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Subsidence Evaluation For <br />ExhibrT 60B South o(Divide Mining Area Page 27 <br />In contrast to surface water containment structures, such as reservoirs, ponds, streams and <br />ditches, springs and water-bearing zones may have water sources that are either in bedrock <br />beneath the blanket of clay-rich surficial material {debris flows, alluvium, and wlluvium), or <br />have a source from within the surficial material. Subsidence may affect a spring or water- <br />bearing zone source located in bedrock, whereas effects may or may not be expected where the <br />spring source is within the surficial material. Tension cracks produced in sandstone bedrock <br />during the subsidence process, for example, may divert water to a lower rock layer and therefore <br />change the flow location_ However, local water-bearing zones in permeable zones, which are <br />interlayered with clay-rich zones (Wasatch clays) in the surficial deposit, may yield to tensile <br />stresses without cracking. There is no field documentation known to the author [o either support <br />or refute this statemetrt. Therefore, it is important to monitor all known spring flows for a few <br />years (to account for seasonal variations) prior to any mining in the area. <br />11.4.1 Springs <br />Decreed Spring 21 is located within the areas of mining influence of un-mined longwall panels <br />E5, E6, and E9 in the NE'/. of Section 5, (Township 14 South, Range 90 West). Maximum tilt <br />and sham is expected to occur in this area, because it is located above the projected hanlageway <br />and barrier pillaz to the haulageway. The overburden depth at this spring site to the E Seam is <br />about 650 feet. <br />Springs mapped in the South of Divide mining area, which have been found flowing at every site <br />• visit, include: 1) a spring located 800 feet west, southwest of the Mimesota Reservoir dam- <br />outside the area of any planed mining influence; 2) a spring located along Dry Fork 700 feet <br />west of the confluence of Poison Creek and Dry Fork, above projected longwall panel E2 in <br />about 650 feet of overburden to the E Seam; 3) a spring located south, and outside of dre area of <br />influence of longwall panel E8. <br />Of the springs mapped, only the decreed Spring 21 and the spring located along Dry Fork and <br />above longwall panel E2, may be impacted by longwall mining. The source of decreed Spring <br />21 may be a local water-bearing zone in bedrock of the Mesaverde Formation, whereas, the <br />source of the spring along Dry Fork (above longwall panel E2) is likely to be a local water- <br />bearing zone in colluvium or alluvium derived from debris flows. <br />11.4.2 Water-Bearing Zones <br />Horizontal strain produced during subsidence could impact local water-bearing zones in bedrock <br />beneath the blanket of clay-rich surficial material. It also may impact local water-bearing zones <br />in su~cial material, where permeable and saturated zones are stratigraphically positioned in <br />zones of tensile strain. Impacts may occur for long periods of time, where the water-bearing <br />zone is located above mine boundaries and bamer pillars, areas where permanent strain occurs. <br />On the other hand, dynamic strains and related cracks produced by subsidence above moving <br />longwall faces in a given area are nil and close when the longwall faces move out of the area of <br />influence of this area. Based on the author's evaluation, any mining effects on local on water- <br />bearing zones can best be identified by monitoring any changes in flow and water levels in <br />springs and ground water wells (as discussed in Section 11.4.3). <br />831-032.690 WirghtWaterEngineers Inc. <br />