DRC-2009-004688 - 0901a06880142f14

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State of Utah
GARY R. HERBERT
Gnvemor
GREG BELL
Lieutenant Governor
October 8, 2009
CERTIFIED MAIL
(Retum Receipt Requested)
David C. Frydenlund
Vice President and General Counsel
Denison Mines (USA) Corp. (DUSA)
1050 Seventeenth Street, Suite 950
Denver, CO 80265
Department of
Environmental QuaHty
Amanda Smith
Acting Executive Director
DIVISION OF RADIATION CONTROL
Dane L. Finerfrock
Director
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Dear Mr. Frydenlund:
SUBJECT: May 26, 2009 DUSA Response Letter: Amendment Requests Relating to Freeboard Limit
Calculations for Tailings Cells; March 23, 2009 DRC Letter: Comments for Request for
Resolution and Modifications; Request for Information
We have reviewed the subject DUSA letter of May 26, 2009. The letter was submitted in support ofa
DUSA request for license amendment related to changes to freeboard limit calculations, dated December
11, 2008. A discussion in the DUSA May 26, 2009 letter describes how DUSA proposes to control storm
water from the probable maximum precipitation (FMP) from overtopping Cell 3, when it is full of tailings,
and when it has received a temporary cover. Information is requested in this letter regarding these two
conditions, i.e. when the ceil is full of tailings, and when it has received a temporary interim cover.
When Cell 3 is Full of Tailings: In the letter of May 26, 2009, DUSA presented that when tailings Cell 3
is full of tailings to the top ofthe flexible membrane liner (FML), the probable maximum flood (PMF)
runofffrom Cell 3 will be controlled via:
A. The top ofthe Cell 3 south dike is 18-inches higher than the FML in Cell 3, which will prevent
runoff from overtopping the south dike.
B.
D.
Runoff will flow laterally to the spillway, because the spillway will be the lowest point ofthe
tailings elevation.
The tailings at the spillway will only be placed to the top of the FML at the spillway, assuring
the spillway will be the lowest point of tailings Cell 3.
On page 2, paragraph 4, in the second sentence of the letter DUSA states that, "Once the
tailings solids are at, or near, the final allowable elevation, the surface area of the tailings is
graded to fill any low spots, or re-contoured to ensure that no areas of the solids are above the
elevation ofthe FML." DUSA did not state to what tolerance the elevation ofthe tailings, or
the frequency and method to be used to assure elevations will be maintained to eliminate
problems from potential high damming of storm water or creation of significant obstructions to
storm water outflow.
168 North 1950 West • Salt Lake City, UT
Mailing Address; P.O. Box 144850 • Salt Lake City. UT 84114-4850
Telephone [phone] • Fax [phone] • T.D.D. [phone]
www.deq.utah.gov
Printed on 100% recycled paper
Page 2
Earlier, the DRC letter of March 23, 2009 brought forward detailed questions on the issue of control of
storm water from Cell 3, when the cell is full of tailings to the top of the FML. In this DRC letter on page
2, paragraph 5, DRC requested DUSA provide "adequate detail [drawings] and demonstrations
[calculations] to show the effectiveness of DUSA's plans." DUSA did not provide this information in its
May 26, 2009 response letter.
When Cell 3 Has Received an Interim Cover: Similar to the full tailings condition discussed above, in the
DUSA letter of May 26, 2009 in excerpts from paragraphs 2, 4, and 6, DUSA states that, "To the extent
interim cover is placed on portions of Cell 3 ... the spillway will nevertheless be maintained until the final
reclamation cover is in place. Most of the precipitation runoff from Cell 3, which would be clean water,
un-impacted by tailings, would naturally flow towards the spillway, being the lowest point in the cell, and
via the spillway into Cell 4A . . ."
. . . Should the precipitation event exceed the available free board capacity of Cell 3, the excess solution
will flow from the pool area through the spillway into Cell 4A. The spillway will be maintained until the
placement of the final reclamation cover; therefore it will continue to act as a low point on the cell to catch
precipitation runoff after interim cover has been placed on the cell and direct such runoff into Cell 4A . . ."
". . . Any possible surface runoff would be off of the interim cover, and would therefore not be
contaminated by Mill tailings."
Any runoff over the dike after interim cover placement would have to be dealt with by preventing
any other impacts downstream.
It appears DUSA proposes to control storm water runoff from Cell 3 under two separate conditions, i.e.
when Cell 3 is full of tailings, and when Cell 3 has received an interim cover. We request that DUSA
provide the following inforraation, including but not limited to:
1. Adequate detail [drawings] and demonstrations [calculations] to show the effectiveness of DUSA's
plans. We remind you that the drawings and supporting calculations need to show that the storm
water flow created by the probable maximum precipitation (PMP) from both Cells 2 and 3 can be
successfully managed by the proposed methods.
a. Adequate descriptive drawings need to show how the final surface of the tailings and the
interim cover are to be graded. Especially vague in the May 26, 2009 DUSA letter are the
grades of the tailings and interim cover upstream in the spillway area. The drawings to be
submitted must include the complete grading of the tailings and the interim cover for Cell
3, including those upstream of the spillway area.
b. The discharge rate of the storm water through the spillway, by the principle of discharge
continuity, corresponds du-ectly upstream to the discharge rate of the storm water on its
final approach to the spillway. The discharge rate of the storm water on its fmal approach
to the spillway will be affected by the length of any drop-off sill, made by the tailings or
the interim cover material, at the beginning ofthe final approach to the spillway.
c. Supporting calculations need to demonstrate that the design grade drawings are adequate,
for both the final grades of the tailings and the interim cover by showing appropriate
calculation methods and results displayed which:
Discharge along a sill, in this case along the edge ofthe tailings or the interim cover, before dropping down to begin the final
approach the spillway, may be estimated by the formula Q = CLH'^ where C = discharge coefficient, L = siil length, and H = head
above the sill. Chow, V.T. 1959, Open Channel Hydraulics, McGraw-Hill Book Company, p. 362.
Page 3
(1). Determine and show where the greatest depth location (GDL) from a PMP
would be, along the Cell 3 southem dike.
(2). Show on tables or spread sheets the depths as well as the maximum depth, as a
function of time, at the GDL along the Cell 3 southem dike created by the PMP.
(a) Show graphically the inflow and outflow hydrographs for Cell 3 from the
PMP.
(b) Show graphically the volume storage of storm water, from the PMP, as a
function of time, in Cell 3. This should identify the time for the maximum
depth of storm water at the GDL, along the Cell 3 southem dike.
2. Specify the tolerances that the fmal elevations of the tailings and the interim cover will be
controlled to.
3. Specify the frequency and method to assure such elevations and tolerances will be maintained to
prevent problematic high damming of storm water and prevent creation of obstructions to storm
water outflow from occurring.
DRC will continue to process the subject action on receipt of this information. On a telephone message left
with Dave Rupp of DRC on October 7, 2009, Mr. Harold Roberts committed that DUSA will fully respond
to this request within 30 days of receipt of this letter.
We remind you that the drawings and supporting calculations need to show that the storm water created by
the PMP from both Cells 2 and 3 can be successfully managed by the proposed method for two conditions,
i.e. when the cell is full of tailings, and when it has received a temporary interim cover.
If you have any questions on this matter, please contact me.
Sincerply,
'/iM
David A. Rupp, P.E.
Geotechnical Services Section
DAR:LBM:dr
Cc: Harold R. Roberts, DUSA
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