GENERAL55787

• Permit No: M1999002
• IBM Index Class Name: General Documents
• Doc Date: 8/18/1998
• Doc Name: COMMERCIAL MINE PLAN SUBMITTED TO BLM SECTION 8
• Media Type: D
• Archive: No

No surface subsidence is expected as a result of the first 30 years of commercial
• mining operations (Agapito 1998). Although surface subsidence of a few feet is
possible beyond this time, subsidence from mining under similar conditions has
been predicted to be limited to 1 to 3 feet over a 100- to 200-year period (Terzaghi
1969). The maximum possible surface subsidence over geologic time after full
consolidation of all voids is likewise predicted to be on the order of 50 to 65 feet
(Agapito 1998). American Soda intends to monitor surface subsidence through time
by periodically surveying elevations within the well field as described in Section 4.2.
If subsidence effects are substantially greater than expected, the Yankee Gulch Project
mining strategy will be adjusted.
Geological impacts that may impact future oil shale recovery are also of concern.
Injection fluid temperature will generally be between 300°F and 420°F, which will
result in cavity temperatures of 300°F to 400°F. These relatively tow temperatures
will have no direct effect on the kerogen in the oil shale. As required by the Yankee
Gulch Joint Venture Leases, as modified (BLM 1998c), solution mining temperatures
will be maintained below the temperature at which the destructive distillation of oil
shale occurs, which is expected to be at temperatures of 800°F to 1,000°F (Lewis 1992).
Therefore solution mining of nahcolite is not expected to have adverse impacts on
oil shale reserves.
It is American Soda's assessment that solution mining of nahcolite will not
adversely affect the minability of overlying oil shale, whereas development of the
solution mining cavities may actually enhance the minability of the oil shale within
the nahcolite mining horizon.
There is no absolute definition of minability nor any specific criteria or
qualifications to judge minability. In this context, "minability" generally refers to
the ability of an operator to mine the oil shale resource within the constraints of
currently available technology and cost such that the sales of recovered products
return a profit to the operators. Technically, it is possible to mine oil shale, but, to
date, viable, economically feasible commercial oil shale mining and processing have
not been demonstrated.
Because there is no active mining of oil shale in the Piceance Creek Basin at this
time, it can be concluded that oil shale is not currently minable in the Piceance
Creek Basin based on the economic definition of minability. However, the removal
of nahcolite by solution mining may actually enhance the economics of oil shale
recovery and, therefore, the "minability" of the oil shale resource.
Several general methods have been suggested to recover oil from oil shale in the
Piceance Creek Basin, including:

American Snda, L.L.P. 8_3
C°mmeraal Mine Plan
August 18, 1998