2011-03-25_PERMIT FILE - C1981019A ‎(8)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 3/25/2011
• Doc Name: East Pit Recl Sequencing & Ditch Designs for Prospect Ditch, N Tribut E Pit Ditch & Final E Pit Ditc
• Section_Exhibit Name: Exhibit 07 Item 14 Appendix Exh7-14R
• Media Type: D
• Archive: Yes

EXHIBIT 7, ITEM 14, PART R — EAST PIT RECLAMATION SEQUENCING
AND DITCH DESIGNS FOR PROSPECT DITCH, NORTH TRIBUTARY EAST
PIT DITCH AND FINAL EAST PIT DITCH
The progression of mining in the East Pit is generally from east to west, climbing upward
in topography and moving away from the Prospect Pond. As a result, the watershed
tributary to the pond in the early years is intercepted by the inactive East Pit, and grows
as backfilling and grading advance westerly. The progress of the backfilling /grading
activity is presented on Map 29. The entire watershed tributary to Prospect Pond is
ultimately 711.1 acres. As of 2010, approximately 550.7 acres of that total is tributary to
the pond, with the remainder being intercepted by the East Pit. The 550.7 acres that
drains to Prospect Pond includes 322.3 acres of disturbed land and 228.4 acres of
undisturbed land. About half of this total, mostly undisturbed land in Section 15 and the
reclaimed land from the Section 16 pit, arrives at the pond by way of the South
Collection Ditch in the southern half of Section 15. The remainder of the watershed is
intercepted by the East Pit and various diversion ditches described in more detail below.
As backfilling progresses westward and up the hill, the tributary area to Prospect Pond
will grow until ultimately the entire 711.1 acres of reclaimed and undisturbed watershed
reports to the pond. As the watershed area changes with the westerly advancement of the
pit, so does the Curve Number for portions of the watershed in various stages of
reclamation. The determination of the worst case condition with respect to ditch design
and sediment pond performance is therefore not obvious. Accordingly, several time
frames were separately evaluated, each representing a further progression of the mining
activity to the west, as described sequentially on Figures Exh.7- 14R -1/2, 7- 14R -3/4 and
7- 14R -5/6. The figures are presented in pairs, one with hatching to describe the
reclamation status, and the other providing acreages and topography.
Ditch Design, overview
As the reclamation advances to the west, three permanent ditches will be constructed to
convey runoff form the disturbed and reclaimed lands southeasterly toward the Prospect
sedimentation pond. From north to south these ditches are Prospect Ditch, North
Tributary East Pit Ditch, and Final East Pit Ditch. Although the total drainage area
tributary to Prospect Pond is 711.1 acres, the largest watershed for any single ditch is
153.3 acres, that being Prospect Ditch just before it releases into undisturbed lands. The
ditches are therefore all designed for the 10 year -24 hour storm in accordance with Rule
4.05.3.
The two southern ditches are rip rap lined for their entire length, while the re- established
Prospect Ditch on disturbed acreage is rip -rap lined only in its lowermost reach. The
upper reaches of Prospect Ditch are at flatter slopes and are adequately protected with a
vegetative lining as described in more detail below.
Alignment and slopes in the ditches are presented on Maps 41 and 33 respectively. All
ditches are trapezoidal with a bottom width of 12 feet and side slopes at 2H:1 V, and a
Exh. 7 -14R -1
Revision Date: 11/3/10
Revision No. TR -87