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2009-01-23_REVISION - C1980007 (3)
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2009-01-23_REVISION - C1980007 (3)
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Last modified
8/24/2016 3:43:04 PM
Creation date
1/26/2009 9:37:56 AM
Metadata
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Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
REVISION
Doc Date
1/23/2009
Doc Name
Mine Plan Decision Document (2 of 2)
From
Mountain Coal Company
To
DRMS
Type & Sequence
PR14
Email Name
TAK
Media Type
D
Archive
No
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discharge from the coal seams into the alluvium of the North Fork of the <br />• Gunnison where the coal seams subcrop underneath the alluvium. This <br />seepage would form a plume of gob leachate in the alluvium that would <br />extend downgradient from the Sylvester Gulch/North Fork confluence <br />toward Somerset. The likely maximum discharge rate of gob leachate <br />into the alluvium would be on the order of 100 gpm based on the <br />maximum head that could develop in the flooded workings. Such a <br />plume would mix with and be diluted by ground water in the North Fork <br />alluvium and would be attenuated where the alluvium significantly <br />widens upgradient from Somerset. North Fork alluvial ground water is <br />monitored upgradient from Somerset at the Bear 3 Mine. <br />Low permeability of bedrock units in and near the West Elk Mine <br />(Rollins Sandstone, B through F seams, and the Barren Member) will <br />prevent any significant seepage of gob leachate into these units. <br />MCC has submitted two plans for sealing the portals upon closure of the <br />mine. One plan calls for perpetual gravity discharge of mine water to the <br />surface, through a four-inch PVC pipe that will be installed in a block <br />wall at the portal. An alternate plan (to be constructed if water is toxic) <br />is to construct water-tight seals within the mine that will withstand the <br />expected hydraulic pressures. Samples taken in the adjacent Oliver Mine <br />• indicate mine waters will not be toxic. <br />Subsidence fractures that develop over mine workings have the potential <br />to dewater natural springs and wetlands in the West Elk permit area. The <br />permit application explains that the risk of such depletion is significantly <br />reduced by the overburden thickness of greater than 280 ft. and the <br />resistance to fracturing of interbedded fine-grained units that would <br />deform ductiley (bending), rather than brittley (fracturing). Monitoring <br />of springs since before the mine was developed has not detected impacts <br />from mining. This monitoring will continue. <br />The operator predicts overall ground water/surface water balance will not <br />be significantly affected if mine inflows are much greater than predicted <br />because mine inflows will ultimately be discharged back to the North <br />Fork of the Gunnison. <br />i. Refuse Material Disposal Impacts on Groundwater - <br />Lower Refuse Disposal Area - Coal mine waste will be disposed <br />in the Lower Refuse Disposal and Refuse Pile Expansion sites. <br />The lower refuse pile is permitted for permanent disposal of 1.09 <br />million cubic yards of mine development waste and sediment <br />• pond cleanout material. The refuse pile expansion is designed to <br />hold 1.38 million tons of material over a life of 9.4 years. The <br />Refuse Pile Expansion is discussed in Permit volume l OB. An <br />34
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