|
Exhibit A
<br />Estimate of spoil spring development time and discharge rate
<br />Note: The areas of the spoil and pitwall referred to below for Collom Lite Pit are between the
<br />elevetions of the pit spillpoint (7275 ft.) and the premining ground water piezometric elevation (7150
<br />ft.)
<br />Collom Lite Pit L. Collom X Pitt Units
<br />(all water
<br />flows
<br />Seepage area in low-wall of pit through)
<br />Net thickness of permeable beds exposed in low-wall 50 N/A ft
<br />X Width of low-wall 5,000 ft
<br />X Effective porosity of permeable beds in low-wall 10% %
<br />Low-wall seepage area 25,000 sf
<br />Seepage velocity of spoil leachate into low-wall of pit
<br />Hydraulic gradient 0.10 WA Wit
<br />X Hydraulic conductivity 0.10 ft/day
<br />+ Effective porosity 10% %
<br />Seepage velocity of spoil leachate into low-wall of pit in ft/day 0.10 ft/day
<br />X Conversion factor 365 days/year
<br />Seepage velocity of spoil leachate into low-wall of pit in ft/yr 36.50 ft/year
<br />Annual seepage volume into low-wall
<br />Low-wall seepage area 25,000 0 sf
<br />X Low-wall seepage velocity 36.56 0.00 ft/yr
<br />Annual volume of seepage into low-wall 912,500 0 cf
<br />Void volume in spoil
<br />Predicted pit spill-point elevation
<br />7,275 6,780 ft
<br /> cf
<br />Cross-sectional area, parallel to dip, of saturated spoil between
<br />premining piezometric surface, (or pit bottom in south end of pit)
<br />and spill-point elevation 462,000 ft
<br />Width of cross-sectional area (parallel to strike) 5,500 ft
<br />Spoil volume 2,541,000,000 WA cf
<br />X (Effective porosity of spoil (voids between spoil particles)and
<br />ineffective porosity inside spoil particles that become partially
<br />saturated) 20% %
<br />Void volume in spoil, in a-f 508,200,000 WA a-f
<br />Annual infiltration of rain and snowmelt into spoil
<br />Annual infiltration 3.1 3.1 inches
<br />X Conversion factor 12 12 inches/cf
<br />Infiltration of rain and snowmelt into spoil in ft/yr 0.26 0.26 ft/yr
<br />X Infiltration area 880 200 acres
<br />Infiltration of rain and snowmelt into spoil in a-f/yr 227 52 a-f/yr
<br />X Conversion factor 43,560 43,560 cf/a4
<br />Infiltration of rain and snowmelt into spoil in cf/yr 9,902,640 2,250,600 cf/yr
<br />Spoil saturation time after pit is backfilled
<br />Infiltration from rain and snowmelt
<br />-- Seepage rate into low-wall
<br />Saturation rate of voids in spoil
<br />9,902,640 2,250,600 cf/yr
<br />912,500 0 cf/yr
<br />8,990,140 2,250,600 cf/yr
<br />Void volume in spoil to be saturated by surface infiltration 508,200,000 WA cf
<br />T Saturation rate of voids in spoil 8,990,140 cf/yr
<br />Time to saturate voids in spoil after pit is backfilled (amount of time
<br />for spoil spring to form) 56.53 MO years
<br />Spoil spring discharge rate after spoil saturation
<br />Annual surface infiltration rate 9,902,640 2,250,600 cf/yr
<br />- Annual seepage volume into low-wall 912,500 0 cf/yr
<br />Spoil spring discharge rate in cf per year 8,990,140 2,250,600 cf/yr
<br />X Conversion factor 31,536,000 31,536,000 sec/yr
<br />Spoil spring discharge rate in cfs 0.29 0.07 cfs
<br />X Conversion factor 448.8 448.8 gpm/cfs
<br />j Spoil spring discharge rate ingpm 128 ` 32 gpm
<br />
|