GENERAL51386

• Permit No: C1981028
• IBM Index Class Name: General Documents
• Doc Date: 11/28/1984
• Doc Name: Memo CORP RESPONSE MIDTERM STIPULATION 14
• From: MLRD
• To: ANNE BALDRIGE
• Permit Index Doc Type: SOILS
• Media Type: D
• Archive: No

•
DEPARTMENT OF NATURAL RESOURCES
David H. Getches, Eaecu[ive Director
MINED LAND RECLAMATION DIVISION
DAVID C. SHELTON, Director
Richartl D. Lamm
Governor
DATE: November 28, 1984
T0: Anne Baldrige
FROM: 'Jim Pendleton
RE: Coors En
I\
G.3C

's Response - Midterm Stipulation No. 14
Pursuant to yout~est, I have reviewed the submission made by Coors Energy
Corporation in response to our Midterm Stipulation No. 14 placed upon the
midterm review for the Keenesburg Coal Mine. This stipulation was placed upon
our review because the Division found that continued spoil slope failures
might jeopardize topsoil placed within reclaimed areas adjoining the active
pits. The operator's response consisted of a stability analysis report
prepared by John D. Nelson, PhD. and PE, consultant to Coors Energy Corp.
Dr. Nelson's report concludes that the spoil failures appear to be the result
of pore water induced failures. He does not believe that these failures are
the result of ground water or surface water infiltrations. Rather, he
concludes that the pore water pressure increase results from the compaction of
spoils under their own weight. The compaction rate exceeds the material's
ability to dewater, resulting in saturation, rise in pore water pressure and
subsequent slope failure. He believes that the abnormally high moisture
levels of the 1983 - 1984 seasons have contributed to the problem by slightly
increasing soil moistures.
All of Dr. Nelson's observations contained within the report appear prudent
and in keeping with the state-of-the-art. As such, however, the submission
does not satisfy the requirements of Stipulation No. 14. The report does
contain a large amount of data with which to begin to select an appropriate
mitigative alternative, as required by Stipulation No. 14. That Stipulation
stated; "Information from this analysis should be used to determine what
feasible measures could possibly be taken to either increase backfilled spoil
stability or maintain an adequate distance between the backfilled spoil and
the edge of the reclaimed area". With some additional testing to determine
the exact consolidation/pore water pressure relationships, the operator could
develop a mitigative program to stabilize the backfilled spoil. This approach
might also yield significant operational benefits by preventing the spoil
failures from covering exposed coal before complete recovery can occur.
Obviously, these events represent lost revenues and lost resources. On the
other hand, sufficient information probably already exists to allow the
consultant to project worst case protective buffer widths in relation to the
excavated pit depth.
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. [phone]