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

stockpile, currently located east of the mine portal, will be extended over time, to the south along the east
perimeter. The extension of the stockpile will result in Pond #4 gradually being shifted to the north and
west as the stockpile is enlarged and extended south. To account for the potential phasing out of Pond #4,
Pond #5 has been increased in volume by an amount equivalent to the volume of Pond #4. Increasing the
volume of Pond #5 will provide for containment for surface runoff water generated from On -Site Basin
#1 as Pond #4 is eliminated. It is assumed that drainage water from this area would have to be temporarily
collected and pumped into Pond 5, as Pond #4 is at a lower elevation and gravity flow would not be
possible.
Sizing the detention ponds to contain the drainage water from the operations site and the intercepted
offsite drainage water employed the use of the Simplified Peak Flow Method of analysis to determine the
volume of runoff generated by the design storm, i.e. the 10 -year. 24 -hour plus the 100- year /24 -hour event.
The analytical parameters and the results of the calculations are presented in Table 4 -Pond Volume
Required to Contain l0 -Year and 100 - Year /24 -Hour Peak Runoff For Operational Area.
Table 4
Pond Volume Required to
Contain 10 -Year and 100- Year /24 -Hour Peak Runoff
For Operational Area (Developed Conditions)
Pond
No.
Drainage
Area,
Ac
Time
of
Con.
Hr
Weighted
CN
Unit Peak
Discharge
cfs /ac -in
24 -Hour
Rainfall
Depth,
in
Direct
Runoff,
in
Runoff
Volume
Ac -Ft /Cu Ft
1
9.18
0.33
74
1.33
3.34
1.10
0.74/32,245
2*
0.276 +0.19
0.19
78
1.80
3.34
1.35
0.08/3299
3
0.33
0.19
78
1.80
3.34
1.35
0.05/2265
4
0.23
0.16
78
1.80
3.34
1.35
0.03/1345
5
6.58
0.32
74
1.33
3.34
1.10
1.30/56,503
5*
6.81
0.32
.74
1.33
3.34
1.10
1.32/57,434
*(Note- Because Drainage Basin #4 is the entrance /portal to the mine and all flows from the basin flow
toward the mine entrance, it was assumed that the drainage water would be collected and pumped to the
closest pond, Pond #2 for disposal, via evaporation or percolation, or used to support underground mining
operations. Basin #4 flows were therefore added to Basin #2 flows to become the total flows into Pond
#2. In addition, because Pond #4 will eventually be phased out as a result of mine operation, the volume
of Pond #4 was added to pond #5 to address the runoff from this area after the Pond #4 is phased out.)
The maximum allowable discharges from the ponds, based on the Manual, are reported in Table 3- Peak
Runoff Resulting from 10 -Year & 1 00- Year /24 -Hour Rainfall Event For Operational Site (Post
Developed Conditions & Pre - Developed Conditions). Discharge and emergency over flow outlet structure
will be placed in each pond to control the discharge and maintain the maximum allowable flow from each
pond. In addition, the over flow structure will provide for the peak flow resulting from the 100 -year, 24-
hour event to be pasted through the structure in the event that a storm event greater than the l 00 -year
event is experienced. Overflow and emergency discharge pipes will be carried to the eastern limits of the
operational area where the water will be discharged. The discharge pipe will be designed with stilling
pools, rock check dams, and /or other means to remove energy from the water before continuing its flow
path to the Dolores River.
20