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`III IIIIIIIIIIIII III 999 Mathews, Dan From: Mathews, Dan Sent: Monday, November 06, 2000 10:48 AM To: Berry, David Cc: Boulay, Mike; Stark, Jim Subject: roadside tr-32 Hi Dave. I fed-exed two copies of the Powderhorn TR-32 adq. response submittal on Saturday, you should have it shortly if not already. A couple things I have noticed about the submittal: The proposed upper diversion is significantly oversized its entire length, and is excavated a minimum of 10 feet below top of refuse, with depth increasing with distance from upper end along each wing of the ditch. The ditch is also significantly steeper (2.5% grade) than the existing ditch, which should significantly reduce the need for maintenance. I would be inclined to accept this design concept. There would still appear to be the possibility that a massive flood would bring down boulders and debris from the cliffs, blocking the ditch, but given the location of the pile, and regulatory considerations regarding coal refuse drainage designs, there probably is nothing that practicably could be done to ensure the geomorphic stability of the pile in perpetuity. The dip section design provided depicts concrete "cut-off' walls at the downstream end of the dip section. I was pretty sure that BLM recommended upstream "wing walls", and that is what you specified in you memo of September 21. I donY know what Stovers reasoning is. A couple changes appear to be needed on amended Exhibit 53. First, there is no Section J-J, which is the cross section for the CRDA-2 perimeter containment ditches. This section needs to be added to the Exhibit. Second, Section D-D which is a section through CBA (borrow area) #2 needs to be amended. The blue line topo is mislabeled "Final Ground"; I believe it is existing topography. The topsoil pile depicted would only be necessary if CRDA-3 is constructed. CRDA-3 is no longer approved, so the pile should not be depicted. Once we have finalized designs that we are prepared to approve, we should have Jim Stark do a cost estimate, to incorporate costs associated with the new CRDA upper diversion construction and riprap installation, and the structural work associated with the modified dip section. We can probably safely assume that excavation of the sediment and removal of the rock structures from the Coal Creek channel would be a wash, since the excavated materials would otherwise have been obtained from CBA-2 for use on CRDA-2 reclamation. Do you agree?