PERMFILE107783

• Permit No: M1977004
• IBM Index Class Name: Permit File
• Doc Date: 6/12/1980
• Doc Name: Meeting Notes
• From: DMG
• Media Type: D
• Archive: No

Permit #: F'( ~~°!7~ Confidental?: _~_
Meeting Notes Class: (~sZri2r i ~" Type-Seq.:
From: 17 ~ ~ TO
Doc. Name: A.r ° a " ~ ~~ ~r?'Y'~~
HOMESTAKE TAILINGS DAM Doc. Date (if no date stamp): ~ Ala - Si'O
June 12, 1980
Introduction by Dravo Engineering (Mike Bone, Engineerl
Z. Total height of tailingsdam r 275 feet
2. Geologic studies in borrow areas not completed. Should be completed
within next month. Studies being conducted on separate b?rroFr a;eas
for embankment material and clay liner.
3. Hydraulic flood control calculations for tailings impoundment,
Anticipate 3,000 CFS capacity diversion ditch above tailings area
to divert drainage from upper watershed around tailings impoundment.
Storage and freeboard calculations based on 1000 runoff for one year
period between the diversion ditch and the dam, Tailings dam ~.'mpoundment
designed to contain that flow as zero discharge pond.
4. Dam embankment to be conducted possibly in two stages. First stage
anticipated 15 year capacity, dam and liner to be staged. Second stage
15 through 25 year capacity, dam and liner to be deleted as second stage,
5. Question arose concerning actual final density and volume of the
tailings. Kenning Associates (?) data suggests densification starting
at about 90 days after deposition. Densities may reach as high as
75 to 80 PCF. If so, volume calculated at conservative 65 PCF
would decrease by 10 to 25~ allowing additional freeboard to accomodate
flood flows and storage for the zero discharge impoundment.
6. Question arose on whether N.R.C. would require freeboard calculation for
project maximum flood storage based on the entire watershed above the
dam versus Dravo's calculation for runoff below diversion ditch.
7. Question arose whether diversion ditch should be demolished and reclaimed,
or left in place when the tailings pond is complete.
8. Under drain system beneath clay liner-sand bed with the collection system,
Clay liner thickness 3 feet. Over drain to collect solidation water
expelled by tailings will be collected in pipe system laid in gravel above
the clay Liner.
9. Discussion ensued concerning state of science in estimating eventual
consolidation of tailings. It now appears that many earlier engineering
designs assumed too high a rate of consolidation. To avoid this problem,
Homestake is assuming conservative 65 PCF average density for tailings,
foregoing anticipation of any consolidation. Actually anticipate consolidation
to increase tailings density from 75 to 80 PCF.
10. Basic design of the embankment.
Downstream of slope 3:1 - upstream face 2-1/2:1
Horizontal sand toe drain beneath toe
Chimney drains to be installed on both upslop and downslope boundarg
of clay core.
11. Clay Liner will have to periodically inspected in order to detect cracking
in that area not covered by tailings. Liner should be trenched for
inspection prior to tailings placement in new areas. Homestake will have
to prepare a monitoring program proposal for submission in the Health
Department application. M. Shaw regs will, if adopted, require weekly
inspections of dam. CDOH requires inspection twice per 8-hour shift;
12. Question arises concerning dust control. Homestake has not resolved issue
as of yet. In original application, committment was made to keep tailings