ML20197B780

Forwards Comments on Draft Remedial Action Plan & Preliminary Design for Tuba City Umtrap.Final Design Will Be Issued in 2 to 3 Wks

ML20197B780
Person / Time
Issue date:	10/16/1986
From:	Hawkins E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:	Themelis J ENERGY, DEPT. OF
References
REF-WM-73 881016, NUDOCS 8610300404
Download: ML20197B780 (4)

Text

DISTRIBUTION Docket File WM-73

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PDR/DCS %

DBangart, RIV nM-73/TT0/86/10/08/0 T01sen RBrich RGonzales SGrace OCT 161985 EHawkins KHargis, NM LLW Branch, WMLU DGillen, WMLU URFO:TTO URF0 r/f Docket No. WM-73 040WM73110E John G. Themelis, Project Manager U.S. Department of Energy Albuquerque Operations Office P.O. Box 5400 Albuquerque, New Mexico 87115 e

Dear Mr. Themelis:

Staff review of the Draft Remedial Action Plan (DRAP) responses to NRC consnents and preliminary design for Tuba City have been completed. As we agreed, our review was conducted on all available data pertaining to the DRAP and Preliminary Design, as per October 6,1986 meeting between DOE and URF0 staff held in Denver, Colorado. DOE stated that the final design will be forthcoming in 2 to 3 weeks.

NRC consnents pertinent to the final design documents will be ' issued upon a review completion.

Should you have any comments or questions, please contact Mr. Tom Olsen of my staff on FTS 776-2813.

Sincerely, tel Edward F. Hawkins, Chief Licensing Branch 1 Uranium Recovery Field Office Region IV

Enclosure:

Consnents 8610300404 861016 PDR WASTE WM-73 PDR OFC *

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l Tuba City UMTRA Project Consnents on DRAP and Preliminary Design Ground Water

1. We understnad that the ground-water study for the site has been revised based on additional information and analyses. Please provide the details of this study.

Connents: Volume III Supplement to Preliminary Design.

Coninents on Volume III Supplement I. Calc. No. 18-839-21-00, " Embankment Design - Toe Drains - Design"

1. Sheet 4: In your conclusions on sheet 4, you state that a minimum freeboard of 0.60 ft. is maintained in toe ditch #1, and that this is adequate under PMF conditions. The cross-section for station 18+00, shown on sheet 15, shows a difference of 1.5 ft. (5063.5-5062.0) between the top and bottom of the ditch. The water depth at this station is 1.1 ft.; therefore, the minimum freeboard is only 0.4 ft.

Accumulation of silt and debris in the channels will probably reduce this freeboard. In addition, since the flow in the D ditch goes from subcritical to supercritical at about station 18+00, the water surface..wil.1 show undulations which will increase the water depth and further reduce the freeborad. You should therefore provide assurance that all the ditches have an

, adequate amount of freeboard. We note that for the interceptor h ditches, you have a minimum freeboard of 2 feet.

2. Sheet 5: You state that toe ditch #1 will discharge into a natural waterway with an exit velocity of 4.4 fps. 110 wever, sheet 4 shows an exit velocity of 4.8 fps. Please correct this apparent discrepancy.

3. Sheet 5: You state that rock toes are provided to prevent erosion as per the Army Corps of Engineers, EM 1110-2-1601.

This EM reconinends rock toe depths of 3 to 5 ft.; however, on sheet 18, you show a toe depth of only 2 feet. Since the exit velocity from ditch I will be either 4.4 or 4.8 fps (see coninents No. 2 above), which is high enough to erode the fine soils found at the site, the rock toe should be 3-5 feet as i reconinended in EM 1110-2-1601.

4 You divided toe ditches 1 and 2 into several reaches and calculated median riprap rock diameters (D50) for each reach.

Which D50 will be used for riprap design? Substantiate the

- selected rock size.

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5. Sheet 15: On the station 10+00 cross-section, you show a ditch sideslope of 5V to 1H. This should be corrected to IV to SH.

II. Calc. No. 18-828-05-00, "Pemanent Site Drainage - Design Flow Rate on East Side of Pile"

1. Sheet 22: Discuss how the infiltration values, used to calculate PMP runoff on sheet 22, were derived. Do these values represent on-site soil conditions? Substantiate your assumptions.

III. Calc. No. 18-828-07-00, " Site Grading and Drainage - Interceptor Ditches"

1. Sheet 3: On sheet 3, you state... "The flow velocity (and flow depth) is estimated using Mannings equation." Mannings equation is applicable where uniform flow conditions exist.

Since the channel bottom slopes and dimensions of the ditches vary from the upstream to the downstream ends, uniform flow conditions do not exist and the use of Mannings equation may not be conservative. Water surface profiles should therefore be calculated using a method which solves the dynamic equation of gradually varied flow, (the Corps of Engineers HEC-2 computer program is one acceptable method) unless you can is demonstrate that the use of Mannings equation results in more conservative estimates.of, flow velocities and depths.

The following comments were discussed with the RAC in a telephone conversation, and additional information has already been provided.

IV. Calc. No. 18-828-05, " Permanent Site Drainage - Design Flow Rate on East Side of Pile"

1. Sheet 7A: A plot of accumulated PMP verses time shows the PMP amount at time zero as being equal to 4.5 inches. This is not correct; the PHP at time zero should be zero. Also, the

PMP-time relationship is not linear and should therefore be l plotted on logarithmic coordinates.

2. Sheet 7A: The maximum 10-minute PHP is given as 5.5 inches.

However, the incremental PMP values used to calculate PMF hydrographs show a maximum 10-minute PMP of 4.3 inches (see sheets 7, 21, 22 and 24). Explain why the maximum PMP value used to calculate hydrographs was not 5.5 inches. Using 5.5 inches instead of 4.3 inches would result in a high PMF peak dischargo. Also, explain how the rainfall. values shown on sheet 7 were derived from the data on sheet 7A.

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3. Sheet 22: On sheet 22, you have tabulated the ordinates of an instant and a final hydrograph. The volumes of these hydrographs are equal, but the peaks are significantly different. Discuss how these two hydrographs are related and what each represents. It appears to us that the PMF peak you calculated (2564 cfs) is too low. The basis for this is that we calculated PMFs using several different approaches and in all cases, the PMF peaks were greater than 2564 cfs. Peaks calculated by the staff were as follows:

Rational method using "C" = 1 4120 cfs SCS method assuming no infiltration 4060 cfs SCS method using a CN = 90 3720 cfs e SCS method using a CN = 80 3160 cfs SCS method using your runoff values from sheet 22 3425 cfs 3

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