2007-10-22_PERMIT FILE - C1981014A ‎(5)‎

• Permit No: C1981014A
• IBM Index Class Name: Permit File
• Doc Date: 10/22/2007
• Section_Exhibit Name: 4.05 Hydrologic Balance
• Media Type: D
• Archive: Yes

greater than a 10-year, 24-hour storm event. These structures discharge
to riprapped aprons at the outflow in order to minimize potential erosion
and their el evation and discharge capacity are designed to provide a
freeboard of approximately 2.4 feet.
Discharge from sedimentation Pond 5 is controled by a principal spillway
consisting of a 24 inch diameter CMP and a 12 inch gated inlet set at an
invert elevation of 6,076.9 feet. The Pond 5 emergency spillway is a
riprapped trapezoidal channel with an invert elevation of 6083.5. The
combination of principal and emergency spillways provides for effective
discharge from Pond 5 while maintaining a freeboard of approximately 3.12
feet.
In all cases,. discharge structures for the sedimentation ponds are sized
based upon calculated flows for the design storm events. Invert
elevations for principal spillways are set above design sediment levels
and all ponds are designed with adequate freeboard consistent with
applicable regulatory requirements.
• With the exception of dead storage in the sedimentation ponds, which is
that water which may be retained between the design and the actual
sediment level and any water which may temporarily retained by controlled
discharge to match normal streamflow conditions, EFCI will not impound
water for any beneficial use in the sedimentation ponds. EFCI does
maintain two (2) separate ponds, Water Treatment and Recycle Pond No. 2,
and Freshwater Pond No. 3, for storage and treatment of water for
beneficial uses. These ponds are both lined ponds with no direct
discharge structures. Pond No. 2 operates in closed circuit with the
preparation plant process water circuit, while Pond No. 3 receives mine
dewatering discharge. Pond No. 3 has a gated discharge which flows to the
mine water supply line. This line allows transfer of make-up water to
Water Treatment and Recycle Pond No. 2 or discharge of any excess storage
which meets effluent water quality limitations through NPDES discharge
point 003. Additional discussion of the two (2) water storage
impoundments is presented in Section 2.05.3, Operation Alan - Permit Area,
under the subtitle, "Mine Facilities", and in Section 4.05.9, Permanent
and Temporary Impoundments.
I!
4.05-17 R Revised - September, 1991