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Sa=m - 2.04.7
<br />is also similar to surface water quality because the flow path between the recharge source and the
<br />discharge point is typically relatively short, resulting in limited water quality degradation. Deeper
<br />perched ground water and stored mine water which has been in prolonged contact with shales and
<br />mudstones exhibit elevated TDS levels due to dissolution of soluble minerals and salts.
<br />Ground water monitoring for the mine permit and adjacent areas was initiated as early as 1978 and
<br />has included monitoring over extended periods for essentially all of the potentially affected ground
<br />water units. While water quality analysis parameters have changed over time as the science of ground
<br />water monitoring and associated regulatory requirements have evolved, most historical monitoring has
<br />included, as a minimum, analysis for pH, electrical conductivity (EC), total dissolved solids (IDS),
<br />total iron (Fe), and total manganese (Mn). Table 2.04.7-T1, Surface and Ground Water Parameters,
<br />lists the analysis parameters for ongoing operational hydrologic monitoring. Generally, baseline and
<br />operational ground water monitoring have focused on specific mine disturbance areas, so there have
<br />been some changes over time in the designated ground water monitoring sites. Table 2.04.7-T2,
<br />Historic Ground Water Monitoring Summary, identifies all of the sites for which ground water
<br />monitoring records are available and notes the monitoring interval(s) for each. The following sections
<br />summarize water quality characteristics, based on available monitoring and analysis information, for
<br />each of the identified ground water units.
<br />Alluvial/Colluvial Aquifer - Information on the quality and characteristics of alluvial/colluvial ground
<br />water is based on sampling and analysis for the primary mine water supply intake, which draws from
<br />an infiltration field in the alluviuni/coUuviurn of the North Fork of the Gunnison River and
<br />alluviaVcoUuvial monitoring wells (TG2, North Fork and WMW-1, Hubbard Creek). Based on
<br />available analysis information, the alluvial/colluvial ground water is dominantly a calcium-carbonate
<br />chemical type. Analysis values indicate a neutral to slightly alkaline pH and relatively low EC, TDS,
<br />hardness, and dissolved iron and manganese. Minor seasonal variations in water quality paralleling
<br />related surface water quality variations have been noted, including elevated TDS in the late summer
<br />and fall as surface flows and associated dilution effects decline. Generally, the quality of the
<br />alluviaVcoUuvial ground water is good and the water is suitable for domestic use with only minimal
<br />treatment (chlorination).
<br />Perched Ground Water - Information on the quality and characteristics of perched ground water is
<br />based on monitoring, sampling, and analysis of identified seeps and springs (EC-1, SP-1, SP-2, SP-3,
<br />SPA, SP-5, SP-6, SP-7, SP-9, SP-10, SP-11) associated with the perched ground water system; and
<br />seeps, springs, monitoring wells, and mine inflows (SG3, SP-8, B-6, H 10, MWS-A MWS-B, MWS-C
<br />MWS-D) associated with the coal seams, which are part of the perched ground water system Based
<br />on available analysis information and as shown by Figures 2.04.7-F7A, Perched Ground Water
<br />Trilinear Diagram, 2.04.7-F7B, B Coal Seam Trilinear Diagram, and 2.04.7-F7C, D Coal Seam
<br />Trilinear Diagram, the perched ground water ranges from a sodium-carbonate to a calcium carbonate
<br />chemical type, with the ground water associated with the coal seams tending to be more strongly
<br />sodic. Analysis values indicate a neutral to slightly alkaline pH and moderate to high EC, TDS,
<br />hardness, and dissolved iron and manganese, as summarized by Tables 2.04.7-T3A, Perched Ground
<br />Water Quality Summary, 2.04.7-T3B, B Goal Seam Water Quality Summary, and 2.04.7-T3C, D Coal
<br />Seam Water Quality Summary.
<br />Shallow perched ground water appears to be more sensitive to seasonal variations in infiltration and
<br />recharge than the deeper perched ground water, although there is no distinct pattern of seasonal
<br />variation. In general, ground water levels for shallow perched ground water increase slightly in early-
<br />to mid-summer following spring snowmelt and then decline to normal stable levels in late summer
<br />and early fall. The increase in water levels may be accompanied by minor increases in TDS and
<br />• soluble constituents as seasonal infiltration flushes through oxidized overburden materials, although
<br />observed increases are not consistent for either individual monitoring points or specific perched units.
<br />Generally, the quality of the perched ground water is fair to good with the primary limitations on use
<br />being somewhat elevated TDS and dissolved metals.
<br />PR04 2.04-40 Revised August 2000
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