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Memo to Berhan Keffelew Update -Underground Workings page 2 Phase 2. This alternative methodology is acceptable to the Division with the following condition. In order to ensure that the treatment is successful, I recommend that the Division require the installation of a suitable detection device, such as some form of linear resonance cable or simple continuity circuit above each of the geogrid shaft installations. Each of these detection devices should be extended separately to a readout location at the periphery of the Phase 2 liner. If any of the shafts collapse, and its resultant settlement deflection were to propagate through the remedial geogrid cover, it could be detected. If that occurrence were simultaneous with evidence of leakage, the location of the problem could be isolated and repaired, In 1990, Aguirre Engineers Inc. (AE1) was contracted by CC&VG to complete a design study and recommendations for treatment of the underground workings beneath Pad No. 2. In 1990 three of the identified workings were excavated and backfilled, as recommended by AEI; Little Nell #3, the Ore House Shaft, and an unnamed shaft, During the subgrade preparation and underdrain construction of Phase 2, conducted in the fall of 1995, these earlier remediated workings were reencountered and one additional shaft, the Raven Beacon shaft was encountered at the ground's surface. Using the earlier AEI report, CC&VG identified what it believed to be the locations of the other historical underground workings. As I understand your verbal comments, CC&VG recently directed its Contractor to excavate each of the suspected locations of the anticipated underground workings. However, CC&VG reports that it did not verify their existence upon excavating to a depth of two feet. Both AEI and Golder Associates originally recommended excavation to 20 feet for backfilling remediation. In addition you reported that CC&VG conducted a ground penetrating radar examination of the phase 2 footprint with negative results. In my opinion it is critically important that the existence of these underground workings, particularly the anticipated shafts, be exhaustively confirmed or refuted. First, the operation and accuracy of the ground penetrating radar unit should be verified by calibration above known underground workings. The surrounding Cripple Creek/Victor mining district should provide more than ample selection of useable calibration sites. If the definitive operation of the ground penetrating radar cannot be demonstrated in the Cripple Creek/Victor District, an alternative diagnostic technique should be identified, calibrated and used. If the results of the resurvey of underground workings, using whatever technology is proven reliable, remains negative, the historical evidence should be revisited to resolve its apparent discrepancy, if possible.