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Sanborn Creek Project Page 4 August 21, 1992 Nest Mine and the head present measured it will be possible to • calculate the rate at which such a borehole would release water into the Sanborn Creek Mine workings. it is recommended that water found to be impounded in the abandoned Hawk's Nest Mine workings be pre-drained to eliminate this potential problem. Standby pumping capacity could be maintained to accommodate such a water inflow. It is also possible to leave protective pillars around the drillhole locations if they can be accurately located. These later courses of action are not recommended. INTRODUCTION This analysis of potential water impoundment problems for multiple seam mining that can reasonably be anticipated from mining of the "C" and "B" Seams in the Sanborn Creek Mine was prepared at the request of Mr. J.E. Stover. Drill logs for four drillholes were provided, as were the lithologic distributions for three of the drillholes. The drillhole logs were used to develop a statistical indication of the lithologic variation within the project site and the variation in interburden thickness between the various seams, Table 1. Maps of the structure and mining plans for the "C" and "B" Seams were provided. A map of the previously mined areas of the Oliver No. 1 Mine and the Hawk's Nest East Portal and West Portal Mines overlying the Sanborn Creek Mine was also provided. A plan was provided of the advance and retreat, panel mining plan. The Sanborn Creek Mine site was visited on July 27, 1992, at which time the portal locations for the Hawk's Nest and Oliver Mines were inspected. The available Sanborn Creek Mine workings were inspected, in particular the access slopes where a minor quantity of water is presently entering the mine. SEAM INTERACTION PREDICTION METHODS Underground mining frequently results in measurable rock response remote from where the mining takes place. Shallow room and pillar mining can breach the ground surface or overlying workings through the collapse of rock above individual mine openings. This type of progressive upward collapse of rock above an extraction is generally called chimney collapse, Figure 1. The collapse chimney is generally centered over the individual extraction. When pillars fail or crush out in room and pillar mining the overlying and adjacent strata deflect downward and laterally toward the area of extraction and pillar failure. This is generally referred to as trough subsidence, Figure 2. The deflection subjects the overlying strata to compressive strain over the center of the extraction area and to tensile strain adjacent to the extraction area. The subsidence trough extends well outside the area of extraction and pillar failure. •