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r • `~ I~~~ , I~,.L ~,Yt ~t. i5c~a~~,<::~ Executive Summary ~~~~; ~ ~;_~~~ , 4. ~ `„ ~~ ~.tx~-, ~,: 1,,. This annual hydrologic report is the tenth annual report submitted for Ute West Elk Mine (formerly the Mt Gunnison No. 1 Mine) and wvers the period from 1 October 1990 through 30 September 1991 (water year 1991). The report describes and interprets hydrologic monitoring data collected at the West Elk Mine during water year 1991 and assesses hydrologic impacu. The report is divided into two sections. The first section descn'bes monitoring activities for water year 1991. The second section interprets the hydrologic data collected doting the year and relates this information to mining and reclamation activities at West Elk to assess the impacts, if any, on the hydrologic balance. This section also ad- dresses hydrologic impacts that might be expected to occur during water year 1992 An extensive bazeline monitoring data baze haz been developed for the West Elk Mine. Operation- al monitoring started in August 1981 with com- mencement of construction activities at West Elk. )\4onitoring data Cor the period 1 October 1990, through 30 September 1991 show no signifignt adverse impacts to the hydrologic balance from mining activities at the West Elk Mine. Mine inflows during water year 1991 were more than during water year 1990. The volume of water discharged from the underground workings in 1991 was about 76 acre feet Areas being mined during water year 1991 were about az wet az during 1990. The quality o[ mine water sampled in 1991 was good. All discharges were well within NPDES effluent limitations without treatment. Mine water discharge in 1991 was from Portal No. 2 into pond M13-1. No water waz discharged from the Sylvester Gulch underground sump nor from Portal No. S. Discharged water had no measurable effect on the quality of the North Fork of the Gunnison River. Activities at the Lower Refuse Pile also had no measurable effects on surface or groundwater quality during water year 1941. Underground mining activities did not product any signifipnt effects on springs, groundwater wells, or surface water monitoring stations during water year 1991. Water year 1992 is expected to be similar to 1991 relative to hydrology at the mine. No significant impacts are expected. C J