ML20198R277
| ML20198R277 | |
| Person / Time | |
|---|---|
| Issue date: | 05/15/1986 |
| From: | Hawkins E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Themelis J ENERGY, DEPT. OF |
| References | |
| REF-WM-48 NUDOCS 8606090485 | |
| Download: ML20198R277 (5) | |
Text
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DISTRIBUTION Docket file WM-48
-PDR/DCS.
DBangart, RIV WM-48/RFB/86/05/13/0 RBrich
' HRose T01sen PGarcia MAY 15 B86 EHawkins URF0 r/f URF0:RFB Docket No. WM-48 040WM048601E John G. Themelis, Project Manager Uranium Mill Tailings Project Office U.S. Department of Energy Albuquerque Operations Office P.O. Box 5400 Albuquerque, New Mexico 87115
Dear Mr. Themelis:
In accordance with your request, we have reviewed the final design -
documents for the Durango site. The documents were submitted by the remedial action contractor and are dated April,1986. The staff's questions and comments are enclosed.
Based on staff review, we conclude that the proposed design is deficient in several areas. Therefore, we cannot conclude that the proposed h
design will meet the EPA standards. The major areas of concern involve surface water hydrology and erosion protection as well as the suitability of radon barrier soils.
Should you have any questions or if you would care to discuss the coments in greater detail, please contact Randy Brich at FTS 776-2811 or me at FTS 776-2805.
Sincerely, i
Edward F. Hawkins, Chief Licensing Branch 2 Uranium Recovery Field Office Region IV
Enclosure:
As stated cc:
J. D' Antonio, DOE J. G. Oldham, M-K OFC :URF
- URF0
+
e6060904s5 860b1S PDR WASTE POR NAME :RBrich/lv
- EHawkins wM-48 Ms:-
DATE :86/05/15
URANIUM MILL TAILINGS REMEDIAL ACTION PROJECT DURANGO, COLORADO FINAL DESIGN FOR REVIEW QUESTIONS AND COMMENTS Subcontract Document, Section 02200, Subsection 3.2, B.2.b, page 02200-10:
1.
During seasonal shutdown, seeding is not an acceptable means to prevent potential erosional losses.
Therefore, please propose an acceptable interim stabilization plan.
~
Volume I, Calculation No. 03-511-02-00:
2.
The information on Sheet 30 indicates that dispersivity and swell
. tests were run on soil samples from the Bodo Canyon site. However,-
we were unable to locate the results of the tests.
Information on the swell and dispersivity potential of soils to be used for the radon barrier must be provided before NRC can determine the acceptability of the proposed design. This comment was included in j
previous NRC comments dated August 21, 1985, and January 9, 1986, and was discussed at a 60 percent design meeting involving DOE, the TAC, the RAC and NRC in Albuquerque on November 20, 1985.
Resolution of this issue is required before concurrence with the RAP can be provided.
Volume II, Calculation No. 03-565-02-00:
3.
Sheets 9,10,11,12,13 and 14 contain irrelevant information.
Varying E on sheets 10-14 without utilizing a source term is not appropriate.
Final cover thicknesses should be based on the results of the additional testing discussed in Comment No. 5.
4.
Sheet 23 - Radon should be Radium 5.
All calculations and supporting data developed in conformance with the recommended testing contained on sheet 1 shall be submitted to NRC for review and approval prior to final site grading.
Volume III, Calculation No. 03-565-05-00:
6.
Our review of the embankment design indicates that the toe of the embankment in the southwest area of the pile will be located in a steep arroyo, with arroyo flows parallel to the embankment toe.
This design, as proposed, is not considered to be acceptable for
2 assuring long-term stability of the remediated pile. This conclusion is based on the following:
A.
The arroyo appears to be very steep (longitudinal slope of greater than 10%), and extremely high velocities and shear forces will be produced even by floods of small magnitude.
Because the erosion protection is not keyed into competent rock, these high velocities can produce lateral erosion of the channel banks, such that undercutting of the erosion protection is likely.
B.
The embankment erosion protection does not appear to be placed above the level of flood flows-in the arroyo.
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C.
The arroyo has some curvature and several natural bends, which will tend to increase shear forces.
D.
There are several other gullies and arroyos opposite the embankment (flowing northeast) where flood flows could impinge directly on the embankment.
In order to resolve the above concerns, design changes such as the following should be considered:
Erosion protection capable of resisting PMF velocities should be provided in the arroyo. This alternative, however, is likely to require extremely large rock ahd may not be practical to implement.
The toe of the embankment should be located above the arroyo PMF level and should be keyed into competent rock, such that the bottom of the key trench is at an elevation above the PMF.
In providing a revised design, further information will be needed regarding the elevations and competency of the bedrock.
Additionally, arroyo cross-sections and details of the embankment tce design will be needed to evaluate water surface profiles and velocities.
7.
Examination of the proposed design indicates that there are several areas of the embankment where the peak runoff rates on the einbankment will be greater than normal sheet flow rates. This is due to outside drainage areas contributing additional runoff to the embankments. Affected areas of the embankment include the extreme southwest corner of the site, the southeast corner (See also Question 8), and the extreme western corner.
3 The erosion protection should be checked, and redesigned if necessary, to assure that the erosion protection is adequate to resist these additional flows.
8.
The rock to be provided for the small embankment, which partially fills an existing arroyo in the southeast portion of the site, has been designed for sheet, rather than concentrated flows. Due to the configuration of the embankment, it is evident that a significant amount of flow concentration can be expected, particularly in the toe area.
In addition, it also appears that the embankment will receive a significant amount of runoff from drainage areas outside the embankment area (See also Question 7). Such runoff will likely be concentrated into the downstream toe area.
Based on these considerations, we conclude that the proposed erosion protection for this embankment area is unacceptable.
Unless the embankment configuration is changed, the erosion protection on the embankment should be redesigned to account for runoff from the total contributing drainage area.
Additionally, since this area will act much like a channel, special measures will be needed to assure that either (1) the exit velocity at the downstream end is non-erosive or (2) the toe of the channel is keyed into competent bedrock, similar to the termination of Ditch No. 1.
The design should be revised, as necessary.
9.
The erosion protection to be placed at the outlet of Ditch No.1 is not designed to resist flow velocities occurring in the channel to the north. Based on a review of the layout of the ditch termination (relative to the north channel), it appears that the erosion protection could be affected by both lateral erosion and headcutting in the north channel.
The riprap in the outlet area should be checked, and redesigned if necessary, to assure that the rock can resist the flow velocities produced by a PMF in the north channel.
An acceptable assumption for such computations would be to assume that an eroded cross-section is formed and that a PMF occurs at this eroded section (for example, if the north channel must widen 94 feet to ernde the outlet erosion protection, an additional channel width of 94 feet may be assumed in the computation of flow velocities).
Additionally, the contributing drainage area for the PMF should include the area of the pile which drains to the north channel; this area was not previously considered in estimating the PMF on the north channel.
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- 10. Our review of the computations associated with flushing of sediment from the drainage ditches indicates that the analyses presented may not adequately reflect conditions that will actually exist.
In general, the assumptions used to compute the flow velocities associated with relatively frequent flood events should not be the same conservative assumptions that were used to compute the magnitude and velocity of the PMF.
The calculations should be revised, using the following:
A.
A runoff coefficient of less than 1 should be used in the rational formula.
B.
The rainfall intensity and discharge should be based on the time of concentration and drainage area at various points along Ditch No. I and Ditch No. 2.
C.
Mannings's 'n' for lesser floods should be assumed to be greater than the 'n' value assumed for the PMF, due principally to decreased depths of flow for lesser floods.
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