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Paae 3-56 Environmental Analysis February 2000 <br />groundwater range from 43 to 2,300 mg/I with concentrations of sulfate, TDS, and manganese <br />sometimes exceeding federal drinking water standards. Well yields from this zone range from 1 <br />to 150 gpm and average about 20 gpm (Ackerman and Brooks, 1985). <br />Colluvial water-bearing units located on valley slopes are generally isolated and are limited in <br />extent. These units are normally saturated seasonally and have a low storage capacity and <br />yield. Most springs and seeps in the region issue from coiiuviai deposits underiaim by iess <br />permeable bedrock. Seasonal spring discharge from colfuvial deposits ranges from 0.2 to 20 <br />gpm and averages 5 gpm (Ackerman and Brooks, 1985). Colluvial deposits do not represent <br />an aquifer in the region, and no reported wells are developed in this zone. However, numerous <br />seasonal springs and seeps issuing from these zones have been developed for livestock <br />watering and support wildlife. Spring development is usually accomplished by the construction <br />of small stock watering ponds in area drainages. <br />The primary bedrock water-bearing zones in the North Fork of the Gunnison River basin are in <br />the sandstone and conglomerate units and fractured zones of the Lower Cretaceous Burro <br />Canyon Formation and Late Cretaceous Dakota Sandstone. Minor groundwater occurrence is <br />reported in the Late Cretaceous Mancos Shale, Mesa Verde Formation, and Tertiary Wasatch <br />Formation. Saturated bedrock units are generally confined in nature, except near outcrops <br />where they are typically unconfined. <br />Well yields from the Burro Canyon Formation/Dakota Sandstone (undifferentiated) are generally <br />greater than 10 gpm {Ackerman and Brooks, 1985). Groundwater from the Mancos Shale is <br />unsuitable for drinking or agricultural use; however, well yields from this formation reportedly <br />range from 0.5 to 15 gpm (Ackerman and Brooks, 1985). Wells completed in the Mesa Verde <br />Formation typiplly yield less than 10 gpm (Ackerman and Brooks, 1985). Limited data from <br />wells completed in the Wasatch Formation indicate yields as much as 25 gpm (Ackerman and <br />Brooks, 1985). No data is available for other Tertiary age deposits im the region. Spring flow <br />from the Mancos, Mesa Verde, and Wasatch formations ranges from 1 to 25 gpm, averaging 10 <br />gpm (Ackerman and Brooks, 1985). <br />Water quality from bedrock wells is generally sodium bicarbonate/sulfate type with TDS <br />concentrations ranging from 490 to 8,200 mg/I, averaging 2,569 mg/I. Concentrations of <br />sulfate, TDS, manganese, and fluoride sometimes exceed federal drinking water guidelines <br />(USEPA, 1994). Water collected from springs issuing from bedrock is calcium sulfate type with <br />TDS concentrations ranging from 56 io 4,300 mg/I, averaging 1,956 mg/I (Ackerman and <br />Brooks, 1985). Concentrations of selenium, sulfate, TDS, and manganese sometimes exceed <br />federal drinking water guidelines (USEPA, 1994). See Figure 19, Groundwater Hydrology. <br />Recharge of the water-bearing zones is by seepage from area streams, direct infiltration of <br />precipitation, and snowmett. Alluvial water-bearing zones are hydraulically connected with <br />adjacent bedrock and intermixing of the two units with groundwater is likely (Ackerman and <br />Brooks, 1985). The shallow alluvial and Colluvial groundwater flow follows local topography. <br />The regional bedrock groundwater flow direction is northeast following the regional geologic dip <br />of about 5 degrees. Locally, bedrock groundwater flow paths follow topography and are <br />affected by numerous drainages bisecting the region. <br />3.6.2.2 Mine Site Hydrogeology <br />Groundwater occurs within the proposed exploration license area and coal lease tracts in the <br />Quaternary alluvial and Colluvial deposits, Wasatch Formation, and Mesa Verde Formation. <br />Final Environmentai Impact Sfatemenf <br />