PERMFILE115827

• Permit No: C1981014
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 23 Part 2
• Media Type: D
• Archive: No

Dorchester Coal Company
• United Bant of Arapahoe Bldg.
Suite 300
9350 East Arapahoe Road
Englewood, Colorado 80t 12
Writer's Direct Dial Number
[phone]
November 15, 1984
Mr. Bob Liddle
Colorado Mined Land Reclamation Division
1313 Sherman Street - Room 423
Denver, Colorado 80203
Re: Semi-Annual Subsidence Survey
Dear Bob:
Enclosed is a summary of the data collected to date for the subsidence
grid located in the southern portion of the permit area and the subsi-
dence monuments along the Florence Water Line. The enclosed map shows
• the orieritation of these monuments in relation to the underground work-
ings.
The subsidence grid was installed in early March, 1983, while development
mining was underway in the underlying panel. Second mining was initiated
in late March and completed by June, 1983,
Maximum subsidence detected to date is 0.9 feet at Monument 4 (western-
most point on the E-b' arm of the grid). This is comparable to the
maximum expected subsidence, as predicted by Rocky Mountain Geotechnical
(Volume 6, Sec. 2.05.6(6) of the permit application) of 1.46 feet.
For the other monuments within the grid which have been undermined, subsi-
dence ranged from less than 0.2 feet to 0.7 feet. Data collected during
the last three quarterly surveys show no significant change in elevation
over that period of time. It is anticipated that additional subsidence
in this area will be minimal.
Data from the southern arm of the subsidence grid are useful far assessing
the angle of draw. The southern limit of pillaring was in vicinity of
Monument 16. Surface subsidence decreases regularly from Monument 16 to
between Monuments 19 and 20. These data indicate that the angle of draw
is between 17 and 22 degrees. This is consistent with the projected angle
of draw of (Rocky Mountain Geotechnical, 1983) 20 to 25 degrees.
•
A Subsidiary of Dorchcsier Gas Corporation