2002-07-01_REVISION - M1983033

• Permit No: M1983033
• IBM Index Class Name: Revision
• Doc Date: 7/1/2002
• Doc Name: Memo: Walstrum Quarry Slope
• Type & Sequence: AM8
• 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: July 1, 2002
TO: Tom Schreiner
Permit #: ~~-~.~3 Confidental?: ~
~ r T eSe _~ DIVISION OF
Class: I s o~ YP - Q" ~ ~~ nom,, MINERAL S
From: n oYU~So To. o,w &
Doc. Name: GMgo: a Y~ u r ° ~( G E O L O G Y
Doc. Date (if no date stamp): ~/ off- /~ R E C L A M A T I O N
MINING•SAFETY
FROM: Allen Sorenson ~~
RE: Stability of Walstrum Quarry Slopes, Al Frei and Sons, Inc.,
Permit No. M-1983-033
Bill Owens
Governor
Greg E. Walther
Executive Director
Ronald W. Cottony
Acting Division Director
The Division of Minerals and Geology (DMG) has completed a review of the REVEY Associates, Inc.
Mazch 2002 report on "Evaluations of Mining Methods Appropriate for Ensuring Stability of
Temporary and Long-Term Rock Slopes in Expanded Development areas of the Walstrum Quarry."
Site investigations conducted by REVEY Associates at the Walstrum Quarry have determined that the
only adverse orientation of rock discontinuity in the quarry azea is north dipping foliation in the
Precambrian gneiss quarry rock. If this is the case and if no other adverse planes of rock weakness aze
uncovered by future quarry operations, the recommendations contained in the REVEY Associates
Report will result in stable final pit wa]ls at the Walstrum Quarry. As a result, the following list of
recommendations from the REVEY report must be made enforceable components of the mined land
reclamation permit.
1. Mining that would create north facing quarry walls striking from N45°W to N45°E is prohibited
unless the excavation is accomplished by gradually extending benches orthogonal to the north
facing wall using progressively shortened blastholes to create a final slope with an angle matching
the dip of the foliation.
2. Air-decked chazges, as described in the REVEY Report, aze required for blasting at all final quarry
perimeter walls.
3. All blasting within 192 feet of final pit walls shall conform to the following millisecond timing
guidelines:
Inter-Row Delay Range
(Per Unit of Burden)
3 to 10 ms/ft
Hole to Hole Delay Range
8 to 17 ms
4. Diameter of explosive chazges shall not exceed 6.5 inches.
It is stated in the REVEY Report that:
Wherever possible, new mining benches should be developed to facilitate mining highest
benches ahead of lower benches. By so doing, lazger horizontal offsets can be maintained
between benches, which lessens the overall pit-slope-angle. Moreover, exposing a series of