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DocuSign Envelope ID: D07924E6-3D94-4398-AO66-B683COBAB33E <br /> PERMIT NARRATIVE CONDITIONS REPORT FORM (continued) <br /> PART E. ADDITIONAL DESCRIPTION INFORMATION INCLUDED (a summary of information attached) <br /> The enclosed report provides the required "update on bench-scale and pilot testing of treatment <br /> options" and "updates on other activities related to the installation of treatment undergone to <br /> ensure the final limitations will be met by 10/1/2023," in accordance with Part I.E.2. of CDPS <br /> Permit # CO-0045161 for Colowyo Mine Outfall 010. During 2020, the sources to Outfall 010 were <br /> evaluated and a surface seep/spring (locally referred to as East Taylor Seep) was collected in a <br /> french drain system for monitoring and sampling. East Taylor Seep is the focus of the treatment <br /> processes, as any stormwater runoff is not anticipated to contain sufficient TDS or sulfate to cause <br /> issues with WET. <br /> This facility has been working with Stantec to design and conduct a bench-scale test of a passive <br /> biological sulfate reduction (BSR) methodology using East Taylor Seep water. The effluent <br /> generated from the bench-scale test was supplied to GEI Consultants laboratory for whole effluent <br /> toxicity (WET) testing to determine if the reductions in sulfate would effectively improve the water <br /> quality. Unfortunately, the bench-scale effluent did not meet the test objectives of passing WET <br /> potentially due to either: (1) excess TDS or (2) calcite oversaturation. Further analysis with pH <br /> adjustment softening were also ineffective at reducing the chronic toxicity. Therefore, BSR <br /> treatment is excluded from the treatment alternatives for this compliance schedule. <br /> The remaining treatment alternatives include membrane separation (reverse osmosis or <br /> nanofiltration), deep well injection, or a combination of these two technologies. The last option <br /> which has been considered is ettringite precipitation; however, it is still considered experimental. <br /> At this time, Tri-State and Colowyo are pursuing the deep well injection option. Stantec is <br /> collecting regional and representative information to support an EPA Region 8 Underground <br /> Injection Control Class 1 well permit application. We will provide an update to the Division on this <br /> permitting alternative to the Division with the next compliance schedule Status/Progress Report <br /> due 12/31/2021 . <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 /> 1 f2arbam 61341� 5/18/2021 <br /> ° n5D5E�d�94EB <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 June 2019 <br />