2008-09-08_REVISION - C1994082 - Laserfiche WebLink

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Technical Revision 37 Response to Adequacy Comments • Page 2 Part I of the As-Built Report was included in the PAP to support the retention of Pond 010 as a permanent postmine feature. Per Rule 4.05.9(2)(c)(ii), the emergency spillway needs to safely pass the 25-year, 24-hour event. The SEDCAD modeling in Part I of the As-Built Report shows that the existing, and conservatively designed and constructed, emergency spillway is more than adequate to convey the peak runoff from a design storm of this magnitude. Part II covers the constructed configuration and includes the 100-year, 24-hour demonstration; therefore, it is unnecessary to include the 100-year, 24-hour event in Part I of the As-Built Report. 2. Pond 011 As-Built Report Introduction page references Pond 010 instead of Pond 011. Please revise this page according. Response: The incorrect reference to Pond 010 has been corrected in Attachment 134A. 3. The subwatershed hydrology detail including peak discharges submitted with the revised Pond 011 As-Built Report are not consistent with the existingpostmine channel designs for YPM-9, YPM-12, and YPM-13 which flow to Pond 011. According to our records YPM-9 was designed in 1998, and YPM-12 and 13 were designed in 2003. The hydrology details for the channel system should be consistent with the input to the model for the Pond 011 As-Built re port. Likewise the existing channel design for YPM-12 which contains information for Pond O 11A appears to have inaccurate information regarding structure details including spillway elevations for Pond 0 11A. Please submit a revised Channel System design for YPM-9, 13, Pond 011A and YPM-12. Please revise the YPM-12 design according so that it matches the existing As-Built information for Pond 011A (Exhibit 13-5C). Response: The Division's records regarding the chronology of the channel designs for YPM-9, 12 and 13 are correct. Please note the 1998 and 2003 material (currently approved and part of the PAP) are des' s, not as-builts. The designs are representative of the minimum configuration needed to convey the estimated runoff from a proposed topography. • The hydrology details contained in the TR-37 demonstrations are representative of current conditions (e.g., fully reclaimed and revegetated, with five plus years of growth) and, the estimated runoff is based upon actual as-built topography. This proposed topography versus actual topography scenario results in a slight difference between the "proposed" and "as-built" hydrology details and, consequently runoff estimations are not the same. Unfortunately, neither SCC nor the Division recognized that "designs" and "as-built" were -different earlier in the permit revision process. If SCC had recognized this issue earlier it would have proposed to leave the original "designs" in Attachment 13-12 and, prepared as-built demonstrations (which would have superseded the design demonstrations) as part of the bond release process. To assure consistency with material currently in the PAP (e.g., the revised "designs" found in Attachment 13-12 prepared as part of TR-36 and TR-37, as well as, the inputs that were used for pond permanent feature demonstrations) the channel demonstrations for YPM-9, 12 and 13 have been revised. The hydrology details used in the TR-37 demonstrations are representative of actual conditions as of September 2007 (e.g., "as-builts). In addition, the Pond 011A As-Built Report (Attachment 13-19) has been revised to reflect actual conditions (as of September 2007) and, to assure it is also consistent with the YPM-9 and 13 inputs. 4. The Postmining channel design SEDCAD4 results (Appendix 13-12.3) was last revised 8107 with TR-36. The table of contents for this appendix (page 13-12.34) does not indicate a design for YPM-12 and YPM-13. Please update page 13-12.3-i. Response: A revised TOC was prepared for the TR-37 submittal. Based on this comment, it appears that page 13- 12.3-i was inadvertently left out of the March 2008 package submitted to the Division. SCC has updated the TOC for this response package to reflect the Division's request that SCC remove postmine channel designs associated with Pond 012 Option 1, as well as the addition of YPM-24. The TOC includes reference to both YPM-12 and YPM-13. 5. On page 1 of revised Attachment 13-12, SCC states that Pond 012A would be used " :.. if Pond 012 continues to lose capacity from . upslope instability previousy experienced ad acent to the pond area." `7f the area stabilizes then Pond 012A will not be constructed" It does not appear that the area isgoing to stabihZegiven recent significant slide activity immediately adjacent to Pond 012. The