2010-06-14_REVISION - C1994082 - Laserfiche WebLink

Home Browse Search

quite steep at disturbance perimeters. In some cases backfill material was placed against undisturbed virgin ground at the top of a final highwall. As indicated in Tab 20 (Backfilling and Grading) of the PAP, slopes may exceed 3(h):1(v) in these areas above the final highwall where the natural slope is originally steeper than 3(h):1(v). Included in the postmine regrading operation was the construction of small swales and hummocks to minimize erosion and to conserve soil moisture and to promote revegetation. SCC generated topographic maps, using photogrammetric methods, of backfilled and regraded areas on an annual basis. The maps were used to determine whether regraded areas are consistent with the approved postmining topography. There were no variances from approximate original contour (AOC) requirements or highwall reclamation requested or allowed in the permit area. Exhibit "D", Post Mine Cross-Sections of the bond release application, provides representative cross-sections showing final topography configuration within the Neck Pit and South Pit reclamation areas. Final topography in the North Pit area had been previously reviewed and determined to be acceptable in the context of Phase I Bond Release SL-1, in 2007, which applied solely to the North Pit area. A couple narrow corridors associated with reclaimed light use roads and channels, and a small slide scarp area, were excluded from the Division's SL-1 approval, but the major portion of the North Pit area was approved for Phase I release within SL-l. These areas that had been excluded in SL-1 were all requested for Phase I bond release with SL-2. The approved Post-Mining Topography Map, Exhibit 20-2, was compared with the Land Use Map (Exhibit 4-1 of the approved PAP), which depicts premining topography over the entire permit area, with a 40' contour interval, and with the Premining Vegetation Map (Exhibit 10-1 of the approved PAP), which depicts premining topography within the Neck Pit and South Mine areas, with a 5' contour interval. The maps were reviewed to verify that post-mine drainages were constructed in appropriate locations with adequate drainage density. Pre-mining topography was also compared with the approved Post-Mining Topography Map to verify that regraded slopes achieved AOC. All regraded slopes were inspected and evaluated for erosional stability during the Phase I bond release inspection and routinely during normal monthly inspections. Results of these evaluations are discussed below in Section III Observations and Findings. The Yoast Mine drains to Sage Creek on the west side and to Grassy Creek on the east side. Sage Creek and Grassy Creek are perennial tributaries to the Yampa River. Annand Draw and Scotchmans Gulch are intermittent drainages which drain from the northern side of the proposed permit area into Grassy Creek. The Yampa River then flows to the Green River and eventually the Colorado River. The final reclamation plan for the Yoast Mine includes retention of numerous ephemeral postmine drainage channels that are ultimately tributary to either Sage Creek or Grassy Creek. The SL-2 evaluation included assessment of drainage density, field check of channel compliance with design specifications of the approved permit, and assessment of channel erosional stability. Based on comparison of permanent drainages depicted on the pre-mine map Exhibit 4-1 and post-mine topographic maps, the density of postmining channels is higher than the density of pre-mining ephemeral drainages. Numerous permanent drainage channels have been approved and constructed, and were evaluated as part of this Phase I bond release. The postmine channels are shown on Exhibit 20-2 and certified 7