1987-12-01_PERMIT FILE - C1981017 ‎(190)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Mine Drainage treatment System
• Section_Exhibit Name: Chapter IV Appendix IV-C-3
• Media Type: D
• Archive: No

July 14 , 1986
Ms. Candace Thompson
Mined Land Reclamation
1313 Sherman St . , Room 423
Denver, CO 80203
RE : Technical Revision - Savage Pond Permit, C-017-81
Dear Candace,
In reviewing • my calculations for the Savage Pond removal
request, I noticed that a mistake had indeed been made in
determining the peak flows for a ten year and 25 year event.
This error was due to the usage of wrong slope interpolation '
factors . After recalculating, I have come up with the fol-
lowing values , which agree with yours , and should supersede
the values listed in our technical revision dated June 19 ,
1986 .
4
AREA DISTURBED CN SLOPE ';SLOPE PEAK DISCHARGE j
ACREAGE INTERPOLATION TABLE S-lA (SCS) _
FACTOR cfs in runoff r
1 11.63 93 11 .1 .96 20.0 z
lA 7.23 75 8.0 .92 12.5
2 3 .49 90 6.5 1 .06 5. 7 µ
- IN RUNOFF TABLE S-3 (SCS ) PEAK DISCHARGE (cfs )
(cont. ) 10 yr. 24 hr. 25 yr. 24 hr. 10 yr. 24 hr. 25 yr. 24 hr.
1.22 1 .50 23 .4 28.8
. 33 .48 3.8 5 .5
1.01 1.27 6 .1 - 7. 7
33 .3 7_F's Total: ,42 .0 cfs
The existing spillway at the Savage Pond is a tee-shaped 18"
dia. CMP set on a 10% grade. This culvert can handle a flow
of 18 cfs . This is more than enough to handle the 7. 7 cfs of
flow generated during a 25 yr./24 hr. event in Area 2.
The existing primary spillways on the four ponds known as
Discharge Point 001 are 18" dia. CMP set on a 10% slope.
These culverts can also handle a flow of 18 cfs . The emer-
gency spillways are ten ft. wide by two -ft. deep trapazoidal
channels lined with riprap. The enclosed calculations show
that these channels can handle a 25 yr./24 hr. event.
If you have any more questions concerning this technical
revision, please feel free to contact me here at the mine .
Sincerely
Scott Jones , Environmental Engr.
enc.
SJ/sj