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~U <br />Page 2 <br />Tom Gillis <br />Hatch I2, 1981 <br /> <br />If a definitive survey monitoriing program was established, which would allow <br />the verification of the maximum subsidence and strain predictions made within <br />the amended application, the need for continued monitoring cf future permit <br />areas could possibly be eliminated. In comhinat.ion with proposed surface <br />"r.•alk-ov~rs" and ground water monitoring rosults, a system of two sets of <br />survey tranects crossing a panel targeted for early retreat extraction (7th <br />east panel or the 5th north Ir<snel otf the 8th east main) should resolve the <br />subsidence 7uestion. <br />The applicant is requested to consider such an amended monitoring program. <br />At a minimum, perpendicular profile lines of permanent monuments, capable <br />of resisting normal traffic arrd climatic extremes, would have to be <br />installed. Monument spacing should be between 0.1 d and O.I5 d (where <br />d is the overburden thickness above the mine workings). The intersecting <br />lines of monuments should extend completely across the targeted panel continuing <br />outside the halo formed by the predicted angle-of-draw. 6onitoring should <br />continence prior to any pillar retreat extraction and continue until concurrence <br />is reached with C'MLRD regarding cessation. A monitoring program of this <br />specific type is not required by the permanent regulatory program, however, <br />it is offered as a suggestion to facilitate the resolution of the remaining <br />subsidence concerns in a timely ma nnrr. <br />CC: C, Pahlke, Senior Rec. Spec., CF]l.RD <br />K. Y.irl:, O.SM <br />F. Johnson, OSh1 <br />/k <br />,I~ ~ , ~ <br />