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DocuSign Envelope ID: EBE28081-13782-41342-BAD13-D8C9313687131B <br />PERMIT NARRATIVE CONDITIONS REPORT FORM (continued) <br />PART E. ADDITIONAL DESCRIPTION INFORMATION INCLUDED (a summary of information attached) <br />This status/progress report on the Colowyo Mine CDPS Permit #CO-0045161 Compliance <br />Schedule is designed to ensure the final limitations (Chronic WET at Outfall 010) will be met by <br />10/1 /2023. The report includes: <br />1) Summary of design details, costs, power and space requirements for the treatment options <br />under evaluation (reverse osmosis/nanofiltration, sulfate bioreactor and evaporator), and <br />2) Update on any other activities related to the treatment installation. <br />The treatment options analysis is Attachment A - Toxicity Reduction Evaluation - Lines of <br />Investigation (Colowyo Mine Outfall 010). The analysis found that enhanced evaporation is <br />infeasible as a stand-alone technology given the poor evaporative conditions in this area of <br />Colorado; however, it was evaluated as supplemental treatment for residual waste brine handling <br />on membrane treatment (reverse osmosis/nanofiltration). Capital costs for nanofiltration <br />(recommended over reverse osmosis) and bacterial sulfate reduction (BSR) reactor ranged from <br />$3.5-12.7 million, and operational costs were estimated between $600,000 and $1.4 million <br />annually. Due to these significant costs, further evaluation of sources and bench -scale testing <br />commenced in 2020. <br />The other activities conducted to date include: <br />(a) Water Balance / Source Water Evaluation (Attachment B), and <br />(b) Commencement of Bench -Scale Testing of the Bacterial Sulfate Reduction (BSR) Reactor. <br />The water balance concluded infiltrated precipitation and infiltration of Taylor Creek water via <br />highwall miner holes are the main sources to the East Taylor Seep. Controls (e.g. lining Taylor <br />Creek) could be considered to reduce seep flows, but they are not anticipated to eliminate flows. <br />Bench -scale testing of the BSR commenced in the fall of 2020. The preliminary results indicate the <br />BSR would not work as a stand-alone technology due to elevated TDS and alkalinity in the product <br />water. Supplemental passive treatment or pre-treatment may be considered, along with other <br />options (i.e. underground injection). The bench -scale testing results will be provided with the <br />5/31/2021 compliance schedule submittal. <br />PART E. CERTIFICATION Required Signatures <br />"I certify under penalty of law that I have personally examined and am familiar with the information submitted in this <br />application and all attachments and that, based on my inquiry of those individuals immediately responsible for obtaining <br />the information, I believe that the information is true, accurate and complete. I am aware that there are significant <br />penalties for submitting false information, including the possibility of fine or imprisonment. <br />"I understand that submittal of this application is for coverage under the State of Colorado Discharge Permit System until <br />such time as the application is amended or the certification is transferred, inactivated, or expired." <br />DocuSigned by: <br />A5D5C24494CD4A7_. <br />12/29/2020 <br />Signature of Legally Responsible Party Date Signed <br />Barbara A. Walz Senior Vice President, Policy & Compliance/Chief Compliance Officer <br />Name (printed) Title <br />Page 3 of 3 <br />June 2019 <br />