ML20211G808

Forwards Comments on Draft Remedial Action Plan for Monument Valley Site,Per 860322 Request.Plan Unacceptable Due to Serious Flooding & Erosion Conditions & Potential Foundation Problems.Use of Alternate Location Suggested

ML20211G808
Person / Time
Issue date:	06/06/1986
From:	Hawkins E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:	Themelis J ENERGY, DEPT. OF
References
REF-WM-70 NUDOCS 8606200197
Download: ML20211G808 (6)

Text

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DISTRIBUTION Docket.Eile WM-70 POR/DCS DBangart, RIV WM-70/RFB/86/06/04/0 RBrich T01sen HRose JUN 0 6126 PGarcia EHawkins LLW Branch, WMLU URF0 r/f TJohnson, WMGT Docket No. WM-70 040WM070301E 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:

i m.-,... . In.,accordance ,with,your , request. dated Marchr3&y4986 rwe~haverreviewed w, - --- w.= -

aha.aMhe-draft Reinedial Aot4cn Fian =(dRAP-)LFon.15& Mon 6snt Valley site. -Tha C- M staff's questions and coments are enclosed.

-- Based on staff review,' we conclude that-the proposed remedial action plan-" ~ ~ - -

is unacceptable. Because of serious flooding and erosion conditions and potential foundation problems at this site, it will be difficult to y provide a design which meets EPA standards and serious consideration should be given to moving the pile to an alternate location.

Should you have any questions, please contact either Randy Brich of my staff on FTS 776-2811 or me.

Sincerely, I si Edward F. Hawkins, Chief Licensing Branch 2 Uranium Recovery Field Office Region IV

Enclosure:

As stated cc: R. Sena, DOE Case Closed: 040WM070301E

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l NRC REVIEW COMMENTS Monument Valley Draft Remedial Action Plan l l

l Surface Water Hydrology

1. Our review of surface water hydrology and erosion protection aspects of the proposed design indicates that the site is located in an extremely flood-prone area and that the proposed erosion protection I may not be adequate.  ;

.._-(.a)-The -apron and erosion protection a1ong-the* southern and - --~~ - --

r northern portions of the pile are designed with fairly steep  ;

slopes (in the direction of flow). It is doubtful that the 1 proposed 4-inch (average D rock can resist velocities l produced by a Probable Maxb)m Flood..(PMF). Regardless of the

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. -,-..-. . .~ .sizemof the watersheds, the-times of"concentrationufor these - -- "- -

2_ ._ .-- - portions of the apron will be very shoriNnd-the -FMF will- h - ~~

likely be larger than expected due to the steepness of the terrain. Your conclusion that there will be no significant flooding impacts (page B-45) is not supported by any information regarding natural bedrock contours or flow velocities.

For the purposes of a draft RAP, provide documentation on the ability of the apron to resist a PMF. Such documentation should include (1) apron width, shape, and cross-sections, including location of bedrock; (2) apron slo e (in the

direction of flow); (3) drainage area (s); (4 PMFpeakflow(s);

(5) PMF velocities at critical points along the apron; (6) riprap and riprap toe requirements; (7) details of exit of ditch to natural topography, including depths to bedrock at the

, exit point; and (8) topographic maps and cross-sections of the area showing washes, channels, and design features.

(b) The apron and erosion protection along the eastern portion of the pile should be designed to. resist a PMF in Cane Valley Wash, assuming that a shift in the main channel occurs.

Geomorphic evidence indicates that there is a potential for major channel changes in the alluvial floodplain. The proposed design, which allows for undercutting of the rock toe and rock apron (with subsequent collapse), is not acceptable, particularly if it is possible to key the erosion protection i into bedrock. The erosion protection should be designed  ;

assuming that the altered channel is very close to the pile, I unless it can be conclusively documented that such a phenomena l

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could not reasonably occur. The erosion protection should be sufficient to withstand PMF channel velocities and should be keyed into bedrock, if possible.

(c) The erosion protection for the east side (and possibly the south side) of the pile should also be designed to resist flooding and lateral erosion in the small tributaries which parallel and discharge to Cane Valley Wash. The information provided is not sufficient to establish what effects these steep washes will have on the pile. In order to document the effects of these channels, provide design information similar to that requested in 1(a), above. Additionally, provide

_. __-. .information on the potential effects 1f 4ateral erosiorrand- - -

, headcutting for these channels considering, PMF velocities and bedrock elevations.

(d) .The erosion protection for the west side of the pile may need e ,,m... .nm.. -.m..,.J to.be designed to withstand .floodingeanderosion since-it- o - ~ - - +

..-. ...ww.~ - appears.that signi ficant potential-exists- fortlateral-erosion - -: - A-and/or gullying. Provide information on this potential, also. i 1

Overall, the NRC staff concludes a significant amount of additional documentation and design changes need to be provided in order to ~~ '

demonstrate the acceptability of the site remedial action design.

3 Because of the site location in a floodplain at the base of steep, '

1 highly-eroded slopes and the potential for significant geomorphic l changes to occur, it is likely that the erosion protection design will require significant modifications, which may prove to be very ,

costly to implement and, in fact, may be very difficult to design. l We conclude that strong consideration should be given to moving the  !

pile to a more stable location, especially in light of the measures '

that will be needed to provide adequate flood protection.

2. The NRC staff does not necessarily agree with the rock durability criteria outlined in DOE's Technical Approach Document (TAD), and does not agree that these criteria are acceptable. In general, the criteria in the TAD are much less stringent than other normally acceptable criteria, such as the United States Bureau of Reclamation (USBR) criteria for good-quality rock. However, we do agree that oversizing may be a viable alternative and can only be evaluated after additional durability tests are performed.

Based on the preliminary data provided, it does not appear that the rock from the Alhambra Rock source will meet USBR criteria for even poor-quality rock. We suggest that additional efforts be made to locate rock of better quality. If such rock cannot be found, l

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provide information on the methods and criteria that will be used to oversize the poor-quality rock that is available.

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Radon Barrier

3. Page 62, paragraph 6 -

Review of reported climatological data indicates that harsh winters and periods of snow cover are infrequent for this region. For example, according to the DEA, for about a 20-year period, Mexican Hat received an annual average snowfall of 3.3 inches. In addition, all normal maximum monthly temperatures were above freezing, while

.,__,__ ..__ ,,only 4 monthly normal minimum temperatures were below-freezing.- - --- -

3 Although the Monument Valley site is situated at a slightly higher elevation than Mexican Hat, the climates should be similar. Thus, it is extremely unlikely that frost will penetrate the rock and bedding material and impact the radon barrier material. Although m..... ..,m.....m..the.-statements in. the draft Remedial . Action Jlan.(dRAP)-maya be ~.- s. -- <

, . _ . .a_2. wpartially true, blanket incorporation 'in thea dRAP-is%ot considered- .~-a-- -

appropriate for this climate.

4. Page 63, Bullet No. 2 -

Please justify the use of average heap leach pad emanating fraction 3 values for the pond area and areas C, D, and E and rubble and roads. -

Specify whether the emanating fraction will be measured for these other areas during subsequent site preparation. If not, the emanating fraction value to be used will be as specified in the NRC's SRP (0.35) for these materials, or justify the use of the heap p leach pad's average value as representative for the materials of <

Concern.

5. Page 63, Bullet No. 3 -

Please justify the use of a diffusion coefficient determined from the heap leach pad material for describing areas C, D, and E and rubble and roads. Review of the dRAP does not indicate if the diffusion coefficient was determined for the pond material. If the pond material's diffusion coefficient was estimated from the heap leach pad material, please state this in the dRAP and justify its use.

6. Page B-25, Emanating Fraction -

The statement discussed in Comment No. 5 apparently contradicts the discussion on emanating fraction. Clarify whether pond material emanating fraction measurements were performed. If they were not,

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4 the NRC's SRP directs the implementation of an emanating fraction value of 0.35 for materials in whicn it was not determined.

7. Page B-32 Justify the use of the heap leach pad's diffusion coefficient as representative for the diffusion coefficient value for areas C, D, and E and rubble and roads.

8. Page B-38, Section B.5.6 Substantiate why a -5 bar suction is a better estimate of the

__ -- ...._.. _ .-long-term moisture value for-the radon barrier-material . - Please ------- ---

provide a reference that supports this statement. Also, -15 bar suction is not necessarily the lowest long-term moisture cortent for soils as evidenced by recent literature reviews; however, according to NRC's SRP, -15 bar suction has been selected as being L . ...,.- -.cepresentati.ve .of the 1ong-term. moisture.. content for-radon . barrier. - . .-- .-.m...

. . . . .a.a....-. material < Therefore, please edit this section-approprbtely. - ~- - --- -- - --

, Geohydrology J

i 9. Page D-224, Section D.7.2.5, second paragraph -

. Chemical and physical characterization of the onsite soils is '

necessary to allow verification of estimated attenuative properties; however, review of this section is not possible until the data is provided. .Therefore, please inform URF0 regarding soil characterization plans.

10. Page D-49, Section D.3.1.5 - Site-Specific UMTRA Project Geologic J Data

{ Please discuss seasonal variations and/or trends that occur in l ground water at the site and vicinity. Also, explain in detail the j i

impact seasonal variations will have on the ground-water regime with  ;

respect to continued contaminant production, plume migration, '

j attenuation and restoration processes. l l

Geotechnical

11. Page 51 The inadequate strength of foundation soils at the site presents a very serious concern. We are very doubtful that this basic flaw can be adequately alleviated through the use of deep dynamic compaction

! techniques. An extremely thorough testing program will have to be 4

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_ _ . . , , , , , _ . . , _ . , _ - _ _ , , , . - _ . . _ . . , , ,, ,. - - v--, ,.m .-__m_.. .,

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5 performed to confirm that the required densification has been achieved.

12. Page 62 The long-term moisture content of 18 percent for the 1-foot thick cover layer is questionable based on the very dry environment which exists at the site and the thickness of the layer. Please justify the use of this value for the long-term moisture content.

13 Page B-9, B-10

. _ ._. .,The-analysis' performed indicates that -the -relative density of - -"- -- ~ - - -

-i foundation soils would have to increase from 46 to 57 percent in order to provide a factor of safety of 1.5 against liquefaction. We are doubtful that adequate assurance of such a gain in relative

._ density can be provided (see No. 11 above).. Even if this assurance i, e...... ..... . m-- can. be-provided, it appears that. cyclic-mobil.ity<could sti.lLcause .a, < - . . -

. . . . . . - m ... . s.;gni ficant disruption of the- cover. A-thorough ~analys is of -the ..~ - u ~ :--

potential for disruption of the cover due to cyclic mobility must be performed.

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