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1/13/22,7:53 AM State.co.us Executive Branch Mail-Re: HC#67752 Colowyo Mine Permit Technical Revision 152 <br /> occurred historically at the Colowyo Mine (orange outlines within the image above). Due to file size constraints of <br /> Gmail, the following Google Drive link includes the above stated approved highwall mining engineering reports. <br /> https://drive.google.com/drive/folders/1 0-ikV3-84TnTac8FVOkP_RgfV25nO8Bf?usp=sharing <br /> For highwall mining, operations occur from within the pit area outside of the mined subsurface regions. All <br /> personnel operate from the outside and do not enter the subsurface area. As a result, no ventilation, associated <br /> surface borehole drilling, and support roads are necessary. Additionally, per Rule 4.23.2(4)(a) of the Regulations of the <br /> Colorado Mined Land Board for Coal Mining require all entry holes from highwall mining to be backfilled and compacted <br /> within 72 hours of completion. <br /> If you have any additional questions, feel free to contact me. <br /> Sincerely, <br /> On Thu, Jan 6, 2022 at 9:02 AM Marques- HC, Matthew <matthew.marques@state.co.us>wrote: <br /> Hi Zach, <br /> We appreciate the additional information provided for our review. We, however, have additional questions and <br /> comments regarding the proposed undertaking. <br /> You noted that the technical revision consists of highwall mining to the northeast and southeast of the South Taylor <br /> Pit. While areas to the northeast of the mine appear to be previously disturbed, it remains unclear where the mine <br /> proposes to expand mining operations to the northeast of the Pit. Could you please clarify the extent of activities that <br /> will occur as a result of the undertaking including in this area to the northeast of the Pit? <br /> We understand that the proposed undertaking will involve subsurface mining activities and that the proposed <br /> undertaking will not result in surface mining. The proposed expansion of subsurface mining operations has the <br /> potential to affect cultural resources through the development of infrastructure (i.e. ventilation, access roads, and <br /> surface borings), temporary use areas, and reclamation activities as well as through reasonably foreseeable effects <br /> such as subsidence and ground vibrations. Similar types of underground operations in similar geological locations <br /> have resulted in subsidence that posed impacts to cultural resources including archaeological sites, rock art sites, <br /> and historic structures. <br /> The Advisory Council on Historic Preservation has previously commented on effects posed by subsidence in <br /> Colorado and noted that"subsidence, in general, with or without subsidence cracks, should be considered an effect <br /> on historic properties as it may include changes in the relationship of a property to its surroundings, including <br /> changes in its surface contours, topography, and erosional patterns. Following the same reasoning it appears that <br /> the opening and subsequent refilling of subsidence fractures, if they were to occur, should be considered at least an <br /> effect on archaeological sites." <br /> According to our records, portions of the mine expansion area have not been previously inventoried by cultural <br /> resource specialists and inventories that were completed were completed between 33 and 44 years ago. These <br /> inventories do not meet current standards and resources considered modern at the time would be considered historic <br /> by current standards. Aerial images show that a high frequency of the proposed expansion areas remain relatively <br /> undisturbed. In particular, the area to the west and south of the Pit remains relatively undisturbed. These <br /> areas show the potential for containing previously unidentified cultural remains. As a result, we recommended a <br /> cultural resource inventory. <br /> The provided map suggests that inventory was completed in a higher frequency of the area than we have in our <br /> files. Has the area recently been inventoried by a cultural resource specialist(s)? If so, could you please send us a <br /> copy of the results of the inventory(ies). If not, we continue to request the completion of a class III cultural resource <br /> inventory considering the reasons discussed above. <br /> Please let me know if you would like to discuss this over the phone or if you have any additional questions. <br /> Thank you, <br /> Matthew Marques <br /> Section 106 Compliance Manager <br /> History Colorado I State Historic Preservation Office <br /> https://mail.google.com/mail/b/ALGkdOy8elLUpphO-cw_b4dRu9Vtn4AuagQgJnHQChhDjud92irb/u/O/?ik=deb7fOcd2O&view=pt&search=all&permthid=t... 2/3 <br />