2004-03-26_REVISION - M1977424

• Permit No: M1977424
• IBM Index Class Name: Revision
• Doc Date: 3/26/2004
• Doc Name: Portal Seal Evaluation
• From: DMG
• To: Western Water and Land Inc.
• Type & Sequence: TR4
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
7313 Sherman 6t., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
DATE: March 2S, 2004
TO: Steve Shuey
FROM: Allen Sorenson
RE: Research Mine Porta[ Closure, Occidental Oil Shale, Inc., Logan Wash,
Technical Revision TR-004, Permit No. M-1977-424
COLORADO
DIVISION O F
MINERALS
GEOLOGY
0.ECLA MATION•MI(JING
SAFETY•SCIENCE
Bill Owens
Governor
Russell George
Executive Director
Ronald W. Catrany
Division DireROr
Natu21 Resource Trustee
The Division of Minerals and Geology (DMG) has completed a review of section 6.1 and appendix C
of the TR-004 submittal, pertaining to the draining (east) Research Mine portal. The Operator has
installed a concrete and shotcrete dam to impound water in the underground workings, preventing
discharges from the portal and lessening the costs of compliance with the site CDPS permit. If it can
be demonstrated through monitoring over time that percolation of water back into the sill and rib of the
underground workings is sufficiently rapid to prevent problematic accumulation of impounded water,
the Operator will be able to consider containment of water in the underground workings for the
purpose of final reclamation and site closure.
The first issue considered in the DMG review is the capability of the concrete dam and the soil backfill
plug to safely contain the water that may be impounded in the mine. The Operator has provided an
engineering evaluation and stability analysis to address this issue. Based on the conclusions of the
stability analyses, DMG has determined that it would not be safe to allow impounded water to overtop
the concrete dam and begin accumulating behind the soil plug. This is due to the potential for internal
erosion and piping failure of the soil plug that could result in the rapid release of hundreds of
thousands of cubic feet of impounded mine water. DMG agrees that an evaluation of the assimilative
capacity of the mine workngs to take in and sufficiently dissipate impounded water has merit, and will
approve the Operator's proposal with limitations and conditions as discussed below.
If water were to impound behind the concrete dam to a depth of 3.S feet, one foot of freeboard would
still be available to prevent overtopping and water contact with the earth plug. The DMG will impose
a condition of the approval of TR-004 that water in the workings be impounded to a depth no greater
than 3.S feet, which equates to 1.5 psi at the external gage. Using the Operator's calculated volume for
the underground mine workings, DMG estimates that impoundment of water to a depth of 3.S feet
behind the dam would equate to a volume of 116,250 cubic feet of water impounded. If indications of
instability or any other problems were to be observed, the Operator would be able to draw down the
mine pool through the six-inch outlet pipe in about four days (average discharge of 0.35 cfs). _
Office of Office of Colorado