2010-05-07_PERMIT FILE - C2009087 ‎(36)‎

• Permit No: C2009087
• IBM Index Class Name: Permit File
• Doc Date: 5/7/2010
• Doc Name: Permanent Impoundment PECOCO
• Section_Exhibit Name: Exhibit 2.05.3-E2 Appendix 2.05.3-E2.D Attachment 2.05.3-E2-D.1
• Media Type: D
• Archive: No

Hydraulics The hydrology of the watershed was analyzed utilizing the SEDCAD computer
program. SEDCAD is an enhanced PC version of the SEDIMOT II computer program. Tab 7,
Appendix 7 -6f, Addendum 7 -6f -A contains a listing and description of the SEDCAD input
variables. In performing this analysis, the characteristics of the minesite and
reclamation procedures along with on -site sediment control procedures were considered. A
complete listing of the SEDCAD inputs and outputs for the 10-year, and the 100-year
design storms are provided in Addendum 2. A design hydrology and sedimentology summary is
provided below.
Description
10 -Yr, 24-Hr
100 -Yr, 24 -Hr
Precipitation Depth
1.6 in.
2.6 in.
Inflow Runoff Volume
0.707 ac -ft
3.486 ac-ft
Pond Volume at Peak Stage
24.68 ac-ft
29.77 ac-ft
Peak Stage
6775.1
6777.4
Peak Inflow Rate
1.567 cfs
18.398 cfs
Peak Discharge Rate
0.475 cfs
6.353 cfs
t
Input consists of precipitation amount (inches), watershed area (acres), time of
concentration (hours), runoff curve number (CN), representative particle -size
distributions of soils in the area, sedimentology information, spillway information, etc.
The drainage area for this sediment pond was measured on a 1" =400' topographic snap (see
Exhibit 7 -7).
Curve Number and " k " Factor The curve numbers are based on information presented in
Table 7-6G-2. The "k" factors were determined information in Tab 9 and are shown on Table
7 -6G -3. The curve numbers and " k " factors were then "weighted" for the watershed, as
shown on Tables 7 -6C-4 and 7 -6G -5.
Precipitation and Storm Type The precipitation amounts at the Seneca it Mine permit area
for the 10-year, and 100 -year storms were obtained from NOAA Precipitation Frequency Atlas
of the Western States - Volume II - Colorado, 1973. A standara SCS type II r•*.orm was
utilized for each analysis.
40 -1 Unit Hvdrograph and Surface Con(iition the SEDCAD computer program provides thr e onl'
hydrograph shapes to choose from in determining the runoff rharactf!ri, tics of a . + ti , r , . hed.
the medium hvdrograph was used to generate the hydrograph.
NOR 006569