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Executive Summary <br />~~ ~:~ <br />This annual hydrologic report is the ninth annual <br />report submitted for the Mt. Gunnison No. 1 Mine <br />and covers the period from lOctober 1989 <br />through 30 September 1990 (water year 1990). The <br />report describes and interprets hydrologic monitor- <br />ingdata collected at the Mt. Gunnison No. 1 Mine <br />during water year 1990 and assesses hydrologic <br />impacts. <br />The report is divided into two sections. The (first <br />section describes monitoring activities for water <br />year 1990. The second section interprets the <br />hydrologic data collected during the year and <br />relates this information to mining and reclamation <br />activities at Mt. Gunnison to assess the impacts, if <br />any, on the hydrologic balance. This section also <br />addresses hydrologic impacts that might De expect- <br />ed to occur during water year 1991. <br />The quality of mine water sampled in 1990 was <br />good. All discharges were well within NPDES <br />effluent limitations without treatment. <br />Mine water discharge in 1990 was Crom Portals <br />No. 2 and No. 5 into pond MB-1. No water was <br />discharged Crom the Sylvester Gulch underground <br />sump. Discharged water had no measurable effect <br />on the quality of the North Fork of the Gunnison <br />River. <br />Activities at the Lower Refuse Pile also had no <br />measurable effects on surface or groundwater <br />quality during water year 1990. <br />Underground mining activities did not produce any <br />significant effects on springs, groundwater wells, or <br />surface water monitoringstations duringwaterycar <br />1990. <br />An extensive baseline monitoring data base has <br />been developed Cor the Mt. Gunnison No. 1 Mine. <br />• Operational monitoring started in August 1981 <br />with commencement of construction activities at <br />Mt. Gunnison. <br />Monitoring data for the period 1 October 1989, <br />through 30 September 1990 show no significant <br />adverse impacts to the hydrologic balance from <br />mining activities at the Mt. Gunnison No. 1 Mine. <br />Mine inflows during water year 1990 were less than <br />during water year 1989. The volume of water <br />discharged from the underground workings in 1990 <br />was about 55 acre feet. Areas being mined during <br />water year 1990 were about as wet as during 1989. <br />Water year 1991 is expected to be similar to 1990 <br />relative to hydrology at the mine. No significant <br />impacts are expected. <br />• <br />