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• The partial extraction zones form protective pillars, the <br />limits of which are defined according to the requirements of <br />the surface area being protected. The limits have been <br />defined by extending a safety zone a distance of fifty feet <br />around the surface feature being protected, and then <br />projecting a line downward at the angle of draw until it <br />intersects the coal seam. <br />The most important protective zone defined extends from <br />the limit of mining up Stevens Gulch to the upstream limit <br />of the Stevens Gulch alluvium. This pillar would provide <br />protection for the stream flowing within Stevens Gulch, the <br />alluvial aquifer, the Muckle House and Morrell's ranch, the <br />CWI well field and associated facilities, and the Pitkin <br />Mesa Aqueduct. The integrity of the aqueduct upstream of the <br />protective pillar would have to be insured by appropriate <br />design of the pipeline or its routing. <br />A similar but less extensive pillar is proposed for <br />Roatcap Creek principally because this creek is used for <br />irrigation water diversion, and also to protect any surface <br />water flow. <br />A final protective zone is proposed Eor a meadow which <br />contains a number of stock ponds in Section 8. This is con- <br />sidered to be the least critical of the three areas <br />• identified as potentially requiring protection. <br />Other measures besides limited extraction zones may be <br />feasible for protecting some of the resources identified. <br />For example, buildings could be removed, streams could be <br />enclosed in flexible conduits, and alternative water <br />supplies could be established. Surface cracks could be <br />repaired as they appeared by backfilling or grouting, or <br />allowed to seal themselves naturally as mining progresses, <br />by sedimentation, or by erosion. However, undesirable en- <br />vironmental consequences may accompany these alternatives. <br />8.4 MO[JITORIN~.; <br />The subsidence monitoring networks which are currently <br />installed or planned at the Orchard Valley Mine provide an <br />adequate basis for monitoring of the existing lease area. <br />The widely-spaced network will provide general information <br />on subsidence magnitudes over the entire lease. The closely- <br />spaced network along and perpendicular to centerline of a <br />typical panel will provide site-specific data on subsidence <br />ci~aracteristics of the Mesaverde Formation, such as angle of <br />draw. because the monitored panel will 'ikely be of <br />• <br />- Ji - <br />