PERMFILE134368

• Permit No: C1981022
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: Water Communication Potential from Overlying Workings /Abel, 1992
• Section_Exhibit Name: Exhibit 2.04-E4 Part 6
• Media Type: D
• Archive: No

Sanborn Creek Project Paqe 13 August 21, 1992
• (1980), Kendorski (1979) and Wardell (1976). The USBM guidelines
state, "Where an upper seam has been mined by room-and-pillar
first working in accordance with these guidelines, underlying
seams should not be mined--except by considering the upper seam as
though it were the base of the surface body of water." This
appears to approximate conditions in the abandoned Oliver No. 1
Mine, "D" Seam, except that "first working" means without robbing
pillars on the retreat. The USBM guidelines suggest the
possibility of room and pillar advance extraction of up to 50
percent of the "B^ and ^C" Seams in the Sanborn Creek Mine
provided the interburden thickness is at least five times the
entry width (5s) or 10 times the mining height (lOt), whichever is
greater. The USBM guideline recommendation would recommend 200
feet of interburden for safe mining, given the combined "C^ and
"B" Seam mining height of 20 feet and room width of 20 feet. The
mean 194 feet interburden thickness is probably sufficient, since
the 20 feet mining height is made up of two seams separated by an
additional minimum 35 feet of interburden and the maximum panel
mining extraction on the advance is only 44 percent.
The 99 percent confidence minimum interburden thickness of
180 feet between the "C" and "D" Seams, shown on Table 1, may be a
bit close. The USBM guidelines provide for a lesser thickness of
interburden provided "at least one competent bed of sandstone or
similar material is present within the solid strata and has a
• thickness at least 1.75 times the maximum entry width, mining at a
lesser cover than Ss or lOt may be considered." In the case of
the "C" Seam advance entry width of 20 feet a 35-foot thick
sandstone would have to be present in the 194 feet of interburden
to even consider panel advance mine without pre-draining the
Oliver No. 1 Mine workings. Several sandstone beds with the
requisite thickness outcrop in the North Fork of the Gunnison
River valley walls in the vicinity of the Sanborn Creek Mine.
However, the thickness of these sandstone beds varies laterally,
from more thaw 35 feet to less than 35 feet.
TROUGH SUBSIDENCE PREDICTION
Panel retreat mining, pillar robbing, as planned for the
Sanborn Creek Mine is similar to the "Panel and Pillar" mining
referred to in the USBM guidelines except the USBM assumes full,
100 percent, extraction on the retreat. The USBM guidelines
provide no guidance for partially extracted panels, such as are
planned for the Sanborn Creek Mine. The USBM guidelines suggest a
minimum interburden thickness of 270 feet or three times the panel
width (3p), whichever is greater, for full extraction room and
pillar panels. For the 520-foot wide panels planned for the
Sanborn Creek Mine this guideline would require 1560 feet of
interburden if full extraction were planned. However, full
extraction is not planned for the Sanborn Creek Mine panels. The
• maximum low-cover panel extraction planned is 81 percent, and the
maximum high-cover extraction is only 60 percent. It would appear
reasonable to reduce the suggested interburden thickness to the