APPCOR11060

• Permit No: C1981014
• IBM Index Class Name: Application Correspondence
• Doc Date: 3/30/1982
• Doc Name: SUPPLEMENTAL SUBMITTAL CONCERNING WASTE PILE DORCHESTER 1 MINE FREMONT CNTR
• From: MLR
• To: CAROL RUSSELL
• Media Type: D
• Archive: No

STATE OF COLORADO RICH nRn D. L4MM. Gove mof
DEPARTMENT OF NATURAL gESOURCES
O. Monte Pascoe, Executive Director
MINED LAND RECLAMATION
423 Centennial Building,1313 Sherman Street
Denver. Colorado 80203 Tel. [phone]
March 30, 1982
TD: Carol Russell
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FROM: Jim Pendleton i- ~~+''"
RE: Supplem=ntal' Submi-C al Concerning Waste Pile,
Fremont Coutrty
iii iiiiiiiiiiiii iii
999
David C. Shelton
Director
Dorchester No. 1 Mine,
Pursuant to your request, I have reviewed the supplemental submittal infor-
mation concerning the coal processing waste pile at the Dorchester No. Z
mine in Frerront County, Colorado. The following deficiencies remain to be
resolved.
(1) Observations made by staff during inspections at the mine site have
discerned that waste is transported to the pile and placed in a dewatering/
ponding facility Located in the northeast corner of the waste pile. The
slurry material is impounded on top of the existing waste material where it
is allowed to dewater. The dewatered waste is then excavated and placed in
a controlled manner on the fill. During the past winter of 1981-1982, a
failure occurred in the area of the dewatering/ponding facility, resulting
in a waste flow.
The description of the waste pile included in the application does not mention
the use or cronstruction of a dewatering/ponding facility. The text and Bfap
No. DOR-6-GTL-1 should be amended to properly describe the dewatering/ponding
facility now being utilized. Further, the stability analysis of the waste
pile should be revised to evaluate the implications of elevated water content
in the area of the dewatering/ponding facility. I suspect that a flatter than
2:1 (horizontal to vertical) slope configuration may be required in this area
in order to assure a static slope safety factor of 1.5.
(2) In order to conform with the requirements of the subsidence regulations
(Rule 2.05.6(6) and 4,20), the applicant will have to project the effects of
subsidence upon the waste pile, which is considered to be a "structure". The
applicant's projections of limited impact should be extended to include a
prediction of subsidence magnitude. The National Coal Board methodology is
commonly employed for this type of prediction. The magnitude of subsidence
is necessary in order to determine whether the 4-foot by 10-foot subdrain will
be sufficient to allow for possible differential settlement due to maximum
projected subsidence. Further, the applicant will be required to designate
specific locations for the proposed subsidence monumentation. The amended
application should include a typical sketch of the monurrent installation
proposed to be used. These subsidence monuments should be substantial and
capable of resisting the effects of normal traffic and meteorological phenomena.