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

I;d 13al:ci
April 8, 2(102
' ('age 6
~/ > 0.008 gal/sec It ..........................................
q > 0.08 gal/sec ft and drill hole
water level drops conspicuously ...............
lJpper limit of fracture zone
...........Upper limit of caved zone
Measurements of the hydraulic Cacture woe height for mining thicknesses up to 29 Ct are
summarized ilt Figure 9 for medium hard rock. "fable 1 presents formulas for predicting fi-aehlre
zone height based on the study.
Table 1. Formulas for Predicting Fracture Zone Heigh
Rock T e° Caved Zone Fractured Zone
YP ~.., t ~.., t
100 H 100 FI
Hard 2
2.1 H+ 16 ± 'S 1.2 H+ 2.0 t 8.9
1
Medium Hard i 2.2 ~ 5.6
4.7 H 19 H 3.6
1.6
1
Soft 6.2 H 32 i 1'S H 5.0 ± 4.0
3.1
1
Weathered 7,0 H 63 ± L2 H 8.0 ± 3.0
S.O
° Ruck types are classified based on [heuniaxial compressive strength, C°: hard rock, C° > 5688 psi (39.23
MPa); medium hard rock , Co = 2844-5688 psi (19.62-39.23 MPa); soft rock,Co < 2844 psi (19.62 MPa).
n la =minion hriaht -
Results of [he longwall study are particularly pertinent for estimating the potential for
aquifer leakage above Panels 1-2. Other approaches, as discussed in the 1995 AAI reportZ, are
useful for qualitatively describing caving effects. Only the Chinese approach includes
quantitative prediction of caving-related changes to hydraulic conductivity based on systematic
field measurements. The range of rock mass Types ("weak" to "hard"} suggests that the database
is applicable to a wide variety of conditions. The "soft" to "medium hard" rock types in Table 1
are thought to be compatible with the low to moderate rock mass qualityg overlying Panels 1
and 2.
Maximum cavity (mining) height is limited to 55 ft nominally in the vicinity of
Cavity #lA (Figure 1). This represents the total dissolution of uahcolite between the bottom of
the Boies Bed and the dissolution surface, which is possible given the life of the cavities.
Because nahcolite grade averages approximately 67% over this interval, the net maximum cavity
height is nominally 37 ft, assuming complete deposition of the insoluble fraction in the bottom of
the cavity and no bulking of the insolubles. Table 2 summarizes the predicted range of cave and
fracture heights fora 37-ft cavity (mining) height (h).
' a J.F.T. Agapito & Associates, Inc. (1988), "Core Hole Summary Report for NaTec-26-88-I, Piceance Creek Basin,
Colorado," Report [o NaTec Mines, Ltd., December.
Agapito Associates, Iltc.