2025-08-01_PERMIT FILE - C1981019

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RULE 2 PERMITS South Taylor – Rule 2, Page 15 Revision Date: 7/21/25 Revision No.: MR-267 The analytical data from the Colowyo boreholes includes: pH, conductivity, saturation percentage, percent sand, silt, and clay, sodium absorption ratio, exchangeable sodium percentage, cation exchange capacity, boron, molybdenum, selenium, nitrate-nitrogen, calcium carbonate equivalent, sulfur forms, non-sulfate sulfur and total sulfur. The AGP and the ANP:AGP ratio for samples collected in 1997 were calculated based on pyritic-sulfur percent. The AGP and the ANP:AGP ratio for samples collected in 1999 and 2000 were calculated based on total-sulfur percent. For samples collect in 2000 if the ABP was negative based on an AGP calculated using total-sulfur then, nonsulfate-sulfur was determined and used to calculate the AGP, ABP, and ANP:AGP ratio for that sample. The criteria shown on Page 2.05-8 of Volume 1 of the current permit will be used to measure reclaimed overburden suitability. These criteria are based on negotiations with the DRMS and in part on the Wyoming Department of Environmental Quality, Land Quality Division (WDEQ-LQD), Guideline No. 1, Topsoil and Overburden, Table I-4 (August, 1994). The WDEQ-LQD guidelines were used since Colorado has no published standards as of the date this permit was revised. The overburden suitability criteria used by WDEQ-LQD are shown in Table 2.04.6-2. A summary of borehole overburden and interburden results compared to the WDEQ criteria is provided in Table 2.04.6-3, and a summary of the percentage of each borehole that is less than “suitable” for each selected WDEQ criterion is shown on Table 2.04.6-4. These comparisons are for informational purposes only, since the criteria on Page 2.05-8 of Volume 1 will determine regraded overburden success in the South Taylor mining areas. Selenium was found to exceed the WDEQ “suitable” criterion of 0.3 ppm in 1.74% of the borehole intervals across South Taylor (Table 2.04.6-4). The Colowyo Mine regraded overburden sampling performed since 1983 and reported by Colowyo in the 2005 Annual Reclamation Report shows mean selenium concentration of 0.03 ppm, with a maximum value of 0.47 ppm and exceedances of the WDEQ “suitable” criterion in only two of the 279 samples. Similarly, boron was found to average 0.34 ppm in 279 samples, with only one sample exceeding the WDEQ boron “suitable” criterion of 5 ppm in the regraded overburden. Only one borehole (83-D3-14) exceeded the boron criterion in one interval with only 0.47% of all borehole samples in South Taylor exceeding the WDEQ boron criterion. Lead did not exceed the existing permit “suspect level” of 20 ppm in any borehole sample, and only one regraded spoil sample out of 279 exceeded this value at 20.9 ppm. Molybdenum did not exceeded the WDEQ “suitable” criterion of 1 ppm from boreholes in South Taylor. Similarly, all seven regraded overburden samples obtained by Colowyo that were analyzed for molybdenum contained 0.4 ppm molybdenum. This information indicates that selenium, boron, lead, and molybdenum are not issues in the regraded overburden in the mined formations using current mining practices. The regraded overburden analyte monitoring shown on page 2.05-8 of the existing permit has been modified with this submittal to reflect this information. A small percentage of the overburden samples are acidic or have a potential to generate acid. Only four samples representing 21 feet or 1.23% of the overburden sampled contained ABP less than –5 tons CaCO3 equivalent/1000 tons material. Thirty-seven samples representing 85.3 feet or 1.8% of the overburden sampled had a saturated paste pH less than 5.5. Three samples representing 10.8 feet or 0.23% of the overburden and interburden sampled had a pH greater than the WDEQ “suitable” criterion of 8.5. Of 308 regraded spoil pile samples reported in the 2005 Annual Reclamation Report, none exceeded any pH criteria, with 8.4 the maximum pH, 6.3 the minimum measured pH, and 7.5 being the mean overburden pH. This indicates that homogenization of the overburden during mining results in overburden that has an ideal paste pH. One hundred and thirty samples representing 805.9 feet or 17.04% of the borehole overburden and interburden sampled in the South Taylorarea had a SAR greater than “suitable” criterion provided in the WDEQ guidelines. These samples are all in interburden and almost exclusively beneath the deeper coal seams (Exhibit 6, Item 6). Mining operations will naturally rebury these deeper interburden layers in the