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2.04.7 Hydrology Information 1) Ground Water (a)(il During November, 1990, Somerset Mining Compa- ny drilled three exploratory holes in the vicinity of its new Sanborn Creek Mine. Hale SC-1 is about 3300 feet from the Bear No. 3 Mine portals. Other than a damp zone encountered at 43- feet this hole was virtually dry above the Rollins Sandstone. Hole SC-1 was completed in the Rollins Sandstone which is identi- fied as a regional aquifer. Water was encountered as the drill hole penetrated the Rollins Sandstone. Holes SC-2 & SC-3, which are about 5800 feet from the Bear No. 3 Mine portals, were drilled from a public road in Coal Gulch. Water was encountered in hole SC-2 in the D-Seam which is some 200-Peet above the C-Seam. No other significant quantity of water was encountered in hole SC-2 above the Rollins Sandstone. Hole SC-2 was completed in the Rollins Sandstone. Water was encountered as the drill hole penetrated the Rollins Sandstone. Hole SC-3 was drilled near SC-2. Hole SC-3 was completed in the area where water was encountered in Hole SC-2. Because of contamination of Hole SC-2 it subsequently replaced by Hole SC-4 which was drilled in the same local area. The Rollins Sandstone aquifer in this region is under artesian conditions with a potentiometric surface eleva- tion at drill holes SC-1 and SC-4 of 6013.9 feet and 6026.4 feet • respectively as of May 1991. The water elevation of the North Fork of the Gunnison River at the Rollins Sandstone outcrop is estimated to be at 5965 feet. The North Fork of the Gunnison would therefore be classified as a gaining stream. The elevation of the B Seam where mining is taking place and will take place in the Bear No. 3 Mine will vary from a low point of 6175 to a high point of 6365. It can be seen that the B Seam is about 150 feet above the indicated potentio- metric surface elevation of the Rollins Sandstone. It is possi- ble that the potentiometric contours of the Rollins Sandstone are very steep so the potentiometric surface of the Rollins Sandstone could be above the B Seam. However, there should be no seepage up into the Bear No. 3 Mine B Seam floor from the Rollins Sandstone aquifer even if the potentiometric levels are higher than mine workings due to the intervening layers of relatively impermeable shale. Mine development to date in the B Seam has not encoun- tered any seepage from below. Thus the underling aquifer appears isolated from the mine workings and will remain so during post mine development unless the pressure differential between the mine workings and the underlying aquifer becomes great enough that some seepage occurs. This is believed unlikely and if it occurs, it will be minor because of the low tranmissivity of the . aquifer. 2.04-29 6/11/91