2011-10-28_PERMIT FILE - C1981012

• Permit No: C1981012
• IBM Index Class Name: Permit File
• Doc Date: 10/28/2011
• Doc Name: SUBSIDENCE CONTROL, MONITORING, AND MITIGATION PLAN
• Section_Exhibit Name: Exhibit 24 Subsidence Control, Monitoring, and Mitigation Plan
• Media Type: D
• Archive: No

October 11, 2011 Page 29
of the Colorado Mined Land Reclamation Division (CMLRD) Regulation for Coal Mining.
According to New Elk officials, stream buffer zone signs have been placed in high- traffic areas
on -site and will be placed along the entire length of the Purgatoire River within the permit
boundary.
Planned Allen Seam mains to be developed under the alluvial bed will have seven 20 -ft-
wide entries and 65 -ft x 75 -ft pillars (center -to- center). The mains have an SF of 4.0, for
development in 4.5 -ft -thick coal at a depth of 500 ft. This geometry results in an extraction of
49 %. Other pillar designs may ultimately be considered, but in no case will the design ARMPS
SF be less than 2.0 and extraction ratio be more than 50 %.
No material damage to renewable resource lands has been recorded which can be
attributed to past mining at the New Elk Mine in the 1980s. No discernible effects can be
attributed to subsidence induced by the old New Elk workings, as evidenced by the stable
condition of the Colorado & Wyoming Railroad right -of -way and SH 12. Any effect of
subsidence on the renewable resource lands located in the Purgatoire River area is considered
unlikely, given the low extraction ratios and adequacy of cover depth between them and the
underground workings. In addition to the above - mentioned mining controls, the following
mitigation and monitoring plan is recommended.
4.14.2 Alluvial Valley Floor Monitoring Plan
To ensure that the control plan is effective, the following monitoring plan is
recommended:
• A pre - mining survey of the alluvial bed within a 10° angle of draw, from the planned
Allen Seam workings, should be performed to collect baseline alluvial morphology.
• Monthly visual observation of the alluvium within the monitoring area should be
performed once the development workings are within a 10° angle of draw, from the
planned Allen Seam workings, until 2 months after development has advanced directly
beneath.
• Any unusual, large crater or crack formation in the alluvium should be noted.
4.14.3 Worst Possible Consequences of Damage to Alluvial Valley Floor
Although unlikely, subsidence damage to alluvium could alter the river bed morphology
by creating large cracks and craters. This may lead to the onset of river bed erosion and loss of
alluvium from the affected areas.
4.14.4 Alluvial Valley Floor Damage Mitigation Plan
In case monitoring indicates the onset of damage or potential for damage to the alluvium
in the Purgatoire River bed, the following mitigation plan should be adopted:
•
Appropriate. personnel at mine and regulatory authorities should be informed in case
anomalies are observed that may indicate the alluvium is being affected.
Agapito Associates, Inc.