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Elk Creek Mine TR-60 Adequacy Review 10 Nov 2008 Page 3 of 5 an area just to the north of the lay down area that will be disturbed. However, this area does not appear to be designated as disturbed on Map 2.05-E1-BCA2. Please explain. 13. In the TR-60 Sedcad designs for the ditches and for the Bear Creek culvert, the horizontal distances used in deriving the time of concentration values for each subwatershed appear to be considerably longer than the hydrologic now path length of their corresponding subwatersheds. For instance, in the Sedcad runs for ditch BCCD-2 and the side postmine channel, the total horizontal distance used for subwatershed area 1 amounts to 24,770 feet, even though the drainage area amounts to only 53.1 acres and, referring to Map 2.05-El-BCA2, the longest hydrologic flow path appears to be no more than 3,500 feet. In another example, for the Bear Creek culvert, the horizontal distances given for subwatershed area 1 add up to 41,383 feet. However, referring to Map 2.05-E1-BCA2 again, the longest hydrologic flow path for the drainage area appears to be less than 30,000 feet in length. Please explain. 14. The summary sheet for the laydown area lists the disturbed area as being 0.13 acres in size. The Sedcad design for the laydown area lists the area to be 0.4 acres. However, referring to Map 2.05-E1-BCA2, the runoff area appears to be much larger since there is no upland diversion ditch for the laydown area. Please explain or revise the Sedcad designs and text for the laydown area accordingly. 15. The Sedcad designs use a permissivity, or flow rate, value of 14 gal/min/ft' for straw bales. As had been discussed previously in Minor Revision No. 64 back in 2002, the Division and Oxbow's consultant disagreed as to the authenticity of that value. Although the value appears in a published work, the value was corrected in a later publication by two of the three original authors. The Division agreed to the use of the value in MR-64 with a disclaimer added to the permit text. Please either justify Oxbow's position in using this value, revise the straw bale permissivity value accordingly in the Sedcad designs and text or omit from TR-60 the proposed use of straw bales as sediment control. 16. In the last paragraph on revised page 2.05-37, it is stated that small area exemptions are identified on Map 2.05-M4. Please add to that sentence that small area exemptions for the Bear Creek fan site are identified on Map 2.05-E1-BCA2. 17. Please add a discussion to Section 2.05.6(3) of the permit application on the probable hydrologic consequences of the Bear Creek fan site on Bear Creek. Rule 4.05.18 - Stream Buffer Zones 18. The drainage area of Bear Creek appears to be greater than one square mile. Prior to issuing a proposed decision to approve TR-60, the Division will be required to