2020-06-24_REVISION - C1981035 (2)

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ENVIRONMENTAL ASSESSMENT Surface Water W-1. Additional surface water monitoring would continue based on the results of a "spring and seep" survey of the southern edge of East Alkali Gulch.The "A" coal seam outcrop of the Menefee formation would be monitored as well as the contact between the Menefee formation and Cliff house Sandstone formation. Surface water monitoring would include the following:temperature, specific conductivity, pH, oxygen reduction potential, dissolved oxygen, and flow rate. Groundwater G-1. GCCE has committed to replacing the existing underground water storage with aboveground water storage as part of its supplemental water supply plan. Closure of the underground water storage will further eliminate risk to groundwater and be reclaimed or recovered per requirements specified by CDRMS and the OSMRE as part of the associated mine permit. Groundwater monitoring would continue to assess water quantity and quality impacts in the Alkali Gulch alluvium from the low cover crossing. Cluster well monitoring would continue to assess influence on nearby residential water supply wells. Subsidence S-1. Compliance by GCCE with CDRMS Regulation 2.03.7(3), Relationship to Areas Designated Unsuitable for Mining, addresses risk of subsidence from underground mining to adjacent surface property. While this is not a typical design feature, it is highlighted here to directly address scoping issues raised by adjacent landowners.The regulation restricts mining to an area outside 300 ft of an occupied dwelling. Furthermore, OSMRE and CDRMS typically requires that "angle-of-draw" be considered in determining a distance where mining is not permitted. Angle-of-draw accounts for the possibility that the effects of subsidence may extend beyond the actual extent of mining,typically figured at a 35-45- degree angle extended to the surface. For added assurance, GCCE has agreed to the following design features: • S-2. As an LPC LUP condition, GCCE has committed to avoiding mining activity within 600 ft measured horizontally of a dwelling without an expressed waiver in writing executed by the dwelling owner. S-3. GCCE 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 ft measured horizontally of the mining activities. • S-4. GCCE 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. • S-5. GCCE has committed to annual subsidence monitoring after snowmelt on UMU surface in accordance with Federal Permit CO-0106C. Vegetation V-1. Disturbed vegetation would be reclaimed in accordance with the Reclamation Plan General Requirements as described in the PAP. V-2. Vegetation impacts resulting from spills or leaks would be minimized by following the mines waste management procedures. GCCE has an approved Spill Prevention, Control, and Countermeasure Plan in place.