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SUBSIDENCE MONITORING ANALYSIS EVALUATION OF EXISTING MONITORING MIDELY SPACED GRID PURPOSE The purpose of tion, delete necessary, REGEIVEfl ocr 4 ~ MINED lANO RECLAMATNDIV OIViSION this analysis is to evaluate past subsidence monitoring informa- monitoring where no longer required, and add monitoring where PLACEMENT OF MONUMENTS The monuments on the widely spaced grid were constructed before permanent pro- gram approval. There were uncertainties in the regulatory programs, therefore, actual monitoring began in 1982 after approval of Orchard Valley Mine Permit Plo. C-038-81, The monuments were constructed for three basic uses: 1, Some monuments were placed in areas that were not ever contemplated for un- dermining, CWI monitored these in baseline studies to determine surveying measurement tolerances. Some of these were even located in areas where no O seam coal was located. 2. Some of the monuments were surveyed over previously advanced-only entries. This data was used to obtain future information from mining in these areas in the future, They were also placed to show the extent of subsidence due to advance-only mining. 3. Some of the monuments were located over previously retreat-mined areas. They were surveyed to show the time dependent nature of subsidence. No in- formation was to be gathered on them about actual subsidence during retreat mining because they were surveyed after retreat mining. METHOD OF ANALYSIS CWI evaulated previous data from the approved widely spaced grid. The analysis was divided up into six different situations. They were: 1. Evaluation of monuments where no mining took place or retreat mining had taken place before surveying of monuments. 2, Evaluation of monuments in which advance-only mining was completed. 3. Evaluation of monuments that have not been undermined and will be monitored in the future. 4. Evaluation of monuments that were to be installed but will be delayed and monitored at a future time. 5. Evaluation of monuments that require continued monitoring. 6. Evaluation of monuments that require 1985 installation and monitoring.