2009-10-06_PERMIT FILE - C1980005 ‎(16)‎

• Permit No: C1980005
• IBM Index Class Name: Permit File
• Doc Date: 10/6/2009
• Doc Name: Postmining Drainage Control
• Section_Exhibit Name: Tab 07 Appendix 7-12
• Media Type: D
• Archive: No

Curve Number. CN
Curve numbers (CN) were approximated based on hydrologic soil type, as well as type and amount •
of ground cover. Curve numbers were obtained from Technical Release No. 55 (Soil Conservation
Service [SCS], 1986). SCC used the following curve number> for the following land use
i
conditions in hydrologic demonstrations at the Seneca H Mine.
I
Disturbed i
Soil Type: B
Ground Cover Type: Newly graded
Ground Cover: Bare
CN: 86
Undisturbed
Soil Type: C
Ground Cover Type: Sagebrush
Ground Cover: Fair
CN: 63
Undisturbed
Soil Type: D
Ground Cover Type: Sagebrush
Ground Cover: Fair
CN: 70
Reclaimed
Soil Type: B
Ground Cover Type: Herbaceous
Ground Cover: Good
CN: 62
The original postmine channel design modeling was completed in' 1986. Since that time the
graded spoil areas have been successfully revegetated. The rou{;h, undulating land surface,
typical of backfilled areas, is conducive to high infiltration, which combined with the
successful revegetation, limits the surface run-off from contributing watershed areas and
supports selection of lower curve number values. Consequently, alcurve number value of 86 is
no longer appropriate for hydrologic modeling at the Seneca H Mine.
The hydrologic modeling for Post Mine Channel SIIPM-1 (lower) was revised for TR-36. SCC
used a curve number value of 62 for the contributing watershed areas that have been
successfully revegetated. Hydrologic modeling demonstrations subsequent to TR-36 have also
used a curve number value of 62 far reclaimed and revegetated arias, except in instances were
the watershed has been re-disturbed. •
TR-41 7-12-4 Revised 04/07