PERMFILE66331

• Permit No: M2000158
• IBM Index Class Name: Permit File
• Doc Date: 2/22/2001
• Doc Name: Adequacy Review
• Media Type: D
• Archive: No

elevations(s) to be expected under a "worst case" flooding scenario and specific mitigation measures
that will be implemented to minimize the potential for any offsite impacts. Mitigation measures
might include mining dry pit slopes at a maximum of l:l, installation of flood control spillways
within the reclaimed lakes, installation of drainage pipes within the internal berms separating pits
and/or armoring reclaimed pit slopes in close proximity to the South Platte River with erosion
control riprap. Legible copies of the Flood Insurance Rate Maps ("FIRIvI") through the mine reach
would facilitate the Division's review.
26. The application specifies 200-foot setbacks from the existing top-oY=bank of the South Platte in
certain sections of the mine reach, and 300-foot setbacks From the existing centerline of the river in
areas where mature trees are growing. It was observed during the Division's pre-operational
inspection of the proposed S & H Mine that sections of the riverbank through the mine reach aze
subject to active erosion and bank cutting. The Applicant is careful to specify that the proposed
setbacks are based on the current position of the river. The application indicates that encroachment
of the river on the pit as a result of bank cutting is likely to occur over time. The Division
recognizes that the Applicant is not responsible for the current bank cutting, that stabilization of the
riverbank is not the Applicant's responsibility, and [hat stabilization may even have an adverse effect
on the dynamics of the stream system. However, if the river eventually cuts into the gravel pits,
adverse impacts to the riverbanks upstream and downstream may result, impacts that would not
occur if the pits were not excavated. The Urban Drainage and Flood Control District, which
regulates the South Platte River south and west of the S & H Mine, has determined that 400 foot
setbacks from the top-of--bank aze adequate to protect the integrity of the river without mitigation
required. The Applicant may want to increase the setbacks to 400 feet or provide an analysis of
potential flooding impacts and a plan for mitigation as discussed in item 2~ above. If flood
mitigation plans are to be prepared, they must specifically address the potential for erosion of the
lateral berms that will carry gas/oil pipelines during mining and following reclamation.
27. The application provides no specifics on topsoil and overburden stockpile configurations and
locations. The Division recognizes that the Applicant is making a commitment to concurrent
reclamation that will minimize the amount of topsoil and overburden that will be stockpiled at any
given time. However, since the pit is in the floodplain the Division is concerned with the stability of
the topsoil and overburden piles during a flood event. The Applicant should provide additional
information on the stockpiles including an estimated maximum volume of topsoil and overburden to
be in stockpile at any time during the life of the operation. The Applicant should further commit to
stockpiling material away from areas where the deepest and highest velocity flooding can be
expected and should align the stockpiles as windrows with the direction of floodwater flow paths.
Review of FIRM for the mine area would be useful in this regard.
Reference: Urban Drainage and Flood Control District, "Technical Review Guidelines for Gravel
Mining Activities," December 1987.
Rule 6.4.8 Exhibit H- Wildlife Information
28. The applicant used the NRCS "general guideline" for the proposed seed mixture, which consists of
Blue Grama, Side Oats Grama, Western Wheatgrass and Intermediate Wheatgrass. The Division of
Wildlife ("DOW") also recommended a seed mixture for the wildlife habitat area consisting of Tall
Wheatgrass, Intermediate Wheatgrass, Reed Canary Grass, Indian Rice Grass, Great Basin Wild
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