2010-12-17_REVISION - C1981019 (110)

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RULE 4 PERFORMANCE STANDARDS CBS Points of Compliance - POINTS OF COMPLIANCE - WATER MONITORING, RIO TINTO COLOWYO MINE MEEKER, COLORADO Prepared by Brant A. Dennis, C.P. G. March 2009 When dealing with point of compliance monitoring of ground water in a mining area, the monitoring is dependent on a continuous, non - perched ground water layer /zone that can be monitored, the geologic and structural conditions, and the topography. Currently at the Colowyo Mine (CM), Meeker, Colorado, where mining started over 30 years ago, the mining zone in both the East and West Pits has not encountered any significant shallow or deep ground water, except for an occasional perched ground water. As discussed in a previous paper, no point of compliance monitoring can currently occur in the current CM mining area. With current mining operations in the South Taylor area and, possibly, the Collom mining area, the following is presented to clarify the geologic and shallow and deep ground water conditions, to assist in determining whether point of compliance monitoring may be necessary for future mining areas. The following is a synopsis of the data submitted in previous permit applications for South Taylor and, more recently, Collom to the Colorado Division of Reclamation, Mining and Safety. This data are then used to determine if point of compliance monitoring at the CM and proposed mining areas is possible. Topography The active Colowyo mine area and associated properties owned by Colowyo are located on a topographic high, known as the Danforth Hills. The elevation in the area of the CM and associated property ranges from 8400 feet on the south to 6550 feet on the north in the incised valleys. In addition, south of the topographic highs, the topography decreases in elevation before another rise to the south. The valleys, themselves, have elevation ranges from approximately 7100 feet on the south to 6550 feet on the north. The current mine area (East, West and South Taylor pits) is bordered on the east and west by deeply incised valleys. These valleys are Good Spring Creek and Wilson Creek, on the east and west respectively. The valleys slope from south to north, with similar topographic slope as found at the higher elevations where the current mining occurs. There are other valleys within the area of the Colowyo mining area and properties, west of Good Spring Creek. However, the headwaters of these valleys (e.g., Taylor Creek, Jubb Creek, and Collom Gulch) tend to originate in the higher elevations within the Colowyo properties. These valleys do not create deep valleys like Wilson and Good Spring Creek, which cross the topographic highs. Geoloay The current mine area and associated properties are located on the Williams Fork Formation of the Cretaceous Mesaverde Group. The Williams Fork Formation is comprised of discordant beds /units of sandstone, siltstone and mudstone and coal seams, with an approximate thickness of 1,200 to 1,300 feet in the both mine area. Collom — Rule 4, Page 14 Revision Date: 1/23/09 Revision No.: PR -03