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Hydrologic Dam lnrerprrrarion and less than one day for all ponds except MB-5. Pond MB-5 is responsive [o a high spring groundwater table and sometimes has to be dewatered more often. • • Ponds MB-3 and MB-4 did not discharge during 1992 and records indicate they have not discharged since they were constructed. MB-t sometimes catches hydraulic oil washdown from the Unit Train Loadout. When this occurs, sorben[ materi- als are placed in the pond to capture the oil product. If a "major" hydraulic oil release enters the pond, the pond is pumped by a licensed con- tract hauler or the MCC vacuum truck. The pumped oil is deposited in the shop waste oil tank which is in turn pumped by a licensed waste oil recycling firm. No spills requiring pond pumping occurred during 1992. Flowmeters are installed on discharge points from sediment ponds which discharge intermittently to continuously record (lows. Information on flows, sampling points, and quality of water discharged from [he mine site sediment ponds during 1992 is included in Appendix J. All water discharged from the ponds was in compliance with NPDES permit effluent limitations. During spring runoff condi- tions, as well as some precipitation events, quality of water in the North Fork of the Gunnison is much worse than the quality of discharges from MCC sediment ponds. It is also well outside NPDES effluent limitations. During winter base- flow and summer conditions water quality in the North Fork is better and is within NPDES effluent limitations. However, this is the time of year when MCC's ponds are rarely discharged. Assessment for rhr Permit and Adjacersr Areas Flow volumes from MCC sediment ponds are low relative to the North Fork of the Gunnison flows. Even during low flow conditions on the North Fork MCC discharges represent an imperceptible difference in stream quality. Based on the analyses, sediment pond discharges have had no adverse impact on the North Fork of the Gunnison River. The quality of discharges usually exceeds the quality of the North Fork. In addition, pond discharge flows are so small the[ incremental changes in concentrations in the North Fork are imperceptible. Discharges of surface runoff in 1993 are expected to be similar to 1992. Adequacy of Monitoring Program An evaluation of [he adequacy of [he current monitoring plan was conducted to determine whether the program is covering anticipated affects. The mine workings map (Figure 2) was overlaid on the resources maps to determine the potential resources which may be affected. Although several are above the mined area and• adjacent to the mined area, overburden depths are great enough (more than 350 feet) so that no~ impacts are anticipated. LAs a result, no additional monitoring activities are proposed. This is the same determination for the 1990 and 1991 AHRs. The only addition to the 1993 monitoring plan will be spring CR-12. 13