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COLORADO <br />Division of Reclamation, <br />Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />November 12, 2015 <br />Interoffice Memo <br />Bowie No. 2 (Permit No. C-1996-083) <br />Technical Revision No. 105 (TR -105) <br />Jason, <br />I have reviewed Bowie No. 2 Technical Revision No. 105 and have the following comments: <br />With the provided revised pages and maps for Bowie's TR -105, there are no indications or <br />discussions that additional piezometers are to be installed in the gob pile 93 expansion. As <br />provided with TR -105, details for an additional underdrain have been included in this expansion <br />area which leaves the impression that the potential for groundwater exists. Water within the <br />foundation and/or gob itself would increase pore water pressure which may impact stability of <br />the gob pile. Additionally, as stated in Huddleston -Berry Engineering & Testing, LLC's (HBET) <br />"Stability Evaluation — Gob Pile #3" (Report), based upon data from gob pile #2, pore pressure <br />will likely increase during the construction of the gob pile. Based upon this, it is my opinion that <br />additional piezometers in the expansion section are needed. Please have Bowie provide details <br />for additional piezometers within gob pile #3 expansion section or reasoning for not including <br />them. <br />Please have Bowie update Volume XI — Coal Mine Waste Disposal Area No.3 Figure 1 to <br />include the addition of piezometers if needed. <br />Stability analysis of gob pile #3 was performed in the Report at critical sections of the pile. The <br />design of the expansion section appears to remain consistent with the current construction and <br />design of gob pile #3 with critical sections remaining unchanged. Thus, HBET's stability <br />analysis is representative of the expanded section so an additional stability analysis isn't <br />necessary. However, please have Bowie provide a cross sectional view of the expanded section <br />of gob pile #3 to ensure the design of the pile remains consistent and allows for the Division to <br />perform a stability "check". <br />This concludes my review of Bowie No. 2 TR -105 If you have questions or need additional <br />information, please contact me. <br />1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us <br />John W. Hickenlooper, Governor I Mike King, Executive Director I Virginia Brannon, Director <br />