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<br />In addition to these leveling points. additional points may be ettab- <br />lashed in the future along the centerlines of development entries where <br />the development entries intersect North and Middle Thompson Creeks. It <br />1s proposed that these creek leveling points be installed only if infor- <br />oration from the DOE subsidence study or monitoring of the existing level- <br />ing points indicate that subsidence may occur as a !@sult of development <br />~: <br />f <br />mining. ~,,. <br />It should be noted that development entries presently exist under North <br />Thompson Creek at No. 1 Mine (Map Aj with no known subsidence effects. <br />I In addition, preliminary data from the first DOE subsidence line under- <br />mined by the longwall indicate that no subsidence occurred as a result of <br />mining a 350-ft face at a depth of approximately 1000 ft. It therefore <br />appears that development entries have not nor will not cause surface sub- <br />sidence. <br />Leveling points. if required, will be positioned along each entry center= <br />line. Actual monument spacing will be 0.1 times the average overburden <br />depth at that location. Monuments will be installed out from the creek <br />centerline to a distance of 200 ft. <br />Leveling points will be constructed of No. 6 rebar, 18 inches long, driven <br />to refusal. Acenter-punched aluminum cap will be installed. Experience <br />on the DOE monitoring net has shown that these type of leveling points <br />work well. <br />• Monitoring of these leveling points will be scheduled during development <br />27-1 <br />(Revision JUNE 1982) <br />