Text

Preliminary Technical Evaluation Rept for Proposed Remedial Action at Tuba City Tailings Site,Tuba City,Az
	ML20148N509
Person / Time
Issue date:	03/07/1988
From:	; NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:	;
Shared Package
ML20148N505	List: ML20148N509;
References
	REF-WM-73 NUDOCS 8804070058
	Download: ML20148N509 (65)
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, i Preliminary Technical Evaluation Report For the Proposed Remedial Action At the Tuba City Tailings Site Tuba City, Arizona I

8804070058 000307 PDR WASTE WM-73 PDR

, _t Table of Contents Section Page

1.0 INTRODUCTION

............................................... I 2.0 GEOLOGY / SEISMOLOGY......................................... 4

. 2.1 Si te Geologic Cha rac te ri za tion. . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Geomo rp h o l ogy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.3 Seismotectonic Si te Characterization. . . . . . . . . . . . . . . . . . 5 2.4 Seismic Design........................................ 5 2.5 Co n c l u s i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.0 WATER RESOURCES............................................ 7 3.1 Su r f a c e Wa t e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1.1 Surface-Wa ter Characterization. . . . . . . . . . . . . . . . . 7 3.1.2 Su rface-Wa te r Qual i ty. . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1.3 Surface-Water Impacts and Restoration. . . . . . . . . . 7 3.2 G ro u n d Wa te r. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.1 Ground-Water Characteriza tion. . . . . . . . . . . . . . . . . . 7 3.2.2 Ground-Water Qualit- ......................... 9 3.2.3 G round-Wa te r impa c ts . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3 Conclusions........................................... 11 4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION............. 11 4.1 Hyd rol og i c De s c ri p t i on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2 Geomo rph i c Cons i de ra t i ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4' 3 Fl ooding Dete rmina ti ons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 15 4.3.1 PHP over Reclaimed Tailings Pile............... 15 4.3.2 PMF f rom Adjacent Drainage Area . . . . . . . . . . . . . . . . 16 4.4 Erosion Protection Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.4.1 Erosion Protection of the Reclaimed Pile....... 18 4.4.2 Erosion Protection of the Diversion Ditches.... 18 4.4.3 Erosion Protection of the East Swale........... 21 4.4.4 Hydraulic Design of the Ditch Outlets. . . . . . . . . . 21 4.4.5 Rock Durability................................ 22 4.5 Conclusions........................................... 23 i 5.0 GE0 TECHNICAL STABILITY..................................... 24 5.1 Slope Stability....................................... 24 5.2 Se t t l eme n t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.3 Liquefaction Potential................................ 27 5.4 Co n s t ru c t i o n C r i te r i a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5.5 Test Fi11s............................................ 28 5.6 Co n c l u s i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.0 RAD 0N ATTENUATION.......................................... 29 7.0

SUMMARY

.................................................... 30 REFERENCES BIBLIOGRAPHY APPENDIX A APPENDIX B

,: 1 1.0 - INTRODUCTION The Tuba City site was designated as one of 24 sites to be reclaimed by the Department of Energy (00E) under the Uranium Hill Tailings Radiation Control Act (UNTRCA) of 1978. UMTRCA requires that the Nuclear Regulatory Commission (NRC) concur in the selection and performance of remedial actions at the 24 sites. The purpose of this report is to document the NRC staff technical review of DOE's proposed remedial action for the Tuba City site.

The Tuba City processing site is located in northeast Arizona, approximately 6 miles east of Tuba City (Figure 1).

The remedial action proposed by 00E consists of stabilization in place of an estimated 600,000 cubic yards of off pile contaminated material and 689,000 cubic yards of tailings pile materials (Figure 2). The contaminated material will be encapsulated and covered with a soil layer to attenuate radon and a rock layer to protect against erosion. Drainage ditches will be provided to direct runoff away from the site.

The proposed remedial action must comply with standards established by the Environmental Protection Agency (EPA). These primary design standards are summarized below:

(a) Be effective for up to one thousand years, to the extent reasonably achievable, and, in any case, for at least 200 years, and, (b) Provide reasonable assurance that releases of radon-222 from residual radioactive material to the atmosphere will not:

(1) Exceed an average release rate of 20 picocuries per square meter pre second, or (2) Increase the annual average concentration of radon-222 in air at or above any location outside the disposal site by more than one-half picocurie per liter.

Final ground-water standards for the remedial actions will be established by EPA in the near future. Interim draf t standards for ground-water quality at Title I UMTRACA sites were proposed by EPA on September 24, 1987 (EPA-52 FR 36000-36008). Final discussions regarding the need for ground-water restoration activities will be made following promulgation of the standards. Other requirements of the standards and UMTRACA 1978, include such things as provisions for monitoring and surveillance, minimization of the need for future maintenance, ownership of the tailings and site by the Federal government, State and Tribal I

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t participation in the development and construction of the remedial action, l concurrence by NRC in the proposed remedial action plan and eventual j remedial actions, licensing of the site by NRC for surveillance and !

maintenance.

The staff review of the proposed remedial action included reviews of the following documents:

(a) Remedial Action Plan (RAP) - dated May 1987 (Reference 1).

t (b) Design Documents - Subcontract Documents, Final Design for Review and Calculations (Volumes I, II, III, IV and V) dated November 1986 (Reference 2).

(c) Draft Environmental Assessment - dated 1985 (Reference 3).

(d) Environmental Assessment - dated November 1986 (Reference 4).

(e) Design Documents - Subcontract Document, Final Design for Review and Calculations, Volume V Supplement, dated April 1987 (Reference 5).

(f) Addendum No. 3 Test Field, dated September 1987 (Reference 6).

(g) Jacobs Engineering Group, Inc. , letter dated September 21, 1987 !

(Reference 7).

(h) Information to Bidders Volumes I, II, III, IV, and V, dated June 1987 (Reference 8).

(i) DOE responses dated December 29, 1987, to previous NRC comments 1 (Reference 9).

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The staff review of the proposed remedial action is based primarily on the Standard Review Plan (Reference 10) developed by the NRC.

l 2.0 GE0 LOGY / SEISM 0 LOGY l

l 2.1 Site Geologic Characterization The Tuba City site is located in northeastern Arizona, approximately 6 miles east of Tuba City. The site is situated within the Navajo i Uplands portion of the Colorado Plateau. The local geologic and .

topographic environment is characterized by broad flat terraces, I steep-wall canyons and dissected drainage systems.

In the vicinity of the site, Jurassic and Triassic strata are exposed. This is a result of erosional and Neogene tectonic activity.

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5 Beneath the site, bedrock is encountered of Jurassic and Triassic age (Figure 3). The first bedrock to be encountered is the Jurassic age Navajo Sandstone which consists of cross-bedded sandstone and is fairly massive. Underlying the Navajo Sandstone is the Kayenta Formation, which consists of sandstone and mudstone. Both the Navajo Sandstone and Kayenta Formation dip to the northeast at approximately 2 degrees in the direction of the Tuba City synclinal axis. Locally pediment gravels, alluvial deposits and eolian sands of Quaternary age overlay much of the area.

2.2 Geomorphology In the vicinity of the site, wind erosion is a dominant erosional factor. In the local area, wind caused features exist as sand dunes and deflation basins. Evidence shows that fine grained tailings have been transported offsite by wind action. Proper care and management will have to be taken during remedial actions to minimize wind action.

2.3 Seismotectonic Site Characterization In the Tuba City area, seismic activity is very low (see Appendix B). The largest historical earthquake recorded in the area was 5.5 on the Richter scale and occurred in 1912. Most small quakes occur in an area southwest of the stabilization site in the San Francisco volcanic field. The Maximum Credible Earthquake (MCE) for this site was determined to be noncritical when applied to design of the site (Reference 1).

The site was analyzed for a floating earthquake, and a local magnitude of 6.2 was utilized. The assumptions used were that a floating quake would occur within a radial distance of 15 kilometers to the site, which would result in a calculated peak horizontal acceleration of 0.219, which is acceptable under present design criteria (Reference 1).

2.4 Seismic Design The site characterization report provided a detailed and conservative determination of seismic design parametes based on a detailed evaluation uf best available regional and site-specific active faulting data, which includes the following: aerial photographs, remote sensing, ground survey, field investigation, geologic information, NOAA earthquake data files, references and published data.

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2.5 Conclusions A review of geologic conditions existing at the site indicate that there is 11ttle likelihood of poor foundation materials, ground settlement and hazards due to slope instability or creep. A review of the seismotectonic data indicates little or low probability that ground accelerations at the site could exceed the design earthquake.

The staff, therefore, concludes that impacts from local geologic and seismic hazards at the stabilization site have been and will continue to be minimal.

3.0 WATER RESOURCES 3.1 Surface Water 3.1.1 Surface-Water Characterization Intermittent surface water in close proximity to the Tuba City site include only the Moenkopi Wash, which drains into the Little Colorado River. The wash.is located approximately 1.1 miles to the southeast of the site (Figure 4).

3.1.2 Surface-Water Quality Surface-water quality for Moenkopi Wash indicates that the water is high in total dissolved solids (TOS), sulfates, iron, sodium, calcium and gross alpha activity (Reference 3).

Surveys utilized by DOE indicate that the wash is not used for domestic water supply purposes at this time.

3.1. 3 Surface-Water Impacts and Restoration The Tuba City site does not significantly contribute to water quality character in Moenkopi Wash. Data does indicate that there is a relationship between constituent concentration increase and distance downstream. However, sampling data suggest that this relationship is probably due to the natural environment. Stabilization of the tailings and minimization of infiltration through the tailings will eliminate to the extent practicable the source of any surface water contamination f rom the site.

3.2 Ground Water 3.2.1 Ground-Water Characterization The uppermost strata in the vicinity of the Tuba City site is the Navajo Sandstone. The Navajo Sandstone consists of a fine

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r to medium grained sandstone with a matrix of carbonaceous cement. Underlying the Navajo Sandstone is the Kayenta Formation, which is an interbedded, fine grain sandstone and mudstone sequence. There is no hydraulic barrier between the l Navajo Sandstone and the Kayenta formation, and together they I make up one continuous aquifer called the N-aquifer.

The recharge area for the N-aquifer is thought to be 40 miles to the northeast of the Tuba City site in the area of Shonto, '

Arizona. At the Tuba City site, the N-aquifer is unconfined, with the water table ranging from 20 to 150 feet below the !

surface. The ground water flows in a southeasterly direction, and flow rates range from 5 feet per year (ft/yr) to 140 f t/yr t (see Appendix A).

3.2.2 Ground-Water Quality i

Data show that the tallings pile has contaminated the N-aquifer to a depth of approximately 100 feet and plume distance of ;

approximately 1,300 feet downgradient of the site (Figure 5).

The plume has high concentrations of selenium, uranium. TOS, ,

sulfates, calcium, cadmium, nitrate, iron and manganese; all of :

which exceed EPA drinking water standards (if applicable). {

3.2.3 Ground-Water Impacts e

As described in the previous subsection, contaraination of the !

N-aquifer at the stabilization site has occurred. It is not i known to what extent contaminated ground water is spreading in ;

the N-aquifer.

Of greatest concern in the proposed design is the infiltration [

of water through the radon cover, as this will control timing i and amount of water flux through the tailings and into the '

ground water. '

Final design of the radon cover has not been completed, and the ;

DOE is presently conducting research through two experimental plots. Evaluation of the proposed design indicated that l i

infiltration into the tailings, with subsequent leachate ;

entering the N-aquifer, could be minimized to the extent ;

practicable if the cover could be constructed to achievt: a hydraulic conductivity of 1 X 10.s em/see or less. The research is to determine if the hydraulic conductivity can be !

achieved in the field and to develop the necessary construction i I

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A RE A OF KNOWN CONTAMINATION AND ARE A LIKELY TO BECOME CONTAMINATED AS PLUME ADVA NCES

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techniques. The information obtained from these plots will enable the DOE to C sign a more effective cell to minimize k t

effacts of infiltration and leaching.

3.3 Conclusions DOE is in the process of re-evaluating potential infiltration and subscquent design of the cell. Therefore, the staff is deferring its conclusions on ground-water strategy at the site until such time as DOE evaluates infiltration of the disposal cell and finalizes its design (this will be based on test-fill studies). Additionally, .'

since the EPA standards for ground water protection are not yet finalized, a finding of compliance with the standards has not been This is also true of the need to perform any ground water '

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cleanup of the N-aquifer downgradient of the site.

4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION 4.1 Hydrologic Description !

The Tuba City tailings site is located on a gently-sloping terrace about 6 miles east of Tuba City Arizona. The closest stream to the >

site is Moenkopi Wash, which runs in a southwesterly direction about 6000 feet south of the site (Figure 4). The elevation of this stream is about 300 feet lower than the tailings pile; consequently,

, the potential for flood waters in Noenkopi Wash reaching the

tailings pile is negligible. Flood runoff at the site is produced i by rainfall occurring directly over the tailings pile and over a J 71-acre drainage area north and east of the pila, i The tailings pile will be stablitzed in its present location. A

typical cross-section of the stabilized pile is presented in i Figure 6. All contaminated material will be consolidated with the !

tailings, and the pile will be protected from flooding and erosion by a soil and rock cover. As shown on Figure 7, the surface of the i cover will be sloped at 3 or 3.5 percent toward the south. The pile sides will be sloped at 20 percent. Flood runoff from the drainage area north and east of the pile will be ( nsit:d around and away

] from the pile by a system of ditches and a swale.

a j In order to comply with EPA standard 40 CFR 192, which requires .

in part that the disposal area be designed to provide s

! reasonable assurance of control of radiological hazards to be

effective for cne thousand years, to the extent reasonably 4

achievable, and in any a

f

' 10CK EROSION .

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l 14 case, for 200 years, the criteria utilized by 00E in designing the flood protection are the Probable Maximum Precipitation (PMP) event and the Probable Maximum Flood (PMF).

A PMF is a hypothetical flood that is considered to be the most severe flood reasonably possible. The PMF is based on extreme rainfall and thus its exceedence probability cannot be quantified. However, it is a rare flood that has a very low probability. The rainfall that produces the PMF is the PHP which is defined at the greatest depth of precipitation that is physically possible at a particular geographical location. PMP estimates usually exceed the rainfall that most people experience. NOAA Technical Report NWS 25, "Comparison of Generalized Estimates of Probable Maximum Precipitation with Greatest Observed Rainfalls," shows observed rainfalls that have equaled or exceeded 50 percent of PHP. This publication shows that in the vicinity of Tuba City, Arizona, all recorded rainfall events have been less than 50 percent of PHP. On this basis, the staff concludes that a hypothetical rainfall amount (PHP) greater than twice the amount ever recorded results in a design flood (PMF) that has a very low probability of

, occurrence. Although it is not possible to assign a l probability to this flood, the staff concludes that the PMP/PMF l criteria meet the 200 to 1000 year EPA requirement.

4.2 Geomorphic Considerations The geomorphic setting at the site is relatively stable. There are l no major stream channels close enough to affect the stability of the site. Moenkopi Wash, which is 6000-feet south of the site, is far enough away so that any meandering and erosion will not af fect the site. In addition, Moenkopi Wash is cut into sandstone units resistant enough to minimize lateral erosion.

A small drainage swale to the east of the pile presents the only possible hazard of channel erosion. However, as discussed in l Section 4.4, the potential for erosion occurring in this swale and affecting the stabilized pile will be minimized by an apron and key l to be constructed at the toe of the pile slope on the side of the pile adjacent to the swale.

l Wind erosion is the dominant geomorphic process presently af fecting the tailings pile. However, placement of the soil and rock cover will significantly reduce the etfects of wind erosion at the site.

- , . , - . , - - ._ , , - = - . . . , . _ .-- _.- ,,, .,

e =

l I

15 4.3 Flooding Determinations To evaluate the effects of flooding and to determine the need for erosion protection features, DOE considered the potential for flooding from two sources; (1) a PHP event occurring directly over the tailings pile and (2) flooding due to a PMF from the adjacent 71-acre drainage area. The staff reviewed the material presented by DOE and concluded that there are no other credible sources of potential flooding that could adversely affect the reclaimed pile.

The staff also concludes that the design events (PMP and PMF) meet the criteria outlined in the Standard Review Plan (Reference 10) and are, therefore, acceptable. Details of DOE's flood computatinns were analyzed as discussed below.

4.3.1 PMP over the Reclaimed Tailings Pile PHP values were estimated by DOE using Hydrometeorological Report (HMR) No. 49 (Reference 11). A 1-hour PMP value of 8.0 inches was used as a basis for estimating cn appropriate PMP value for use in calculating a PHF for the pile top and outslopes. The PHP must correspond to the time of concentration (t . DOE assumed a t of 2.5 minutes and determinedthatE)2.5-minutePMPwouTdbeequalto27.5 percent of the 1-hour PHP. This resulted in a 2.5 minute PMP depth of 2.2 inches (.275 X 8 inches).

The staff reviewed DOE's procedures for estimating an appropriate PHP value to use in determining design flows for the pile top and concluded that a 1-hour PHP of 8 inches is acceptable. The staff also concluded that the percentage (27.5 percent) used to estimate a 2.5-minute duration PMP depth of 2.2 inches is an appropriate value to use and is in accordance with recommendations contained in NUREG/CR-4620 (Reference 12).

DOE utilized the Rational Formul' (Reference 13) to compute the PMF peak sheet flow down the pile top and outslopes. The Rational Formula requires that rainfall be expressed in inches per hour. Converting a rainfall rate of 2.2 inches in 2.5 minutes, results in a rainfall intensity (I) equal to 52.8 inches per hour. 00E further assumed that 100 percent of the rain that falls on the pile top and outslopes would result in runoff, so a runoff coef ficient (C) of 1.0 was used.

Based on a review of DOE's calculations, the staff concludes that the use of the Rational Method together with a C = 1 and an I = 52.8 in/ hour, results in a conservative flood discharge estimate and is thus acceptable.

l

16 4.3.2 PMF fron. Adjacent Orainage Area As shown on Figure 7, flood runoff from the area north of the tailings pile will be conveyed away from the pile by two interceptor ditches and two toe ditches. A swale will intercept flood runoff from the area to the east.

For the interceptor and toe ditches north of the pile, 00E used the Rational Method. As discussed in the previous section, the staff finds this' procedure acceptable because it results in conservative PMF estimates.

To check the adequacy of DOE's calculations, the staff independently estimated PNF peak discharges for the outlets of Toe Ditch No. 1 and Interceptor Ditch No. 1. A comparison between DOE's estimates and the staff's estimates is presented in Table 4-1.

Table 4-1 Comparison of PNF Discharges Ottch PMF Peak Discharge DOE Analysis NRC Analysis '

Toe Ditch No. 1 outlet 547 cfs 520 cfs Interceptor Ditch No.1 outlet 1286 cfs 1190 cfs

The staff, on the basis of this comparison, concludes that DOE's estimates of PMF discharges for the toe and interceptor ditches are conservative and thus acceptable for use in design of the ditches. A discussion of the erosion protection features of the toe and interceptor ditches follows in Section 4.4.

' The 1-hour PMP value of 8 inches (discussed in Section 4.3.1 above) was also used as a basis for estimating a PNF for the diversion swale east of the tailings pile. PMF values for durations less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> were determined using factors recommended in NUREG/CR-4620 (Reference 12). A PMF hydrograph was then calculated using a rainfall-runoff simulation model known as the Santa Barbara Urban Hydrograph Method. This resulted in a PMF peak discharge of 2606 cfs for the East Swale. The staff reviewed the iaformation provided by DOE and independently calculated a PMF using procedures described in Design of Small Dams (Reference 14). This evaluation resulted in a PMF of 3160 cfs which ir, slightly larger than DOE's

,,<,---w ,.--,-r-,- --e-+4--e me' v- -"----" " ' - * ' - - ~ ~ * - ' --'

17 estimate of 2606 cfs. A discussion of DOE's design process using a discharge of 2606 cfs follows below together with the staff's independent evaluation using a discharge of 3160 cfs.

Using Manning's equation with a design discharge of 2606 cfs and a roughness coefficient of 0.03, 00E estimated the depths, velocities and extent of flooding in the East Swale. The flow velocities calculated in this manner varied from 1.7 ft/sec to 5.3 ft/sec. The higher of these velocities are larger than what would be preferred to avoid erosion of the in-situ soils.

However, DOE addressed this potential for erosion by locating the East Swale such that flooding from a PMF event would remain at least 50 feet away from the toe of the pile. 00E also assumed a worst-case scenario by postulating that the swale would erode only in the direction of the pile. The depth of potential erosion was estimated and an apron and key trench were designed for the toe of the pile alongside the swale.

Design of this erosion protection feature is discussed in Section 4.4.3.

The staff independently estimated depths, velocities and the extent of flooding due to a discharge of 3160 cfs. This analysis indicated that velocities would be about 0.3 ft/sec greater than 00E's estimate, depths of flooding would be about 0.2 f t higher and the edge of the PMF flood plain would be about 45 ft away from the reclaimed pile as compared to the 50 ft estimated by 00E. Since the differences in flow velocities and flood depths are very small and the staff's PMF flood plain is only 5 ft closer to the reclaimed pile, the staff concludes that DOE's PMF peak discharge of 2606 cfs is acceptable for use in designing the East Swale.

4.4 Erosion Protection Design To minimize erosion of the pile top and outslopes, 00E proposes to l line them with a layer of riprap (rock) designed to withstand runoff from a PMP event.

The diversion channels have been designed to withstand PMF events.

These extreme flood events will result in flow velocities in the channels which may be high enough to cause erosion. To prc'ent excessive erosion from occurring, the interceptor and toe ditches will be armored with riprap.

l i

The East Swale will not be armored because its centerline is at least 200 ft away from the toe of the slope of the reclaimed pile.

l The toe of the reclaimed pile adjacent to the East Swale will be protected by an apron and key to assure that if there is erosion in l

the swale, the reclaimed pile is not adversely affected.

l

, :o 18 4.4.1 Erosion Protection of the Reclaimed Pile The top of the pile slopes toward the south and southwest at a maximum slope of 3.5 percent. The sides (outslopes) of the pile are sloped at 20 percent. The riprap for these slopes was designed using the Stephenson Method (Reference 15). The adequacy of the rock size was then checked using the Safety Factors Method (Reference 16).

For the pile top, DOE proposes to provide a 6-inch thick layer '

of riprap having a median diameter (Oso) of 1.6 inches. For the outslopes on the north, northwest and east sides, the proposed riprap is a 12-inch layer of 1.6-inch Oso rock. The riprap for the south and southwest outslopes has to be larger because these slopes receive runoff from the pile top. DOE proposes a 12-inch layer of rock having a D 3 o of 3.6 inches for these slopes.

The staff reviewed DOE's calculations and performed an independent analysis to verify the adequacy of the riprap.

This analysis was performed using procedures discussed in NUREG/CR-4651 (Reference 17). The staff calculated a Oso of 1.6 inches for the pile top. Since this is exactly the same Oso as DOE's value, the staff concludes that DOE's riprap design for the pile top is acceptable. Because the procedures used by DOE to design riprap for the outslopes are the same as

those used for the pile top, the staff did not perform an j independent evaluation for the outslopes. However, based on a i

review of DOE's calculations, the staff concludes that the

! erosion protection design for the outslopes is also acceptable.

i

! 4.4.2 Erosion Protection of the Diversion Ditches Two interceptor ditches will be located north of the reclaimed pile. The function of these ditches is to divert most of the flood runoff from the drainage area north of the pile away from the toe of the pile (Figure 7).

Runoff from the intervening drainage area between the interceptor ditches and the pile will be diverted away from the i pile by two toe ditches located along the north and west toes of the pile slopes.

Median rock sizes (Oso) were estimated by DOE using the Safety Factors Method (Reference 16). Table 4-2 shows Oso sizes for the interceptor ditches and Table 4-3 for the toe ditches.

l

19 4

Table 4-2 Riprap Erosion Protection - Interceptor Ditches Station Dso (in.) Riprao Thickness (in.)

Interceptor Of tch No.1

.0+00 3.6 12 9+00 18

, 15+00 9 24 16+00 i

- 36 20+00 12 24 22+00 6 15 22+50 Interceptor Ditch No. 2 0+00 18 12+00 9 24 13+50 15 "6 a

16+50 1 24 17+00 18 ,

17+50 l e

L

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e e 20

' Table 4-3 Riprap Erosion Protection - Toe Ditches 8 0 Dso (in.) Riprap Thickness (in.')

Toe Ditch No. 1 0+00 9 24 5+00 24 10+00 6 36 16+00 6 18 17+60

.6 12 18+00 Toe Ditch No. 2 0+00 9 24 5+00 24 10+50 24 12+00 18 13+00 u mme iminuini -

21 The. staff checked DOE's proposed 30 o sizes using the Shear Stress Method (Reference 18). Boundary shear in the channel bends was also checked to assure that the riprap can withstand the higher shear expected in the channel bends. On the basis of this analysis, the staff concludes that the riprap sizes proposed by DOE for the toe and interceptor ditches are acceptable since the staff's estimates were in agreement.

4.4.3 Erosion Protection of the East Swale As discussed in Section 4.3.2, the East Swale is not provided with any erosion protection except at the toe of the pile on the east side. The centerline of the East Swale is at least 200 feet away from the east toe of the reclaimed pile. During a PMF, the., edge of the flood plain would get no closer than about 50 feet away from the toe; consequently, it is probable that any erosion of this swale will not adversely affect the pile. 00E, however, conservatively assumed that the swale would erode in such a manner that the erosion would migrate westward so that eventually flood flows would come in contact with the east toe of the pile. A 20-foot apron keyed into the adjacent soil below the expected scour depth was designed to protect the pile against any potential erosion. An evaluation of the appropriate rock size was made using the Shear Stress Method (Reference 18) and the Safety Factorc Method (Reference 16). This evaluation showed that the apron key should be provided with riprap having a Oso of about 4.5 inches. For conservatism, 00E has proposed a Oso of l

6 inches for the apron key.

The staff reviewed DOE's calculations and concludes that both methods used to estimate the 03 o size for the apron key provide acceptable design values. Since DOE proposes to use a larger i Dso than required, the staff concludes that providing riprap with a Dso of 6 inches in the key trench is adequate to prevent excessive erosion of the east toe of the reclaimed pile.

4.4.4 Hydraulic Design of the Ditch Outlets The outlet sections on both the toe ditches and the interceptor ditches are flared to reduce discharge velocities before flood l flows are transitioned onto the existing soils. In addition, flared sections will be provided with rock toes to minimize erosion at the discharge end of the ditches.

l The rate at which a ditch diverges (flares out) must be limited or else the flow will not spread out and occupy the entire j width of the channel to dissipate the energy and reduce the

(

l L

22 flow velocity. The staff performed independent calculations using procedures from Design of Small Dams (Reference 14) to assure that the flared outlets provide an acceptable transition for their respective PMFs. These calculations showed that actual angles of divergence for both toe ditches are less than the allowable angles of divergence and, therefore, PMF floves will spread out as desired. For the interceptor ditches, however, the actual divergence angles are greater than the allowable, and the PHF flow will not spread out as desired.

The staff therefore concludes that the flared outlet designs of the toe ditches are acceptable. For the interceptor ditches however, the designs will require modification to provide a more gradual transition of the flared outlets.

The toes of the flared outlets will be keyed into the in situ soil to minimize the potential for downstream erosion. The staff compared DOE's design of the outlet toes with several designs suggested by the U.S. Army Corps of Engineers in EM 1110-2-1601 (Reference 18). On the basis of this comparison, the staff concludes that the outlet-end erosion protection ve - e of the toe and interceptor ditches is acceptabl\

4.4.5 Rock uutability The rock to be used for riprap should be hard, dense and durable and should be able to resist long exposure to i weathering. All stones should be contained reasonably well within the layer thickness, and surface irregularities should be minimal. The specifications should prescribe a gradation that will result in a dense, well graded mass that will prevent migration of the underlying material into the riprap.

I i

The rock proposed by 00E to be used as a source of riprap is

! dense basalt from the Shadow Mountain Quarry. Durability tests were performed on samples of the rock, and results were evaluated using procedures described in NUREG/CR-4620 (Reference 12) and NRC 1987 (Reference 19). The 00E evaluation indicated that the rock did not meet all the recommended durability requirements, and accordingly should be oversized by 27 percent for use in frequently saturated areas and 7 percent

for use in occasionally saturated areas. Frequently saturated areas are defined as natural and man-made channels, toes and l aprons. The occasionally saturated description applies to the pile top and outslopes.

l

s e 23 The designs of the pile top, outslopes and diversion ditches were completed prior to DOE's determination that the riprap would have to be oversized. Therefore, the specifications must be revised to reflect the increased rock sizes.

The staff reviewed DOE's calculations and agrees that oversizing will be required for rock from the Shadow Mountain Quarry. Since the oversized rock requirennents are not in the specifications, the staff concludes that the erosion protection specifications have to be revised. These specifications will have to be submitted to NRC for review and approval.

The staff also reviewed DOE's gradation requirement; using criteria described in NUREG/CR-4620 (Reference 12), ETL 1110-2-120 (Reference 23) and Design Standards No. 13 (Reference 20). This re':lew indicated that the gradation specifications are acceptable.

4.5 Conclusions The staff has reviewed the information provided by DOE and concludes that the site design meets the EPA requirements of 40 CFR 192, with regard to flood design measures and. erosion protection design except for the following open items:

1. The Oso riprap to be used in diversion ditches must be

oversized as required and the specifications revised to reflect the oversized rock.

2. Oversizing of the rock may require a revision of the gradation requirements.

3. The flared outlet sections of the interceptor ditches must be modified to provide a smooth transition to the unprotected in-situ soils.

Until these items are resolved, the erosion protection design cannot be considered final. Also, if DOE's research being conducted on two test filis indicates that there could be excessive infiltration into the pile, the pile configuration could change and possibly affect the riprap design of the pile top and outslopes. Flattening of the outslopes could also require relocation of the toe ditches, i

-.. m a i 24 5.0 GE0 TECHNICAL STABILITY 5.1 Slope Stability 00E presented static and pseudo-static slope stability analyses based on exploration and testing programs which demonstrated that the reclaimed facility will meet the minimum factors of safety recommended in Regulatory Guide 3.11, "Design, Canstruction, and Inspection of Embankment Retention Systems for Uranium Hills,"

Revision 2, dated December 1977 (Reference 21).

Parameters used in the stability models were based on "114 borings, 26 piezocone soundings, and 8 test pits in the disposal area and 10 test pits" for the borrow area. Locations of explorations are shown in Figures 3.4 through 3.6 of the RAP (Reference 1).

L$boratory testing on selected samples from the foundation soils, tailings pile, and borrow area is presented in Appendix 0 of the RAP (Reference 1). Volume V Supplement of the Final Design for Review, April 1987 (Reference 5) presents additional testing performed by DOE in 1987. The additional testing supported the design properties from Appendix 0 and the Final Design or indicated that the Final Design stability model's parameters were conservative.

A summary of the cross-sections analyzed, the soil design properties, and the resulting factors of safety from the computer modeling program STABL (Reference 2) are presented in Volume III of the Final Design for Review, November 1986 (Reference 2). 00E reported minimum long-term factors of safety for the critical slope of 3.2 under static conditions and 1.8 under "dynamic" conditions with a seismic coefficient of .15. Minimum short-term factors of safety were reported to be 2.7 under static conditions and 1.8 under "dynamic" conditions with a seismic coefficient of .10.

Pseudo-static rather than dynamic analyses were deemed appropriate as it was determined that "there is no possibility that these materials will lose significant strength during earthquakes." This conclusion was based on field and static laboratory testing and on the lack of ground water within the tailings pile and foundation.

The Maximum Credible Earthquake (HCE) for the Tuba City site has a magnitude of 6.2, with a recommended peak horizontal acceleration of 0.219. One-half and two-thirds of this expected acceleration were utilized as "seismic coefficients" for short and long-term studies, respectively. These seismic coefficients utilized in the pseudo static modeling were conservative, in that such values are generally associated with earthquakes of magnitudes IX and X (Reference 22).

t

25 NRC review of 00E's stability models found the presentation of results to be inadequate, as only selective results appeared to have been presented. Further inquiry indicated that the design data was no longer available and new analyses were reported for the critical section. Also noted was the discrepancy between soil design values reported in the RAP (Reference 1) and the values used in the modeling (Reference 2). The new analyses resulted in a mini'pum short-term "dynamic" factor of safety of 2.2 with a seismic coefficient of .10 and a minimum long-term "dynamic" factor of safety of 1.7 with a seismic coefficient of .15. These new analyses utilized the same soil parameters as the original modeling rather than the RAP design values. The reported "dynamic" minimum short-term factor of safety was greater than the minimum reported in the Final Design due to the tangent depth utilized in the new model and obviously does not represent a minimum.

To verify the stability analysis, the critical slope was independently analyzed using a modified Bishop program developed by USBR. A homogeneous critical section with minimum strength parameters was modeled. As in the 00E studies, no phreatic surface was utilized in the cross-section. This conservative analysis resulted in a static factor of safety greater than the minimum factor of safety of 1.5 recommended in Regulatory Guide 3.11 (Reference 20). Generally, if slopes meet or exceed the recomended requirement under static conditions, the minimum pseudo-static requirements will also be met when seismic coefficients of less than

.20 are used.

Based on the information presented by 00E and on the independent study, the NRC staff conclude:i that the design meets the requirements outlined in the SRP in that:

1. Sufficient cross-sections and profiles of the site were characterized.

2. The critical properties of the materials utilized in the stability modeling were substantiated and fell within expected limits.

3. The ground-water situation within the tailings disposal area was addressed.

4. Sufficient static and pseudo-static models were presented to determine reasonable minimum factors of safety for critical sections within the tailings pile which demonstrated an adequate margin of safety.

s i 26

5. The use of pseudo-static models in lieu of dynamic analysis was supported, and acceptable seismic coefficients were applied.

6. Independent analysis of a conservative model resulted in factors of safety well in excess of NRC's recommended minimum static factor of safety for impoundments.

5.2 Settlement An analysis of the settlement expected during and following construction activities at the disposal site was performed to evaluate the potential for disruption of the radon barrier and erosion protection layers. The 00E settlement analysis is in Volume II of the Final Design for Review, November 1986 (Reference 2), and indicates that up to 8 inches of settlement can be expected after the embankment cover has been placed. The resulting horizontal tensile strain on the radon barrier is expected to be .05 percent. The maximum differential settlements were calculated to be 0.7 percent. The studies took into consideration laboratory and field testing data and layering within the soil profiles under initial and final loading conditions.

The staff review, in accordance with the acceptance criteria set forth in the SRP (Reference 10), of the settlement analysis performed by the DOE indicates that the analyses utilized (1) commonly accepted procedures on representative profiles and (2) reasonably conservative average soil parameters in their settlement analysis.

However, the analyses did not support the determination that expected settlements would represent tolerable behavior, as it was not established that the submitted analysis of the cracking potential of the radon barrier material would approximate field conditions.

The maximum tensile strains that would be expected on the radon cover were calculated to be .05 percent by 00E. The 00E design procedure relates the plasticity index (PI) of the cover material to allowable tensile strains. According to the DOE design procedure, the lower bound of tensile strains that cause failure (cracking) in soils that are compacted no drier than about 3 percent below optimum is also about .05 percent. This lower bound is associated with a plasticity index (PI) of 0. The calculations in Volume II of the Final Design for Review (Reference 2) are based on an average PI of the Greasewood Lake borrow material of 11. With a PI of 11, the acceptable strain in the cover material prior to cracking is

.08 percent. However, the construction specifications propose to allow placement of non plastic material in the radon barrier fill, I

as 00E concluded that the PI of the cover material need not be greater than zero to prevent cracking. It is not generally accepted

e .

27 that DOE's design procedure will produce accurate estimates of cracking potential. Therefore, the staff does not consider it acceptable to design the cover with expected strains equal to the stain calculated to cause failure. A margin of safety is introduced if the selected material has a minimum PI of 11, for example, which has been estimated to be able to tolerate strains up .08 percent.

It is accepted that the PI of a material is an indicator of a behavior characteristic and should therefore be considered in the design process. In general, a larger PI would indicate that a material would exhibit a greater flexibility or resistance to cracking than a material with a lower PI. Therefore, the staff cannot consider the exclusion of a minimum PI requirement prudent and will require that such a requirement be included in the specifications prior to concurrence.

5.3 Liquefaction Potential DOE's liquefaction study used four different methods to evaluate the potential for liquefaction of the reclaiaed tailings pile; Koizumi's Method, Relative Density Comparison, Seed and Idriss's Simplified Method, and the Chinese Method. Based on the results of these analyses, DOE concluded that large-scale flow failure associated with liquefaction would be unlikely to occur under the design earthquake.

Due to the numerous assumptions made in the analyses (specifically the use of average soil properties), an independent Seed analysis using US8R procedures was performed on the 13 borings on which limited data was available. The independent analysis, like the 00E analyses, assumed that the materials were saturated. Several sand layers were identified as being potentially liquefiable. Review of the ground-water situation at the facility, however, indicates that the water level is well below the tailings pile foundation.

Therefore, the potentially liquefiable sands can only become saturated from outside sources such as percolation of rainfall.

The current design of the cover system will require that the radon barrier material demonstrate a permeability of 10 8 cm/sec or less.

This will effectively limit infiltration if the radon barrier remains structurally sound, making the possibility of saturation of the pile, and resulting liquefaction, negligible.

5.4 Construction Criteria The earthwork specifications are contained in Section 02200 of Appendix E of the RAP (Reference 1) and are summarized herc.

Contaminated and uncontaminated fill materials are to be compacted

. . _ _ ~ _ . .. .- . _ _ . .

i- .

28 to at least 90 percent of the maximum dry density and are to be placed in loose lifts no greater than 12 inches in depth. Radon barrier material is to be compacted to at least 100 percent of the maximum dry density at a moisture content at or up to 3 percent above optimum moisture content. Radon barrier material is to be excavated from a 4-foot face from the central portions of the borrow area as shown on drawing No. TU8-PS-10-0831 Revision 1. The soil must be classified as a SC or SM material with a maximum particle size of 2 inches and having at least 20 percent passing the No. 200 sieve by weight. No other limitations, such as minimum PI, are required in the specifications.

Quality control will consist of the following:

(a) In place density and moisture tests: one test per 500 cubic yards of radon barrier placed; one test per 1,000 cubic yards of contaminated and uncontaminated fill placed.

(b) Classification tests: one test per 2,000 cubic yards of fill placed (excluding contaminated fill).

(c) Gradation tests: one test per 2,000 cubic yards of fill placed (excluding contaminated fill).

Acceptance test procedures are provided in paragraph 1.6.8.

The staff review of the construction criteria and quality control program provided in the RAP indicates that the criteria are consistent with standard engineering practice, in accordance with the acceptance criteria set forth in the SRP (Reference 10) and are, therefore, acceptable. However, prior to concurrence, the specifications must include a lower bound for the plasticity index l of acceptable radon barrier materials (see Section 5.2).

l 5. 5 Test Fills To verify that the proposed radon barrier borrow will perform up to design standards, two test fills are to be constructed. One fill will be constructed with material from the Greasewood Lake borrow I

l and the other fill will use material from Greasewood Lake borrow combined with about 5 percent sodium bentonite. The test fills will define the construction procedures that will be necessary to meet the specified vertical permeability of 10 8 cm/sec. Details of the test fills and the construction specifications are presented in the l

RAP and in Section 02220 of Appendix E (Reference 1).

As construction techniques, sampling, and laboratory test procedures meet standard engineering practices, the staff considers the

e e 29 construction of the test fills and the associated testing program acceptable.

5. 6 Conclusions The staff considers that the construction of the test fills should provide an acceptable method for determining if the minimum vertical permeabilities can be achieved in the field. Until the ground-water concerns associated with infiltration have been satisfactorily addressed (partially from the results from the test fills), the design cannot be considered final. If the test fills and related models indicate that infiltration into the facility will be unacceptable, the pile configuration could change, which could possibly adversely affect the stability and settlement analyses.

Liquefaction may become a consideration if infiltration into the pile through the cover system will allow the liquefiable sand zones to become saturated. The geotechnical stability of DOE's plan is, therefore, considered an open item.

Also, final concurrence will not be given until the specifications include an acceptable lower bound for the PI of the radon barrier material.

6.0 RADON ATTENUATION As indicated by Volume I and Volume II of the Final Design for Review (Reference 2), calculations for the radon barrier will be incorporated in the "Final Design." The DOE calcul:tions are to be revised to reficct changes in earthwork specifications and additional test data that will be obtained from the test fills and during the placement of onsite and offsite contaminated materials.

The current design models a 12-layer tailings system, each 2.5 foot thick layer being assigned an appropriate activity, covered by 2.3 feet of onsite, offpile contaminated material and 7.6 feet of offsite contaminated material. The RAECOM computer code (Reference 24) was used to optimize the cover thickness. Several different cover systems were evaluated with the selected system requiring no recontouring of tailings and 3.5 feet of radon barrier material from the Greasewood Lake borrow area. Activities and emanation coefficients were based on testing of the materials. Long-term moisture contents were derived by 15-bar moisture tests, the Rawls/Brakensiek equation, and the Rogers' equation (Reference 10). The submitted cover analysis utilized the most conservative long-term moisture contents resulting from these methods.

To verify DOE's analysis, the RADON computer code (Reference 25) was used to model a tailings and cover system similar to DOE's. However, since the final design will use actual field data for fills of cot:taminated

A e =

30 material and the radon barrier material, the associated parameters (density and porosity) for each of these layers were conservatively given "default" values which were programmed into the computer code.

This analysis using conservative values, which would represent a maximum possible cover thickness, resulted in a required cover thickness of approximately 4.4 feet, about 1 foot more than DOE's analysis.

Therefore, DOE's estimated cover thickness of 3.5 feet is reasonable for preliminary acceptance. Any minor increase in the cover depth could easily be accommodated in the field, if required by the final design.

The design of the radon barrier will be evaluated when it is submitted for review. Therefore, radon attenuation will remain an open item.

7. 0

SUMMARY

This Technical Evaluation Report summarizes the NRC staff review of the proposed remedial action for the Tuba City tailings site. Additional information is needed prior to unconditional concurrence by NRC. The deficient areas have been noted in the text and additional information requested from D0E. Staff review of the additional information will be presented as a supplement to this report and will include the NRC concurrence position on the proposed remedial action. '

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REFERENCES

1. U.S. Department of Energy, "Remedial Action Plan and Site Design for Stabilization of the Inactive Uranium Mill Tailings Site at Tuba City, Arizona," UMTRA-00E/AL 050518.000, Docket WM-73, May 1987.

Available in the NRC Public Document Room (POR) for inspection and copying, for a fee.

2. U.S. Department of Energy, "Subcontract Documents, Final Design for Review," Calculation Volumes I, II, III, IV, V, Uranium Mill Tailings Remedial Action Project, Tuba City, Arizona, Docket WM-73, November 1986. Available in the NRC POR for inspection and copying, for a fee.

3. U.S. Department of Energy, "Draft Environmental Assessment of Remedial Action at the Tuba City Mill Tailings Site, Tuba City, Arizona,"

Docket No. WM-73, 1985. Available in the NRC POR for inspection and copying, for a fee.

4. U.S. Department of Energy, "Environmental Assessment-Remedial Action for the Uranium Mill Tailings Site at Tuba City, Arizona,"

UMTRA-DCE/EA-0317, Docket WM-73, November 1986. Available in tha NRC POR for inspection and copying, for a fee.

5. U.S. Ocpartment of Energy "Subcontract Documents, Final Design for Review," Calculation Volume V Supplement, Uranium Mill Tailings i Remedial Action Project, Tuba City, Arizona, Docket WM-73, April 1987. Available in the NRC POR for inspection and copying, for a

( fee.

G. U.S. Department of Energy, "Addendum 3-Subcontract Documents, 1986,"

Docket WM-73, September 1987. Available in the NRC POR for inspection and copying, for a fee.

l

7. Letter dated September 21, 1987, from Ned 8. Larson, Jacobs i

Engineering Group Inc. , to Tom Olsen, Nuclear Regulatory Commission, j Subject, Addendum 3 for the Tuba City Subcontract. Available in the NRC POR for inspection and copying, for a fee.

I

8. U.S. Department of Energy, "UMTRA Project - Tuba City, Information j to Bidders Volumes I, II, III, IV, IV," 4005-TU8-R-01-01110-00, t

2543U/634, Docket WM-73, June 1987. Available in the NRC POR for l Inspection and copying, for a fee.

l

9. Letter dated December 29, 1987, from W. John Arthur, III, Department l of energy, to Edward F. Hawkins, Nuclear Regulatory Commission, l Subject, 00E responses to NRC comments dated November 17, 1987, on Docket WM-73. Available in the NRC POR for inspection and copying, for a fee.

10. U.S. Nuclear Regulatory Commission, "Standard Review Plan for UMTRCA Title I Mill Tailings Remedial Action Plans," USNRC, Division of Waste Management Report, October 1985. Available from NRC's Division of Low-Level Waste Management and Decommissioning.

11. U.S. Department of Commerce, U.S. Army Corps of Engineers, Hydrometeorological Report No. 49, "Probable Maximum Precipitation Estimated, Colorado River and Great Basin Orainages,"

September 1977.

12. Nelson, J.D. , et al. , "Methodologies for Evaluating Long-Term Stabilization Designs of Uranium Mill Tailings Impoundments,"

NUREG/CR-4620, June 1986.

13. Chow, V.T., "Handbook of Applied Hydrology," McGraw Hill Book Company, New York, N.Y., 1964.

14. U.S. Bureau of Reclamation, U.S. Department of the Interior, "Design of Small Dams," 1973.

15. Stephenson, D. , "Rockfill Hydraulic Engineering Development in Geotechnical Engineering #27," Elsevier Scientific Publishing Company, 1979.

16. Simons, D. B., and Senturk, F., "Sediment Transport Technology,"

Fort Collins, Colorado,1976.

17. Abt, S. R. , et.al. , "Development of Riprap Design Criteria by Riprap Testing in Flumes: Phase I," NUREG/CR-4651.

18. U.S. Army Corps of Engineers, "Hydraulic Design of Flood Control Channels," EM 1110-2-1601, 1970.

19. U.S. Nuclear Regulatory Commission, Draf t Document, "Rock Durability-Criteria for Selection and Oversizing of Rock,"

November 17, 1987.

20. U.S. Bureau of Reclamation, "Design Standards No.13 - EMBANKMENT DAMS," Chapter 5 - Protective Filters, May 13, 1987,

21. U.S. Nuclear Regulatory Commission, Regulatory Guide 3.11. "Design, Constrdction, and Inspection of Embankment Retention Systems for Uranium Mills," December 1977. Copies are available from the U.S.

Government Printing Office, Washington, D.C. 20402, ATTN:

Regulatory Guide Account (16).

22. Seed, H. Bolton, "Earthquake-Resistant Design of Earth Dams," ASCE, May 1983.

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23. U.S. Army Corps of Engineers, "Additional Guidance for Riprap Channel Protection," ETL 1110-2-120, May 14, 1971.

24. U.S. Nuclear Regulatory Commission, "Radon Attenuation Handbook for Uranium Mill Tailings Cover Design," NRC Report NUREG/CR-3533, April 1984. Available for purchase from National Technical Information Service, Springfield, Virginia 22161.

25. U.S. Nuclear Regulatory Commission, "Calculation of Radon Flux Attenuation by Earthen Uranium Mill Tailings Covers," NRC Draft Regulatory Guide, May 1987.

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BIBLIOGRAPHY Atwell, P. 8. and I. W. Farmer, "Principles of Engineering Geology,"

Chapman and Hall, 1986.

Campbell, K. W. , "Near-Source Attenuation of Peak Horizontal

Acceleration," Bulletin of the Seismological Society of America, 71, 2039-2070 (1981).

t 4

Rahn, P. H. , Engineering Geology, Elsevier,1986. '

Seed and Idriss, "Ground Motions and Soil Liquefaction During ,

Earthquakes," Earthquake Engineering Research Institute, Berkeley, '

California, 1982.

Slemmons, D. 8., P. O. O'Malley, R. A. Whitney, D. H. Chung, and D. L. Bernreuter, "Assessment of Active Faults for Maximum Credible ,

Earthquakes of the Southern California-Northern Baja Region,"

University of California, Lawrence Livermore National Laboratory Publication No. UCID 19125, 48 p., 1982.

U.S. Department of the Navy, "Soil Mechanics," NAVFAC DM-7.1,1982. [

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j U.S. Nuclear Regulatory Commission, "Hydrologic Design Criteria for i 1

Tailings Retention Systems," Division of Waste Management Staff l

Technical Position WM-8201, January 1983. Available from NRC's l i

Division of Low-Level Waste Management and Decommissioning. !

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.., ., . _ _ - - , _ _ _ _ . . - ,_. ___ . . , . . _ _ _ . _ _ _ _ _ _ . _ _ _._ __. _ _ _, . , _ , ...__,.._-J

o e APPENDIX A Ground-Water Hydrology l

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(AFTER 00E, 1985)

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, o Borehole data Boring

Casing Screened diameter diameter interval formation of (in) completion Coments Well no. (in) (dbls, ft) 901 6.6 2 58 78 Navajo Ss 902 6.5 2 63-73 Kayenta Fmn.?

903 6.5 2 28 48 Navajo Ss 904 6.6 2 32 42 Navajo 55 905 6.6 2 65-80 Navajo Ss Dry 906 6.6 2 32-52 Navajo SS 907 6.0 2 49-69 Navajo Ss 908 6.6 2 52-67 Navajo Ss 909 6.6 2 68-83 Navajo 55 910 8.5 4 97 197 Navajo Ss 911 8.5 4 311-351 Navajo Ss .

912 8.5 4 123-163 Navajo 55 913 8.5 4 331-371 Navajo Ss 914 8.5 4- 139-156 Navajo Ss 915 8.5 '4 172-182 Navajo Ss 916 8.5 4 348 358 Navajo Ss 917 8.5 4 130-150 Navajo Ss 918 8.5 4 63-68 Navajo Ss 919 8.5 4 340-350 Navajo Ss 920 8.5 4 116-156 Navajo Ss 921 8.5 4 315-355 Navajo Ss e

, i Range of grvund-water flow rates calculated from slug test data

' Hydraulic . s Well conductivity Hydraulica Speed ID formation (ft/yr) gradient Porosity (ft/yr)

Minimum 902 Kayenta 48.3 2.9x10-2 0.35 Average 4.0 247.0 2.9x10-2 0.30 23.9 Maximum 904 Navajo Ss 892.0 2.9x10-2 0.25

, 103.0

2 .

Hydraulic gradient calculated as follows: f= .

hi = 5025.23 ft (well No. 907),

h2 4703.87 f t (well No. 902), 61. = distance from No. 907 to No. 902.

bPorosity from range reported by Cooley et al. (1969) for Navajo Sandstone .

25 percent to 35 percent. .

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Water-quality analyses of ground-water samples exhibiting contaminant levels above background concentrations Un Location: 906 906 907 907 Constituent measure Date: 01/05/85 03/31/85 01 M5/85 03/30/85 Alkalinity mg/l CACO 3 691.000 857.000 625.000 1151.000 Aluminum mg/l <0.100 <0.100 <0.100 <0.100 Annonium og/l 1.300 0.500 138.000 250.000 Antimony mg/l <0.003 <0.003 <0.003 <0.003 Arsenic mg/l <0.010 <0.010 <0.010' <0.010 l Barium mg/l <0.100 <0.100 <0.100 <0.100 Boron mg/l 0.060 0.300 0.140 0.400 Cadmium mg/l <0.001 <0.030 0.002 0.031 Calcium mg/l 580.000 760.000 350.000 540.000 Chloride mg/l 74.000 100.000 60.000 110.000 Chromium mg/l <0.010 , 0.030 <0.010 0.030 Cobalt mg/l <0.050 <0.050 0.150 0.220 Cond, in-situ Umho/cm ---

3950.000 ---

6000.000 Conductance Umho/cm 4390.000 --- 4300.000 --- -

Copper m9/1 <0.020 0.030 <0.020 0.030 Cyanide ag/l --- <0.010 ---

<0.010 Fluoride mg/l 0.150 0.100 0.230 0.200 Gross alpha pC1/1 - --- <20.000 --- <120.000

, Gross beta pC1/1 ---

64.000 ---

87.000 Iron mg/l <0.030 0.060 1.140 0.570 lead mg/l <0.010 <0.010 <0.010 <0.010 Magnesium mg/l 210.000 260.000 246.000 460.000 Manganese ag/l 0.150 0.150 2.020 2.400 Marcury mg/l <0.000 <0.000 <0.000 <0.000 Holybdenum mg/l <0.010 0.070 <0.010 0.020

Nickel mg/l <0.040 0.160 0.080 0.260 Nitra te og/l SA0.000 920.000 630.000 1400.000 NO2 & NO3 mg/l --- 1.200 ---

1.J00 j Org. carbon mg/l 6.000 7.000 3.500 20.000

Pb-210 pC1/1 <1.500 0.700 <1.500 1.000 i pH SU 6.630 6.470 6.690 6.390 Phosphate .mg/l <0.150 <0.100 <0.150 <0.100 Ps-210 pC1/1 <1.000 0.100 <1.000 0.200 Potassium mg/l 5.290 5.900 26.200 30.000 Ra-226 pC1/1 <1.000 0.200 <1.000 0.300 Ra-228 pC1/1 <1.000 0.300 <1.000 0.300 Selenium mg/l 0.015 0.027 0.012 0.024 Silicon mg/l 8.600 --- 12.400 ---

Silica mg/l --- 19.000 ---

24.000 Silver mg/l . <0.010 0.020 <0.010 0.020 S:dium mg/l 135.000 200.000 236.000 450.000 Strontium mg/1 4.430 7.900 2.600 5.500 Sulfate mg/l 1200.000 1800.000 1300.000 2500.000

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Water-quality analyses of ground-water samples exhibiting contaminant levels above background concentrations (Continued)

Unit of Location: 906 906 907 907 i Ceast1tuent measure Date: 01/05/85 03/31/85 01/05/85 03/30,/85 i Sulfide mg/l --. <0.100 ---

<0.100

Temp. in-situ C-degree --- 15.000 --- 14.000 Temperature C-degree 13.000 - . -

13.000 ---

Th-230 pC1/1 <1.000 0.000 <1.000 0.000 '

Tin mg/l <0.005 <0.050 <0.005 <0.050 Total solids mg/l 3820.000 5000.000 3660.000 6200.000 '

TOK mg/l --- <0.100 --- <0.100 U-234 pC1/1 122.000 --- 41.000 ---

U-238 pC1/1 95.000 ---

22.000 ---

Uranium mg/l --- 1.000 -.

0.210 Vanadium mg/l 0.010 <0.010 0.040 <0.010 Zinc mg/l 0.211 0.110 0.078 0.100 4

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e i Water-quality analyses of ground-water samples exhibiting i contaminant levels above background concentrations (Continued)

Unit of Location: 908 908a 908a goga goga Constituent measure Date: 01/29/85 03/29/85 03/29/85 03/29/05 03/29/85 Alkalinity mg/l CACO 3 Aluminum mg/l 1105.000 1243.000 1243.000 1243.000 1243.000

<0.100 <0.100 <0.100 <0.100 <0.100 Annonium mg/l 89.000 110.000 110.000 110.000 120.000 Antimony mg/l <0.003 <0.003 <0.003 <0.003 <0.003 Arsenic mg/l <0.010 <0.010 <0.010 <0.010 Barium <0.010 mg/l 40.100 . <0.100 <0.100 <0.100 <0.100 Boron mg/l 0.150 0.300 0.300 0.300 0.300 Cadmiura mg/l <0.001 0.036 0.033 0.039 0.035 Calc h a mg/l 537.000 - 540.000 520.000 550.000 550.000 Chloride og/l 120.000 120.000 100.000 96.000 Chromium 100.000 ag/l <0.010 0.040 0.040 0.040 0.040 Cobalt ag/l <0.0$0 0.080 0.060 0.060 0.060 Cond in-situ Umho/cm ---

6000.000 6000.000 6000.000 6000.000 Conductance Umho/cm 8590.000 --- --- -- ---

Copper mg/l <0.020 0.020 0.030 Cyanide

., 0.020 0.030 mg/l .

--- <0.010 <0.010 <0.010 <0.010 Firsoride mg/1 0.160 <0.100 <0.100 <0.100 Gross alpha <0.100 pC1/1 ---

<120.000 ( , - - . --- ---

Gross beta pC1/1 ---

76.000 --- --- ---

1ron mg/l <0.030 0.050 0.050 0.050 0.050 lead mg/l <0.010 <0.010 '<0.010 <0.010 Magnesium <0.010 mg/l 847.000 710.000 670.000 700.000 690.000 Manganese mg/l 0.290 0.330 0.320 0.330 0.350 Mercury mg/l <0.000 <0.000 <0.000 <0.000 Holybdenum <0.000 mg/l <0.010 <0.010 <0.010 <0.010 <0.010 '

Nickel mg/l <0.040 0.190 0.170 0.210 0.?10 N1trate mg/1 1300.000 1300.000 1300.000 1300.000 1500.000 NO2 & N03 mg/l ---

0.700 0.700 0.700 0.600 Org. carbon mg/l 4.000 4.000 2.000 4.000 Pb-210 pC1/1 <1.500 0.900 0.700 0.900 pH 0.600 ,

SU 6.940 6.370 6.370 6.370 6.370 Phosphate mg/l <0.150 <0.100 <0.100 <0.100 <0.100 Po-210 pC1/1 <1.000 0.000 0.100 0.000 0.300 Potassium og/l 21.100 21.000 20.000 21.000 21.000 Ra-226 pC1/1 <1.000 2.000 0.200 0.100 0.600 Ra-228 pC1/1 <1.000 0.100 0.200 1.200 0.300 Selenium mg/l 0.040 0.058 0.060 0.053 5111 con 0.053 mg/l 12.400 --- --- ---

Silica mg/l --- 26.000 26.000 25.000 2t 000 Si %er mg/l <0.010 0.020 0.030 0.030 SGN :uta 0.12C mg/l 585.000 580.000 550.000 560.000 560.001 Stronitum mg/l 5.600 5.500 5.300 5.300 4.800 Sulfate mg/l 3900.000 3900.000 3900.000 3700.000 3900.000

f Water-quality analyses of ground-water samWes exhibiting contaminant levels above background concentrations (Continued) j Unit of Location: 908' 908a 908a 906a 908a Constituent measure Date:

01/29/85 03/29/85 03/29/85 03/29/85 03/29/85 Sulfid'e mg/l ---

<0.100 <0.100 1emp, in-situ C-degree <0.100 <0.100 Temperature 12.500 12.500 12.500 12.500 C-degree. 10.900 --- --- ---

Th-230 pC1/1 <1.000 0.000 Tin 0.100 0.100 0.000 mg/l <0.005 <0.050 <0.050 Total solids mg/l <0.050 <0.050 8550.000 8200.000 8100,000 7900.000 8100.000 TUX mg/l --- <0,100 - - - ---

U-234 pC1/1 70.000 --- ---

U-238 pC1/1 37.000 ---

Uranium mg/l -- -

0.190 0.180 0.200 0.180 Vanadium mg/l 0.020 <0.010 0.010 0.010 0.010 Zinc mg/l 0.111 0.066 0.068 0.060 0.061 aSample purposes.from well number 908 was split four, ways for quality assurance

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Water-quality analyses of ground-water samples exhibiting contaminant levels above background concentrations (Continued)

Unit of Location: 909 909 Constituent measure Date: 01/04/85 03/29/85 Alka 11nity -mg/l CACO 3 331.000 347.000 Aluminum mg/l <0.100 0.200 Annonium mg/l 0.200 0.200 Antimony mg/l <0.003 <0.0C3 Arsenic mg/l

<0.010 <0.010 Barium mg/l <0.100 <0.100 Boron mg/l 0.090 0.400 Cadmium mg/l <0.001 0.033 Calcium mg/l 846.000 800.000 Chloride mg/l 216.000 200.000 Chromium mg/l <0.010 0.030 Cobalt mg/l <0.050 0.060 Cond, in-situ Umho/cm --- 3500.000 Conductance Umho/cm 4890.000 ---

Copper mg/l -

<0.020 0.030 Cyanide mg/l --- <0.010 Fluoride mg/l <0.010 <0.100 Gross alpha pC1/1 --. <10.000 Gross beta pC1/1 --- 26.000 Iron mg/l 1.960 0.060 Lead mg/l <0.010 <0.010 =

Magnesium mg/l 169.000 160.000 Manganese mg/l 0.090 0.070 Hercury mg/l <0.000 <0.000 Molybdenum mg/l <0.010 <0.010 Nickel mg/l <0.040 0.180 Nitrate mg/l 1100.000 1100.000 NO2 & it0 3 mg/l ---

<0.100 Org. carb2n mg/l 1.400 1.000 Pb-210 pC1/1 <1.500 0.900 pH SU 6.673 6.660 Phosphate mg/l <0.150 <0.100 Po-210 pC1/1 <1.000 0.000 Potassium - mg/l 6.040 3.500 Ra-226 pC1/1 <1.000 0.30 Ra-228 pC1/1 <1.000 0.900

Selenium mg/l 0.006 0.005 Silicon og/l 9.700 ---

Silica mg/l ---

18.000 Silver mg/l <0.010 0.010 Sodium mg/l 164.000 160.000 Strontium mg/l 6.960 7.900 Sulfate mg/) 1400.000 1600.000 m

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i Water-quality analy.as of ground-water samples exhibiting l contaminant levels above background concentrations (Concluded)

Unit of Location: 909 909 Constituent measure Date: 01/04/85 03/29/85 l Tuifide mg/l --- <0.100 1

Teep, in-situ C-degree --- 14.500 l' Temperature C-degree 13.000 ---

Th-230- pC1/1 !

<1.000 0.000 !

Tin mg/l 0.007 <0.050 lotai solids mg/1 4470.000 4600.000 i T0A mg/l --- 0.900 U-234 pC1/1 48.000 ---

U-238 pC1/1 22.000 ---

t Uranium mg/l --- 0.088 l vinadium mg/l 0.020 <0.010 Zinc mg/l 0.050 0.051 -

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APPENDIX B Seismic Data l

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(AFTER 00E, 1987)

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l EARTHOU AKE EPICENTER MAP FOR A 200km R ADIUS OF THE TUBA CITY TAILINGS SITE, WITH D ATA FROM THE NOA A C ATALOG l OF E A RTHOU A KES THROllGH 1985 (NO A A /NGn C.19 85)

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,, Department of Energy

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Albuquerque Operations Office

.i P.O. Box 5400

.+ Albuquerque, New Mexico 87115 FF.H 5 FEDERAL EXPRESS 2426016305 $ p O'y r; h Dale Smith /

Director, Uranium Recovery

,Q

/g/ffj II,

$*U k' Field Office Q T.14 Region IV $ H FE0 0 01988 > "!

-[f 730 Simm Street, suite 100A e Golden, CO 80401 ?q, \- um m O s ig.3av 9 cxur can

Dear Mr. Smith:

J 4 .::.

Enclosed for your execution are six (6) original concurrence signature pages for the "Reneiial Action Plan aM Site Design for Stabilization of the Inactive Uranium Mill Tailings Site at Tuba City, Arizona." Per the February 3,1988, telephone cx>nversation between Debbie Mann of my staff and ' Ibm Olsen of your staff, the NBC is prepared to provide conditional concurrence on the Tuba City RAP / design, Please sign the enclosed signature pages to indicate NRC's concurrence with the Tuba City PAP / design and return them to this office along with NBC's forml letter of conditional concurrence. Following execution of the signature pages by NIC, the final RAP / design will be incorporated as Appendix B of Cooperative Agreemnt No. DE-Et'04-85AL26731 between DOE, the Navajo Nation, and the Hopi Tribe. In addition, a final published version of the PAP / design will be forwarded to you for your files.

Should you have riuestions regarding this mtter, please contact Dabbie Mann at FTS 846-1243. .

Sincerely, .

W. John Arthur, III Acting Project Manager Uranium Mill Tailings Project Office Enclosure i oc w/o enclosure

! E. Banks, JD3 ,,

l G. Gnugnoli, NBC-!O l

J. Oldham, MK-F T. Olsen, NBC-URFV l

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. e in U.S. Department of Energy Agreement No. DE-FC04-85AL26731 Appendix B (Remedial Action Plan)

SIGNATURE PAGE THE UNITED STATES OF AMERICA NAVAJO NATION DEPARTMENT OF ENERGY M - 4/ 1 -

BY: , et // J'? BY:

. James R. Anderson Date Hava j gg,on;.y. : e Date Project Manger, Uranium Mill Tailings Project Office M TM C'd '~ '

HOPI BY: hia H o'p i T r i b e Date h

CONCURRENCE NUCLEAR REGULATORY COMMISSION DEPARTMENT OF INTERIOR BY BY #7 R. Dale Smith Date Eoe wilson qsrbdr, Jr. Dater Director Uranium Area Director Recovery Field Of fice, Navajo Area Office Region IV Bureau of Indian Affairs BY: /jb]M / j Wa'T t e r R . Mills Date

.I!. D # rA r e a D i r e c t o r Phoenix Area Office Bureau of Indian Affairs l

s- e U.S. Department of Energy Agreement Ao. DE-FC04-8 5 AL 2 6 7 31 Appendix B (Remedial Action Plan)

SIGNATURE PAGE THE UNITED STATES OF AMERICA NAVAJO NATION DEPARTMENT OF ENERGY

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U.S. Department of Energy Agreement No. DE-FC04-85AL 26731 Appendix B (Remedial Action Plan)

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/ James R. Anderson Date 'Nava o Nation Date Project Manger, Uranium E WM^h.

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U.S. Department of Energy Agreement No. DE-FC04-85AL26731 Appendix B (Remedial Action Plan)

SIGNATURE PAGE THE UNITED STATES OF AMERICA NAVAJO NATION DEPARTMENT OF ENERGY DY: *

James R. Anderson 8'3- 27 Date BY: /

Navajo Nation

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CONCURRENCE NUCLEAR REGULATORY COMMISSION DEPARTMENT OF INTERIOR BY .

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R. Dale Smith Date Area Mrector '

Director Uranium Navajo Area Office Recovery Field Office, Bureau of Indian Affaire Region IV g i BY: //IfgM WEller R. Mill's Date ACIM Area Director Phoenix Area Office '

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U.S. Department of Energy Agreement No. DE-FC04-85AL 26731 '

Appendix B (Remedial Action Plan)

SIGNATURE PAGE THE UNITED STATES OF AMERICA NAVAJO NATION DEPARTMENT OF ENERGY b a "

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U.S. Department of Energy Agreement No. DE-FC04-85AL26731 Appendix B (Remedial Action Plan)

SIGNATURE PAGE

.THE UNITED STATES OF AMERICA NAVAJO NATION DEPARTMENT OF ENERGY BY . e ~ // I7 BY: JU N 1 7 ti"3

/ James R. Anderson Date JNava o Nation Date Project Manger, Uranium C h h .n d '

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b.I N Date CONCURRENCE NUCLEAR REGULATORY COMMISSION DEPARTMENT OF INTERIOR BY: .

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Text

1.0 INTRODUCTION

SUMMARY

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SUMMARY

Dear Mr. Smith:

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