2008-06-12_REVISION - C1981019

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 6/12/2008
• Doc Name: Preliminary Adequacy Review Letter
• From: DRMS
• To: Colowyo Coal Company
• Type & Sequence: TR73
• Email Name: JRS
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
12 June 2008
Mr. Ryan Pawlowski
Colowyo Coal Company, LP
5731 State Highway 13
Meeker, CO 81641
Re: Colowyo Mine C-1981-019
Preliminary Adequacy Review - Technical Revision 73
Dear Mr. Pawlowski:
COLORADO
D IV IS I ON OF
RECLAMATION
MINING
SAFETY
Bill Ritter, Jr.
Governor
Harris D. Sherman
Executive Director
Ronald W. Cattany
Division Director
Natural Resource Trustee
The Division has received the Colowyo submittal of Technical Revision 73 - changes to
the hydrologic curve numbers for sediment pond design. The revision was received on 5
May 2008 and deemed complete on 13 May 2008. The Division has reviewed the
revision submittal and has the following adequacy questions.
The cover letter states that this revision is intended to change the
"Methodologies and Assumptions for Sedimentation Pond Design
Evaluations" in Volume 2D. In the following paragraph the states that
"Volume 13, Exhibit 7, Item 20 contains similar text... However, we are not
proposing to modify this text..." The reason Colowyo gives for not
modifying the Volume 13 text is that the methodologies and assumptions in
that text is specific to the three South Taylor Ponds (the West Taylor Pond,
the Section 21 Pond and the Section 28 Pond). The Division agrees with this
statement but also believes that none of the new assumptions will be used to
remodel any of the current Colowyo area sediment ponds. Based on
conversations with Tom Peterson, all of the proposed changes in the curve
numbers will be used for day-forward SEDCAD modeling, which the
Division also agrees with. This information, however, needs to be detailed in
the permit text. Please include a narrative in the "Methodologies and
Assumptions" portion of Exhibit 7 that states specifically the intent of the
changes to the SEDCAD curve number. More specifically, please include
a statement that the new curve number ranges are for day-forward
designs and that none of the current structures modeled with the "old"
curve numbers will be remodeled. Please include a list of the ponds,
ditches and other structures that will not be changed or remodeled.
Additionally, please include a brief rational for the changes.
Office of Office of
Mined Land Reclamation Denver - Grand Junction - Durango Active and Inactive Mines