2010-12-23_REVISION - C1981019

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 12/23/2010
• Doc Name: Adequacy Review #2 Memo
• From: Kent Gorham
• To: Jim Stark
• Type & Sequence: TR87
• Email Name: KAG
• Email Name: JRS
• Email Name: SB1
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215 COLORADO
Denver, Colorado 80203 D I V I S I ON OF
Phone: [phone] RECLAMATION
FAX: [phone] Interoffice Memo MIN I N G
SAFETY
To: Jim Stark
From: Kent Gorham
CC: Sandy Brown
Date: December 23, 2010
RE: Adequacy review #2, TR-87, Colowyo Mine, #C-1981-019
I have completed my review of the latest materials submitted (November 9, 2010) for Technical
Revision No. 87 (TR-87) for the Colowyo Mine, permit #C-81-019. My comments are as
follows.
Previously mentioned deficiencies with permanent drainage designs outside of the East Pit will
be handled separately in TR-81.
I have included my questions from my previous memo below in italics.
(Adequacy letter question #8) Page Exh. 7-14R-2 describes the Prospect watershed
condition in three future years, with the 2017 condition identified as the worst case
hydrologic condition. Please demonstrate through modeling that the Prospect Pond
spillway system complies with Rule 4.05.9(2)(c)(ii) for the 25-year 24-hour storm event
for the 2017 watershed condition.
Response accepted and resolved; Colowyo provided the 25-year, 24-hour storm event
modeling for the 2017 worst case hydrologic condition showing that the event can be
safely passed through the Prospect Pond spillway system.
2. (Adequacy letter question #4) Page Exh.7-14R-3 narrative discusses the use and design
of temporary ditches to divert runoff from spoil and reclaimed areas to the unreclaimed
East Pit. These temporary ditches result in areas that are excluded from producing
runoff in the SEDCAD modeling for the Prospect Pond. The text narrative references
Figure Exh.7-14R-7 and describes the ditches as "short term in nature and will be
removed as reclamation progresses. " Figure Exh. 7-14R-7 shows one of the ditches
extending a significant distance northeast into previously reclaimed areas. Please
explain in more detail in the text narrative on page Exh.7-14R-3 how and when these
ditches will be used and when each will be removed or reclaimed.
Response accepted and resolved partially; Removal of temporary ditches is discussed.
Reference is made to the powerline ditch which is also to remain as a road for inspection
and/or maintenance activities of the powerline. If this is to remain as a road, it should
be permitted as a permanent road and not a ditch. If it is to remain as a road,
office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines