2013-12-16_REVISION - M2013064

• Permit No: M2013064
• IBM Index Class Name: REVISION
• Doc Date: 12/16/2013
• Doc Name: Permit Application Adequacy review
• From: DRMS
• To: Varra Companies, Inc
• Email Name: PSH
• Media Type: D
• Archive: No

Per your request, I have reviewed the slope stability analysis for the Varra- Coulson Resource Project
prepared by Joby Adams of AWES, LLC dated June 27, 2013. This stability analysis was prepared as part
of the reclamation permit application. The analysis indicates that the proposed mining plan should not
pose significant hazard to structures under the assumed conditions used in the modeling. The comments
below should be considered as part of the adequacy response for DRMS.
It is my understanding that during the mining operation, the extraction slopes will be 1.25H:1 V
and the slopes will be de- watered. The reclaimed slopes will be 3H:1 V with the natural
groundwater level (currently about 5 ft below ground surface) as a reservoir. The stability report
addressed the slope stability for the pits during the proposed mining activity described in the
application.
• No sample locations or stability section locations were included in the report. It is difficult to
fully understand the geometry of the section being analyzed and the subsurface characteristics
being evaluated without this data. Please provide a cross section location map, cross sections,
and evaluation data for this analysis.
The material properties used during the analysis are based on only three samples from two
boring locations for an area of approximately 62 acres. The Terracon report, where the samples
are reported, states that "test values should be used in conjunction with published ranges of
values based on soil classifications, relative densities, and experience ". Based on the DRMS
reference range, and the very sparse sample density, it would be prudent to err on the
conservative end of the value range for soil parameters for analysis.
• The analysis focuses on conditions during active mining, while the pit is dry. Please provide
analysis regarding the post- mining scenario where the pit is flooded, to ensure long -term stability
following reclamation.
• Because the analysis is based on generalized conditions, and the safety factor is less than 1.3,
structure agreements should be in place for any structures, roads, or utilities in the vicinity of the
proposed mining area prior to mining. Should actual conditions vary from the assumptions made
in the analysis, the safety factors may be insufficient.
• Please provide DRMS with any slope stability monitoring specifications that will be used during
mining operations.
Office of
Office of
Mined Land Reclamation Denver - Grand Junction - Durango Active and Inactive Mines
STATE OF
COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
14
1313 Sherman St., Room 215
COLORADO
Denver, Colorado 80203
D I V I S I O N OF
RECLAMATION
Phone: [phone]
MINING
FAX: [phone]
SAFETY
DATE:
October 17, 2013
TO:
Peter Hayes, DRMS
John W. Hickenlooper
FROM:
TC Wait, DRMS
Governor
SUBJECT:
Varra- Coulson Resource Project(M- 2013 -064)
Mike King
Executive Director
Geotechnical Review of Stability Analysis (6/27/13 by
AWES, LLC)
Loretta E. Pineda
Director
Per your request, I have reviewed the slope stability analysis for the Varra- Coulson Resource Project
prepared by Joby Adams of AWES, LLC dated June 27, 2013. This stability analysis was prepared as part
of the reclamation permit application. The analysis indicates that the proposed mining plan should not
pose significant hazard to structures under the assumed conditions used in the modeling. The comments
below should be considered as part of the adequacy response for DRMS.
It is my understanding that during the mining operation, the extraction slopes will be 1.25H:1 V
and the slopes will be de- watered. The reclaimed slopes will be 3H:1 V with the natural
groundwater level (currently about 5 ft below ground surface) as a reservoir. The stability report
addressed the slope stability for the pits during the proposed mining activity described in the
application.
• No sample locations or stability section locations were included in the report. It is difficult to
fully understand the geometry of the section being analyzed and the subsurface characteristics
being evaluated without this data. Please provide a cross section location map, cross sections,
and evaluation data for this analysis.
The material properties used during the analysis are based on only three samples from two
boring locations for an area of approximately 62 acres. The Terracon report, where the samples
are reported, states that "test values should be used in conjunction with published ranges of
values based on soil classifications, relative densities, and experience ". Based on the DRMS
reference range, and the very sparse sample density, it would be prudent to err on the
conservative end of the value range for soil parameters for analysis.
• The analysis focuses on conditions during active mining, while the pit is dry. Please provide
analysis regarding the post- mining scenario where the pit is flooded, to ensure long -term stability
following reclamation.
• Because the analysis is based on generalized conditions, and the safety factor is less than 1.3,
structure agreements should be in place for any structures, roads, or utilities in the vicinity of the
proposed mining area prior to mining. Should actual conditions vary from the assumptions made
in the analysis, the safety factors may be insufficient.
• Please provide DRMS with any slope stability monitoring specifications that will be used during
mining operations.
Office of
Office of
Mined Land Reclamation Denver - Grand Junction - Durango Active and Inactive Mines