APPCOR11840

• Permit No: C1981039
• IBM Index Class Name: Application Correspondence
• Doc Date: 2/1/1984
• Doc Name: GRASSY GAP MINE SEDIMENT POND NO 4
• From: MLRD
• To: DAN MATHEWS
• Media Type: D
• Archive: No

III IIIIIIIIIIIII III
999
DEPARTMENT OF NATURAL RESOURCES
David H. Getchea, Executive Director
MINED LAND RECLAMATION DIVISION
DAVID C. SHELTON, Director
Richard D. Lemm
Governor
T0: Dan Mathews
FROM: Candy Thompson L 'r
RE: Grassy Gap Mtne - Sediment Dond No. 4
DATE: February 1, 1984
The following problems have been found in design calculations for sediment
pond No. 4.
1. Used incorrect 10 year 24 hour rainfall for the site - 1.8 Inch. vs. 1.6
Inch.
2. Did not account for the Watershed Shape Factor as found to Appendix E of
Peak Flow in Colorado.
This caused a great overestimation of peak Inflow into the pond during the 10
year 24 hour event. Therefore the hole size needed to dewater in 24 hours was
also overestimated. The hole size derived by the engineer was not converted
to diameter. His calculations give a 5 inch radius hole converting to a 10
inch diameter hole.
Due to the above Incorrect data, the storage volume needed is also incorrect.
Therefore the primary spillway elevation needs to be recalculated.
/th
cc: Brian Munson
Dac. No. 9126
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. [phone]