REP10185

• Permit No: C1981014
• IBM Index Class Name: Report
• Doc Date: 5/3/1993
• Doc Name: C-81-014 EFCIS SOUTH FIELD MINE MIDTERM REVIEW
• From: DMG
• To: CATHY BEGEJ
• Permit Index Doc Type: SUBSIDENCE REPORT
• Media Type: D
• Archive: No

~•

I~I II~II~II~III~ II~
STATE OF COLOI~UU
DIVISION OF MINERALS AND GEOLOGY
Department o(Natural Resources
131 J Sherman 51., Raom ? 15
Denver, CO 80203
Phone: 0011 dG6-3567
FAX: [phone]
To: Cathy Begej, Reclamation Specialist
From: Bruce Stover, Technical Support
Date: May 3, 1993
Re: C-81-014 EFCI's South Field Mine, Mid-Term Review
OF'CO~
IHR° pq
~o
.A
• ~ r8P6
Roy Romer
Govemur
Michael B. Lnng
Drviaon Director
I have reviewed the materials you gave me regarding EFCI's responses to items 22, 32, 34,
and 35. My comments follow below. Items 22 and 34 address subsidence issues; item 32
discusses a proposed compaction testing program, and item 35 addresses the overburden
isopach map.
Items 22 and 34:
It appears that EFCI has backed off their commitment to the 29° angle of draw, and have
instead adopted a variable 22° to 26° angle of draw on the revised mine plan map. This is
probably because they were uncomfortable with the resulting amount of subsidence affected
area which would be outside the existing permit area on the southwest, and they likely do
not want to have to revise the permit boundary. Even at the 22° to 26° angle of draw, there
are small affected areas of potential subsidence which fall outside the permit boundary.
I agree that 29° is probably the upper limit of a variable angle of draw, however, their own
data has shown this figure several times in the past (May to Oct.1990 data set, and May to
Oct. 1991 data set). Recall that the fact that the entire subsidence monitoring array is
within the subsidence affected area requires assumptions which may or may not be true, as
I discussed in my February, 1992 memo. I believe it is most desirable to use the maximum
measured angle of draw so that a conservative approximation of the subsidence affected
area will be shown on the mine plan map. In this case, however, the additional affected
areas outside the permit boundary which would result from a 29° angle will only have the
potential for very slight subsidence. There are no structures in these areas except for the
county road and power lines.
Your team will have to decide if it is a requirement to have the affected area lines on the
mine plan map conservatively shown (29°), and deal with having some small areas of
potential subsidence outside the permit boundary, or alternatively, if the rules permit you
to make an exception in this case, since the actual effects of the additional subsidence will
be very minor.