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I?d Ral:cr April K, 2002 Page 2 provide a rational basis for predicting potential Pancl 2 impacts to (I) the USDW aquifers overlying the cavities, and (2) the Mahogany Zone. Our expectation is that planned Panel 2 solution mining poses minimal risk for adversely impacting the three overlying USDW aquifers. Longwall mining case histories suggest that measurable changes in overburden hydraulic conductivity resulting lrom caving extend a limited distance above the mining horizon. Any significant influence to hydraulic conductivity from Panel 2 solution mining is most likely to attenuate within the R-6 aquitard, which isolates the lower most USDW aquifer (B Groove) from the solution mining horizon. In the unlikely event that communication channels open in response to mining, balanced pumping practices in the cavities prevent the possibility of solution mining fluids migrating upward and mixing with the USDW aquifers. Any flow would be expected downward as controlled by the natural hydraulic gradient. The volume of tlow, if any, would depend upon the increase in rock mass conductivity, the magnitude of the natural hydraulic gradient, and regional groundwater flow. I-Iowever, longwall experience shows that caving-induced channels tend to close with time due to compaction of the overburden, supporting our expectation that any induced flow would be transient, rather than permanent. We believe that Panel 2 plans pose minimal risk to the fitture mineability of the Mahogany Zone. "fhe potential oil shale mining horizon lies in what is anticipated to be the continuous deformation zone produced by very high extraction mining. While hydraulic impacts ' are expected to be insignificant due to attenuated connectivity between fractures and bed separations, these same features pose some potential for ground control diftculties during future oil shale mining. Possible problems could include pillar weakness, rib sloughing, roof falls, floor ' heave, offsets in the mining horizon, and generally less predictable conditions, similar to conditions in the vicinity of faults or other naturally occurring disturbance zones. However, these hazards are more likely to be infrequent, rather than ubiquitous over a cavity. Although ' some difficulties are possible as a consequence of Panel 2 solution mining, the impacts are not likely to be pervasive enough or severe enough in nature to preclude successfultnining of tlrc Mahogany Zone in the future. ' Background Historically, similar concerns for the protection of overlying USDW aquifers and the Mahogany oil shale mining zone existed at the planning stage for Panel 1 solution mining. These were first investigated by Agapito Associates, Inc., (AAI) in 1988. The study concluded ' that 60-fr-wide pillars separating solution cavities would provide sufficient stability to minimize the risk of disrupting the overlying aquifers and Mahogany 'Lone resource. Solution mining was assumed to be confined to the Boies Bed. Conclusions were based on a review of lithologic data, ' overburden structure, regional iss situ stresses, calculated rock mass strength, the bulking potential of caved strata, and numerical simulation of cavity roof stability. t ~ J.F.T. Agapito & Associates, Ina (1988), "Caving Above Solution Cavities, IRI Leases, Piceance Creek Basin, Colorado," Letter report by M. P. liardy to Mc Harold Raymond, RMF Mineral Swvices, hic., Job.No. 134-I, ' August 10. ' Agapito Associates, Inc.