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Sensitive structures undermined by long-wall mining, or retreat mining processes, such as powerlines, gas pipeline, secondary mining test areas, water impoundments, and archaeological sites will have very accurate subsidence rronitoring systers which will be installed and surveyed by Northern Coal Company. This will be necessary to erasure that subsidence is not occurring on protected zones and to detect any damage that may occur to the structures as a result of the subsidence. The Colorado dined Land Reclamation Division (G'~4..R) had approved Northern's subsidence and hydrologic monitoring program for advance mining of the G seam under Curtis Creek. The details of this program and quarterly reports are included in the correspondence provided in the follaving map pocket. The precise location of the approved sub- sidence monitoring monuments are depicted on ~dribit S-5 and the locations of hydrologic monitoring stations are depicted on F7dribit G-1. 4Yre rroni- tori.ng program for the FF seam in the area of Curtis Creek will be roughly similar to that approved for the G seam in terns of nnnument spacing and monitorting frequency with appropriate modifications made to reflect any differences in the hydrologic and geologic circumstances of the proposed • operations in those seams. The engineering details of the proposed moni- toring program for the FF seam will be developed in the near future and submitted within 60 days (after full consultation with 06M and CA'ILR technical staff), as was done with the G seam program. Afonument spacing around the structures and frequency of the surveys performed by Northern Coal will be dependent upon the sensitivity of the structures. Test areas for secondary mining in the FF seam (see Eydribit S-2) and for longwall mining in the J seam (see 15ctribit S-3) will be very closely rmnitored as they will provide the first subsidence infor- mation. kbnitoring of the state highway and the Jensen Ranch will be frequent while advance mining is being performed underneath then and secondary mining near than. monitoring will continue until it is deter- rmned that subsidence is not adversely affecting these structures. The water impoundments, paverlines, gas pipelines and archaeological sites will be rronitored closely while secondary mining occurs beneath than. After the subsidence has ceased, these structures will no longer be irnnitored.