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Sam- 2.04.5 <br />varying due to upstream control of discharge from Paonia Reservoir, seasonal climatic factors, and <br />• extensive downstream agricultural withdrawals of water for irrigation. <br />The watershed of the North Fork is generally characterized by relatively steep mountainslopes and <br />high mountain pazks that are intersected by numerous steep, narrow, drainage valleys, as shown by the <br />Regional Geology/Hydrology Map, (Map 2.04M2). Smaller area drainages typically demonstrate an <br />ephemeral flow pattern, flowing only in response to spring snowmelt or major thunderstorms. Larger <br />drainages may draitt significant sub-watershed areas and carry intermittent or perennial flows. The <br />valley associated with the North Fork h generally narrow and v-shaped with a broad, deeply incised <br />flow channel and limited floodplairr. Relatively thick deposiss of coarse alluviaVcolluvial material <br />occur along the margins of the narrow floodplain, as remnant terraces or pediments associated with <br />previous river levels as the river cut its way downward. Surface water quality is generally fair to good <br />with a calciurrrcazbonate chemistry and relatively low dissolved solids. Natural suspended solids <br />levels can be high, particulazly during snowmelt runoff and major thunderstorm events, due to the <br />steep terrain and relatively high runoff and flow velocities. Dissolved metals concentrations are <br />chantteristically low, but total metals concentrations can be significantly higher and are generally <br />associated with the elevated suspended solids. <br />Regional Ground Water Hydrology <br />The regional ground water basin, which includes the mine permit and adjacent areas, generally <br />corresponds to surface watershed area for the North Fork of the Gunnison River. Due primarily to <br />the rugged terrain, with deeply incised drainages and some faulting, ground water is generally not <br />available near the ground surface except as isolated occurrences of perched ground water and in the <br />alluvium associated with the North Fork The North Fork alluvium is considered an important <br />aquifer in the area with direct recharge from and discharge to the river depending on river levels. <br />• Downstream alluvial wells have reported yields of several hundred gallons per minute (gptr~. Fetched <br />ground water occurrences are limited in both volume and flow and, since they are dependent on <br />surface recharge and direct infiltration, may dry~up during any prolonged periods of drought. <br />Ground water flows are commonly associated with some of the coal seams and associated clastic <br />interburden sequences due to the increased secondary permeability of these units resulting from <br />natural fracture and cleat panerns. The Rollins Sandstone, which is the lowermost unit of the Mesa <br />Verde Formation, is also know to contain some water in fracttued zones, but u not considered an <br />aquifer and u not utilized as a ground water source due to iss depth, low permeability, low porosity, <br />and high TDS values. <br />Ground water quality can be highly variable dependent on its source. Generally, perched ground <br />water discharges and alluvial waters associated with the Noah Fork drainage have similar chemistry <br />and quality to surface waters. Ground waters associated with both the coal seams and Rollins <br />Sandstone are commonly of poorer quality with increased levels of dissolved solids and slightly higher <br />PH <br />2.04.6 -Geology Description <br />This section of the permit application describes site-specific geologic conditions in the mine permit <br />and adjacent areas as a basis for chantterization of mining conditions, evaluation of potential mining- <br />related impacts, and development of any appropriate plans for conservation of resources and control <br />or mitigation of impactss related to site geology The information presented in this section u based on <br />research of available published reports and documents; contatts with Federal, State, and local <br />agencies; and the results of several exploration prograrru over the period from 1954 through 1998. <br />• The vazious exploration drilling programs involved drilling and logging of a total of over 90 <br />exploration drillholes and sampling and analysis of selected core samples from these drillholes. <br />PR04 2.04-8 Revised Atrgttst 2000 <br />