REV106248

• Permit No: C1982057
• IBM Index Class Name: Revision
• Doc Date: 8/8/2005
• Doc Name: Adequacy Review Memo
• From: Mike Boulay
• To: Dan Mathews
• Type & Sequence: PR5
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
INTEROFFICE MEMORANDUM
DIVISION OF MINERALS AND GEOLOGY
TO: Dan Mathews
FROM: Mike Boulay (~,~
DATE: August 8, 2005
SUBJECT: Seneca Coal Company (Permit No. C-82-057),
Permit Revision No. 5 -Adequacy Review
OLORADO
( V I S I O N O F
IN SRALS
EOLOGY
:LANATION•NININO
SAFETY•ECIENCE
Bill Owens
Governor
Russell George
Executive DlreClOr
Ronald W. Cattany
Division Director
Na[u21 Resource Trustee
I have completed my review of the Permit Revision No. 5 application package. I have the
following comments regarding the proposed post-mine drainage channels and stock ponds.
1. Exhibit 20-2A shows that disturbed area drainage from Post mining Channel PM-4
discharges to a light-use road. Drainage from the disturbed area shall be passed through a
sedimentation pond or other treatment facility. It appears that there should be a culvert
beneath the light-use road to convey the runoff to the drainage above Pond 015. Please
clarify this and provide a culvert design for this location, or otherwise, provide alternate
treatment for the disturbed area runoff from PM-4.
The vegetated channel design for PM-IA (page 20-1-148) does not provide sufficient
freeboard for the given capacity analysis design. The construction depth is always taken
from the capacity analysis (1.08 ft for the 7% slope). As proposed the channel has a 1-foot
bottom width and 3.0:1 side slopes giving a total channel depth of 1 foot. As designed the
channel will overtop during the passage of the 10-year, 24-hour precipitation event. The
Divisio0n recommends increasing the bottom width or using a triangular channel with a
minimum depth of 1.25 feet. Please revise the vegetated channel design accordingly.
3. The riprap channel designs for PM 2-2 and PM-2A-1 do not have sufficient bottom widths
for the 2-6% and 8-10% designs, respectively. For both designs at lesser slopes, the one-
foot bottom width and 3.0:1 side slopes give total channel depths of one foot. This does not
provide sufficient freeboazd during the passage of the 10-yeaz, 24-hour event. Please revise
the channel designs for PM-2-2 and PM-2A-1 accordingly.
Office of Office of Colorado
Mined Land Reclamation Active and Inactive Mines Geological Survey