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MINED LAND RECLAMATION DIVISION Department of Natural Resources 1373 Sherman St.. Room 215 Denver, CO 80203 303 866-3567 Fn x: 303 832-8106 III IIIIIIIIIIIIIIII N~ STATE Ol `i V9Y/ Vl rl .DO t~,, c , t`L~fjU OF~CO/p .p ~.~~ng ~~ ~e /\ r ~ f816 ~ Roy Ramer. Gavemor Fred R. Banta, Division Dir¢ctor DATE: January 13, 1992 T0: Carl Mount ~--, FROM: Jim Pendleton ~ ~' -~' ~ -""- .. ~-~ -~ =~ ,. RE: Cyprus Energy Corporation - Minor Revision MR 91-19 - Supplemental Developmen~.i~rgTJnder Structures and Renewable Resource Lands (Permit No. C-81-044) I have reviewed the supplemental submittal regarding minor revision application MR 91-19, submitted by CEC for its Eagle No. 6 underground coal mine. This supplemental submittal was made in response to our earlier adequacy comments. As you will recall, CEC is requesting permission to extend its mains and submains beneath the Denver Rio Grande and Western railroad spur, Colorado State Highway No. 13, and the Williams Fork River and its associated alluvial valley floor, during its next five year mining permit term. As a portion of the minor revision application, CEC proposed to monitor the performance of the underground pillars' as a method of subsidence monitoring. Because the requirement to monitor subsidence could extend beyond the closure of the underground workings, and it is also of value to verify the surface stability of the potentially affected structures and renewable resource lands separate from the effects of subsidence, I requested that the operator install surface monuments to monitor surface movement. Following the issuance of my original adequacy memo in June of 1991, I discussed my concern with Rick Mills of CYC on several occasions. The operator subsequently submitted a supplemental proposal to install three subsidence monuments identified as H-1, H-2 and H-3. The proposed locations, adjoining Colorado Route 13 above the proposed entryways, are identified on Map 31, as amended. The purpose of these monuments shall be to supplement the underground pillar stability monitoring program conducted by the operator. These monuments shall be installed and initially surveyed twice prior to mining advancing to within the area possibly affected by the angle of draw of 20 degrees from vertical. Following initial installation and surveying, these monuments shall be monitored annually and reported within the annual subsidence monitoring report. If the underground pillar stability inspection is curtailed, the surface monument monitoring frequency shall be increased to twice per year. Monitoring shall continue until cessation is approved in writing by the Division. The operator shall also briefly summarize the results of their underground pillar observation studies within the annual subsidence monitoring report.