2001-12-11_PERMIT FILE - C1981028A ‎(2)‎

• Permit No: C1981028A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: APPENDIX K SURFACE WATER/SEDIMENT CONTROL
• Media Type: D
• Archive: Yes

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19 October 1979
tor. Neil G. Jaquet
Water Resources Specialist
Adolph Coors Company
Golden, Colorado 80401
Re: Keenesburg Coal Mine
Sediment Pond
Dear Mr. Jaquet:
At your request in our meeting of 16 October 1979, we have undertaken the design
of sediment ponds and drainage ditches for the Adolph Coors Company surface coal
mine near Keenesburg, Colorado. The purpose of the sediment ponds and drainage
ditches is to collect stormrater runoff and sediment from the spoil piles, haul
roads, and work areas of the mine. We utilized the data which you gave to us
regarding the size and location of the sediment ponds and the location of the
drainage ditches.
HYDROLOGY
The design frequency of the sediment ponds volumes is the 24-hour precipitation
which has a return period of 10 years. In addition, storage is provided for sed-
iment. The size of the sediment pond is based upon the hydrologic work conducted
by Dr. D.6. McWhorter, Colorado State University, and is shown on the drawing which
you provided to us labeled "Mining Plan, Exhibit C" dated 23 March 1979 with the
latest revision of 19 July 1979. The design frequencies of the drainage ditches
and spillways of the sediment ponds are the storms with a return period of 10-
year and 25-year, respectively. The drainage areas contributing to the sediment
ponds are very small (less than 40 acres). The time of concentration of runoff
for these drainage areas is very short. Therefore, we determined that it was more
appropriate to use short-duration, high-intensity storms for designing the drain-
age ditches and spillways of the sediment ponds. The 30-minute intensity storms
were utilized in the Rational Formula to calculate the peak flow rates in the
drainage ditches and into the sediment ponds. The Rational Formula is defined
in the following equation:
Q = CIACf
l Cf is a frequency factor which equals 1.0 for the 10-year and 1.1 for the 25-year
~r frequency storms. The calculated peak runoff rates in the drainage ditches are
indicated on the attached drawings. i; I 1 ~.. ~~i)I ~,
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