GENERAL45528

• Permit No: M1983033
• IBM Index Class Name: General Documents
• Doc Date: 12/20/2001
• Doc Name: GEOTECHNICAL EVALUATION OF QUARRY WALLS WALSTRUM QUARRY AL FREI AND SONS INC PN M-1983-033
• From: DMG
• To: ENVIRONMENT INC
• Media Type: D
• Archive: No

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III DIDDIDDIDd00~ DID rE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
DeDanmem of Natural Resources
131 3 Sherman 8t., Room 215
Denver, Colorado 80203 DIVISION O F
Phone: [phone] MINERAL S
FAX: [phone] &
GEOLOGY
DATE: Thursday, Decetnber 20, 2001 R E C L A M A T I O N
MIN ING•SAFETY
TO: Steve O'Brian, Environment, Inc. Bill ovens
Governor
FROM:. Allen Sorenson, Division of Minerals and Geology Greg E. Walther
ExecuUVe Dlreclor
Michael B. Long
RE: Geotechnical Evaluation of Quarry Walls, Walstrum Quarry, Division Dnector
Al Frei and Sons, lttc., Permit No. M-1983-033 ~'
In order to gain Cleaz Creek County approval of the proposed expansion of the Walstrum Quarry, Frei
and Sons commissioned a study of rock slope stability conducted by Revey and Associates, Inc. The
Division of Minerals and Geology has reviewed the Revey report and concurs with the methods,
conclusions, and recommendations contained therein. However, the Revey report relies on the
structural geology description provided in a previous report by Stephen D. Schwochow titled "Review
of Geology and Critical Geologic Factors in Operation of the Walstrum Quazry Clear Creek County,
Colorado." The Schwowchow report relies heavily on published reports of regional geology to
describe the structural geology in the vicinity of the quarry, then using some assumptions to
speculatively describe the structure at the quazry site. The Schwowchow report concludes by stating
"(w)ith carefrtl measurements of the foliation and joint. trends. the operator can more specifically
analyze potential:stability problems and design appropriate bench and highwall configurations..."
In order to demonstrate the pit wall design included in the Revey report will be stable the Division of
Minerals and Geology would require that site specific measurements of structural geology at the
Walstrum Quarry be taken and statistically analyzed to determine dominant trends for rock
discontinuities. A convenient method for statistical analysis of field measurements is to plot the
measured orientations on Schmidt equal-area nets. If the site-specific measurements ratify the
sttvctural geology assumed to be present as discussed in the Schwowchow report, the
recommendations included in the Revey report will be accepted. If any other adverse joint sets or
foliation are present, the pit wall designs may have to be reconsidered. Attached to this memo aze
documents relating to a pit wall stability evaluation that was done recently for a small quarry in
southern Colorado that provides an example of how site specific measurements of joints, fractures,
faults, and foliation are useful in demonstrating that a pit design will be stable.
attachment(s)
cc: Fred Rollenhagen, Clear Creek County, (w/attachments)
Carl Mount, DMG (w/o attachments)
c:UlyDocumentslwalstum georech.doc