2010-01-22_REVISION - C1981008 (2)

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C-1981-008 PR-06 PAR 22-Jan-2010 Page 9 of 26 duplicates of adjacent pages. Please review these pages, and remove any that are truly blank or redundant. Rule 2.05.3(4) - Ponds, impoundments, other treatment facilities and diversions 22. WFC submitted a re-design for Pond 01 1 and new As-built Certification. WFC indicates on page 2.05.3(3)-14-2 that the drainage basins in both pre mine and post mine situations have changed. The pre mine drainage basin should remain constant. Please clarify and explain how the pre mine drainage basin situation has changed. 23. Pond 011 is being re-designed because it will receive a greater drainage area than originally designed due to the decision by WFC to eliminate Pond 010. There are no proposed changes to spillway configurations and only design input parameters will be modified. Both the Engineering and Hydrologic Design and the As-Built SEDCAD demonstration were re- submitted along with a new Map 2.05.3(3)-17 As-Built Certification. The revised application materials presented for design and as built configuration are consistent. Only one minor error was noted. The Stage Storage Curve on the new Pond 011, As Built shows an incorrect principal spillway elevation as compared to the SEDCAD runs and the approved As-Built Certification. Please check this elevation and make the necessary correction to Map 2.053(3) -17. 24. The revised text on page 2.05.3(3)-12-3 does not clearly explain why a revised pond design is necessary for Pond 012. In the third paragraph WFC states that "the post mine drainage area is larger than the pre-mine", but also in that same paragraph states "the pre-mine drainage area is 55.1 acres while the post mine area is 38.1 acres". This is inconsistent and it is unclear if the as built pond is sufficient to handle the revised drainage area. If the As- Built Certification is correct and no pond configuration changes are proposed then a new design would be unnecessary. Further, numerous inconsistencies were identified with the new Pond 012 design information that was submitted with PR-6. The SEDCAD demonstrations for the l OYr and 25 Yr designs show fatal flaws in that the spillway elevations and dam height do not match the approved Pond 012 As-Built (Map 2.05.3(3)-12-4). For example, the top of the dam on the revised SEDCAD runs is 5610' and the top of embankment is 5613" on the As-Built. The top of riser is 5611' on the As-Built (which would place the invert of the spillway one foot above the top of dam as proposed with PR-6. In the new revised pond description (see page 2.05.3(3)-12-4) the Emergency Spillway is shown at an elevation of 5609'which also is not consistent with other information. There are no Emergency Spillway elevations shown in the new SEDCAD demonstrations for either the l OYr or 25 Yr events. This information is required for the 25Yr-event to show that the pond meets the requirements of 4.05.9 (7) (d).