2011-06-29_PERMIT FILE - C1981019 ‎(15)‎

• Permit No: C1981019
• IBM Index Class Name: Permit File
• Doc Date: 6/29/2011
• Doc Name: Attachment 1 to Attachment 12
• Section_Exhibit Name: Exhibit 07 East Taylor Pond 010A
• Media Type: D
• Archive: No

• EXHIBIT 7, ITEM 20, PART ET
EAST TAYLOR SEDIMENTATION POND
The location of the East Taylor Sedimentation Pond is presented on Map 41. The profiles
of the associated permanent tributary ditches are presented on Map 33. These tributary
ditches consist of East Taylor Ditch and Taylor Tributary Ditch, including its tributrary
ditches Taylor Ditch, East Taylor West and East Taylor East Tributary Ditches. Channel
design of the East Taylor Ditch, the Taylor Ditch, and the Taylor Tributary Ditch are
found respectively in Vol. 2C, Exhibits Exh. 7 -14I, Exh. 7 -14L and Exh. 7 -14C
respectively. Channel design of the East Taylor West Tributary Ditch and East Taylor
East Tributary Ditch are found in Volume 13, Exhibit 7, Item 20, Part E (Exh. 7 -20E).
Exh 7 -ET- Figures 1 and 2 included it his section show the layout of the drainage areas
and hydrologic conditions, primarily area, reclamation status, and consequent runoff
Curve Number for the inflow calculations for this sedimentation pond in the Active
Mining phase. Exh 7- ET- Figures 3 and 4 of this section show the component hydraulic
structures and networking for the Post Mining Phase.
To minimize the size of the structure needed to provide the requisite sedimentation
control, a variety of control features will be utilized. For the post- mining phase, four
temporary in- stream sedimentation traps (sumps) will be constructed. These will be
incised impoundments located at strategic locations along the main tributary streams to
the East Taylor Sedimentation Pond, and will be generally 2 acre feet in volume, operated
. in a normally dry condition by pumping them out after runoff events unless they drain
themselves naturally by seepage. They will be constructed concurrent with the earthwork
for the permanent channels at their respective locations once the active mining pit has
advanced beyond that point and final grading and topsoiling has been completed. The life
of each structure will therefore vary, dictated by the advance of the active pit and the
progress of port- mining regrading. The sediment traps will be approximately 10 feet
deep, with 2:1 or flatter side slopes, and surface area of approximately 0.4 acres each.
The following pages present the SEDCAD computer runs that were utilized to evaluate
the expected performance of the West Taylor Sedimentation Pond under the revised
mining and reclamation plan presented in TR -81, for two distinct mining phases, one
during active mining, and the other for the post- mining condition. The first is an
intermediate active mining condition wherein the reclaimed lands have been topsoiled
and seeded, but revegetation is not yet mature in all places and may not yet exist in others.
However, in this active mining scenario slightly more than half of the watershed is
intercepted by the active pit and does not report to the sedimentation pond. The other
phase, wherein reclamation is farther advanced but not yet fully mature throughout the
watershed, but the entire watershed is nevertheless reporting to the sedimentation pond
upon completion of the mining and reclamation activities.
Two design storms were evaluated for each case, a 10 year /24 hour storm to assess
expected effluent quality, and a 25 year /24 hour storm to assess the capacity of the
• emergency spillway to safely discharge the design storm.
Exh. 7 -ET -2 Revision Date: 12/31/10
Revision No.: TR -81