2020-06-25_REVISION - C1981035 (35)

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Environmental Assessment subsidence may extend beyond the actual extent of mining,typically figured at a 35-45-degree angle extended to the surface. See the diagram below. For added assurance, GCC has agreed to the following design features: ■ As a LPC LUP condition,GCC has committed to avoiding mining activity within 600 feet measured horizontally of a dwelling without an expressed waiver in writing executed by the dwelling owner. ■ GCC has committed in its subsidence monitoring program prepared and undertaken pursuant to Rule 2.05.06(6)(c)of the Regulations of the Colorado Mined Land Reclamation Board for Coal Mining to include all dwellings within 1,000 feet measured horizontally of the mining activities. ■ GCC has agreed to measure and monitoring on a quarterly basis the static groundwater level in the wells identified within CDRMS Technical Revision-26 or as amended, and within 10 days of measuring the static groundwater post the results on a publicly accessible website. ■ GCC has committed to annual subsidence monitoring after snowmelt on UMU surface in accordance with Federal Permit CO-0106A. Design Feature 4a: Noise and vibration from the facility GCC has implemented the following measures to minimize on-site and off-site noise and vibration from its mining operations and facilities. ■ GCC limits operation of the coal crushing and screening facility on the surface to daylight hours. Coal crushing and screening on the surface is normally limited to 6 to 10 hours per day. ■ The largest source of noise generated at the facility is the ventilation fan at the mine portal (Matheson Mining Consultants 2013). Although the 2013 noise study did not detect fan noise at nearby residences, it was reported anecdotally that under certain atmospheric and wind conditions, some mine noise could be detected as much as a few miles away. Additional noise studies were completed in 2015 by Aimone-Martin (hired by LPC) and in 2016 by Wave Engineering (hired by GCC) and Braslau Associates (hired by a landowner; David Braslau Associates, Inc. 2016). In response to the findings in these studies (additional detail provided in Section 3.11 Noise and Vibration), GCC installed noise-reduction equipment on this fan in April 2015 and will install similar or newer technology noise-reduction equipment on other large fans that may be used at the mine in the future. ■ GCC learned that noise from surface equipment startup alarms and backup alarms at the mine site could be heard at neighboring residences. Several subsequent actions were undertaken to eliminate or reduce alarm noise. Two alarms that emitted a loud two-tone chirp several hundred times daily were eliminated entirely. Alarms required for safety or by law were replaced or modified so as not to project sound beyond the site boundaries. Finally, all alarm sounds were reduced to the minimum level required to meet safety and legal standards. ■ GCC also modified facility load-out procedures to reduce activation of truck backup alarms during the loading process. DOI-B LM-CO-S010-2011-0074-EA September 2017 -46-