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Colorado Division of Reclamation, Mining and Safety <br />To: <br />Tabetha Lynch <br />From: <br />Zach Trujillo <br />CC: <br />Dan Hernandez <br />Date: <br />March 11, 2019 <br />Re: <br />Foidel Creek Thickener Tank <br />As requested, I have reviewed Foidel Creek Mine's (Foidel) proposed material associated <br />with the new thickener tank construction that were provided in response to the Division's <br />meeting with Foidel's representatives. Foidel has provided most of the material requested <br />in regards to the foundation design of the proposed thickener tank. Generally, the design <br />specifications of what was recommended in NWCC's engineering report have been met <br />in regards to the foundation and underdrain. However, when comparing the proposed <br />underdrain to the recommendations of NWCC, the magnitude of the underdrain appears <br />to have been more liberally designed. Only one lateral perforated drainpipe was installed <br />and no perimeter drainage system was included in the design. <br />It should be noted that NWCC's engineering report does leave the option open based on <br />the discretion of Foidel with the understanding of the potential consequences from <br />hydrostatic uplift. With that said, Foidel's proposed thickener tank underdrain design still <br />lies within the scope of what was recommended by NWCC. However, since the proposed <br />underdrain system appears to be a lesser design than what was recommended, Foidel <br />needs to provide additional information that ensures that the actual proposed design will <br />be sufficient in alleviating potential hydrostatic uplift on the thickener tank foundation. <br />Additionally, there still has been no provided documentation of the underdrain system <br />outside of proposed design drawings. Also, as discussed, please ensure all engineering <br />field reports are provided to the Division as they become available. This concludes my <br />review of the provided thickener tank foundation design for the Foidel Mine. If you have <br />any questions, feel free to contact me. <br />Sincerely, <br />Zach Trujillo <br />Environmental Protection Specialist <br />(303) 866-3567 ext. 8164 <br />