PERMFILE119639

• Permit No: M1979094HR
• IBM Index Class Name: Permit File
• Doc Date: 9/24/1979
• Doc Name: FN 79-94
• From: COTTER CORP
• To: MLR
• Media Type: D
• Archive: No

Mr. Robert C. Campbell
Colorado Division of Natural Resources September 24, 1979
-3-
(vi) The waters to be encountered in mining operations have not historically
been tributary to any stream system and their removal in the proposed
program will cause no injury to any vested rights of other water
users, either surface or underground.
(vii) the mine's domestic needs will be met by haulage of water purchased
from a local supplier.
3. The response set forth below addresses a concern expressed in a telephone
conversation on September 21, between Mr. David Holme, MLR staff member, and
Mr. Tim Smith of Cotter Corporation. Mr. Holme noted that the design of
post mining diversion channels across the overburden pile using flow rates
caused by a 10 year storm is not acceptable, and that some means of
spreading this flow as it reaches the undisturbed soils at the toe of the
overburden pile should be specified.
Cotter has redesigned these channels using the 100 year storm runoff and
conservative assumptions regarding the soil characteristics and vegetative
cover. The revised channel dimensions and flow characteristics are listed
below.
A 243 acre watershed above the overburden disposal area will conservatively
yield 140 c.f.s. as the result of a 100 year precipitation event. Referring
to revised Figure D.5-11, this volume rate will be collected at eight points
along the undisturbed slope/overburden pile interface, conducted across the
reclaimed overburden pile, and onto the undisturbed surface area at the toe
of the overburden disposal area. At this juncture, three 35 ft. wide x 1 ft.
deep channels will be constructed to conduct 50 c.f.s. each.
The eight initial tributaries have been conservatively designed according to
the following criteria:
(a) The two western-most tributary channels will each have dimensions
of 15 ft. x l ft. and will carry approximately 30 c.f.s.
(b) The central grouping of tributaries is comprised of four channels,
each with dimensions of 10 ft. x 1 ft. and designed to carry 15 c.f.s.
(c) The eastern-most tributary system will consist of two channels each
with dimensions of 15 ft. x 1 ft. and each designed to carry approx-
imately 30 c.f.s.
Revegetation of the channel bottoms using native grasses resulting in "B"
retardance will control the flow velocity at 2.7 ft./sec., while the install-
ation of locally derived rip-rap at the undisturbed slope/overburden interface
and at the overburden/undisturbed surface interface will dissipate energy
and reduce flow velocity to minimize erosion.