2010-11-16_PERMIT FILE - C1996083A (24)

Home Browse Search

(3) Protection of Hydrologic Balance The applicant has prepared a drainage and sediment control system which will minimize changes to the surface water and to the prevailing hydrologic balance in the facilities area by detaining run -off in sediment ponds or treating runoff with alternative sedimentation control. The sediment ponds are designed to contain the run -off from the 10 year precipitation event. The sedimentation control plan is presented in Volume III, Exhibit 8, and on Maps 20, 21 -1, 21 -2, 21 -3, 21 -4, 22 -13, 22 -C, 22J, 35, 36, 36a and Volume IV. There is very little if any beneficial use made of surface run -off from the ephemeral drainages in the permit and adjacent areas. These ephemeral drainages typically only flow during spring snowmelt and significant precipitation events. Sediment ponds B & C should alleviate the problem of the ditches (Deer Trail Ditch & Fire Mountain Canal) plugging with sediment and /or completely washing out do to previously uncontrolled runoff events. • • The construction of mine entries, ventilation shafts and the mining of the coal could cause water to move from formations above the coal seam into the mine. This potential water migration would be magnified by roof collapse and fracturing caused by subsidence. Although the permeability of the coal seam and surrounding strata is low and the quantity of water stored in the formation is also low, some water will occasionally seep into the mine. The Freeman Gulch vent shaft was raise bored to an 8 -foot diameter. The shaft was lined with a 6 -foot diameter steel casing. The steel casing was grouted through the water bearing zone which is approximately 0 to 140 feet deep. The grout liner through this zone is approximately 1 -foot thick. To prevent surface drainage from entering the shaft, the steel liner was extended at least 3 -feet above the ground surface (see Map 35). A screen was placed on the top of the steel liner. The Freeman Gulch shaft has been backfilled a capped with concrete. This backfill will protect the integrity of the grouted liner to contain the water bearing zone. The concrete cap will ensure no surface run -off will enter the backfilled shaft. Thus, the shaft backfill and concrete shaft will protect the hydrologic balance. The Hubbard Creek vent shaft was blind drilled to a 14 -foot finished diameter. The shaft was steel lined to a finished diameter of 12 -feet. The 500 foot deep shaft was grouted through water bearing zones. To prevent surface drainage from entering the shaft, the concrete collar was extended above the ground surface. During idle periods, a screen is placed on the top of the concrete shaft. Because of the method of shaft construction, there was no measurable water inflow during shaft construction. The pre - grouting PR -12 2.05-100 06/10 A PPRov6 -b