2008-08-25_REVISION - M1980244 (3)

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suggested that the overall design of the cover configuration be reviewed and consideration be given to placing a clayey sand/gravel layer on top of the compacted clay (maybe 1.5 to 2 feet thick) before placing the topsoil. Such a layer will further protect the integrity of the compacted clay layer and thereby reduce the infiltration in the long-term. 5. Conclusions I appreciate the opportunity to review portions of the permit for the Cresson project. Phase 5 of the VLF will increase the footprint as well as the height of the heap. Based on my review of the selected topics above I provide the following conclusions: • The materials that I reviewed and discussed with Adrian Brown and John Lupo clearly indicates the high level of professionalism and dedication of the designers. This is only possible with the ongoing support and encouragement of CC&V. It is clear that the high standards set by CC&V and the State of Colorado during the initial stages of the Cresson VLF design has been maintained and that the commitments to environmental protection have not changed. • The Phase 5 VLF design follows similar approaches as before and it is a seamless extension of the previous Phases. There was a concern expressed about the final heap height of 800 feet. While this is a significant heap height, my review shows that the design is based on an exhaustive set of evaluations that considered liner integrity and leachate collection. I conclude that the 800 feet high heap can be constructed and operated with an acceptable margin of safety. • The dynamic water balance is an improvement over the static water balances previously presented for the Cresson project as it allows for the inclusion of dynamic relationships between the various components. It also allows the inclusion of flexible operating conditions. • The design of the East Cresson overburden storage facility takes advantage of the present site conditions and its location on the Cripple Creek Diatreme. The design follows a very sound concept. I would suggest a rethink of the cover system to provide further reliability against potential erosion and cracking. It is suggested that the compacted clay layer be covered by 1.5 to 2 feet of clayey materials to better protect this layer. Thank you for the opportunity to complete this review. Please contact me if there are any questions or if I can provide further clarification. Sincerely, Dirk van Zyl, P.E., Ph.D. Consultant 7