PERMFILE122693

• Permit No: M2005045
• IBM Index Class Name: Permit File
• Doc Date: 3/27/2006
• Doc Name: Proposed Detention Pond Second Adequacy Review
• From: DMG acs
• To: dmg
• 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]
DATE: March 27, '1006
TO: Kate Pickford
FROM: Allen Sorenson
RE: Proposed Detention Pond, Second Adequacy Review, Rock Dog #1 Pit,
Gravel LLI:, File No. M-2005-045
COLORADO
DIVISION OF
MIN SRALS
GEOLOGY
REC EAMATION•MIN ING
SAFETY•SCIENCE
enl Owens
Governor
Russell George
Executive Director
Ronald W. Cottony
Division Director
Natural Resource Trustee
The Division of Minerals and Geology (DMG) engineering staff have reviewed the information in the permit
application file for the proposed detention pond shown on the mining plan map for the Rock Dog #1 Pit. That
review resulted in the issuance of an adequacy memo dated January 25, 2006. Subsequently, the Applicant has
provided to DMG a letter report and attachments dated February 27, 2006 that addresses the issues of concern
identified by DMG. The fi~llowing issues of concern remain to be addressed based on DMG's review of the
February 27, 2006 letter report.
1. Diversion Ditches
Drawings two and three from the letter report provide designs for the proposed south diversion ditch that will
route runofffrom the disturbed area to the detention pond. No design drawings are provided for the proposed
north diversion ditch. Designs for the north diversion ditch are required, or the Applicant must clarify that the
north ditch will be constructed to the same dimensions as the south ditch.
2. Run-on Diversion
The detention pond designs in the February 27, 2006 letter report are sufficient to provide containment of the 10-
year, 24-hour runoff, and to safely pass the 100-year, 24-hour runoff from the Phase A mining area and the
proposed staging area along the Florida River. However, unless runoff from undisturbed areas up-gradient of
the mining and staging areas is diverted around the detention pond potentially large amounts of additional runoff
would report to the pond during the design storm events, resulting in the discharge of untreated water to the
river, and potentially causing failure to the proposed spillway and embankment. The maps provided with the
permit application show berms oftopsoil and overburden ringing the proposed pit. These could conceivably be
used to divert run-on from undisturbed areas around the detention pond. Using these berms as diversion
structures is problematic for the following reasons:
a) The maps provided in the permit application show the proposed topsoil berms at the outer perimeter of
the affected land, with the overburden berms located inside of the topsoil berms. This configuration
would use topsoil stockpiles as run-on diversion dikes in conflict with Rule 3.1.9(3) of the Construction
Materials Rules of the Colorado Mined Land Reclamation Board, which states, in part: "Topsoil
stockpiles shall be stored in places and configurations to minimize erosion..." If perimeter berms were
to be approved by DMG to divert run-on, they would have to be constructed of overburden or other
suitable material, not topsoil.
b) It is stated in DMG's January 2S, 2006 adequacy memo "The detention pond and diversion ditches shall
be constructed before any disturbance of the pit area to be drained into the pond." The reference to
diversion ditches i.n this quotation is To run-on diversion ditches that would be constructed up-gradient of
the proposed affected land, which is the run-on control method forming the primary content of a
Office of Office of Colorado
Mined Land Reclamation ARive and Inactive Mines Geological Survey