ML20136H939
| ML20136H939 | |
| Person / Time | |
|---|---|
| Issue date: | 12/23/1985 |
| From: | Fliegel M NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Hawkins E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| REF-WM-48 NUDOCS 8601130072 | |
| Download: ML20136H939 (3) | |
Text
-
WM s/f (Memr/ Hawk /Durango o
TJ/85/16) lden, t/
DEC 2 31985 WMGT r/f
" 3 MEM0/ HAWK /DURANG0/85/12/16/TJ RBrow ng MBell JBunting MKnapp MEMORANDUM FOR:
ED HAWKINS, URF0 TJohnson & r/f MFliegel PDR FROM:
MYRON H. FLIEGEL, WMGT
SUBJECT:
REVIEW 0F RAC PRELIMINARY DESIGN _ DURANG0 (BOD 0 CANYON)
SITE In accordance with your recent verbal requests, Ted Johnson has reviewec' surface water hydrology and erosion protection aspects of preliminary design documents for the Durango (Bodo Canyon) site. These documents were submitted by the remedial action contractor (RAC) and are dated November,1985. Our questions and comments are enclosed. As agreed between you and Ted, these comments were written in an abbreviated style to meet schedule requirements.
In general, we conclude that the design, as proposed, is deficient in several areas and will not meet EPA standards.
These deficiences are detailed in the enclosure.
If you have any questions, please contact Ted Johnson at extension 74490.
j f
/5/
Myron H. Fliegel, WMGT
Enclosure:
As Stated WM Record fila gyg p,, :g j f DodttNo. _
POR V D!striNFo,m
-~
8601130072 851223
}]
- U --~ ~ ~-]
PDR WASTE PDR WM-48 C' him to 'Jm 52j.33).... _ _ _
hFC :WMGT
- WMGT h
h _ _ _ _ : _ _ _ _3.,.y')_ _ _ : _ _ _l i e g e l___0 ____:____________:__
!AME :TJohrmop
- MF
____:_______u____:________g __:____________:____________:____________.____________..__________
TE :85/12/ D
- 85/12/ p'/
1
WMs/f(Enclosure /TJ/Dura WMGT r/f NM5S r/f M23%
RBrowning MBell ENCLOSURE /TJ/DURANG0 JBunting MKnapp TJohnson & r/f MFliegel PDR Surface Water Hydrology and Erosion Protection Questions and Comments Durango (Bodo Canyon) Preliminary Final Design 1.
In the determination of peak flood flows in the ditches, the minimum time of concentration that was used was 5 minutes, even though the actual times of concentration are much aarter than 5 minutes in many cases. The NRC staff considers that rainfall intensities should be extrapolated to the appropriate time of concentration (tc) or to a minimum of 21 minutes (per NRC/ TAC /RAC agreements). Additionally, the method used to compute tc may not be applicable to small steep drainage areas. Peak flows in the ditches should be reevaluated, as necessary.
2.
At those locations where the diversion ditches transition into the existing channels and where the erosion protection blanket transitions into natural ground, the erosion protection that will be keyed into bedrock has not apparently been adequately designed.
In developing the proposed design, the computational method allows for a significant portion of the flow to pass through the rock.
In these areas, where the slope transitions from IV on 5H to IV on 2H, the flow will not be carried in the rock voids, because the rock toe will be covered with soil and the voids will be filled.
Even if the rock toe is not covered with soil, it is unreasonable to expect that the flow will suddenly go into the voids on the IV on 2H slope after flowing over the top of the IV on SH slope.
In addition, it is also unreasonable to expect that the voids will always be available to carry flows, since sedimentation is likely to cause blockage over long periods of time.
Rock sizes in the ditches and rock toes should be recomputed assuming no flow through the rock voids. (See also Comment 4).
In addition, turbulence and energy dissipation need to be considered in the design, especially for the rock toes and ditch junctions.
3.
Riprap sizes should be increased in those portions of the diversion ditches located at channel bends. Corps of Engineers EM1110-2-1601 provides acceptable guidance.
4.
The computations of rock sizes for the ditches appear to be very sensitive to selection of a Manning's "n" value.
In addition, it is difficult to understand why riprap sizes are larger for certain citch segmnets where the computed velocities are actually lower than in cther segments. One reason is the "n" values (and resulting velocities) may not vary as widely as shown in the calculations. Another reason is that flow is assumed to pass through the voids of the rock layer.
We conclude that no credit should be taken for flow through the rock voids in the ditches or in those 3FC
- WMGT WMGT 1AME :TJohnson
- MFliegel LATE :85/12/
- 85/12/
y ENCLOSURE /TJ/DURANG0
_2_
locations where the ditches are keyed into bedrock.
The flow should be assumed to pass over the rock layer, with appropriate adjustments made to "n" values. (See also Comment 2).
5.
The erosion protection that will be keyed into bedrock should also be designed to resist the flow velocities produced in adjacent eristing off_ pile gullies which will flow approximately parallel to the remediated pile. Calculations should be provided which document the ability of these rock layers to resist PMF velocities in the existing gullies to the north and southwest of the proposed pile.
Particularly in the north gully termination, additional protection (in both size and areal extent) may be needed to adequately prevent off-pile flooding from affecting the integrity of the rock toe.
OFC
- WMGT
- WMGT NAME :TJohnson
- MFliegel DATE :85/12/
- 85/12/