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Technical Revision No. 80 August /9, 1998 Page 4 Coring through the coal during the construction of monitoring wells may have produced considerable secondary fracturing in the walls of the borehole. Therefore, the permeability determined during slug testing might describe the combined factors of coal permeability and secondary fracture permeability. It should be noted that MCC's experience within the West Elk Mine support the very low permeability of the B-Seam coal as calculated from slug tests. For example, there were relatively dry coal faces just prior to mining through the high-pressure fault inflow areas; and most importantly, after drilling the NW sump #1 horizontal drill hole 215 feet, water was first encountered in the hole, only 17 feet from the filled sealed sump. /5. Perrdir:g concerns regarding potential outflows from the Wes[ Elk Mine to the Bear Mtrre are addressed at numbers 13 and 14 above. Please see the responses to comments 13 and 14. 18. In marry sitrrattorts, pumping tests may provide more aecrrrate data than slug tests. On page 12 of the MCC response both slug ar:d pumping tests are referenced. l~r your response to number /4, MCC presents only slug test data. Please provide the data from any pumping tests performed as referenced on page 12 of your rerportse letter. The Division reiterates its concern regarding potential groundwater ou~ows from the West E!k Mine to off-site areas and any additional informaliorr from premping tests would be useful to the Division. MCC concurs that pumping tests can provide more accurate data than slug tests. However, in very tight formations with low permeabilities (such as the B-Seam), pumping tests are not feasible under these conditions, since very low pumping rates are required to maintain water in the well. Slug tests are typically performed on wells completed in strata with low permeabilities. This was the reason that slug tests were completed on MCC's monitoring wells. MCC's actual experience when mining near the B-East Mains and 14SEHG faults, as well as when the NW Sump #1 horizontal hole was drilled, provides important verification of the low permeability of the B-Seam. Slone Stability Implications of Sump Outflows 21. Wright Water Engineers (WWEJ has completed a subjective evaluation of the relationship between projected lumping of water in the B Seam, invasion into the Bear and Edwards mines abandoned workings, migrattor: through the subcrop into the colluvial wedge, and slope stability of the colluvial wedge down slope from the B Seam subcrop. WWE concludes that historically the instability of the colluvial slope below the B Seam subcrop is directly related [o the availability of moisture; i. e. landslides occur predominantly irr the wet years. Further, instability of the colluvial wedge below [he B Seam subcrop is predomtnar:tly "shallow" irr nature. WWE projects that the increase irr soil moisture due to irrereased migration from the B Seam workings should be irrsignifrca»t