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James A. Kiger <br />February 22, 2010 <br />Page 2 <br />3. In situations where a bottom to top cement plug is not specifically required by regulation, <br />the Division recommends a minimum of fifty feet of cement plug be placed at the lowest <br />point inside the solid casing, above the perforated interval of the well. The cement plug <br />should be a minimum of fifty (50) feet in length and should extend a minimum of fifty <br />(50) feet above the zone to be protected. An inflatable packer, bridge plug, or other <br />mechanical plug approved by the Division shall be utilized as a foundation for the cement <br />plug. This additional closure recommendation is deemed appropriate to provide <br />protection against post-closure methane migration to water and land resources. Such <br />migration must be prevented. <br />The Division recognizes that subsidence effects associated with longwall mining may <br />compromise the integrity of the gob vent borehole. Subsidence due to removal of coal <br />from the longwall section and the subsequent caving of overlying strata may damage the <br />well. The well casing may be collapsed or sheared as longwall panels are retreated <br />beyond the location of the methane drainage well. The Division recommends that the <br />total depth of the well be measured prior to initiating plugging procedures to determine if <br />the well has been damaged. If the casing is damaged and the packer or plug cannot be set <br />at the proposed depth, then a bridge plug/packer and cement plug should be placed at the <br />lowest point possible in the well, as close to the perforated casing interval as practicable. <br />These recommendations are set forth in our guidance document Installation, Operation, <br />and Abandonment of Coal Mine Methane Drainage/Monitoring Wells in Colorado, which <br />was provided to coal mine operators in 2004. A copy of this document is enclosed. <br />Although OMLLC's gob vent boreholes consist of a steel casing already cemented in <br />place, the Division has determined that these additional recommended steps are prudent <br />to prevent methane migration to the extent possible. <br />4. In the PAP three identified groundwater units are described. Of these, one unit (the <br />alluvial/colluvial aquifer system) provides adequate quantities of water of suitable quality <br />to support beneficial use. As further described in the PAP there are documented <br />groundwater rights in the mine and adjacent areas. Groundwater use in the area includes <br />individual domestic water supply, small stock watering and irrigation, small municipal <br />water supply, and mine use. Please ensure that the plan for sealing gob vent boreholes is <br />adequate to protect these groundwater resources and describe measures to be taken to <br />protect all water and land resources from potential methane migration. <br />If you have any questions, please contact me. <br />Sincerely, <br />at4a P. Bolt/ <br />Michael P. Boulay <br />Environmental Protection Specialist <br />Enclosure