1992-02-10_GENERAL DOCUMENTS - C1981017 (2)

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Mr, Jim Herron September 12 1983 Page We have no knowledge or evi ence of subsidence other than the apparent move- ment of the monitoring poin s. There has not been, nor do we believe there will be any diminution of t e land surface. (There are no visible signs of subsidence.) Enclosed is a map showing t e configuration of the subsidence monitoring net- work we now propose for the remainder of our current five-year plan. The additional monitoring points shown in red have been added to provide increased monitoring density in the v'.cinity of our present mining operations. See enclosed excerpts from "Cha acterization of Subsidence over multiple lift longwall panels" by Collin itewart of Mine Subsidence Engineering Co. , showing construction of survey monuments and control points. Measurements and field observations of these stations over the next few years will provide us with sufficient detail to determine the need for additional stations in future years as the mining progresses. Our investigations of subsi ence have led us to the conclusion that in nearly every case most of the sur ace subsidence occurs within weeks or even days after extraction of the co 1. All our operations are now concentrated in a relatively small portion of the mine plan area. Because of the remoteness of r many of. the established monitoring points from the current mining operations, and because of the very hi h cost of surveying these points by helicopter, we further request that only hose points in close proximity to areas from which coal is• being extracted be monitored at the frequency now specified in our approved plan (see map), a d that those remote stations outside the area of mining influence (computed with a draw angle of 35 degrees) be surveyed only in the last year of the pr sent five-year plan. Your earliest possible coniur ideration is requested, as we are rapidly approach- ing the end of the 1983 fiid season for outside work at elevations above 10,000 feet. We will use best efforts to install the additional monitoring stations as quickly as possible following agreement on the scope of work to be done and your confirmat ion that the revised monitoring network will meet current M4RB requirements. 1 Please contact me if additional information is needed or if I can be of further h assistance. Yours very truly, Environmental Coordinator g t" = DWBowman:ms +�- Enclosures ajT� t