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i <br />TWENTYMILE COAL COMPANY - FOIDEL CREEK MINE <br />PR09-08 TECHNICAL ADEQUACY RESPONSE (10/09) <br />6) Please add to the prediction of worst possible consequences from subsidence either "a", or "b" <br />below. <br />VFW <br />a) The information previously requested for the springs, for a scenario in which: M12 J 09 <br />DIVI-.- _ ."iaf?iation, <br />a. The main source of each springs is the intersection of the regional potintiotrcetAaeafety <br />surface with the land surface along the outcrop belt, and <br />b. Faults between the Western Mining District and the springs are not significant barriers <br />to flow. <br />b) Detailed geologic information for each spring that demonstrates: <br />a. The local lateral permeability change or geologic structure that completely (or nearly <br />so) isolates the source of the spring from the regional ground water flow, and <br />b. There is no reasonable probability that a significant source of the spring is the <br />intersection of the regional potentiometric surface with the land surface along the <br />outcrop belt. <br />Resoonse: Site geologic factors effectively preclude any influences on the identified springs from the <br />proposed underground mining operations and related subsidence. The following discussion, as <br />referenced to the attached exhibits, provides the requested demonstration: <br />Exhibit 1 shows the West Mining District, minimum and maximum angle-of-draw limits, the outcrops <br />of the Twentymile and Trout Creek Sandstones (from high-resolution aerial photos - also see Exhibits <br />5, 6, 9, and 10), and the locations of the identified springs. Given their location on the anticlinal <br />structure, any springs located to the west of the Trout Creek Sandstone outcrop (Boeddeker Springs #1 <br />and #2, Spencer Spring #2, Bear Run Spring, House Spring #1, and Coyote Spring), overlie units <br />below the Wadge Coal Seam, which have been documented in the Probable Hydrologic Consequences <br />Section of the PAP as being unaffected by the proposed mining activities. These springs, as well as the <br />other springs in the area tend to occur in ephemeral or intermittent drainages, and are recharged from <br />shallow ground water flows, as evident from the aerial photos (Exhibits 3 and 9). <br />Exhibits 1 and 5 show the Perry Springs (#145) as occurring to the south of the previously mined <br />underground workings. If underground mining were going to affect these springs, those effects would <br />have occurred in conjunction with the previous mining activities. The springs still exist and are <br />actively being utilized, even though the Perry Springs #1 and #2 are directly above the previously <br />mined area. In addition, Perry Springs #4 and #5 lie south of, and on the downthrown side, of a major <br />fault, which dips to the southwest and has displacements on the order of 40-90 feet (Refer to Exhibits <br />5, 7, and 8). Faults in the area have proven to be relatively "tight" with little groundwater flow in fault <br />zones. Even if groundwater flow were to occur, it would be in the direction of the dip of the fault and <br />toward, rather than away from the downthrown side. <br />The two remaining springs of interest; Gertie Spring and Livestock Spring #2 lie near the outcrop of <br />the Twentymile Sandstone, as shown by Exhibits 1-5 and 8-10. As previously noted, these springs <br />occur in ephemeral or intermittent drainages (as shown on Exhibits 3 and 9), lie over the sandstones, <br />shales and colluvium of the Holderness Member (see Exhibits 6, 9, and 10), and are alluvial springs, <br />recharged from shallow groundwater flows. Contacts with the local representative of the Division of