ML20236A780
| ML20236A780 | |
| Person / Time | |
|---|---|
| Issue date: | 09/23/1987 |
| From: | Starmer R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-72 NUDOCS 8710230123 | |
| Download: ML20236A780 (3) | |
Text
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- 1 SEP 2 31987
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l MEMORANDUM FOR: Myron Fliegel, Section Leader Uranium Recovery Section m _
Operations Branch FDR _
Division'of Low-level Waste Mana'@eteenten LPD1 ~ ~~~~~~~
and Decommissioning
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R. John Starmer, Section Leader &TeiQ"yg g.gy2 -
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FROM:
Siting Section
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Technical Branch
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Division of Low-Level Waste Management and Decommissioning
SUBJECT:
.SP0OK WY0 MING SITE DRAFT REMEDIAL ACTION PLAN Enclosed please find comments on the Spook Wyoming Site Draft Remedial Action Plan. The major recommendation to come out of our review so far is that DOE consider use of rock cover on the tailings pile.
Information necessary for reviews of groun@ater remedial actions will not be available until we receive the draft EA. We will review those portions cf the RAP when the required information is available.
if you have any questions or comments, please contact Kristin Westbrook of my staff on X74543.
Ori61nal 81 ned By 6
R. John Starmer, Section Leader Siting Section Technical Branch Division of Low-level Waste Management and Decommissioning, HMSS
Enclosure:
As stated DISTRIBUTION:
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@AME :KWestbrook :RJStarmer DATE :09/;n3/87
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SM-72/JPG/DRAP. page'D-36 and -37, Site erosion by tributary headcutting This'section of the dRAP and Figure D.3.11 portray headcutting by tributaries
'which would. lead to erosion of the stabilized tailings. The staff agree at this time that lateral erosion'and headcutting associated with tributaries of.
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- Dry Creek appear to be the only significant geomophic hazards to the-i pit-disposal option.
In the staff's view,. however, DOE's predictions of future
- erosion do not appear to~.be based on conservative assumptions.
'For example, Figure D.3.11 models a future cha'nel headcutting.into the n
Ldisposal area from the site's main wash. The analysis assumes that the channel will naturally adopt'a slope similar to that of the soil-bedrock interface, approximately 0.076, and shows that erosion in the main w' ash in excess of 50 feet would be' required to expose'the tailings. This slope gradient is extremely steep for a natural stream and no justification is shown that it is reasonable. Staff analysis indicates that a shallower slope, such as 0.030, would require only 21-feet of downcutting in the main wash to result in a tailings release.
Furthermore, DOE states that erosion resistance of the Wasatch Formation is likely to prevent erosion beyond 35-40 feet. This assertion is unsupported by field or laboratory data, or. literature citation regarding resistance and durability of the Wasatch.
00E should provide a more thorough explanation of the. calculations and assumptions, and show they are reasonable and-conservative.
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SThBILIZATIONOFAML' COVER i
The. intent of the remedia1Laction design and the: AML. design, as presented in
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the. draft RAP!(pages,60-67), is to' promote-positive drainage from-the cover.
to prevent the; occurrence of ponding and limit the. amount of
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' infiltration /into the tailings.. The cover design, ras presented in " Report of l
. Investigation, Abandoned Mined Lands-Program 15-3," by Hydro-Engineering
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(1987),: includes a vegetated earth cover surrounded by [ lined] diversion ditches. We do not consider the proposed cover adequate to reduce ponding and.
1 infiltration to a minimum and therefore it.will be difficult to demonstrate that.
groundwater quality.will.not be affected during the.200 - 1000 year design lifetime of the site.
First, the'.ditchesLfor.; diversion of flood flows around the pit are designed -
for a11000-year precipitation event of 2.4 inchas in one hour. A 1000-year e
. precipitation event can not be determined using.the limited Wyoming precipitation data base.
Furthermore, it'is doubtful that the 1000-year event properly represents. an upper. limit.of rainfall potential (ref.)..Since the one' hour PMP [for Wyoming] is approximately 14 inches, from HMR No 55, Plate
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lb, the 1000-year event is not_even close to the normal design basis event used for other UMTRA sites. The PMP and PMF events should be used to design the ditches in. order to minimize the potential for erosion and overflowing of the? ditches which could lead to water being concentrated on the pile cover and result in increased infiltration.
.Second, the proposed soil cover is to be protected only by vegetation.
Since a vegetative cover is unlikely to be self-sustaining in this arid climate, it is doubtful that it can prevent gullying, caused by concentration of runoff.
from a major precipitation event. The sheet flow assumption used by the designers is not likely to be valid under the above conditions._ Gullying will disrupt the cover, and it is possible that specific areas of ponding, erosion, and deposition could occur directly above the tailings. This would lead to j
increased infiltration and possibly exhume some tailings. Therefore, a rock j
cover,' designed in accordance with normal VMTRA design procedures, should be provided,'or justification should be provided that the soil cover can prevent l
the initiation of gullying and prevent growth of gullies once they form, for
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the 200 - 1000 year design period.
j The design of both the diversion ditches and the cover should be modified to coincide with criteria that have been past UMTRA practice and have been accepted by NRC. Factors that need to be more thoroughly addressed include
the: impacts of extreme flood events on the cover and ditches; the potential
~ for flooding if ditches fail and the impacts of gully growth on the integrity
.of the tailings pile, n
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