REV96560

• Permit No: C1981018
• IBM Index Class Name: Revision
• Doc Date: 10/11/1996
• Doc Name: DESERADO MINE C-81-018 TR 42
• From: DMG
• To: DAN MATHEWS
• Type & Sequence: TR42
• Media Type: D
• Archive: No

III IIIIIIIIIIIIIIII
999
STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Depanmem of Nalu ral Resources
1 31 3 Sherman 51., Ronm 215

Denver, Color. do BIRf 13 Ili~~

Phone 1303) A66 3567 I
FAX: [phone]?-8106
DEPARTMENT OF
NATURAL
RESOURCES
DATE: October 11, 1996
Roy Romer

TO: Dan Mathews Governor
lames S Lochhead
~ Executive Director
FROM: Susan Burgmaier rnichael B. Lung
Division Director
RE: Deserado Mine (C-81-018)
Technical Revision No. 42
have completed a preliminary review of WFU's application for TR 42 at the Deserado Mine.
have the following questions and comments for the operator.
WFU submitted a "working map" showing the proposed final contours of the refuse pile.
The map indicates there is a l po slope from the center of the refuse pile out to the east
and west sides. This apparently ensures drainage is divided between ponds RP-4 and RP-
5. It is not apparent, though, whether the top of the pile will be at 5610' sloping down
1% to the sides and ending up at a lower elevation, or if the pile will be sloped up 1%
to a higher elevation from 5610'. Please provide contour lines for the top of the pile, so
it is clear how the slope will be achieved. It does not appear that the pile can be
constructed as shown on Map 150, since the entire surface of top of the refuse pile is
shown at 5610'. If the entire top surface is 5610', there would not be a 1% slope.
2. WFU should consider a plan to slope the top of the combined piles at 2-3%, rather than
1%. The elevation change from the crown to the east or west ditches, at 1%, would only
be about 7 feet. This slight change in elevation would be difficult to maintain on such
a lame surface area, and could result in low spots where water would be bonded. In
addition to diving WFU the additional margin to maintain drainage, the additional slope
would also increase the volume of the pile.
The SEDCAD+® models for the refuse pile should be based on a scenario where
drainage and; er sediment contribution would be at their maximum amount. DMC
predicts this would be at the closure of the pile, when topsoil has been redistributed and
the area seeded (prior to emergence of vegetation). WFU should revise the models using
a curve number of 94 (D type soil -newly graded area, pervious, no vegetation) for the
drainage areas.
4. The SEDCAD+® runs for the ponds indicate there are trickle tube s~iillways in each.
Are the trickle tubes gated, or do they allow the ponds to de-water passively? If they are
gated, they should not be included in the run as a passive spillway.
The SEDCAD+® runs indicate the riser elevations for ponds RP 2-3 and RP-4,
respectively, are 5496' and 5506'. Maps 79 and 80 indicate the elevations are 5495.47'
and 5504.48'. If the elevations used in the model are correct, the maps should be revised.
If the elevations shown on the maps are correct, then those numbers should be used in
the models so that the volumes of the ponds generated by the program are accurate. If
the model generates a volume greater than what is actually available, the predictions of
the performance of the ponds will be worthless.