REP50243

• Permit No: M1983194
• IBM Index Class Name: Report
• Doc Date: 4/21/2003
• Doc Name: Submittal of Geotechnical Reposts from 2002
• From: Natural Soda Inc.
• To: DMG
• Media Type: D
• Archive: No

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been achieved, reportedly without adverse surface and subsurface ~ rbsidence effects. "fhe
estimated shape and size of the active Panel I cavities are shown in I~ig re 4. Cavity shapes in
the ligure represent nahcolilc recovery confined to the I3oies I3ed. Sli~Jllly nan'ower caverns are
expected if recovery has occurred above the Upper Qoies Qed (U[3f3j. While the actual size and
shape of the cavities at any one location is uncertain, ligure 4 provides a~'rsa~rttrb}c~"estimate of
the global shape of the cavities based on fhe historical location of injection and recovery points
and the anticipated variation oFliqua• solvency along the solution stream.
Panel 2 Mining Plans
Planned extraction ratios will remain nominally the same (40%4) for most Panel 2
solution mining. Locally, however, higher extraction ratios are possible. Like Panel 1, cavities
are located on 220-ft centers separated by intervening strip pillars (Pigw~e 1). Plans call for
intersecting the four westernmost Panel 2 cavities with Cavity #lA to take advantage of existing
development and enhance production. In the vicinity of the cavity intersections, potential exists
for attaining volumetric extraction ratios substantially larger than previously achieved or
considered by previous designs (i.e. >40%).
Cavity growth is illustrated in figures 5 and 6 for the plamted flow scheme. Carly plans
are to double the current injection rate (450-500 gpm to 900-1000 gpm in well WRNM lA-4I-[)
to support two production wells (WRNM lA-SFI and proposed well SH). Figure 5 illustrates the
possibility of substantial cavity growth resulting from increased solvent flow immediately
downstream from the primary injection point. Further downstream, the flow will be split
between cavities #lA and #5. Cavern growth is likely to diminish substantially downstream of
this point due to halved flow rates and increased saturation of the solution stream. Later-stage
cavity growth is described by Figure 6. The fgure illustrates the potential for very large cavities
after all four western Panel 2 wells have been brought into production.
Notably, the potential for very high extraction and large cavities is not exclusive to the
flow scheme described in fhe figures. Similar potential exists for other flow schemes which
might utilize Cavity #lA and/or high flow rates for long periods of time. However, cavity size
for any plan is practically limited by diminishing dissolution efficiency with increasing cavity
width. Mechanisms governing dissolution efficiency include thermal loss, flow channelization,
face blinding, ore burial under insolubles, and flow restrictions resulting from roof collapse. For
these and other reasons, the likelihood of attaining very high extraction ratios decreases rapidly
beyond a certain limit. This effect is described schematically in Figure 7. The complexity of the
dissolution process and natural geologic variability make auy estimate of this practical limit
uncertain. However, experience in Panel 1 suggests such a limit exceeds the current design
target of 40%4, giving rise to the possibility of attaining very high extraction ratios for any one of
a variety of flow schemes should economics alone control resource recovery.
' In the event that very high extraction ratios are achieved, Uiere will be increased risk of
disturbing the overlying USDW aquifers and Mahogany oil shale resource. Geoteclmical
consequences of very high to complete extraction include increased caving and fracturing in the
. overburden and subsurface/surface subsidence. These effects are likely to extend greater
Agapito Associates, hie.