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11 <br />' Colorado. The Rito Seco bi-sects the site with the mine facilities and some waste rock <br />disposal areas being located north of the stream and the beneficiation facilities and the <br />remaining waste rock disposal areas located south of the stream. The topography is comprised <br />of steep and rugged mountainous terrain with gradients averaging approximately seven percent <br />' in the valleys to 20 percent along the ridges. The average elevation of the sine is 8,600 feet- <br />msl. <br />' Permitting and baseline studies for an open pit precious metal mining and beneficiation <br />operation initiated in 1987 with the issuance of the Colorado Mined Land Reclamation Board <br />' (CMLRB) Permit No. M-88-112 on March 22, 1989. Initiation of mining and beneficiation <br />operations began January 1990. Mining and beneficiation facilities consisted of two open pits <br />' (i.e., each being fully or partially backfilled upon completion of operations), Live waste rock <br />facilities, a milling and CIP/CIL recovery circuit facility, a tailings disposal facility, and <br />' various ancillary support facilities. Mining operations terminated in mid-October 1996 with <br />the exhaustion of mineable ore reserves in the West Pit area, while beneficiation operations <br />' continued until November 1996. Since termination of mining and beneficiation operations, <br />surface reclamation and monitoring activities have been conducted at the site. The West Pit <br />area backfill was completed in August 1997 and revegetated in October 1997. <br />2.2 GEOLOGY <br />The geological setting in the vicinity of the West Pit is comprised of three principal geological <br />' formations. These fottttations consists of (1) the Rito Seco alluvial deposition comprised <br />primarily of unconsolidated deposits of sands, silts, and clays, (2) the Santa Fe Conglomerate, <br />which consists of clays, silts, sands, and conglomerates, (3) the pre-Cambrian crystalline <br />bedrock, composed of pink gneiss, underlain by biotite and biotite-amphibole gneiss. The <br />' general locations of these geologic formations wi[h respect to each other, the West Pit and the <br />Rito Seco are illustrated in Figures 2 and 3. <br />The pre-mining geologic structure in the vicinity of the West Pit consisted of the pre-Cambrian <br />bedrock, which hosted the ore body, overlain by the Santa Fe Formation. A thin veneer of <br />' Rito Seco alluvium overlaid the Santa Fe Formation along the southern boundary of the West <br />Pit. A fault zone in the pre-Cambrian bedrock, which contains a thick layer of clay, crossed <br />1 <br />4 <br />