PERMFILE64146

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 6/5/2002
• Section_Exhibit Name: Exhibit 07 Item 11 Small Depressions/Tanks 1997
• Media Type: D
• Archive: No

Serving Our Clients Since 7980 - ~~`4 ~' ~ ~'"~ i ,
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AO/V/SION OF WESTERN WATER CONSULTANTS, INC.
Civil .Environmental Mining Water Resources
611 Skyline Road Laramie, Wyoming 82070 [phone] • FAX [phone] E-mail: [e-mail]
May 23, 2002
Ms. Kim Wolf
Colowyo Coal Company L.P.
5751 State Highway 13
Meeker, CO 81641
RE: Colowyo Impoundment Hazard Assessment, Permanent Ponds
Deaz Ms. Wolf:
WWC Engineering (WWC) has completed a hazard assessment of the sediment control
ponds for Colowyo Coal Company. The ponds were evaluated for compliance with Section
4.05.9 of the Division of Minerals and Geology regulations. The ponds were also subjected to a
flood hazard evaluation according to the Soil Conservation Service TR-60 guidelines and
determined to be either Class A or Class B ponds.
As part of the assessment process, WWC conducted a flood hazazd evaluation of thirteen
post-mining stock ponds. These post-mining stock ponds are distributed within the watersheds
of four sediment control ponds. The post-mining stock ponds are mostly incised ponds (i.e.,
much of the storage is below grade and would not be released even in the event of embankment
failure) that intercept very small drainage basins.
The watersheds for the four sediment control ponds are described below.
Streeter Pond (001) Watershed. The post-mining stock ponds in this watershed
include Pond A, Pond $, Pond C, Pond D, Pond E and Pond F. These ponds have
a combined capacity of only 0.53 ac-ft, approximately half of which is below
grade. These ponds intercept an insignificant amount of drainage azea in terms of
the design flood calculations (40.8 acres out of a total drainage azea of 1,337.2
acres).
2. Gulch A Pond (004) Watershed. The post-mining stock ponds in this watershed
include Pond L and Pond M, which have a combined capacity of only 0.13 ac-ft,
much of which is below grade. These ponds intercept an insignificant amount of
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