PERMFILE127170

• Permit No: M2000158
• IBM Index Class Name: Permit File
• Doc Date: 4/18/2001
• Doc Name: S & H MINE 112 APPLICATION PLATTE SAND & GRAVEL LLC FN 3RD HYDROLOGIC ADEQUACY REVIEW
• From: DMG
• To: ERICA CROSBY
• Media Type: D
• Archive: No

• • iii iiiiiiiiniu iii
STATE OF COLORADO
iJIVI~ION OF ~V1INERALS AND GEOLOGY
Department of Natural Resources
I }1 3 Sherman $1., Room 215 DIVISION O F
Denver, Colorado B020J
Phone: [phone] MINERAL S
FAX: [phone] &
GEOLOGY
Dale : April 18, 2001 MENINGMSAFE TN
To : Erica Crosby, Carl Mount cn'v°;,o; `
Greg E. Walther
From : Tom Schreiner Executive Director
Michael B. Long
Division Director
RE: S & H Mine 112 Application, Platte Sand & Gravel LLC, File No. M-2000-158
3rd Hydrologic Adequacy Review
I have reviewed the comments received on April 12, 2001 from Pickett Engineering, Inc.
regazding flood elevations and velocities as well as recommended mitigation measures for the S
& H Mine. As you may recall, I had requested in my previous memo that the applicant clazify
the flood elevation and peak flow velocity expected during a "worst case" flooding event and
specific measures that the operator will implement to minimize the potential for any offsite
impacts. The PEI comments include flood flow velocities and depth information for both a 100-
yeaz and a 500-year event. The PEI letter also recommends four (4) different mitigation
measures that can be employed to minimize potential flooding impacts. The Division is in
agreement with the information and recommendations provided; however, the applicant is still
absent an approvable flood controUmitigation plan for the S & H Mine. Such a plan is needed to
mimimize the potential for excessive scouring and erosion of pit slopes and of berms protecting
critical structures such as gas pipelines. Prior to mining (excavation) in flood prone aeeas at the
S & H Mine the applicant should provide the Division with a map showing the location of any
and all "sensitive" areas that aze likely to experience significant erosion during a flooding event.
The applicant should also commit to no excavation in any "sensitive" area until such time that
the Division has reviewed and approved a flood controUmitigation plan. A flood
controUmitigation plan may be provided as a permit modification and should include the
following components:
a map showing the location(s) of any sensitive azea(s) with potential for excessive erosion
during a flooding event, such aeeas will be those requiring flood control mitigation measures
representative plan views and cross-sectional designs for riprap, pipe connections, flood
control spillways, or other mitigation measures to be installed
itemized costs for installation of each flood control mitigation measure
a map showing or describing the specific mitigation measure(s) to be employed for each