2009-06-18_REVISION - C1981019 ‎(2)‎

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 6/18/2009
• Doc Name: Memo Regarding Review of SEDCAD Design
• From: Mike Boulay
• To: Jim Stark, Sandy Brown, and Marcia Talvitie
• Type & Sequence: TR76
• Email Name: JRS
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
&-4?4
1313 Sherman St., Room 215 C J
O L O P LA
D O
Denver, Colorado 80203 D I V I S 1 o N O F
Phone: [phone] INTEROFFICE MEMORANDUM RECLAMATION
FAX: [phone] MINING

SAFETY
DATE: June 18, 2009 Bill Ritter, Jr.
Governor
TO: Jim Stark> Sandy Brown> and Marcia Talvitie Harris D. Sherman
Executive Director
!7 _ Ronald Cattany
FROM: Mike Boulay Fl/?? Division Director
Natural Resource Trustee
RE: Colowyo Mine (Permit No. C-81-019)
Technical Revision No. 76 (TR-76)
I have reviewed the SEDCAD design submitted for the South Taylor Haul Road Ditch. I
also reviewed Map 25 C showing the location, longitudinal profile and cross-section of
the haul road. Just a single ditch design was provided for the ditch to be located in a cut
slope along the western edge of the haul road. There are no culverts proposed because of
the configuration of the road with no other significant drainage or road crossings.
The ditch design is adequate and I found no major flaws. The ditch is to be constructed
in competent rock and the design is conservative with 2 feet of freeboard. More than 70
percent of the contributing area to the ditch will be from the undisturbed slope above the
ditch. A low curve number was used for the undisturbed drainage to the ditch resulting
in very little runoff from this sub watershed, which is deemed appropriate. The sub-
watersheds for the ditch design are not delineated on a map but this is not a significant
concern because there is no flow going to a sediment pond.
The road is assumed to have a slight crown over the centerline resulting in half of the
road surface shedding water westward to the South Taylor Haul Road Ditch, and the
ditch is adequately designed to handle this flow. One concern that I have is that due to
the crown half of the running surface will shed water eastward over the fill slope. This
may result in the embankment becoming saturated over time and could result in
embankment failure or slide damage below the road fill. This is the same situation that
happened at the Yoast Mine at Haul Road D contributing to significant slope failure
above Pond 012. One of the mitigation measures employed at the Pond 012 slide was to
entirely cant the road surface back to the ditch so that runoff could no longer saturate the
road fill/embankment. I think this should be periodically field checked at the South
Taylor Haul Road embankment to ensure that there is not significant erosion or saturation
of the road fill occurring.
Colowyo has met all of our design criteria for the road ditch and I have no comments to
be forwarded to the operator. Please let me know if you have questions.
C: Denver File
Office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines