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Colorado Division of Reclamation, Mining and Safety <br />To: Janet Binns <br />From: Zach Trujillo <br />Date: March 14, 2019 <br />Re: Bowie No. 2 Mine TR-118 <br /> <br />As requested, I have reviewed Bowie No. 2 Mine (Bowie) Gob Pile #3 changes <br />associated with the proposed TR-118 for compliance with Rule 4.09, 4.10, and 4.11. As <br />proposed, Bowie has provided all information necessary to satisfy the above mentioned <br />Rules. <br />With the proposed reduction to Gob Pile #3, there was no inclusion of any stability <br />analysis with TR-118. However, with the slope and general design of the gob pile <br />remaining unchanged (outside of total height of pile), the currently approved analysis <br />performed by HBET still remains valid. In HBET’s analysis, they evaluated Gob Pile #3 <br />in two base failure types, circular and block, both attaining a factor of safety (FS) greater <br />than 1.5. HBET then expanded its analysis with two additional circular failure tests to <br />include 15-foot increments of elevated groundwater within the Gob Pile #3. With <br />groundwater elevated to 30 feet within the pile, a FS of 1.44 was attained by HBET <br />analysis. This is below the minimum 1.5 FS as required by Rule 4.10.4(2). With that <br />being said, with a properly functional underdrain, groundwater elevations are not <br />expected to reach to a height of 30 feet within the Gob Pile #3. Additionally, while a FS <br />of 1.44 is below the required minimum as stated earlier, it is still considered stable and <br />with the groundwater levels of that elevation unlikely, no concerns are raised with these <br />results. <br />This concludes my review of Bowie No. 2 Mine TR-118. If you have any questions, feel <br />free to contact me. <br />Sincerely, <br /> <br /> <br /> <br /> <br />Zach Trujillo <br />Environmental Protection Specialist <br />(303) 866-3567 ext. 8164 <br />Zach.Trujillo@state.co.us <br /> <br />