2008-12-16_REVISION - C1981022 (3)

Home Browse Search

Elk Creek Mine TR-60 2nd Adequacy Review 16 Dec 2008 Page 6 of 9 The Division has no further concerns. The time of concentration values used in the Sedcad designs for ditches BCCD-1 and BCCD-2 and for the Bear Creek culvert BCC-1 were revised in the November 26, 2008 submittal. 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. The Division has no further concerns. In the November 26, 2008 Sedcad design submittal, Oxbow revised the acreage for the laydown area and for the watershed area that is up-gradient of the laydown area. 15. The Sedcad designs use a permissivity, or flow rate, value of 14 gal/min/ft2 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. Permit text associated with the Sedcad designs state that a permissivity value of 5.6 gpm/ft2was used in the designs. However, as stated in comment number 7A above, the Division is not clear if that value was actually used in the Sedcad designs. 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. The Division has no further concerns. The November 26, 2008 submittal contained an appropriately revised page 2.05-37. 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. The Division has no further concerns. The currently approved discussion in the permit application also applies to the Bear Creek fan site area. In order to update the discussion, however, in the November 26, 2008 submittal, Oxbow provided revised permit text pages 2.05-89, 93a and 93b that include references to the Bear Creek fan site facility.