DRC-2009-003282 - 0901a0688012ddc3

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DENISONJ^i
MINES
Denison Mines (USA) Corp.
1050 17th Street, Suite 950
Denver, CO 80265
USA
Tel : [phone]
Fax:[phone]
www.denisonmines.com
July 13, 2009
Mr. Dane Finerfrock
Executive Secretary
Utah Radiation Control Board
State of Utah Department of Environmental Quality
Division of Radiation Control
168 North 1950 West
Salt Lake City, Utah 84114-4850
Dear Mr. Finerfrock: /^sz*?'-
Re: White Mesa Uranium Mill
Dam Safety Inspection (Engineering Module 71)-May 6, 2009
UDEQ Request for Information
In accordance with the Department's correspondence dated June 9, 2009 (and received by
Denison on June 11, 2009), this letter responds to two areas of inquiry stemming from the
subject inspection of May 6, 2009. Accordingly, each UDEQ request is listed below and is
followed directly by Denison's response to that area of inquiry.
June 9, 2009 Letter. Item 2:
"There were several locations observed where exterior rivulet erosion had cut shallow channels
in the exterior dikes at Cells 3 and 4A. These were observed at several locations, but are not
always easy to see due to the growth of vegetation. Mr. Turk agreed that DUSA would repair all
current rivulet erosion on the exterior dikes prior to June 30, 2009. "
Denison Response
Consistent with the Department's request, Denison has repaired the erosion "rivulets" in the
extemal dikes of Cells 3 and 4A which had been observed during the May 9, 2009 inspection.
More specifically. Mill maintenance crews re-graded the observed areas of erosion and all
"rivulet" repairs were completed by the end of May, 2009.
June 9. 2009 Letter. Item 4:
"An east-west bridge for a pipeline was installed along the southern edge ofthe upper section of
the spillway between Cells 3 and 4A. A column to support this bridge, at its center, has been
installed in the spillway about on the north-south centeriine ofthe spillway. The bridge structure
and the pipeline may protrude into flood flow ofthe spillway.
Please demonstrate that the spillway between Cells 3 and 4A will have adequate capacity to
convey the probable maximum flood for the for the tailings cells, with the existing pipeline
bridge configuration in place, and not cause undue erosion to the dike. "
Denison Response:
Denison requested that Greg Corcoran, Geosyntec Consultants, review the spillway design and
evaluate the capacity with the support beam installed. Based on the original calculations, the
PMP event was estimated to be 2,510 cfs, while the as-built spillway has an estimated capacity
of 3,050 cfs (including 1 foot of freeboard). The surplus allowance for flow above the PMP (540
cfs) represents a significant safety factor of 21.5% beyond the flow expected from the PMP.
The subject 6-inch column located in the middle of the spillway channel (located to support the
overlying piping) occupies approximately 2 square feet of the 204 square feet available in total
depth of the channel (1 % of the total cross sectional area). Because this column represents only
1 % of the total available charmel area, a safety factor of 20% remains even with the column
present in the channel. As such, the columns potential for obstructing flow during a PMP event
would be insignificant and will not cause undue erosion of the dike (i.e. all flow can be easily
accommodated by the channel).
If you should have further questions or require additional information regarding this matter
please contact me.
Yours truly.
jteven D. Landau
Denison Mines (USA) Corp.
Manger, Environmental Affairs
OENisohrJi
MINES