ML20058P460

Draft TER for Proposed Remedial Action at Naturita, Colorado Uranium Mill Tailings Site

ML20058P460
Person / Time
Issue date:	10/08/1993
From:	NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
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ML20058P451	List: ML20058P447 ML20058P460
References
REF-WM-66 NUDOCS 9310250041
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ABSTRACT This draft technical evaluation report (TER) summarizes the U.S. Nuclear Regulatory Commission (NRC) staff's review of the proposed remedial action for 1 the Naturita Uranium Mill Tailings Disposal Site (Naturita site). The sections of the TER are arranged by technical discipline to correspond to the i Environmental Protection Agency's (EPA's) standards in Title 40 of the Code of Federal Regulations (CFR), Part 192, Subparts A through C (EPA,1987). The NRC staff review of the DOE preliminary final Remedial Action Plan (RAP), MK Remedial Action Inspection Plan (D0E,1993a-e; MK,1993), and associaied documents identified significant open issues in erosion protection, ground-water hydrology, and radon attenuation and site cleanup as presented in Table 1.1 (Summary of Open Issues). The information to resolve the open issues should be provided in the final RAP. i F L L t i ) i I t NATURITA dTER October 8, 1993 l i

L '< TABLE OF CONTENTS i Section PJLat

1.0 INTRODUCTION

1-1 1.1 EPA Standards........................ 1-1 I 1.2 Site and Proposed Action 1-2 1.3 Review Process 1-2 1.4 TER Organization 1-9 1.5 Summary of Open Issues 1-9 2.0 GEOLOGIC STABILITY 2-1 2.1 Introduction 2-1 2.2 Location 2-1 2.3 Geology........................... 2-1 2.3.1 Physiographic Setting 2-1 2.3.2 Stratigraphic Setting 2-3 2.3.3 Structural Setting.................. 2-3 2.3.4 Geomorphic Setting.................. 2-3 2.3.5 Seismicity...................... 2-5 2.3.6 Natural Resources 2-7 2.4 Geologic Stability 2-7 2.4.1 Bedrock Suitability 2-9 2.4.2 Geomorphic Stability 2-9 2.4.3 Seismotectonic Stability............... 2-9 2.5 Conclusions........................ 2-10 3.0 GE0 TECHNICAL STABILITY 3-1 3.1 Introduction ........................ 3-1 3.2 Site and Material Characterization 3-1 ) 3.2.1 Site Descriptions 3-1 3.2.2 Site Investigations 3-2 i 3.2.3 Dry Flats Disposal Site Stratigraphy......... 3-3 i 3.2.4 Testing Program 3-3 3.3 Geotechnical Engineering Evaluation............. 3-4 3.3.1 Slope Stability Evaluation.............. 3-4 3.3.2 Settlement and Cover Cracking 3-5 3.3.3 Liquefaction..................... 3-5 3.3.4 Cover Design..................... 3-5 3.4 Geotechnical Construction Details.............. 3-7 3.4.1 Construction Methods and Features 3-7 3.4.2 Testing and Inspection................ 3-7 3.5 Con cl u s i on s......................... 3-7 4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION 4-1 4.1 Hydrologic Description and Site Conceptual Design...... 4-1 4.2 Flooding Determinations................... 4-1 4.2.1 Selection of Design Rainfall Event 4-1 4.2.2 Infiltration Losses 4-2 munu em i ocrater a, im

s' 4.2.3 Times of Concentration 4-2 l 4.2.4 Rainfall Distributions................ 4-3 4.2.5 Computation of PMF 4-3 4.2.5.1 Top and Side Slopes 4-3 4.2.5.2 Apron / Toe 4-4 4.3 Water Surface Profiles and Channel Velocities 4-4 4.3.1 Top and Side Slopes 4-4 4.3.2 Apron / Toe 4-4 4.4 Erosion Protection 4-5~ 4.4.1 Sizing of Erosion Protection............. 4-5 e 4.4.1.1 Top Slopes and Side Slopes 4-5 4.4.1.2 Apron / Toe 4-6 i 4.4.1.2.1 Lower Side Slope 4-6 4.4.1.2.2 Toe 4-6 4.4.1.2.3 Collapsed Slope 4-6 4.4.1.2.4 Natural Ground 4-6 4.4.2 Rock Durability 4-7 4.4.3 Testing and Inspection of Erosion Protection 4-8 4.5 Upstream Dam Failures 4-9 4.6 Conclusions 4-9 5.0 WATER RESOURCES PROTECTION 5-1 5.1 Introduction 5-1 5.2 Hydrogeologic Characterization 5-1 5.3 Conceptual Design Features to protect Water Resources.... 5-1 5.4 Disposal and Control of Residual Radioactive Materials (RRM)............................ 5-1 5.5 Cleanup and Control of Existing Contamination........ 5-1 5.6 Conclusions......................... 5-1 6.0 RADON ATTENUATION AND SITE CLEANUP 6-1 6.1 Introduction 6-1 6.2 Radon Attenuation...................... 6-1 6.2.1 Evaluation of Parameters 6-1 6.2.2 Evaluation of Radon Attenuation Model......... 6-5 6.3 Site Cleanup......................... 6-6 6.3.1 Radiological Site Characterization.......... 6-6 6.3.2 Cleanup Standards 6-7 6.3.3 Ve ri fi c at i on..................... 6-8 6.4 Conclusions 6-8 i

7.0 REFERENCES

7-1 l i I \\ l l NATURITA dTER ii October 8, 1993 l m

LIST OF FIGURES Fiaure Eggg FIGURE 1.1 LOCATION MAP OF THE NATURITA SITE, COLORADO......... 1-3 FIGURE 1.2 PRESENT CONDITIONS AT THE NATURITA SITE, COLORADO...... 1-4 FIGURE 1.3 EXTENT OF CONTAMINATION AT THE NATURITA SITE, COLORADO 1-5 FIGURE 1.4 LOCATION OF THE DRY FLATS DISPOSAL SITE, COLORADO...... 1-6 FIGURE 1.5 FINAL CONDITIONS AT THE ORY FLATS DISPOSAL SITE, COLORADO.. 1-7 FIGURE 1.6 TYPICAL CROSS SECTION OF THE DRY FLATS DISPOSAL CELL 1-8 FIGURE 2.1 PHYSIOGRAPHIC PROVINCES OF DRY FLATS DISPOSAL SITE REGION.. 2-2 FIGURE 2.2 GE0 LOGIC CROSS SECTION OF THE DRY FLATS DISPOSAL SITE.... 2-4 FlGURE 2.3 AREAS OF MINERAL RESOURCE DEVELOPMENT IN DRY FLATS REGION.. 2-8 LIST OF TABLES Table Eagg TABLE 1.1

SUMMARY

OF OPEN ISSUES.................. 1-10 TABLE 2.1 ESTIMATED MAXIMUM MAGNITUDE, INTENSITY, AND ACCELERATION FOR DRY FLATS SITE REGION.................. 2-6 t I NATURITA dTER iii

LIST OF ACRONYMS Acronym Definition ALARA As low As Reasonably Achievable CDH Colorado Department of Health CFR Code of Federal Regulations COE U.S. Army Corps of Engineers DOC U.S. Department of Commerce DOE U.S. Department of Energy DOI U.S. Department of the Interior DOT U.S. Department of Transportation EPA U.S. Environmental Protection Agency HMR Hydrometeorological Report LTSP Long-Term Surveillance Plan MCL Maximum Concentration Limit, or Maximum Contaminant Level NEPA National Environmental Policy Act NOAA National Oceanographic and Atmospheric Administration NRC U.S. Nuclear Regulatory Commission PMF Probable Maximum Flood PMP Probable Maximum Precipitation P0C Point of Compliance RAIP Remedial Action Inspection Plan RAP Remedial Action Plan RAS Remedial Action Selection Report SRP Standard Review Plan TER Technical Evaluation Report UMTRA Uranium Mill Tailings Remedial Action NATURITA dTER iv October 8, 1 M

t: l UMTRCA Uranium Mill Tailings Radiation Control Act of 1978 VCA Vanadium Corporation of America l p h t i t e f i NATURITA dTER V october 8, 1993 I

l.0 INTRODUCTION The Naturita site was designated as one of 24 abandoned uranium mill tailings piles to receive remedial action by the U.S. Department of Energy (00E) under the Uranium Mill Tailings Radiation Control Act of 1978 (UMTRCA). UMTRCA requires, in part, that the U.S. Nuclear Regulatory Commission-(NRC) concur with DOE's selection of remedial action, such that the remedial action meets appropriate standards promulgated by the U.S. Environmental Protection Agency (EPA). This draf t Technical Evaluation Report (TER) documents the NRC staff's review of the DOE Remedial Action Plan (RAP), Remdial Action Inspection Plan (RAIP) (00E,1993a-e; MK,1993) and all associated documentr. tion pertinent to the proposed remedial action. 1.1 EPA Standards As required by UMTRCA, remedial action at the Naturita site must comply with regulations established by the EPA in 40 CFR Part 192, Subparts A through C (EPA, 1987). These regulations may be summarized as follows: 1. The disposal site shall be designed to control the tailings and other residual radioactive material for 1000 years to the extent reasonably achievable and, in any case, for at least 200 years [40 CFR 192.02(a)(1)]. 2. The disposal site design shall provide reasonable assurance that releases of radon-222 from residual radioactive materials to the atmosphere will not exceed 20 picocuries/ square meter /second or increase the annual average concentration of radon-222 in air at any location outside of the disposal site by more than 0.5 picocurie / liter [40 CFR 192.02(a)(2)]. l 3. The remedial action shall ensure that radium-226 concentrations, in land that is not part of the disposal site, averaged over any area of 100 square meters, do not exceed the background level by more than 5 picocuries/ gram (pCi/g) averaged over the first 15 centimeters of soil below the surface and 15 pCi/g averaged over any 15-centimeter-thick layer of soil more than 15 centimeters below the land surface [40 CFR 192.12(a)]. On September 3,1985, the U.S. Tenth Circuit Court of Appeals remanded the ground-water standards (40 CFR Part 192.2(a)(2)-(3)) and stipulated that EPA promulgate new ground-water standards. EPA proposed these standards in the form of revisions to Subparts A-C of 40 CFR Part 192 in September 1987. The proposed standards consist of two parts; a first part, governing the control of any future ground-water contamination that may occur from tailings piles after remedial action, and a second part, governing the cleanup of contamination that occurred before the remedial action of the tailings. In accordance with UMTRCA Section 108(a)(3), the remedial action shall comply with the EPA proposed standards until such time as the final standards are promulgated. At that time, DOE has committed to re-evaluate its ground-water protection plan and undertakt such action as necessary to ensure that the final EPA standards are met. muma enn 1-1 octot r a,1993 i

i' j 1.2 Site and Proposed Action The Naturita uranium mill processing site is located in Montrose County, Colorado, approximately two miles northwest of the town of Naturita along Colorado State Highway 141 (Figure 1.1). The designated site encompassing about 53 acres includes the former tailings area, the mill facility and ore buying station, and the adjacent ore storage area (Figure 1.2). No tailings pile remains at the site due to the removal and reprocessing activities by Ranchers Exploration and Development Corporation g)t Vancorum (Durita facility). Approximately 547,000 cubic yards (yd of contaminated material 3 at the Naturita processing site includes 115,000 yd from 14 acres of mill 3 3 yard, 12,000 yd from 12 acres of former ore storage area, 295,000 yd from 3 196 acres of windblown /other material (areas A through G), 117,000 yd from 3 27 acres of fomer tailings area, and 8,000 yd of demolition debris (Figure 1.3) The proposed remedial action for the disposal and stabilization of the contaminated materials is to relocate them to the Dry Flats disposal site (Figure 1.4). The Dry Flats disposal site is located approximately six road miles southeast of the Naturita processing site, and is at the top of the drainage divide between the San Miguel River to the north and the Dolores River to the south. The disposal cell will be configured as shown in Figure 1.5, and will have a typical cross section as shown in Figure 1.6. 1.3 Review Process The NRC staff review was performed in accordance with the Standard Review Plan (SRP) for UMTRCA Title I Mill Tailings Remedial Action Plans (NRC,1993) and consisted of comprehensive assessments of DOE's proposed remedial action plan and site design. Staff review of the RAP and designs submitted by DOE indicate that there are still open issues as presented in Section 1.5 and discussed in further detail in Chapters 2 through 6 of this draft TER. All issues must be addressed before the NRC staff can concur with the proposed remedial action. The NRC will review all revisions to the RAP submitted by DOE in this regard. Upon resolution of the open issues, the NRC staff will revise this TER into final form to include evaluations and conclusions with respect to the additional information submitted by D0E. P L NATURITA dTEa 1-2 october 8, 1993

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) The remedial action information assessed by the NRC staff was provided primarily in the following documents (DOE,1993a-e; MK,1993): 1. DOE, 1993a. " Remedial Action Plan and Site Design for Stabilization of the Inactive Uranium Mill Tailings Site at Naturita, Colorado, Preliminary Final," UMTRA-D0E/AL/62350-40PF, August 1993 (NAT-RAP), Remedial Action Selection Report. 2. DOE, 1993b. NAT-RAP, Attachment 1, consisting of Subcontract Documents (June 1993), Calculations (Volumes I-IV, June 1993), Information for Reviewers (June 1993), and Information for Bidders (Volumes I-IV, June 1993). 3. DOE, 1993c. NAT-RAP, Attachment 2, Geology Report (August 1993). 4. DOE, 1993d. NAT-RAP. Attachment 3, Groundwater Hydrology Report (August 1993). 5. DOE, 1993e. NAT-RAP. Attachment 4. Water Resources Protection Strategy (August 1993). 6. MK-Ferguson Company, 1993. "UMTRA Project, Naturita Remedial Action Inspection Plan, Rev 0," August 1993. 1.4 TER Organization The purpose of this draft TER is to document the NRC staff review of DOE's RAP and RAIP for the Naturita site. The following sections of this report have been organized by technical discipline relative to the EPA standards in 40 CFR Part 192, Subparts A-C. Sections 2, 3, and 4 provide the technical basis for the NRC staff's conclusions with respect to the long-term stability standard in 192.02(a). Section 5, Water Resources Protection, summarizes the NRC staff's conclusions and remaining open issues regarding the adequacy of DOE's compliance demonstration with respect to EPA's ground-water protection requirements in 40 CFR Part 192. Section 6 provides the basis for the staff conclusions and identifies open issues with respect to the radon control standards in 192.02(b) and soil cleanup standards in 192.12. 1.5 Summary of Open Issues The NRC staff review of the proposed RAP er.d final design has identified open issues, which are discussed in more detail in the following Sections. A brief summary of these open issues has been provided in Table 1.1. 4 NATURITA dTEa 1-9 octote a, m3 )

1 r' TABLE 1.1

SUMMARY

OF OPEN ISSUES OPEN ISSUE TER Subsection 1. DOE needs to provide additional 4.4.3 information to assure that durability testing is representative of the rock that will be produced for erosion protection. In addition, DOE should provide information and specifications regarding the actual procedures that will be used during construction to assure that a layer of uniformly-mixed rock will be placed. The specifications should be based on the amounts of less durable rock that are present in the layer, as determined from the durability testing program. 2. DOE should revise the RAP to describe 5.1 where the process water for the mill was derived. 3. DOE states that the uppermost aquifer 5.2 at the disposal site is Class III, based on low yield (< 150 gallons per day). DOE must provide a calculation, based on existing site characterization data, that shows that the sustained yield of the uppermost aquifer at the disposal site is < 150 gpd. 4. Demonstrate compliance with EPA's final 5.5 ground-water clearup standards in 40 CFR 192, Subparts B and C. Resolution may be deferred until a separate phase of the UMTRA Project. 5. In the radon barrier design calculation 6.2.1 (17-741-02-01) provided in this Preliminary Final RAP, DOE indicates that additional field investigation and laboratory testing were performed in April-May 1993, and the results have not yet been included in. the analysis. This new data needs to be incorporated into the analysis presented in the Final RAP. NATURMA dTEa 1-10 october s, 1993 L i 4

OPEN ISSUE TER Subsection i 6. DOE should resolve the inconsistency 6.2.1 A concerning the contaminated material placement sequence, i.e., whether there is layering or mixing of the ore storage area and mill yard materials. 7. Since the windblown material represents 6.2.1 A the largest volume of the contaminated i material, and will be next to the radon barrier, DOE should either 1) establish a long-term moisture content for the windblown material based on actual test data, or 2) provide specific discussion and reference to soil data to justify the assumption that the 12 percent mill yard material value can be conservatively applied to the windblown material. 8. The DOE Technical Approach Document 6.2.1 A (DOE, 1989) indicates that an average diffusion coefficient will be determined from samples of each distinct contaminated material. In keeping with this, DOE should have additional (at least three) diffusion coefficient tests for both the windblown and tailings pile area contaminated materials, or otherwise provide justification that conservative values were used for the model. 9. Additional testing of the radon barrier 6.2.1 B long-term moisture and diffusion coefficient should be run on SM materials to provide a representative average, or changes should be made to the specifications to require a material (CL) that fits the parameters of the tested material. Furthermore, additional in-situ moisture data should be obtained to resolve the questionable data presented in the RAP. 10. The discussion needs to mention whether 6.3.1 the site has areas that could have had conditions that preferentially mobilized Th-230. matunna otra 1-11 october e, 1993

OPEN ISSUE TER Subsection 11. In order to provide adequate Th-230 6.3.1 characterization, more samples at the depth limit for Ra-226 excavation should be analyzed for Th-230, particularly in the former tailings pile and are storage areas. 12. Since DOE did not discuss the presence 6.3.1 of natural, elevated radioactive material, or the presence of are spillage along the road, DOE should indicate the possible reason for the elevated uranium, and what further exploration will be performed. 13. DOE should provide more background Ra-6.3.1 226 data. 14. DOE should either remove the 6.3.2 calculation until such time as supplemental standards are proposed in a PID, or modify the RAS section to indicate that the supplemental standards discussed in the calculation are a part of the present RAP review. 15. DOE should delete the phrase referring 6.3.2 to working level determination for Th-230 at depth. 16. If material is non-radiologically 6.3.2 contaminated hazardous, it is neither residual radioactive material nor mixed waste. Therefore, it should be disposed of offsite in a manner approved by the appropriate authority. DOE should revise Section 02081, Part 3.3.J, of the Specifications accordingly. 17. DOE should correct page 6-9 of the RAS 6.3.3 to conform to the verification sampling plan outlined in the generic thorium policy, or present justification for any deviation. j 1 ) NATURITA dTEa 1-12 octobu a, m 3 i ?

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2.0 GE0 LOGIC STABILITY 2.1 Introduction This section of the TER documents the staff's review of regional geologic l information for the proposed remedial action at the Naturita uranium mill l processing site and the Dry flats disposal site in southwestern Colorado. Since DOE has proposed to postpone cleanup of the groundwater at the Naturita processing site until a separate phase of the UMTRA Project, the emphasis in this section is on the geologic information relative to the disposal of the contaminated material at the Dry Flats disposal site. i The EPA standards (40 CFR 192) do not include generic or site-specific i requirements for characterization of geologic conditions at UMTRA Project l sites. Rather, 40 CFR 192.02(a) requires that control mechanisms be designed to be effective for up to 1,000 years, to the extent achievable, and in any case for at least 200 years. NRC staff has interpreted this standard to mean that certain geologic conditions must be met in order to have reasonable assurance that the long-term performance objectives vill be achieved. L Guidance with regard to these conditions is specified in the SRP (NRC, 1993). 2.2 Location The Naturita uranium mill processing site is located in Montrose County, Colorado, approximately two miles northwest of the town of Naturita. The Dry flats disposal site is located approximately six road miles southeast of the Naturita processing site. Section 1.0 gives a more detailed description and map location for the sites. 2.3 Geology DOE characterized regional and site-specific geology by referring to published and unpublished geologic literature, aerial photographs, and maps; reviewing subsurface geologic data, including logs of exploratory boreholes drilled on the site; and conducting field investigations as recommended in SRP Section 2.2.2.1. A summary of DOE's geologic characterization is presented below. 2.3.1 Physiographic Setting The site region lies in the Paradox Basin within the Canyon Lands section of the Colorado Plateau physiographic province (Hunt,1967) (Figure 2.1). The Canyon Lands are characterized by deeply incised drainages and isolated mesas with elevations ranging from 5,000 to 7,500 feet (ft) above mean sea level. The surface topography of the Dry Flats disposal site region results from resistant outcrops of the Dakota Sandstone Formation on the crest of an anticlinal structure. The site is at the top of the drainage divide between the San Miguel River to the north and the Dolores River to the south. NATURITA dTEn 2-1 october a,1993

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? l 2.3.2 Stratigraphic Setting DOE characterized stratigraphy by: referring to published and unpublished geologic literature and maps; reviewing site-specific subsurface geologic data, including logs of exploratory boreholes drilled on the site; and conducting field investigations as recommended in SRP Section 2.2.2.1. i Bedrock in the site region consists of a thick sequence 01 inarine and continental sedimentary rocks of Paleozoic and Mesozoic Age._ Tertiary Age sediments are not present. At the Dry Flats site in the Paradox Basin, the ' t Precambrian basement rocks are overlain by Cambrian to Mississippian Age-limestones and shales and a thick sequence of Paleozoic evaporites and clastics. Immediately underlying the site is a thin (one to two ft) soil layer, 100 to 150 ft of the Dakota Sandstone Formation (sandstone with a~ claystone and dark carbonaceous shale unit), and up to 180 ft.of the Burro Canyon Formation (sandstone with some mudstone). The NRC staff has reviewed the details of the regional and site stratigraphy ~ as provided in the RAP by DOE and concludes that the characterization of the Dry Flats disposal site adequately establishes the regional and site l stratigraphy. 2.3.3 Structural Setting DOE characterized the region's structural setting by referring to published regional geologic maps, aerial reconnaissance, field observations, and mapping of features critical to assuring the long-term stability of the remedial - i action. These studies were recommended in SRP Section 2.2.2.3. A summary of l DOE's structural characterization is presented below. The Dry Flats disposal site is in the Paradox Basin which is ~ characterized by l graben-faulted anticlinal structures. These anticlines were produced by-diapiric intrusion of salt into the overlying strata from the deeply underlying thick evaporite beds and by compressional folding stress from the-Larimide Orogeny. As compressional forces relaxed, graben faulting developed j on the crests of the salt anticlines causing their collapse. A second phase of collapse was caused by dissolution of the salt due to the deep incision of the drainage with flowage of the salt towards the rivers (Cater,1970). The i beds underlying the disposal site are relatively flat lying. Figure 2.2 is a j cross-section illustrating this structure. The NRC staff has reviewed the details of the regional and site structure of the Dry Flats disposal site as provided in the RAP by DOE, and concludes that the characterization adequately establishes the regional and site structural setting. 2.3.4 Geomorphic Setting DOE characterized the site geomorphology by referring to published literature ~ and topographic maps, as recommended in SRP Section 2.2.2.2. Site geomorphic.- utuam om 2-3 ocrate a,1993 l ~- g-

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l- + conditions were characterized by aerial photographic interpretation and field observations. A summary of DOE's geomorphic characterization is provided bel ow. i The Dry Flats disposal site is located near the crest of a low anticlinal ridge. The average slope across the site is 2.6 to 5.8 percent with a vertical relief of about 40 ft. Weathered shale-claystone underlies the site in about 20 percent of the area below the cell. The expor n, resistant sandstone surfaces of the remainder of the site provide a local base level for erosion. The denudation rates for the soils and weathered shale is estimated for small basins at 2 to 8 ft per 1000 years (Bronson and Owen,1970). The topographic location of the disposal site near the top of a ridge indicates that the drainage area is small and the erosion rate should be limited. In the Paradox Basin, downdip migration of structurally controlled drainages is relatively inactive at the present because the base level of the master stream of the region, the Dolores River, is being lowered very slowly (DOE, 1993c). The annual precipitation ranges from 10 to 15 inches. The NRC staff has reviewed the details of the regional and site geomorphology as provided in the RAP by DOE and concludes that the characterization of the Dry Flats disposal site adequately establishes the regional and site geomorphology. 2.3.5 Seismicity DOE characterized the regional seismicity by obtaining earthquake data bases provided by the National Oceanographic and Atmospheric Administration (NOAA), by applying accepted techniques to determine earthquake magnitudes, and by employing methods suggested in SRP Section 2.2.2.3 for calculating peak horizontal ground acceleration generated by a design basis event. A summary of DOE's seismic characterization is provided below. The seismic risk analysis is based largely on studies of the geologic and seismotectonic setting, Cenozoic geologic history, and geomorphic evidence of Late Tertiary and Quaternary fault movements. DOE considers it unlikely that the structural features of the Paradox Basin can generate earthquakes having a magnitude larger than 5.0 (Kirkham and Rogers,1981) even though the large subsurface faults in the vicinity are not exposed and it is not known if they are presently capable. Table 2.1 shows the estimated maximum earthquake magnitudes based on regional source zones as reported by four authors. There has been only one earthquake recorded by the National Geophysical Data Center within the 65-kilometer site region. This was a magnitude 4.0 event that occurred in 1970 located 25 miles southeast of the site near the boundary of the Paradox Basin. Non-tectonic sources of seismic activity occur within the site region related to salt flow near deep potash mines in the Moab, Utah area. Studies have indicated that the maximum earthquake from this source could be as much as 3.0 (D0E, 1993c). NATURITA dTER 2-5 octot.r s,1993 i 1

TABLE 2.1 ESTIMATED MAXIMUM MAGNITUDE, INTENSITY, AND ACCELERATION FOR DRY FLATS SITE REGION (After DOE, 1993c) Maximum. Source no " - -ne estimate Source magnitude (M ) region Intensity Acceleration - L f Uu and 7.0 Utah DeCapua (1975) 6.5 Colorado IV O.02g (100-year return intervall Algermissen 6.1 Paradox Basin 0.07 er el. (1982) 7.3 Uncompshgre-0.12 San Juan 90% probability of no Mountains exceedence in 250 years Thenhaus (1983) 6.0 Paradox Sasin Not given 6.5 Uncompshgro-San Juan Mountains Kirkham and 5.5-6.5 Colorado Pieteau Not given Rogers (1981) 6.O-6.5 Western Mountains 4 i uruniu erra 2-6 octon.c s 19 e t )

One study (Wong and Simon, 1981) observed that seismicity in the Paradox Basin i portion of the Colorado Plateau has been and will continue to remain at a low level. A 15 month seismic monitoring program found that all of 230 events recorded were within the Precambrian basement rocks, not in the salt diapiric { structures. The highest earthquake magnitude recorded within the Colorado Plateau is estimated to be 5.5 to 5.75. This event occurred on July 21, 1959, near Fredonia, Arizona. Kirkham and Rogers (1981) estimated the maximum event for the Colorado Plateau to be a magnitude of 5.5 to 6.5. The NRC staff has reviewed the details of the regional and site seismicity as provided in the RAP by DOE and concludes that the characterization of the Dry Flats disposal site is adequate to establish the regional and site seismicity. 2.3.6 Natural Resources DOE characterized the regional and site-specific natural resources by an analysis of regional and local publications, regional geologic maps, topographic maps, and field observations. A summary of DOE's characterization of the natural resources is as follows. Potential economic resources in the disposal site region consist of gas and j oil, uranium, potash, and minor amounts of coal. The most abundant resource developed in the region was uranium. Potash occurs in the greatest abundance but only at presently uneconomic depth. Oil and gas leases cover land within one mile of the site although there is no close production. A small coal f l strip mine is located three miles from the site. There has been no I development on the site area. Figure 2.3 shows the location of developed { resources. l The NRC staff believes that DOE has categorized the mineral resources in the RAP sufficiently to identify potential or active mineral resources on the disposal site. 2.4 Geologic Stability Geologic conditions and processes are characterized to determine the site's ability to meet standards in 40 CFR 192.02(a). In general, site lithologic, stratigraphic, and structural conditions are considered for their suitability as a disposal foundation and their potential interaction with tailings leachate and groundwater. Geomorphic processes are considered for their potential impact upon long-term tailings stabilization and isolation. Potential geologic hazards, including seismic shaking, liquefaction, on-site fault rupture, ground collapse, and volcanism are identified for the purpose l of assuring the long-term stability of the disposal cell and success of the remedial action design. utuam eta 2-7 october e, m 3 i

I j ) ) N / a M 0, l MESA CO. r, DELTA CO. e o w i ,#j Cy s'tT E e I R ADlu S r 5 MONTROSE CO. 9 + $/ San })1 } si C glTE 4, SAN JUAN CO. l A OUR AY ' l ( { 4 C O. i SAN MIQUEL CO. ') z g DOLORES CO. + b JUAN CO, MONTEZU A CO. EXPLANATION 3 ggggg d URANtUM PRODUCTION AREA 1 MILOM M RS e GAS PRODUCTION AREA X THERMAL SPRING + OOALMNNG APTER WOOOWARD-CLYDE CON SULT ANTS. 1983 j FIGURE 2.3 AREAS OF MINERAL RESOURCE DEVELOPMENT IN DRY FLATS REGION NATURITA dfEa 2-S october 8, 1993 i

D., p e p ? 2.4.1 Bedrock Suitability ( DOE's evaluation of the site region, as described in TER Section 2.3 and the l RAP, ir,dicated no evidence of bedrock instability, capable tectonic faulting within 40 miles of the disposal site, or other structural condition affecting the stability of the site. A study presented evidence that the bedrock would not be conducive to lateral migration or seepage of contaminants from the disposal cell and that the bedrock materials are nonreactive with tailings effluent. The carbonaceous shales and thin coaly seams aid in attenuation of organics and metals (DOE, 1993c). The NRC staff, therefore, concurs with DOE's assessment that bedrock stratigraphic and structural conditions at the site should have no effect on the design's ability to meet standards for long-term stability of the remedial action. r 2.4.2 Geomorphic Stability The site will be protected from geomorphic processes by its position near the drainage divide and by the erosion resistant Dakota Sandstone Formation on which the site will be situated. The likelihood of salt core flow inducing and de aloping collapse structures adjacent to the site is unlikely given the present stability of the Colorado Plateau and the region. The small drainage area precludes rapid erosive forces due to water flow. The NRC staff, based on the information provided by DOE in the RAP, has reasonable assurance that geomorphic conditions of the site have been adequately characterized and that the remedial action described herein will not be adversely affected by natural forces. 2.4.3 Seismotectonic Stability Studies by DOE to analyze seismic hazards included search for a design-basis fault, selection of a design earthquake, calculation of the estimated peak horizontal ground acceleration, evaluation of potential on-site fault rupture, and recognition of potential earthquake-induced geologic failures at the site. The seismic activity for the site region, as described by DOE and presented in Section 2.3.5 of this TER, identifies the significant structures and delineates the tectonic provinces. That section provides analysis of the regional characteristics to determine sources that could generate ground motion that would most affect the site. The maximum earthquakes (ME) for the adjacent seismotectonic provinces are based on recommendations by Kirkham and Rogers (1981). This study had estimated a range of 5.5 to 6.5 for the Colorado Plateau Province. The larger magnitudes are consistent with the fault lengths of the significant faults of these provinces and are selected as the MEs for these adjoining provinces. The design earthquake at the site was determined to be an M - 7.1 event t occurring at a distance of 14.9 miles from the site based on the conservative assumption that the largest critical tectonic fault was capable. Although u tua m o m 2-9 october e, 1993

~i this fault does not exhibit Quaternary activity, the Uncompahgre Uplift structure has been shown to be tectonically active. The peak horizontal acceleration of bedrock at the site is estimated to be 0.25 g. The duration of the design earthquake for the bedrock at the site is 26 seconds. The floating earthquake (FE) is the largest event not associated with a specific structure and is determined on the basis of seismic history and tectonic character. Since the largest earthquake considered possible without ground rupture is a magnitude 6.2 event, this magnitude is considered as the FE, representing the seismic potential of unknown structures in the region. This event is considered to occur at a radial distance of 15 km (9.3 miles) i from the site and would result in an acceleration of 0.21 g at the disposal 1 site. The NRC staff has reviewed the data presented by DOE in the Naturita RAP and agrees that therpeak horizontal acceleration for the design earthquake is 0.25 g. Staff find the data inputs and the cited results to be reasonable and conservative for DOE's calculation of the seismic coefficient for the site. 2.5 Conclusions Based upon review of the RAP, the staff has reasonable assurance that regional and site geologic conditions for the Naturita UMTRA Project disposal site have been characterized adequately to meet 40 CFR Part 192. b m unin s u 2-10 oct e r 8. 1993

I 3.0 GE0 TECHNICAL STABILITY 3.1 Introduction This section presents the results of the NRC staff review of the geotechnical engineering aspects of the proposed remedial actions at the Naturita, Colorado UMTRA Project site, as detailed in DOE's Preliminary Final Remedial Action Plan (DOE,1993a-e) and Remedial Action Inspection Plan (MK-Ferguson,1993). The remedial action consists of the removal of all remaining contaminated materials from the processing site to the disposal cell at Dry Flats. The disposal cell will be an engineered embankment extending 30 ft above current grade level. Contaminated material will be consolidated and encapsulated in the cell and will be covered by a 1.5-foot-thick compacted earth radon / infiltration barrier, a 3.0-foot-thick compacted earth frost barrier, and a 1.5-foot-thick bedding and riprap layer. The geotechnical engineering aspects reviewed include: (1) geotechnical information related to the processing site, disposal site, and borrow sites; (2) materials associated with the remedial action, including the foundation and excavation materials, building debris, and other contaminated materials; and (3) design and construction details related to the disposal site, disposal cell, and its cover. The staff review of related geologic aspects such as stratigraphic, I structural, geomorphic, and seismic characterizations of the site is presented in Section 2.0 of this report. 3.2 Site and Material Characterization 3.2.1 Site Descriptions l A. Processing Site The processing site (Figure 1.1) is located in Montrose County, Colorado, about two miles to the northeast of the town of Naturita (off State Highway 141). The Naturita Processing Site consists of the following: 1) the abandoned Naturita Millyard; 2) the former Tailings Pile area which is located on the flood plain of the San Miguel River between Highway 141 to the west and the San Miguel River to the east; and 3) the Former Ore Storage area which is located to the west of Highway 141. During 1976-77 the tailings at the Naturita Processing site were transported for reprocessing to the Durita Facility heap leach plant, which is located adjacent to the proposed Coke Oven Borrow Area. Although the Naturita 3 l Processing site no longer contains a tailings pile, the site has 539,000 yd of residual contamination which is distributed as described in Section 1.2 of this TER. The processing site also includes buildings and foundations, and has considerable amounts of scrap metal, process equipment, water tanks, miscellaneous machinery, trucks and tires, with lower contamination levels than the soils. The total volyme of these materials, upon demolition, is estimated to be about 8,000 yd utuam em 3-1 octote a,1993

B. Disposal Site at Dry Flats The Dry Flats disposal site is about six road miles to the southeast of the Naturita Processing Site (Figure 1.4). The embankment will be located near a drainage divide. The disposal cpil will cover approximately 22 acres and will contain approximately 547,000 yd of contaminated materials. The actual quantity will depend on the extent of contaminated materials excavated during construction. The grade break of the embankment is at elevation 5,960 ft. The top slopes of the embankment range from 2 to 5 percent, and the sideslopes will be 5H:lV. The disposal cell configuration is shown in Figure 1.5 and it's typical cross section in Figure I.6. Bedrock outcrops occur under the footprint of the disposal cell at the Dry Flats site. In some locations, there is a shallow cover of 1 to 2 ft of clayey or silty, sandy soil, which is underlain by weathered sandstone. The topsoil at the site is suitable for use in final grading, for reclamation of the Coke Oven borrow site, or for fill material at the processing site. C. Borrow Materials Site The borrow material (silty and sandy clay) for the radon barrier layer will be obtained from the Coke Oven borrow site, which is approximately one mile southwest of the disposal site. Frost protection layer sources include both the Coke Oven and Dry Flats sites. Additional potential borrow areas are currently being evaluated for suitability as sources for frost protection, bedding, and riprap materials. The four prime sources were identified as the Hendrickson, Cotter, S.W. Redimix, and Pinon Pit locations. 3.2.2 Site Investigations Geotechnical investigation and site characterization programs were performed at the mill site, the disposal site, and the borrow sites. The data obtained during the characterization programs were reported in DOE's Information to Bidders, Volumes II, III, and IV. The scope of the geotechnical investigations included excavating test pits and drilling boreholes. Information from monitor well installation was also obtained. The borings and test pits were logged by a field engineer. The locations of test pits, boreholes, and monitor wells were given in Vol. II of the Information to Bidders for the Naturita processing site, Vol. III of the Information to Bidders for the Dry Flats disposal site, and Vol. IV, Section I for the Coke Oven site and Vol. IV, Sections J and K, for the fine-grained and sand and gravel materials respectively. Subsurface investigations for material properties of the underlying soil at the processing site were carried out in conjunction with the investigation to define the limits of contamination. The resulting samples of site materials were tested and analyzed in the laboratory to evaluate the engineering characteristics of the materials. Test pits were excavated with a tracked backhoe. Bulk soil samples were collected from the pits. Individual borehole logs provide precise information about the drilling methods used. Generally, hollow-stem augers (6.5-inch) NATURITA dTEa 3-2 octoter a.1993

were used until refusal; thereafter, a rotary bit (4.0 inches) and casing were used to bedrock. Three sampling methods were used: the Standard Penetration test (ASTM D-1586); a 2.42-inch inside diameter, ring-lined, split-barrel sampler; and a 3.0-inch diameter, thin-walled Shelby tube. The data obtained from the field investigations and laboratory tests were used to construct stratigraphic sections, and to define the engineering parameters of the soils to be incorporated into the cell. 3.2.3 Dry Flats Disposal Site Stratigraphy The Dry Flats disposal cell will rest on a bedrock terrace approximately 600 ft above the San Miguel River. The bedrock at the disposal cell locatior, is overlain by a thin (less than two-foot-thick) layer of spoil that will be excavated prior to cell construction. The bedrock directly beneath the cell consists of the Dakota Sandstone. The bedrock at the site is reported to be stable. Additional information in this regard can be found in Section 2.4 of this TER. The Dry Flats site is underlain by sandstone and shale-mudstone of the Dakota Sandstone. The only shallow groundwater at the site exists as a thin saturated zone in the underlying Burro Canyon bedrock, approximateiy 200 ft below the surface. The presence of this groundwater has no effect on tha stability of the site. The staff has reviewed the details of the test pits and borings as well as the scope of the overall geotechnical exploration program discussed in Section 3.2.2 above. The staff concludes that the geotechnical investigations conducted at the Naturita processing and Dry Flats disposal sites adequately establish the stratigraphy and the soil conditions, that the explorations are in general conformance with applicable provisions of Chapter 2 of the NRC Standard Review Plan, and that they are adequate to support the assessment of the geotechnical stability of the stabilized contaminated material in the disposal cell. 3.2.4 Testing Program The materials at the three sites were classified according to the Unified Soil Classification system (ASTM D-2487). Atterberg limits (ASTM D-4318) and gradation tests (ASTM D-422) were performed on selected samples to classify the soils. In addition, the following tests were conducted: specific gravity (ASTM D-854), compaction (ASTM D-698), saturated and unsaturated hydraulic conductivity, consolidation (ASTM D-2435), shear strength (EM 1110-2-1906), radon barrier erodability (Crumb test, STP 623; dispersion, ASTM D-4221; and pinhole, STP 623), and erosion barrier durability. The results of the individual tests are included in the Information to Bidders. The testing program was consistent with the needs of the proposed remedial action; representative samples of construction materials and samples of geotechnical materials that may affect or be affected by the remedial action were tested. The number of samples tested is considered sufficient to support the necessary geotechnical analyses described in the subsequent sections. In muun ma 3-3 october s, 1993

i particular, the testing approach is consistent with the SRP and the TAD. Samples were tested in accordance with standard procedures. Quality assurance and quality control were performed in accordance with standard UMTRA Project procedures. 3.3 Gaotechnical Engineering Evaluation 3.3.1 Slope Stability Evaluation ) The staff has reviewed the exploration data, test results, critical slope characteristics, and methods of analyses pertinent to the slope stability aspects of the remedial action plan for the Naturita UMTRA Project disposal embankment. The analyzed cross-section with the longest 5 horizontal to 1 vertical sideslope has been compared with the exploration records and the design details. The staff finds that the most critical sicpe section has been considered for the stability analysis. Soil parameters for the various materials in the stabilized embankment slope have been adequately established by appropriate testing of representative material. Values of parameters for other earthen materials have been assigned on the basis of data obtained from geotechnical explorations at the site and data published in the literature. The staff also finds that the DOE evaluation has employed the appropriate methods of stability analysis (Bishop's Modified Method and infinite slope), and has addressed the likely adverse conditions to which the slope may be subjected. Factors of safety against failure of the slope for seismic loading conditions cnd static loading conditions have been evaluated for both the short-term (end-of-construction) and long-term state. The values of the seismic coefficients used in the analysis are 0.179 for the long-term condition and 0.13 g for the short-term condition. These values were derived from the 0.25 g peak horizontal bedrock acceleration (see Section 2.4.3) in accordance with the recommended methods in the SRP, and are acceptable to the staff. The staff finds that the use of the pseudo-static method of analysis for seismic stability of the slopes is acceptable considering the flatness of the slopes and the conservatism in the soil parameter values. The minimum factors of safety against failure of the slope were 3,14 and 1.86 for the short-term static and pseudo-static conditions, respectively, compared to required minimums of 1.3 and 1.0, respectively. The minimum factors of safety against failure of the slope were 3.33 and 1.03 for the long-term static and pseudo-static conditions, respectively, compared to accepted minimums of 1.5 and 1.0, respectively. Based on review of these analyses and the results, NRC staff concludes that the slopes of the disposal cell are designed to endure the effects of the geotechnical natural forces to which they may reasonably be subjected during the design life of the cell. The analyses have been made in a manner consistent with Chapter 2 of the SRP. uTunna erra 3-4 octoe=r a, m 3 l

3.3.2 Settlement and Cover Cracking i The staff has reviewed the analysis of total and differential settlement of the disposal cell and foundation materials and the resulting potential for cracking of the radon barrier. Calculations indicate that all settlement due to placement of the relocated contaminated materials, radon barrier, frost protection layer, and erosion protection will include immediate (elastic) and secondary (creep) components. The foundation is assumed to be incompressible, since it will consist of competent bedrock. Forty-nine locations on four section lines were selected for settlement analysis. The staff agrees that appropriate sections have been chosen to assess the most critical conditions for differential settlement. Calculated settlements along the profiles varied from 0.54 inches to 14.01 inches, with a resulting maximum horizontal strain of 0.016 percent. The calculated tensile failure strain for the proposed radon barrier material (PI-0) was 0.05 percent. DOE has concluded that total and differential settlement of the materials comprising the proposed disposal cell will not have an adverse effect on the ability of the cell to meet the stability standards. The staff agrees that settlement generally will be small due to the compaction of the materials in the cell and the granular nature of much of the material. Differential settlement should not cause ponding concerns due to the sloping configuration of the cell. Cracking of the cover due to settlement should not occur, since the resulting maximum strain is well below the calculated tensile failure strain. 3.3.3 Liquefaction The staff has reviewed the information presented on the potential for liquefaction at the site based on the results of geotechnical investigations, including boring and test pit logs, test data, soil profiles, and other information. The soils in the disposal cell will be compacted to a minimum of 90 percent of maximum Standard Proctor density (ASTM D-698) and will be in an unsaturated condition; therefore the disposal cell is not considered susceptible to liquefaction. The groundwater table at the site is reportedly at depths of 200 ft below the bottom of the disposal embankment. The foundation beneath the disposal cell is stable bedrock and thus insusceptible to liquefaction. Because of the absence of water and liquefiable soil, there is no potential for liquefaction of material within or beneath the disposal cell and the applicable provisions of Chapter 2 of the SRP have been met. 3.3.4 Cover Design This cover system provides a total of from 5 to 5.75 ft of cover over the-contaminated material, and collectively is designed to limit infiltration of precipitation, protect the pile from erosion, and control the release of radon from the cell. Details of the staff review of the cover's performance related to erosion protection features is presented in Section 4.0 of this TER; the review of the cover's performance related to limiting infiltration are addressed in Section 5.0; and the review of the radon attenuation aspects of j munm me 3-5 octotar 8,1993

the cover is presented in Section 6.0. However, there are certain other aspects of the cover (frost protection, gradation / filter design, etc.).that are addressed herein. The Remedial Action Plan (DOE,1993a) indicates that the radon / infiltration barrier will consist of compacted silty to clayey soil that will limit infiltration and inhibit radon emanation. The gradation requirements call for a minimum of 40 percent by weight passing the No. 200 sieve, and a maximum of 10 percent by weight retained on a No. 4 sieve. Testing has indicated that the borrow soil should generally meet the requirements, and that inspection procedures will verify gradation. Test results indicate that infiltration / radon barrier material, when compacted to at least 95 percent of maximum dry density (ASTp D-698)will produce a laboratory saturated permeability on the order of 10' cm/sec. The frost protection layer will consist of materials excavated from the Dry flats Disposal Site and/or the Coke Oven borrow area. DOE has determined the frost depth using the BERGGREN. BAS computer code developed at the U.S. Army Corps of Engineers (COE, 1968). This code has been used for other UMTRA Project sites. The total 200-year frost penetration depth at the disposal site is calculated to be 41.1 inches. The cover design provides for the appropriate depth by the total thickness of riprap (12 inches), bedding (6 inches), and frost protection layer (36 inches), above the radon barrier (Figure 1.6). The staff has reviewed the input data used in determining the total frost penetration depth, and concluded that these values are a reasonable representation of the extreme site conditions to be expected in a period of 200 years. Since DOE's calculation was based on the 200-year rather than the 1000-year frost depth, actual frost penetration is likely to be somewhat in excess of the stated values. NRC staff accepts this approach for the Naturita site because the additional frost penetration, if it were to occur, would not adversely affect the stability of the cell. The RAP indicates that the layer immediately above the frost protection layer is to be a 6-inch-thick bedding / drain layer, intended to drain water laterally off the cell and protect the radon barrier from the riprap. Although a source for the bedding material has not yet been identified, a satisfactory gradation for the material has been specified. The top layer of cover on the side slopes is proposed to consist of 1-foot of Type B riprap with a minimum D, of 3.5 inches. The proposed erosion 3 protection for the top slope is a 1-foot-thick Type A riprap with a minimum D of 1.5 inches. Details of the review of the erosion protection design are 3a found in Section 4.0 of this report. The cover design has been evaluated by NRC staff for geotechnical long-term stability and for these aspects the design is acceptable. umuu m 3-6 october s. m 3

3.4 Geotechnical Construction Details 3.4.1 Construction Methods and Features The staff has reviewed and evaluated the geotechnical construction criteria provided in Attachment I to the RAP. Based on this review, the staff concludes that the plans and drawings clearly convey the proposed remedial action design features. In addition, the excavation and placement methods and specifications represent accepted standard practice. 3.4.2 Testing and Inspection The staff has reviewed and eva tated the testing and inspection quality control requirements provided in the Remedial Action Inspection Plan (RAIP). In general, the RAIP is found to provide an acceptable program for testing and inspection that is consistent with the Staff Technical Position on Testing and Inspection (NRC, 1989a). 3.5 Conclusions Based on the review of the design and the geotechnical engineering aspects of the proposed remedial action, as presented in the Naturita preliminary final RAP and supporting documents, NRC staff has reasonable assurance that the long-term stability aspects of the EPA standards will be met. E l 1 j 1 NATURITA dTEa 3-7 october s, m 3 1 i

4.0 SURFACE WATER HYDROLOGY AND EROSION PROTECTION 4.1 Hydrologic Description and Site Conceptual Design The processing site is located in Naturita, Colorado, near the San Miguel River. DOE proposes to transport contaminated materials from this site to the Dry Flats disposal site, which is located about six road miles southeast of the processing site. The average elevation of the disposal site is about 5,900 ft above mean sea level (MSL). The site straddles a drainage divide, and little or no offsite drainage area exists. In order to comply with EPA standards, which require stability of the tailings for 1,000 years to the extent reasonably achievable and, in any case, for at least 200 years, DOE proposes to stabilize the contaminated materials in an engineered embankment to protect them from flooding and erosion. The design basis events for design of the erosion protection included the Probable Maximum Precipitation (PMP) and the Probable Maximum Flood (PMF) events, both of which are considered to have low probabilities of occurrence during the 1000-year stabilization period. As proposed by DOE, the tailings will be consolidated into a single pile, which will be protected by a rock cover. The rock cover will have a slope of 2 to 5% on the top slopes and 20% on the side slopes. The embankment will be surrounded by aprons which will safely convey flood runoff away from the tailings and prevent gully intrusion into the stabilized c. ell. 4.2 Flooding Determinations The computation of peak flood discharges for various design features at the site was performed by DOE in several steps. These steps included: (1) selection of a design rainfall event; (2) determination of infiltration losses; (3) determination of times of concentration; and (4) determination of appropriate rainfall distributions, corresponding to the computed times of concentration. Input parameters were derived from each of these steps and were then used to determine the peak flood discharges to be used in water surface profile modelling and in the final determination of rock sizes for erosion protection. 4.2.1 Selection of Design Rainfall Event One of the most disruptive phenomena affecting long-term stability is surface i water erosion. DOE has recognized that it is very important to select an appropriately conservative rainfall event on which to base the flood protection designs. DOE has concluded and the NRC staff concurs (NRC, 1990) that the selection of a design flood event should not be based on the extrapolation of limited historical flood data, due to the unknown level of accuracy associated with such extrapolations. Rather, DOE utilized the PMP, which is computed by deterministic methods (rather than statistical methods), and is based on site-specific hydrometeorological characteristics. The PHP has been defined as the most severe, reasonably possible, rainfall event that could occur as a result of a combination of the most severe meteorological conditions occurring over a watershed. No recurrence interval is normally m ua m e m 4-1 october 8. m 3

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• I P

assigned to.the PMP; however, DOE and the NRC staff have concluded that the I probability of such an event being equalled or exceeded during the 1000-yaar ~ stability period'is small. Therefore, the PMP is considered by the NRC staff to provide an acceptable design basis. Prior to determining the runoff from the drainage basin, the flooding analysis requires the determination of PMP amounts for the specific site location. Techniques for determining the PMP have been developed for the entire United States primarily by the National Oceanographic and Atmospheric Administration (NOAA) in the form of hydrometeorological reports for specific regions. These i techniques are widely used and provide straightforward procedures with minimal variability. The staff, therefore, concludes that use of these reports to derive PMP estimates is acceptable. A PMP rainfall depth of approximately 7.7 inches in one hour was used by DOE to compute the PMF for the small drainage areas at the disposal site. This rainfall estimate was developed by DOE using Hydrometeorological Report (HMR) 49 (DOC, 1977). The staff performed an independent check of the PMP value, + based on the procedures given in HMR 49 (DOC, 1977). Based on this check of the rainfall computations, the staff concludes that the PMP was acceptably derived for this site. 4.2.2 Infiltration Losses l t Determination of the peak runoff rate is dependent on the amount of } precipitation that infiltrates into the ground during the occurrence of the t rainfall. If the ground is saturated from previous rains, very little of the rainfall will infiltrate and most of it will become surface' runoff. The loss rate is highly variable, depending on the vegetation and soil characteristics of the watershed. Typically, all runoff models incorporate a variable runoff coefficient or variable runoff rates. Commonly-used models such as the Rational Formula (DOI, 1977) incorporate a runoff coefficient (C); a C value of I represents 100% runoff and no infiltration. Other models such as the U.S. Army Corps of Engineers Flood Hydrograph Package (HEC-1) separately I compute infiltration losses within a'certain period of time to arrive at a runoff amount during that time period. In computing the peak flow rate for the design of the rock riprap erosion protection at the proposed disposal site, DOE used the Rational Formula. In this formula, the runoff coefficient was assumed by DOE to be unity; that is, DOE assumed that no infiltration would occur. ~ Based on a review of the 9 computations, the staff concludes that this is a very conservative assumption and is, therefore, acceptable. -} 4.2.3 Times of Concentration The time of concentration (tc) is the amount of time required for runoff to I reach the outlet of a drainage basin from the most remote point in that basis. l-The peak runoff for a given drainage basin is inversely proportional to the time of concentration. If the time of_ concentration is computed to be small, the peak discharge will be conservatively large. Times of concentration and/or lag times are typically computed using empirical relationships such as nuunna ena 4-2 ocrate s. m3 l t

those developed by Federal agencies (D0I,1977). Velocity-based approaches are also used when accurate estimates are needed. Such approaches rely on estimates of actual flow velocities to determine the time of concentration of a drainage basin. The times of concentration for the riprap design were estimated by DOE using the Kirpich Method (D0I, 1977) and the Manning's Equation (Chow, 1959), which estimates actual flow velocities. Such velocity-based methods are considered by the staff to be appropriate for estimating times of concentration. Based on the precision and conservatism associated with such methods, the staff concludes that the tc's have been acceptably derived. The staff further concludes that the procedures used for computing tc are representative of the small steep drainage areas present at the site. For very small drainage areas with very short times of concentration, DOE utilized tc's as low as 2.5 minutes; the staff considers such tc's to be conservative. 4.2.4 Rainfall Distributions After the PHP is determined, it is necessary to determine the rainfall intensities corresponding to shorter rainfall durations and times of concentration. A typical PMP value is derived for periods of about one hour. If the time of concentration is less than one hour, it is necessary to extrapolate the data presented in the various hydrometeorological reports to shorter time periods. DOE utilized a procedure recommended in HMR 49 (DOC, 1977) and by the NRC staff (NRC, 1990). This procedure involves the determination of rainfall amounts as a percentage of the one-hour PMP, and computes rainfall amounts and intensities for very short periods of time. DOE and the NRC staff have concluded that this procedure is conservative. In the determination of peak flood flows, PMP rainfall intensities were derived by DOE as follows: Rainfall Duration Rainfall Intensity (minutes) (inches /hr) 2.5 54 5 44 60 7.7 The staff checked the rainfall intensities for the short durations associated with small drainage basins. Based on a review of this aspect of the flooding determination, the staff concludes that the computed peak rainfall intensities are conservative. 4.2.5 Computation of PMF 4.2.5.1 Top and Side Slopes The PMF was estimated for the top and side slopes using the Rational Formula, which provides a standard method for estimating flood discharges for small drainage areas. For the top slope and the side slope, DOE estimated the peak natuam ma 4-3 october 8, e

flow rates to be 0.45 cubic feet per second per foot of width (cfs/ft)'and 0.55 cfs/ft, respectively. These estimates are based on the conservative use of a top slope of 5%, which DOE states may be necessary to accommodate additional materials. Based on staff review of the calculations, the estimate is considered to be conservative. 4.2.5.2 Apron / Toe The PMF flow rate for the downstream apron was computed similarly to the design flow rate for the top and side slopes. As discussed above, the flow rate is considered to be conservative. 4.3 Water Surface Profiles and Channel Velocities Following the determination of the peak flood discharges, it is necessary to determine the resulting water levels, velocities, and shear stresses associated with that discharge. These parameters then provide the basis for the determination of the required riprap size and layer thickness needed to assure stability during the occurrence of the design event. 4.3.1 Top and Side Slopes In determining riprap requirements for the top and side slopes, DOE utilized the Safety Factors Method (Stevens, et al., 1976) and the Stephenson Method (Stephenson, 1979), respectively. The Safety Factors Method is used for relatively flat slopes of less than 10 percent; the Stephenson Method is used for slopes greater than 10 percent. The validity of these design approaches has been verified by the NRC staff through the use of flume tests at Colorado State University. It was determined that the selection of an appropriate design procedure depends on the magnitude of the slope (Abt, et al., 1987). The staff therefore concludes that the procedures and design approaches used by DOE are acceptable and reflect state-of-the-art methods for designing riprap erosion protection. 4.3.2 Apron / Toe The design of the apron at the toe of the disposal cell is based on the following considerations: 1. provide riprap of adequate size to be stable against the design storm (PMP), 2. provide uniform and/or gentle grades along the apron and the adjacent ground surface such that runoff from the cell is distributed uniformly at a relatively low velocity to minimize the potential for flow concentration and erosion, and 3. provide an adequate apron thickness to prevent undercutting of the disposal cell by: (a) local scour that could result from the PHP, or 4-4 octoter s, m s u tua m s ta

n (b) potential gully encroachment that could occur due to gradual headcutting over a long period of time. The key elements which DOE evaluated in the design of riprap protection for the apron / toe are: 1. the lower part (approximately the last 15 ft) of the 33% side slope immediately upstream of the grade break, 2. the toe, which is the relatively flat lower slope (5%) immediately downstream of the grade break formed when the side slope meets the

apron, r

3. the downstream portion of the apron which is assumed to have i collapsed due to scour or long-term erosion, and 4. the ground surface adjacent to the apron. DOE used several analytical methods for designing the riprap apron / toe. Additional detailed discussion of the riprap design of various components of the apron / toe can be found in Section 4.4.1.2, below. L 4.4 Erosion Protection 4.4.1 Sizing of Erosion Protection Riprap layers of various size and thicknesses are proposed for use at the Dry. Flats site. The design of each layer is dependent on its location and purpose. 4.4.1.1 Top Slopes and Side Slopes The layer of riprap on the top slope has been sized to withstand the erosive velocities resulting from an on-cell PHP, as discussed above. DOE proposes to use a 1-foot-thick layer of rock with a minimum D of 1.5 inches (Type A). 3a The riprap will be placed on a 0.5-foot-thick bedding layer. The Safety Factor Method was used to determine the rock size. The rock layer on the side slopes is also designed for an occurrence of the local PMP. DOE proposes to use a 1-foot-thick layer of rock with a minimum D of approximately 3.5 inches (Type B). The rock layer will be placed on a sa 0.5-foot-thick bedding layer. Stephenson's Method was used to determine the required rock size. Conservative values were used for the rock specific gravity, the rock angle of internal friction, and porosity. Based on staff review of the DOE analyses, and the acceptability of using appropriate design methods, as discussed in Section 4.3, above, the staff concludes that the proposed rock sizes are adequate. l NATURITA dTER 4-5 october a, m s

.-{ .] 4.4.1.2 Apron / Toe 00E evaluated the design of the apron / toe in four separate segments, as discussed in Section 4.3.2, above. Following is the staff evaluation of each of the segments. 4.4.1.2.1 Lower Side Slope for the lower 15-foot length of the side slopes, DOE proposes to use'a 1 1.25-foot-thick layer of rock, gradually increasing in thickness to a four-foot-thick layer of rock, with a minimum D size of 7 inches (Type C). Although several methods were used to estimate b e rock size required for the_ toe apron, the U.S. Army Corps of Engineers (C0E) method for sizing rock in stilling basins (C0E,1970) was selected as the best available method for the conditions at the toe of the disposal cell. DOE determined the velocity associated with PHP flows down the side slope and assumed that turbulence would be created on the lower portion of the slope where it meets the toe. To account for this turbulence (and energy L dissipation), DOE increased the velocity in accordance with COE recommendations. This is accomplished by using a turbulence coefficient; DOE selected neither the most nor the least conservative coefficient. The coefficient selected increased the required rock size. Based on staff. analysis of DOE's methods and assumptions, the Type C rock proposed for this t portion of the slope is acceptable. 4.4.1.2.2 Toe For the actual toe area, which will have a 20-foot. length and a 2-5% slope, DOE used the COE tractive shear stress method (COE, 1970) to determine the required rock size. The shear stress produced was conservatively doubled to account for turbulence and non-uniform flow. The rock size calculated using i this method was found to be smaller that the proposed size of 7 inches. Based l on our review of DOE's calculations, the rock size is acceptable. 4.4.1.2.3 Collapsed Slope As part of the analysis of the toe area, DOE conservatively assumed that the natural ground downstream of the toe would be eroded due to cumulative local j scour and/or erosion at its base, resulting in the collapse of the rock into J the eroded area. DOE assumed that the collapsed slope of the rock would be 1 l vertical (V) on 3 horizontal (H). The required rock size for flow over this slope was calculated using the Stephenson Method, as recommended by the staff. Using this method, the required size was calculated to be less than the proposed size of 7 inches. Based on staff review of the calculations, the ) rock size is acceptable. 4.4.1.2.4 Natural Ground In order to determine the depth to which the toe must be placed, DOE estimated the depth of scour which will occur to the graded natural ground slope just downstream of the toe. DOE assumed that a flow concentration factor of 3, ) NATURITA dTER 4-6 October 8,-1993 .) i

+ corresponding to gully flows, would occur. Using methods developed by the U.S. Departmant of Transportation (DOT,1975), the scour depth was estimated to be about 3 ft. However, DOE proposes to place the toe to a depth of 4 ft (or to key the riprap into the Dakota Sandstone) to provide added conservatism to account for a possible increased erosion of the topsoil layer. Staff review of the calculations indicates that the methods are appropriate and conservative. 4.4.2 Rock Durability The EPA standards require that control of residual radioactive materials be effective for up to 1000 years, to the extent reasonably achievable, and, in any case, for at least 200 years. The previous sections of this report examined the ability of the erosion protection to withstand flooding events reasonably expected to occur in 1000 years. Rock durability is defined as the ability of a material to withstand the-forces of weathering. Factors that affect rock durability are (1) chemical reactions with water, (2) saturation time, (3) temperature of the water, (4) scour by sediments, (5) windblown scour, (6) wetting and drying, and (7) freezing and thawing. 00E conducted investigations to identify acceptable sources of rock in the site vicinity. The suitability of the rock as a protective cover was then assessed by laboratory tests to determine its physical characteristics. DOE conducted the tests and used the results of these tests to classify the rock's quality and to assess the expected long-term performance of the rock. In accordance with past DOE rock-testing practice, the tests included: 1. Petrographic Examination (ASTM C295). Petrographic examination of rock is used to determine its physical and chemical properties. The examination establishes if the rock contains chemically unstable minerals or volumetrically unstable materials. 2. Bulk Specific Gravity (ASTM C127). The specific gravity of a rock is an indicator of its strength or durability; in general, the higher the specific gravity, the better the quality of the rock. 3. Absorption (ASTM C127). A low absorption is a desirable property and indicates slow disintegration of the rock by salt action and mineral hydration. 4. Sulfate Soundness (ASTM C88). In locations subject to freezing or exposure to salt water, a low percentage is desirable. 5. Schmidt Rebound Hammer. This test measures the hardness of a rock and can be used in either the field or the laboratory. 6. Los Angeles Abrasion (ASTM Cl31 or C535). This test is a measure 1 of rock's resistance to abrasion. j NATURITA dTER 4-7 Octoter 8, W 1

7. Tensile Strength (ASTM D3967 or ISRM Method). This test is an indirect test of a rock's tensile strength. DOE then used a step-by-step procedure for evaluating durability of the rock, in accordance with procedures recommended by the NRC staff (NRC, 1990), as follows: Step 1. Test results from representative samples are scored on a scale of 0 to 10. Results of 8 to 10 are considered " good"; results of 5 to 8 are considered " fair"; and results of 0 to 5 are considered " poor". Step 2. The score is multiplied by a weighting factor. The effect of the weighting factor is to focus the scoring on those tests that are the most applicable for the particular rock type being tested. Step 3. The weighted scores are totaled, divided by the maximum possible score, and multiplied by 100 to determine the rating. Step 4. The rock quality scores are then compared to the criteria, which determines its acceptability, as defined in the NDC scoring procedures. DOE examined 4 rock sources and has determined that the rock sources proposed for the disposal site scored as follows: Source Score Hendrickson Pit > 80 Cotter Pit > 80 Pinon Pit 79 Southwest Redimix 79 The staff concludes that rock from any of these sources will be of sufficient quality to meet EPA standards. 4.4.3 Testing and Inspection of Erosion Protection The staff has reviewed and evaluated the testing and inspection quality control requirements for the erosion protection materials. Based on a review of the information provided, the staff concludes that the proposed testing program is generally acceptable. However, based on direct observations of the probable rock sources for the erosion protection, the riprap layer likely will consist of a mixture of various types of rock. These rock types, while predominantly alluvial igneous rocks, will also include sandstones and other types of rock, which may be less durable that the igneous rock. This rock source may be difficult to test for durability, since it may be difficult to obtain representative samples where all of the rock types are uniformly mixed. In addition, it may be difficult to place such a rock layer without munna ena 4-8 octotar s m

~ a I segregation of the rock, where the less durable rock types are not uniformly mixed with the more durable rock types, resulting in pockets of poor-quality rock. DOE should provide additional information and testing specifications to ensure that the durability testing is representative of the various types of rock that will actually be produced from the rock source. DOE should determine the actual amount of each general rock type that is present in the rock source and should provide durability test data for each general type of rock. This information should then be used to develop a testing program for overall rock durability and the need for possible oversizing of the rock layer. In addition, DOE should provide information and specifications regarding the actual procedures that will be used during construction to assure that a layer i of uniformly-mixed rock will be placed. The specifications should be based on the amounts of less durable rock that are present in the layer, as determined from the durability testing program. This is an open issue. 4.5 Upstream Dam Failures There are no impoundments near the site whose failure could potentially affect the site. 4.6 Conclusions Based on its review of the information submitted by DOE, the NRC staff concludes that the site design will meet EPA requirements as stated in 40 CFR 192 with regard to flood design measures and erosion protection. The staff concludes that an adequate hydraulic design has been provided to reasonably assure stability of the contaminated material at the Dry Flats disposal site for a period of 1,000 years, or in any case, at least 200 years. However, as advised above, DOE needs to provide additional information to assure that durability testing is representative of the rock that will be produced for erosion protection. l l 1 hATURITA dTEg 4-9 Octoter 8,1993 J

1 ., e ;. n 5.0 . ATER RESOURCES PROTECTION W 5.1 Introduction 5.2 Hydrogeologic Characterization 5.3 Conceptual Design. Features to protect Water Resources 5.4 Disposal and Control of Residual Radioactive Materials (RRM)- 5.5 Cleanup and Control of Existing Contamination-5.6 Conclusions The NRC staff has performed the initial Water Resources Protection review and ' site visit of the Naturita, Colorado UMTRA Project. site. Based on this initial review, NRC staff concurs that the conceptual ground-water protection strategy described in the Remedial Action Plan conforms to EPA's proposed ground-water protection standards in 40 CFR 192, Subparts A - C. Three open issues were 1 identified during this stage of the review and are provided in Table 1.1 (Summary of Open Issues) of this TER. The detailed review and accompanying Water Resources Protection chapter will-be completed at a future date and transmitted under separate cover. Additional open issues may be identified as 't a result of this review, and will be forwarded with the _ completed TER' chapter. l I i e 9 { NA WR MA m a 5-1 oct e.r a, i m r 1 [

c ~ 6.0 RADON ATTENUATION AND SITE CLEANUP 6.1 Introduction This section of the TER documents the staff evaluation of the radon' attenuation design and processing site cleanup for the planned remedial action at the Naturita, Colorado, UMTRA Project site. The evaluations are primarily of the material characterization, radon barrier design, radiological characterization, proposed remedial action, and site verification plan to assure compliance with the applicable EPA standards. The review followed the SRP (NRC, 1993). 6.2 Radon Attenuation To meet the EPA standards for limiting release of radon-222 from residual radioactive materials to the atmosphere, DOE proposes that the contaminated material be relocated to the Dry Flats disposal site and capped with a cover consisting of the following layers: 18-inch radon barrier, 36-inch frost protection, 6-inch bedding, and 12-inch riprap. The radon barrier layer has been designg/s.d to limit the average release of radon to meet the EPA standard of 20 pCi/m The NRC staff review of the cover design for radon attenuation included evaluation of the pertinent design parameters for the contaminated materials and radon barrier soil, and a review of the specifications for materials placement. The staff considered that the barrier layer is designed to satisfy criteria for construction, settlement, cracking, and infiltration of surface water, as well as reduction of radon gas release at the surface of the completed cell. The other layers of the cover were evaluated for their ability to protect the radon barrier layer from drying and disruption. The stability of the cell as a whole was also assessed because of the potential for cracking of the barrier layer due to settlement or heaving. These aspects of the cell design are discussed in detail in Sections 3 and 4 of this TER. NRC staff evaluated DOE's input values for the RAECOM computer code that were used to calculate the radon barrier thickness required to meet the radon flux limit. The RAECOM parameter input was analyzed as discussed below. The staff then performed an independent analysis of the design using the RADON code (NRC, 1989b), which is a modification of the RAECOM code. 6.2.1 Evaluation of Parameters The required thickness of the radon barrier depends on the characteristics of the radon barrier soil and the underlying contaminated materials. NRC staff evaluated the physical and radiological data for the contaminated materials and the radon barrier soil used for input into the RAECOM and RAD 0N computer l codes. NRC staff evaluated the justifications and assumptions made by DOE, and determined if each parameter value was representative of the material, consistent with anticipated construction specifications, conservative, and based on long-term conditions. The sampling and testing methods for the NATURITA dTER 6-1 October 8, 1993 i l

materials were also reviewed to determine their appropriateness and to insure that the data was sufficient. The design parameters of the contaminated and barrier materials that were evaluated include: long-term moisture content, bulk density, specific gravity, porosity, material layer thickness, and radon diffusion coefficient. In addition, the radium content and radon emanation fractions of the contaminated materials were evaluated. However, in the radon barrier design calculation (17-741-02-01) provided in this Preliminary Final RAP, DOE indicates that additional field investigation and laboratory testing were performed in April-May 1993, and the results have not yet been included in the analysis. This new data needs to be incorporated into the analysis presented in the Final RAP. This is an open issue. A. Contaminated Materials Although the Naturita procesging site no longer has a tailings pile, the site hasapproximately547,p00yd of contaminated material, including approximately 8,000 yd of site debris (DOE, 1993a), as described in detail in Section 1.2 and shown in Figure 1.3 of this TER. The radon attenuation design is based on a 4.0-foot layer of relatively low contamination material (windblown) between the radon barrier and the higher level contaminated materials. The specified material excavation and placement sequence (Spec. 02200, 3.3.8.4; RAS, page 3-11; and Information for Reviewers, page 2-19, 3-1) is:

1) ore storage materials,

2) mill yard materials (including retention basin and ditch soils, vicinity property materials, and demolition debris), 3) former tailings pile area materials, and 4) windblown materials. However, the RAECOM calculation (17-741-02-01) considers the mill yard, ore storage, vicinity property material, and debris to be combined as a single mixed layer, and the RAS states (page 6-4) that these materials are to be mixed.

DOE should resolve this inconsistency concerning the contaminated material placement sequence, i.e., whether there is layering or mixing of the ore storage area and mill yard materials. This is an open issue. Most physical characteristics of the contaminated materials were determined from laboratory testing of representative samples. These materials will be compacted during placement to 90 percent of maximum dry density (ASTM D-698), and the tests were performed on material at this level of compaction. The results from 11 density measurements on the various contaminated materials ranged from 1.20 to 2.09 gm/cc. Results from 5 specific gravity measurements ranged from 2.51 to 2.80. These values were used to calculate porosity, and are summarized in the following table. Material Densitv* # Tests Spec. Gravity # Tests Porosity mill yard 1.49 4 2.71 3 .45 are storage 1.47 1 2.51 1 .41 l tailings area 1.73 5 2.70 0 .36 i windblown 1.44 1 2.76 1 .48 debris 2.4 0 3.0 0

• gm/cc at 90 percent compaction 6-2 octoter a, m3 utuatta dice l

u. l P DOE determined the long-term moisture content by measuring the 15-bar capillary moisture. The average long-term moisture from five samples from the i tailings pile area was 5.1 percent. Test results on 3 samples of mill. yard - material averaged 12.0 percent. This value was ci.osen by DOE to also represent the windblown and ore storage materials. DOE stated that no tests were necessary for these materials since their geotechnical properties are similar to the mill yard soils. Since the windblown material represents the largest volume of the contaminated material, and will be next to the radon i barrier, DOE should either 1) establish a long-term moisture content for the windblown material based on actual test data, or 2) provide specific t discussion and reference to soil data to justify the assumption that the 12 percent mill yard material value can be conservatively applied to the windblown material. This is an open issue. { DOE used a single soil sample from each of the mill yard, ore storage and windblown contaminated materials to measure radon diffusion coefficients. Each sample was tested at five different moisture contents and a best fit i curve prepared. The diffusion coefficient value corresponding to the estimated long-term moisture of the matp/s represents the mill yard / ore rial was selected by D0E. An average r radon diffusion coefficient of 0.018 cm he same value was derived for the windblown storage layer in the cell and }/s represents the tailings pile area, although material. A value of 0.030 cm no sample from this material was tested. This limited testing is inadequate t for final design. The DOE Technical Approach Document (DOE,1989) indicates i that an average diffusion coefficient will be determined from samples of each distinct contaminated material. In keeping with this, DOE should have additional (at least three) diffusion coefficient tests for both the windblown l and tailings pile area contaminated materials, or otherwise provide t justification that conservative values were used for the model. This is an open issue. DOE stated that testing indicated that the' radon emanation property of the material at the Naturita processing site is independent of its moisture content and Ra-226 concentration. Twelve measurements on contaminated material ranged from 0.06 to 0.35. The average emanation fraction for the mill yard / ore storage (four samples each) was 0.33, and 0.22 for the windblown material (four samples). No tests were performed on former pile area material l so the largest measurement (most conservative) of 0.35 was selected by DOE. The NRC staff considers these values acceptable for use in the RAECOM model. 4 The radium content of the contaminated materials was determined primarily by gamma spectroscopy. Incremental Ra-226 depth profiles were constructed by DOE for each measurement grid point. The average Ra-226 concentration was determined for each sub-area by integrating the profiles over the volume, based on the excavation depth. Volume-weighted average Ra-226 concentrations were calculated for each layer in the disposal cell as follows: i NATURITA dTER 6-3 octoter a, 1993

c;4 4 m'4 r .JJ L.i m. s,y 4, 4 A_rga Ra-226 foci /a) # Samoles Volume (x1000 yd ) Thickness (cm) i 3 Mill Yard 127 78 115 125*, 128 Ore Storage 75 27 12 Tailings pile 90 56 117 122 [ Vicinity properties 25 (assumed) 'O.3 j Debris 256 20 8 i Windblown 38 281 295 177*, 299 (* if supplemental standards applied) l The amount of Ra-226 that would result-in 1000 years from decay of the Th-230 that is present was not assessed because the Ra/Th data presented indicates that these radionuclides are in equilibrium. However, further testing of Th-230 at depth is expected, as discussed below in Section 6.3.1. If significant quantities of Th-230 are found, the 1000-year Ra-226 concentration would have to be considered in the design. The thickness of the various layers of contaminated material were derived from. the estimated volumes noted above. DOE stated that the quantities for windblown and ore storage areas has been multiplied by a contingency factor of. 25 percent to allow for unexpected depth of contamination. A contingency I property material. DOE has determined that if supplemental standards, as ~ factor of 50 percent is included in the quantities for debris and vicinity proposed in calculation 17-730-02-00, are applied to windblown materials (see Section 6.3.2 of this TER), the windblown material layer will be 5.8 feet i (177 cm) thick instead of 9.8 feet (299 cm) thick, based on a decrease in i 3 volume of approximately 128,600 yd. B. Radon Barrier The physical properties of the radon barrier material (silty and sandy clay) were selected by DOE based primarily on the results of laboratory testing of sanoles from the Coke Oven borrow site. The specifications require the radon l barrier soil to contain a minimum of 40 percent fines (material passing the-i No. EM sieve), and be compacted to 95 percent Standard Proctor density at from optimum moisture content to 3 percent above optimum moisture content. The average specific gravity for the radon barrier soil was 2.71 (11 tests). l The average density at 95 percent compaction, based on separate measurements made on 10 samples, was 1.68 g/cc resulting in a calculated porosity of 0.38. These values are acceptable for use in the RAECOM model. Capillary moisture tests (-15 bar) were run on eight samples of the Coke Oven borrow material, resulting in an average -15 bar moisture of 16.4 percent. At this moisture content, a radon diffusion coefficient of 0.0031 was derived from eight samples. The average in-situ moisture content of the eight -15 bar i test samples was 9.1%, and of all Coke Oven borrow samples was 7.0 percent. I DOE indicated that these in-situ moisture values were questionable due to-possible sample drying, and therefore, ignored the values in considering the long-term moisture. NATURITA dTER 6-4 Octotwr 8, W93 (

1 ~ l Based on a review of the summary of soil test results from the Coke Oven site, it appears that testing for radon barrier design has been performed on borrow material which is not representative of the total radon barrier source. The tests were run on only silty-clay (CL) material, with an average of 83 percent fines. In actuality, many of the samples indicate that the borrow area contains a great amount of silty-sand (SM) material. This corresponds to the specification that the radon barrier material can have as little as 40 percent fines. Additional testing of the radon barrier long-term moisture and diffusion coefficient should be run on SM materials to provide a representative average, or changes should be made to the specifications to require a material (CL) that fits the parameters of the tested material. Furthermore, additional in-situ moisture data should be obtained to resolve the questionable data presented in the RAP. This is an open issue. C. Ambient Radon The ambient air radon concentration is another required parameter value for the RAECOM model, and has been measured in the Naturita area. The average value is 0.6 pCi/1. The technique used to measure the radon concentration, and the result of the measurement are acceptable to NRC staff. 6.2.2 Evaluation of Radon Attenuation Model The thickness of the radon barrier layer (18 inches) is set by the design to satisfy construction considerations. This is acceptable to NRC staff as long as this thickness provides reasonable assurance that the radon flux standard can be met for at least 200 years. This is discussed below. DOE did not present a model representing the frost penetration damage to the radon barrier soil because they estimated the maximum frost penetration (using a frost barrier moisture of 7 percent) to be 49 inches. With the 36-inch-thick frost protection layer and the 18-inch thick bedding and riprap cover, the radon barrier soil would not be affected. See further discussion in TER Section 3.3.4. DOE used the RAECOM computer code to evaluate the radon attenuatip/s. n of the cover for compliance with the EPA radon flux standard of 20 pCi/m DOE's RAECOM analyses (calculation 17-741-01) used the parameters discussed above, in six different models. DOE modeled baseline (average values) and " worst case" (average +/- SEM) scenarios with the various situations for the low contamination windblown material as follows: (1) without application of supplemental standards for windblown areas (9.8 foot-thick layer), (2) with supplemental standards (5.8 foot-thick layer), and (3) for only a 4 foot-thick layer. In the " worst case", with the thinnest Jayer of windblown material, DOE calculated the radon flux would be 20 pCi/m /s at the top of a 10.2 inch (26 cm) thick radon barrier layer. Since DOE proposes to place an 18-inch-thick layer, they concluded that there is reasonable assurance the EPA standard will be met. NRC staff used the RADON computer code to model the radon flux using the more conservative combination of parameters proposed by DOE, but input the 18 inch (45 cm) barrier thickness. The analysis resulted in an estimated radon flux NATURITA dTER 6-5 october 8, 1993

l 2 of 9.7 pCi/m /s. However, since some of the parameter values are in question, staff also ran a more conservative model using moisture values of 10 and 12 percent (instead of 12 and 16 percent in DOE's model) for the windblown and radon barrier layers, respectively. The code calculated diffusion coefficients were also employed for all layers. The diffusion coefficient values were significantly different for only the yindblown and barrier layers. The resulting estimated radon flux was 28.8 pCi/m /s, which exceeds the EPA standard. NRC staff recognize that the frost protection layer above the radon barrier will provide additional attenuation and, therefore, may be addressed in presenting a case for meeting the EPA standard. However, any model including the frost protection layer must consider the degradation of the material due to freeze-thaw cycles, through use of appropriate material parameter values. Based on review of the design and analyses presented in the RAP and associated documents, NRC staff concludes that the radon attenuation model must be revised to include:

1) the additional testing referred to in the RAP calculation, and 2) other additional testing and analyses addressed in the issues above.

6.3 Site Cleanup 6.3.1 Radiological Site Characterization Field sampling and radiological surveys at the Naturita site identified contaminated materials covering 133 acres at the processing site and adjacent areas. In Section 6.5.1 of the Remedial Action Selection Report, DOE presents a discussion of the radiological site characterization. The discussion needs to mention whether the site has areas that could have had conditions that preferentially mobilized Th-230. This is an open issue. Calculation 17-730-01-01, Appendix A, Table B-3 lists the Th-230 analysis results. NRC staff estimated from the coordinates given, that only one sample each from the former tailings pile and ore storage areas were analyzed for Th-230. In order to provide adequate Th-230 characterization, more samples at the depth limit for Ra-226 excavation should be analyzed for Th-230, particularly in the former tailings pile and ora storage areas. This is an open issue. Three soil samples had elevated uranium levels (one at the 24-48 inch depth interval). Since DOE did not discuss the presence of natural, elevated radioactive material, or the presence of ore spillage along the road, DOE should indicate the possible reason for the elevated uranium, and what further exploration will be performed. This is an open issue. Background levels of Ra-226 were measured in the Naturita area and the average value is 2.3 pCi/g. The value was based on four samples ranging from 1.1 to 3.4 pCi/g. This limited sampling is not acceptable to NRC staff since DOE is basing the cleanup criterion on a value that includes this background value. DOE should provide more background Ra-226 data. This is an open issue. NATURITA d4R 6-6 October 8, 1 M

9 ', j., e ' 6.3.2 Cleanup Standards DOE has committed to excavate contaminated areas to meet the EPA standard of 5 pCi/g (surface) and 15 pCi/g (subsurface) plus background, for Ra-226 in soil, and to place the contaminated materials in an engineered disposal cell. Excavation will be monitored to ensure that cleanup efforts are-complete. 'The r cleanup plan is to stockpile the debris and vicinity property material in the - mill yard, and begin excavation at the higher elevations. The surface will be ~ restored to a grade that controls surface drainage. DOE states they may submit an application for supplemental standards to exclude remediation of certain contaminated areas such as steep slopes, f wetlands, and utility easements. Calculation 17-730-02-00 of the RAP is titled " Proposed Supplemental Standards Areas," and provides information on. j the justification for use of the supplemental standards. DOE should either remove the calculation until such time as supplemental standards are proposed in a PID, or modify the RAS section to indicate that the supplemental. standards discussed in the calculation are a part of the present RAP review. This is an open issue. Regardless of-when this is proposed, DOE should provide in the supplemental standard application, a drawing that clearly represents areas that should not be excavated, and provide documentation (letters from Corp of Engineers and gas company or telephone conversation logs) as to the reason for the application to specific areas. j All buildings on the site will be demolished, and all contaminated debris will be disposed of in the disposal cell. Therefore, cleanup of buildings or equipment is not required. + Subsoil conditions in the tailings pile area generally consist of a high l percentage of cobbles and gravels greater that a number 4 sieve. Therefore, DOE proposes use of the generic procedure for determining the bulk radium and thorium content of cobbly soil for excavation control and verification. A report on the detailed site-specific procedures used will be provided in the Completion Report. l DOE stated that for Th-230 contamination, supplemental standards will be based on the NRC-approved generic thorium policy. The' discussion on residual bulk Th-230 (RAS, page 6-8) refers to determining the working level when excavations are greater than 8 feet deep. This could be misinterpreted to indicated that at any depth greater than 8 feet, the removal could stop if the working level estimate met the criterion. This is not NRC staff's understanding of the final generic thorium policy. To avoid confusion, DOE should delete the phrase referring to working level determination for Th-230 at depth. This is an open issue. j 1 Uranium concentrations, after the Ra-226 has been removed to meet standards, j will be assessed by a pathway analysis of potential environmental and health i impacts. If remedial action is indicated, a supplemental standard will be j proposed. With regard to other hazardous materials, Section 02081, Part 3.3.J, of the construction specifications refers to a plan to "... dispose of the non-m un m e m 6-7 october a, m 3

..,i radiologically contaminated hazardous and non-hazardous materials into the disposal cell." If material is non-radiologically contaminated hazardous material it is neither residual radioactive material nor mixed waste. Therefore, it should be disposed of offsite in a manner approved by the appropriate authority. DOE should revise Section 02081, Part 3.3.J, of the Specifications accordingly. This is an open issue. 6.3.3 Verification The final radiological verification survey for land cleanup will be based on 100-square-meter areas. The standard method for Ra-226 verification is analysis of composite soil samples by gamma spectrometry, but DOE may use several other measurement techniques, depending on particular circumstances. If the nine-point composite gamma measurement technique or the RTRAK detection unit are used in the windblown areas, as suggested by DOE, adequate justification should be provided in the Completion Report. DOE stated that verification for Th-230 will follow the generic thorium policy. The policy indicates that areas known or suspected of containing elevated levels of Th-230 below the depth of Ra-226 remediation, will have 100 percent of the grids analyzed. Windblown areas will not be analyzed for Th-230, but the subpile area will have 10 percent of the grids analyzed. The RAS indicates that the mill yard will have 4 percent of the grids verified for Th-230. DOE should correct page 6-9 of the RAS to conform to the verification sampling plan outlined in the generic thorium policy, or present justification for any deviation. This is an open issue. No on-site structures at the processing site will require radiological verification, since all structures will be demolished and the debris will be buried at the disposal cell. 6.4 Conclusions Based on review of the physical and radiological parameter values assigned by DOE to the contaminated materials and radon barrier material that were considered in the radon barrier design, NRC staff concludes that adequate testing of these materials, as discussed in the issues in Section 6.2 above, needs to be performed. l DOE has stated (RAS, page 6-10) that the final cover design will be based on j final measurements of the bulk Ra-226 depth distribution and associated j emanation factors. NRC staff accepts this situation with the understanding I that the final data and the revised RAECOM analysis incorporating this data, I will be provided for review as part of the Completion Report. The staff finds that the radiological characterization program, and the proposed processing site cleanup and verification plans require more information, or modification, as delineated in the issues presented in Section 6.3 above. The thirteen open issues resulting from the evaluations for this section of the TER are listed in Table 1.1. NATURITA dTER 6-8 October 8, 1993

t i,..

7.0 REFERENCES

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