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Executive Summar <br />This annual hydrologic report is the sixth report submitted for the Mt. Gunnison <br />t No. 1 Mine and covers the period from October 1, 1986 through September 30, <br />1987. The report provides a summary and interpretation of hydrologic monitoring <br />data at the Mt. Gunnison No. 1 Mine through Water Year 1987 and an assessment of <br />' hydrologic impacts. Detailed listings of monitoring data for the year are <br />contained in the quazterly reports, "Hydrologic Studies". <br />This report is divided into twu sections. The first section describes <br />' monitoring activities through Water Year 1987. The second section interprets <br />the hydrologic data collected during the year and relates this information to <br />mining and reclamation activities at Mt. Gunnison to assess the impacts, if any, <br />' on the hydrologic balance. This section also addresses hydrologic impacts that <br />might be expected to occur during Water Yeaz 1988. <br />' An extensive baseline monitoring data base has been developed for the Mt. <br />Gunnison No. 1 Mine. Operational monitoring started in August 1981 with <br />commencement of construction activities at Mt. Gunnison. <br />Monitoring data for the period October 1, 1966, to September 30, 1987, shows no <br />significant adverse impacts to the hydrologic balance from mining activities at <br />the Mt. Gunnison No. 1 Mine. <br />' Mine inflows during water year 1987 were about the same as water year 1986. The <br />volume of water discharged from the underground workings in 1987 was 33.8 acre <br />feet versus an estimated 28.8 acre feet in 1986. <br />Precipitation was generally lower in 1987 than in 1986. Spring runoff and <br />stream flow rates reflected this lesser precipitation. <br />' Areas being mined during water year 1987 were wetter than previous years, dut to <br />location and conditions. Although the area extent of the wet areas was larger <br />' than previous years, flows were not significantly higher. <br />The quality of mine water sampled in 1987 was good (see tables 1.4-1, 1.4-2, and <br />1.4-4), and all discharges were well within NPDES effluent limitations without <br />' treatment. <br />Mine water discharge in 1987 was from the Sylvester Gulch underground sump and <br />t Portal No. 2 into pond MB-1. This discharge had no measurable effect on the <br />quality of the North Fbrk of the Gunnison River. <br />' Activities at the Lower Refuse Pile had no measurable effects on surface or <br />groundwater quality during water year 1987. <br />Underground mining activities have not produced a significant effect on any <br />' springs, groundwater wells, or surface water monitoring stations during water <br />year 1987. Some influence of subsidence was seen in the 38-H wells during 1987. <br />' Water year 1988 is expected to be similar to 1987 with repect to hydrology at <br />the mine. No significant impacts are expected. <br />' -ii- <br />1 <br />