2021-07-21_PERMIT FILE - C1981019 (5)

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Point of Compliance Well Investigation AECOM 5 which was consistently dry during the baseline monitoring period. Additionally, Colowyo decided to stop sampling POC-7 after the April 2020 monitoring event due to the high total dissolved solids (TDS) concentration in the well (21,000 to 45,700 milligrams per liter [mg/L]), and its location as the farthest downgradient temporary monitoring point, making it an unlikely location for a permanent compliance well. 2.3 Analytical Program Groundwater samples collected from the temporary wells were analyzed for the groundwater constituent list contained in Section 4.05.13 of the Mine Permit. The analytical constituents and laboratory methods are listed below: • pH by Standard Method (SM) 4500 HB; • Electrical Conductivity by SM 2510B; • TDS by SM 2540; • Alkalinity by SM 2320B • Hardness by SM2340B; • Ammonia as Nitrogen (N) by Environmental Protection Agency (EPA) Method 350.1; • Nitrate as N, nitrite as N, nitrate + nitrite as N, orthophosphate as phosphorus, and sulfate by EPA Method 300.0; • Total Phosphorus by EPA Method 200.7; • Calcium, magnesium, and sodium by EPA Method 200.7; • Dissolved Metals by EPA Methods 200.7 and 200.8; and • Mercury by EPA Method 245.1. Colowyo also added chloride and potassium to the analyte list for the 2020 sampling events to complete the analytical suite for major ion chemistry. Chloride was analyzed by EPA Method 300.0, and potassium was analyzed by EPA Method 200.7. 2.4 Temporary Well Abandonment Consistent with Colorado Division of Water Resources permit requirements for monitoring and observation holes, the temporary monitoring wells were abandoned within 18 months of installation. Cascade Environmental abandoned the temporary wells on March 29, 2021. The Well Abandonment forms are provided in Appendix C.