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Subsidence Iaq~acts 1990 <br />• Cyprus Orchard Valley ca~leted pillar extraction of Panel H, advance development <br />of the II West Submains throix~ crosscut 48, the initial advance development of <br />panel A (4 crosscuts), and the initial advance development of panel A+ (3 <br />crosscuts). 'It~e following discussions first summarize the history ani wrrent <br />status of the subsidence monitoring program and then address the ooav^rprce of <br />1990 subsidence impacts as detected by survey monitoring and visual obsea:vations. <br />Subsidence Monitorira History <br />CpII RD regulations, Section 2.05.6(6)(b), require that a determination be made <br />with regard to whether or not subsidence, if it occurred, could cause material <br />damage or diminution of the reasonably forP~+oahle use of stnx.-tiu-es and <br />renewable resource lands within the permit and adjacent area. If a negative <br />determination is reached, regulations call for a monitoring program (Section <br />2.05.6(6)(c)) to be implemented to substantiate the accuracy of that <br />determination. If a positive determination is reached, as was the case at <br />Orchard Valley, regulations call for additional information to be includes in the <br />permit in the form of either a subsidence survey (Section 2.05.6(6)(e)), or a <br />subsidence control plan (Section 2.05.6(6)(f)). <br />Permit No. C-81-038 contains a subsidence survey, a subsidence control plan, and <br />a subsidence monitoring program. 'IY~e subsidence monitoring program is called for <br />within the subsidence survey to verify the predictions made therein arxi consists <br />• of a wide-spaced monitoring grid intended to provide general information on <br />horizontal and vertical displacesrent magnitudes throughout the general mined <br />area; a series of high resolution grids located over selected pillan~ areas <br />designed to provide site specific data with regard to subsidence magnitude and <br />areal extent under differing geologic and topographic conditions; and periodic <br />visual walkovers in areas undermined by pillaring techniques. Modifications to <br />the subsidence monitoring program are to be presented in the Annual Subsidence <br />Report submitted to the Division. Subsidence monitoring is to continue until <br />cessation is approved by the Division in writing. <br />Wide-Spaced Monitoring Grid Station Su~mnarv <br />'Ihe following discussions present a station by station assessnent of survey <br />information available at each wide-spaced monitoring grid station. Monin'torirx3 <br />station data sheets are appended to this report for reference along with a <br />summarized tabulation of monument and control station elevation change:>. <br />Stations 1-2: Surveys were initiated in 1982 and continued into 1984. <br />Stations 1 and 2 were initially surveyed after retreat' mining <br />had occurred in the 1st West panel off the 1st North mains, <br />showed no significant movement thereafter, and were <br />subsequently discontinued. <br />Station 6: Surveys were initiated in August 1982 and continued bizuu~ually <br />• thrax~i July 1984. Surveys were reinitiated in 1987 and <br />conducted annually through 1990. Station 6 is located on <br />approximately 350 feet of overburden and lies approximately <br />3 <br />