PERMFILE60793

• Permit No: M2005045
• IBM Index Class Name: Permit File
• Doc Date: 1/25/2006
• Doc Name: Proposed Detention Pond
• From: DMG kap
• To: DMG
• Media Type: D
• Archive: No

STATE OF COLORADO
~~iDIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman 5[., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
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! COLORADO
DIVISION O F
MINERALS
GEOLOGY
0.ECLAMATION•MINING
SAFETY~SC IENCE
RECEtVE®
Bill Owens
DATE: f/~January 25, 2006 ' ~.0 ~ ~ c°~ern°r
• Russell George

IJ~ TO:
KatePickford Executive Director
plr~iaoolMiemalseedBoobRlt
Ronald W. Cattany
Division Director
FROM: Allen Sorenson Natural Resource Trustee
RE: ~~Proposed Detention Pond, Rock Dog #1 Pit, Gravel LLC, File No. M-2005-045
The Division of Minerals and Geology (DMG) engineering staff have reviewed the information in the
permit application file for the proposed detention pond shown on the mining plan map for the Rock Dog #1
Pit. A discussion of this proposed pond was held with Matt Carnahan, agent for Gravel LLC. The purpose
of the pond is to detain storm water runoff from the areas disturbed by mining. From discussions with Matt
Carnahan, the DMG understands that runoff from up gradient undisturbed land will be diverted around the
pit bypre-existing, reconstructed, or newly constructed ditches. The DMG requires that a design plan be
submitted for the sediment pond, impoundment, other treatment facilities and diversions proposed to be
constructed. The following elements aze to be included.
1. A surface water hydrology report with a determination of the peak inflows to the proposed pit area from
the up gradient basin for both the 10 and 100-year, 24- hour precipitation events, and determination of
the volume of inflow to the detention pond from the 10-year, 24-hour event. The determinations should
be made in general accordance with the procedures described in Natural Resource Conservation Service
Technical Release TR-55, ftp://ftp.wcc.nres.usda.QOV/downloads/hydrolog~hydraulics/tr55/tr55.Ddf.
2. A floodplain report. The DMG understands that a Flood Insurance Rate Map (FIRM) for the proposed
pit azea has not been produced. From discussions with Matt Carnahan, the DMG understands that peak
flows in the spring of 2005 were the highest observed by local residents during that past 50-years, and
that flooding from these flows reached the location of the residential trailer located to the west and south
of the proposed detention pond. Mr. Carnahan stated that the residential trailer is approximately four or
more feet lower in elevation than the proposed pond. For the floodplain report, these observations and
elevation differences must be verified and quantified. Also, the Florida River floodplain to the north of
the proposed pit location has been mapped (FIRM Community Panel No. 080097 0415 B). The Flood
Hazard Investigation Report used to prepare this FIRM must be consulted, and an analysis of
information on the map and in the report, as it may relate to the proposed gravel pit and detention pond,
must be provided to DMG.
3. Designs and plans for the construction of the pond and diversion ditches to include:
3.1 Plans and cross sections sufficient to show the lines and grades for the pond and ditches.
3.2 Earthwork specifications for topsoil stripping and preservation, excavation and grading of the
incised portion of the pond, embankment foundation preparation, and embankment construction.
3.3 A design with plans, specifications, and details for outlet works and spillways.
Ofilce of Office of Colorado
Mined Land RKlamation ARive and Inactive Mines - Geological Survey