APPCOR12923

• Permit No: C1981021
• IBM Index Class Name: Application Correspondence
• Doc Date: 4/14/1981
• Doc Name: PRELIMINARY ADEQUACY REVIEW BOURG STRIP FILE C-021-81
• From: MLR
• To: FLATIRON COMPANIES
• Media Type: D
• Archive: No

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U. Mnnlc Pascoe. Ev rcolrvc Uvenor
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423 Centennial Building, 1313 Sherman Street
Denver, Colorado 60203 Tel. [phone]
David C. Shelton
Director
MEMORANDUM
T0: Mike Savage
FROM: R.A. Domingue
RE: Walden Coal Company's Bourg Strip Application
File No. C-021-81
Hydrologic Concerns:
1. Maps: The area of several of the watersheds feeding sediment ponds
on the site extends beyond the area covered in the maps provided by W.C.C.
During the life of the permit the contributing area to each of the ponds
may change and new structures are to be built at various eras of the
permit period. Several of the watersheds delineated on plate 17 conflict
with the apparent natural drainage.
WCC must:
a. provide a map showing the entire areal extent of watersheds
contributing to their sediment ponds and collection ditches;
b. provide maps showing contributing areas and proposed structures
for each mining stage when the sediment control system is changing;
c. delineate watersheds according to topography existing at the time.
2. USLE Calculations: The value of 0.05 given to the CP(Z) factor for
undisturbed areas is very low and unverifiable with data provided.
Using vegetative cover figures given in the vegetative studies appendix
I was unable to justify the figure. WCC must explain how they arrived
at this value.
3. Water Storage: In the section on Water Information (Section I) WCC
describes the use of sediment pond H as a water supply reservoir. The
storage volume is given as 1.66 Ac ft. WCC uses a simple routing
technique to insure inflow volume to pond C will not exceed the spillway
capacity during the 25 year event. However, it is apparent that the process
ignores the storage of the 1.66 AC ft. mentioned above. WCC must provide
a stage area chart which is highly legible for pond H and route the 25
yr. flood volume through the pond with the pond storing 100Y of the sedi-
ment volume and all of the aforementioned 1.66 Ac. ft. of water storage.
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