PERMFILE53867

• Permit No: M1977004
• IBM Index Class Name: Permit File
• Doc Date: 8/31/1984
• Doc Name: Response to Adequacy
• From: Homestake
• To: DMG
• Media Type: D
• Archive: No

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R~esp_onse: The spillway of the South Pit lake is designed with a broad V-notch
wei o flow control set within a broad crest, rectangular weir. The
principal objective of the V-notch weir was to ensure control over the discharge
into the receiving channel. Trash racks have been considered to protect the
V-notch weir from plugging, but trash racks also require maintenance. The
wide cross section of the spillway channel located above the V-notch weir
will provide for passage of flow in the unlikely event the bottom of the
V-notch weir becomes plugged. Homestake has undertaken observations regarding
the debris that may be anticipated to enter the South Pit lake and, during the
final design phase, will evaluate the trade-offs between the flow control
requirements and structures which will resist clogging. Our observations to
date indicate little accumulation of debris in the channels. These design
considerations are included in the surety in Exhibit L under the heading
"Engineering Investigations and Design."
Item: The amendment should quantify erosion rates off dumps and reclaimed
areas and should specify what erosion control measures are necessary to
minimize rill and gully formation and ensure vegetative growth.
Response: Currently, in the opinion of Homestake and its consultant, no
suitable method capable of predicting sediment yield from waste dumps such
as these at Pitch, exists. Reclaimed areas will be observed and managed
to ensure long-term re vegetation success. Problems caused by the formation of
rills or gullies will be corrected as soon as possible.
In view of the uncertainty of erosion characteristics of premining
conditions, the evidence collected to date regarding reclamation success at
the site, and the fact that a number of "flow attentuation areas" wilt be
established, including the South Pit Lake, and that these will serve to
allow sediment to settle, Homestake does not believe that the additional
hypothetical calculations will be of value to the reclamation effort.
Item: Drainage designs should specify how run-off from the dump terrace
i.e., Tie Camp, Indian Creek) will be safely routed to the base of the
pile without causing undue erosion of the shoulders of the pile.
Response: Experience has shown that run-off that would occur will create
negligible erosion of the dump face. Sloping of the dump terraces slightly
inward minimizes potential for erosion. The detailed designs are necessary to
assess the need for additional erosion controls at locations where drainage
is dropped to lower levels of the shoulders of the pile. If necessary,
inclusion of relatively coarse rock, including exposed bedrock, at the edge
of the waste dumps would further control erosion, and aid in routing water
to the base of the pile,
As final drainage designs are developed, the placement of energy
dissipation devices, arranging of channels, and diversion of surface run-off
along the dump terraces will be addressed in a site-specific manner. In all
cases, the desired approach will be to limit drainage areas and flows to
relatively small amounts and to direct flows along the more stable, low
sloping areas. Where this is not possible, drainages will be examined to
determine the erosive character of the channel material, and covering to
enhance resistance to erosion will be added when necessary.