2011-08-29_REVISION - M1986002 ‎(13)‎

• Permit No: M1986002
• IBM Index Class Name: REVISION
• Doc Date: 8/29/2011
• Doc Name: Amendment to CN-01
• From: Greg Lewicki and Associates
• To: DRMS
• Type & Sequence: CN1
• Email Name: THM
• Media Type: D
• Archive: No

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STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY `I
Departrnent of Natural Resources
COLO RADO
1313 Sherman SL, Room 215 C O L O 0 N o r
Denver, Colorado 80203 RECLAMATION
1
Phone: [phone]
FAX [phone] SAFETY
MEMORANDUM him W. " doper
Governor
Muw ram
Emu** Okada
Loft moot
To: Travis Marshall for
From: Tim Cazier, P.E. /rC
Date: June 23, 2011
Re: Craig Ranch Pit — General Stormwater Comments, Permit No. M -1986 -002 /
CN -01
The Division of Reclamation, Mining and Safety (Division) engineering staff has completed its
review of the stormwater management aspects of the subject project.
The Craig Ranch Pit is proposed in an area characterized by an and environment with mild to
steep gradients sloping north towards the Gunnison River. 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 and 6.3.3(g)
and (i) of the Minerals Rules and Regulations of the Colorado Mined Land Reclamation Board
for the Extraction of Construction Materials.
1. Page D -5, fourth paragraph: This paragraph describes collection ditches to be placed on
the northern most portion of the mining area and states these ditches will be placed "to
ensure that no stormwater is allowed to leave the site during mining." This statement
implies the collection ditches are designed to convey the probable maximum precipitation
(PMP) event. However, no sizing information is included in the exhibits.
a. The Applicant shall provide sufficient information (e.g., hydrologic analyses — see
Comment No. 10 and hydraulic computations — sec Comment No. 11) for the
Division to evaluate the collector ditch sizing in accordance with Rule 6.3.3(g).
Please note because these ditches are to be part of the post mine land use, the
Division recommends they be sized to convey runoff from the 100 -year, 24 -hour
storm event, not the PMP. Also note Comment No. 5 below.
b. The applicant should revise the fourth paragraph on page D -5 to state what
specific design storm the collection ditches are designed to control.
2. Map C -2 is referenced on page D -5, fourth paragraph. The collection ditches in Mining
Area 1 appear to drain toward four ponds labeled as "Wash Ponds ". On Map F, the two
northern ponds are labeled "Sediment Ponds ".
Once of
Mined Land Reclamation
Office of
Denver • Grand Junction • Durango Active and Inactive Mines