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• ` • !*', II I I II III I II IIII III <br />H F;~ ^G\Oqo DEPARTMENT OF NATURAL RESOURCES 999 <br />tiQ ;~` {f'~+ 90 D Monte Pascr~a E.acuove Uner,inr <br />.:r ~~ ,,.. MINED LAND RECLAMATION DIVISION <br />.,. <br />i ~~~r DAVID C. SHELTO N, Director <br />' f876' /~.~, <br />A¢ua.n D Lamm ~ 'yip. <br />Gove~no~ ' <br />UNTE: Auyust 2b, 19tS3 -` <br />Tv: Carol Russell <br />~ / ~ -- <br />FRUM: Jim Pendleton ~ ~~~ " <br />~-= -~~~~ - <br />RE: Dorchester.Coal Coyp-afiy's "South Subsidence Grid Report", <br />Uorchester~l Coal Mine <br />Pursuant to your request, 1 have reviewed the subsidence monitoring <br />report suomitted by the Dorchester Coal Company. The report presents the <br />I4arch and June, 1943 su"rvey data for ,t heir "South Subsidence Ionitoring <br />Grid" installed at the Dorchester No. 1 Kline in Fremont County, Colorado. <br />The operator has suomitted a surveyor's plot Inap of the subsidence <br />monument locations and a data sheet presenting Horizontal locations and <br />elevations for each point in March and on June 24. I have compared the <br />two separate sets of survey data and determined that monuments are <br />exhibiting movements of between .13' of rise and .l' of drop. This is <br />not uncoininon above panels in the development process stage. <br />The purpose of a subsidence monitoring report is to allow verification of <br />the subsidence projections made by the applicant within the permit <br />application document. In order to facilitate this task, I included a <br />stipulated submission of a subsidence report format within the proposed <br />geotechnical findinys which I forwarded to you reyardiny Dorchester's <br />permanent program permit application. because the company is not yet <br />privy to that document, I recommend that you require the inclusion of the <br />following items within future subsidence monitoring reports: <br />(1) A map which superimposes the subsidence monument locations upon the <br />planned underyround workings of that portion of the mine plan. <br />This Inap should also indicate those underground workinys existing <br />at the time the survey was completed. This allows deduction of <br />specific spacial relationships between the monuments and the <br />existing underground workings. <br />(2) The survey data should be clearly tabulated and included within the <br />subsidence monitoriny report. These tabulations should include <br />calculated cumulative vertical and horizontal deviations of each <br />subsidence monument from its original location. <br />423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. (303) 866-3567 <br />