ML20141H142
| ML20141H142 | |
| Person / Time | |
|---|---|
| Issue date: | 12/26/1985 |
| From: | Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Martin D NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-58 NUDOCS 8601130442 | |
| Download: ML20141H142 (4) | |
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-DAN MARTIN, WMLU MFliegel PDR
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MYRON H. FLIEGEL, WMGT DGillen(WMLU)
EHawkins(URF0)
SUBJECT:
SHIPROCK PHASE II DESIGN REVISIONS
.In accordance with your request (Ticket #WM-51106), we have reviewed surface water hydrology and erosion protection aspects of "UMTRA PROJECT - SHIPROCK
. PHASE IIEDESIGN REVISIONS", dated December, 1985. Our comments and questions are enclosed.
-Based on our review,'we are unable to conclude that the design revisions
, adequately demonstrate that the requirements of 40 CFR 192 have been met.
In
' general, the. proposed ditch and erosion protection designs are not adequate to meet the EPA long-term stability criteria.
These questions were discusset ith Mr. T. Wathen of Morrison-Knudsen by telephone on December 24, 1985..Mr. Wathen indicated that he expected several more revisions to be made and that these revisions would likely be submitted to NRC,(through DOE) by about mid-January, 1986.
This review was performed by Ted Johnson.
If you have any questions, he may be reached at extension 74490.
Myron H. Fliegel WMGT
Enclosure:
As Stated WM Record File WM Project _.5E Dc:ket No.
PDR /
LPDR Distribution:
8601130442 851226 i
PDR WASTE l
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' 85/12/v, DATE :85/12/x
SHIPROCK/COMM/TJ/85/12/24/1 SHIPROCK PHASE II DES!GN REVISIONS SURFACE WATER HYDROLOGY AND' EROSION PROTECTION QUESTIONS AND COMMENTS 1.
Based on a review of the calculations provided, it is not clear if the channel riprap design includes an allowance for increased shear stresses in the areas of channel bends. While it appears that the alignment, configuration, and sizing of the ditches have been adequately addressed (in accordance with appropriate Corps of Engineers references), additional calculations should be provided to document that the erosion protection at channel bends has been properly designed.
Corps of Engineers EM 1110-2-1601 provides acceptable guidance for determining shear stress increases and for designing erosion protection at channel bends.
2.
We note that statistical extrapolation of data was used to determine the "1,000-year" storm.
However, there is no basis to support such extrapolations, especially for small ungaged watersheds with limited flooding and precipitation data bases.
We further note that several of the drainage ditches will be designed to accomodate only this "1,000_ year storm", which is also 18% of the PMP.
The benefits to be gained by labeling the storm a 1,000-year storm are questionable. We suggest that any reference to a 1000-year storm be deleted.
It should be simply called 18% of the PMP.
3.
The elimination of ditches D-3 and D-4 has resulted in a design where runoff is directed over an apron directly over unprotected slopes into the excavated borrow area east of the embankment. While this design concept may be acceptable, it is not immediately evident how erosion of the borrow area slopes will be prevented. Slopes of 5% in silty soils and 10% in gravelly soils (Reference Drawing SHP-PS-10 0022) may not be sufficiently flat to prevent erosion and gullying of the slopes over long time periods. This is particularly true if concentrated, rather than sheet, flow occurs on the slopes. Based on the design presented, it appears that concentrated flow could occur, gullies could form, and the gullies could eventually enlarge and headcut toward the protected embankments. In order to resolve this potential erosion problem, the NRC staff suggests that one or more of the following be performed:
a.
Provide calculations which document that the unprotected 5-10%
slopes will not be gullied and eroded.
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b.
Provide ditches which prevent discharges from flowing over the borrow area side slopes. (Depending on the configuration, there will likely always be some discharges down the slopes due to direct rainfall and runoff).
c.
Provide erosion protection for the borrow area side slopes so that gullying and erosion will not occur.
d.
Flatten the slopes (possibly by filling) in the borrow area.
Regardless of the design selected, the final grading plan and design for the borrow area slopes should be provided for NRC review and approval.
4.
The redesign of ditches D-1 and D-2 has resulted in a design where only 18% of the PMP will be carried in the ditches and the remainder of the flood peak will overflow the ditches. While this design concept is acceptable, it is not clear if the site grading is such that ditch overflow and off-site floods could possibly enter the ditches further downstream. Examination of the topography in the immediate area of the d, itches indicates that ditch overflow will not be directed away from the ditches and that off-site floods could actually overflow into the ditches.
Accordingly, documentation and drawings should be provided to demonstrate that:
a.
overflow from the ditches will either not reenter the ditches further downstream or that the ditches are designed to safely convey this volume of flow; b.
off-site floods wither will not enter the ditches or will be safely conveyed by the proposed ditch design. (Note that floods entering ditches D-1 and D-2 may also affect either ditches further downstream); or c.
the apron and erosion protection to be provided on the outside portions of the ditches are capable of resisting (1) PMF velocities produced by overflow out of the ditches and (2) velocities produced by an off-site PMF flowing along the outside toe of the ditch where it meets existing ground.
Additionally, if credit is taken for the diversion ditch to be placed around the perimeter of the M-K borrow area, the ditch should be i
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. ; designed;for a PMF and resulting velocities. Calculations and
- documentation should be provided to demonstrate that the ditch has been adequately. designed.
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