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Me, Jim Herron September 12, 1983 Pale 2 <br /> We have no knowledge or evidence of subsidence other than the apparent move- <br /> ment of the monitoring points. There has not been, nor do we believe there <br /> will be any diminution of the land surface. (There are no visible signs of <br /> subsidence.) <br /> Enclosed is a map showing the configuration of the subsidence monitoring net- <br /> work we now propose for the remainder of oiir current five-year plan. The <br /> additional monitoring points shown in red have been added to provide increased <br /> monitoring density in the vicinity of our present mining operations. See <br /> enclosed excerpts from "Characterization of Subsidence over multiple lift <br /> longwall panels" by Collin Stewart of Mine Subsidence Engineering Co. , showing <br /> construction of survey monuments and control Doints. Measurements and field <br /> observations of these stations over the next few years will provide us with <br /> sufficient detail to determine the need for additional stations in future <br /> years as the mining progresses. <br /> Our investigations of subsidence have led us to the conclusion that in nearly <br /> every case most of the surface subsidence occurs within weeks or even days <br /> after extraction of the coal. All our operations are now concentrated in a <br /> relatively small portion of the mine plan area. Because of the remoteness of <br /> many of the established monitoring points from the current mining operations, <br /> and because of the very high cost of surveying these points by helicopter, we <br /> further request that only those points in close proximity to areas from which <br /> I coal is being extracted be monitored at the frequency now specified in our <br /> approved plan (see map) , and that those remote stations outside the area of <br /> mining influence (computed with a draw angle of 35 degrees) be surveyed only <br /> in the last year of the present five-year plan. <br /> Your earliest possible consideration is requested, as we are rapidly approach- <br /> ing the end of the 1983 field season for outside work at elevations above <br /> 10,000 feet. We will use our best efforts to install the additional monitoring <br /> stations as quickly as possible following agreement on the scope of work to <br /> be done and your confirmation that the revised monitoring network will meet <br /> 1 current M4RB requirements. <br /> t <br /> Please contact me if additional information is needed or if I can be of further <br /> assistance. <br /> Yours very truly, <br /> AW-44,1�� A <br /> A4A <br /> Environmental Coordinator <br /> DWBowman:ms <br /> r <br /> Enclosures <br />