2010-11-12_REVISION - M2009076

• Permit No: M2009076
• IBM Index Class Name: Revision
• Doc Date: 11/12/2010
• Doc Name: Technical Revision to Application/Adequacy Review Response.
• From: Venture Resources, Inc.
• To: DRMS
• Email Name: JLE
• Media Type: D
• Archive: No

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Venture Resources, Inc.
PO Box 1974 [phone]
Idaho Spi•i igs, CO 80452 Fax: [phone]
venttu•eresources(q ?att.net
November 10, 2010
CO Division of Reclamation, Mining & Safety
1313 Sherman St., Room 215
Denver, CO 80203
Attn: Jared Ebert
RE: M-2009-076 Application
Subject: Technical Revision, Revised Exhibit C - reflecting enhanced Tailings Impoundment stability design
Dear Mr. Ebert:
Venture Resources is submitting this Technical Revision as a partial response to the DRMS' September 8"' Second
Adequacy Review and to discussions held with DRMS on November 8"'. In this Technical Revision we are
presenting an enhanced Tailings Impoundment design that incorporates geosynthetics and a network of "French
drains". By the addition of these elements, the Tailings Impoundment stability will greatly be increased for both
static and seismic conditions.
This Technical Revision is intended to address Items #1 - #3 of page 1 of the September 86 Second Adequacy
Review and prescribed parameters given during our November Wh meeting. The remaining items in the Review are
secondary to these stability issues and will be addressed after DRMS acceptance and affirmative approval of this
Technical Revision concerning Tailings Impoundment stability enhancement. This letter will serve as an outlined
presentation of the changes and additions made to the design. A revised Exhibit C and Exhibit E Drawing E11 have
been attached in original duplicate containing the amendments.
DRMS Statement in Review Item #I:
"Analysis of impoundment with saturated slimes and under static conditions yields an unacceptably low safety
factor of 1.05. The minimum acceptable safetyfactor given the current degree of certainty of tailing characteristics,
and the variability in tailing properties that will occur under the proposed mine plan, is 1.5 for static conditions and
1.1 under seismic loading. "
Venture Resources Response to Review Item #1:
Requiring this design to be evaluated at saturated water levels at total buildout does not conform to real or practical
considerations. Carefully adhering to the operating and embankment construction parameters set forth in Exhibit C
of our last Technical Revision, and again within this submittal, ensures proper impoundment stability behavior.
These parameters prescribe a method of tailings impoundment, dewatering practices and embankment geometry
relationships which will minimize elevated phreatic zones. The design was developed based on the preeminent
works on this subject: Steven G. Vick's Planning, Design, and Analysis of Tailings Dams, 1990 and the US Army
Corps of Engineers (USACE) Slope Stability, EM 1110-2-1902.
It appears these factors of safety are of DRMS' own choosing since there is no mention of specific values of factors
of safety in the Hardrock Rules. In a meeting with DRMS staff on November 8"', Venture Resources was specifically
instructed to meet the following factors of safety requirements:
Un-Saturated Tailings, Static Conditions - minimum Factor of Safety = 1.5
Un-Saturated Tailings, Seismic Conditions - minimum Factor of Safety = 1.1
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