_GENERAL DOCUMENTS - C1981017 ‎(239)‎

• Permit No: C1981017
• IBM Index Class Name: GENERAL DOCUMENTS
• Doc Name: Bid Documents ‎(IMP)‎ 1982 Technical Revisions Rock Tunnel Trash Pile
• Permit Index Doc Type: General Correspondence
• Media Type: D
• Archive: No

.OF COO
o DEPARTMENT OF NATURAL RESOURCES
'
* O * David H.Getches,Executive Director _55-
T '1MENN'r * MINED LAND RECLAMATION DIVISION
�876 DAVID C.SHELTON, Director
Richard D.Lamm
Governor
M E M O R A N D U M
22 Ma 1986
T0: Candace Thompson �,,--��"''�
FROM: Jim Pendleton
RE: Coal Basin Mines.: ni al Revision Application - Expansion of
Sutey Coai-'Ref Pile Configuration (Permit #C-81-017)
Coal Basin Mines has an approved coal processing disposal structure located on
the Sutey parcel , adjoining its surface facility area. The applicant's
original proposal projected construction of a 7.8 million cubic yard structure
over a 47 year project life span. The applicant received specific approval
for the Phase I, 920,000 cubic yard five-year configuration of the pile, which
assumed a waste production rate of 175,000 cubic yards per year.
Following approval of Phase I of the Sutey waste disposal structure, the Coal
Basin Mines' waste production rate has increased to approximately 430,000
cubic yards per year, due to contract quality and quantity modifications. As
a result the Phase I life of project has been significantly shortened. For
this reason, in order to continue production and deposition of refuse,
Mid-Continent Resources, Inc. is requesting approval to expand the total
approved disposal volume from 920,000 cubic yards to 2,620,000 cubic yards.
The added 1 ,700,000 cubic yards of waste will accommodate four additional
years' waste production.
As in the case of the Phase I portion of the pile, the Phase II design
incorporates extension of the underdrain system. Waste material is to be
placed in horizontal lifts not to exceed 24 inches in thickness. Compactive
effort is to be applied to achieve a Standard Proctor relative density of 90
percent. The pile' s outslopes are not to exceed 2h:ly (horizontal to vertical
grade), with a top slope of 2 percent to promote drainage of the pile. The
maximum height of Phase II is 200 feet.
The applicant's consultant, Golder Associates, Inc. , has completed a
mathematical stability analysis of proposed Phase II expanded configuration of
the structure. The analysis projects a static slope safety factor of 1 .9 for
failures which might occur within the waste embankment, and a static slope
safety factor of 1 .5 for failures which might penetrate the foundational
materials beneath the pile. In accordance with Division request in response
to their Phase I application, the consultant has included a pseudostatic
stability analysis, which applies a horizontal acceleration factor of 0.05.
This analysis projects a pseudo-static slope safety factor of 1 .7 for failures
within the waste material and a pseudo-static slope safety factor of 1 .3 for
failures penetrating the foundational materials.
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. [phone]