ENFORCE32567

• Permit No: C1981019
• IBM Index Class Name: Enforcement
• Doc Date: 7/8/1993
• Doc Name: COLOWYO MINE C-81-019 NOV C-93-073
• From: DMG
• To: LARRY ROUTTEN
• Violation No.: CV1993073
• Media Type: D
• Archive: No

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STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Depanmenl of Natural Resources
1313 Sherman 51., Room 215
Denver, CO 80203
Phone: [phone]
FAX: [phone]
DATE: July 08, 199:1
TO: Larry Routten
FROM: Susan Morrison
RE: Colowyo Mine (C-81-019)
Notice of Violation C-93-073
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Roy ROme~
Gavcmor
Michael B Lang
Division Di~caor
Per your request, I Il:nre completed an analysis of the hydrologic conditions at the Colowyo
Mine at the time of the storm damage which resulted in the issuance of the above mentioned
notice of violation. B:ISCd on a comparison of results. from a Sedcad+ model of existing
conditions on site to estimated flow during the storm, it would appear that the storm event was
greater than the probable 10 year - 24 hour event. Following is a brief summary of the
methods and assumptions used to arrive at this conclusion.
1. Measurements of cross sectional area were taken at four points on the South
Collection Ditch on May 27, 1993. Estimated flow from the May 17, 1993 storm
was back calculated. Results of those calculations are listed on the table below.
Details of the calculations are on the attached sheets.
2. Estimated runoff from a 10 year - 24 hour event is 1.8", taken from Volume III
of the NOAA Precipitation-Frequency Atlas.
3. The total watershed draining through the South Collection Ditch to the Prospect
Pond is approximately 937 acres, 181 of which have vegetation and topsoil
removed.
4. Curve members, based on soil and vegetation maps contained in the permit
application <lnci CDMG staff observation, and using USDA-SCS Technical
Release 55 as a reference, are as follows:
91 -topsoil removed
newly graded areas, hydrologic soil group C
63 -sage brush communities
sagebrush with grass understory cover type, 30% to 70%
ground cover/fair hydrologic condition, hydrologic soil
group C