APPCOR10654

• Permit No: C1981039
• IBM Index Class Name: Application Correspondence
• Doc Date: 8/21/1984
• Doc Name: PIT 1 SEDIMENT CONTROL GRASSY GAP MINE
• From: MLRD
• To: C THOMPSON
• Media Type: D
• Archive: No

iii iiniiiiiiiii iii
DEPARTMENT OF NATURAL RESOURCES
David H. Getchea Executive Director
MINED LAND RECLAMATION DIVISION
DAVID C. SHELTON, Director
Richard D. Lamm
Governor
MEMORANDUM
T0: D. Mathews
FROM: C. Thompson (~ ~
DATE: August 21, 1984
RE: Pit No. 1 Sediment Control - Grassy Gap Mine
1. The 25 year, 24 hour peak runoff has been underestimated. When accounting
for the equivalent drainage shape factor, Figure S-lA should be entered with
the equivalent drainage area not the real drainage area.
2. Calculations should be submitted showing appropriate sizing of the
emergency spillway for the pond and appropriate riprap sizing to protect from
erosion for the 25 year event.
3. The applicant must state in the revision the contour furrow spacing that
will be used.
4. Calculations should be submitted showing sizing of the contour furrows
required to contain the 10 year event and sediment yield.
5. The cover (C) factor used for the reclaimed area seems low based on
communication with Mike Savage. He and Dan Mathews surveyed Pit No. 1 for
cover and the average cover of grass and litter was found to be 52%. This
would give a C factor of 0.07. Therefore, further justification is needed of
the C factor used for the revision of 0.02.
6. Numerous typographic error are present in the calculations submitted.
These typos have made review of the submittal difficult.
CT/baw
Doc. No. 3631
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. [phone]