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concept. This cover is meant to reduce (not eliminate) infiltration of water and <br />also restrict air movement. <br />The present design (Figure 5 of the Adrian Brown report) calls for a 2 ft layer of <br />proof rolled clayey sand/gravel to be placed on top of the regarded overburden <br />material, followed by a 1 ft layer of compacted clayey sand and gravel and then <br />6 inches of growth medium. I have a concern about the thin cover on top of the <br />compacted clayey sand and gravel as the compacted clayey layer can be <br />subjected to erosion and cracking due to settlement of the underlying <br />overburden materials. Freeze-thaw cycles may further degrade this material. It is <br />suggested that the overall design of the cover configuration be reviewed and <br />consideration be given to placing a clayey sand/gravel layer on top of the <br />compacted clay (maybe 1.5 to 2 feet thick) before placing the topsoil. Such a <br />layer will further protect the integrity of the compacted clay. layer and thereby <br />reduce the infiltration in the long-term. <br />5. Conclusions <br />I appreciate the opportunity to review portions of the permit for the Cresson <br />project. Phase 5 of the VLF will increase the footprint as well as the height of the <br />heap. Based on my review of the selected topics above I provide the following <br />conclusions: <br />• The materials that I reviewed and discussed with Adrian Brown and John <br />Lupo clearly indicates the high level of professionalism and dedication of <br />the designers. This is only possible with the ongoing support and <br />encouragement of CC&V. It is clear that the high standards set by CC&V <br />and the State of Colorado during the initial stages of the Cresson VLF <br />design has been maintained and that the commitments to environmental <br />protection have not changed. <br />• The Phase 5 VLF design follows similar approaches as before and it is a <br />seamless extension of the previous Phases. There was a concern <br />expressed about the final heap height of 800 feet. While this is a <br />considerable heap height, my review shows that the design is based on an <br />exhaustive set of evaluations that considered liner integrity and leachate <br />collection. I conclude that the 800 feet high heap can be constructed and <br />operated with an acceptable margin of safety. <br />• The dynamic water balance is an improvement over the static water <br />balances previously presented for the Cresson project as it allows for the <br />inclusion of dynamic relationships between the various components. It <br />also allows the inclusion of flexible operating conditions. The dynamic <br />water balance was calibrated with site conditions in 2006 and is therefore <br />based on site specific experience. <br />• The design of the East Cresson overburden storage facility takes <br />advantage of the present site conditions and its location on the Cripple <br />8