2016-08-08_PERMIT FILE - C1981019 ‎(49)‎

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 8/8/2016
• Doc Name: Geotechnical Report - Collom Temporary Spoil Fill and Pond
• Section_Exhibit Name: Volume 20 Exhibit 23 Item 2
• Media Type: D
• Archive: No

Colowyo Coal Company, L.P.
Attn.: Mr. Juan Garcia
March 10, 2015
Page 2 of 7
SHA l 474 �,Wlt_SON. INC.
COMPARISON OF REVISED FILL LOCATION AND CONFIGURATION
The footprint of the revised spoil fill and the previous spoil fill is shown on Figure 1. Additional
details of the revised fill are shown on Figure 2 with a cross section on Figure 3. A comparison
of the configuration of the revised and previous temporary spoil fills and Little Collom Gulch
valley conditions is shown in Table 1.
TABLE 1
SUMMARY OF SPOIL FILL AND VALLEY GEOMETRY
Notes: 1. Longitudinal valley slope along centerline within about 2,000 feet of spoil toe.
OPINIONS REGARDING VALIDITY OF PREVIOUS STUDY
The previous stability analyses focused on a cross-section from the crest to the toe of the fill at
the bottom of Little Collom Gulch (longitudinal along the valley). The width, depth and
properties of the soils below the valley floor and groundwater conditions control the stability
analysis results. Our opinions regarding the validity of our previous analyses are based on
several factors.
The comparison in Table 1 indicates the configuration of the revised fill slope has the
same overall slope angle with a lower maximum height. This indicates the spoil
23-1-01403-002
Spoil Fill
Valley
Top Elevation
Toe Elevation
Maximum
Fill Slope
Slope'
(feet)
(feet)
Height (feet)
(H:V)
(Degrees)
Previous
7625
6775
850
3 :1
Spoil
1.7
Fill
Revised
7700
6925
775
3:1
3.2
Spoil Fill
Notes: 1. Longitudinal valley slope along centerline within about 2,000 feet of spoil toe.
OPINIONS REGARDING VALIDITY OF PREVIOUS STUDY
The previous stability analyses focused on a cross-section from the crest to the toe of the fill at
the bottom of Little Collom Gulch (longitudinal along the valley). The width, depth and
properties of the soils below the valley floor and groundwater conditions control the stability
analysis results. Our opinions regarding the validity of our previous analyses are based on
several factors.
The comparison in Table 1 indicates the configuration of the revised fill slope has the
same overall slope angle with a lower maximum height. This indicates the spoil
23-1-01403-002