2014-03-07_PERMIT FILE - M2013070

• Permit No: M2013070
• IBM Index Class Name: PERMIT FILE
• Doc Date: 3/7/2014
• Doc Name: Response to Preliminary Adequacy Review
• From: Souder, Miller & Associated for Liberty Mining LLC
• To: DRMS
• Email Name: GRM
• Media Type: D
• Archive: No

As with the roadway analysis, the site drainage basins were determined and the areas contributing to each
basin was delineated and the parameters of each identified basin was then determined. The parameters
determined included the area of the basin, the flow length within the basin, and the average slope of the
basin from the top of the basin to the bottom of the4 basin. These parameters were in addition to the
earlier described parameters of soil types, rainfall, data, vegetation cover, runoff coefficient, etc. See
Figure 5- Drainage Basin Delineation Operation Area, for basin configurations.
Detention basins are sized based on the criteria provided in the Manual, i.e. "On -site detention is required
for all new development or redevelopment to limit 10 -year peak stormwater discharges to the l 0 -year
storm runoff based on pre- development conditions. In addition to the l0 -year detention, detention of the
100 -year storm event and release at the pre - development rates will be required." Therefore, based on
theses requirements, each pond's capacity will be of a sufficient size to contain the 100 -year, 24 -hour
event's runoff plus the runoff from a l0 -year, 24 -hour event, post development conditions, with releases
at a rate equal to or less than peak stormwater discharge for the l0 -year, 24 -hour storm event, pre -
development conditions. The 10 -year and the l 00 -year peak runoff rates, for developed conditions, are
provided in Table 3- Pear- Runoff Resulting from l0 -Year & 100- Year /24 -Hour Rainfall Events for
Operational Area.
Table 3
Peak Runoff Resulting from
10 -Wear & 100 - Year /24- 1-lour Rainfall Event
For Operational Site
(Post- Developed Conditions & Pre - Developed Conditions)
Drain
Basin
Length
Avg.
ToC,
10-
10-
100-
10-
Basin
Area,
of
Slope
Min
Year /24-
Year /24-
Year /24-
Year /24-
No.
Acre
Flow
of
(For
Hour Pre-
Hour Post-
Flour Pre-
Hour Post-
Path,
Basin,
Dev
Dev
Dev
Dev
Feet
%
Event)
Runoff Q,
Runoff Q,
Runoff Q,
Runoff Q,
CFS
CFS
CFS (Peak
CFS
(Peak
(Peak
Discharge)
(Peak
Discharge)
Discharge)
Discharge)
1 *
6.58
1600
14.84
19.8
4.30
(Offsit
e)
2*
11.53
1600
15.63
19.4
7.60
7.60
(Offsit
e)
l
1 0.234
100
9.00
10.60
0.20
0.30
0.9
0.90
2
0.276
240
3.30
11.30
0.30
0.30
1.0
1.0
3
0.320
240
6.24
11.30
0.30
0.30
1.2
1.2
4
0.190
150
13.33
10.80
1 0.20
0.20
0.7
0.7
* Flow from offsite drainage Basins l * and 2* is not generated from the Operations Area; however the
runoff from these areas do impact the Operations Area. Runoff from these areas will be managed with
retention ponds #1 and #5 on and/or adjacent to, and west of the Operations Site.
Because On -Site Basin #4 is for the portal to the mine and all flows from the basin flow toward the mine
entrance, it was assumed that the drainage water from sub -basin 4 would be collected and pumped to the
closest pond, i.e. Pond #2 for disposal. As a result, On -Site Basin #4 flows were added to the On -Site
Basin #2 flows to become the total flows into Pond #2. It should also be noted that the flows from On -Site
Basin #I are being directed to Pond #4; however, under current operation plans, the excavated waste rock
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