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

1?d 13ake~
April 8, 2002
' Page 7
Table 2. Cstimatcd Cavc and Fracture Zone Heights for Complete Cxtraction Panel I-2
Solution Mining
Overburden Rock
Cave Zone Fracture Zone
' Mass Type
Top Top
Minimum Memi Maximum Minimum Mean Maximum
' I-lard Rock 85 fr 93 ft 102 ft 209 ft 238 ft 268 ft
Medium Hard Rock 44 fi 51 ft 59 ft 153 ft 171 ft 189 ft
' Soft Rock 31 ft 36 ft 41 ft 80 fi 93 ft l06 ft
Distance Below Top of R-6 Unit Distance Below Top of R-6 Unit
'
Minimum Mean Maximum Minimum Mean Maximum
Hard Rock 204 ft 195 ft 187 fi 80 ft 50 ft 21 ft
' Medium Hard Rock 245 ft 237 ft 230 ft 136 ft 118 ft 99 ft
Soft Rock 257 ft 252 ft 248 ft 209 ft 196 ft 183 ft
Based on formulas presented in Table 1.
'
' Implications are that (l) the hydraulic fracture zone will terminate within the R-6
aquitard, and (2) the overlying aquifers will lie in the continuous deformation zone. Any
mining-induced hydraulic conductivity changes in the upper R-6 aquitard are expected to be
' insignificant relative to the natural variation in hydraulic conductivity. Even for very brittle,
poor bulking material represented by "hard" rock in Table I, the risk of leakage near the
B Groove aquifer is considered minor. Actual fracture zone heights are expected to fall within
' the range predicted by "weak" to "medium hard" rock (80 to 189 fr). Even in a brittle
environment where large lateral movements along bedding planes are characteristic, vertical
water migration is often limited by poor connectivity between mining-induced fractures.
' Measurements show that both horizontal and vertical fractures tend to close with time due to
compaction of the overburden, further reducing the effective height of the fracture zone.
' The risk of aquifer disturbance is further mitigated by the fact that solution mining is not
likely to realize a "critical" cavity width, which is characteristic of the longwall caves measured
in the Chinese study and reflected in the Table 1 formulas. Figure 7 illustrates the point that the
' fracture zone height, and the corresponding risk of aquifer disturbance, is less than maximum at
the practical limit for cavity size anticipated for economic mining.
' In the unlikely event that communication paths develop between the B Groove and
dissolution surface aquifers, the natural hydraulic gradient will induce downward flow from the
B Groove to the dissolution surface aquifer. The dissolution surface aquifer is reported to be
' under-pressurized relative to the overlying USDW aquifers. Because "balanced" pumping is
practiced, mining activities will not influence the natural vetical hydraulic gradient. Any flow
that does occur in response to overburden disturbance will be downward and is no[ likely to
1
Agapito Associates, Inc.