ML20138H001
| ML20138H001 | |
| Person / Time | |
|---|---|
| Issue date: | 10/11/1985 |
| From: | Knapp M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Higginbotham L, Rich Smith NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV), NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-64 NUDOCS 8510280169 | |
| Download: ML20138H001 (4) | |
Text
...
ISTRIBUTION:
WM-64 sf NMSS ri OCT 11896 WMGT rf RBrowning M-6 J/85/10/09
- MBeH,
_3 JBunting MKnapp TJohnson & rf MFliegel EHawkins, URF0 MEMORANDUM FOR:
R. Dale Smith, Director Uranium Recovery Field Office kN Leo B. Higginbotham, Chief WM R:ccrd file WM Pn;j.x 1_
Low-Level Waste and Uranium Recovery Projects Branch Decket Ma.FD., -
Division of Waste Management, NMSS n
LPDR i.
FROM:
Malcolm R. Knapp, Chief U ME Geotechnical Branch Division of Waste Management, NMSS - --
.... L (v, a.c Wl, OMn
~
SUBJECT:
REVIEW 0F LAKEVIEW REVISED RAP
~
~ ~~~
In accordance with your requests, Ted Johnson has reviewed the revised Remedial Action Plan (RAP) for the Lakeview site, with respect to surface water hydrology and the design of erosion protection.
Our questions and comments are enclosed. Based on our review, we conclude that the design, as presented, may not meet EPA long-term stability requirements as outlined in 40 CFR 192. Our principal concerns are with the computational methods used to determine riprap requirements for the protection of the pile and the diversion ditches.
If you have any questions, please contact Ted Johnson at x7-4490.
t h
Malcolm R. Knapp, Chief Geotechnical Branch Division of Waste Management, NiiSS
Enclosure:
As stated es10280169 e51011 PDR WASTE l
j l 7C :
WMGT WMGT I WMGT
._ _f_ _ :
j 3.___:______ g :_MFliegel MME :
Tdormf
- MRKnapp 85/10/ [ : 85/10/ @
[ ATE :85/10/10
SURFACENATERHYDROLOGYANDEROSION PROTECTION QUESTIONS AND COMMENTS 1.
Flow Concentration on Top and Sides of Pile.
Our review of the information presented in the RAP indicates that flow concentration has net been considered in the design of the erosion protection to be placed on the top and sides of the remediated pile.
The NRC staff concludes that flow concentration will occur on the top of the pile, where the rock voids will be filled with soil.
This will cause the formation of preferential flow paths as the soil is eroded, resulting in rills and gullies which will enlarge as time goes on.
The rock on the 20% side slopes will also be affected (even though no soil will be used in the rock voids), because the flow from the top slopes will emerge onto the side slopes from these concentrated paths, rather than uniformly over the slope.
Previous agreements reached between NRC and DOE have indicated that flow concentration does not have to be separately considered if the analysis technique used incorporates its effects.
However, among other considerations, this applies only when flood runoff is able to flow through the rock voids.
In this particular case, however, the Safety Factor Method was used for flow over, not through the rock layer,and there will be soil in the rock voids. Therefore, flow concentration must be separately considered in the analyses.
An acceptable method for resolving our concerns is to consider flow concentration in the analyses of peak flow using methods similar to those used in the Canonsburg, PA design, where the rock voids were also filled with soil, and flow concentration was considered in designing the erosion protection.
The erosion protection designs for the top and sides of the pile should be resized, as necessary, and the analyses and computations should be submitted for NRC review and approval.
Additionally, flow concentrations due to differential settlement should be considered in the analyses for rock protection.
If differential settlement will not occur, the analyses which document that conclusion should be provided (or cross-referenced).
If differential settlement will be mitigated by engineering measures such as overbuilding or surcharge loading, the RAP should provide a comitment to implement such further measures.
i
- n,
se 2
2.
Peak Shear Stresses in Ditches. Our review of the revised erosion protection analyses (dated 8/27/85) indicate that calculated peak shear stresses were used to design the riprap in the East ditch but that average shear stresses were used in the design of the West and South ditches.
This results in riprap which is undersized by about a factor of 2.
It is the position of the NRC staff that peak, rather than average, shear stresses should be used to design erosion protection, particularly in ditches where there will be a large variation in shear stress across the section.
The erosion protection designs should be revised to reflect peak shear stresses in the west and south ditches accordingly, and the revised calculations should be provided for NRC review and approval.
Additionally, the calculational procedure should be iterated, as necessary, to verify that proper Manning's 'n' values are being used to compute the flow velocity, hydraulic radius, and flow depth, which are, in turn, used to compute riprap size.
Methods for verifying that the assumed 'n' values are very close to the computed 'n' values may be found in EMll10-2-1601, Plate 4.
(This is also applicable to design of rock on the top and sides of the pile.
See comment 1, above).
3.
Peak Flow in Ditches. Based on an examination of the most recent calculations (dated 8/27/85), it appears that the peak flows in the diversion ditches may be underestimated.
If the rainfall-intensity curve developed in the revised calculations is used, it appears that rainfall intensities and amounts will be greater than assumed in previous calculations, with a corresponding increase in peak flows in the ditches.
Ilowever, the peak flows in the ditches are unchanged from previous estimates. These discrepancies should be further analyzed and revisions should be made to the peak flows in the ditches, as necessary.
4.
Channel Transitions and Junctions. We note from our review of the RAP that the final details of the designs for channel transitions, junctions, and bends will be developed in the near future by the RAC.
While we recognize that such final details may be postponed, the design criteria for these details should be proy.ided in the RAP.
The RAP should go into some detail on the criteria and concepts that will be used (1) to transition the man-made channels into the existing channels at the site, (2) to design the erosion protection associated with channel junctions, bends, or transitions where flow direction may abruptly change and (3) to determine the locations where erosion protection inculd be terminated at the downstream end of the natural channer to prevent headcutting and/or lateral erosion.
v
- - ~ _.
3 i
In addition, drawings and gross-sections should be submitted to provide preliminary information on the designs that are being considered, especially in those cases where it appears that extensive rock protection may be necessary to prevent erosion.
1 4
4
+
l
!l
)
i I
-.