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• s s ~~ SUBSIDENCE MOttITORING PROGRAM ~ ORCHARD VALLEY MIt7E PAONIA, COLORADO SEPTEt4t3ER, 1979 Colorado Westmoreland has developed this Subsidence Monitoring Program in order to comply with applicable regulations under 30 CFR 784.20. It also complies with the follow in p, performance standards: 30 CFR 817.121, 124, and 126. C[•II's Subsidence Monitoring Program was designed in such a manner as to give accurate pre-mining measurements of specified points over the area to be mined and allow for accurate measurement of those same points on a periodic basis after mining has occurred. The monitoring program has been developed and partially implemented. This program consists of four phases: Phase I - This initial phase of work consists of establishing co- n o points on the ground. Map No. 23 ("Subsidence Monitoring Program") shows the location of these monitoring or control sta- tions, together with instrument stations that will be used in Phase III of the program. 1'he control or instrument stations are located on 1/4 section corners east and west, and 1/2 mile apart north and south. Typical construction of a control and/or instrument station is as follows: The control stations consist of an iron pipe set to bedrock or the frost line and extending twelve inches above the ground with a permanent ten foot range pole mounted on it. The bottom of the pipe will be set in concrete so as to assure long- term stability. The location of each point has been precisely surveyed to provide horizontal and vertical control so that any future movement can be easily detected. Twenty-eight (28) such monitoring points are already in place over the area which will be mined at the Orchard Valley Mine. The instrument stations have been constructed so as to facilitate ease of surveying at future dates and have been tied together by an accurate triangu- lation net. Phase II - Each time that control points are set, they are sur- veye or elevation to within one foot of accuracy. Initially, CWI had a photo flight of the area done for purposes of checking elevations through a digital analysis of the nho[os. The actual elevation of the monitoring points is listed on Map No. 23, "Sub- sidence Monitoring Program". As mining progresses further to the north, additional monitoring points wil]. be established and their elevations will be surveyed to within one foot of accuracy.