INSPEC40802

• Permit No: M1977215
• IBM Index Class Name: Inspection
• Doc Date: 3/15/1994
• Doc Name: BULLDOG MINE HYDROLOGIC EVALUATION
• From: CANONIE ENVIRONMENTAL
• To: ENVIRONMENTAL AFFAIRS
• Media Type: D
• Archive: No

r
Mr. Luke Russell 3
March 15, 1994
Table 3
Alternative Windy Gulch Design Criteria

Design
Flow (cfs)

Channel
Slope (ft/ft)

Side Slope
H:V
Existing
Bottom
Width (ft)
Required
Bottom
Width (ft) Required
Maximum
Stone Size
(inches)
360 0.10 1:1 4 12 30
1:1 30 30 i 13
1:2 18 18 17
0.25 1:2 18 28 24
To my knowledge, rock riprap over approximately 14-16 inches is not readily available
within or in close proximity to the mine area. Anew quarry may be required to access
large rock riprap meeting the requirements of a 360 cfs runoff event as shown in
Table 3. This may entail additional permitting activities from the Forest Service and/or
other government regulatory agencies having jurisdiction near the Bulldog Mine.
In summary, I believe using the criteria in Table 1 for upgrading the channel will
provide adequate protection against channel erosion, headcutting and undercutting of
of the waste dump for a theoretical 100-year, 24-hour runoff of 140 cfs based on a
drainage basin CN of 68. Further, it is my opinion that if the channel is upgraded using
Table 1 criteria, and the waste dump fails as a result of a runoff event greater than
140 cfs, the downstream impact of such a failure relative to future hydraulic stream
flow routing in Windy Gulch would be minimal. As the waste dump is comprised of
relatively well angular rock, any "dam" resulting from such a failure would act as a
relatively porus rock drain, allowing runoff to flow through the rock, as in the case of
a rock drain constructed in a gravity sorted, valley fill waste dump. i do not believe
that it would temporarily detain water, fail, then release a "flood wave" downstream.
I hope this information is helpful in assisting Homestake with completing the
reclamation and closure of the Bulldog Mine. If I can be of further assistance in this
matter, please contact me at 1406) 586-9496.
Sincerely,
v ~'~/
Scott Benowitz, P.E!
56/ke
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