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COLORADO <br /> Division of Reclamation, <br /> Mining and Safety <br /> Department of Natural Resources <br /> Date: July 31, 2020 <br /> To: Robin Reilley <br /> CC: Jared Ebert and Jason Musick <br /> From: Zach Trujillo <br /> RE: Trapper Mine, DRMS File No. C-1981-010 <br /> Trapper Mine PR-09 Response Review Memo <br /> Robin, <br /> As requested I have reviewed Trapper Mine's (Trapper)PR-09 response(dated July 16, 2020)to the <br /> Division's adequacy letter regarding the associated engineering report submitted with PR-09. Trapper has <br /> provided additional information and discussions associated to the following comments in my original <br /> adequacy letter dated June 17, 2020: <br /> Division Comment 1: During a Division pre-site visit and inspection in November of 2018, it was <br /> observed that the A pit is partiallyfilled with compacted ash material. However, there was no discussion <br /> or inclusion of this material in the stability analysis. Please provide the Division with additional <br /> discussion about the ash material.found in the Apit and include it in the stability analysis performed by <br /> AAI. <br /> Trapper states that rationale behind not simulating the fly ash within the stability analysis is three-fold: <br /> 1. Simulations of spoil backfill in all three analyzed pits (L-Pit,F-Pit and Ash-Pit) kept the analysis <br /> simple and easy to compare. <br /> 2. The fly ash matrix is anticipated to possess greater overall strength compared to spoils, making <br /> AA's analysis conservative from the global stability perspective. <br /> 3. Detailed depositional history of fly ash deposit is unavailable, as some of the fly ash backfill has <br /> been deposited as-received, whereas fly ash along the bottom of deposit have been mixed with <br /> spoils. <br /> Of the three rationales provided, Trapper comment 2 and 3 (above)were mainly reviewed as they provide <br /> substance that address the Division's comment and assist in the subsequent review. In Trapper's response, <br /> they state that the overall strength properties of the fly ash is greater than the onsite spoil based on <br /> material testing. In addition, chemical analysis of the fly ash has determined that approximately 8% of the <br /> Trapper Mine PR-09 Response Memo July 31,2020 <br /> of C�lo <br /> 1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us I * * <br /> Jared S. Polis, Governor I Dan Gibbs, Executive Director I Virginia Brannon, Director *+► * <br />