ML20246A326
| ML20246A326 | |
| Person / Time | |
|---|---|
| Issue date: | 06/06/1989 |
| From: | Hawkins E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Matthews M ENERGY, DEPT. OF |
| References | |
| REF-WM-48 NUDOCS 8907060237 | |
| Download: ML20246A326 (3) | |
Text
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REGION IV URANIUM RECOVERY FIELD OFFICE
+,v,,,+,o BOX 25325 DENVER. CoLORAoO 90225 I
JUN 61989 c
U.1FO: R0G Docket No. WM-48
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Mark Matthews, Acting Project Manager-Uranium Mill Tailings Project Office U.S. Department of Energy P.O. Box 5400.
Albuquerque, New Mexico 87115
Dear Mr. Matthews:
We have completed our review of the surface water / erosion protection aspects-of the Durango Redesign of the Disposal Embankment which you submitted by letter dated December 23, 1988.
Our specific comments are provided in the enclosure
'~to this letter.
These comments were provided informally to Ms. Damler of your l
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staff on June 2, 1989.
'If you have any questions, please contact Ray Gonzales'at FTS 776-2805.
Sincerely, Edward w ins, Branch C Uranium Recovery Field Office Region IV
Enclosure:
As stated y
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REVIEW COMMENTS ON THE, SURFACE WATER / EROSION PROTECTION FEATURES OF THE DURANGO P.EDESIGN OF.THE DISPOSAL EMBANKMENT 1.
In analyzing the potential for gullying of the pile top (Calculation No. 03-591-09-00), you used a rainfall inten::ity of S.4 in/hr for an-assumed time of concentration (tc) of 2.5 minutes.
This led you to conclude that-the soil on the pile top would not erode.. There appears to be an error in your calculations because for such a short tc, the rainfall intensity should 54.7 in/hr (see shee't' 36-P of your Calculation No. 03-565-05-04).
For an intensity of this magnitude and a top slope of
-2 percent, it is probable that gullying will occur.
The design of the riprap on the pile top (type "A")'and on the side slopes (types "B" and "B1") should therefore be reviewed to assure that they are adequate to resist the shear forces in the gully.
We recognize'that it is difficult to predict the shape and depth of'a gully that could-form on the pile top over a 1000 year period. ' However, it is reasonable to assume that a gully will erode to a depth of 3 feet, which is the thickness of the frost protection soil cover.
The bio-intrusion rock layer, assuming it is adequately designed, should prevent the' gully from eroding any deeper than 3 feet. The shear forces acting on the riprap can be computed using this 3-foot depth, and the adequacy of the riprap on both the pile top and on the side slopes can be determined using the Safety Factors Method.
2.
On sheet 5 of Calculation No. 03-565-05-04, you state that, "the rock sources for the riprap will probably be river run."
Since river rock generally-bas a rounded shape, it does not interlock and wedge.as well as angular rock and thus is not as stable.
Therefore, if rounded. rock is used, it-should be oversized by about 40 percent to provide the same level of. protection as angular riprap.
3.
Sheets 4 and 5 of Calculation No. 03-565-05-04 state that the pile top slope will be 2 to 4 percent.for construction flexibility.
In your gully analysis (Calculation No. 04-591-09-00), you assumed a slope of 2 percent.
Please provide assurance that the pile top is capable of resisting the shear forces on a 4 percent slope.
4.
On sheet 41(c) of Calculation No. 03-565-05-04, it appears that incorrect drainage areas were used to calculate flood flows for designing Ditch No. 2 (see your sheet 36-L for the correct areas).
Please review your calculations and provide assurance that the design of Ditch No. 2 is
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adequate.
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WM-48/ROG/89/06/02/L l~
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. DISTRIBUTION-.
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.' Docket File WM-48
.l. %PDR/DCStA la-OABBeach, RIV'
- RGonzales
,5 Grace.
T':ese.
~BGarcia, RCPD, NM STMorgan, NM NWeber,-NM'
'LLO Branch, LLWM URF0'r/f
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CONCURRENCE:
DATE:
RGonzales/URF0
((J 57 f.
SGrace/URF0 5%
6-5-89 EHawkins/URF0 b
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