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Page S-8 Summary February 2000 Stream flow in the North Fork of the Gunnison River has been monitored at a US Geological Survey station near the community of Somerset since 1933. The drainage area al the Somerset station is 526 square miles. The highest annual mean Flow at this station during the period of record was 829 cubic feet per second (cfs) in 1984. The highest instantaneous peak flow of 9,220 cfs was recorded on May 24, 1984. The lowest annual mean flow for the same station and period of record was 114 cfs in 1997. Various National Pollutant Discharge Elimination System (NPDES) permits granted to mine operators in the North Fork Valley regulate impacts of current and historic mining on local streams. Monitoring on the North Fork of the Gunnison River shows little impact to the water quality from current or historic mining. Occasional increased concentrations of metals have been observed during periods of increased runoff during the spring. Somewhat elevated sulfate concentrations have been noted in gulches down-drainage of historic mining operations, but these concentrations do not impact the water quality of the North Fork of the Gunnison River. Environmental Consequences -Potential environmental consequences of leasing (and subsequent mining of) the Iron Point and Elk Creek Coal Lease tracts and granting the Iron Point Exploration License include the following impacts: Dewatering of the D coal seam could decrease flow on some sections of Hubbard Creek, which are fed from the D seam; Water discharge from mine to surface streams could impact the quality of water in the receiving streams; but mines must comply with terms and conditions of National Pollutant • Discharge Elimination System (NPDES) permits, so quality impacts should be minimal. Subsidence caused by longwall mining could potentially disrupt stream flows and ponds directly above the underground mining and within the angle of draw. Other impacts could include changes in drainage channel morphology resulting in changes in general surface gradients, which could lead to head cutting, pooling, soil erosion, and sedimentation; and, Exploration, construction activities, and use of surface facilities could increase sedimentation; but any exploration and mining activities must comply with the erosion and sediment control standards of the BLM, Forest Service, OSM, and Colorado DMG. Sedimentation impacts should be minimal. S~.6 Groundwater Existing Conditions -The principal groundwater-bearing zones in the North Fork of the Gunnison River Basin occur in Quaternary alluvial and Colluvial deposits. Some water also occurs in Cretaceous bedrock. Alluvial deposits along the North Fork of the Gunnison River represent a major aquifer. The municipal water supply for the town of Paonia is derived from springs in Colluvial deposits on the north side of Mt. Lamborn. The water quality of alluvium groundwater is calcium bicarbonate type and good quality. The total dissolved solids (TDS) concentrations of the groundwater range from 43 to 2,300 mg/I with concentrations of sulfate, TDS, and manganese sometimes exceeding federal drinking water standards. Well yields from this zone range from 1 to 150 gpm and average about 20 gpm. ! Colluvial water-bearing units located on valley slopes are generally isolated and are limited in extent. These units are normally saturated seasonally and have a low storage capacity and yield. Most springs and seeps in the region issue from Colluvial deposits underlain by less permeable bedrock. Seasonal spring discharge from Colluvial deposits range from about 0.2 up to 20 gpm, and average about 5 gpm. Colluvial deposits do not represent an aquifer in the region, and no reported wells are