2008-05-29_REVISION - M1977285

• Permit No: M1977285
• IBM Index Class Name: REVISION
• Doc Date: 5/29/2008
• Doc Name: Drainage report for Sunday Mines Group
• From: Denison Mines
• To: DRMS
• Type & Sequence: AD1
• Email Name: RCO
• Media Type: D
• Archive: No

Section 2
Topaz Mine
Qloo - - I I8.4(A)0.715
where:
Q100 =100-year peak flow in cubic feet per second (cfs)
A = drainage area in square miles
The standard error of the above regression equation is approximately 78 percent. If
the data are assumed to be normally distributed, the standard error means the
difference between the mean and upper (or lower) 68 percent confidence limits. Due
to the error associated with the regression equation, CDM increased the calculated
discharge from the.flood-frequency equation by the standard error (78 percent). CDM
used the increased discharge as the design peak discharge. Table 2-1 presents Tetra
Tech's and CDM's estimated 100-year peak discharges for each basin of the Topaz
Mine.
We 2-1 1 00- ear Peak Dischar es f or the Topaz Mine Basins
r e
h
di
a
sc
00-year peak
Area Tetra Tech CDM increased by SE
(cfs)
Basin ac s -mi (cfs) (cfs)
26
3 5.79
1 4.20 0.00656 3.01 .
239 4.25
2 2.72 0.00425 1.99 32
3 6.45
3 4.88 0.00763 6.85 ::J
33
2 4.15
4 2.63 0.00411 2.39 .
CDM's estimate of the 100-year peak discharges is greater than the discharges
determined by Tetra Tech for all basins with the exception of Basin 3. While the
difference is not considerable, CDM used the USGS approach as a conservative
measure (e.g. larger discharges) to design the storm water drainage structures.
2.4 Surface Water Control Structure Design
Tetra Tech designed two diversion channels (Channels 1 and 2) to catch offsite run-on
from Basin 1 and Basin 2 and route flows around the surface mine facilities to the
ephemeral drainages. Storm water runoff from Basin 3 will be captured and detained
by a proposed earthen berm along the crest of the waste rock area (WRA). Storm
water runoff from Basin 4 will be captured in a berm and routed to a catchment basin.
2.4.1 Channel Design
Channels 1 and 2 were designed to convey the 25-year peak discharge from Basin 1
and Basin 2 to the two ephemeral drainages. Tetra Tech used Manning's equation to
calculate the flow velocity and depth in Channels 1 and 2 based on the values found
in Table 2-2. CDM reviewed the design by Tetra Tech to determine if Channels 1
and 2 have adequate capacity to convey the 100-year discharges listed in Table 2-1.
F?
2-2
0:\64988 - Denison\Task Order 1 - Sunday Mines Drainage StudyV2eporl\Final Report\Final Sunday Mines Drainage Report_052208.doc