PERMFILE114435

• Permit No: C1981013
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 30 SANTISTEVAN AVF STUDY
• Media Type: D
• Archive: No

•
•
RESULTS
Results of the field activities and
interpretation of the data are contained in the
sections below.
Geoloev
The Raton Formation formed on a gently
sloping alluvial plain cut by a meandering fluvial
system with extensive backswamps where thick
deposits of pea[ formed. This environment
created the thick coal beds of the upper zone of
the Raton Formation, which are being mined in
this area. These coal beds are sometimes split by
siltstone and sandstone overbank deposits. In
places, faults and flexures occur through the
various strata of the area. These "down to the
east" faults can create fracturing of brittle
sandstones and siliceous shales and folding of
more ductile deposits such as coal. The fault or
fracture zone encountered in the Golden Eagle
mine in 1988 is probably one of these "down to
the ease" faults which apparently are truncated
below the surface, yet have created a flexure in
the upper rocks. An increase in ground water
and natural gas flow was noted as the mining face
got closer to the fracture zone where a massive
breakthrough of water and gas occurred. Other
inflows of water may occur if a sandstone channel
or sand deposit cuts into the coal seam. Because
there is no apparent surface expression of this
fault it is nearly impossible to predict the location
of other such fracture zones in that area as well
as the area to be mined in Santistevan Canyon.
Exploration drilling may be the only way to
identify potential fracture zones.
On the surface, the canyon dissects the flat
lying (dip NE at 2 degrees) rocks of the Poison
and Raton Formations. These rocks consist of
interbedded siltstones, sandstones, coals and
shales. Outcrops of sandstone along the valleys
create ridges or steps due to their resistant
nature. Walls of the Canyon are steep and the
bottom is 100 to 300 feet wide. Terraces exist in
places along the canyon, and are remnants of
deposits (ormed when the stream bed was at a
higher position in the canyon. These older
deposits have been cut and totally eroded in
places, as the stream cut deeper into the bedrock
These terrace deposits represent the only
potential sites for an alluvial aquifer in the
canyon, with the most promising ones being tested
with a drill hole, monitoring piezometer and a
test pit. Canyon cross section data collected at
drill bole locations is presented in Appendtx 1.
Ground Water
In order to identify the existence of an
alluvial aquifer in Santistevan Canyon, six ground
water monitoring piezometers were installed.
Each hole was drilled to bedrock, logged, and
completed with slotted PVC pipe to allow for
water level monitoring. The piezometers were
installed in areas exhibiting thick soil, colluvium
or alluvial deposits. Areas where the canyon floor
had exposed bedrock were avoided. The canyon
can be characterized as fairly straight with a
slightly sinuous nature. The width of the valley
floor is generally 100 to 300 feet. A lag of each
well with associated cross section data is
presented in Appendix 1.
As the stream crosses more resistent bedrock
layers a small step is formed. These steps have
caused a scouring of the rock on the step. Often
times these steps are associated with a
constriction or narrowing of the canyon. As this
combination occurs, alluvial and/or colluvial
material is deposited. As the stream channel is
eroded into the bedrock by major storm events,
remanent deposits are left as small benches or
terraces in the valley bottom. During periods of
high moisture, each step and its remnant terraces
will retain water and surface [low is established.
Following the storm event or wet period, water
will flow until the limited storage capacity is
depleted. The length of flow depends on the
amount and frequenry of rainfall, the amount of
evapotranspiration, and the size of the deposits.
In some areas, springs may outcrop and
provide a constant source which will supply water
to the terraces and promote surface flow. This is
the case with the spring identified in upper
Santistevan Canyon (Figure 1). The spring issues
into the stream channel and flows on the surface
for a distance of approximately 100 yards over a
resistant sandstone step and through a
constriction in the canyon. Once over the step,
3