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West Elk Mine '~ Assuming an average gradient of 0.05 in the mine workings, an avera~e horizontal porosity of 0.1 (Mayo, 1998), and a horizontal connectivity of 1.0 x 10-0 to 1.0 x 10- ft/d, the average horizontal seepage velocity in the Rollins Sandstone would range from 0.18 to 1.8 ftlyr. However, these calculations have limited value for predicting flow rates in the compartmentalized Rollins Sandstone. In the journal article Mayo and Koontz (2000) demonstrated that the Rollins Sandstone groundwater systems, in the mine permit area, occur as hydraulically isolated bodies that are not horizontally continuous. In addition, Mayo and Koontz (2000) report horizontal hydraulic conductivity values for the Rollins Sandstone from in-mine permeameter testing between 2.4 x 10-3 and 1.3 x 10-r ft/d. These data show that, with the exception of the fractured portion of the formation, the permeability of the Rollins Sandstone is low. In fact, Mayo (1998) states that of the fifteen analyzed core samples taken from the Rollins Sandstone between the BEM and 14HG Faults, only one "had sufficient permeability to transmit water" and "the low permeability of all other samples make them effective barrier to groundwater flow." This is further documented in the permit revision submittal and decision documents for the Jumbo Mountain (PR-O5, 10/21/94), Apache Rocks (PR-06, 1/26/96), Box Canyon (PR-08, 1125/00)areas, where it is reported that drill holes which penetrated the Rollins Sandstone near the Orchard Valley Mine (now Bowie No. 1 Mine) had an insufficient yield to sustain groundwater supply wells. . As discussed previously, groundwater monitoring wells completed in the Rollins Sandstone do not provide reliable information on the groundwater systems within the unit (Mayo and Associates 1998 and 1999). In addition, the groundwater systems aze not azeally extensive and not in hydrodynamic communication with each other, For these reasons, MCC does not plan to continue monitoring or complete any additional monitoring wells in the Rollins Sandstone, because it has concluded that this formation does not produce sufficient quantities of groundwater for beneficial use. A review of SEO permitted wells in the vicinity of the West Elk Mine confirms that there are no water wells producing from the Rollins Sandstone. However, the information obtained from Rollins Sandstone monitoring well observations have played an important role in understanding the interaction of this major beach/offshore bar deposited sand with the damaged zones associated with the BEM and 14HG Faults. From these observations, Mayo and Associates Exhibit 18B has been able to make correlations to the Bowie Sandstone (of similar depositional history, mineralogical composition, geometry, and structural architecture to the Rollins Sandstone) as it relates to the proposed E Seam mining in the South of Divide permit revision area. • 1.04 -64 Revised Navem6er 1004 PRI G