REV103481

• Permit No: C1980006
• IBM Index Class Name: Revision
• Doc Date: 8/11/1993
• Doc Name: DIVISION CONCERNS 720 PIT DEWATERING MARR STRIP MINE C-80-006
• From: DMG
• To: KERR COAL CO
• Type & Sequence: TR11
• Media Type: D
• Archive: No

~II ~I~~I~~II~~~~~I~
999
STATE OF COLORADO

DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1713 Sherman SL, Room Z15
Denver, CO 80203
Phone: [phone]
FAX: [phone]
August 11, 1993
Mr. George Patterson
Kerr Coal Company
P.O. Box 487
Walden, Colorado 80480
RE: Division Concerns, 720 Pit Dewatering, Marr Strip Mine (C-80-006)
Dear Mr. Patterson:
of ~°to
R'~ 4
Horn ~O
~. ~ra~
Roy Rnine~
Govcrno~
Michael B Long
Dlvieion Dneaur
With the accelerated reclamation of the 720 pit, the Division is concerned that the
accumulated water in this pit may require discharging when backfilled overburden displaces
the water in the pit. The method, quality and quantity of the discharge is of concern to the
Division. Currently the permit application does not specifically have a plan for dewatering the
720 pit. To determine the possible affects, and to minimize them, the Division is requesting
that Kerr Coal Company address the following concerns. The requested information should
be submitted as a technical revision and the permit application updated.
1. What is the estimated volume of water that may be discharged and at what maximum rate
will the water be discharged? A rough calculation that I performed shows that the pit is being
backfilled at a rate of about 25 ft3 per second (given the capacity of the scrapers and a
turnaround time of 5 minutes). If the pit is filled, until the water tops over, the pond would
receive inflows at the rate of 25 ft a per second. Given the high bentonitic nature of the
overburden and the past problems that the mine has had with suspended solids, does pond A
have the capacity to treat these inflows and still meet effluent standards? Are the ditches to
pond A, sized to handle the overflow from the 720 pit?
2. What is the water quality of the pit?
3. Kerr should update the dewatering plan to cover the 720 Pit. Page 780-107 aaR of the
permit application addresses the dewatering of pit No. 2 to pond H but dewatering of the 720
pit is not addressed. A demonstration should be submitted to show that pond A has the spare
capacity to treat the 720 pit pumpage and simultaneously have the capacity to treat the 10
year, 24 hour event. How will the pond level be monitored to maintain the storm capacity?