risk of subsidence cracks occurring <br />anywhere within the zones. High risk zones include areas <br />where the overburden is less than 500 to F00 feet thick, and <br />where the geologic conditions are unfavorable. Subsidence <br />cracks could result in disruption of surface water flows and <br />aquifers. <br />These zones extend from the point where mining is <br />initiated at the inside of the outcrop barrier pillars <br />• northward. Because of the steeply rising *_errain which is <br />present over much of the proposed long-term lease area, the <br />zone is generally fairly limited in extent. It is most <br />extensive where the overburden cover is reduced by the <br />presence of valleys and gulches, such as Roatcap Creek and <br />Stevens Gulch on the west of the area and Terror Creek along <br />the eastern boundary. <br />There are no known buildings located within these zones <br />where future subsidence is predicted. The Pitkin Mesa <br />Pipeline crosses zones of mar.imum subsidence within Stevens <br />Gulch just upslope of the seam outcrop. Substantial areas of <br />both Stevens Gulch and Roatcap Creek lie within the zone of <br />maximum subsidence. <br /> <br />-53- <br />