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<br />Colorado Division of Reclamation, Mining and Safety <br />To: Tabetha Lynch <br />From: Zach Trujillo <br />CC: Dan Hernandez <br />Date: February 27, 2019 <br />Re: Foidel Creek Thickener Tank <br /> <br />As requested, I have reviewed Foidel Creek Mine’s (Foidel) provided material associated <br />with the new thickener tank construction. As you are aware, it appears that Foidel has <br />opted to go with the “Alternate Foundation Recommendation” provided in the <br />engineering report, Subsoil and Foundation Investigation, Wash Plant – Thickener Tank, <br />Twenty Mile Coal Mine, Routt County Colorado (the Report), by North West Colorado <br />Consultants, Inc. (NWCC). After reviewing the alternative foundation recommendation, I <br />have no concerns regarding the associated design for the thickener tank. However, with <br />the presence of expansive soils and high elevations of groundwater, the potential for <br />differential settlement issues and/or hydrostatic uplift exists which could negatively affect <br />the foundation to the thickener tank. This concern is also noted in the Report. Given the <br />site’s characteristics, it is imperative that the construction of the foundation be completed <br />as stated in the Report. <br />Along with the Report, Foidel included five field reports of the foundation construction <br />performed by NWCC dating from January 8 – 22, 2019. Of these reports, NWCC noted <br />issues due to water saturation or excess moisture content of the compacted fill material in <br />three of those five reports. In one of the reports, NWCC required the excavation and re- <br />compaction of the fill material. Additionally, in field report no. 5, NWCC states the <br />moisture content of the fill material exceeds the acceptable range necessary for optimal <br />compaction. However, no follow-up field report by NWCC regarding this issue has been <br />provided to the Division. At this point, it is unsure on whether Foidel addressed the <br />concerns stated in NWCC’s field report no. 5. <br />After reviewing the NWCC field reports as well as the Report, Foidel has not provided <br />any indication of installation of the recommended underdrain system. As the Report <br />reads, it appears that the underdrain system is independent of either of foundation <br />recommendations and should have been installed. Again, it is imperative that the <br />construction of the foundation be completed as recommended in the Report which also <br />includes the installation of the underdrain system. As stated in NWCC’s Report, “The <br />lower level of the tank must be protected from ground intrusion by an underdrain system <br />and the structure must be designed to resist hydrostatic uplift as discussed above.