PERMFILE47451

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 51 Lower Refuse Pile
• Media Type: D
• Archive: Yes

Mountain Coal Company, L.L.C. Exhibit 51
West Elk Mine ~ Lower Refuse Pile
To estimate residence time within the pile, groundwater movement was analyzed utilizing partially
• saturated flow conditions. Using the permeability value of 1.2 x I OJ cm/s and assuming that the material is
homogeneous and isotropic, the maximum time for deep percolating groundwater infiltrating from the
surface to the base of the pile and begin to mound would be less than 30 days (duration of Stage l flow
using McWhorter-Nelson procedure). Regardingresidence time, the conserva[iveapproach is to assume the
colluvium/refuse interface represents an impermeable boundary (which may not be true as seepage could
likely pass through the interface and into the colluvium). Under this assumptiort a shallow mound will form
and grow until drain outflow equals the infiltration inflow. Using the procedures recommended by Glover
to analyze the development of the mound, an estimated ~.4 to 5.0 years will be required for the mound to
reach its full height. However. during the development stage, the volume within the mound is estimated [o
turn over in less than one vear, so the total residence time is estimated to be less than eleven months. The
vertical and horizontal permeabilities are likely to not be equal. Thus assuming that the vertical
permeability is one order of magnitude less, the vertical residence time (duration of State I) will increase to
approximatelyone year. If the horizontal permeability remains the same, the motind development and rate
of drainage laterally wil I not be affected. Total residence time in this case would increase to 1.8 years.
If the worse case is considered and the permeability of the refuse material is an order of magnitude less in
both the vertical and horizontal direction. then the mound development would be significantly affected. In
this case it would take approximately 3.1 to 3.4 years for the mound to develop to its full height and for.
outflow to equal inflow. Due to the reduced permeabilities. the amount of time required to turn over the
volume within the mound would increase to approxima[e1y4.3 years. Vertical residence time (duration of
State 1) remains at approximately one year. therefore, the total residence time for this condition would be
approximately 5.3 years. This is considered to be a conservative value and not likely to be realistic,
particularlywhen the additional infiltration that will occur through [he interface be[weer. the refuse pile and
• the colluvium is not considered in this analysis.
Table 5 - Results of In-Situ Falling Head Permeability
Soil Boring Number Average K (centimeters/second)
5 7.8 x 10-s
4 2.4 x ] 0'
8 5.5 x 10's (Test I )
9 3.6x 10.s
5.x.2 Leachate Data
5.x.2.1 Leachate Estimate Performed for Phases i through IV
Leachate volume is a function of the amount of infiltration into the pile. An estimate of this volume can be
produced by applying the mean annual precipitation minus the volume lost to runoff and the volume lost to
evaporation. Althoueh runoff is significant in a large storm event, the small precipitation events which
compromise the majorih• of mean monthly precipitation produce little or no runoff. A conservative
estimate would be that 9~% of the mean annual precipitation enters the soil profile through infiltration.
However. only a portion of this volume will be ultimately retained through deep percolation because water
• is lost through evaporationand transpiration. A mean annual precipita[ionvalue of 14 incheshas been used.
Transpiration effects have been neelected in order to provide conservative data. Evaporation has been
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