2010-03-11_PERMIT FILE - M2008012

• Permit No: M2008012
• IBM Index Class Name: PERMIT FILE
• Doc Date: 3/11/2010
• Doc Name: Application preliminary adequacy review
• From: DRMS
• To: BCI Engineers and Scientists
• Email Name: GRM
• 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]
DATE: March 9, 2010
TO: Russ Means
FROM: Allen Sorenson
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
RE: Engineering Review, Nuvemco, LLC, Last Chance Mine, File No. M-2008-012
The application describes abandonment of dry drill holes by backfilling with cuttings topped by a five foot
bentonite plug topped by a three foot cement cap. If and when holes so abandoned are undermined, the
cuttings supporting the column of bentonite may lose integrity; therefore DRMS will require that the upper
five to eight feet of each hole be plugged with neat cement grout. The holes that will penetrate the Entrada
Formation must be sealed utilizing a high-quality sodium bentonite-type gel, specifically developed for use
as an abandonment fluid, or an equivalent material or technique approved by the DRMS to maintain the
integrity of the Summerville Formation as a confining unit. Cuttings are acceptable in these holes from the
top of the Summerville Formation to the base of the required cement grout plug, but cuttings may not be
placed into the hole until the abandonment fluid has had time to set. The Applicant must provide a revised
plan and commitments for borehole plugging and abandonment.
The application provides descriptions of storm water controls, but includes few details of the structures to be
used. Run on controls are described as berms and ditches, including ditch work associated with the county
road, that will route storm water around the waste rock dump and other affected land. Sediment traps are
described, and illustrated on the maps provided, that will capture and retain runoff from the waste rock
dump. Rip rap armored overflow structures for the sediment traps are described. The application states that
runoff from the ore stockpile will be routed to flow into the underground mine workings. The DRMS will
require the following information to evaluate the proposed storm water controls.
1. Runoff from a one-percent annual chance (100-year) storm event must be safely and non-erosively passed
around or through the affected land. The Applicant must provide a runoff analysis of the up-gradient land
mass and design details for proposed diversion structures demonstrating that the structures will fully
intercept and non-erosively divert the peak flow of the runoff. If the county road ditches are to be relied
upon for diversion, the Applicant must commit to and provide Montrose County permission to maintain the
ditches.
2. The Applicant must provide runoff analysis for the area within the up-gradient diversion network and
tributary to the sediment traps, and design details for the sediment traps demonstrating that the volume of
runoff from a ten percent annual chance (10-year) storm will be fully contained in the traps and that peak
flow from a 100-year stonn will be safely and non-erosively passed through overflow structures.
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Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines