2011-12-14_REVISION - M2005050

• Permit No: M2005050
• IBM Index Class Name: REVISION
• Doc Date: 12/14/2011
• Doc Name: Stormwater Management Review TR-02
• From: DRMS
• To: Rimrock Exploration
• Type & Sequence: TR2
• Email Name: GRM
• Media Type: D
• Archive: No

DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St, Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
To: Russ Means
From: Tim Cazier, P.E.
Date: December 6, 2011
MEMORANDUM
STATE OF COLORADO
Re: J Birds Mine Surface Water Management — Stormwater Comments, Permit
No. M- 2005 -050 / TR -02
Mined Land Reclamation
COLORADO
D I V I S I O N O F
RECLAMATION
MINING
— &—
SAFETY
John W. Hickenlooper
Govemor
Mike King
Executive Director
Loretta Pineda
Director
The Division of Reclamation, Mining and Safety (DRMS) engineering staff has reviewed the
October/November, 2011 responses to the DRMS September 26, 2011 spillway and hydrology
comments for the J Birds Mine. The following comments are posed to ensure adequate
engineering analyses and design practices are implemented to eliminate or reduce to the extent
practical the disturbance to the hydrologic balance expected by the mining operation with respect
to water quality and quantity in accordance with Rules 3.1.6(1), 6.4.21(10), and 7.3.1
Hydrology Comments:
1. There appears to be an error in the Win TR -55 runoff depth. DRMS has duplicated the
error using the Win TR -55 software. The runoff depth for basin U -1 (assuming a CN =
86 & P = 1.97 inches) should be 0.826 inches, not 0.506 inches. Correcting this
software output error, yields a 10 -year storm runoff volume of 2,187 cu -ft, thereby
making the 1,396 cu -ft design volume too small. There is a similar error for the runoff
depth from basin L -1. It should be 0.773 inches, not 0.748 inches. However, the increase
in runoff volume from 8,146 cu -ft to 8,415 feet is capable of being stored in the 8,528 cu-
ft design volume. Please increase the storage capacity of the Upper Pond to store the
estimated runoff volume of 2,187 cu -ft.
2. Based on our understanding of the design presented on the 10/25/11 "Upper Pond
Details" drawing and referencing the 8/27/11 "Revised Drainage" map, DRMS concludes
that discharge from the Upper Pond spillway will make its way to the Lower Pond (if no
other way than flowing parallel to the silt fence identified on the "Revised Drainage"
map. The spillway in the Lower Pond should include the 100 -year design peak discharge
(routed appropriately) from the Upper Pond. Please revise the design flow for the Lower
Pond spillway as appropriate.
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Denver • Grand Junction • Durango Active and Inactive Mines