C153705 Feasibility Study

• Contract/PO #: C153705
• Contractor Name: Beaver Reservoir Company
• Contract Type: Loan
• Water District: 59
• County: Gunnison
• Bill Number: SB 94-029
• Loan Projects - Doc Type: Feasibility Study

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Beaver Reservoir Company
Attention: Mr. Neil Thompson
February 4, 1993
Page 8

minor amounts of coal. A subsurface profIle along the dam axis is presented on Figure 3.
Along the left abutment test hole WCC-l encountered beneath the dam embankment
approximately 30 feet of highly broken, fractured, and baked sandstone, shale, and clinker.
In this zone the core recovery from the drilling was generally poor, recovery 50 percent
or less, and the RQD (rock quality designation) was very poor, generally 20 percent or
less. Rock quality designation is that portion of.the recovered core which is 4-inches or
more in length versus the tota11ength of recovered core. The physical character of this
portion of the bedrock has been interpreted to be the result of the burning of a coal seam
resulting reduction in material volume, collapse, and the fracturing of the rock. The
fractured nature of the bedrock was furthered indicated by the necessity to add
approximately 20 gallons of water to the test hole during drilling. The fractured zone of
baked sandstone and shale is underlain by a moderately thick section of sandstone.
Although this sandstone is relatively soft, the core recovery and RQD percentage for this
portion of the test hole is relatively'high.~_Test hole WCC-l is located approximately
midway between test holes DH-4 and DH-8 cOinpleted by the Bureau. In general, the
correlation between these three test holes and test hole DH -5, another Bureau test hole
located upslope on the abutment, was good, indicating that a large section of the left
abutment is underlain by poor quality rock and that a thick portion of this poor quality rock
is present beneath the dam embankment.

The only test hole in the dam foundation footprint which encountered a signifIcant coal
seam was test hole DH-7. This test hole is located upstream of the dam and approximately
midway along the dam crest. In this test hole an approximate 4 foot layer of coal with a
thin 6-inch ~layer, of. shale was encountered at a elevation of 7996 feet.

Test holes completed in the right abutment area have moderate to poor correlation between
holes. This is shown in the comparison between test hole WCC-2 at dam centerline station
4+45 \lnd,test hole DH-I at dam centerline station 5+05. The lower portion of test hole
WCC-2'consists of shale with the exception of one 13-inch layer of sandstone. The lower
portion of test hole.DH-l consists of an alternating series of sandstone and shale layers.
In addition, a zone of crushed or sheared shale was observed in the zone between a depth
of 24 to 32 feet in test hole WCC-2. In the same test hole at a depth of approximately 32
to 34 feet bedding within a sandstone layer was observed as approximately 60 degrees to
the horizontal as compared with approximately 25 degrees measured at exposures. The
bedding was observed to be approximately 25 degrees to the horizontal deeper in the hole
at a depth of approximately 50 feet.

23067/LE10 02-04-93(4:24pm)/RPT