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

-9-
Item: The need for ground water monitoring in the low grade ore piles was
discussed.
R~espo~ns~e_: In view of the low concentrations of elements anticipated to be
~n' t e eachate, Homestake does not believe additional ground water monitoring
of the low grade piles would provide useful information for the reclamation
effort. It is not anticipated that the piles would have to be dewatered
through such wells. If infiltration is sufficient to create saturated zones
within the low-grade ore piles, the likely result will be to produce some
seepage through the sides of the pile near the base. It would not appear that
wells would be necessary.
Item: Water rights impacts should be assessed through contact with the State
Engineer's office.
Response: As previously noted in response to the letter from Mr. Hal Simpson
of the Colorado Division of Water Resources, we noted that development of an
augumentation plan did not appear necessary. Further it was shown that the
amount of evaporation that could occur was very small compared to the water
yield of the affected watersheds.
Item: Are there observations that could substantiate the contention that a
Souk Pit Lake could form?
Response: Observations of the filling during last winter of the temporary
impoundment formed in the North Pit indicate that water should be available
for the South Pit Lake. The calculation regarding the time necessary to
reach the outflow elevation was developed on the basis, principally, of
surface water inflows. Ground water inflows were considered the lesser
contributor.
Preliminary water quality analysis of water currently impounded in the
North Pit indicates acceptable levels for constituents at or below NPDES
discharge limits. The most recent data (June, 1984) show uranium at 0.7 mg/1
and radium-226 at =0.3 pCi/1.
Item: It might be appropriate for the operator to predict the life expectancy
of the sedimentation pond dam.
Res onse: The dam and reservoir were designed to retain the flood volume
of the 25-year, 24-hour storm event under maximum mining disturbance conditions.
The design hydrology precipitation and freeboard hydrology precipitation
were based on the 6-hour, 100 year rainfall adjusted for the 6-hour probable
maximum precipitation event and were calculated to be 4.15 and 10,0 inches
respectively, The peak discharge would be 3620 cfs. These calculations
correspond to high hazard design criteria of the USDA.
The design criteria were contained in the previous submission to the
Division and to the State Engineer and approvals to construct were obtained
based on geotechnical and hydrologic criteria. Homestake is advised by
its consultant that the design is sufficiently conservative to give a high
probability of exceeding 400 years of operation.