2008-08-22_ENFORCEMENT - C1981019

• Permit No: C1981019
• IBM Index Class Name: ENFORCEMENT
• Doc Date: 8/22/2008
• Doc Name: Memo Regarding Prospect Pond August 9 Storm Event
• From: Kent Gorham
• To: Jim Stark
• Violation No.: CV2008004
• Email Name: KAG
• Media Type: D
• Archive: No

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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]
Interoffice Memo
COLORADO
D IV IS I ON OF
RECLAMATION
MINING
SAFETY
To: Jim Stark
From: Kent Gorham
CC: Sandy Brown; David Berry
RE: Prospect Pond August 9 Storm Event, Colowyo Mine, #C-81-019
Bill Ritter, )r.
Governor
Harris D. Sherman
Executive Director
Ronald W. Cattany
Division Director
Natural Resource Trustee
Jim, I reviewed the documentation and photographs you provided to me regarding the
Prospect Pond storm event that occurred on August 9, 2008. My recommendation is that a
Notice of Violation should be written.
Typical modeling for sediment ponds in Colorado use a Type II storm event that more
accurately models the delivery of the rainfall for conditions likely to occur in most of the
United States excluding both coasts and the deep south. Colowyo has correctly used Type II
storms to design sediment ponds at the Colowyo Mine.
As you know, the Prospect pond watershed has been a concern for the Division for many
years and these concerns have been openly discussed between Colowyo and the Division in
the recent past. The Divisions concerns included post mining drainage gradient, post mining
channel protection, sumping of runoff from backfilled and graded area, under-design of storm
runoff from the watershed, worst case conditions within the watershed, and reclamation
practices in the watershed. Some of these issues and questions remain outstanding at this
time as documented in previous correspondence.
Colowyo presented evidence that the total rainfall on August 9th did not exceed the 10-year
24 hour storm event of 1.8 inches but explains that 1.19 inches of rainfall occurred in
approximately 45 minutes. While the delivery of the actual storm event does not perfectly
match the delivery of a Type II storm in the SEDCAD design model, it should be noted that
the model does account for delivery of over 50% of the Type II design storm event within a
period of slightly over one hour. I do not believe that perceived inaccuracies of modeling
design and input parameters are justification for a pond to be exempt from compliance with
Rule 4.05.6(3)(a) that requires "adequate capacity to contain or treat the runoff or inflow
entering a pond as a result of a 10-year, 24-hour precipitation event." This Rule goes on to
state "In determining runoff volume, the characteristics of the mine site and reclamation
procedures, and on-site sediment control practices shall be considered." The Division has
consistently and repeatedly questioned the lack of channel protection in the lower portion of
the Prospect post-mining ditch, strongly suggested reclamation practices such as surface
roughening and stock ponds to reduce runoff and peak flows, and requested design
information for a pit sump that was, and apparently continues to be, used in the watershed.
Colowyo has generally ignored or delayed completing these requests specifically meant to
ensure the integrity and function of the Prospect pond. The Division is more than willing to
consider measures to reduce storm runoff in the Prospect watershed and in fact, has strongly
suggested numerous methods and practices as mentioned. There is no question that
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