United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington DC 20460
March 1983
EPA 520/1-82-022
Draft Environmental
Impact Statement
for Standards
for the Control
of Byproduct Materials
from Uranium Ore Processing
(40 CFR 192)
..cCi'.QU RGENC
i"",; j. u&i/.
> : , *• i .; " • '
Lt» 520/1
82-022
-------
EPA 520/1-82-022
Draft
Environmental Impact Statement
for
Standards for the Control
of
Byproduct Materials from
Uranium Ore Processing
(40 CFR 192)
March 1983
Office of Radiation Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
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CONTENTS
Page
1. INTRODUCTION 1-1
1.1 Scope of Proposed Standards 1-1
1.2 Contents of the Analysis 1-3
References , 1-5
2. THE URANIUM MILLING INDUSTRY 2-1
2.1 History of the Uranium Milling Industry 2-1
2.2 Conventional Milling Processes 2-2
2.3 Waste Management at Uranium Mills 2-5
2.4 Uranium Recovery by Heap-Leaching 2-7
2.5 Currently Licensed Uranium Mills 2-8
2.6 Future Uranium Supply and Demand 2-8
References 2-13
3. ENVIRONMENTAL RELEASES FROM URANIUM MILLING WASTES 3-1
3.1 Composition of Tailings Solids and Pond Liquids 3-1
3.1.1 Radioactivity in Tailings 3-1
3.1.2 Toxic Elements and Other Chemicals in
Tailings 3-4
3.2 Routine Environmental Releases from Tailings 3-4
3.2.1 Air Contamination 3-5
3.2.2 Land Contamination 3-9
3.2.3 Water Contamination 3-11
3.3 Nonroutine Releases 3-14
3.3.1 Accidents and Acts of God 3-14
3.3.2 Misuse of Tailings Sands 3-15
111
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CONTENTS (Conti.nued)
Page
3.4 Environmental Releases from Heap-Leaching Operations .. 3-15
References 3-16
4. MODEL SITE AND TAILINGS PILE 4-1
4.1 Model Site 4-1
4.1.1 Meteorology 4-1
4.1.2 Demography 4-1
4.1.3 Hyd ro lo gy 4-6
4.1.4 Agricultural Productivity 4-6
4.2 The Model Tailings Pile 4-6
4.2. 1 Physical Description 4-6
4.2.2 Contaminants Present 4-8
4.2.3 Radioactive Emissions to Air 4-8
4.2.4 Emissions of Contaminants to Water 4-8
References 4-11
5. ENVIRONMENTAL PATHWAYS 5-1
5. 1 Contaminants 5-1
5.1.1 Particulates 5-1
5.1.2 Radon 5-2
5.1.3 Liquid Contaminants 5-2
5.2 Atmospheric Transport 5-3
5.2.1 Near the Tailings 5-3
5.2.2 Regional 5-3
5.2.3 National 5-5
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CONTENTS (Continued)
Page
5.3 Hydro logical Dispersion 5-5
5.3.1 Surface Water 5-5
5.3.2 Groundwater 5-6
5.4 Environmental Concentrations 5-7
5.4.1 Calculational Procedures 5-7
5.4.2 Air Concentrations 5-8
5.4.3 Ground Surface Concentrations 5-10
5.4.4 Dietary Intake 5-16
5.4.5 Water Concentrations 5-17
References 5-21
6. HEALTH IMPACT OF TAILINGS BASED ON MODEL TAILINGS PILE 6-1
6.1 Introduction 6-1
6.1.1 Radon and Its Immediate Decay Products 6-3
6.2 Estimated Effects on Health Due to Radioactive
Releases from the Model Tailings Pile 6-4
6.2.1 Effects of Radioactive Particulate Releases
from the Model Tailings Pile 6-4
6.2.2 Effects of Radon Emissions from
Tailings Piles 6-9
6.2.3 Effects of Gamma Radiation Emissions from
Tailings Piles and Windblown Tailings 6-10
6.3 Effects from Misuse of Tailings 6-11
6.4 Estimated Effects on Health Due to Toxic Releases
from the Model Tailings Pile 6-11
6.5 Effects Expected in Plants and Animals 6-13
References 6-14
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CONTENTS (Continued)
Page
7. CONTROL OF TAILINGS DURING MILLING OPERATIONS 7-1
7.1 Objectives of Control Measures 7-2
7.1.1 Wind Erosion 7-3
7.1.2 Radon 7-3
7.1.3 Water Contamination 7-3
7.2 Control Methods 7-3
7.2.1 Wind Erosion 7-3
7.2.2 Control of Radon 7-6
7.2.3 Control of Groundwatsr Contamination 7-6
7.3 Cost and Effectiveness of Control Measures for Model
Tailings Pile 7-7
7.3.1 Control of Wind Erosion of Tailings 7-7
7.3.2 Control of Radon . 7-8
7.3.3. Control of Seepage to Groundwater 7-8
7.4 Cost-Effectiveness Analyses 7-11
7.4.1 Wind Erosion 7-11
7.4.2 Control of Radon 7-12
7.4.3 Control of Seepage to Groundwater 7-15
References 7-16
8. OBJECTIVES AND METHODS FOR TAILINGS DISPOSAI 8-1
8.1 Health and Environmental Protection Objectives 8-1
8. 2 Longevity of Control „ . 8-3
8.2.1 Human Intrusion ,. 8-4
8.2.2 Erosion 8-4
VI
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CONTENTS (Continued)
Page
8.2.3 Floods 8-4
8.2.4 Longevity of Control 8-6
8.3 Disposal Methods and Effectiveness 8-7
8.3.1 Earth Covers 8-7
8.3.2 Basin and Pond Liners 8-10
8.3.3 Thermal Stabilization 8-11
8.3.4 Chemical Processing 8-13
8.3.5 Soil Cement Covers 8-13
8.3.6 Deep-Mine Disposal 8-14
8.3.7 Solidification in Concrete or Asphalt 8-14
8.4 Selection of Disposal Method for this Analysis 8-15
References 8-16
9. ALTERNATIVE STANDARDS FOR TAILINGS DISPOSAL 9-1
9.1 Form of the Standards 9-1
9.1.1 Dose or Exposure Rate Limits 9-1
9.1.2 Concentration Limits in Air and Water 9-1
9.1.3 Release Rate Limits 9-2
9.1.4 EngLneering/DesLgn Standards 9-2
9.2 Alternative Disposal Standards 9-3
9.3 Estimated Costs of Methods for Alternative Standards .. 9-5
9.3.1 Disposal Methods for Existing Tailings Piles ... 9-6
9.3.2 Disposal Methods for New Tailings Piles 9-8
9.4 Accidental and Radiation-Induced Deaths from Disposal.. 9-12
References 9-14
v 1.1
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CONTENTS (Continued)
Page
10. ANALYSIS OF COSTS AND BENEFITS FOR ALTERNATIVE TAILINGS
DISPOSAL METHODS 10-1
10.1 Benefits Achievable by Disposal of Tailings 10-1
10.1.1 Benefits of Stabilization 10-2
10.1.2 Benefits of Radon Control 10-6
10.1.3 Benefits of Protecting Water 10-7
10.2 Benefits and Costs for a Model Tailings Pile 10-7
10.2.1 Alternative Standard A 10-7
10.2.2 Alternative Standard B 10-8
10.2.3 Alternative Standard C 10-9
10.2.4 Alternative Standard D 10-9
10.2.5 Alternative Standard E 10-10
10.2.6 Alternative Standard F 10-11
APPENDICES
APPENDIX A: (Reserved) A-l
APPENDIX B: Estimated Costs for Disposal of Active
Uranium Mill Tailings B-l
APPENDIX C: Health Basis for Hazard Assessment C--1
APPENDIX D: Water Management at Uranium Ore Processing Sites ... D-l
TABLES
2-1 Uranium Production 2-2
2-2 Currently Licensed U.S. Uranium Mills 2-9
2-3 Projected Demands for Uranium Yellowcake 2-11
2-4 Projections of Demand, Production, and Inventory of
Uranium Yellowcake 2-11
viii
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CONTENTS (Continued)
Page
3-1 Description of Mill Tailings Piles at Licensed Mills 3-6
3-2 Dissolved Substances in Tailings Pond Liquids at
Selected Sites 3-8
3-3 Average Concentration of Elements Found in Inactive Uranium
Mill Tailings 3-10
3-4 Contamination in Shallow Aquifers Compared with Estimated
Background Near Active Tailings Ponds 3-12
3-5 Elements Found in Elevated Concentrations in Groundwater
Near Inactive Tailings Sites 3-14
4-1 Annual Average Joint Frequency Distribution for Winds in
the Model Mill Region 4-2
4-2 Population Distribution at a Remote Uranium Mill
Tailings Site 4-4
4-3 Population Distribution at a Rural Uranium Mill
Tailings Site 4-5
4-4 Summary of Principal Physical Characteristics of the Model
Tailings Pile 4-7
4-5 Chemical and Radiological Properties of Tailings Wastes
Generated by the Model Mill 4-9
4-6 Radioactive Emissions to Air from Model Tailings Pile 4-10
5-1 Regional Air Concentration of Radionuclides by Distance and
Particle Size (Operational Phase) 5-11
5-2 Regional Population Inhalation Intake and Exposure (per
Operational Year) 5-12
5-3 National Population Exposures and Intakes 5-12
5-4 Regional Air Concentration of Radionuclides by Distance and
Particle Size (Post-Operational Phase) 5-13
5-5 National Population Exposures and Intakes Per Year (Post-
Operational Phase) 5-14
5-6 Regional Ground Surface Concentrations for Radionuclides.... 5-14
IX
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CONTENTS (Continued)
Page
5-7 Regional Population Ground Surface Exposure for
Radionuclides (per Operational Year) 5-15
5-8 Regional Ground Surface Concentrations for RadionucLides
by Distance (Post-Operational Phase) 5-15
5-9 Regional Food Utilization Factors for an Individual 5-16
5-10 Regional Individual Annual Ingestion for Radionuclides
(Operational Phase) 5-18
5-11 Regional Individual Annual Ingest ion for Radionuclides
by Direction (Post-Operational Phase) 5-19
5-12 Regional Population Ingestion for Radionuclides
(per Operational Year) 5-20
6-1 Regional Individual Lifetime Risk of Fatal Cancer
(Operational Phase) 6-5
6-2 Regional Individual Lifetime Risk of Fatal Cancer
(Post-Operational Phase) 6-6
6-3 Number of Fatal Cancers per Operational Year for the
Regional Population 6-7
6-4 Number of Fatal Cancers per Post-Operational Year for the
Regional Population 6-7
6-5 U.S. Collective Risks due to Radon-222 Release per
Operational Year 6-8
6-6 U.S. Collective Risks due to Radon-222 Release per
Post-Operational Year 6-8
7-1 Chemical Stabilization Agents Used for Dust Suppression ... 7-5
7-2 Costs and Effectiveness of Methods for Controlling
Wind Erosion at a Model Tailings Pile 7-9
7-3 Costs and Benefits of Various Levels of Control of
Dust Emissions for Model Tailings Pile During
Operational Phase 7-12
7-4 Costs and Benefits of Various Levels of Control of Dust
Emissions for Model Tailings Pile During Post-
Operational Phase - 7-13
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CONTENTS (Continued)
Page
7-5 Costs and Benefits of Various Levels of Control of Radon
Emissions from Model Tailings Pile During
Operational Phase . . * 7-14
8-1 Soil Erosion Rates in the United States 8-5
8-2 Estimated Earthen Cover Thickness (in meters) to Reduce
Radon Emissions to 20 pCi/m^s 8-9
8-3 Percent Reduction in Emanating Ra-226 at Temperatures
from 500° to 1200° C 8-12
9-1 Alternative Standards for Disposal of Uranium Mill Tailings 9-4
9-2 Control Methods Assumed to Satisfy the Alternative
Standards 9-7
9-3 Summary of Cost Estimates for Disposal of Active Uranium
Mill Tailings 9-11
9-4 Accidental and Radiation-Induced Deaths Associated with
Alternative Levels of Tailings Control 9-13
10-1 Benefits of Controlling Uranium Mill Tailings at
Existing Active Sites 10-3
10-2 Benefits of Controlling Uranium Mill Tailings at Active
Mill Sites through the Year 2000 for the Baseline
Estimate 10-4
10-3 Benefits of Controlling Uranium Mill Tailings at Active
Mill Sites through the Year 2000 for the Low Growth
Estimate 10-5
10-4 Total Costs of Controlling Uranium Tailings at Active Sites 10-8
FIGURES
2-1 Flow Diagram of the Generation of Uranium Tailings Solids
and Liquids from the Acid-Leach Process 2-4
3-1 The Uranium-238 Decay Series 3-2
3-2 Radon Production In a Tailings Pile 3-3
5-1 Radon Concentrations Near the Pile 5-9
8-1 Percentage of Radon Penetration of Various Covers by
Thickness 8-8
XI
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Chapter 1: INTRODUCTION
In the Uranium MilL Tailings Radiation Control Act of 1978, Public
Law 95-604, 42 USC 7901 (henceforth designated as "the Act"), Congress
directed the Environmental Protection Agency (EPA) to "promulgate
standards of general application for the protection of the public
health, safety, and the environment from radiological and non-
radiological hazards associated with the processing and with the
possession, transfer, and disposal of byproduct material... at sites at
which ores are processed primarily for their source material content or
which are used for the disposal of such byproduct material." The term
"byproduct material' as defined by the Act means, for these sites,
"...the tailings or wastes produced by the extraction or concentration
of uranium or thorium from any ore processed primarily for its source
material content." The Act assigns the responsibility for imple-
mentation and enforcement of these standards to the Nuclear Regulatory
Commission and its Agreement States through their licensing activities.
The Act also requires EPA to promulgate standards for cleanup and
disposal of uranium tailings at inactive processing sites. EPA issued
standards for cleanup of contaminated open lands and buildings and for
disposal of tailings at inactive uranium processing sites on January 5,
1983 (48 FR 590).
1.1 Scope of Proposed Standards
Standards are required for the control of effluents and emissions
from the tailings both during milling operations and for the final
disposal of tailings. The Act specifies that standards for non-
radioactive hazards must provide protection of human health and the
environment consistent with applicable standards established under
Subtitle C of the So 1. id Waste Disposal Act, as amended.
The sites that are affected by these standards currently include
about two dozen conventional uranium mills and 4 heap-leaching
locations; these sites are licensed by NRC or its Agreement States.
Approximately 86 percent of all uranium produced in 1980 was produced
from ore mined in underground or open-pit mines and processed in
1-1
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conventional uranium mills. Solution mining contributed 8 percent, and
about 5 percent came from heap-leach plants, mine water extraction and
conventional milling of low-grade stockpiles of ore.
Only conventional uranium mills and heap-leaching operations are
covered by these proposed standards. Solution mining and phosphoric
acid byproduct operations are not included because large amounts of
tailing wastes are not involved in these operations. The Act was
directed primarily toward the solution of environmental problems from
the radioactive tailings piles resulting from conventional milling
operations.
A number of environmental standards already apply to tailings.
EPA promulgated 40 CFR Part 190, Environmental Radiation Protection
Standards for Uranium Fuel Cycle Operations, on January 13, 1977 (42 FR
2858). These standards specify the radiation levels below which normal
operations of the uranium fuel cycle must operate. Radiation exposures
due to environmental release of and from uranium byproduct material are
covered by these standards, with the exception of emissions of radon
and its decay products. Under the Clean Water Act, EPA issued effluent
limitations guidelines on December 3, 1982, for new source performance
standards for wastewater discharges from the mining and dressing of
uranium, radium, and vanadium ores (40 CRF 440, 47 FR 54598).
Discharges of both radioactive and nonradioactive materials to surface
waters from uranium byproduct materials are covered by these effluent
guidelines. Because these guidalines and proposals have already been
issued, we have not evaluated control measures for discharges to
surface water in this DEIS.
EPA promulgated 40 CFR Part 261, Subpart F—Groundwater
Protection, on July 26, 1982 (47 FR 32274) under the Solid Waste
Disposal Act (SWDA), as amended by the Resource Recovery and
Conservation Act. The Act requires that standards for nonradioactive
hazards from uranium byproduct materials be consistent with standards
promulgated under SWDA for such hazards. Also, the Act requires that
the NRC establish general requirements which are, to the maximum extent
practicable, at least comparable to requirements applicable to the
possession, transfer, and disposal of similar hazardous material
regulated by EPA under the SWDA. NRC Agreement States are required by
the Act to adopt standards which are equivalent, to the maximum extent
practicable, or more stringent than, standards adopted and enforced by
the NRC. These responsibilities must be carried out by the NRC whether
or not EPA promulgates standards for groundwater protection. We have
included groundwater protection in this analysis to determine whether
or not the SWDA standards should be supplemental or modified by the
standards proposed under the Act.
Thorium mill tailings are included in the definition of byproduct.
material and must be licensed by the NRC or an Agreement State under the
same provisions of the Act as uranium mill tailings. However, standards
for thorium tailings are not included in this analysis because the only
1-2
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thorium currently being recovered from ore is as a secondary product at
the W.R. Grace Co. facility near Chattanooga. There are also thorium
byproduct materials at four inactive sites located in New Jersey,
Illinois, Ohio, and West Virginia. The current demand for thorium is
small, and there appears to be little growth potential. The two major
uses of thorium are as a source material in nuclear applications and as a
thin ceramic lantern mantle that gives off a bright light. Neither of
these uses is expected to increase significantly in the next few years.
There are a few other licensed sites contaminated with uranium and
thorium and their decay products. Two or three of these sites may
contain uranium and thorium byproduct material as defined by the Act.
These sites are not included in this analysis, because the quantities of
material are relatively small and would not affect the overall analysis.
There are now about 170 million tons of tailings at the licensed
mill sites. Of these, about 56 million tons were generated under
government contracts. Most of these 56 million tons of tailings are not
separated from other tailings and are commonly designated "commingled"
tailings. The Department of Energy (DOE) has recently issued a report on
commingled tailings in response to Congressional concern over whether the
government or industry should pay for disposal of these tailings
(DOE82). The analysis for these standards is not significantly affected
by this issue. However, government sharing of costs would lead to a
lesser impact on the industry, as reflected, for example, in fewer mills
closing under certain alternatives for environmental requirements. Thus,
government sharing of costs could permit application of more stringent
standards. Our economic analysis assumes the total costs of compliance
will be borne by the industry. Any government sharing of disposal costs
would thus improve industry's economic position compared to that
projected in this analysis.
1.2 Contents of the AnalysLs
In this document, we examine (1) alternative standards for disposal
of uranium mill tailings, and (2) alternative standards for control of
environmental releases from tailings during the operational phase of
uranium mills. Both radioactive and nonradLoactive releases are
considered. Potential effects of tailings on health are estimated, along
with the effectiveness and costs of different control approaches.
In Chapter 2 we briefly describe the uranium industry and summarize
projections of uranium production to the year 2000. Chapter 3 contains a
description of the uranium tailings themselves, with emphasis on their
hazardous components and releases of contaminants to the environment. A
model site and tailings pile is described in Chapter 4 for use in
carrying out the analysis of benefits and costs of control. In Chapter 5,
pathways through which radioactive and hazardous materials may cause
1-3
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exposure to man are examined. Based on the information in Chapters 4
and 5, potential health effects are estimated on local, regional, and
national populations in Chapter 6. Chapter 7 contains a review of
emission control measures for the operating period of the mill and
estimates of the effectiveness and costs of these systems.
In Chapter 8 we examine the efficacy and longevity of the principal
methods for disposal of tailings. Chapter 9 contains cost estimates for
representative disposal methods for existing and future tailings at model
sites. In Chapter 10 we analyze costs and benefits for tailings disposal.
standards options.
1-4
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REFERENCES
DOE82 Department of Energy, "Commingled Uranium Tailings Study,"
DOE/DP-OOll, June 1982.
1-5
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Chapter 2: THE URANIUM MILLING INDUSTRY(O
2.1 History_ of the Uranium^ Milling Indust_ry_
The uranium milling industry has undergone considerable change in
the last 35 years, as uranium developed from a commodity of minor
commercial use to one vital for nuclear weapons and for producing
electrical energy. To meet military needs in the early 1940's, uranium
ore was obtained from the rich pitchblendes (greater than 10 percent
U3°8 equivalent) of the Belgian Congo and the Great Bear Lake
deposits in Canada, supplemented by production from a few small mines
in the Colorado Plateau area. These high-grade ores and concentrates
were refined by an ether extraction technique adapted from analytical
chemistry procedures. The processes used for low-grade ores were
relatively crude and reflected little change from methods used at the
turn of the century. Milling costs were high and uranium recovery was
relatively inefficient.
After the Atomic Energy Act was passed in 1946, strong emphasis
was placed on the discovery and development of new sources of uranium
and on development of improved processing techniques. The Atomic
Energy Commission (AEC) purchased 3 x 10' MT^) of U30g between
1948 and 1970, with approximately 55 percent from domestic sources.
Table 2-1 illustrates the size of the industry from 1948 to the
present. During the peak production years of 1960 to 1962, there were
up to 26 operating mills (excluding plants producing byproduct uranium
from phosphates) with an annual production rate exceeding 1.5 x 104 MT
of U^Og from 7 x 10" MT of ore (average grade of 0.21 percent).
1.1 ./Much of the information in this chapter is based on the Nuclear
Regulatory Commission's "Final Generic Environmental Impact Statement
on Uranium Milling," NRC80, Chapters 2 and 3 and Appendix B. Material
from other sources is separately referenced.
(^Metric ton (MT) or 1000 kg, equivalent to 2200 pounds or 1.1 short
tons (ST).
2-1
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Table 2-1. Uranium Production^3)
Year
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
U3°8
(1000 MT)
0.1
0.2
0.4
0.7
0.8
1.1
1.5
2.5
5.4
7.7
11.3
14.7
16.0
15.7
15.4
12.9
10.7
Year
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
U3°8
(1000 MT)
9.5
9.6
10.2
11.2
10.5
11.7
11.1
11.7
12.0
10.5
10.5
11.6
13.6
16.8
17.0
19.8
17.5
(^Adapted from DOE82. Includes l^Og production obtained
by mine water, heap-leaching, solution mining, or as a by-
product of another activity.
Reduced military requirements and the slow development of
commercial nulcear power resulted in fewer operating mills and lower
uranium production in the period from 1963 to 1970. About 3.4 x 10-"
MT of U-jOg had been produced by the end of 1981, resulting in about
1.8 x 10^ MT of tailings. Approximately 15 percent of the tailings
are at 23 inactive mill sites covered under Title I of the Act, and the
balance (85 percent or about 1.5 x 10° MT) is located at currently
active mill sites considered by this analysis.
Mill capacities in 1978 ranged from 360 to 6300 MT of ore per day,
with an average capacity of 1800 MT per day. In early L978, 19 mills
were operating; this increased to 21 in early 1980. Although there are
several new mills proposed and some present ones are being shut down,
these changes would not significantly alter the conclusions.
2.2 Conventional Milling Processes
In the uranium milling process, uranium is extracted from the
crude ore and concentrated into an intermediate semirefined product
called "yellowcake." The remainder oE the material, essentially the
total mass for low-grade ores, is disposed of in mill tailings piles.
Most of the radioactivity associated with the ore goes to the tailings
2-2
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pile. This radioactivity consists primarily of radium and its decay
products, which are not removed with the uranium during milling.
Historically, about 90 percent or more of yellowcake has been
produced by conventional mills. In 1980 about 15 percent of yellowcake
was produced from solution mining, mine water, copper dump-leach
liquor, or wet process phosphoric acid effluents.
There are two basic conventional processes for removing uranium
from ore: the acid-leach process and the alkaline-leach process.
About 80 percent of the current milling capacity uses a sulfuric acid
leach process. Since it is not economical to leach those ores having a
high alkaline content with acid, these ores are leached with an
alkaline solution. Several mills include circuits for both processes.
Primary emphasis is placed on the acid-leach process in this analysis.
Comments on the alkaline process are limited to differences between the
processes that are pertinent to their environmental releases.
Figure 2-1 is a flow diagram of the process at a conventional mill
leading up to the generation of waste tailings solids and liquids. In
a conventional miJ I, the first step is grinding the ore to a size
suitable for leaching oat the jranium. Ore characteristics and the
leaching process dictate the degree to which ore must be ground. For
the acid leaching )f sandstone ores, the ore is ground to the natural
gra in si ze.
Alkaline leaching requires much finer grinding. The ore is
conveyed from the .-rushing circuit to the grinding circuit by belt
feeders. Samples are taken at points between the crushing and grinding
circuit for routine laboratory analysis. Rod and ball mills are
usually used to grind the ore to approximately 28 mesh (600 microns)
f.jr the acid-leach process or to 200 mesh (74 microns) for the alkaline-
leach process. The ores are wet ground (water added) with the aid of
classifiers, thickeners, cyclones, or screens that size the ore and
return coarser particles for further grinding, resulting in a pulp
density of 50 to b5 percent soj ids. Water consumption is reduced by
recircul =H ing mill solutions (e.g., by recycling the clarified effluent
from the grinding circuit" thickener.) Wet milling can be used in place
of both the crushing _md fine grinding. This process uses a rotating
steel cylinder. The tumbling action of the lifters, large pieces of
ore, and a small Charge of 8- to 10-centimeter steel balls are used to
break down the ore.
After ;;r i ml i .i>;, thf ore is leached to remove uranium. IT 1976,
the acid-leach process was used by 32 percent of the industry. Acid
leaching i -; preferred tor ores with 12 percent or less limestone.
Those with more than 12 percent limestone require excessive quantities
oi acid and, for >>conomic reasons, ar^ best extracted by al'-cal ine
leaching. The sulphuric-acid leaching process is compatible with
several .;onc'.Mit rai ion and puriLicat ion processes, including i m
exchange, solvent extract ion, or a combination of both processes. The
-------
Ore
Crushing and
Grinding
Water
Sulfuric
Acid and
Sodium Chlorate
Flocculant
Wet
Grinding
T
Leaching
1
Tailings Pond
(Tailings sand and slimes,
liquid wastes)
Water
Countercurrent
Decantation
(CCD)
Barren raffinate
Pregnant Liquor
Solvent
Extraction
Further
Processing
Figure 2-1. Flow Diagram of the Generation of Uranium Tailings
Solids and Liquids from the Acid-Leach Process.
2-4
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slurry from the grinding operation (50 to 65 percent solids) is
discharged into the leaching circuit, which consists of several tanks
in series. Sulfuric acid is continuously added to maintain the pH
between 0.5 and 2.0. For U.S. ores treated exclusively for uranium
extraction, acid consumption ranges from 20 to 60 kilograms of sulfuric
acid per MT (40 to 120 Ibs/tons) of ore.
An oxidant, either NaC103 or MnC>2, is also continuously added
with the sulfuric acid to oxidize tetravalent uranium in the ore to
hexavalent uranium, which is more soluble. Iron must be present in the
solution for NaC103 or MnC>2 to be an effective oxidant for tetrava-
lent uranium. Either oxidant acts to oxidize ferrous iron to the
ferric state, and the ferric iron in turn oxidizes the uranium. Ore
leaching proceeds at atmospheric pressure and a little above room
temperature. Most of the uranium in the ore is dissolved, as well as
some other materials, such as some uranium daughter products, iron, and
aluminum. The residence time in the leaching tank is about 7 hours.
After ore leaching is completed, the "pregnant" leach liquor
containing the dissolved uranium is removed from the tailings solids.
This is carried out in a countercurrent decantation (CCD) circuit. In
this operation, the slurry is first sent to hydrocyclones (liquid
cyclone separators) that separate the coarse sand fraction as an
underflow, and the sand fraction is subsequently washed Ln a series of
classifiers. The overflows from the classifier and the hydrocyclone
are combined, and the slimes are washed. Flocculants are added to
promote settling of the suspended solids. The solids are washed with
fresh water and recycled (barren) raffinate from the solvent extraction
circuit. After thorough washing, the sands and slimes are pumped as a
slurry to the tailings pond. After solid-liquid separation in the CCD
circuit, the leach solution is sent to the solvent extraction and
further processing.
The acid-leach and alkaline-leach processes have considerable
chemical differences, and the ore is milled to a smaller size for
carbonate leaching. However, this does not appear to cause any
significant differences in environmental releases. A larger fraction
of the thorium-230 is solubilized in the acid-leach process than in the
carbonate-leach process, but the thorium is precipitated in the
tailings pond when the acidity is reduced. Thus, except in the early
stages of liquid discharges before the solution is neutralized, this
difference is negligible.
2. 3 W_a_s_t._e__Manaj|ement_^t Uranium Mills
During the early history of uranium milling, tailings liquids were
discharged to surface waters. As late as 1975, Sears (Se75) noted that
two mills were discharging liquid effluents to surface waters. In
1981, only the Uravan, Colorado, mill was still discharging treated
liquid effluents directly to surface waters.
2-5
-------
The alternative to discharging liquid effluent is the impoundment
of both solids and liquids in a tailings pond. Initially, tailings
ponds were located near the mill based on economics and accessibility.
The pond areas were formed from dikes built with tailings sands or from
soil and rock from the pond area. As the pond was filled, the dikes
were raised with mill tailings sands, separated from the slurried waste
with cyclone separators. This design was used for most of the inactive
tailings piles (EPA80) and many of the older active piles. Current NRC
regulatory practice discourages the use of tailings for dike materials
(NRCSOa, NRC77). However, this practice still, continues for many of
the existing active sites (e.g., Homestake and Kerr-McGee near Grants,
New Mexico). Although the ponds were generally designed as evaporation
ponds, there are instances where seepage has equaled or exceeded the
evaporation rate (Ka75, EPA75). There are still seepage releases to
groundwater and probably to surface water at several mills (See Chapter 3.)
It was not until 1976 that the NRC made a concerted effort to
control uranium mill tailings. Performance objectives were issued in
1977 and again in revised form in Regulatory Guide 3.11 (NRC77). These
objectives provide location criteria, require the elimination of wind-
blown tailings, and require reducing post-reclamation gamma exposure
to offsite areas to essentially background levels. Furthermore, this
guidance discourages the use of upstream dam construction techniques
(the dam is raised in stages on the tailings material) and specifies
minimizing seepage from the tailings ponds by the use of clay or
artificial liners. The guidance requires designs that improve the
tailings stability and reduce the seepage from tailings disposal
systems.
EPA collected information on active mills and waste disposal
practices in 1978 (Ja79). Some of the notable conclusions are:
• Tailings and effluent disposal methods practiced in
the United States generally consist of impoundment of
mill wastes in unlined ponds. This disposal method
is not state-of-the-art. It is usually inadequate,
since up to 85 percent of the liquid effluent
impounded may be lost by seepage and, subsequently,
pollute groundwater.
• Treatment of mill effluents to reduce pollutant
levels and/or to recover uranium or uranium
byproducts is seldom practiced.
• Treatment and discharge as a method of effluent
disposal is practiced at only one of the currently
operating, conventional uranium mills in the United
States.
2-6
-------
• All effluent streams from the mills sampled Ln this
study, were they to be discharged, would require
treatment to comply with effluent limitation
guidelines for point-source discharges. Currently,
none of the streams sampled is being discharged.
• Unlined ponds, properly located, may be
environmentally acceptable as a means of mill waste
disposal under some local soil and hydrogeological
conditions, because some native soils can mitigate
the adverse effects of seepage, by exhibiting low
permeabilities, thereby reducing seepage rates,
and/or possessing characteristics that favor the
uptake and fixation of seepage-borne contaminants.
• Total dependence on native soils above the water
table for purification of seepage from unlined ponds
is not technically sound, since uptake capacity is
both unpredictable and time dependent, and anions
such as sulfate, chloride, and nitrate are not
removed.
• Lined ponds represent a recent advance in
state-of-the-art technology for containment of
millwastes, since they afford a greater degree of
seepage prevention than unlined ponds and ensure
protection of groundwater.
• Clay or treated clay liners are preferred for lining
ponds containing mill tailings wastes.
After a mill ceases operations, the tailings impoundment will
slowly dry up over a few years. In such a condition, tailings are
continually vulnerable to spreading by wind and water erosion or by
such uses as for fill around buildings. Some of these dry tailings
piles have been the subject of a variety of stabilization schemes
involving earth cover placement and revegetation. Stabilization
attempts to date have not been generally successful, and none has
been designed for the long term.
2.4 Uranium Recovery by Heap-Leaching
Most mills are not designed to process uranium ores of less than
0.04 percent l^Og. However, uranium is often extracted from such
ores by a heap-leach process. Heap-leaching is also used when the ore
body is small or situated far from the milling facilities. Shipping a
high-grade solution or a crude bulk precipitate (the product of heap-
leaching) to the mill is less expensive than hauling low-grade ore to
the mill.
2-7
-------
Uranium recovery by heap-leaching has been used for low-grade
(0.01-0.03 percent u^Og) sandstone uranium ores. The ore to be
heap leached is typically placed upon a gently sloped impermeable pad
and saturated from above with a leaching solution. Pad impermeability
is generally achieved by laying down a plastic sheeting, but other
materials such as asphalt and concrete have been used on a pilot
scale. Just above the pad, a network of pipes and drain tiles is put
in place to collect the leachate that percolates to the bottom of the
ore piles. The percolated leachate is collected and recirculated until
the uranium concentration in the solution reaches 0.06 to 0.1 grams of
u3°8/Per li-ter. At this point the leachate is sent to resin
ion-exchange columns for extraction of the uranium.
If mine water is used, uranium already in the water, as well as
that extracted from the heap leach, is recovered. The most commonly
used leach reagents are sulfuric acid and ammonium carbonate. In an
efficient operation about 80 percent of the uranium will be extracted
from the ore. Heap-leach piles are commonly about 100 meters long, 6
to 8 meters high, with beams separating the piles in segments about 20
meters wide. After completion of operations, the leached ore may be
limed, graded, and stabilized by covering and revegetating the
surface. A state-of-the-art heap-leaching operation is described in
detail in a recent document (NRC78b).
2.5 Currently Licensed Uranium Mi__
There were 27 licensed uranium mills, of which 16 were operating,
in the United States as of September 1982. These mills are listed in
Table 2-2. Edgemont, South Dakota, which is not an operating mill, has
been included since it is licensed and has been excluded from the
designated inactive sites (EPA80). The Tennessee Valley Authority
(TVA) owns the site and had planned to reactivate the mill. However,
TVA is now planning to clean up the site and move the milling
operation. The Ray Point, Texas, site has also been shut down for
several years. Eight mills closed during the period from January 1981
to September 1982. Another mill has been constructed and licensed, but
it has never started operation. The data in Table 3-1 summarizes the
operational features of the mills with significant tailings (NRC80a and
Ja79, supplemented with private communications).
2.6 Future_ Uranium Supply_and Demand
Uranium is required for both the nuclear power industry and
defense activities. Projections of uranium needs for nuclear power can
be reasonably accurate for the next 20 years, since 10 to 15 years Ls
required from the decision to build a reactor until it is producing
power. Power reactors ordered now will not be producing power until
the 1990' s. Uranium needs for defense purposes are much more difficult
to project since they are greatly influenced by political considera-
tions. However, it is likely that nuclear power needs will greatly
2-i
-------
Table 2-2. Currently Licensed U.S. Uranium Mi
Location
_0wne_r
OPERATING MILLS
Colorado
Uravan
Canon City
New Me_xico
Milan
Ambrosia Lake
Union Carbide Corporation
Cotter Corporation
Homes take Mining
Kerr-McGee Nuclear
Texas
Panna Maria
Utah
Blanding
La Sal
Moab
Washington
Ford"
Wyoming
Gas~HiIls
Gas Hills
Powder River
Powder River
Red Desert
Shirley Basin
Shirley Basin
Chevron Resources
Energy Fuels Nuclear
Rio Algom Corporation
Atlas Minerals
Dawn Mining Company
Pathfinder Mines
Union Carbide
Rocky Mountain Energy
Exxon Minerals
Minerals Exploration Co.
Pathfinder Mines
Petrotomics
SHUT-DOWN MILLS
New Mexico
Blnewater
Seboyeta
Church Rock
Marque 2
Dakota
Edgemont
Texas
FaTu City
Ray Point
Anaconda Minerals Company
Sohio-Reserve
United Nuclear
Bokum Resources
Tennessee Valley Authority
Conoco-Pioneer Nuclear
Exxon (Susquehanna-Western)
(cont inued)
Sei? footnote at end of table.
2-9
-------
Table 2-2. Currently Licensed U.S. Uranium Mills(a)
(Continued)
Location Owner
SHUT-DOWN MILLS (Continued)
Utah
Hanksville Plateau Resources
Washington
Wellpinit Western Nuclear
Wyoming
Jeffrey City Western Nuclear, Inc.
Gas Hills Federal-American Partners
s of September 1982.
outstrip defense needs during the next 2Q years. Thus, only demand for
the nuclear power industry is projected in this analysis.
Projections of uranium demand are made for two cases. A "high"
case is based on the raid-range nuclear generating capacity scenario of
the U.S. Department of Energy (DOE) (DOE81). A "low" case is based on
the DOE installed reactor capacity projection identified as the firm
nuclear base scenario (DOE81). These estimates are presented in Table
2-3.
Yellowcake requirements are calculated by using the NRG
assumptions given in their generic KIS for uranium milling (NRCSOa). A
conversion factor of 185 MT U30g in yellowcake per GWe-year is
used. This assumes a 3 percent fuel enrichment, 0.20 percent tails
assay, and an effective average nuclear generating plant capacity
factor of 75 percent.
Conventional mills (as described in Section 2.2) are not assumed
to satisfy the total demand for uranium. About 80 percent of the
present uranium demand is supplied by conventional milling. This
fraction is expected to vary during the next 20 years. The fraction of
uranium assumed to be supplied by conventional mill ing is listed in
Table 2-3 (NRCSOa). The demand for conventional milling production,
estimated by multiplying the total uranium demand by this fraction, is
presented in Table 2-3 for the 20-year period 1980 to 2000.
Another important factor in projecting demand for uranium is the
inventory held by utilities, reactor manufacturers, and fuel
fabricators. A normal inventory level is about a 1-year level of
consumption. Currently an abnormally large inventory of uranium is
2-10
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Table 2-3. Projected Demands for Uranium Yellowcake
Year
Generating Capacity
(GWe)
(High) (Low)
(a)
Yellowcake
Demand
(1000 MT/y)
(High) (Low)
Fract ion
(High & Low)
Convent ional
Mill Demand
(1000 MT/y)
(High) (Low)
1980
1985
1990
1995
2000
54
96
128
145
175
54
96
122
125
120
14.2
20
25.5
30.1
36.2
14.2
20.6
22.9
22.6
18.9
.884
.790
.714
.747
.784
12.5
16.6
18.1
22.5
28.4
12.5
16.3
16.3
16.9
14.8
^a'High—DOE mid-range nuclear capacity scenario. Low—DOE firm nuclear base
scenario. (DOESOc)
Table 2-4. Projections of Demand, Production, and Inventory
of Uranium Yellowcake
(1000 MT/y of U308)
Year
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
Conventional
Demand
High Low
12.5
13.6
14.9
15.3
16.0
16.6
17.3
18.0
17.9
17.9
18.2
18.7
19.2
20.3
21.4
22.5
23.5
24.6
25.8
27.0
28.4
12.5
13.6
14.9
15.2
15.8
16.3
16.8
17.1
16.7
16.4
16.3
16.5
16.6
16.7
16.8
16.9
16.8
16.9
16.1
15.4
14.8
Production
High Low
13.8
9.9
9.4
9.6
10.6
11.4
12.9
14.2
15.8
17.5
19.2
20.7
22.2
22.3
23.5
24.1
26.0
27.3
28.6
29.8
31.0
13.8
9.9
9.4
9.6
10.6
11.4
12.7
13.6
14.6
15.6
16.5
17.2
17.7
17.2
17.6
17.6
17.9
17.8
17.2
16.4
15.7
Ending Inventory
High Low
48.9
45.1
39.6
33.9
28.5
23.3
18.9
15.1
13.0
12.6
13.6
15.6
18.0
20.6
22.7
24.3
26.8
29.5
32.3
35.1
38.4
48.9
45.1
39.6
34.0
28.8
23.9
19.8
16.3
14.2
13.4
13.6
14.3
15.4
15.9
16.7
17.6
18.7
19.6
20.7
21.7
22.6
2-11
-------
being held. It is assumed that this inventory will be reduced to more
normal levels over a 6-year period. This inventory reduction will
result in less uranium production. These projections are shown in
Table 2-4 for both high and low cases. The demands are from Table 2-3
and the production and inventory values are calculated using the 6-year
inventory reduction assumption.
The total quantities of tailings produced by conventional milling
from L980 to 2000 is projected to be about 430 million tons for the
high case and about 330 million tons for the low case. [The conversion
factor used is 1,075 MT of tailing per MT of l^Og as yellowcake
(NRCSOa) and assumes 0.1 percent uranium in ore, a 93 percent recovery
rate during milling, and an average 85 percent mill capacity factor.]
2-12
-------
REFERENCES
DOE81 Department of Energy, "1980 Annual Report to Congress, Volume
3: Forecasts," DOE/EIS-0173(80)/3, March 1981.
DOE82 Department of Energy, "Statistical Data of the Uranium
Industry," GJ-100(82), Grand Junction Area Office, Colo.
EPA75 Environmental Protection Agency, 1975, "Water Quality Impacts
of Uranium Mining and Milling Activities in the Grants Mineral
Belt, New Mexico," EPA Region VI, Dallas, Texas, EPA
906/9-75-002.
EPA80 Environmental Protection Agency, Office of Radiation Programs,
1980, "Draft Environmental Impact Statement for Remedial
Action Standards for Inactive Uranium Processing Sites,
40 CFR 192," EPA 520/4-80-011, EPA, Washington, D.C..
Ja79 Jackson B. , Coleman W., Murray C., and Scinto L., 1979,
"Environmental Study on Uranium Mills," TRW Inc. contract
with the U.S. Environmental Protection Agency, Contract
No. 68-03-2560.
Ka75 Kaufmann, R.E., G.G. Eadie, C.R. Russell, 1975, "Summary of
Groundwater Quality Impacts of Uranium Mining and Milling in
the Grants Mineral Belt, New Mexico," Technical Note
ORP/LV-75-4, U.S. Environmental Protection Agency, Office of
Radiation Programs, Las Vegas Facility, Las Vegas, Nevada.
NRC77 Nuclear Regulatory Commission, 1977, "Design, Construction and
Inspection of Embankment Retention Systems for Uranium Mills,"
Regulatory Guide 3.11, NRC, Washington, D.C.
NRC78a Nuclear Regulatory Commission, 1978, "Final Environmental
Statement Related to the Operation of the Highland Uranium
Solution Mining Project, Exxon Minerals Company, U.S.A.,"
NUREG-0489, NRC, Washington, D.C.
NRC78b Nuclear Regulatory Commission, 1978, "Final Environmental
Statement Related to the Sweetwater Uranium Project, Minerals
Exploration Company," NUREG-0505, NRC, Washington, D.C.
NRCSOa Nuclear Regulatory Commission, 1980, "Final Generic
Environmental Impact Statement on Uranium Milling,"
NUREG-0706, Vol. 1, 2, 3, NRC, Washington, D.C.
NRC80b Nuclear Regulatory Commission, 1980, "Radiological Effluent
and Environmental Monitoring at Uranium Mills," Regulatory
Guide 4.14, NRC, Washington, D.C.
2-13
-------
REFERENCES (Continued)
Se75 Sears, M.B. , Blanco R.E. , Dahltnan R.C., Hill G.S., Rejon A..D. ,
and Witherspoon J.P., 1975, "Correlation of Radioactive Waste
Treatment Costs and the Environmental Impact of Waste Effluents
in the Nuclear Fuel Cycle for Use in Establishing "As Low as
Practicable" Guides-Milling of Uranium," ORNL-TM-4903 Vol. 1,
Oak Ridge National Laboratory, Oak Ridge, Tennessee.
2-14
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Chapter 3: ENVIRONMENTAL RELEASES FROM URANIUM MILLING WASTES
In this chapter, we discuss the composition of uranium mill
tailings solids (sands and slimes), tailings pond liquids, and heap-
leaching wastes. We also discuss the extent to which radioactive
elements, toxic substances, and other contaminants from these wastes
have been released to the environment through human activity and/or by
natural causes. We defer to Chapter 4 the development of projections
of releases from a model site.
3.1 Composition of Tailings Solids and Pond Liquids
Uranium mill tailings solids and pond liquids contain essentially
all the radioactive and toxic elements of the original uranium ore,
except for about 90 percent of the uranium which is extracted during
the milling process. The tailings also contain a variety of chemicals
used as part of the. extraction process described in the previous
chapter.
3.1.1 Radioactivity in Tailings
Most of the uranium recovered from ore is uranium-238, a
radioactive isotope that decays, over billions of years, to become
lead-206, a stable (i.e., nonradioactive) element. The lengthy decay
process includes a number of intermediate stages (called decay
products). These, too, are radioactive. Figure 3-1 traces the steps
in this decay process. Since the ore was formed millions of years ago,
uranium has continued to decay and an inventory of all of these decay
products has built up. There are also radioactive materials from two
other decay processes in uranium ore, the uranium-235 series and the
thorium-232 series, but these are present in much smaller amounts, and
we have concluded that it is not necessary to include them in our
analysis (see Section 4.1).
When ore is processed most of the uranium is removed, and most of
the subsequent decay products become part of the tailings. As a
result, thorium-230 is the radionuclide with the longest half-life'^'
^ 'A half-life is the time it takes for a given quantity of a
radioactive isotope to decay to half of that quantity. Figure 3-1
shows the half-lives of the members of the uranium-238 decay series.
3-1
-------
Uranium-238
4.5 billion
years
alpha
1
f
Thorium-234
24 days
Protactinium
234
1.2 minutes
x
/
/ beta,
gamma
Uranium-234
240,000
years
X
, beta.
gamma alpha,
gamma
Thorium-230
77,000
years
i alpha,
gamma
Radium-226
1,600 years
alpha,
gamma
Radon-222
3.8 days
i alpha,
gamma
Polonium-218
3.1 minutes
alpha
I
f
Lead-214
27 minutes
(ELEMENT)
(HALF-LIFE)
(PARTICLE OR
RAY EMITTED
I
t
Polonium-214 Polonium-210
.00016 seconds 140 days
j 4/
/beta, beta
Bismuth-214 gamma Bismuth-210 d'
20 minutes alpha, 5.0 days gamma
gamma 1
1 1
s \ s \
' /
beta, /beta
/gamma Lead-210 / gamma Lead-206
22 years stable
Figure 3-1. The UranLum-238 Decay Series.
3-2
-------
of significance in tailings. Thorium decays to produce radium-226.
Radium decays in turn to produce radon-222, a radioactive gas. Because
radon gas is chemically inert, some of it escapes from the tailings
particles in which it is produced, diffuses to the pile surface, and is
carried away into the atmosphere. Airborne radon produces a series of
short half-life decay products that are hazardous if inhaled. If the
radon does not escape from the tailings, its decay products remain
there, and the gamma radiation they produce may increase the hazard to
people near tailings.
Since thorium-230 has a much longer half-life than its two
immediate decay products, radium and radon, the amounts of
radioactivity from radium and radon remain the same as that from
thorium. The amount of radon released from a tailings pile, therefore,
remains effectively constant on a year-to-year basis for many thousands
of years, decreasing only as the thorium, with its 77,000-year
half-life, decreases.
In Figure 3-2 we show how the yearly production rate of radon in a
tailings pile will decrease with time. It falls to 10 percent of its
initial value in about 265,000 years. This time scale illustrates the
long-term nature of most of the significant radiological hazards
associated with uranium mill tailings.
CO 0)
•H 4-1
J-J Cfl
•H erf
c
M C
o
M-l -H
O 4-1
O
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O M
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When discharged from the mill, tailings have both solid and liquid
components. The solid portion of tailings is composed of particles
ranging in size from coarse sands to fine slimes. In both the acid
process and the alkaline process, the residual uranium and radium
content of slimes is about twice that of sands. In the acid-leach
process, about 95 percent of the thorium in the original ore remains
with the solid tailings, while the balance is dissolved in the tailings
liquids. Less than one percent of the radium is dissolved in the
liquids. In the alkaline process, less than one percent of both the
thorium and radium is dissolved in the tailings liquids.
In Table 3-1 we show, for licensed uranium mills (as of January
1980) with tailings piles, the quantity of tailings, area of the pile,
average ore grade, and estimated average radium content in the solids.
Also included are the estimated radon emissions from each pile and
other factors relevant to emissions from tailings piles. Tailings at
most future uranium mills are expected to fall within the range of
values shown in Table 3-1. The ore grade at the different mills
typically varies from 0.15 percent to 0.3 percent uranium, and the
radium concentration (and presumably other radionuclides in the
uranium-238 decay series) varies from 200 pCi/g to 900 pCi/g. This
should be compared with the background radium concentration in average
soil from 0.2 pCi/g to 3 pCi/g.
In Table 3-2 we have compiled selected available data on
radioactivity and toxic element levels in tailings pond liquids. Many
levels are more than two orders cf magnitude above EPA drinking water
standards (these are listed in Table 3-4), but large variations occur
among the mills. The wide variation is caused by the characteristics
of uranium ore and the process (i.e., acid- versus alkaline-leach).
Again, the values in Table 3-2 are expected to characterize liquid
wastes at future uranium mills.
3.1.2 Toxic Elements and Other Chemicals in Tailings
A number of toxic materials from ore or from chemicals used in
processing have been found in both liquid and solid uranium mill wastes
(Se75, FB76-78). The contaminants present depend on the ore source and
the type of processing. In Table 3-3, we indicate the average concen-
tration of 15 elements commonly found in the solids of 19 inactive
tailings piles (MaSla). The concentrations of these elements show wide
variations among the piles, as well as wide variations above and below
values for "typical soil." This data is believed to be representative
of tailings at active mills as well as tailings to be generated at
future mills. In Table 3-2, we showed the concentration of toxic
substances and other chemicals in tailings pond liquids at existing
uranium mills.
3.2 Routine Environmental Releases from Tailings
Releases from tailings wastes may occur to land, groundwater,
surface water, and air. Land is contaminated chiefly by tailings
3-4
-------
transported by wind and water erosion; groundwater by the leaching of
radionucLides, toxic elements, and other chemicals in solid tailings,
or from seepage of tailings pond liquids; surface water from inputs
from contaminated groundwater and also from runoff over contaminated
areas; air from emissions of radon and fine wind-suspended tailings
particles.
3.2.1 Air _Cqnt arni^na t_io_n
Radon Emissions
In the uraniutn-238 decay series, radon is unique because it is a
chemically inert gas and therefore freely migrates by diffusion from
the tailings into ambient air. In Table 3-1 we show calculated radon
emission rates^l^ from the 27 active sites. These calculated rates
range from 200 pCi/m^s to 900 pCi/m^s. Radon emission rates from
uncontaminated soils are much lower, averaging close to 1 pCi/m2.s,
with a range of perhaps as much as a factor of 2 or 3 higher and
lower. To estimate the annual radon release rates reported in
Table 3-1, we assumed that the radon emission rate per unit area is
1.0 pCi/m^s per pCi/g radium; this value was also used by NRC (NRC80,
Appendix G). It is consistent with the assumption that the piles are
dry, homogeneous, uncovered, and at least 3 meters deep. By way of
comparison, Haywood (Ha77) has calculated values of 0.35, 0.65, and 1.2
pCi/m^s radon per pCi/g radium for wet, moist, and dry tailings,
respectively.
The radon release rates listed in Table 3-1 are likely to be
greater than the actual release rates for active piles because these
piles still contain significant quantities of entrapped water. Many
active piles also contain large areas of standing water on their
surface. Both conditions significantly inhibit the release of radon to
air. In assessing the health impact from active tailings piles, we
have considered the effect of the pond area in reducing radon
emissions. However, with regard to assessing the impact of tailings
piles when the mill is not active, we consider it more reasonable to
assume that, over the time period of interest for the hazards
associated with radon release (hundreds of thousands of years), the
piles would be dry most of the time.
There have been few systematic ambient air measurements of radon
emissions from tailings piles. However, studies to date (Mo82, PHS69)
demonstrate good agreement between field measurements and the
^ 'The term emission rate is used rather than fluence rate or flux
density, which, although more precise, are terms generally less familiar.
3-5
-------
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prediction of mathematical models. The data in these studies support
the following conclusions:
• Radon levels immediately above tailings
piles typically are above 10 pCi/1.
• At 0.5 km from some piles, radon
concentration may exceed the average
background by 1 pCi/1.
• Significant increases above background have
been measured at distances up to 1.5 km
downwind of tailings piles.
Emission of Tailings _Part_icles
Tailings piles also release fine tailings particles to the air in
moderate-to-high winds. Schwendiman, et al., have studied particle
release rates from an active pile (Sc80). Their data show that for
wind speeds from 7 mph to 25 mph, the airborne mass loading downwind
from the pile is roughly 5 x 10~^ g/m^. This is an order of
magnitude greater than the mass loading measured just upwind of the
site.
The airborne concentrations of several radioactive and toxic
elements were also measured, confirming that the windblown particles
from a tailings pile contain a variety of radionuclides, as well as the
toxic elements selenium, lead, arsenic, mercury, and molybdenum.
However, the air concentrations of toxic elements observed were well
below the 8-hour threshold limit values to which workers can be
repeatedly exposed without suffering adverse effects. (These values
for occupationally exposed workers were established by the American
Conference of Governmental Industrial Hygienists (AC81).) We conclude,
therefore, that the primary hazard arises from breathing radLonucLides,
and their buildup on land surfaces.
3.2.2 Land Contamination
The action of wind and water can erode tailings from unstabilized
piles onto nearby land. To determine the extent of this contamination
at inactive sites, we conducted gamma radiation surveys at most of the
inactive tailings sites in the spring of 1974 (Do75). We used the
measured gamma radiation levels to estimate the extent of radium
contamination in the surface soil (EPA80). If levels above 5 pCi/g,
averaged over the top 15 centimeters, are considered to represent
significant contamination, then, typically, windblown tailings have
contaminated an area near each pile that is more than three times the
area of the pile itself. It is reasonable to assume that, if
uncontrolled, contamination at existing uranium mills will be
comparable to that at inactive sites within a decade or so after the
existing mills become inactive. Little data is available concerning
contamination of land with windblown toxic materials. However, because
3-9
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whole tailings particles are transported, it is likely that the ratio
of toxic materials to radioactive materials in contaminated land is in
generally the same proportion as the ratio of these materials in the
tailings. Surface runoff may also deposit tailings particles and,
therefore, toxic materials in the vicinity of the pile. In these cases
also, the amount of radioactivity should usually be a reasonably good
indicator of the presence of elevated levels of toxic elements because
like radioactive elements, they are, for the most part, relatively well
fixed in tailings particles.
3.2.3 Water Contamination
Tailings can contaminate both surface and groundwater; we discuss
what is known about each at both active and inactive tailings piles.
As we shall see, the potential for water contamination at inactive
piles is far less than the corresponding potential contamination at
active sites.
Groundwater
Most of the potential for groundwater contamination arises from
seepage of liquid waste from the tailings pile when the mill is
active. Kaufmann, et al. (Ka75), estimated that 30 percent of the
process water from two active tailings ponds in New Mexico had seeped
into the ground. Purtyman, et al. (Pu77), estimated a 44-percent
seepage loss from another pile in New Mexico during its active life.
The NRC (NRC80) assumes that a model site will experience a 40-percent
water loss by seepage and uses a mathematical model to estimate the
movement of the seepage through unsaturated soil, formation of a seepage
"bulb" in the saturated soil zone, and the movement of pollutants with
groundwater. For its model mill in an arid region, where the evapora-
tion rate far exceeds the precipitation rate, the NRC concluded that
about 95 percent of the possible contamination of groundwater would be
associated with the active phase of the pile and only 5 percent with
with long-term loses from an inactive nonstabilized pile (NRC80). A
more detailed description of groundwater contamination can be found in
Appendix D.
Case histories showing water contamination problems near selected
active uranium mills and mines are given in a recent report (UI80).
Contamination that extends up to 8,000 feet from active tailings piles
has been found, but this has been confined to shallow alluvial aquifers
(UI80). Contamination of deep aquifers near these mills has not been
observed. In Table 3-4 we have summarized the data from groundwater
monitoring around these active tailings ponds. In general, the data
support the following conclusions regarding the shallow aquifers:
• Unless pond water is contained by a natural clay or
synthetic liner, contamination of groundwater near
the pile may be expected. More than perhaps one-
third of all active tailings piles show at least
limited contamination of a shallow aquifer.
3-11
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• Contamination is accompanied by highly elevated
levels of total dissolved solids, with sulfate
being the chief constituent. Such water is
rendered essentially useless for all puposes.
Because of the lack of background data on the aquifers and sites
in question, no other general conclusions can be made. It is often
difficult to prove that tailings are the cause of an elevated
concentration of a substance in groundwater unless the background
concentration of the aquifer is well characterized and there are no
nearby potential sources of additional contamination. This situation
is seldom realized. However, at one mill, heavy molybdenum contamina-
tion has been confirmed. Other sites show strong evidence of
contamination from selenium and uranium (UI80).
There is evidence that groundwater in shallow aquifers is
contaminated near some inactive sites, probably due to seepage of
liquids from tailings ponds during and soon after their active use
(Dr78). Groundwater contaminant concentrations near the inactive mills
have been surveyed (FB76-78). Although it is not possible to positively
ascribe the source of this contamination to tailings, some cases of
elevated concentrations were found.
In Table 3-5, we summarize the toxic elements found in elevated
concentrations in groundwater near inactive tailings piles. Markos has
shown that many of the soluble elements in piles tend to precipitate
and form a barrier when liquids move downward in the pile to the soil
at the tailings-soil interface (Ma79a, MaSlb, MaSlc). This would
prevent contamination of groundwater from tailings piles during the
inactive phase. However, it is not known how long this barrier will
last, and there could be channels through the barrier at locations
other than those sampled. DOE is currently sponsoring additional
studies of these potential routes of groundwater contamination.
Surf ace _Wat_e_r
Standing water with elevated concent rations of toxic materials has
been reported on and adjacent to some tailings sites (MaSlc, FB76-
78). Usually, these concentrations are intermediate between those
reported for waters within piles and normal levels in surface water.
Surface water runoff from rains and floods can wash surface salt
deposits and tailings from an unprotected pile, causing spread of toxic
and radioactive elements to nearby land and streams. A more likely
route for the contamination of surface water is seepage of contaminated
groundwater into a nearby stream or reservior. Some degradation of
water quality in nearby streams has been reported at active sites.
However, studies of the inactive tailings piles do not show that nearby
streams are being contaminated (FB76-78).
3-13
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Table 3-5. Elements Found in Elevated Concentrations in Groundwater
Near Inactive Tailings Sites
Tailings Site
(a)
Elements
(b)
Gunnison, Colorado
Ambrosia Lake, New Mexico
Falls City, Texas
Green River, Utah
Ray Point, Texas
Arsenic, Barium, Chromium, Iron,
Lead, Selenium, Vanadium
Barium, Lead, Vanadium
Arsenic, Barium, Chromium, Iron,
Lead, Selenium, Radium, Vanadium
Arsenic, Chromium, Lead, Selenium
Arsenic
(a)(FB76-78).
^•k'At most sites there are other potential sources of this toxic material
contamination; see orginal reports for details.
3.3 Nonroutine Releases
3.3.1 Accidents and Acts of God
The most credible accident that could lead to a widespread release
of tailings solids and pond water is a dam failure at a tailings pond.
This actually occurred at the United Nuclear mill in Church Rock,
New Mexico on July 16, 1979, and 100 million gallons of tailings-pond
water and 1000 tons of solid tailings were released into the Rio
Puerco, a large ephemeral stream. Following the spill, abnormally high
concentrations of radionuclides and toxic elements were recorded as far
as 36 miles downstream. However, after several weeks, water quality of
the Rio Puerco susbstantially improved to within background levels of
contaminants. In addition to surface-water contamination, some
groundwater contamination in shallow wells adjacent to the Rio Puerco
was also detected. Contaminated sediment was found in the Rio Puerco
for several miles downstream of the spill.
The spill prompted a commitment of resources from several Federal
and State agencies to study the failure and to monitor the
contamination. At the urging of the State of New Mexico and the Navajo
Nation, United Nuclear conducted a cleanup of contaminated areas and
supplied the Navajos with replacement water. The ultimate cost of the
entire incident will probably be several million dollars.
3-14
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Although the Church Rock tailings-dam failure occurred
spontaneously, natural events could also precipitate such a failure:
most notably severe flooding or an earthquake. In Chapter 8, the
probabilities of such events are discussed, along with engineering and
site selection options for minimizing these probabilities. Also
discussed in Chapter 8 are the impacts of events such as tornadoes and
glaciation on the effectivness of contaminant controls.
3.3.2 Misuse__of Tailings Sands
In the recent past, uranium mill tailings have been used
extensively as a building material, chiefly as fill around and under
foundations and concrete slabs. The tailings sands have ideal physical
characteristics for this purpose. However, such use typically results
in building occupants being exposed to high levels of radon decay
products and thereby incurring a significant lifetime risk of lung
cancer. In Grand Junction, Colorado, over 700 buildings have been
identified as contaminated and requiring remedial action. In other
mill towns, it is estimated that more than 350 buildings are
contaminated. In addition to buildings, many thousands of other
locations have been identified (e.g., sidewalks, lawns, gardens,
driveways) in mill towns where tailings have been used. These
buildings and locations were contaminated by tailings from inactive
mills. We have not assessed the extent of existing misuse near active
mills.
3.4 Environmental Releases from Heap-Leaching_ Operations
The principal solid waste from heap leaching is the barren material
remaining after uranium recovery. Airborne emissions from
heap-leaching operations include particulates suspended by wind erosion
of the pile and radon gas. The particulates will contain toxic
elements and radionuclides in proportion to the ore concentrations.
The amount of radon and particulates given off will be proportional to
the size of the operation. These have been calculated for the
heap-leaching cell covering about 0.5 acre in area described in Chapter 2,
Particulate emissions from the dry portion of a heap-leaching cell
are estimated to be about 1 MT annually. The radon emanation rate from
this operation is calculated to be 25 Ci/y (NRC78). This is less than
one-half as much as a tailings pile per unit acre.
Releases of contaminants to groundwater could result from the
seepage of leachate containing elevated concentrations of radionuclides
and toxic elements. This, however, would not normally pose a problem
during operations since an efficient heap-leaching operation requires
an impermeable pad and all leachate is collected for processing. After
termination of operations, normal rainfall could lead to some leaching
from the piles, but we expect this to be no greater threat than
leaching from an unstabilized conventional tailings pile.
3-15
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REFERENCES
AC81
Bo66
Do75
Dr78
EPA80
FB76-78
FB78
Ha77
Ka75
Ma79a
American Conference of Governmental Industrial Hygienists,
"Threshold Limit Values for Chemical Substances in Workroom
Air Adopted by ACGIH for 1981," ACGH, 6500 Glenway Ave., Bldg
D-5, Cincinnati, Ohio
Bowen H.J.M., "Trace Elements in Biochemistry," Academic
Press, New York, 1966.
Douglas R.L. and Hans J.M. Jr., "Gamma Radiation Surveys at
Inactive Uranium Mill Sites, Technical Note ORP/LV-75-5,
Office of Radiation Programs, USEPA, Las Vegas, Nevada, August
1975.
Dreesen D.R., Maple M.L. and Kelley N.E., "Contaminant
Transport, Revegetation, and Trace Element Studies at Inactive
Uranium Mill Tailings Studies at Inactive Uranium Mill
Tailings Piles," in: Proceedings of the Symposium on Uranium
Mill Tailings Management," Colorado State University, Fort
Collins, Colorado, 1978.
Environmental Protection Agency, Office of Radiation Programs,
1980, "Draft Environmental Impact Statement for Remedial
Action Standards for Inactive Uranium Processing Sites, 40 CFR
192," EPA 520/4-80-011, EPA, Washington, D.C.
Ford, Bacon & Davis, Utah, Inc., "Phase II-Title I,
Engineering Assessment of Inactive Uranium Mill Tailings," 20
contract reports for Department of Energy Contract No.
E(05-l)-1658, 1976-78.
Ford, Bacon & Davis, Utah, Inc, "Engineering Assessment of
Inactive Uranium Mill Tailings, Edgemont Site," prepared for
U.S. Nuclear Regulatory Commission,
1978.
Washington, D.C., 20555,
Haywood F.F., Goldsmith W.A., Perdue P.T., Fox W.F., and
Shinpaugh W.H., "Assessment of Radiological Impact of the
Inactive Uranium Mill Tailings Pile at Salt Lake City, Utah,"
ORNL-TM-5251, Oak Ridge National Laboratory, Tennessee, 1977.
Kaufmann R.F., Eadie G.G., and Russell C.R., "Summary of
Ground Waste Quality Impacts of Uranium Mining and Milling in
the Grants Mineral Belt, New Mexico," Technical Note
ORP/LV-75-4, Office of Radiation Programs, USEPA, Las Vegas,
Nevada, 1975.
Markos G., "Geochemical Mobility and Transfer of Contaminants
in Uranium Mill Tailings," in: Proceedings of the Second
Symposium on Uranium Mill Tailings Management, Colorado State
University, November 1979.
3-16
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REFERENCES (Continued)
MaSlb Markos G. and Bush K.J., "Physico-Chemical Processes in Uranium
Mill Tailings and their Relationship to Contamination,"
Presented at the Nuclear Energy Agency Workshop, Fort Collins,
Colorado, October 1981.
Ma81c Markos G., Bush K.J. and Freeman T., "Geochemical Investigation
of UMTRAP Designated Site at Canonsburg," Number ET-44206, U.S.
Department of Energy, Washington, D.C.
Mo82 Momeni M.H. and Zielen A.J., "Comparison of Theoretical
Predictions and Measured Radon and Radon Daughter
Cencentrations: Toward Validation of the UDAD Code," from
Third Joint Conference on Applications of Air Pollution
Meteorology, American Meteorogical Society, Boston, Mass.
NM80 New Mexico Health and Environment Department, "Water Quality
Data for Discharges from Uranium Mines and Mills in New
Mexico," July 1980.
NRC77 Nuclear Regulatory Commission, "Final Environmental Impact
Statement related to the Operation of the Lucky Me Gas Hills
Uranium Mill," NUREG-0557, Washington, D.C., November 1977.
NRC78 Nuclear Regulatory Commission, "Final Environmental Impact
Statement related to the Operation of Sweetwater Uranium
Project," NUREG-0505, Washington, D.C. 20555.
NRC79 Nuclear Regulatory Commission, "Final Environmental Impact
Statement related to the Operation of Moab Uranium Mill,"
G-0453, Washington, D.C. January 1979.
NRC80 Nuclear Regulatory Comtnision, "Final Generic Environmental
Impact Statement on Uranium Milling, Volume II," NUREG-0511,
USNRC, Washington, D.C. 1979.
PHS69 Public Health Service, "Evaluation of Radon-222 Near Uranium
Tailings Piles," DER 69-1, Department of Health, Education, &
Welfare, Washington, D.C., 1969.
Pu77 Purtyman W.D., Wienke C.L., and Dreesen D.R., "Geology and
Hydrology in the Vicinity of the Inactive Uranium Mill Tailings
Pile, Ambrosia Lake, New Mexico," LA-6839-MS, Los Alamos
Scientific Laboratory, New Mexico, 1977.
Sc80 Schwendiman L.C., Sehmel G.A., Horst T.W, Thomas C.W. and
Perkins R.W. "A Field Modeling Study of Windblown Particles
from a Uranium Mill Tailings Pile," NUREG/CR-14007, Battelle -
Pacific Northwest Laboratory, Richland, Washington, June 1980.
3-17
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REFERENCES (Continued)
Se75 Sears M.B., et al., "Correlation of Radioactive Waste
Treatments Costs and the Environmental Impact of Waste Effuents
in the Nuclear Fuel Cycle for Use in Establishing 'As Low as
Practicable' Guides—Milling of Uranium Ores," Report
ORNL-TM-4903, Two Volumes, Oak Ridge National Laboratory,
Tennessee, 1975.
UI80 University of Idaho, "Overview of Ground Water Contamination
Associated with Operating Uranium Mills in the United States,"
College of Mines and Mineral Resources, University of Idaho,
1980.
3-18
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Chapter 4: MODEL SITE AND TAILINGS PILE
This chapter summarizes the specific characteristics of the model
site and tailings pile used for the analyses presented in Chapters 5
and 6.
4.1 Model Site
The "model mill" chosen for this analysis is the one developed for
the NRC's Final Generic Environmental Impact Statement on Uranium
Milling (NRC80). The model mill is based on features of uranium mills
in operation in the 1970's. The characteristics, operating procedures,
and effluents of the model mill were derived from data for existing
mills as described in the technical literature and in environmental
reports (MP80). Since the Act relates only to the tailings resulting
from operation of the mill, the "model site" used for the analysis in
Chapters 5 and 6 is defined as the area within a radius of 80
kilometers from the center of the model mill tailings pile.
4.1.1 Meteorology
The meteorology of the model site is typical of semiarid regions
of the western United States. The average annual precipitation of the
model site is 31 cm (12 inches). Potential evaporation exceeds
precipitation, averaging 150 cm (60 inches) per year. Joint frequency
of the annual average wind speed, direction, and atmospheric stability
for the model site are presented in Table 4-1.
4.1.2 Demography
Two population distributions were used for the model site to
represent a range of potential impacts from the model tailings pile:
(1) the population distribution from the NRC model site (NRC80), and
(2) the population distribution near the tailings pile in Edgemont,
South Dakota (NRC81). The NRC model site represents a location where
only a few people live close to the tailings pile (referred to here as
a "remote" site). The Edgemont site represents a location with a
larger population living near the tailings pile (referred to here as a
"rural" site). Tables 4-2 and 4-3 present these population distribu-
tions as a function of distance and direction from the model tailings
pile.
4-1
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4.1.3 Hydrology
The surface waters near the model pile are short-lived streams and
small ranch impoundments used for livestock watering. These ephemeral
streams have their maximum flows in June and July and are dry from
September to February. Rivers and reservoirs are several miles away
from the model pile. In some cases, the nearby surface water is good
(of drinking water quality), but nearby surface water will contain
relatively high concentrations of dissolved solids, making it
unsuitable for many purposes. The groundwater resources near the model
uranium mill tailings pile are an unconfined surface aquifer (often
alluvial) plus deep aquifers separated from the surface by an
impermeable layer. For calculating the movement of contamination from
the model pile, the NRC assumed the water table (the top of the surface
aquifer) is 25 meters below ground level. The deep aquifers often lie
below 300 meters. The surface aquifer is the most commonly used,
chiefly for domestic and stock water.
The deep aquifers are used for large industrial applications.
Uranium mills, for example, often obtain mill process water from deep
aquifers. Water quality of both the surface and deep aquifers is
variable.
4.1.4 Agricultural Productivity
Uniform agricultural productivity rates for vegetables, meat, and
milk in units of kg/y-km^ were applied over the entire area of the
model site except the controlled areas occupied by the mill and
tailings pile. The production rates used are:
Product kg/y-km^
Vegetables 1020
Meat 1180
Milk 1140
These production rates are averages of production rates in States where
uranium milling takes place (NRC80), weighted by the expected uranium
development activity in each state.
4.2 The Model Tailings Pile
' The tailings are assummed to be generated by an acid-leach mill.
We. generally assume the same characteristics as chosen by the NRC for
their generic assessment of the uranium milling industry (NRC80).
4.2.1 Physical Description
The model tailings pile is typical of uranium mills in operation
in the 1970's. The model mill generates 1800 MT of solid tailings
slurried in water to about 50 percent solids by weight. When
discharged from the mill, the slurried tailings material is pumped
4-6
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through pipes to the tailings pond impoundment. The pond is initially
a square basin formed by building low earthen embankments. The initial
embankment is assumed to be 3 meters high, 3 meters broad at the top,
and 15 meters wide at the base. Each side of the square is assumed to
be 947 meters long at the center line of the embankment. The final
embankments are assumed to be 10 meters high, 13 meters wide at the
top, and 53 meters at the base; the initial centerline dimensions are
unchanged. The total tailings disposal area is about 100 hectares (250
acres) of which 80 hectares contain tailings. It is assumed that,
during operations, one-fourth of the tailings area is covered by water,
and another one-eighth is wet.
After milling operations cease, it is assumed a few years pass
before the tailings have dried and settled sufficiently to accommodate
heavy equipment. The ultimate height of the tailings pile i.s assumed
to be about 8 meters. In this post-operational phase, the emissions
from tailings and the controls are different from those during the
operational phase.
The principal physical characteristics of the model tailings pile
are summarized in Table 4-4.
Table 4-4. Summary of Principal Physical Characteristics
of the Model Tailings Pile
Par amee r
Operational life of tailings pile 15 years
Operating days per year 310
Dry solid waste generated (tailings) 1800 MT/day
Tailings density (slurry) 1.6 g/cm^
Gross water flow to tailings pond 1800 MT/day
Tailings pond water recycled 30%
Net water consumption for tailings slurry 1260 MT/day
Area of tailings impoundment 100 ha
Area of tailings 80 ha
Ponded area on tailings (operational) 20 ha
Ponded area on tailings (post-operational) 0 ha
Wet beaches 10 ha
Average depth of tailings (post-operational) 8 m
4-7
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4.2.2 Coiitaminants Present
The ore grade processed by the model mill from 1982 to 2000 is
assumed to average 0.1 percent. The uranium recovery efficiency is
assumed to be 93 percent. These values result in the tailings
radioactivity listed in Table 4-5. Also listed are the assumed
concentrations of toxic substances and other chemicals in the tailings
pond liquids of the model pile (NRC80). The values in Table 4-5 are
representative of tailings piles generated by acid leach mills. For an
alkaline-leach mill, the most significant difference is that the
concentration of thorium-230 in tailings liquids would be more than an
order of magnitude lower.
4.-2.3 Radioactive Emiss_ions to _Air
Radionuc lides are released into air from tailings piles in the
form of small dust particles and radon gas. Table 4-6 lists the
assumed annual release rates of radionuc lides from the model tailings
pile. Particulate emissions are listed in two particle size
distributions with characteristic diameters of 5 and 35 microns,
respectively, and a density of 2.4 g/cm^. The Activity Median
Aerodynamic Diameters (AMADs) for these particle size distributions are
7.75 and 54.2 Mm, respectively. A detailed description of the methods
used for estimating these release rates is given in Appendix G-l of the
Generic Environmental Impact Statement on Uranium Milling (NRC80).
4.2.4 Emissions of Contaminants to Water
For the model pile, it is assumed that there are no routine
releases to surface water. This is achieved through proper siting of
the pile along with the minimal engineered controls required to
substantially eliminate surface water runoff from the tailings pile.
The assumed routine emissions to groundwater are more substantial.
NRC calculates a seepage rate of 0.22 million MT of water per year
during the operational phase, and 5 percent of this value during the
post-operational phase. We have made no estimates of the specific
contaminants released with this water because they will vary with the
ore used, the milling process, the geochemistry of the soil, and other
factors.
-------
Table 4-5. Chemical and Radiological Properties of
Tailings Wastes Generated by the Model Mill(a)
Parameter Unit Value
Dry Solids
U308 wt% 0.007
Uranium (natural)(tO pCi/g 39
Radium-226 pCi/g 280
Thorium-230 pCi/g 280
Tailings Liquid
pH
Aluminum
Ammonia
Arsenic
Calcium
Cadmium
Chloride
Copper
Fluoride
Iron
Lead
Manganese
Mercury
Molybdenum
Selenium
Sodium
Sulfate
Vanadium
Zinc
Total dissolved solids
Uranium (natural)
Radium-226
Thorium- 2 30
Lead-210
Polonium-210
Bismuth-210
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
pCi/L
pCi/L
pCi/L
pCi/L
pCi/L
pCi/L
2
2,000
500
0.2
500
0.2
300
50
5
1,000
7
500
0.07
100
20
200
30,000
0.10
80
35,000
3,300
250
90,000
250
250
250
a(NRC80).
^k/A 1.5 microgram mass of natural uranium has activities of
0.49 pCi each of uranium-238 and uranium-234 and 0.023 pCL of
uranium-235.
4-9
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Table 4-6. Radioactive Emissions to Air from Model Tailings Pile
Radionuclide
Operational Phase Post-Operational Phase
Particulate Emissions , (mCi/y)
Particle size
Uraniutn-238
Uranium-234
Thorium-230
Radium- 2 26
Lead-210
Polonium-210
5 ym
2.6
2.6
36
36
36
36
35 urn
6.1
6.1
84
84
84
84
5 Mm
4.2
4.2
58
58
58
58
35
9
9
134
134
134
134
Mm
.8
.8
Radon-222
Gaseous Emissions (Ci/y)
4400 7000
4-10
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REFERENCES
(MP80) J.F. Facer, Jr., "Production Statistics," U.S. Energy Research
and Development Agency, presented at the Uranium Industry
Seminar, Grand Junction, Colorado, 19-20 October 1976.
M.B. Sears, et al., "Correlation of Radioactive Waste
Treatment Costs and the Environmental Impact of Waste
Effluents in the Nuclear Fuel Cycle for Use in Establishing as
Low as Practicable Guides—Milling of Uranium Ores," Oak Ridge
National Laboratory, Oak Ridge, Tenn., ORNL-TM-4903, Vol. 1,
May 1975.
"WIN Reports on Uranium Ore Analysis," National Lead Company,
Inc., Raw Materials Development Laboratory, U.S. AEC Contract
No. 49-6-924; WIN Reports #3, 5, 14, 39, 44, 45, 49, 50, 56,
58, 60, 64, 65, 67, 70, 71, 72, 76, 77, 79, 89, 97, and 106,
dated 7 January 1957 to 10 July 1958.
D. A. Brobst and Pratt W.P. (editors), "United States Mineral
Resources," Geological Survey Professional Paper 820, U.S.
Dept. of the Interior, Geological Survey, 1973.
"Mineral Facts and Problems," U.S. Dept. of the Interior,
Bureau of Mines Bulletin 667, 1975.
"Final Environmental Statement—Bear Creek Project, Rocky
Mountain Energy Company," U.S. Nuclear Regulatory Commission,
Docket No. 40-8452, NREG-0129, January 1977.
"Draft Environmental Statement—Lucky Me Uranium Mill, Utah
International, Inc.," U.S. Nuclear Regulatory Commission,
Docket No. 40-2259, NREG-0295, June 1977.
"Draft Environmental Statement—Moab Uranium Mill, Atlas
Minerals Division, Atlas Corp.," U.S. Nuclear Regulatory
Commission, Docket No. 40-3453, November 1977.
"Final Environmental Statement—The Highland Uranium Mill
(Exxon Co., U.S.A.)," U.S. Atomic Energy Commission,
Directorate of Licensing, Docket No. 40-8102, March 1973.
"Environmental Report—Sweetwater Uranium Project, Sweetwater
County, Wyoming," Minerals Exploration Company, November 1976.
"Final Environmental Statement—Shirley Basin Uranium Mill,
Utah International, Inc.," U.S. Atomic Energy Commission,
Directorate of Licensing, Docket No. 40-6622, December 1974.
4-11
-------
REFERENCES (Continued)
NRC80 Nuclear Regulatory Commission, "Final Generic Environmental
Impact Statement on Uranium Milling," NUREG-0706, NRC,
Washington, D.C., 1980.
NRC81 Nuclear Regulatory Commission, "Draft Environmental Statement
Related to the Decommissioning of the Edgemont Uranium Mill,"
NUREG-0846, NRC, Washington, D.C., 1981.
4-12
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Chapter 5: ENVIRONMENTAL PATHWAYS
In this Chapter the pathways through which radioactive and toxic
materials from mill, tailings may cause exposure of man are examined
and, where possible, quantified. While consideration of the impact of
tailings piles on man depends on the status—operational or postopera-
tlonal—of the mill, the contaminants which are expected to be present
are the same. The projected health impacts of these materials are
developed for the various pathways in Chapter 6, using the results
obtained in this chapter Cor the model site.
5.1 Con tarn inan_t£
The pathway analysis considers three general forms of
contaminants. They are particulates (dust), radon (gas), and liquids
(leachate). An introductory discussion of each form is given first,
and the actual transport mechanisms are presented in the following
sections. The model mill has been described in Chapter 4. The source
terms and other model parameters are more fully described in the Final
Generic Environmental Impact Statement on Uranium Milling (NRC80).
Since the Act addresses only the tailings resulting from mill
operations, only the model mill, source terms applicable to the tailings
pile are employed.
5.1.1 Particulates
The mechanism of movement of tailings particles by wind is similar
to the movement of soil and is dependent on wind velocity, physical
properties of the tailings, and the nature of the tailings surface.
Wind forces can generate three basic modes of partir.le movement:
surface creep, saltation, and airborne suspension. Surface creep,
which spreads the tailings pile, involves particles ranging in size
from 500 to 1000 pm. These particles are rolled along the surface by
the push of strong winds and the exchange of momentum after impact with
smaller particles in saltation. Saltation causes individual particles
to jump and lurch within a few centimeters of the ground. Particles
that saltate are from 100 to 500 pm in size, depending on shape and
density, and are quickly brought back to the ground by gravitational
force. The resulting exchange of momentum with other particles can
initiate surface creep, saltation, or suspension. Particles in
5-1
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suspension are small enough (less than about 100 ym) to have a
gravitational velocity of fall lower than the upward velocity of the
turbulent wind. These particles may be carried through the atmosphere
for long time periods and to distances far from their original
location. While airborne, these suspended particles contribute to the
inhalation pathway of exposure of man; when deposited, they contribute
to the ingestion and external surface exposure pathways.
5.1.2 Radon
As shown in Figure 3-1, the radon decay process involves seven
principal decay products before ending with nonradioactive lead. The
four short half-life radioactive decay products immediately following
radon are the most important sources of cancer risk. These decay, for
the most part, within less than an hour. Members of the decay chain
with relatively long half-lives (beginning with lead-210, which has a
22-year half-life) are more likely to be ingested than breathed and
pose much smaller risks.
The principal short half-life products of radon are polonium-218,
lead-214, bismuth-214, and polonium-214. Polonium-218, the first decay
product, has a half-life of just over 3 minutes. This is long enough
for most of the electrically-charged polonium atoms to attach to
microscopic airborne dust particles that are typically less than a
millionth of a meter (ym) across. When breathed, these small particles
have a good chance of sticking to the moist epithelial lining of the
bronchial tubes in the lung.
Exposure to radon decay products is expressed in terms of a
specialized unit called the Working Level (WL). A Working Level is any
combination of short half-life radon decay products that emits 130,000
million electron volts (MeV) of alpha-particle energy in I liter of
air. The unit of cumulative exposure to radon decay products is the
Working Level Month (WLM), which is exposure to air containing 1 WL of
radon decay products for a working month, which is defined as 170
hours. (These units were developed to measure radiation exposure of
workers in uranium mines.) Continuous exposure of a member of the
general population to 1 WL for 1 year is equivalent to about 27 WLM.
For exposures occurring indoors, we assume a 75 percent occupancy
factor. Thus, an indoor (residential) exposure to 1 WL for 1 year is
equivalent to about 20 WLM (EPA79a).
5.1.3 Liquid Contaminants
Airborne transport of tailings, with subsequent deposition on the
ground and on surface waters, and transport or leaching of tailings by
water used for drinking or irrigation can lead to exposure of man to
radioactive and toxic substances. Future contamination of surface or
groundwater is also likely if there is erosion of toxic elements from a
pile by rain, by flooding, or, possibly, by the flushing action of
seasonal changes in the water table when it can reach a pile from
5-2
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below. Severe floods have a greater, but difficult to evaluate,
potential for producing significant contamination of streams and
rivers. Future groundwater contamination from the seepage and flushing
action of seasonal changes in the water table is uncertain. The degree
of detail with which we can accurately treat these potential pathways
varies. Modeling of water pathways requires site-specific data on
sources and uses of water. The existence of actual water pathways for
radioactive and toxic materials from tailings piles has not yet been
verified, so we discuss these pathways in general terms only.
Concentrations of dissolved substances in the tailings pond water at
the model mill are shown in Table 4-5.
5 . 2 Atmospheric Transport
Airborne particulates and radon are analyzed using essentially
the same calculational procedure. For the purpose of evaluating
environmental impact, the analysis has been performed for both regional
and national populations, using appropriate meteorological models for
each. Because of the short half-life of radon, the worldwide impact is
not significantly greater than the sum of the impacts of these two
groups, and is therefore not calculated for this analysis. The term
"regional" is defined to include local and regional populations at
distances up to 50 miles (80 km) from the tailings site and "national"
to cover the remainder of the contiguous United States.
5.2.1 Nearthe Ta iH
We estimated radon concentrations over and close to the edge of
generic, uncovered tailings piles, which, for calculational
convenience, we take as circular in shape. For these calculations we
assumed that the radon emission rate is a uniform 280 pCi/m^s from
the tailings. Concentrations for other emission rates would be
proportionately higher or lower. The concentration calculations were
made using generic wind data from the NRC GE IS (NRC80) and the
AIRDOS-EPA dispersion model (EPA79b).
5.2.2 Regional
Meteo ro lo g_y
Airborne transport within the region is governed by meteorological
conditions at the model mill site. These are detailed in Chapter 4.
The transport mechanisms considered are described below.
D_ispers_ip_n
The AIRDOS-EPA code (EPA79b) uses a modified Gaussian plume
equation to estimate airborne dispersion of rad ionuc I ides from the
pile. Calculations are site-specific and require detailed knowledge of
the joint wind direction, wind speed, and stability frequencies. Since
the accuracy of these projections decreases with distance, we limit
5-3
-------
calculations with this method to regional (less than 50 miles distant)
locations. Values calculated are annual averages, since we are not
concerned with diurnal or seasonal variations.
Deposition
AIRDOS-EPA estimates the annual average concentration of each
radionuclide in air at ground level (corrected for deposition) as a
function of direction and distance from the source. Deposition rates
at each location are calculated for each radionuclide, and from these,
the ground concentration levels at the desired locations. The
radionuclides are deposited on the ground in the model by both
precipitation and direct dry deposition.
Ingrowth of Radon Decay Products
At the point where radon diffuses out of the tailings, the
atmospheric concentration of associated radon decay products is zero,
because those decay products generated prior to diffusion from the
surface have been captured in earth. As soon as radon is airborne,
atmospheric decay product ingrowth commences and a secular equilibrium
between the amount of radon and the amount of each decay product is
approached. At such secular equilibrium, there is equal activity of
all the short half-life radon decay products in air, and alpha
radiation per unit of radon concentration is maximized. To account for
incomplete equilibrium before this state is achieved, we define the
"equilibrium fraction" as the ratio of the potential alpha energy from
those decay products actually present to the potential alpha energy
that would be present at complete equilibrium. As radon and its decay
products are transported by the wind, the equilibrium fraction
increases with distance from the pile. Depletion processes, such as
dry deposition or precipitation scavenging, selectively removes decay
products (but not radon), so complete equilibrium with the radon is
seldom, if ever, reached.
When radon enters a structure, it remains for a mean time that is
inversely proportional to the ventilation rate and proportional to its
half-life. Since the former is much smaller than the latter, the
building ventilation rate is a principal factor affecting further
changes in the equilibrium fraction. It can also be affected by other
considerations, such as the indoor surface-to-volume ratio and the dust
loading in indoor air (Po78). We assume a 70-percent equilibrium
fraction for indoor radon and its decay products.
We have also assumed that, on the average, Americans spend
approximately 75 percent of their time indoors, mostly in their
homes (Mo76, Oa72). We have weighted the indoor and outdoor equili-
brium fractions for a given location by factors of 0.75 and 0.25,
respectively, to estimate an effective value for calculating exposure
to radon decay products from tailings piles. Since indoor exposure is
the dominant form of exposure due to radon, this effective equilibrium
fraction does not depend strongly on the distance from the tailings
pile.
5-4
-------
5.2.3 National
The inert radon gas emitted from tailings piles can be transported
beyond the 50-mile regional cutoff. A trajectory dispersion model
developed by NOAA (Tr79) has been used to estimate the national impact
of radon emissions from the model pile. This model calculates the
potential radiation exposure to the United States population for radon
released from four typical mill site locations. (Descriptions of these
typical mill sites—Casper, Wyoming; Falls City, Texas; Grants, New
Mexico; and Wellpinit, Washington—are given in (Tr79).) Only
exposures taking place beyond the 50-mile regional limit are
considered. Details of the model are given in He75. The model yields
radon concentrations (pCi/L) in air which were converted to decay
product concentrations by assuming that 100 pCi/L of radon corresponds
to a decay product concentration of 0.7 WL.
5.3 Hydrological Dispersion
There are two basic types of water resources considered in the
impact assessments: (1) surface water (water on the surface of the
earth, such as in lakes and rivers) and (2) groundwater (water occurring
below the surface of the earth in a zone of saturation). The impacts
on these two types of water resources in the model region are discussed
in the following subsections for the case of an unlined tailings
disposal area.
5.3.1 Surface Water
Operational
During operation of the mill, seepage from tailings ponds could
add heavy metals, suspended solids, radioactive contaminants, and
soluble salts to surface waters. Three routes of contamination might
occur as a result of this seepage:
1. Seepage water from the tailings pond could intercept an
aquifer and contaminate groundwater. This contamination could also
degrade surface water quality under certain conditions. Irrigation
wells or water supply wells could also penetrate aquifers that have
been contaminated by seepage from tailings ponds. Water pumped from
such wells would normally discharge into a surface water irrigation
ditch or canal and ultimately into a stream. Contaminated water
extracted via such wells would remain contaminated when it entered a
surface water stream.
2. Seepage water could form surface pools downgrade from the
tailings pond. Consideration of the transport time and concentration
data for the seepage pools indicates that the trace materials in the
pools would have the same initial composition as the tailings pond.
This surface water would be subject to a high rate of evaporation,
5-5
-------
which would result in a concentration of the soluble ions as the volume
of seepage water decreases. During periods of local precipitation and
spring runoff, this contaminated water could enter surface streams or
rivers.
3. During dry periods, seepage water might reach the ground
surface and be subject to a high evaporation rate, which would result
in salt deposits. These areas would be exposed to surface runoff
during periods of precipitation or during periods of snowmelt, at which
time the precipitates again would be subject to dissolution and
transport, resulting in a pulse of contaminated water reaching surface
waters. Depending on the amount of materials in the runoff and the
dilution capacity of the existing streamflow, the water quality of some
streams, on rare occasions, could reach toxic levels.
Post-Operational
After mill operations cease, seepage from the tailings would be
substantially reduced since discharge of water from the mill ends. The
permanent seepage rate caused by precipitation falling on uncovered,
abandoned tailings is estimated to be about 5 percent of the rate
during the 15-year operational period (NRC80).
5.3.2 Groundwater
The impacts of uranium milling operations on groundwater are
generally site-specific (because of regional and local variations in
geology and hydrology) and thus are difficult to discuss on a generic
basis. For illustrative purposes, however, a set of geological and
hydrological characteristics has been assumed for the model region.
The effects of mining on groundwater can be fairly extensive and
in many cases cannot be logically separated from the effects of nearby
milling operations. For the model mill, however, we assume that the
mines will be sufficiently far from the tailings pond to have no effect
on effects due to tailings pond seepage.
Operat ional
By far the greatest impact on groundwater resulting from operation
of a model mill would be from seepage from the tailings pond. The term
"tailings pond" is used in the general sense in this context, and is
intended to include evaporation ponds or any other type of unlined
facility which receives mill waste water. The model mill contains an
unlined tailings disposal area. The principal contaminants in the
acidic tailings pond liquid are radium, thorium, sulfate, iron,
manganese, and selenium (Table 4-5).
Post-Operational
After mill operations cease, seepage from the tailings would be
substantially reduced because of the cessation of discharge of water
5-6
-------
from the mill. It should be emphasized that this analysis assumes that
no new wells are permitted which would withdraw contaminated
groundwater from the aquifer affected by the seepage.
During the post-operational period, an advancing front of seepage
water containing nonradioactive contaminants would be moving
downgradient. In this analysis, contaminant concentrations have been
calculated on the assumption that there would be no lateral dispersion;
this is a conservative assumption in that it results in overestimation
of downgradient concentrations of contaminants. As these contaminants
disperse downgradient, their concentrations would be reduced.
5.4 Environmental Concentrations
We calculate environmental concentrations, radiation doses, and
health risks due to airborne releases using three computer
codes—AIRDOS-EPA (EPA79b), RADRISK (Du80), and DARTAB (Be81).
AIRDOSE-EPA estimates, for a given source term, the amount of
intake of each radionuclide, or the external concentration, at the
point of exposure. RADRISK calculates the radiation dose and risk from
unit intake of a given radionuclide. DARTAB is a control code that
scales the unit estimates of RADRISK to match the actual exposure
levels calculated by AIRDOS-EPA and then displays the results in a
useful format.
5.4.1 Calculational Procedures
The regional environmental concentrations resulting from airborne
emissions presented in this Chapter are obtained using the AIRDOS-EPA
code. The RADRISK and DARTAB health risk calculations are described in
Chapter 6 and Appendix C.
The AIRDOS-EPA code was developed for EPA by the Oak Ridge
National Laboratory. It is a modification of AIRDOS-II, a code in use
for many years, also developed by ORNL. Terrestrial food chain models
used by the code are based on those used by the U.S. Nuclear Regulatory
Commission, as provided in Regulatory Guide 1.109.
A modified Gaussian plume is used to estimate dispersion of as
many as 36 radionuclides from point or area sources. Radionuclide
concentrations in air, rates of deposition on ground surfaces, ground
surface concentrations, and intake rates due to inhalation and
ingestion (meat, milk, fresh vegetables) are then calculated.
Meteorological, population, and other data characteristics of the site
can be used to give more accurate assessments of a specific source.
When a source continually emits long half-life radionuclides, the
environmental concentration levels build up for as long as the source
continues to emit. This is not a significant consideration for air
5-7
-------
concentrations, but is for those concentrations which result from
deposition on the ground surface. Our calculations assume that the
particulates which deposit on the ground surface are removed by
environmental processes, such as leaching, at a rate of 2 percent per
year. (In addition, only 20 percent of the radon which results from
the decay of deposited radium is assumed to escape). Since the
environmental concentrations are not constant, they are calculated for
specific times appropriate to the analysis. For the operational
period, this is at the end of 15 years (the expected duration of mill.
operation) for the assessment of individual exposure and at the end of
100 years for the assessment of population exposures. The release
rates used for these calculations are those shown in Table 4-6.
For the post-operational period, the environmental concentrations
are calculated at the end of 100 years of releases. The release rates
for this period assume the tailings pond no longer exists and that the
entire tailings pile area (80 ha) contributes to the releases. Because
of the 2 percent per year removal rate assumed for deposited
particulates, these concentrations are close to equilbrium.
Radon decay product concentrations (WL) are calculated from the
atmospheric radon concentration (Ci/ro.3) using an effective
equilibrium fraction as described in Section 5.2.1.
5.4.2 Ai r Cojic^ent rations
Near the Pile_
Average concentrations near the pile are shown in Figure 5-1 for a
small (5 hectares or 12 acres), a medium (20 hectares or 49 acres), and
a large (80 hectares or 196 acres) tailings pile. Our calculations
show that the average concentration near the center of the pile and at
the edge of the pile are relatively insensitive to the size of the
pile. For the 20-hectare pile, Figure 5-1 also shows the results in
the directions for which the concentration is maximum or minimum. The
wind data (and therefore the dispersion) and the shape of the pile at
actual sites would differ from the one used for these calculations.
Although we have not performed site-specific calculations, we believe
that the higher wind direction asymmetry at actual tailings sites would
increase the maximum concentration at the edge of the tailings to about
4 pCi/L. This is the only calculation which uses dimensions different
from those of the model pile described in Chapter 4.
Regiona1
Regional air concentrations for particulates and radon are shown
in Table 5-1. These concentrations are based on the operational phase
source terms given in Table 4-6. In Table 5-1 and subsequent tables,
the column heading "average" refers to the arithmetic average over the
sixteen directions for which concentrations are calculated. The
heading "maximum" is the value for the direction of maximum risk (see
5-5
-------
o
Q.
O
<
QC
I-
01
O
O
u
2
O
Q
500
1000
DISTANCE FROM CENTER OF PILE (M)
Figure 5-1. Radon Concentration Near the Tailings Pile.
Radon Emission Rate is 280 pCi/m2s.
5-9
-------
Chapter 6) at that distance. The directions may differ since "risk"
implies that an individual or population is present. In general, the
direction of maximum concentration is the same as that of maximum risk;
in those situations where it is not, the concentration for the
direction of maximum risk does not differ in any practical sense from
that in the direction of maximum concentration. Data in Table 5-1 and
subsequent tables are presented to two significant figures to
facilitate comparisons and not to indicate that environmental values
can be calculated to that level of accuracy.
Table 5-2 shows population inhalation intakes of particulates and
radon decay product exposures, calculated for a year's release during
the operational period. The population distributions are shown in
Tables 4-2 and 4-3. Note that the total intake/exposure values for the
remote site are less than those for the rural one even though the
remote site has a larger regional population. The larger nearby
population of the rural site substantially increases the regional
intakes and exposures for that site. Post-operational regional
concentrations for particulates and radon are shown in Table 5-4. The
entire tailings pile area is assumed to be dry in this period, so the
emissions are 80/50 times the values for the operational phase.
National
National population exposures during the post-operational phase of
the model mill are calculated in the same way as those for the
operational phase. The radon source term, Table 4-6, during this phase
is 7000 curies per year and the exposures shown in Table 5-5 are the
total exposures for each year that the tailings pile continues to exist.
Annual national population exposures to radon emissions during the
operational phase of the model mill are shown in Table 5-3. The total
source term of 4400 curies per year (from Table 4-6) is attributed to
each site in turn; the average value for all sites Ls also shown.
These exposures assume an equilibrium fraction of 0.7 and exclude the
population living within 50 miles of the sites. The values represent
the total exposure to this population which results from each year's
operation of the mill.
5.4.3 Ground_ Surface Conee.n.trations^
Operational
Table 5-6 shows the regional ground surface concentrations oE
radionucI ides for the operational phase of the mill. These values are
calculated after 15 years oE operation. The "average" and "maximum"
headings again refer to the average for all directions and the
direction of maximum risk for all pathways.
5-10
-------
Table 5-1. Regional Air Concentration (Ci/m^)
of Radionuclides
by Distance and Particle Size
(Operational Phase)
Distance
(meters)
600
1000
2000
3000
4000
5000
10000
20000
600
1000
2000
3000
4000
5000
10000
20000
600
1000
2000
3000
4000
5000
10000
20000
Average
5 pm 35 ym
238u, 234u
3.7E-16 6.5E-17
1.1E-16 1.8E-17
2.8E-17 3.5E-18
1.2E-17 1.4E-18
7.0E-18 6.9E-19
4.6E-18 4.2E-19
1.2E-18 7.5E-20
3.2E-19 1.3E-20
230Th, 226Ra, 210Pb,
5.2E-15 9.3E-16
1.6E-15 2.5E-16
3.9E-16 5.0E-17
1.8E-16 2.0E-17
l.OE-16 9.8E-18
6.6E-17 6.0E-18
1.6E-17 1.1E-18
4.6E-18 1.9E-19
222Rn
1.3E-09
4.4E-10
1.4E-10
7.0E-11
4.6E-11
3.4E-11
1.3E-11
5.6E-12
Maximum
5 ym 35 ym
6.3E-16
2.2E-16
6.3E-17
2.9E-17
1.7E-17
1.1E-17
3.0E-18
8.8E-19
210Po
9.0E-15
3.1E-15
9.0E-16
4.2E-16
2.4E-16
1.6E-L6
4.2E-17
1.3E-17
2
7
2
1
9
6
2
1
1.5E-16
5.6E-17
1.3E-17
5.5E-18
2.8E-18
1.7E-18
3.1E-19
5.4E-20
2.2E-15
7.9E-16
1.9E-16
7.8E-17
4.0E-17
2.4E-17
4.4E-18
7.7E-19
.OE-09
.7E-10
.7E-10
.4E-10
.5E-11
.9E-11
.6E-11
.1E-11
^a'Value averaged over all directions.
^ 'Value for direction of greatest risk.
5-11
-------
Table 5-2. Regional Population Inhalation Intake and Exposure
(per Operational Year)
Inhalation
(person-pC i)
Radon Decay
Distance
(km)
20
20-40
40-80
Total
20
20-40
40-80
Total
Number of
Persons
16
4,572
52,840
57,428
2,273
5,314
14,235
21,822
238u,
5 ym
6.9
4.9
2.6E+01
3.8E+01
2.0E+03
1.2E+01
2.8
2.0E+03
234U
35 ym
Remote
1.5
7.5E-02
7.3E-01
2.3
Rural
1.8E+02
4.4E-01
3.6E-02
1.8E+02
23°Th, 226Ra,
5 um
Site(a)
l.OE+02
6.9E+01
3.7E+02
5.4E+02
Site'*'
2.8E+04
1.8E+02
4.0E+01
2.8E+04
210Pb, 210Po
35 ym
2.2E+01
1.1
l.OE+01
3.3E+01
2.5E+03
6.3
5.1E-01
2.6E+03
rrouuc u
Exposure
(person-WLy)
2.4E-02
1.5E-01
7.3E-01
8.9E-01
7.0
2.0E-01
1.4E-01
7.3
(a)
See Chapter 4 for description of sites.
Table 5-3. National Population Exposures and Intakes
(per Operational Year)
Exposures Pb Intakes
222
Rn Radon Decay Product Inhalation Ingest ion
Release Site (person-Ci-y/m ) (person-WLy) (person-Ci) (person-Ci)
New Mexico
Grants 3.1E-07
Texas
Falls City 4.8E-07
Washington
Wellpinit 2.6E-07
Wyoming
Casper 3.7E-07
Average 3.5E-07
2.2 7.7E-07 4.4E-06
3.3 8.2E-07 2.7E-06
1.9 7.9E-07 5.3E-06
2.6 9.4E-07 4.8E-06
2.5 8.3E-07 4.4E-06
5-12
-------
Table 5-4. Regional Air Concentration (Ci/m )
of Radionuclides
by Distance and Particle Size'3'
(Post-Operational Phase)
Distance
(meters)
600
1000
2000
3000
4000
5000
10000
20000
Average
5 Mm 35 um
5.9E-16
1.8E-16
4.4E-17
2.0E-17
1.1E-17
7.4E-18
1.8E-18
5.2E-19
238U, 234U
l.OE-16
2.8E-17
5.6E-18
2.2E-18
1.1E-18
6.7E-19
1.2E-19
2.1E-20
230Th, 226Ra, 2i°Pb,
600
1000
2000
3000
4000
5000
10000
20000
600
1000
2000
3000
4000
5000
10000
20000
8.4E-15
2.6E-15
6.3E-16
2.8E-16
1.6E-16
1.1E-16
2.6E-17
7.3E-18
2
7
2
1
7
5
2
9
1.5E-15
4.0E-16
8.0E-17
3.2E-17
1.6E-17
9.6E-18
1.7E-18
3.0E-19
222Rn
.OE-09
.1E-10
.2E-10
.1E-10
.4E-11
.4E-11
.OE-11
.OE-12
Maximum
5 pm 35 um
l.OE-15
3.5E-16
l.OE-16
4.7E-17
2.7E-17
1.8E-17
4.8E-18
l^+E-18
210po
1.4E-14
5.0E-15
1.4E-15
6.7E-16
3.9E-16
2.6E-16
6.8E-17
2.0E-17
3
i
4
2
1
1
4
1
2.4E-16
8.9E-17
2.1E-17
8.7E-18
4.4E-18
2.7E-18
4.9E-19
3.6E-20
3.5E-15
1.3E-J5
3.0E-16
1.2E-16
6.3E-17
3.9E-17
7.0E-18
1.2E-18
.2E-09
.2E-09
.4E-10
.3E-10
.5E-10
.1E-10
.1E-11
.8E-11
;a^Value averaged over all directions.
(b)
Value for direction of greatest risk.
5-13
-------
Table 5-5. National Population Exposures and Intakes Per Year
(Post-Operational Phase)
222_
Exposures __
Radon Decay
"Rn „ Products
210
Pb Intakes
Release Site ^erspn-Ci/^y/m ) _(person-WLy)
Inhalation Ingestion
(person-Ci) (person-Ci)
New Mexico
Grants
4.9E-07
3.5
1.2E-06
7.0E-06
Texas
"Falls City
Washington
Wellpinit
Wyoming
Casper
Average
7.6E-07
4.2E-07
5.8E-07
5.7E-07
5.3
3.0
4.1
4.0
1.3E-06
1.3E-06
1. 5E-06
1.3E-06
6.4E-06
8.4E-06
7.7E-06
7.0E-06
Table 5-6. Regional Ground Surface Concentrations
for Radionuclides^-3'
(Operational Phase)
238,, 234
230n
226
Distance
(meters)
600
1000
2000
3000
4000
5000
10000
20000
u,
Average
3.9E-09
1.1E-09
2.4E-10
l.OE-10
5.5E-11
3.5E-11
7.7E-12
1.9E-12
U
Maximum
8.1E-09
2.9E-09
7.4E-10
3.2E-10
1.7E-10
1.1E-10
2.4E-11
5.9E-12
Ave rage
5.5E-08
1.6E-08
3.5E-09
1.5E-09
7.8E-10
5.0E-10
1.1E-10
2.7E-11
Ra
Maximum
1.2E-07
4.2E-08
1.0E.08
4.6E-09
2.5E-09
1.6E-09
3.5E-10
8.4E-11
""Pb,
Average
5.3E-08
1.5E-08
3.3E-09
1.4E-09
7.5E-10
4.8E-10
1.1E-10
2.6E-11
Po
Maximum
1.1E-07
4.0E-08
l.OE-08
4.4E-09
2.4E-09
1.5E-09
3.3E-10
8.1E-11
^'Average: value averaged over all directions.
Maximum: value for direction of greatest risk.
5-14
-------
9
Table 5-7. Regional Population Ground Surface Exposure (person-Ci/m )
for Radionuclides (per Operational Year)
Distance
(km)
20
20-40
40-80
Total
20
20-40
40-80
Total
Number of
Persons
16
4,572
52,840
57,428
2,273
5,314
14,235
21,822
238u, 234u
Remote
3.3E-08
9.9E-09
5.9E-08
l.OE-07
Rural
5.8E-06
2.9E-08
5.9E-09
5.8E-06
230_, 226D
Th, Ra
Site(a)
4.7E-07
1.4E-07
8.4E-07
1.5E-06
Site(a)
8.3E-05
4.1E-07
8.4E-08
8.3E-05
21°Pb, 21°Po
4.2E-07
1.2E-07
7.4E-07
1.3E-06
7.3E-05
3.6E-07
7.5E-08
7.3E-05
Chapter 4 for description of sites.
Table 5-8. Regional Ground Surface Concentrations
for Radionuclides by Distance*-3'
(Post-Operational Phase)
Distance
(meters)
600
1000
2000
3000
4000
5000
10000
20000
238u,
Average
2.1E-08
5.9E-09
1.3E-09
5.5E-10
2.9E-10
1.9E-10
4.1E-11
l.OE-11
234u
Maximum
4.3E-08
1.6E-08
3.9E-09
1.7E-09
9.2E-10
5.9E-10
1.3E-10
3.2E-11
23°Th,
Average
2.9E-07
8.4E-08
1.8E-08
7.8E-09
4.2E-09
2.7E-09
5.9E-10
1.5E-10
226D
Ra
Maximum
6.2E-07
2.2E-07
5.6E-08
2.4E-08
1.3E-08
8.4E-09
1.8E-09
4.5E-10
21°Pb,
Average
2.6E-07
7.4E-08
1.6E-08
6.9E-09
3.7E-09
2.4E-09
5.2E-10
1.4E-10
21°Po
Maximum
5.5E-07
2.0E-07
4.9E-08
2.2E-08
1.2E-08
7.4E-09
1.6E-09
4.4E-10
(a)
Average: value averaged over all directions.
Maximum: value for direction of greatest risk.
5-15
-------
Regional population surface exposures for the operational phase
corresponding to these concentrations are shown in Table 5-7. These
values give the total exposure to the population for each year's
operation of the mill.
The national population dose resulting from deposition of radon
decay products, primarily the long-lived lead-210, is dominated by the
ingest ton pathway. For this reason, separate ground surface exposures
are not given here. Intakes due to ingestion are discussed in
Section 5.4.4.
Post_j3p_era_t ional
Post-operational regional ground surface concentrations are given
in Table 5-8. These representative values are calculated for the end
of a 100-year release period.
Since only the magnitude of the source term is different,
post-operational surface exposures are not listed separately. They
may be obtained by multiplying the values in Table 5-7 by factor 1.6.
Separate national ground exposures are not shown, since they are
not significant compared to Lngestion doses, which are given below.
5.4.4 Dietary Intake
Food consumption fractions for the regional population are shown
in Table 5-9. We have assumed that the mill is sited in a region of
low agricultural productivity and that area residents produce the same
amount of their own food supply as urban residents.
Table 5-9. Regional Food Utilization Factors for An Individual
Home Produced Total Annual
Type of Food (Percent) Consumption
Leafy vegetables 7.6 18 kg
Other produce 7.6 176 kg
Milk 0.0 112 L
Meat 0.8 85 kg
5-16
-------
Annual ingestion intakes for an individual residing in the region
are given in Table 5-10 Eor the operational phase and in Table 5-11 for
the post-operational phase. Annual regional population ingestion
values for the operational phase are given in Table 5-12. Since the
only difference is in the source term, values for the post-operational
phase are a factor of 1.6 larger than those in Table 5-12.
Annual national population exposures due to the ingestion of
long-lived radon decay products are dominated by lead-210. Dose and
risk calculations take account of the lead decay products as they build
up within the body following lead-210 intake. Table 5-3 gives the
annual population exposure resulting from dietary intake of lead-210
during the operational phase of the model mill. Post-operational
exposures are shown in Table 5-5.
5.4.5 Water Concentrations
In general, meaningful modeling of water pathways can be done only
on a site-specific basis, since any model depends strongly on the
hydrological and geological characteristics of the area. NRC (NRC80)
has performed a detailed analysis for the model mill based on a set of
assumed parameters. However, the environmental impact of a given
tailings pile depends on so many factors, i.e., wind erosion, floods,
slides into nearby streams, seepage through the pile, runoff of
rainwater, etc., that each must be evaluated on an ad hoc basis.
gurface Water
During operation of the mill, the pathways noted in Section 5.3
could cause the transfer of contaminants to surface waters. However,
based on the rainfall in the model mill region, the quantities of
material washed or leached into flowing surface waters could be so
dispersed and rapidly diluted that it is unlikely that surface water
would pose a significant health problem. Since the moisture content of
the tailings is reduced after mill operations cease, the potential for
surface water contamination is even less.
Under the Clean Water Act, effluent guidelines are already in
effect for uranium mills. In addition, EPA has New Source Performance
Standards for new uranium mills that would eliminate the discharge of
process waste water. In view of this comprehensive regulatory program
for surface water discharges from the uranium milling industry, surface
water contamination is not addressed in this analysis.
Groundwater
The modeling of groundwater contamination by tailings piles
depends strongly on the chemical and physical properties of the
underground environment. The NRC model predicts that, in spite of the
initial presence oC radioactive materials in the seepage, no
5-17
-------
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5-19
-------
radioactive contamination of groundwater would be expected during or
after mill operation. Based on their parameters, many of the
contaminants present in the acidic tailings pond water would
precipitate out or undergo ion exchange and be removed by soil from the
tailings seepage water. Potential contamination, as indicated by this
model, would be limited to toxic materials having relatively high
mobility. The health aspects of these materials are discussed in
Chapter 6.
Since control of groundwater pollution is already required for
conformance with existing water protection regulations, we have not
performed a detailed analysis for this pathway.
Table 5-12. Regional Population Ingestion (person-pCi)
for Radionuclides (per Operational Year)
Distance
(km)
20
20-40
40-80
Total
20
20-40
40-80
Total
Number of
Persons
16
4,572
52,840
57,428
2,273
5,314
14,235
21,822
238U, '234U 230Th
226
Ra
210
Pb
210
Remote
1.4 1.8E+01
4.1E+02 5.3E+03
4.7E+03 6.0E+04
5.1E+03 6.5E+04
Rural_
3.0E+02 3.9E+03
7.1E+02 9.1E+03
1.9E+03 2.4E+04
2.9E+03
3.7E+04
5.6E+01
1.6E+04
1.8E+05
2.0E+05
1.2E+04
2.8E+04
6.9E+04
1.1E+05
2.3E+01
6.5E+03
7.5E+04
8.2E+04
4.7E+03
1.1E+04
2.9E+04
4.5E+04
Po
2.7E+01
7.8E+03
9.0E+04
9.8E+04
5.0E+03
1.2E+04
3.1E+04
4.8E+04
(a)
See Chapter 4 for description of sites.
5-20
-------
REFERENCES
Be81 Begovich C.L., Eckerman K.F., Schlatter E.G., Ohr S.Y., and
Chester R.O., "DARTAB: A Program to Combine Airborne
Radionuclide Environmental Exposure Data with Dosimetric and
Health Effects Data to Generate Tabulations of Predicted
Health Impacts," ORNL-5692, Health and Safety Research
Division, ORNL, Oak Ridge, Tennessee, 1980.
Du80 Dunning D.E., Leggett R.W., and Yalcintas M.G., "A Combined
Methodology for Estimating Dose Rates and Health Effects from
Exposure to Radioactive Pollutants," ORNL/TM-7105, Health and
Safety Research Division, ORNL, Oak Ridge, Tennessee, 1980.
EPA79a Environmental Protection Agency, "Indoor Radiation Exposure
Due to Radium-226 in Florida Phosphate Lands," EPA
520/4-78-013, Office of Radiation Programs, EPA, Washington,
D.C, July 1979.
EPA79b Environmental Protection Agency, "AIRDOS-EPA: A Computerized
Methodology for Estimating Environmental Concentrations and
Dose to Man from Airborne Releases of Radionuclides,"
EPA 520/1-79-009, Office of Radiation Programs, USEPA,
Washington, D.C., December 1979.
He75 Heffter J.L., Taylor A.D., and Ferber G.J., "A
Regional-Continental Scale Transport, Diffusion, and
Deposition Model," NOAA Tech. Memo, ERL/ARL-50, 1975.
Mo76 Moeller D.W. and Underbill D.W., "Final Report on Study of the
Effects of Building Materials on Population Dose Equivalents,"
School of Public Health, Harvard University, Boston, December
1976.
NRC80 Nuclear Regulatory Commission, "Final Generic Environmental
Impact Statement on Uranium Milling," NUREG-0706, USNRC,
Washington, D.C. 1980.
Oa72 Oakley D.T., "Natural Radiation Exposure in the United
States," ORP/SID 72-1, USEPA, Washington, D.C., 1972.
Po78 Porstendorfer J., Wicke A., and Schraub A., 1978, "The
Influence of Exhalation, Ventilation, and Deposition Processes
Upon the Concentration of Radon, Thoron and Their Decay
Products in Room Air," Health Physics 34_ (465).
Tr79 Travis C.C., Watson A.P., McDowell-Boyer L.M., Cotter S.J.,
Randolph M.L., and Fields D.E., "A Radiological Assessment of
Radon-222 Released from Uranium Mills and Other Natural and
Technologically Enhanced Sources," ORNL/NUREG-55, ORNL,
Oak Ridge, Tennessee, 1979.
5-21
-------
Chapter 6: HEALTH IMPACT OF TAILINGS BASED ON MODEL TAILINGS PILES
In this chapter we consider the health impact of material coming
from the model, pile. When feasible, projections, based on these
results, for the total impact of the industry are developed in
Chapter 10. Data on the concentrations of radioisotopes for
individuals or populations at various distances from the model pile,
taken from Chapter 5, were combined with the risk coefficients
described in Appendix C to estimate the risks to individuals and
populations living around the model pile. Potential effects on local,
regional, and national populations are estimated.
6.1 Int rodu_ct ion
Among metallic ore wastes, uranium tailings piles are unusual
because of the amount of radioactivity they contain. Radioactivity
probably constitutes the principal source of hazard to health from
these wastes, although nonradioactive toxic chemicals, such as arsenic,
lead, selenium, mercury, sulphates, and nitrates are usually present.
Milling of uranium ore removes about 90 percent of the uranium in the
ore. The remainder, along with most other radioactive materials and
toxic chemicals, is discarded in the liquid and solid wastes discharged
to tailings piles.
The principal isotope of uranium, uranium-238, decays over
billions of years to become lead, a stable nonradioactive element.
This lengthy decay process involves a series of intermediate
radioactive decay products, such as thoi: iutn-230, radium-226, and
radon-222. The decay of uranium since the ore was formed millions of
years ago has built up an inventory of these decay products, which are
present in uranium mill tailings in various concentrations.
The dominant hazard from tailings is due to the radioactive decay
products of uranium-238, particularly radium-226 and its short
half-life decay products. Each gram of natural uranium ore contains
about 490 pCi each of uranium-238 and uranium-234 and additionally
about 23 pCi of uranium-235 and 2 pCi of thorium-232. Because they
occur in relatively small proportions and/or pose much less risk to
health, uranium-235 and thorium-232 and their radioactive decay
products may usually be ignored in evaluating the hazard of uranium
tailings.
6-1
-------
Uranium tailings emit three kinds of radiation: alpha particles,
beta particles, and gamma rays. All are forms of ionizing radiation,
which breaks up molecules into electrically charged fragments called
ions. In biological tissues, this ionization can produce harmful
cellular changes. At the low radiation levels usually encountered in
the environment, we expect the effects of such changes to be difficult
to detect. Studies show, however, that people exposed to radiation
have a greater chance of developing cancer. If the ovaries or testes
are exposed, the health or development of future generations of
children may also be impaired due to genetic damage.
One cannot predict with precision the increased chance of cancer
or genetic damage after exposure to radiation. We have based our risk
estimates on studies of persons exposed at doses higher than those
usually resulting from tailings and the assumption that at lower doses
the effects will be proportionally less. This assumption may over-
estimate or underestimate the actual risk, but it is the best that can
be done at present (EPA76).
Alpha, beta, and gamma radiations from mill tailings can cause
cancer or genetic damage. However, the major threat comes from
breathing air containing radon decay products with short half-lives—
polonium-218, for example—and exposing the lungs and other internal
organs to the alpha radiation these decay products emit. In addition,
people may be directly exposed to gamma rays from radioactive material
in the tailings pile, and radioactive tailings particles may be
transported into the body by breathing or ingestion.
The body's internal organs would still be exposed to radiation
from radionuclides even if uranium tailings piles suddenly disappeared,
because radon, radium, uranium, thorium, and other radioactive elements
occur naturally in the air, rock, and soil. One picocurie of radium
per gram of soil is a typical concentration; outdoor air contains a few
tenths of a picocurie of radon per liter (UN77). Normal eating and
breathing introduce these and other radioactive materials into the
body, increasing the potential for cancer and genetic changes. This
discussion, therefore, also compares the health risks from tailings to
those from normal exposure—not to justify the tailings risk, but to
provide a realistic context for comparison.
Tailings also contain toxic elements that could eventually be
inhaled or ingested by man and animals or absorbed by plants. Windblown
tailings inhaled by man or animals are unlikely to cause any toxicity
problems because the mass of inhaled material is so small. However,
the toxic elements in windblown tailings could be absorbed by plants
growing near a pile and could be a potential pathway leading to chronic
toxicity diseases in men or animals eating those plants. Moreover,
toxic elements from tailings could leach or seep into water supplies
used for irrigation or drinking. Finally, windblown tailings and radon
decay products could be deposited directly onto some foods, such as
lettuce and spinach.
6-2
-------
It is important to distinguish between acute and chronic
toxicity. Acute toxicity (or poisoning) occurs when enough of the
toxic element is consumed to interfere with a vital body or organ
function. The severity of the poisoning is usually proportional to the
amount of the toxic element consumed, and in extreme cases death or
permanent injury will occur. Chronic toxicity is more insidious. It
occurs when small amounts of a toxic element are consumed over a
prolonged period of time. A small fraction of each intake may be
deposited in tissues or organs. Toxic symptoms appear when the
cumulative deposit exceeds a critical level. Alternatively, each
intake of a toxic element may cause a small increment of organ damage.
Symptoms of toxicity become apparent when this damage accumulates to a
critical extent. Symptoms of chronic toxicity may be reversible if
consumption of the toxic element is stopped, or they may be
irreversible, progressive, or both.
In the case of tailings, acute toxicity would be a problem only if
standing water adjacent to or on a pile is consumed. Chronic toxicity
is more likely and is therefore examined in later discussions.
6.1.1 Radon and its Immediate Decay Products
Since the milling and extraction processes have removed most of
the uranium from the ore, the longevity of the remaining radioactive
members of the uranium series is determined by the presence of
thorium-230, which has a 77,000-year half-life. The thorium-230 decay
product, radium-226, has a 1,600-year half-life. Both thorium and
radium are relatively insoluble and immobile in their usual chemical
forms. However, the decay product of radium-226 is radon-222, an inert
radioactive gas, that readily diffuses through interstitial spaces to
the surface of the tailings pile where it becomes airborne. The
half-life of radon-222 is 3.8 days, so some radon atoms can travel
thousands of miles through the atmosphere before they decay.
As shown in Figure 3-1, the radon decay process involves seven
principal decay products before ending with nonradioactive lead. The
four short half-life radioactive decay products immediately following
radon are the most important sources of cancer risk. These decay, for
the most part, within less than an hour. Members of the decay chain
with relatively long half-lives (beginning with lead-210, which has a
22-year half-life) are more likely to be ingested than breathed and
represent much smaller risks.
The principal short half-life products of radon are polonium-218,
lead-214, bismuth-214, and polonium-214. Polonium-218, the first decay
product, has a half-life of just over 3 minutes. This is long enough
for most of the electrically charged polonium atoms to attach themselves
to microscopic airborne dust particles that are typically less than a
millionth of a meter across. When breathed, these small particles have
a good chance of sticking to the moist epithelial lining of the
bronchi al.
6-3
-------
Most inhaled particles are eventually cleared from the bronchi by
mucus, but not quickly enough to keep the bronchial epithelium from
being exposed to alpha radiation from polonium-218 and polonium-214.
This highly ionizing radiation passes through and delivers radiation
doses to several types of lung cells. The exact doses delivered to
cells that eventually become cancerous cannot be characterized
adequately. Also, we do not have detailed knowledge of the deposition
pattern of the radioactive particles in the lung and the distances from
them to cells that are susceptible. Further, there is some disagreement
about the types of bronchial cells where cancer originates. Therefore,
we have based our estimates of lung cancer risk on the amount of inhaled
radon decay products to which people are exposed, rather than on the
dose absorbed by the lung.
6.2 Estimated Effects on Health Due to Radioactive Releases from the
Model~Tailings "
Risk factors from Tables C-3 to C-10 (see Appendix C) were used in
the DARTAB computer code to determine individual and population
lifetime risks for continuous exposure to emissions from the model
tailings pile. The calculated health impact on individuals and
populations is shown in Tables 6-1 through 6-6. The risk averages
given are population averages over the indicated sector. As shown in
these tables, about 99 percent of the inhalation risk is due to radon
and its daughters.
Values in these tables are shown to two significant figures solely
to facilitate comparisons and additional calculations; these projec-
tions have overall uncertainties of at least a factor of 2 or 3. The
individual health risks are for a lifelong exposure to the environmental
concentrations discussed in Chapter 5. A shorter period of exposure
may be assessed by assuming that the risk due to that exposure or
intake had been spread over the individual's lifetime. For example,
the risk from a 15-year exposure would be approximated as 15/70.76
times the lifetime (70.76 years is the expected lifespan of an
individual in the RADRISK cohort). The population health effect values
are the number of cancer deaths per year calculated at equilibrium for
a stationary population living at the calculated environmental
concentration levels. These values are equivalent to the number of
health effects committed per year of operation. (The age distribution
of the stationary population is that for the U.S. population in 1970, a
constant birth rate, and no external migration.)
6.2.1 Ef f ec_ts _ of Ra_d_i_qact i_ve Part iculate R_e_leases from the Model
Tai lings Pile ~
Individual s and Regional Populat ions
Windblown tailings from the model tailings pile may be inhaled by
persons in the vicinity of the pile. They may also be deposited on
soil or vegetation, be transferred to edible plants and ingested by
members of the population around the pile. The contribution of these
6-4
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Table 6-3. Number of Fatal Cancers per Operational Year for the Regional Population
Distance
(km)
20
20-40
40-80
Total
20
20-40
40-80
Total
Numb e r of
Persons
16
4,572
52,840
57,428
2,273
5,314
14,235
21,822
(a'See Chapter 4 for
Table
Distance
(km)
20
20-40
40-80
Total
20
20-40
40-80
Total
Radioactive Particulates
Invest ion
l.OE-08
2.9E-06
3.4E-05
3.7E-05
2.1E-06
4.9E-06
1.3E-05
2.0E-05
description
6-4. Number of Fatal
Number of
Persons
16
4,572
52,840
57,428
2,273
5,314
14,235
21,822
Inhalation Ground Surface
2.0E-06
1.3E-06
6.9E-06
l.OE-05
5.4E-04
3.3E-06
7.5E-07
5.5E-04
of sites.
Cancers per
Remote Site'3'
9.4E-06
2.8E-06
1.7E-05
2.9E-05
1.6E-03
8.3E-06
1.7E-06
1.7E-03
Post-Operational Year
Subtotal
i.lE-05
7.0E-06
5.8E-05
7.6E-05
2.1E-03
1.7E-05
1.5E-05
2.3E-03
for the
Radioactive Particulates
In^estion
1.6E-08
4.6E-06
5.4E-05
5.9E-05
3.4E-06
7.8E-06
2.1E-05
3.2E-05
Inhalation Ground Surface
3.2E-06
2.1E-06
1.1E-05
1.6E-05
8.6E-04
5.3E-06
1.2E-06
8.8E-04
Remote Site^3'
1.5E-05
4.5E-06
2.7E-05
4.6E-05
Ru ral S ite^3'
2.6E-03
1.3E-05
2.7E-06
2.7E-03
Subtotal
1.8E-05
1.1E-05
9.2E-05
1.2E-04
3.5E-03
2.6E-05
2.5E-05
3.6E-03
Radon Decay
Products
5.7E-04
3.5E-03
1.7E-02
2.1E-02
1.7E-01
4.8E-03
3.3E-03
1.8E-01
Total
5.8E-04
3.5E-03
1.7E-02
2.1E-02
1.7E-01
4.8E-03
3.3E-03
1.8E-01
Regional Population
Radon Decay
Products
9.1E-04
5.6E-03
• 2.7E-02
3.4E-02
2.7E-01
7.7E-03
5.3E-03
2.9E-01
Total
9.3E-04
5.6E-03
2.7E-02
3.4E-02
2.7E-01
7.7E-01
5.3E-03
2.9E-01
Chapter 4 for description of sites.
6-7
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Table 6-5. U.S. Collective Risks due to 222ftn Release
per Operational Year
(Fatal Cancers)
Release Site
New Mexico
Grants
Texas
Falls City
Washington
Wellpinit
Wyoming
Casper
Average
Table
Release Site
New Mexico
Grants
Texas
Falls City
Washington
Wellpinit
Wyoming
Casper
Average
21°Pb Intake
Inhalation Ingestion
l.OE-04 2.1E-04
1.1E-04 1.3E-04
1.1E-04 2.5E-04
1.3E-04 2.3E-04
1.1E-04 2.1E-04
6-6. U.S. Collective Risks due tc
per Post-Operational Year
(Fatal Cancers)
21°Pb Intake
Inhalation Ingestion
1.6E-04 3.3E-04
1.8E-04 2.1E-04
1.7E-04 4.0E-04
2.0E-04 3.7E-04
1.8E-04 3.3E-04
Total
3.2E-04
2.4E-04
3.6E-04
3.5E-04
3.2E-04
> 222Rn Rel
Total
5.0E-04
3.8E-04
5.7E-04
5.7E-04
5.1E-04
Radon Decay
Product
Exposure
5.2E-02
8.0E-02
4.4E-02
6.1E-02
5.9E-02
.ease
Radon Decay
Product
Exposure
8.2E-02
1.3E-01
7.1E-02
9.8E-02
9.5E-02
6-8
-------
two pathways is included in the ri.sk estimates listed in Tables 6-1 to
6-4. The period for greatest rLsk from windblown particulates Is
during the post-operational phase of the -nill after the tailings pile
has been allowed to dry (Tables 6-2, 6-4).
The risk (expectation of developing a fatal cancer) to an
individual for a 1 ifelong exposure is shown in Tables 6-1 and 6-2 as a
function of distance from the center of the pile. Risks from all
pathways of exposure are listed for the maximum exposed individual at
each distance. Depending on whether the local population density is
high or low, e.g.. a rural sile versus a remote site, the expected
number of fatal cancers in the regional population may vary by orders
of magnitude as shown in Tables 6-3 and 6-4.
6.2.2 Effects of _R_adon_Emi ssi_on_s from Tailings Piles
Individuals and Regional Populations
Detailed information is needed to determine the exposure due to
radon decay products in a population. An accurate calculation of the
collective exposure from a particular pile would require, in addition
to the number of people exposed, the site and ventilation
characteristics of each person's residence and work place, the length
of time a person spends at each place, and the average annual
distribution of w»nd speed and direction.
We have estimated local and regional exposure at the model site
using the methods to estimate exposures described in Section 5.4.
Although we have fixed our population at 1970 values, subsequent
changes are almost certain. We have not attempted to update our
population estimates because the data available reflect changes at
large levels of aggregation (e.g., a State) which do not give
information about the increases and decreases which have taken place at
a more local level.
The excess risk *-Q people due to exposure to radon decay products
depends on their distance from the pile. Tables 6-1 and 6-2 list
estimated excess risks to individuals for lifetime residency, as a
function of distance from a model pile during operational and
post-operatLonal phases of the pile, respectively. The decay product
concentrations are based on a dispersion factor that depends on the
area of the, pile out to a distance of several pile diameters. Beyond
that distance the theoretical pile can be considered as a point source
for the purpose of estimating concent rat i-on levels. The estimates for
this pile are based upon the relative risk model and assume a
stationary population.
The estimated risk of lung cancer from naturally-occurring radon
decay products found in homes that are not near mill tailings or any
other specifically identified radon source is 0.004 to 4 chances in
1,000 (EPA82). National data on radon decay products in homes (EPA82)
6-9
-------
are scanty and vary widely among individual houses. These estimates
are based on the assumption that the average radon decay product
concentration is 0.004 WL in homes and that they are occupied 75
percent of the time. This assumed average level of radon decay
products is based on recent data on 21 houses in New York and New
Jersey (Ge78) and on 26 houses in Florida (EPA79) and is consistent
with data obtained in other countries (UN77). For comparison, these
risks are about 10 percent of the expected lifetime risk of lung cancer
death from all causes (0.029) in a stationary population having 1970
U.S. lung cancer mortality rates.
Effects on the U.S. Population
Radon emissions from a tailings pile may affect the health of
populations beyond 80 kilometers from tailings piles. The aggregate
effect on persons living more than 80 kilometers from the. pile is
summarized in Tables 6-5 and 6-6. These results are estimates of the
total risk committed over 100 years to an exposed population of 200
million persons. Although the U.S. population increase has not been
uniform, an increased risk on the order of 20 percent should provide a
rough estimate of the risk to the current population.
Effects from Long-Lived Radioactive Decay Products of Radon
The long-lived decay products of radon, beginning with lead-210
(see Figure 3-1), are also potential hazards. A quantitative estimate
of the impact of eating and breathing long-lived decay products from
the model pile cannot be established without site-specific
information—on food sources (Tr79), for example. The only detailed
study available was prepared by Oak Ridge National Laboratory (Tr79)
for the four sites listed in Chapter 5. We used these results in an
input to our risk models to compare their importance to that of the
short-lived decay products of radon. These comparisons are shown in
Tables 6-5 and 6-6. These results should not be taken as quantitative
estimates of the actual risk at specific inactive sites.
The four sources of exposure in this analysis are shown in
Tables 6-1 to 6-4. The largest risk is from breathing short-lived
radon decay products; the risk is 100 to 1000 times greater than the
next highest risk, for both individuals and for the regional
population. Persons living more than 80 kilometers from a model pile
are less exposed, and their risk would be considerably below that
indicated in Tables 6-1 to 6-4. But again, the risk from breathing
short-lived radon decay products is about 100 times greater than from
other pathways (Tables 6-5 and 6-6). We conclude that the risks from
these pathways can be ignored compared to that from breathing short-
lived radon decay products.
6.2.3 Effects of Gamma Radiation Emissions from Tailings Piles and
Windblown Tailings ~
Gamma radiation exposure of individuals depends on how close
to the edge of a pile people live or work and how tailings from the
6-10
-------
pile are distributed by the wind. The collective gamma radiation dose
depends on both the number of people exposed and their doses. Potential
individual doses can be approximated from available data, but accurate
estimates cannot be made without a variety of detailed information,
such as where people live and work and the amount of shielding provided
by buildings.
Gamma radiation from tailings exposes the entire body so that all
organs are at risk. The estimated frequency of fatal cancer and
serious genetic effects due to exposure of 1 mrad/y are listed in
Tables C-l and C-2 in Appendix C. People who live or work near
tailings piles will incur additonal risk from long-term exposures in
proportion to the excess of their average lifetime annual dose rate
above the normal background rate (approximately 100 mrem per year).
The estimated contribution of gamma radiation emissions to individuals
and populations in the vicinity of the model tailings pile is shown in
Tables 6-1 to 6-4 in the column headed "Ground Surface."
6.3 Effects from Misuse of Tailings
When tailings are used in building construction, there can be
serious risks to the health of those who live in such buildings. The
Grand Junction experience is an example of what can happen when this
kind of misuse occurs. There, about 700 buildings are contaminated
with enough tailings to increase average indoor radon decay product
levels by at least 0.01 WL; a few houses have levels higher than 0.5 WL.
If it is assumed that the useful lifetime of these buildings is 70
years, we estimate about an additional 70-150 lung cancers would occur
if remedial measures were not taken.
The estimated risks to individuals exposed to these high levels of
radon decay products are very large. For persons living in a house
with a concentration of 0.1 WL, the potential excess lifetime risk of
lung cancer is 0.5 to 1 chance in 10.
Other misuses of tailings, e.g., tailings used in gardens or
underneath detached buildings, can cause effects on health, but these
cannot be estimated easily. The risks depend on the particular way in
which the tailings are used, and effects on health may be due to gamma
radiation, ingestion of radionucl Ides through food chains, or
inhalation.
6.4 Estimated Effects on Health Due to Toxic Releases from the Model
Tailings Pile
Toxic materials have been considered in this E1S if they are in
substantially greater concentration in tailings than in native rocks or
soils or in a relatively mobile form (as either anions or cations). We
have included materials that are harmful to livestock and plants as
well as those potentially affecting humans directly. Evaluating the
potential risks from nonradioactive toxic substances in tailings
6-11
-------
requires different methods from those used for radioactive
substances.'!' With nonradioactive toxic materials the type of
effect varies with the material; the severity of the effect—but not
its probability of occurring—increases with the dose. Moreover,
because the body can detoxify some materials or repair the effects of
some small doses, often no toxic effects occur below a threshold dose.
We cannot construct a numerical risk assessment for nonradioactive
toxic substances because we do not have enough information. We can,
however, qualitatively describe risks of toxic substances in terms of
their likelihood of reaching people (or animals, or agricultural
products), concentrations at which they may be harmful, and their toxic
effects.
No acute effects—death in minutes or hours—could occur except by
drinking liquid directly from a tailings pond. Severe sickness, or
death within days to weeks, from the use of highly contaminated water
is possible, but very unlikely.
Chronic toxicity from the continuous consumption of contaminants
at low concentrations could be a problem. Toxic substances can
accumulate slowly in tissues, causing symptoms only after some minimum
amount has accumulated. Such symptoms of chronic toxity develop
slowly, over months or years.
In Table 4-5 we listed many chemical elements and ions that have
been found in tailings piles. Many of these occur in tailings in only
slightly higher concentrations than in background soils, and they also
have low toxicity when taken orally (Ve78). The following elements are
in this category: lanthanides, including cerium, europium, lanthanum,
and terbium; silicates; and zirconium, scandium, boron, gallium, and
aluminum. Some other elements may be in elevated concentrations in
tailings, but they, too, are not very toxic. These include copper,
manganese, magnesium, cobalt, iron, vanadium, zinc, potassium,
chloride, and sulfate. Some elements and ions at concentrations well
below levels toxic to humans and animals will cause water to have an
objectionable taste and color. Examples are iron, copper, manganese,
chloride, and sulfate.
Other substances are both present in tailings and are regulated
under the National Interim Primary Drinking Water Regulations (NIPDWR).
Listing in the NIPDWR is an indication of a significant need to limit
nonradioactive substances can induce cancer in experimental
animals (Go77, Ve78). However, for nonradioactive substances found in
uranium mill tailings, we do not feel that dose-response relationships
adequate for estimating such risks for oral intake have been developed.
6-12
-------
direct human consumption of these substances. The NIPDWR cover the
following elements: arsenic, barium, cadmium, chromium, lead, mercury,
nitrate, selenium, and silver. The toxicologies of these substances
are discussed in Appendix C. Molybdenum is both toxic and present in
tailings in elevated concentrations; its toxicity is also discussed in
Appendix C. Appendix C also discusses both the chemical and
radiological toxic effects of ingesting radium, thorium, and uranium.
Tailings are not known to be significant sources of other toxic
materials regulated under the NIPDWR, such as organic substances,
microbiological organisms, and man-made radioactivity.
6.5 Effects Expected in Plants and Animals
No significant adverse effects are expected in plants or animals
from radioactive emissions from the model tailings pile.
No attempt to estimate health effects from toxic materials
released from the model tailings pile is made since such estimates
require site-specific data on concentrations in water used for
irrigation or watering livestock, agricultural practices, and so
forth. Data on toxicity and an approach to estimating levels toxic to
plants and animals are detailed in Appendix C. In a properly
controlled tailings pile, there should be no hazard to plants or
animals.
6-1 3
-------
REFERENCES
EPA76 Environmental Protection Agency, "ORP Policy Statement on the
Relationship Between Radiation Dose and Effect, March 3, 1975;
Drinking Water Regulations, Radionuclides," Federal Register,
41.28409, July 9, 1976.
EPA79 Environmental Protection Agency, "Indoor Radiation Exposure
Due to Radium-226 in Florida Phosphate Lands," EPA
520/4-78-013, Office of Radiation Programs, USEPA, Washington,
D.C., July 1979.
EPA82 Environmental Protection Agency, "Final Environmental Impact:
Statement for Remedial Action Standards for Inactive Uranium
Processing Sites," EPA 520/4-82-013-1, Office of Radiation
Programs, USEPA, Washington, D.C., October, 1982.
Ge78 George A.C. and Breslin A.J., "The Distribution of Ambient
Radon and Radon Daughters in Residential Buildings in the New
Jersey-New York Area," presented at the Symposium on the
Natural Radiation in the Environment III, Houston, Texas,
April 1978.
Go77 Goyer R.A. and Mehlman M.A., editors, "Advances in Modern
Toxicology," Vol 2: Toxicology of Trace Elements, John Wiley
& Sons, New York, 1977.
NRC80 Nuclear Regulatory Commission, Final Generic Environmental
Impact Statement on Uranium Milling, NUREG-0706, NRG,
Washington, D.C., 1980.
Tr79 Travis C.C., Watson A.P., McDowell-Boyer L.M., Cotter S.J.,
Randolph M.L., and Fields D.E., "A Radiological Assessment of
Radon-222 Released from Uranium Mills and Other Natural and
Technologically Enhanced Sources," ORNL/NUREG-55, ORNL,
Oak Ridge, Tennessee, 1979.
UN77 United Nations Scientific Committee on the Effects of Atomic
Radiation, "Source and Effects of Ionizing Radiation, Report
to the General Assembly," U.N. Publication E.77.IX.1, United
Nations, N.Y., 1977.
Ve78 Venugopal B. and Luckey T.D., "Metal ToxicLty in Mammals,"
Vol. 2, Chemical Toxicity of Metals and Metaloids, Plenum
Press, New York, 1978.
6-1 4
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Chapter 7: CONTROL OF TAILINGS DURING MILLING OPERATIONS
Releases of radioactive and nonradioactive hazardous materials
from tailings during milling operations are controlled by existing
standards and regulations, for the most part. Also, the Act requires
that environmental standards for nonradioactive hazardous materials be
consistent with standards under the Solid Waste Disposal Act (SWDA), as
amended. Therefore, we briefly summarize existing standards and
regulations applicable to releases from uranium tailings before we
analyze controls for such releases during the operational phase of
uranium byproduct material management.
EPA promulgated Environmental Radiation Protection Standards for
Nuclear Operations on January 13, 1977 (40 CFR Part 190). These
standards specify the radiation levels below which normal operations of
the uranium fuel cycle are determined to be environmentally
acceptable. Radiation exposure due to releases from uranium byproduct
material is included under these standards with the exception of
emissions of radon and its decay products. Alternative standards for
radon emissions from uranium byproduct material are considered in this
Chapter. We also briefly review controls for radioactive releases
other than radon for the purpose of determining if the existing
standards remain cost effective in requiring their specific protection
levels.
EPA promulgated standards for discharges of process waste water
from uranium mills on December 3, 1982, as Ore Mining and Dressing
Point Source Category; Effluent Limitations Guidelines and New Source
Performance Standards, Subpart E - Uranium, Radium and Vanadium Ores
Subcategory (40 CFR Part 440). The purpose of these rules is to
establish new source performance standards (NSPS) under the Clean Water
Act. The NSPS require that "...there shall be no discharge of process
wastewater from mills using the acid leach, alkaline leach or combined
acid and alkaline leach process for the extraction of uranium or from
mines and mills using in situ leach materials."
7-1
-------
EPA promulgated Standards for Owners and Operators of Hazardous
Waste Treatment, Storage, and Disposal Facilities under Subtitle C of
the Solid Waste Disposal Act (SWDA) on July 26, 1982, (40 CFR Part
264). Radioactive materials controlled under the Atomic Energy Act of
1954, as amended, are not included under the Solid Waste Disposal Act.
However, the Act requires that standards for nonradioactive hazards
under the Act shall provide for the protection of human health and the
environment consistent with the standards required under Subtitle C of
the Solid Waste Disposal Act, as amended, which are applicable to such
hazards.
The Act also required the NRC to insure that management of uranium
byproduct materials is carried out in such a manner as conforms to
general requirements established by the NRC, with the concurrence of
EPA, which are, to the maximum extent practicable, at least comparable
to requirements applicable to the possession, transfer, and disposal of
similar hazardous material regulated by EPA under the SWDA, as amended.
EPA standards under the SWDA, as amended, specify concentration
limits for toxic materials in groundwater and also specify that there
shall be no increase in background levels in groundwater for hazardous
constituents listed in Appendix VFI1 of 40 CFR Part 261. These rules
basically require that: 1) a plastic liner should be placed on the
bottom of a tailings pond to prevent seepage of leachate into the
groundwater; 2) an active leachate management program should be
conducted to treat, process, recycle, etc., the leachate collected from
the tailings pond; 3) groundwater adjacent to the liner should be
monitored; and 4) a corrective action plan should be implemented if
hazardous constituents are detected above background levels in the
groundwater.
The Nuclear Regulatory Commission issued rules on October 3, 1980,
which specify licensing requirements for uranium and thorium milling
activities, including tailings and wastes generated from these
activities (10 CFR Part 40). These rules specify technical, surety,
ownership, and long-term care criteria for the management and final
disposition of uranium byproduct material.
The NRC also enumerated the authorities reserved to the NRC in
Agreement States under the provisions of the Act, and specified
requirements for Agreement States to implement the Act (10 CFR Part
150). Under the Agreement State program, Agreement States can issue
licenses for uranium processing activities, including uranium byproduct
material generated from these activities.
7.1 ObJe_ct_ives of Cont^ro_l_ Me_a_sii_re_s
Releases of radionuclides and toxic elements to air and water from
uranium mill tailings piles during milling operations can be reduced or
eliminated by a variety of control measures. Some of these are
appropriate for temporary control, and others have a more lasting
7-2
-------
tect. Releases to air are in the form of windblown tailings dust and
don gas. Releases to water are primarily from seepage from tailings
nds into underlying aquifers. This section discusses available
:thods for controlling these releases and the benefits achievable.
.1.1 Wind Erosion
Wind can erode exposed tailings embankments and dry beach areas
md transport small tailings particles away from the site. These
releases cause radiation doses to people living near the tailings pile,
primarily through inhaling the airborne tailings particles. Radiation
doses can also occur, but to a lesser extent, from ingesting food
contaminated with tailings particles or from external exposure to
offsite tailings deposited on the ground. Tailings also contain toxic
elements that could be ingested eventually by man and animals or
absorbed by plants.
7.1.2 Radon
Since radon-222 is an inert gas, it readily diffuses through the
interstitial spaces of a tailings pile to the surface, where it escapes
into the air. Radon-222 can cause large radiation doses to the lungs
of people living near tailings piles and, because radon can travel long
distances through the atmosphere before decaying, it also causes small
radiation doses to large numbers of people distant from tailings
piles. Control measures can reduce radon emissions from the tailings.
7.1.3 Water Contamination
Wind and water flowing over or through tailings can carry
radionucLides and toxic elements to surface or underground water. The
primary concern during milling operations is when water seeps from the
tailings ponds into an underground aquifer, contaminating the water
with radionuclides and toxic elements and presenting potential health
risks to people using the water. The objectives of control measures
for water protection are to reduce or eliminate seepage from tailings
ponds and to prevent the contamination of water resources.
7.2 Contro1_Methods
7.2.1 W ind_ JErp sion
Wind erosion can be controlled by stabilizing tailings by any of
the following methods:
1. Physical Methods—wetting the tailings or covering the
tailings with soil or other restraining materials.
7-3
-------
2. Chemical Methods—treating the tailings with a chemical
which interacts with the fine-sized materials to form a
crust.
3. Vegetative Methods--growing plants in the tailings or in
cover materials.
4. Staged or below-grade disposal.
During the operational phase of a mill tailings pile,
airborne-dust is usually controlled by wetting the surface of the
tailings or by treating the dry surfaces with chemicals. During the
post-opera*"; nal phase more permanent methods can be used, either
physical or vegetative methods, or a combination of these methods.
However, vegetative procedures are unsuitable for many locations
because of the low rainfall and the high alkalinity or acidity of the
tailings.
Keeping tailings surfaces wet with tailings solution or sprinkling
them with water can suppress dusting. This can be done, for example,
by discharging tailings slurry from multiple discharge points, as
opposed to a single point. Alternatively, sprinkling systems or tank
trucks can spray dried areas. Because surfaces of the tailings
impoundment can dry out rapidly, this method of dust suppression
requires continuous attention.
Chemical stabilization involves interaction of a reagent with
tailings to form an air- and water-resistant crust or layer that will
effectively stop dust from blowing. Resinous adhesives; 1 ignosulforiates;
elastomeric polymers; milk of lime; mixtures of wax, tar, and pitch;
potassium and sodium silicates; and neoprene emulsions have been used for
such purposes (De74). In tests by the U.S. Bureau of Mines, resinous
adhesives, lignosulfonates, and elastomeric ploymers were shown to be the
most promising chemicals for stabilizing tailings. Calcium
1ignosulfonate (Norleg A) and an elastomeric polymer (DCA-70) were tested
on the tailings at Tuba City, Arizona, with reasonably good results,
although periodic maintenance was needed (Ha69). More recently,
wood-fiber-based materials (Conwed-200) and magnesium chloride (Dust
Guard) have been used affectively for tailings dust control (Ma82).
Table 7-1 lists chemicals that have been used for suppressing tailings
dust and their estimated unit costs.
Various cover materials have been used or tested for stabilizing
tailings and controlling wind erosion, including soil, rock, slag, bark
or straw, vegetation, and synthetic covering such as asphalt. The most
common cover materials used are soil and vegetation because of their
relative ease of application and economy. Although vegetative cover can
sometimes be used by itself, it is normally used in conjuntion with soil
cover or with a chemical stabilizing agent. However, for areas of low
rainfall, vegetative cover will require irrigation.
7-4
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Table 7-1. Chemical Stabilization Agents Used for Dust Suppression
(1981 dollars)
Product
Aerospray-70
Soil Card
Dust Binder
Concentrate
Co he rex
Type
elastomeric
polymer
elastomeric
polymer
elastomeric
polymer
resinous
adhesive
Application
Rate
230 gal/acre
420 gal/acre
240 gal/acre
730 gal/acre
Unit Cost
U/acre)
$1300
1800
1600
900
Norlig A
Conwed-200
Conwed-200
& Terra-Tac 1
Dust Guard
lignosulfonate
wood fiber
wood fiber
Magnesium
Choride
2.4 tons/acre
1.5 tons/acre
0.75 tons/acre
& 40 Ibs/acre
0.75 tons/acre
40 Ibs/acre
12 tons/acre
250
350
850
^•a'Based on application rate used by Bureau of Mines (Ha69).
(b)NRC estimate (NRC80).
Several recent tailings Impoundment designs have incorporated
progressive reclamation schemes into overall tailings management
programs. These schemes segment large tailings areas into a number of
smaller c^lls, with sequential construction, filling, and reclamation.
Such schemes substantially reduce dust emissions by reducing the
available surface area of exposed tailings.
Tailings can also be stored and disposed of through the use of
existing open mine pits or special excavations, so that the tailings
are below grade, thus virtually eliminating exposure of the tailings to
surface erosional effects.
7-5
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7,2.2 Control^ of. Radon
Radon releases from uranium mill tailings can be controlled by
minimizing the exposed dry beach areas of tailings by keeping the
tailings covered with water, soil, or some type of synthetic material.
Management practices involving staged reclamation of the tailings are
also a practical way of limiting the area of exposed tailings.
Radon diffusion through tailings is significantly affected by the
moisture content of tailings. Tailings covered by water do not release
any significant quantity of radon to air, and the release rate of radon
from w%t beach areas is only about 25 to 30 percent of the release from
dry bea^ch areas (NRC81). For most existing older tailings piles, this
method of controlling radon is dependent on the design of the tailings
pile and appears to have limited application. Although radon emissions
can be reduced somewhat by discharging tailings slurry onto the pile
and keeping it wet, large areas of exposed tailings will still exist
because of upstream construction methods and the need to maintain
adequate freeboard. However, for new or future tailings piles, design
and management techniques can be used that will keep all but a small
area of the tailings either wet or covered with water (NRC80).
Radon emissions to the atmosphere can be controlled by covering
the exposed tailings with soil (see Section 8.3). Relatively thick
covers (1 to 2 meters) are needed to reduce radon emissions
significantly (see Figure 8-1). Soil covers to reduce radon emissions
are more applicable to final disposal of the tailings than as an
interim measure to reduce radon emissions during milling operations..
Applying soil covers to tailings beach areas during operations is not
practical because new beach areas are constantly being formed.
Several recent tailings impoundment designs have incorporated
progressive reclamation schemes into overall tailings management
programs. These schemes segment large tailings areas into a number of
smaller cells, with sequential construction, filling, and reclamation.
Such schemes substantially reduce radon emissions by reducing the of
exposed surface area of tailings.
Land restrictions can prevent people from living near tailings
piles and thus reduce the health risks from radon emissions from
tailir^s. The greatest risks occur to people living close to the
tailings piles (i.e., 0.5 to 1 mile), with the individual risks
decreasing significantly with distance from the pile (see Table 6-1).
7.2.3 Cp_n_t_ro_l of Ground water Contamina t ion
The principal available means for controlling groundwater
contamination from .uranium mill tailings is using liners in the
tailings pond to prevent seepage. This method is primarily applicable
to new tailings piles because the liners must be installed when the
tailings impoundment is originally constructed, unless the pile is
7-6
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removed and replaced. Other methods for controlling potential
groundwater contamination involve removing the pollutants from the
tailings liquids or dewatering the tailings before disposal. These
methods also are most applicable to new mills. Methods for controlling
seepage to groundwater under existing tailings piles are limited to
pumping contaminated water back to the tailing pond or to separate,
lined evaporation ponds.
Placing compacted clay over the ground surface under a tailings
pile will act as a sealant and inhibit seepage from the tailings pond.
Furthermore, the ion-exchange characteristics of the clay will further
retard the transport of contaminants to the underlying aquifer. The
sealing property of clay results from its ability to expand when wet.
The expanded clay particles decrease the pore space of the soil,
decreasing its permeability.
Many types of synthetic materials can be used as liners to inhibit
seepage from tailings ponds, including plastics, elastomers, and
asphalt coatings. Plastics and elastomers are usually used with
polyester or nylon reinforcement artd are flexible liners. Careful
preparation of the tailings pond base and of the protective soil layer
placed after installation of the liner is necessary to avoid damage to
the liner.
Chemical processes which remove pollutants from the tailings
solution could be used to control groundwater contamination. For
example, removing contaminants from the water by lime neutralization or
ion exchange are two such processes (NRC80). Lime neutralization
precipitates radionuclides and most toxic elements as insoluble
hydroxides. Ion-exchange resin can absorb contaminants from the
solution. Information on the practicability of these processes is
limited, and such processes generally have not been used in the uranium
milling industry in the United States (We80).
Based on available information, using liners appears to be the
most practical method for preventing groundwater contamination from
tailings piles.
7.3 Cost and Ef fej:tivenes^s j^f Contro 1 Measures for Model Tailings Pile
7.3.1 ControJ. _of_ ^ind__Ero_s_io_n of Tailings
During the operational phase of uranium mill tailings piles, wind
erosion of tailings may be most easily controlled by spraying the dry
beach areas with water or treating those areas with a chemical
stabilization agent. During the post-operational phase of a mill
tailings pile (i.e., before final disposal), a thin cover may be used
to prevent wind erosion. Although many types of cover material are
available, soil appears to be the most practicable cover for this
purpose. The cost and estimated efficiency of these control methods
are shown in Table 7-2.
7-7
-------
For new tailings piles, efficient design and management practices
can reduce the amount of airborne dust released from the piles. Staged
disposal (see Appendix B) can reduce the amount of tailings dust by
about 70 percent (NRC80). Below-grade disposal will shield the dry
tailings areas from wind erosional effects and significantly reduce the
amount of tailings dust. We assign a control efficiency of 90 percent
to the below-grade disposal option described in Appendix B. No direct
costs are assigned to dust control for these management options, since
dust control is obtained at no additional cost when these management
options are selected based on disposal considerations. Appendix B
contains a discussion of the costs of these management options.
7.3.2 Contro!_ of Radon
Methods for reducing radon emissions to air from tailings are not
easily applied to existing tailings piles during the operational
phase. Using cover materials is not practical since new tailings beach
areas are continuously being formed. Although radon emissions can be
reduced by enlarging the area of tailings covered by water, such an
approach is affected by the design of the tailings pile and is a
complex function of seepage, evaporation and recycling rates, and
tailings embankment strength and stability. For purposes of subsequent
analyses, we conclude that using water covers to obtain large
reductions in radon emissions is not generally applicable to existing
tailings piles. By wetting the tailings surfaces with tailings liquids
or by sprinkling with water, a small reduction (20 percent) in the
radon emissions can be achieved (NRC80).
For new tailings piles, the use of staged disposal can reduce
radon emissions by about 70 percent. Designs that maximize the amount
of tailings covered by water can achieve a greater-than 90 percent
reduction of the radon emissions (NRC80). No direct costs are assigned
to these methods for controlling radon, since the control is obtained
at no additional cost when the management option is selected based on
disposal considerations.
7.3.3 Control of Seepage to Groundwater
During the operational phase of the mill, contamination of
groundwater can be controlled by using a plastic or clay liner on the
bottom and sides of the tailings pond. Estimated costs for a clay
liner at a new tailings pond are presented in Appendix B for the model
tailings pile as $12 million (1981 dollars), which includes $2 million
for overhead and contingencies. The estimated cost for a clay liner at
a new tailings pile using the staged disposal method is $8.9 million,
which includes $1.5 million for overhead and contingencies. The staged
disposal method has a lower estimated cost primarily because the
tailings are arranged in a thicker layer than they are for surface
storage, thereby reducing the area requiring a liner.
7-8
-------
Table 7-2. Costs and Effectiveness of Methods for Controlling
Wind Erosion at a Model Tailings Pile
(1981 dollars)
Control Method
Water Spray (Truck)
Water Spray (Piped)
Chemical
Stabilization^3)
Water Spray (Truck)
Water Spray (Piped)
Chemical
Stabilization^3)^)
Soil Cover (1 foot)
Capital Annual Present Estimated Control
Co_s_t^s__ __Co_s_ts_ N2£th_ Efficiency (%_)_
()PERATIONAL PHASE
33 250
400 160 1,220
50 380
?2.Sll.OPERATIONAL PHASE
53 48
240 260 260
80
500
73
500
50 (NRC80, PE82)
90 (PED82)
80 (NRC80, PE82)
50 (NRC80, PE82)
90 (PE82)
80 (NRC80, PE82)
90-100 (PE82)
(a)
Cost based on an annual application of the chemical agent, Norlig A.
The estimated 1980 cost of a Hypalon (plastic) liner was $8.25
million (see Alternative 5 in (NRC80)). Correcting this cost to 1981
figures and adding 20 percent for overhead and contingencies, we
estimate a plastic liner to cost $10.9 million. This estimate is for
the model tailings pond, which has an effective tailings storage area
of 80 hectares.
Chemical treatment of tailings at a new tailings pond by the
addition of lime is estimated to cost $11.8 million at an acid-leach
mill and $10.8 million at an alkaline-leach mill (We80). The
alkaline-leach tailings are assumed to be blended with acid-leach
tailings before treatment with lime. The key cost item is the sludge
storage lagoon for both acid- and alkaline-leach tailings.
Options for protecting groundwater at existing tailings ponds
varies from site to site. The control costs for groundwater protection
at existing tailings ponds can range from zero, where no action is
needed, to the costs of constructing a new, lined tailings pond as
7-9
-------
presented in Appendix B. An intermediate-cost remedial action is being
applied at the Homestake mill in New Mexico. Two rows of wells were
drilled across the groundwater hydraulic gradient down from the
tailings pond. Water is pumped from wells in the first row, closest to
the pond, and recycled. Fresh water is injected into the wells in the
second row to dilute any contaminated groundwater. During September
1978, 3.7 million gallons were injected. The estimated present value
of the future costs for this pumping is about $85,000, which includes
capital costs for 15 pumps and drilling 15 wells and an annual
operating cost corrected to present value at a 10 percent discount rate.
The effectiveness of plastic liners results from the physical
barrier that these liners provide. A plastic liner will retain all the
liquid in the tailings pond, including the dissolved hazardous and
toxic materials. This is advantageous since it prevents the seepage
into groundwater of chemical forms of these materials that are highly
soluble and difficult to remove with chemical processes. It also
avails us of the option to issue standards requiring control of
materials that are currently not listed under Subtitle C of the SWDA,
as amended. Protection of groundwater achieved with plastic liners
would control both the hazardous materials listed under Subtitle C of
the SWDA, as amended, and other potential pollutants found in uranium
tailings.
Molybdenum is found in some uranium ores and is present in
tailings after the ore is processed (see Chapter 3). Molybdenum is
estimated to be potentially toxic to humans and also has a narrow
safety margin, e.g., a low ratio of toxic intake to adult required
intake, as discussed in Appendix C. This inorganic has been found in a
shallow aquifer at the Cotter mill, Canon City, Colorado, at estimated
potentially toxic concentrations, as shown in Chapter 3. Also,
molybdenosis has been observed in cattle grazing on land contaminated
with molybdenum from the processing of uranium ores in North Dakota and
Texas, as noted in Appendix C. All this, in addition to the fact tViat
molybdenum will be controlled by the same methods used to control toxic
and hazardous materials, allows us to consider control of molybdenum
seepage from uranium tailings storage areas.
Radioactive materials are not included under the SWDA regulations
since most of them are controlled under the Atomic Energy Act and thus
are exempted by the SWDA, as amended. Tailings contain large
quantities of radioactive materials as shown in Chaper 3.
Contamination of groundwater by radioactive materials should be
controlled since they are potentially the most hazardous constituents
of tailings. The same methods used to protect groundwater from other
toxic and hazardous constituents will also prevent contamination by
radioactive materials.
Concentration limits for toxic materials in the SWDA regulations
were adopted directly from the National Interim Primary Drinking Water
7-10
-------
Regulations (40 CFR Part 141). Thus, the concentration limits for
radionuclides, as specified in the drinking water standards, can be
adopted for application to tailings since this is consistent with
standards under SWDA, as amended. These include limits of 5 pCi of
radium-226 and radium-228 per liter of water and of 15 pCi of gross
alpha particle activity per liter of water. The gross alpha particle
limit excludes uranium which is present in large quantities in tailings
and has been found in high concentrations in shallow aquifers as shown
in Chapter 3. However, uranium is indigenous in groundwater in many
uranium producing areas. Therefore, rather than specifying a
concentration limit for uranium, a nondegradation approach is more
suitable. This would require that there would be no increase in the
concentration of uranium above background levels in the local area of
the tailings.
Protecting groundwater by controlling seepage from tailings with a
plastic liner would eliminate seepage as a discharge pathway for excess
wastewater. At some sites this is a significant discharge pathway.
New Source Performance Standards (NSPS) under the Clean Water Act
prohibit the discharge of process wastewater from uranium mills as the
degree of effluent reduction currently attainable. Taken together,
these controls may pose a problem of what to do with excess waste water
at certain locations where average annual precipitation approaches or
exceeds average annual evaporation. At these locations the only
discharge pathway for excess wastewater would be evaporation. It
appears from Table 3-1 that Texas is the only currently developed
uranium producing region where this may be a problem.
However, future uranium producing locations may be developed in
regions where the average annual precipitation exceeds annual average
evaporation. For these situations the NSPS may not apply since these
standards were developed for environmental conditions where the average
annual evaporation exceeds the average annual precipitation. The
standards also contain provisions in the event that the annual
precipitation exceeds the annual evaporation. This potential problem
may also arise for a new tailings impoundment at an existing uranium
processing site. In this case a determination would be required as to
whether a new impoundment would be considered a new source.
7. 4 Cos t-Ef f ec t iveness__Anal_y_s_es
7.4.1 W^ind E r o s ion
The levels of risk to the public from dust particle emissions from
uncontrolled tailings piles are relatively low. During the operational
phase of the model pile, the lifetime risk of fatal cancer to the
nearest individuals is estimated to be about 10~->, and the number of
cancer deaths in the population from 15 years of dust emissions range
from 0.03 for a rural site to 0.001 for a remote site. These risks can
be reduced to even lower levels through the use of dust control
measu res.
7-11
-------
Costs and benefits (health risk reductions) for various levels
of dust control for the model tailings pile for both the operational
and post-operational phases are presented in Tables 7-3 and 7-4,
respectively. A combination of chemical stabilization and water
sprinkling can achieve a 90-percent reduction in dust emissions. This
would result in a reduction from 10~5 to 10~° in the lifetime risk
of fatal cancer to the nearest individual and will prevent up to 0.03
fatal cancers (in the population living around the tailing pile at a
rural site) during the operation phase of the tailings pile, at a cost
of $630 thousand. For new tailings, the use of staged disposal in
combination with chemical stabilization can achieve a 94 percent
reduction in dust emissions. This would result in a reduction of the
risks similar to those just described, but at a smaller incremental
cost of $114 thousand.
7.4.2 Con tro_l^ of Radon
Costs and benefits for controlling radon emissions during the
operational phase of the model pile are presented in Table 7-5. For
existing tailings, keeping the tailings surface wet is the only
practical control method. Water sprinkling would achieve about a
20-percent reduction in the radon emissions. Over the term of the
operational phase this would prevent about 0.7 fatal cancers in the
population at a rural site and 0.2 fatal cancers at a remote site, but
would result in only a small reduction in the lifetime risk of fatal
cancer to the nearest individuals (i.e., from 1 x 10~3 to 8 x 10~^).
Table 7-3. Costs and Benefits of Various Levels of Control of Dust
Emissions for Model Tailings Pile During Operational Phase
(1981 dollars)
Present
Emission Worth Fatal Cancers
Reduction Cost Lifetime Risk ( Cancer s7l5~yT
Controls
None
A
B
A & B
B & D
(%)
0
50
80
90
94
($1000)
0
250
380
630
114
to Individual
l.OE-5
5.0E-6
2.0E-6
l.OE-6
6.0E-7
Rural Site
3.0E-2
2.0E-2
6.0E-3
3.0E-3
2.0E-3
Remote Site
l.OE-3
5.0E-4
2.0E-4
l.OE-4
6.0E-5
A=Water spray (truck).
B=Chemical Stabilization (Norlig A).
D=Staged Disposal (applicable to new tailings piles only).
Note: See Chapter 4 for description of rural and remote sites.
7-12
-------
Table 7-4. Costs and Benefits of Various Levels of Control of Dust
Emissions for Model Tailings Pile During Post-Operational Phase
(1981 dollars)
Controls
None
A
B
C
A & B
B & D
C & D
Emission
Reductior
(%)
0
50
80
90
90
94
97
Present
Worth
i Cost
($1000)
0
48
73
500
120
22
150
Lifetime Risk
to Individual
3.0E-6
2.0E-6
6.0E-7
3.0E-7
3.0E-7
2.0E-7
9.0E-8
Fatal_
( Cance
Rural Site
2.0E-2
l.OE-2
4.0E-3
2.0E-3
2.0E-3
l.OE-3
6.0E-4
Cancers.
rs7f5£T(a)
Remote Site
6.0E-4
3.0E-4
l.OE-4
6.0E-5
6.0E-5
4.0E-5
2.0E-5
A=Water spray (truck).
B=Chemical Stabilization (Norlig A).
C=Soil cover.
D=Staged Reclamation (applicable to new tailings piles only).
Note: See Chapter 4 for description of rural and remote sites.
^a'This is the lifetime risk to an individual who lives nearest the pile
during the 5-year post-operational period. The risks from the various
pathways are adapted from Tables 6-1 and 6-2.
7-13
-------
Table 7-5. Costs and Benefits of Various Levels of Control
of Radon Emissions from Model Tailings Pile During Operational Phase
(1981 dollars)
Controls
None
A
D
E
D & E
Emission
Reductior
(%)
0
20
70
90
95
Present
Worth
i Cost
($1000)
0
250
0
0
0
Lifetime Risk
to Individual
l.OE-3
8.0E-4
3.0E-4
l.OE-4
5.0E-5
Fatal
(Cance
Rural Site
3.6
2.9
1.1
4.0E-1
l.OE-1
Cancers
rs/lSyT^
Remote Site
1.2
1.0
4.0E-1
l.OE-1
4.0E-2
A=Water Sprinkling.
D=Staged Reclamation (applicable to new tailings piles only).
E=Below grade disposal in excavated pit with tailing covered with water
(applicable only to new mills).
Note: See Chapter 4 for description of rural and remote sites.
^a'Fatal cancers include those occurring in local, regional, and national
populations (see Tables 6-1 through 6-6 for the proportions in each).
7-14
-------
For new tailings, using staged disposal in combination with
below-grade disposal would allow most of the tailings to be covered
with water during the operational phase. This method can achieve a
high level of radon control (i.e., greater than 95 percent). This
would result in a reduction of the lifetime risk of fatal cancer to the
nearest individuals from 1 x 10~3 to 5 x 10"-* and would prevent 3.5
fatal cancers in the population at a rural site and 1.1 fatal cancers
at a remote site.
Using water covers or wetting the tailing surfaces are not
appropriate radon control methods during the post-operational phase.
The purpose of this predisposal period is to allow the tailings to dry
out to allow final disposal. The only way to reduce radon emissions
during the post-operational phase is to minimize the amount of exposed
tailings through the application of staged reclamation. This method is
applicable to new tailings only and would reduce the radon emissions
during the post-operational phase by 70 percent for the model tailings
pile. This would result in a reduction of from 1 x 10~3 to 3 x
10~^ in the lifetime risk to the nearest individual and would prevent
1.3 fatal cancers in the population at a rural site and 0.4 fatal
cancer at a remote site.
7.4.3 Control^ of. Seepage^ _to Groundwater
The benefits of groundwater protection are not easily
quantifiable. Maintaining the quality of the groundwater for future
uses is the primary benefit of protecting groundwater. At new tailings
piles, this can be accomplished by a two-step program:
1. Install a liner to prevent seepage of leachate into the
groundwater or, alternatively, select a site with
characteristics that have a high probability of protecting
groundwater, and
2. Conduct monitoring on a schedule that will assure early
identification of any hazardous constituents from the
tailings in the groundwater.
The cost of liners ranges from $9 to $12 million to achieve this
benefit. The additional cost of selecting a "good" site are
anticipated to be small compared with the cost of a liner. The cost of
a monitoring program is negligible when compared to liner costs.
At existing tailings piles the benefits of groundwater protection
are the same, i.e., preserving the groundwater quality for future
uses. Costs, however, can range from small, where groundwater is
currently adequately protected due to site characteristics, up to
large, when transfer of tailings to a new, lined tailings pond is
required to protect groundwater.
7-15
-------
REFERENCES
De74 Dean K.C., Havens R., and Glantz M.W. , "Methods and Costs for
Stabilizing Fine-Sized Mineral Wastes," Report No. 7896, Bureau
of Mines, U.S. Department of the Interior, Salt Lake City,
Utah, 1974.
Ha69 Havens R. and Dean K.C., "Chemical Stabilization of the Uranium
Tailings at Tuba City, Arizona," Report 7288, Bureau of Mines,
U.S. Department of the Interior, Salt Lake City, Utah, 1969.
Ma82 Private communication; Paul Magno of the Environmental
Protection Agency with the Nuclear Regulatory Commission, 1982.
NRC80 Nuclear Regulatory Commission, "Final Generic Environmental
Impact Statement on Uranium Milling," NUREG-0706, USNRC,
Washington, D.C., September 1980.
NRC81 Nuclear Regulatory Commission, "Radon Release from Uranium
Mining and Milling and their Calculated Health Effects,"
NUREG-0757, USNRC, Washington, D.C., February 1981.
PE82 PEDCO Environmental, Inc., Evaluation of Costs to Control
Fugitive Dust from Tailings at Active Uranium Mills, EPA
Controct No. 68-02-3173, Task No. 053, USEPA, Washington, D.C.,
March 1982.
We80 Werthman P.H. and Bainbridge K.L., "An Investigation of Uranium
Mill Wastewater Treatability," EPA Contract No. 68-01-4845,
1980.
7-16
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Chapter 8: OBJECTIVES AND METHODS FOR TAILINGS DISPOSAL
8.1 Health and Environmental Protection Objectives
Based on the results in the preceding chapters, we have identified
the following objectives for these standards.
1. To prevent future use of tailings in or near buildings. The
widespread past use of tailings around foundations or in
construction materials has caused an increase of radon decay
products in buildings, leading to increased risk of
radiation-induced lung cancer.
2. To protect people from radon emanating from tailings piles.
Radon exposure of people living in the vicinity of tailings
piles leads to increased risk of lung cancer. Also, since
radon is a chemically inert gas with a radioactive half-life
of 3.8 days, radon released from tailings can travel long
distances before it decays. As the radon decays, it exposes
large numbers of people to low levels of radiation.
3. To prevent the surface spread of tailings. Tailings may be
spread by wind and water. This can cause radiation exposure
of local residents from both radon decay products and gamma
radiation. In addition, the spread of tailings may
contaminate surface water.
4. To protect groundwater. Contamination of groundwater occurs
when water comes in contact with tailings or leaches
radioactive and toxic materials from the tailings and then
moves into a groundwater aquifer through fissures, percolation,
or by other means. The degree of risk to man and livestock
depends on the concentrations of contaminants in the water and
the uses of the water (human consumption, livestock watering,
irrigation, etc .).
Because of the long lifetimes of the radioactive contaminants in
tailings and the presence of toxic materials (which do not decay), the
potential for harming people by any of the above pathways will persist
essentially indefinitely. It is therefore necessary to satisfy the
-------
above objectives for as long a period as practical. Many factors
affect the long-term effectiveness of tailings disposal methods. They
include external phenomena, such as erosion by wind and rain,
earthquakes, floods, and glaciers; internal chemical and mechanical
processes in the piles; and human activities. Predictions of the
stability of disposed tailings become less certain as the time period
increases. Beyond several thousand years, long-term geological
processes and climatic change will govern the effectiveness of most
control methods.
These objectives are interrelated. For instance, radon control
may be achieved by placing a thick earth cover over the tailings. This
method also controls the spreading of tailings, attenuates external
gamma radiation, prevents groundwater contamination, and isolates the
tailings.
Methods to prevent radon emissions into the atmosphere range from
the use of simple barriers to delay the release of radon until it has
decayed, to more complex means, such as incorporating tailings into
asphalt or concrete, or chemical processing to remove the radium and
thorium. Radon control assessment is straightforward and can be
quantified for most disposal methods.
Various methods can be used for isolating tailings, ranging from
temporary measures, such as fencing, to more permanent measures, such
as using a simple earthen cover or deep disposal. Greater amounts of
material, such as earth, placed between the tailings and the environment
increase the isolation of the tailings. Isolation here means the
degree to which man is discouraged from intruding into the tailings.
Protection from external gamma radiation is achieved by placing
materials of sufficient mass over the source of the penetrating (gamma)
radiation. Thus, a plastic sheet will have essentially no effect on
gamma levels, whereas a layer of earth is quite effective.
Methods for control of windblown and precipitation-carried
tailings include soil and plastic coverings, chemical and asphalt
binders sprayed on the tailings, grading and contouring to eliminate
steep slopes, rock covers, and revegetation. Some methods, such as
chemical and asphalt sprays, do not last long on tailings and are more
suitable for use during the operating phase of a mill.
Methods for preventing contamination of groundwater fall into four
groups:
1. Placing a barrier between the tailings and the aquifer which
will either prevent the movement of water from the tailings to
the aquifer (or vice versa) or will remove hazardous materials
by adsorption.
2. Fixing the tailings into a solid mass that prevents the
leaching of hazardous materials from tailings by water.
8-2
-------
3. Contouring and covering to minimize the movement of
precipitation into tailings.
4. Selecting a site that is far removed from aquifers, with
characteristics that minimize the movement of water into or
out of tailings, and/or that provide natural adsorption of
hazardous materials.
Not all these methods are feasible for every tailings pile. Some
are only appropriate for new tailings. A significant factor is that
most existing uranium mills are located in arid areas of the western
United States where natural evaporation generally exceeds precipi-
tation. The selection of a site can eliminate the need for a liner, if
the soil has the needed permeability and adsorption characteristics.
Disposal methods could also be different for mill sites where abandoned
surface mines or natural land depressions are nearby.
8.2 Longevity of Cont_rol
Mill tailings will be hazardous for hundreds of thousands of
years. Although economically feasible methods which assure control for
such long-term periods are beyond present knowledge and experience, we
do know enough to provide protection at reasonable cost--for periods of
hundreds to thousands of years.
Control failures can occur through natural phenomena or through
human intrusion. Natural phenomena, such as erosion and deposition,
flooding, climatic change, earthquakes, vulcanism, and glaciation can
change the landscape. Human disturbance can also take a number of
forms, ranging from constructing buildings to drilling, mining, and dam
building. Not all of these activities would cause control failures,
however; at some sites, human intrusions and natural phenomena may
actually increase isolation of the tailings by depositing additional
materials or soil on the tailings. The longevity of protection
achievable will vary considerably from site to site.
In the following discussion we group controls into two broad
classes: those that depend on active institutional maintenance, and
those that do not. Active measures include fences, guards, repair of
drainage channels, replacement of eroded cover, and maintenance of
vegetative cover. Unfortunately, there is no general consensus on the
length of time human institutions will remain effective or reliable to
continue such active measures. In this regard, failure of institu-
tional controls does not necessarily imply a complete breakdown of
societal structure. The more likely situation would be failure of
institutional controls through program reductions, reorganization,
changes in priorities, or through the failure of special funding
mechanisms.
8-3
-------
8.2.1 Human Intrusion
The effectiveness of controls in preventing intrusion over long
time periods is difficult to evaluate. Probably the worst scenario is
the use of tailings as a resource for construction material by
residents of a nearby population center. This can (and has) led to
widespread use of tailings around, under, and in residences, schools,
and other inhabited structures. Any easily removable or attractive
control materials have a potential for promoting misuse. Examples are
fences and small-sized rock covers.
Prevention of intrusion for long periods is more likely to be
successful by using passive methods. Thick earth covers, for example,
provide significant long-term passive protection against intrusion.
Other effective passive methods include heavy rock cover, deep-mine
disposal, below-grade disposal, solidification in a cement or asphalt
mixture, or coverings of a tailings-cement mix.
8.2.2 Ero s_io_n
All surface disposal methods are subject to erosion. Some
representative values for average coil erosion rates in the United
States are given in Table 8-1. These erosion rates are averages and
thus do not mean that the surface is lowered uniformly by that amount.
Widely varying rates of erosion, and also of deposition, can be
found within any drainage basin. High gradient and elevated areas will
experience much higher-than-average rates, and depressed areas will, in
general, experience deposition, rather than erosion. These rates are
most applicable to the below-grade surface disposal option.
Erosion rates for above-grade disposal will be greater. Erosion
rates for the Colorado River basin vary between 0.09 and 0.25 meters
per 1,000 years. Wind erosion is expected to be much greater for
tailings disposed of above grade, depending on the effectiveness of
vegetative or other surface treatment. Loss of vegetation will
increase water erosion. Rock cover will greatly reduce wind erosion.
The maximum rate of erosion occurs in areas with about 10 inches (25
cm) of rainfall per year (Fo71). This annual rainfall is typical of
the uranium milling areas in the western United States.
8.2.3 floods
Floods are probably the greatest natural hazard to the integrity
of tailings piles. Piles can be protected against floods by
constructing appropriate barriers or by not locating them Ln flood
plains. Some of the measures available for protecting piles left in
place are: grading the piles so that the sides of the piles have
gradual slopes; providing protective rock covers on the slopes (and on
the top if needed); and constructing embankments or dikes on the sides
of the piles or at other locations to divert anticipated rapidly moving
8-4
-------
flood waters. The exposed sides of embankments can be protected by
rock. When the vulnerability to floods is so great that disposal in
place is inadequate, piles can be moved to less vulnerable sites.
Table 8-1. Soil Erosion Rates in the United States
Erosion Rate
(cm/1,000 years)
6
4
17
5
9
5
25
5
3
Measurement
Technique
River load*
River load
River load
River load
River load
Radioactive
dating
River load
River load
River load
Comments
Average for U.S.
Columbia River
Colorado River
Mississippi River
Colorado River
Amount of erosion of
volcanic extrusion
southern Utah
Colorado River
Average for U.S.
Average for North
American continent
Reference
Ju64
Ju64
Ju64
Ha75
Ha75
Ha75
in
Yo75
Da76
Pr74
*River load refers to erosion rate estimates based on the sediment
load (dissolved and detrital particles) carried by rivers.
Flood protection design must be based on prediction of infrequent
high-magnitude floods.
It is customary to rank the severity of floods in terms of the
average time over which floods of a given size or greater may be
expected to recur. For example, there will be an Average of 5 floods
in 1,000 years that exceed the "200-year flood." The maximum probable
flood (MPF), on the other hand, is the largest flood that one would
expect to occur in a given region in a given climatic era. Historical
records are generally of too short a duration to determine the size of
3-5
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such floods. Geomorphic data are most useful for determining the past
rate of occurrence of these very large floods (Cob78). When such data
are unavailable, the MPF can be estimated from historical records, but
such estimates are frequently inadequate.
Another measure of flood severity that is sometimes used as a
design criterion is the Standard Project Flood (SPF), which results
from the most severe combination of weather and hydrologic conditions
that are reasonably characteristic of the region involved, excluding
extremely rare combinations.
The "design flood" is the flood adopted as the basis for flood
protection for a facility after considering both hydrologic and
economic factors. In most areas, the characteristics of relatively
short-term floods, such as the 50-year flood, have been well
established, and engineers can routinely design facilities to be
protected from such events. Where the failure of flood protection
systems could result in loss of lives and/or great property damage,
however, a design based on the MPF may be justified. The SPF is often
considered an appropriate intermediate design basis for situations in
which some risk is tolerable, and the added cost of providing greater
protection is significant. Fortunately, the differences between these
classes of floods is not always great in terms of the projected height
of flood waters or the design characteristics required for protection.
However, difference in water velocity at different locations can be
significant, and protective systems must be designed for the site.
Uncertainties in the performance specifications required may
affect the practical design of long-term flood protection systems. The
characteristics of very long-term floods, such as the 1,000-year flood,
are usually much less certain than those of floods that have recurred
frequently during historical periods. Furthermore, because of
potential damage from erosion and earthquakes, confidence in the
ability of conventional flood protection systems to withstand a flood
declines with time. In view of these combined uncertainties,
conservatively designed systems are required to satisfy very long-term
flood protection requirements.
8.2.4 Longe_vity o_f _Cpntrol
We have chosen two time periods for evaluating the longevity of
effective control. A short time period of 100 years was chosen for one
case, since this has been proposed as the limit for reliance on
institutional controls (EPA78). A period of about 1,000 years was
selected for the second case. This case displays the difference
between active and passive controls, as well as the expected variation
of effectiveness of controls over longer time periods.
8-6
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In general, the longevity of controls over time can be rated as
follows:
Highest • Deep geological disposal.
• Below-grade surface disposal.
e Above-grade surface disposal, entire area covered
with thick earth and rock cover.
• Above-grade surface dispoal, entire area covered
with thick earth, slopes covered with rock.
• Above-grade surface disposal, entire area covered
with thick earth.
Lowest e Above-grade surface disposal, entire area covered
with thin earth and maintained.
This ranking assumes the tailings pile is located where erosion
occurs. If tailings are located where soil deposition is taking place,
the ranking will be equal for all cases as long as deposition continues.
8.3 Disposal Methods and Effectiveness
8.3.1 Earth Covers
Earth placed over tailings slows the movement of radon into the
atmosphere by various attenuation processes. When the earth is moist,
attenuation increases. Different soils have different attenuation
properties; these can be quantified in terms of a quantity called the
"half-value layer" (HVL). The HVL is that thickness of cover material
(soil) that reduces radon emission to one-half its value. Figure 8-1
shows the percentage of radon that would penetrate various thicknesses
of materials with different HVLs. These values are nominal; the actual
HVL may vary significantly. From Figure 8-1 it can be seen that 3
meters of sandy soil (HVL =1.0 meters) will reduce the radon released
from tailings by about 90 percent. Soils with better attenuation
properties would require less thickness to achieve the same reduction.
For example, 1 meter of compacted moist soil (HVL = 0.3 meters) would
also reduce the radon release by about 90 percent.
A more complete treatment of radon attenuation based on the work
of Rogers (Ro81), is given in Appendix P of the NRC Generic EIS for
mill tailings. That analysis concludes that the effectiveness of an
earthen cover as a barrier to radon depends most strongly on its
moisture content. Typical clay soils in the uranium milling regions of
western United States exhibit ambient moisture contents of 9 percent to
12 percent. For nonclay soils, ambient moisture contents range from 6
percent to 10 percent. The following table provides, as an example,
8-7
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06
W
o
o
M
i
H
W
loo r
90 -
SANDY SOIL (HVL =1.0 m)
SOIL (HVL = 0.5 m)
COMPACTED, MOIST SOIL
(HVL = 0.3 m)
CLAY (HVL = 0.12 m)
2345
COVER THICKNESS (METERS)
Figure 8-1. Percentage of Radon Penetration of Various
Covers by Thickness.
8-8
-------
the cover thicknesses needed to reduce the radon emission to
20 pCi/m^s for the above ranges of soil moisture. Three examples of
tailings are shown that cover the probable extreme values of radon
emissions from bare tailings at existing sites (100 to 1000 pCi./m2.s);
the most common values lie between 300 pCi/m2s and 500 pCi/rn?s,
Table 8-2. Estimated Earthen Cover Thickness
(in meters) to Reduce Radon Emissions to 20 pCi/m2,s
Radon Emission
from Tailings
Percent Moisture Content oE'Cover
(pCi/m s) 6 8
10
12
100
300
500
1000
1.
2.
3.
4.
7
8
4
1
1.
2.
2.
3.
3
1
6
2
1.
1.
2.
2.
0
5
0
4
0.
1.
1.
1.
7
1
5
8
These values are for simple homogeneous covers. In practice,
multilayer covers using clay next to the tailings can significantly
reduce the total thickness required (Ge81).
The thickness of earthen cover needed to provide isolation is not
directly calculable. Perhaps the best approach is to review the depths
to which excavations for common activities are made. Excavations are
routinely made to 6 to 8 feet for public utilities (water and sewer
pipes, power lines, telephone lines). Footings for house foundations
are often placed at an 8-foot depth. In colder climates it is
important that water lines and foundations be placed below the frost
depth to avoid freezing problems. Graves are also dug to a depth of 6
feet or more.
Since digging to or below these depths is common, a significantly
greater thickness would be required for isolation against the unlikely
event that structures are built on or utility piping is installed al
tailings disposal sites. To provide reasonable isolation against such
hazards, an earthen cover should have a minimum thickness of 3 meters.
The amount or thickness of earth that will attenuate gamma
radiation to one-half its initial value is also called a half-value
layer (HVL). As with radon adsorption, the HVL for gamma attenuation
depends on soil composition, compaction, moisture content, and otJier
factors. The average HVL of compacted soil for gamma radiation from
tailings is about 0.1 meter. Therefore, a soil thickness of 0.5 meter
will reduce the gamma radiation to about 3 percent of its initial value
8-9
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from the uncovered tailings, and 1 meter of soil would reduce it to
about 0.1 percent of its initial value.
A model tailings pile is assumed to have a radium-226
concentration of 280 pCi/g. This produces a gamma-absorbed dose rate
in air of about 4,000 mrad/year on top of the uncovered tailings,
assuming a homogeneous distribution of radium-226 in the tailings. An
earth covering of 1 meter would reduce this absorbed dose rate in air
to about 7 mrad/year. This is slightly less than the total gamma dose
from the uranium-238 series under average background conditions.
Earthen covers can also prevent the movement of tailings by wind
and water. A combination of grading and contouring slopes, covering
with 0.5 meter of earth, landscaping, and continuing maintenance is
considered the minimum control for these pathways, as long as
maintenance is continued. Longer term protection can be provided by
thicker earth covers, and rock or other forms of surface stabilization.
8.3.2 Basin and Pond Liners
Liners are materials placed on the botton of a tailings retention
basin or pond to prevent or reduce the seepage of water into the
underlying soil. Liners can be made of clays, asphalts, concretes, and
polymers (plastics), or various combinations of these (Ba81, Bu81,
NRC80).
Agency policy on the use of liners for groundwater protection was
delineated in recently promulgated regulations under the Solid Waste
Disposal Act (EPA82). A liner placed beneath the waste in a land
disposal unit is often a key element of a general liquids management
strategy. However, liners are just one component of an overall liquid
management system. A liner is a barrier that prevents or greatly
restricts migration of liquids into the ground. No liner, however, can
keep all liquids out of the ground for all time. Eventually, liners
will either degrade, tear, or crack and will allow liquids to migrate
out of the unit. It is, therefore, important that liquids be removed
during the time that the liner is most effective. Leachate collection
and removal systems at landfills and measures to remove free liquids
from surface impoundments at closure are the principal techniques used
to remove liquids.
The Agency view of the function of a liner contrasts with that of
some members of the public and the regulated community. Some view
liners as devices that provide a perpetual seal against any migration
from a waste management unit. The more reasonable assumption, based on
what is known about the pressures placed on liners over time, is that
any liner will begin to leak eventually. Others have argued that
liners should be viewed as a means of retarding the movement of liquids
from a unit for some period of time. While this view accords with how
liners do in fact operate, this represents an incomplete regulatory
8-10
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strategy for groundwater protection because it achieves only a delay of
the appearance of groundwater contamination rather than a permanent
solution. Accordingly, liners should be viewed as a barrier best used
to maintain control of liquids prior to their removal from the waste
management unit during its active life. Assurance of long-term
protection is best achieved by a combination of removal of excess
liquids and prevention of influx of new liquids after disposal.
Thus, while liners may remain effective for preventing migration
from the unit until well after disposal, their principal role occurs
earlier. In final disposal, the Agency believes that a protective cap
becomes the prime element of the liquids management strategy. A
well-designed and carefully maintained cap can be quite effective at
reducing the volume of liquids entering a unit and therefore can
substantially reduce the potential for leachate generation at the unit
for long periods.
The Battelle Pacific Northwest Laboratory group has performed a
comprehensive review of liners (Bu81). They selected seven materials
for laboratory testing (Ba81) on the basis of their potential
usefulness as liners for uranium mill tailings ponds. These materials
were asphalt concrete, asphalt rubber, catalytic airblown asphalt,
Hypalon (a chlorosulphonated polyethylene), sodium-bentonite, saline
seal-100 bentonite, and GSR-60 bentonite. They also tested a native
soil at one of the alternative disposal sites for the Durango,
Colorado, inactive tailings pile. The materials were tested for
permeability (increased permeability is caused by failures through
chemical attack of the asphalts and synthetics or through reduction of
the ion exchange capacity of the clays), physical stresses, and
radiation damage. Based on laboatory tests, expected field
effectiveness, and a cost analysis, the liners selected for field
studies were a catalytic airblown asphalt-and-soil amended with
sodium-bentonite.
For this analysis, to protect groundwater before the final
disposal of the tailings, a 1-meter clay liner must be installed on the
bottom and sides of a disposal pit. The clay must have permeability
and adsorption properties appropriate for the site and tailings
contaminants. Earthen cover is assumed to provide an adequate cap,
after disposal, to control influx of water in the arid western regions
typical of U.S. uranium mills.
8.3.3 Thermal Stabilization
Thermal stabilization is a process in which the tailings are
sintered at high temperatures. The Los Alamos Laboratory has conducted
a series of tests on tailings from four different inactive mill sites
(Dr81). Tailings were sintered at temperatures ranging from 500° to
1200° C. Tests were then run on the various properties of these
tailings. The results are presented in Table 8-3.
8-11
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Table 8-3. Percent Reduction in Emanating Ra-226
at Temperatures from 500° to 1200° C^a^
Sintering
Temperature
500
600
700
800
900
1000
1100
1200
Shiprock, N.M. , Pile
Sands Fines
15
29
44
63
83
92
96.4
97.7
16
27
37
58
84
96.1
98.8
99.2
Durango, Colo., Pile
Sands Fines
48
64
76
87
92
95.5
99.0
99.5
61
68
80
88
91
92
99.
99.
8
8
(a)r treated tailings
untreated tailings
^"'Original emanating Ra-226:
Shiprock sands = 39 pCi/g.
Shiprock fines = 214 pCi/g.
Durango sands = 140 pCi/g.
Durango fines = 473 pCi/g.
These results indicate that thermal stabilization can be quite
effective in preventing the release (emanation) of radon from
tailings. The authors note that before thermal stabilization can be
considered as a practical disposal method, information is needed on the
following:
1. The long-term stability of the sintered material exposed to
physical degradation and chemical attack (e.g., solubility of
new minerals and amorphous material found in thermally
stabilized tailings).
2. The interactions of the tailings and the refractory materials
lining a kiln.
3. The gaseous and particulate emissions produced during
sintering of tailings.
4. Revised engineering and economic analysis as more information
is developed.
B-12
-------
Since gamma radiation is still present, protection against the
misuse of sintered tailings is still required. While the potential
health risk from external gamma radiation is not as great as that from
the radon decay products, it can produce unacceptably high exposure
levels in and around occupied buildings. Also, the potential for
groundwater contamination may require the use of liners.
8.3.4 Chemical Processing
The Los Alamos National Laboratory has also studied various
chemical processes to remove thorium-230 and radium-226 from the
tailings, along with other minerals (Wm81). After removal from the
tailings, the thorium and radium can be concentrated and fixed in a
matrix such as asphalt or concrete. This greatly reduces the volume of
these hazardous materials and allows disposal with a higher degree of
isolation than economically achievable with tailings.
The NRG has considered the processing of uranium ore in a nitric
acid mill (NRC80). This chemical process would strip a large fraction
of the thorium and radium from the ore, along with uranium and other
minerals. The thorium and radium would then be concentrated, fixed in
a matrix, and disposed of in a manner similar to the process just
described for sulfuric acid treatment of the tailings.
The major question regarding both these processes is whether they
reduce the thorium and radium values in the stripped tailings to safe
levels. If processing efficiencies of 80 percent to 90 percent were
attained, radium concentrations in tailings would still be in the 30 to
60 pCi/g range. This concentration can cause excessive levels of radon
decay products in occupied structures if these treated tailings were
placed under or around the structures. Thus, careful disposal of the
stripped tailings would still be required to prevent misuse. Another
disadvantage of chemical processing is the cost, although some of the
costs might be recovered from the sale of other minerals recovered in
the processing (Th81). The value of other minerals can be expected to
vary greatly (Th81) from ore to ore.
8.3.5 Soil Cement Covers
A mixture of soil and Portland cement, called soil cement, is
widely used for stabilizing and conditioning soils (PC79). It is used
to condition subsoils under highway pavements, to serve as a base for
large parking lots where it is covered with asphalt, and to stabilize
slopes by preventing erosion, among other uses.
The aggregate sizes of tailings appear suitable to make a good
quality soil cement, which is relatively tough, withstands freeze/thaw
cycles, and has a compressive strength of 300 to 800 psi. When
combined in a disposal system with a 1-meter earth cover over it, soil
(tailings) cement would be likely to provide reasonable resistance to
8-13
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erosion and intrusion, to substantially reduce radon releases, and to
shield against penetrating radiation. Its costs are expected to be
comparable to those of thick earth covers.
The long-term performance of soil cement is unknown, especially as
tailings piles shift or subside with age. Also, soil cement cracks at
intervals when placed over large surface areas. The importance of this
cracking on the effectiveness of soil cement has not been evaluated,
but is expected to be small.
8.3.6 Deep-Mine Disposal
Disposal of tailings in worked-out deep mines offers several
advantages and disadvantages compared to surface disposal options. The
probability of intrusion into and misuse of tailings in a deep mine is
much less than that achievable with surface disposal. Radon releases
to the atmosphere would be eliminated, for practical purposes, as would
erosion and external radiation.
The greatest problem with deep mine disposal is the potential
contamination of groundwater. This problem is most difficult to
evaluate, especially over the long term. Also, this method would be
cost-effective for only those mills near deep mines because of the high
cost of transporting tailings.
8.3.7 Solidification in Concrete or Asphalt
This disposal method separates the sands fraction of the tailings
from the slimes fraction. The sands make up the greatest part of the
tailings weight, while most of the radioactive material is in the
slimes. After separation, the sands are washed and discharged into a
surface pit. The slimes are separated from the water, dried and then
solidified in concrete or asphalt. The solidified slimes can then be
disposed of in the pit with the sands or by other methods offering more
isolation. The NRC analyzed this method in some detail, including a
cost evalution (NRC80).
Since about 15 percent of the radioactivity is in the sands, this
fraction will contain about 40 pCi/g of radium-226.
This concentration can lead to an excessive buildup of radon in
structures if these sands are misused under and around structures.
Thus, the sands fraction will require a barrier, such as an earth
cover, to isolate them and to prevent misuse . Also, since toxic
metals will be present in both fractions (CoaSl), a liner may be needed
to protect groundwater from the sands fraction.
Overall, this method is costly, provides a relatively high level
of protection from 85 percent of the radioactivity in the tailings, but
provides little protection from the remaining radioactivity and toxic
materials unless additional controls are used.
8-14
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8.4 Selection of Disposal Method For This Analysis
Earthen covers were selected for analysis for the following
reasons:
1. Thick earthen covers are effective in preventing
misuse of tailings, in reducing radon emissions,
in protecting groundwater for long-term periods,
and in resisting erosion.
2. Thick earthen covers can be made long lasting by
stabilizing the surface with vegetation and/or
rock.
3. Costs are relatively low and can be estimated
with some degree of certainty.
An option providing a very high degree of protection was also
selected for the analysis. In lieu of any clearly superior disposal
method, regardless of cost, the solidification method was chosen.
8-15
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REFERENCES
Ba81 Barnes S.M., Buelt J.L., and Hale V.Q., "Accelerated Aging Tests
of Liners for Uranium Mill Tailings Disposal," DOE/UMT-0205,
PNL-4049, Pacific Northwest Laboratory, Richland, Washington,
9935?, Nove-nber 1981.
Bu81 Buelt J.L., Hale V.Q., Barnes S.M., and Silviera D.J., "An
Evaluation of Liners for a Uranium Mill Tailings Disposal Site -
A Status Report," DOE/UMT-0200, PNL-3679, May 81.
CoaSl Cokal E.J., ireesen D.R., and Williams J.M., "The Chemical
Characteristics and Hazard Assessment of Uranium Mill Tailings,"
in: Proceedings of the 4th Symposium on Uranium Mill Tailings
Management, Fort Collins, Colorado, October 1981.
Cob78 Costa J.R., "Holocene Stratigraphy in Flood Frequency Analysis,"
Water'Resources Research, pp. 626-632, August 1978.
Da76 Davis S.N., Reitan P.M. and Pestrong R., "Geology, Our Physical
Environment," McGraw-Hill, New York, 1976.
Dr81 Dreesen D.R., Williams J.M. and Colsal E.J., "Thermal
Stabilization of Uranium Mill Tailings," in: Proceedings of the
4th Symposium on Uranium Mill Tailings Management, Fort Collins,
Colorado, October 1981.
EPA78 Environmental Protection Agency, "Criteria for Radioactive
Wastes," Federal Register, 43 FR 53262, November 15, 1978.
EPA82 Environmental Protection Agency, "Hazardous Waste Management
System; Permitting Requirements for Land Disposal Facilities,"
40 CFR Part 264 (47 FR 32274), July 26, 1982.
Fo71 Foster R.J., "Physical Geology," 2nd ed., Merrill, Columbus,
1971.
Ge81 Gee G.W., et. al., "Radon Control by Multilayer Earth Barriers:
2. Field Tests," in: Proceedings of the 4th Symposium on
Uranium Mill Tailings Management, Fort Collins, Colorado,
October 1981.
Ha75 Hamblin W.K., "The Earth's Dynamics Systems," Burgess,
Minneapolis, 1975.
Ju64 Judson S. and Ritter D.F., "Rates of Regional Denudation in the
United States," Journal of Geophysical Research, Vol. 69, pp. 3395-
3401, 1964.
8-16
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REFERENCES (Continued)
NRC80 Nuclear Regulatory Commission, "Final Generic Environmental Impact
Statement on Uranium Milling," NUREG-0706, September 1980.
PC79 Portland Cement Association, "Soil-Cement Construction Handbook,"
EB003.09S, Skokie, 111., 1979.
Pr74 Press F. and Siever R., "Earth," W.H. Freeman and Company, San
Francisco, 1974.
Ro81 Rogers V.C. and Nielson K.K., "A Handbook for the Determination of
Radon Attenuation Through Cover Materials," NUREG/CR-2340, Nuclear
Regulatory Commission, Washington, B.C., November 1981.
Th81 Thode, E.F. and D.R. Dreesen, "Technico-Economic Analysis of
Uranium Mill Tailings Conditioning Alternatives," in: Proceedings
of the 4th Symposium on Uranium Mill Tailings Management, Fort
Collins, Colorado, October 1981.
Wm81 Williams J.M., E.J. Cokal, and D.R. Dreesen, "Removal of
Radioactivity and Mineral Values from Uranium Mill Tailings," in:
Proceedings of the 4th Symposium on Uranium Mill Tailings
Management, Fort Collins, Colorado, October 1981.
Yo75 Young K., Geology: "The Paradox of Earth and Man," Houghton-
Mifflin, Boston, 1975.
8-17
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Chapter 9: ALTERNATIVE STANDARDS FOR TAILINGS DISPOSAL
In this chapter we first consider the various quantities which can
be used to express limitations on environmental releases. We then
formulate alternative standards that accomplish, in varying degrees,
the objectives set forth in Chapter 8. Finally, we determine the cost
of controls required to implement each of these alternatives.
9.1 Form of the S_tan_dards
9.1.1 Dose or Exp_psure Rate Limits
Health protection standards based on radiation dose or exposure
have two major advantages. First, the health risk to an individual can
be limited directly. Second, the cumulative risk from all pathways to
humans from the source is included. Partly because of these advantages,
the Federal Radiation Council Radiation Protection Guidance for Federal
Agencies (FRC60) and the Environmental Radiation Protection Standards
for Uranium Fuel Cycle Operations (40 CFR 190) (EPA77), with the
exception of the standards for certain long-lived radionuclides, are in
this form.
However, dose or exposure rate limits are not useful in
establishing health protection standards in connection with the
disposal of uranium mill tailings because they have an inadequate
relationship with some of the principal objectives of disposal, such as
preventing misuse of the tailings and controlling radon emissions from
tailings for a long period of time. Establishing an environmental dose
rate limit (or Working-Level Limit) near a tailings pile gives no
assurance of providing a long-lasting barrier controlling radon or of
inhibiting the use of tailings. In addition, limits on dose imply a
need to know the locations of individuals for long periods of time in-
to the future. Unless an exclusion area can be maintained indefi-
nitely, conformance to a dose limit could not be assured.
9.1.2 Concentration Limit_s__in Air and Water
The primary advantage of standards specifying concentration limits
of hazardous or toxic materials in air or water is ease of compliance.
Most monitoring involves measurements of concentrations in environmental
media. Thus, monitoring results can be compared to concentration
9-1
-------
limits to determine compliance. This is a useful approach in
evaluating the. performance of emissions and effluent controls at
operating facilities.
Concentration limits of radon in air can assure a given level of
performance of control measures. The relationship between radon
emissions from a pile and off site concentrations of radon in air is
presented i ri Chapter 5.
Concentration limits are appropriate for the water pathway; EPA
groundwater protection policy, which dictates the form of groundwater
standard i-- cities concentration limits.
9. 1.3 Releas_e^ Rate Limits
This form or standard is useful for controlling emissions when
either total quantities discharged or ambient levels of a pollutant are
of concern. It is also useful for controlling emissions and effluents
when it is desirable to force a specific level of control.
Because of these advantages a release rate limit approach appears
to offer the best choice of- accomplishing the primary objectives of
these standards. A release rate limit can assure that an effective and
durable barrier controls radon emissions and isolates the tailings from
the environment. This barrier can also provide significant assurance
that the tailings would not be removed from the site and used in and
around occupiable structures.
9.1.4 Erigi ne e r i ng/De_s_ign S ta^d££d_£
Engineering or design standards specify methods or procedures and
the critical dimensions or characteristics of the method. Such
standards have the advantage of directly assuring a solution of the
problem, For tailings disposal, a design standard could require that
tailings be covered with a certain type of soil to a minimum thickness
and with a maximum slope. Soil stabilization methods could also be
spelled out, such as rock cover on the slopes and vegetation over the
remainder of the disposal site.
Several disadvantages are inherent in design standards. They tend
to squelch ingenuity and initiative to develop improved and less costly
methods. They do not reflect the variations in local conditions that
may lead to greater health protection if properly utilized or exploited.
They are difficult to change or modify. The disadvantages of design
standards appear to outweigh the advantages for use in the disposal of
uranium mill tailings. In addition, the legislative history of the Act
does not support the use of such standards.
A second approach in engineering/design standards can be based on
probabilities considerations. In this form, the primary objective of
the standard is stated clearly. Then probabilities (in quantified
9-2
-------
terms) are assigned for achieving the primary objective during various
future periods. For example, in the near term, the numerical
probability assigned to meeting the primary objective could be high.
For longer periods, the probability could be reduced, reflecting
inability to predict the effectiveness of controls over longer times.
Compliance with a probability-based standard uses models, which
project the future performance of control methods, and expert views.
The advantage of this approach is that it forces an appraisal of the
long-term hazards associated with the tailings. However, the present
state of the art for tailings disposal does not permit the use of
numerical probability-based design standards.
9. 2 Alt_ernative Pispos_a!__Standa r ds
We have evaluated a range of alternatives for disposal standards
based on the objectives described in Section 8.1, the most likely
disposal method chosen in Chapter 8, and the form of the standard
considered in Section 9.1. These alternatives are presented in
Table 9-1. The requirements selected to meet the objectives are shown
tor each alternative. Most of the requirements are expressed quantita-
tively, and in combination they achieve the overall objective of
reducing risks to people from tailings. The ranges of the controls
vary widely, from no control (Alternative A) to high levels of control
(Alternatives E and F).
Uranium mill tailings will remain hazardous for hundreds of
thousands years due to the 75,000-year half-life of thorium-230.
Protecting public health for such periods of time is difficult to
conceptualize, much less assure. On a practical basis, controls
reasonably can be relied on for periods defined as:
• Active control—a maximum period of about 100 years.
• Available and practical engineering controls—a period
extending from a few hundred years to perhaps 1,000 years.
• Controls featuring great isolation—a period of thousands of
years limited by major geological activity.
These periods will be used in the ensuing discussions of
alternative standards.
Alternatives A through F were designed to consider 6 progressively
more stringent levels of protection.
Alternative A. This alternative is the "no standards" case and
represents conditions if nothing is done. The piles will remain
hazardous for a long time, taking about 265,000 years for the
radioactivity to decay to 10 percent of current levels. The radon
9-3
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Table 9-1. Alternative Standards for Disposal of Uranium Mill Tailings
C
D
E
F
Minimum Time
Controls Should
Prevent Erosion
Radon Emissions
Permitted from
Expected Time
Controls Should
Alternative
Standard
A
B
and Misuse
(years)
None
100 (with
Top of2Pile
(pCi/m -sec)
No limit
No requirement
Protect Groundwat«
(years)
None
100
institutional
controls)
Indefinite
200-1,000
1,000
> 1,000
60
20
20
2
> 100
1,000
1,000
> 1,000
9-4
-------
emission rate from a model pile is estimated to be 280
compared to a background rate for typical soils of about 1
We also know that the concentration of some toxic chemicals in the
tailings Ls hundreds of times background levels in ordinary soils, so
that the potential for contaminating groundwater is present and
continues indefinitely.
AlEernative B. This alternative specifies that control measures
include a durable cover that is subject to inspection and maintenance
requirements for 100 years. Institutional controls (inspection and
maintenance) would also be required to prevent significant contamina-
tion of groundwater, or groundwater would be treated before use. No
radon emission rate is specified.
_Al_ternati_ve _C. The number of years over which the integrity of
control measures shall be designed to be maintained is not specified,
but controls should be chosen to endure without near-term maintenance;
they would thus remain effective for an "indefinite time." The radon
emission limit specified is 60 pCi/m^s. Control measures used to
meet this limit should prevent significant contamination of groundwater
for a few hundreds of years.
Alternative D. In this alternative control measures are designed
to be effective for 1,000 years, and in any case for at least 200
years. The radon emission limit is 20 pCi/m^s. Water quality is to
be maintained so that current uses can be continued and potential uses
preserved. This is accomplished by specifying concentration limits in
groundwater for toxic substances and by not allowing any increase above
existing concentrations for hazardous constituents.
Alternative E. Control measures are designed to be effective for
1,000 years. The radon emission limit is 20 pCi/m^s. Water quality
is to be maintained so that current uses can be continued and potential
uses preserved. This is accomplished by specifying concentration
limits in groundwater for toxic substances and by not allowing any
increase above existing concentrations for hazardous constituents.
Alternative F. Control measures are designed to be effective for
at least 1,000 years. The radon emission limit is 2 pCi/m^s. Water
quality is to be maintained so that current uses can be continued and
potential uses preserved. This is accomplished by specifying
concentration limits in groundwater for toxic substances and by not
allowing any increase above existing concentrations for hazardous
constituents.
9.3 ^£timated_Costs_of_ Methods £.or__Alternative J^tandjard_s
Costs are estimated for the levels of control which will satisfy
the levels of health protection shown in Table 9-1. A range of
thicknesses of earth covers provides the various protection levels.
9-5
-------
Various protective materials are used to increase the long-term
effectiveness of the cover. Table 9-2 depicts the relationship between
the Alternative Standards and the disposal methods considered. De-
tailed cost estimates are given in Appendix B.
Because the large differences in the sizes of existing tailings
piles at licensed sites can lead to large cost differences, these piles
have been separated into three groups: 2 million tons (MT), 7 million
tons, and 20 million tons. Their characteristics are given in Appendix B,
This grouping is for costing purposes only. While the divergence in
estimated costs for existing piles is great, the range in potential
health risks is small. Estimates of potential health risks are largely
dependent on the area covered by the tailings. The area of the model
pile (Chapter 4) and a listing of existing piles (Chapter 3) indicate
the areas vary by a factor of only about two:
Ra_t io _of_ _Area^ of
Existing Pile_s__tp Area
Area (hectares) of~_the Model Fife
Model pile 100 1.0
Existing 2 million tons 48 0.48
Existing 7 million tons 56 0.56
Existing 20 million tons 98 0.98
Thus, potential health risk estimates can be treated uniformly,
regardless of the pile size.
9.3.1 Dis£o_sal^ Method_s__f o_r _Existj.ng_ Tailings_ Piles
Methqd_ETl
The edges of the square tailings pile are graded and contoured to
a 5:1 (H:V) slope. The entire area is then covered with 0.5 meters of
earth obtained nearby. A 6-feet high, 6-gauge aluminum chain link
fence is placed around the exclusionary zone, which is assumed to be
0.5 kilometer from all sides of the pile. The covered pile is
landscaped, assuming that suitable loam or topsoil is available
onsite. The borrow-pit is reclaimed. Maintenance and inspection are
added for a 100-year period.
Method ET2
The sides of the tailings piles are graded to 5:1 (H:V) slope.
The tailings are covered with 1 meter of earth obtained locally and the
slopes are covered with 0.5 meter of rock cover. There is no
maintenance and inspection of the pile. A fence is installed to form
an 0.5-kilometer exclusion area around the disposed tailings. The
borrow pit is reclaimed.
9-6
-------
Table 9-2. Control Methods Assumed to Satisfy the
Alternative Standards
Alternative _ Control Method
A NT1
B NT2 and ET1
C NT3 and ET2
D NT4 and ET3
E NT5 and ET3
F NT7 and ET5
NT New Tailings. ET Existing Tailings.
Method E_T3
For this method the sides of the square tailings pile are graded
to a 5:1 (H:V) slope. The entire tailings area is covered with 3
meters of earth obtained locally. Then the slopes are covered with
0.5-meter rock, and the tailings are landscaped. No fence is
necessary. The borrow pit is reclaimed.
Method ET4
The sides of the tailings piles are graded to a 8:1 (H:V) slope,
then the entire area is covered with 3 meters of earth obtained
nearby. The slopes are coverd with 0.5-meter rock, and the tops of the
tailings are landscaped. No fence is needed. The hot row-pit is
reclaimed.
Method ET5
The edges of the tailings piles are contoured to a slope of 8:1
(H:V). The entire area is then covered with 5 meters of earth obtained
locally. The slopes are covered with 0.5-meter rock, and the tops of
the tailings are landscaped. No fence is necessary. The borrow-pit is
reclaimed.
Method ET6
The sides of the tailings piles are graded to a 5:1 (H:V) slope.
The entire area is then covered with 1 meter of eirth obtained locally,
9-7
-------
after which a cover of 0.5-meter rock is added to the entire pile. A
fence is installed to form an 0.5-kilometer exclusion area around the
disposed tailings. The borrow pit is reclaimed.
Method ET7
This disposal method provides for below-surface disposal of
tailings, with a 3-meter earth cover over the tailings and a 1-meter
clay liner below the tailings. For the 2-million-ton pile, a 366-meter
square pit is excavated to a 12-meter depth adjacent to the pile. The
bottom of the pit is assumed to be above the groundwater table. The
pit is lined with 1 meter of purchased clay hauled 3.2 kilometers. The
tailings are moved into the pit with scrapers, after which they are
covered with 3 meters of the excavated earth. The disposal area is
landscaped. The area covered by excess excavated earth is restored.
The disposal pit for the 7-million-ton pile is 614 meters square by 15
meters deep, and the pit for the 20-mi11 ion-ton pile is 1,047 meters
square by 15 meters deep. Both pits are assumed to be above the
groundwater table. Because of the large sizes, hauling by trucks for
an average off-road distance of 3.2 kilometers is assumed. The
disposal method and landscaping are similar to those of the 2-million-
ton case.
9.3.2 Disposal Methods _Eo_r_New TaJ/Lin£s_ Piles
Method NTl
This method is the same as the base case in the NRC analysis
(NRC80). An initial square basin would be formed by building low
earthen embankments along each side, 947 meters in length at the
centerline. The mill tailings would be slurried into the basin, and as
the basin filled, the coarse fraction of the tailings (sands) would be
used to raise and broaden the embankments. The final dimensions of the
embankments would be 10 meters high and 13 meters wide at the top.
When the mill ceases operations, no control measures for disposal would
be applied.
Method NT2
This method is similar to ET1, since both use a thin earth cover
on the tailings and rely on institutional controls for maintenance and
to prevent misuse. A pit is excavated close to the mill and measures
930 meters square by 2 meters deep. Embankments are constructed along
each side, 947 meters long, 10 meters high, and 13 meters wide at the
top. The pit is lined with 1 meter of clay obtained locally. Tailings
are pumped directly into the pit during operation of the mill. It is
assumed that water from the pond will be recycled to the mill, thereby
negating the need for an evaporation pond.
9-8
-------
At the end of mill life, the embankments are excavated and placed
on top of the tailings to a depth of 0.5 meters. The slopes of the
covered tailings are graded to 5:1 (H:V). The entire area is
landscaped. A fence is placed around the disposal area and provides a
0.5-kilometer exclusion zone. The site is maintained for 100 years by
irrigation of the vegetative cover and inspection and repair of the
earth cover and fence.
Method NT3
This method is similar to ET2, since both use a 1-meter earth
cover and 0.5-meter rock to cover the slopes. A pit is prepared and
used in the same manner as that described for method NT2.
At the end of mill life, the embankments are excavated and placed
on top of the tailings to a depth of 1 meter. The slopes of the
disposed tailings are graded to 5:1 (H:V) and then covered with
0.5-meter rock. The top of the disposed tailings area (that part not
covered with rock) is landscaped. A fence is constructed around the
site at a distance of 0.5 kilometers from the edge of the disposed
tailings.
Method NT4
This method is similar to ET3, since both use 3 meters of earth
cover and 0.5-meter rock to cover the slopes. A pit is excavated,
prepared, and used in the same manner as that described for method NT2.
At the end of mill life, the embankments are excavated and placed
on top of the tailings. Additional earth cover is obtained from a
nearby borrow-pit so that the final earth cover over the tailings is
3 meters deep. The slopes of the covered tailings are graded to 5:1
(H:V) and are covered with 0.5-meter rock. The top of the
earth-covered tailings is landscaped. The borrow-pit is reclaimed.
Method NT5
This method is somewhat similar to the staged or phased disposal
method described by the NRC's GEIS (NRC80). This method uses 6 pits,
300 meters square and 13 meters deep. Two pits are constructed
initially and lined with 1 meter of clay. Tailings are pumped to the
first pit until it is full and then pumped to the second pit. When the
first pit is sufficiently dry, the third or fourth pit is excavated,
and the excavated earth is used to cover the first pit to a depth of 3
meters up to the original contour. This process continues sequentially
until the end of mill life. An evaporation pond is needed in this
method. Costs for this pond are taken from the NRG Generic EIS and
corrected for inflation.
9-9
-------
At the end of mill Life there are four completed pits, which are
covered with 3 meters of earth to the original ground contour, and 2
uncovered pits. When sufficiently dry, these last two pits are covered
with 3 meters of excavated earth to the original ground contour. The
disposal area is landscaped. The areas covered by the evaporation pond
and excess excavated earth are restored.
Method NT6
This method is the same as Alternative 7 in the NRC GEIS (NRC80).
The tailings are pumped to the edge of a depleted mine pit, where the
sands (coarse fraction) and slimes (fine fraction) are separated. The
sands are washed, dried, and deposited in the mine pit. The slimes are
partially dried, mixed with cement, and deposited in the mine pit where
the cement and fine slurry would harden.
Method NT7
This method is similar to ET5, since both use a 5-meter earth
cover and 0.5-meter rock to cover the slopes. A pit is excavated,
prepared, and used in the same manner as that described for Method NT2.
At the end of mill life, the embankments are excavated and placed
on top of the tailings. Additional earth cover is obtained from a
nearby borrow-pit so that the final earth cover over the tailings Is 5
meters deep. The slopes of the covered tailings are graded to 8:1
(H:V) and are covered with 0.5-meter rock. The top of the
earth-covered tailings is landscaped. The borrow-pit is reclaimed.
Cost Estimat_e£
Cost estimates for the disposal of tailings at active uranium
milling sites are presented in Table 9-3 along with a summary of
critical design features. The cost estimate details are developed in
Appendix B, which also includes characteristics of tailings piles, unit
costs, and descriptions of disposal methods (NT-1 to 7 and ET-L to 7).
All cost estimates in Table 9-3 include an increase of 20 percent
for contingency, overhead, and profit, but do not include the cost of a
liner for the tailings pond. The disposal costs for the model pile are
greater than for the existing 7-MT pile. The difference is due to the
larger size of the model and the costs of preparing the initial
tailings impoundment. The model pile, taken directly from the NRC
Generic EIS (NRC80), appears oversize when compared with industry
practice. This leads to the considerably greater costs for the model
pile when compared to an existing pile containing about the same
quantity of tailings. These cost estimates for the NT methods can be
considered maximum costs.
9-10
-------
Table 9-3. Summary of Cost Estimates for Disposal
of Active Uranium Mill Tailings
(a)
Cost Cover Rock Vege- Below
(1981 dollars in Maximum thickness cover tation grade
Method _ millions) _ slope (m) _ (0.5 m) _cover disposal
NEW TAILINGS
NT-l(b) 1.2 - -
NT-2 13.8 5:1 0.5 - Yes
NT-3(<0 15.4 5:1 1.0 On slopes Yes
NT-4 21.5 5:1 3.0 On slopes Yes
NT-5(e) 27.0 - 3.0 - Yes Yes
NT-6(f> 91.2 - 3.0 - Yes Yes
NT-7 31.9 8:1 5.0 On slopes Yes
EXISTING TAILINGS
By pile size
ET-l(c)
ET-2(d)
ET-3
ET-4
ET-5
ET-&(d)
ET-7(g)
2
3.9
3.8
6.9
7.6
11.9
12.8
10.3
7
5.
7.
11.
13.
19.
17.
38.
7
0
4
9
9
4
4
(MT)
20
11.1
14.4
22.3
29.2
40.6
32.5
111.7
5:1
5:1
5:1
8:1
8:1
5:1
0.
1.
3.
3.
5.
1.
3.
5
0
0
0
0
0
0
On
On
On
On
_
slopes
slopes
slopes
slopes
Yes
Yes
Yes
Yes
Yes
_
-
—
—
-
Total area
-
Yes
Yes
^a'Costs include a 20 percent increase for contingencies, overhead, and profit,
but do not include the cost of a tailings pond liner.
'b'Base case; no disposal.
^c'Fenced and maintained.
(d)Fenced.
^•e'Phased disposal.
'Solidified in concrete/asphalt.
is moved.
9-11
-------
9.4 Accidental and Radiation-Induced Deaths from Disposal
One of the costs of control is the possibility of accidental
deaths during the disposal of tailings and when moving tailings.
Table 9-4 shows our estimate of the number of accidental deaths that
could be associated with each alternative disposal standard. These
estimates include accidental deaths of workers and premature,
radiation-induced deaths of construction workers at the tailings sites.
In our review of the existing tailings sites, we identified only
two sites that may be vulnerable to flooding. Even for these two
sites, it is not clear that the tailings would have to be moved to
provide protection against flooding. Thus, we have made no estimate of
the number of deaths that might occur, primarily to workers and the
public, from transportation accidents if the tailings piles are moved.
The most important parameter in this simplified analysis of
accidental deaths is the number of person-hours of labor required to do
the job. This is used to estimate the number of construction-related
deaths, as well as the number of premature deaths from radiation
exposure.
The labor required for piles that are to be controlled onsite is
proportional to the amount of earthmoving to be done; a gradual slope
requires more earthmoving than a steep slope, roughly in proportion to
the ratio of the slopes, and a thick cover requires more earthmoving
than a thinner one. Based on figures from a DOE contractor (DeWSl), we
estimate that Alternative NT2 would require about 110 person-years of
labor for the model pile. The labor requirements for Alternative NT3
would be 220 person-years; for NT4 and NT5, 280 person-years; and for
NT6 about 200 person-years, assuming the solidified tailings would
require some cover. The labor requirements for each ET alternative are
estimated by scaling directly by the area covered by the tailings (see
Section 9.3), using an effective area of the model pile of 80 hectares.
The occupational deaths resulting from this are estimated from
mortality statistics for the construction industry: 60 deaths per
100,000 worker-years (NS78). This corresponds to 6 x 10~4 accidental
deaths per person-year.
Radiation-induced deaths are difficult to estimate since it is
impossible to anticipate measures that might be used to protect
workers. However, in the worst case, the gamma radiation exposure rate
over a bare tailings pile (typically 1 mrem/h) for a working year would
lead to exposures of about 2 rem/y. Inhalation of radon decay products
would, at most, lead to a comparable risk. In Table 9-4, we have
assumed that the maximum risk of premature, radiation-induced death is
equivalent to the risk from an exposure of 4 rem (whole-body equivalent)
of gamma radiation per person-year of labor. Radiation-induced deaths
are estimated at the rate of 2 x 10~6 per person-rem. Since radiation
exposures will be significantly reduced as the earth cover is added,
the radiation-induced death estimate was taken as one-half the value
obtained without credit for shielding by the cover.
9-12
-------
Table 9-4. Accidental and Radiation-Induced Deaths Associated
with Alternative Levels of Tailings Control
Method
Accidental Deaths
Rad iation-Induced
Deaths
For a Model Pile
NT2
NT 3
NT4 and NT5
NT6
NT7
For 2-mil Lion-ton piles:
(10 piles)
ET1
ET2 and ET6
ET3 and ET4
ET5
For 7-mi 11 ion-ton jailes :
(10 piles)
ET1
ET2 and ET6
ET3 and ET4
ET5
For 20-mil.lion-ton piles:
(3 piles)
ET1
ET2 and ET6
ET3 and ET4
ET5
TOTAL:
ET1
KT2 and ST6
ET3 and ET4
ET5
NEW TAILINGS
0.07
0.13
0.17
0.12
0.19
EXISTING TAILINGS
(As of January 1980)
0.4
0.8
1.0
1.2
0.5
1.0
1.2
1.4
0.2
0.5
0.6
0.7
1.1
2. 3
2.8
3.3
0.04
0.09
0.11
0.08
0.13
0.3
0.6
0.7
0.8
0.3
0.6
0.8
0.9
0.2
0.3
0.4
0.5
0.8
1.5
1.9
2.2
9-13
-------
REFERENCES
DeWSl Telephone conversation between Michael DeWitt, Sandia National
Laboratories, Albuquerque, New Mexico, and EPA staff, 1981.
EPA77 Environmental Protection Agency, "Environmental Radiation
Protection Standards for Nuclear Power Operations (40 CFR
190)," January 1977.
EPA82 Environmental Protection Agency, "Hazardous Waste Management
System; Permitting Requirements for Land Disposal Facilities
(40 CFR Part 264)," July 26, 1982.
FRC60 Federal Radiation Council, "Radiation Protection Guidance for
Federal Agencies," Federal Register 4402, May 18, 1960.
NRC80 Nuclear Regulatory Commission, "Final Generic Environmental
Impact Statement on Uranium Milling," NUREG-0706, USNRC,
Washington, D.C., 1980.
NS78 National Safety Council, "Accident Facts," 444 N. Michigan
Ave, Chicago, Illinois.
9-14
-------
Chapter 10: ANALYSIS OF COSTS AND BENEFITS FOR ALTERNATIVE TAILINGS
DISPOSAL METHODS
10.1 Benefits Achievable Through Disposal o_f_ Tailings
The estimated benefits of disposal of tailings include:
1. Reducing the likelihood of misuse of tailings,
and the resulting risk of lung cancer deaths from
inhaling radon decay products.
2. Reducing the risk of lung cancer deaths caused
by radon and its decay products.
3. Reducing the contamination of water with
radioactive and other hazardous or toxic materials.
4. Reducing the spread of radioactive and other
hazardous or toxic materials.
5. Eliminating, for practical purposes, exposure
to gamma radiation from tailings.
All of these benefits are achieved by stabilizing the tailings by
adding earthen cover material and instituting protective measures for
groundwater, where needed.
The benefit we are best able to quantify is the number of lung
cancer deaths averted by controlling radon emissions. We can estimate
the reduction in radon emissions resulting from the placement of a
given thickness of earthen cover, and translate this reduction into
lung cancer risk averted (see Chapter 6). The benefits of radon
control are quantified for both the total risk to populations of lung
cancer death that is averted and for the reduction in risk to
individuals living near the piles. These benefits are proportional to
the length of time the control remains effective.
Most of the other benefits of controlling the tailings piles are
not quantifiable, although the goals are well defined: the reduction
of health risks from exposure to the hazardous materials contained in
10-1
-------
the tailings. For example, we are unable to translate flood protection
measures into the number of health effects averted. The missing
linkages are: 1. The translation from specific flood protection
measures to flood damage averted; 2. The translation from flood damage
to the pile to distribution of tailings spread along the downstream
river valley; and 3. The translation from the tailings spread along
the river valley to the number, length, and level of exposures. There
are similar problems with quantifying the chance of misuse. The
permanence of erosion control, i.e., the years of erosional spreading
avoided and the years of water quality protection can be evaluated,
but, the consequences avoided are not readily quantified.
The benefits for each alternative standard are displayed in
Tables 10-1 through 10-3 and are quantified when possible.
The benefits of controlling tailings at existing sites are
summarized in Table 10-1. There were about 150 million tons of
tailings at 23 active mill sites January 1980. Table 10-1 is presented
primarily to show the cost effectiveness of controlling existing
tailings, which may be different than the cost effectiveness of
controlling future tailings.
The benefits of controlling tailings at all sites, both existing
and new, are summarized in Tables 10-2 and 10-3. The benefits are
summarized for the baseline projection (see Section 2.6) in Table 10-2
and for the low growth projection in Table 10-3.
10.1.1 _Benef_its of JStabTUzation
The benefits of stabilizing the tailings are expressed in terms of
the reduced chance of misuse, the permanence of controls for inhibiting
misuse, and the years of erosional spreading avoided. The number of
health effects averted cannot be estimated.
The major benefit of stabilizing a pile is the prevention of the
hazards associated with human intrusion and misuse of the tailings
piles; this can be expressed only in qualitative terms. We have
estimated, as best we can, the number of years that control is
anticipated to inhibit misuse. This ranges from 0 years for the
no-requirements standard (A) to 1,000 years for the standards having
more stringent requirements (F). The alternatives with thick earth
covers are estimated to inhibit misuse for a period of hundreds to
thousands of years. Also, the below-grade disposal method, with a
3-meter earth cover up to the original ground contour, is expected to
provide greater inhibition of misuse than above-grade disposal with the
same cover thickness.
The likelihood of misuse during the period of effectiveness of
these alternatives ranges from most likely for the no-requirements
alternative to unlikely for alternatives with 3 meters of earth cover
and very unlikely for the method with 5 meters of earth cover.
10-2
-------
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10-5
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The Grand Junction cleanup program is an example of the kind of
expensive remedial actions that stabilization should prevent. The
tailings in Grand Junction buildings are now being cleaned up at a
costof about $23 million, to avoid an estimated 75 to 150 lung cancer
deaths. The additional cost of cleaning up contaminated offsite land
is estimated at $22 million to $31 million.
A second benefit of stabilization is the prevention of erosion.
The benefit of preventing tailings erosion can be expressed in a
semiquantitative way by estimating the number of years that erosional
spreading is prevented. Protection from erosion is estimated to range
from a few hundred years to many thousands of years for the various
alternatives. Since erosion may now be taking place at some sites,
benefits can be derived from any remedial measure that reduces erosion.
A third benefit of stabilization is prevention of floods from
washing tailings downstream to flood plains, where land use is
residential and agricultrual. Should this happen, expensive remedial
measures would probably be needed. A recent tailings "spill" (failure
of a dam containing a tailings pile at an active mill) in the Southwest
contaminated hundreds of acres of land (of limited value) over a
distance of about 20 miles. We estimate the cost of cleanup of that
spill to be $1 million to $5 million, depending on the cleanup criteria
used. The total radioactivity spilled was less than 5 percent of that
in an average inactive pile.
10.1.2 Benefits of Radon Contro^
The estimated benefits of radon control can be quantified. For
individuals living near a tailings pile, the benefit is a reduction in
health risk. The maximum risk of death to nearby individuals during
their lifetime is estimated to be about 4 chances in 100 for the
no-requirements of Alternative (A). This risk drops to 2 chance in "LOO
for Alternative B and to 2 chances in 1,000 for Alternatives D and E..
The greatest risk reduction is achieved by Alternative F, which has a 2
pCi/m^s radon emission limit and reduces the risk to about 2 chances
in 10,000.
The total national lung cancer death rate from radon emissions
from existing active piles is estimated at 450 per century If no
controls are used. This estimate will increase as additional tailings
are produced if controls are not used. Alternatives with a 20 pCi/m^s
radon emission rate (D and E) would reduce this rate to about 22 per
century for hundreds to thousands of years. The benefit from a more
restrictive radon emission rate (F) would be the virtual elimination of
the radon risk. Alternative F is estimated to provide greater than 99
percent control of radon for at least 1,000 years.
10-6
-------
10.1.3 Benefi ts ofPr o tctin|g Water
Protection of water quality is a benefit that cannot be
quantified, because future uses of the water cannot be estimated.
Unlike air, which must be breathed, water may or may not be used in
ways that might cause an increase in health risks. Also, water may be
tested for contaminants and, if polluted, it may be cleaned to levels
suitable for its projected use, or may be rejected, if an alternative
is available. However, after disposal the protective cover, or cap,
over the tailings can be quite effective at reducing the volume of
liquids entering the tailings and therefore can substantially reduce
the potential for contamination of groundwater for long periods.
The benefit of protecting groundwater is the preservation of its
existing quality for future uses. These uses are drinking, lifestock
watering, and limited irrigation. A specific benefit of groundwater
protection would be the reduction, or elimination, of molybdenosis in
cattle, which has occurred at a site in Colorado where molybdenum from
a tailings pond contaminated groundwater.
Existing uranium tailings are located in areas with low
precipitation. This means there is little need to discharge waste
water to surface waters. Waste water can be held in ponds, where it
evaporates or can be recycled back to the process. Only one uranium
mill currently has a National Pollution Discharge Elimination System
(NPDES) permit, under the Clean Water Act, for example. However,
uranium mining and milling may occur in wetter areas in the future
where discharges to surface waters may be unavoidable. In these cases,
the operator would be required to obtain a NPDES permit, which would
assure protection of surface water quality.
10.2 Benefits and Co^s_ts_ for_a_Model TaiJ^ngs__Pi_:L_e
The benefits derived from disposal of tailings have been estimated
as shown in Tables 10-1 through 10-3 for the various alternative
standards. The total costs of these methods have been estimated as
listed in Table 10-4. In this section these benefits and costs are
evaluated for each alternative standard.
10.2.1 Alternative S t_andard_ A
This alternative is used as a baseline to which the benefits of
other methods can be compared. While this alternative would not
achieve the goals or objectives of the disposal standards, it has the
significant benefit of preventing the flagrant discharge of all
tailings into surface waters. This control has been practiced by the
industry for some time, however, and is considered appropriate as a
baseline .
10-7
-------
Table 10-4. Total Costs of Controlling UranLum Tailings
at Active Sites
(1981 dollars in millions discounted at 10%)
All Tailings at Active,Sites
Alternative Existing Tailings to the Year 2000
Standards
A
B
C
D
E
F
(as of Jan. 1980)
0
98
115
190
190
334
Baseline Scenario
10
337
384
530
549
818
Low Growth Scenario
6
267
310
440
452
709
10.2.2 Alternati ve Standard JJ
The concept underlying this alternative is active control and
maintenance. The thin earth cover, loam, and vegetation would reduce
radon emanation and associated health effects by about 50 percent for
the 100-year period maintenance is performed. This would reduce deaths
from radon to about 6 per century from a remote site and 18 per century
from a rural site. The total radon deaths avoided would be 2,800 for
the baseline projection and 2,400 for the low growth projection from
all tailings generated to the year 2000. The chance of misuse is small
for 100 years because of a fence and continuing human activities such
as maintence and inspection. Annual inspection and repair actions
would provide protection against windblown and surface water
contamination and external radiation for as long as such actions
continue.
The benefits for this alternative are considered to end when
maintenance activities cease. Once the sprinkling (irrigation) of the
vegetation stops, chemicals from the tailings will probably kill the
vegetation, and the thin cover will be denuded and rapidly eroded.
However, this scenario could be modified by selection of a site where
the deposition of material exceeds the erosion of material. Even in
this case the deposition rate is likely to be low, thus allowing
continued radon releases and significant chances of misuse for a long
period.
10-8
-------
The estimated total cost for Alternative B is $337 million for
both new and existing tailings sites under the baseline projection and
$267 million Eor the low growth projection.
The estimated number of accidental and radiation induced deaths
for Alternative B is 8 for the baseline projection and 6 for the low
growth projection.
10.2.3 Alternative Standard C
This alternative would require control of about 80 percent of the
radon for most soils. This control reduces the deaths from radon to
about 2 per century for a remote site and 8 per century from a rural
site. The total radon deaths avoided would be in the thousands for
both the baseline and low growth projections. The chance of misuse
would be low during an initial period, especially if large size rock is
used on the slopes. However, with the passage of time the chance of
misuse would increase as reasons to avoid the pile (disposed tailings)
were forgotten or became obscure and erosion began to uncover the
pile. It is estimated that this initial period would be about 100
years, after which the likelihood of misuse would increase. The
benefits of preventing windblown and surface water contamination and
protecting against external gamma radiation are estimated to last
hundreds of years.
The estimated total cost for Alternative C is $384 million for
both new and existing tailings sites under the baseline projection and
$310 million for the low growth projection.
The estimated number of accidental and radiation induced deaths
for Alternative C is 15 for the baseline projection and 13 for the low
growth projection. This includes control of existing tailings plus all
tailings generated to the year 2000.
10.2.4 AU_ernative Standard D
Controls required by this alternative should reduce radon releases
by a factor of about 20, using almost any type of soil. This reduction
is like.ly to be greater in most cases since many soils have attenuation
properties that would redvice radon releases by a factor of about 100.
Using a control factor of 95 percent, the number of radon related
deaths would be reduced to about one per century for a remote site and
two per century for a rural site. The total radon induced deaths
avoided would be in the many thousands for both the baseline and low
growth projections.
The significant benefit of this alternative is the substantial
reduction in the probability of human intrusion, especially over the
long term. A major undertaking would be required to remove significant
quantities of tailings. The use of heavy equipment with attendant
expenses would probably involve a thorough review of property ownership
10-9
-------
and tailings characteristics, and approvals by local governments. All
this would appear to make it likely that the hazardous nature of the
materials would be recognized before they were recovered and used.
This "inhibition of misuses" benefit would probably extend for a period
of hundreds of years.
The benefits derived from preventing contamination of surface
waters and soil surfaces and from reduction of external radiation are
estimated to last for 1,000 years.
The estimated total cost for Alternative D is $530 million for
both new and existing tailings sites under the baseline projection and
$440 million for the low growth projection.
The estimated number of accidental and radiation-induced deaths
for Alternative D is 19 for the baseline projection and 16 for the low
growth projection. This includes control of all tailings (existing
plus future) generated to the year 2000.
10.2.5 Al_te rna t i ve S t anda.rd E
This alternative would require staged disposal of the tailings,
whereby several tailings storage ponds are used during the lifetime of
a mill. After each pond is filled, it is allowed to dry and is then
covered with 3 meters of earth. This has the additional benefits over
Alternative D of reducing the total quantity of tailings requiring
disposal at the end of mill life and of controlling part of the radon
emissions during operations. This latter benefit is discusssed in
Chapter 7. Staged disposal is considered feasible for new impoundments
only. Existing tailings piles, which may contain future tailings, are
controlled to levels described in Alternative D.
The benefits of this alternative include reductions in radon
deaths that are the same as those under Alternative D, a greatly
reduced chance of misuse for hundreds of years, and virtual elimination
of surface water and land contamination and external radiation
exposure. The chance of misuse is likely to be less for Alternative E
than for Alternative D because the tailings disposal site should be
indistinguishable from the surrounding terrain. By placing the
tailings below grade and covering them to the initial land contour,
there would be no easily identifiable pile with rock covered slopes,
clearly an indication of human activity.
The estimated total cost for Alternative E is $549 million for
both new and existing tailings sites under the baseline projection and
$452 million for the low growth projection.
The estimated number of accidental and radiation-induced deaths
for Alternative E is 19 for the baseline projection and 16 for the low
growth projection.
10-10
-------
10.2.6 Al_ternatiye _S tandard F
Alternative F provides greater benefits by specifying a more
stringent radon emission rate of 2 pCi/m^s. Thus, radon releases are
reduced by greater than 99 percent. This provides a benefit of
reducing the total radon related deaths by many thousands. The
benefits of inhibiting misuse are also substantially greater than for
alternatives specifying a less stringent radon emission rate.
It is expected that this alternative would be met by using thicker
earth covers of about 5 meters. The extra thick cover and the long,
gradual slopes covered with rock would probably provide protection
against misuse for at least 1,000 years.
The benefits of external radiation control and prevention of land
and surface water contamination would probably last thousands of years.
The total costs for Alternative F are $818 million for the
baseline projection and $709 million for the low growth projection.
This alternative considers the benefits and costs of a very thick
cover (5 meters). The estimated number of accidental and
radiation-induced deaths is estimated as 22 for the baseline projection
and 19 for the low growth projection.
10-11
-------
APPENDIX A
(Reserved)
-------
APPENDIX B
ESTIMATED COSTS FOR DISPOSAL OF URANIUM
BYPRODUCT MATERIALS
-------
Appendix B: ESTIMATED COSTS FOR DISPOSAL OF URANIUM
BYPRODUCT MATERIALS
CONTENTS
Page
B.I Characteristics of Model Tailings Piles B-5
B.2 Tailings Disposal Unit Costs B-7
B.3 Descriptions of Disposal Methods B-10
References B-23
TABLES
B-l Unit Costs ^ B-8
B-2 Reclamation Costs for a Borrow Pit on Flat Terrain B-ll
B-3 Disposal Cost Summary: Method ETl B-12
B-4 Disposal Cost Summary: Method ET2 B-14
B-5 Disposal Cost Summary: Method ET3 B-15
B-6 Disposal Cost Summary: Method ET4 B-16
B-7 Disposal Cost Summary: Method ET5 B-17
B-8 Disposal Cost Summary: Method ET6 B-20
B-9 Disposal Cost Summary: Method ET7 B-21
B-10 Disposal Cost Summary: Methods NTl Through NT6 B-22
B-3
-------
Appendix B: ESTIMATED COSTS FOR DISPOSAL OF URANIUM
BYPRODUCT MATERIALS
B.1 Characteristics of Model Tailings Piles
The costs for disposal of uranium byproduct materials are
estimated in this appendix for alternative disposal standards. The
disposal methods, with one exception, use earth covers of various
thicknesses which are stabilized with vegetation and rock. We believe
this is the most likely method of disposal. The one exception is a
tailings solidification method which is described in detail by the
Nuclear Regulatory Commission (NRC80).
The costs of liners on the bottoms of tailings impoundments are
included for completeness since they represent a significant capital
cost. In practice, a liner is an operational control that protects
groundwater during the operational phase of a tailings pond. Long-term
protection of groundwater is provided by the cover. The estimates are
arranged so that costs of liners can be easily subtracted for analysis
purposes. Additional cost estimates for protecting groundwater are
presented in Chapter 7.
Existing Tailings Piles
In early 1980, there were 23 licensed uranium mills with tailings
piles. An analysis of these piles indicated that since they vary
widely in size, control costs would also vary greatly. Consequently
the piles were grouped into model piles as follows:
a. a 2-million-ton pile on 48 hectare with an
average depth of 2.37 meters.
Number of piles in this group = 10
Average tons per pile =1.8 million
(Range = 1.0 to 2.8 million tons)
Average area covered = 48 hectares
(Range = 13.8 to 98.4 hectares)
B-5
-------
b. a 7-million-ton pile on 56 hectares with an
average depth of 7.72 meters
Number of piles in this group = 10
Average tons per pile = 6.85 million
(Range = 4.2 to 11.0 million tons)
Average area covered = 56 hectares
(Range = 31.1 to 86.6 hectares)
c. a 20-million-ton pile on 98 hectares with an
average depth of 12.85 meters
M' Her of piles in this group = 3
Average tons per pile = 19.9 million
(Range = 17.1 to 24.6 million tons)
Average area covered = 98 hectares
(Range - 82.6 to 106.2 hectares)
Separate calculations are needed for each model pile and for each
disposal method.
Another important feature of the model piles is the additional
area that would be covered by tailings when the sides of the tailings
piles, which consist of the sands (coarse fraction), are sloped or
contoured to provide additional erosion control. Two values are used
for the slopes of the pile edges after grading, 5:1 (H:V) and
8:1 (H:V). The volume of tailings moved is estimated by calculating
the volume of the sloped tailings where the vertical distance is the
average depth of the pile and the horizontal distance is 5 or 8 times
the vertical. The pile is assumed to be square. The amount of
additional land covered and the volume of tailings moved by sloping the
edges of the piles are:
Additional Land Tailings Moved
Covered (ha) (thousands of cubic meters)
P i 1 e Size 5:1 slope 8:1 slope 5 : 1 slope 8:1 si or
2
7
20
mil
mil
lion
lion
million
tons
tons
tons
3
12
26
.3
.3
.6
5
19
44
.4
.7
.0
39
459
1,690
63
746
2,760
These values can increase the cost significantly for those methods
involving disposal in place. It may be more economical to move the
tailings into the center of the pile, thereby forming a hemisphere rather
-------
than cover the additonal land area with soil. However, it is not clear
that this method would be less costly, since the grading and shaping of
such large volumes is also costly.
New Tailings Piles
Information on tailings to be generated at a model new mill are
taken from the NRC GEIS (NRC80). The NRC model mill has an
ore-processing capacity of 1,800 MT per day. The ore grade is expected
to average 0.1 percent uranium, and the uranium recovery efficiency is
assumed to be 93 percent. The mill is operated 310 days per year (i.e.,
85 percent capacity utilization rate), and the average annual production
is 580 MT yellowcake, which is 90 percent 0303. The model pile
covers an area of 80 ha with earth embankments around the tailings,
bringing the total area to 100 ha. The ultimate depth of the tailings is
about 8 meters.
The tailings will be generated at a rate of 1,800 MT per day, or 558
thousand MT per year, or 8.4 million MT during the assumed 15-year
operating period of the mill. The tailings are discharged to an
impoundment in the base case, which is analyzed later in this appendix as
case NTl.
B.2 Tailings Disposal Unit Costs
The most likely methods for disposal of the tailings involve
covering the tailings with earth, as discussed in Chapter 8. The unit
costs for earth work, transportation, fencing, landscaping, rock cover,
and maintenance and inspection are shown in Table B-l. All costs
(except rock cover, maintenance, and inspection) were taken from the
"Dodge Guide to Public Works and Heavy Construction Costs" (DG81). The
unit cost for rock cover is taken from Means (Me82).
Maintenance and inspection costs are calculated for: (1) an
irrigaton system for maintaining vegetation on thin earth covers, (2)
fencing maintenance, and (3) annual inspections, including groundwater
monitoring and repair and revegetation of eroded areas.
Irrigation
The irrigation system design was developed for EPA by PEDCO
Environmental, Inc. (PE82). The design is for a 40-acre site (about 16
hectares) and consists of a 150-hp motor and pump unit, polyethylene
piping, and plastic spray heads. The capital costs of this system are
$127,000, and it is assumed that it must be replaced every 20 years. The
present value of capital requirements for 100 years of operation is
$149,000, using a 10 percent discount rate and replacement at 20, 40, 60,
and 80 years. Annual costs of operation are $12,000 per year for
maintenance and labor; $9,300 a year for electrical power; and $6,000 per
year for overhead, assuming the system is operated 8 hours per week, 8
months per year. The present value of these annual costs is $273,000 for
B-7
-------
Table B-l Unit Costs
(1981 Dollars)
Task
Cost
Earth work:
Grading:
Move and spread by dozer.
Placing clay liners and covers:
Purchase clay, haul 2 miles,
dump, spread, and compact.
Placing earthern cover:
Excavate, haul, spread, and
compact by scrapers for 3,500 feet.
Excavate, load, haul by truck for
2 miles off the highway; dump, spread,
and compact.
Excavating pits:
Excavate, haul, and spread, by
scrapers, for 3,500 feet.
Moving tailings:
Excavate by drag line. Load, haul
2 miles off highway, spread, and
compact.
Transportation:
Over highway hauling of earth, tailings,
clay, loam, etc.
Rock cover:
18" thick.
$1.07/y3
£8.84/y3
($11.58/m3)
$2.06/y3
($2.70/m3)
$2.00/y3
($2.62/m3)
$1.83/y3
($2.40/m3)
$2.50/y3
($3.28/m3)
$0.40/y3/mile
($0.52/m3/mile;
fc0.33/m3/km)
$13.60/y2
Ul6.27/m2)
Landscaping:
Loam from site used. Preparation of
area, spread loam 6 inches thick, and
hydraulically spread lime, fertilizer,
and seed.
Loam purchased and hauled 2 miles. Prepare
area, spread loam 6 inches thick, and
hydraulically spread lime, fertilizer, and seed.
$3,000/acre
U7,400/ha)
$7,900/acre
($19,500/ha)
B-8
-------
Table B-l. Unit Costs (Continued)
(1981 Dollars)
Task Cost
Fencing:
Chain link, 6 feet high, 6-gauge aluminum. $21.60/ft
($70.87/m)
Maintenance and inspection:
Installation and operation of $10,500/acre
an irrigation system for 100 years - ($26,000/ha)
present worth at 10% discount rate.
Maintenance of fencing at 1% of capital 0.10 x capital
cost per year. Present value at 10% cost of
discount rate for 100 years. fencing
Annual inspections including ground- $95,000/site
water monitoring and repair and revegetation
of eroded areas. Present value at 10% discount
rate for 100 years.
100 years using a 10-percent discount rate. Therefore, the total
present value of providing irrigation for 100 years is $422,000 for a
40-acre site, or $10,500 per acre.
Fencing
Maintaining the fence for 100 years is assumed to cost 1 percent
of the installation cost annually. The present value of this
maintenance cost for 100 years at 10-percent discount rate is:
Present Value of Fencing Maintenance = 0.10 x fencing capital cost.
Annual Inspections
The cost for annual inspections at a site is taken directly from
Appendix R of (NRC80). For this purpose, we used NRG Scenario IV,
which requires only limited maintenance. Their inspection costs are
$10,500 annually. This includes $1,000 per year for maintenance of the
fence. Since this cost is already considered, it is subtracted, giving
an annual cost of $9,500 per site. The present value is $95,000 per
site, using a 10 percent discount rate for 100 years.
B-9
-------
Borrow Pit Reclamation
The costs for reclaiming borrow pits were estimated for 3 cases:
borrow pit in flat terrain; borrow pit on a 10:1 slope; and borrow pit
on a hilltop or knoll. For all three cases, stripping and saving 15
centimeters of top soil and revegetation following replacement of the
top soil were assumed. The four side walls in the flat terrain pit and
the high wall on the 10:1 slope pit were graded to an 8:1 slope before
top soil replacement and revegetation. No grading was required for the
hilltop case. The hilltop case had the least costs for most methods,
and the 10:1 slope case had the greatest costs for all methods.
Therefore, to represent an average estimate, the costs for the flat
terrain case were used for borrow-pit reclamation. These costs are
presented in Table B-2.
B.3 Descriptions of Disposal Methods
Existing Tailings Piles
Method ET1
The edges of the square tailings pile are graded and contoured to
a 5:1 (H:V) slope. The entire area is then covered with 0.5 meter of
earth obtained nearby. A 6-feet high, 6-gage aluminum chain link fence
is placed around the exclusionary zone, which is assumed to be 0.5
kilometer from all sides of the pile. The covered pile is
landscaped,assuming that suitable loam or topsoil is available onsite.
The borrow-pit reclamation cost is taken from Table B-2. Maintenance
and inspection are added for a 100-year period. The costs for this
method are summarized in Table B-3.
Method ET2
The sides of the tailings piles are graded to 5:1 (H:V) slope.
The tailings are covered with 1 meter of earth obtained nearby and the
slopes are covered with 0.5 meter of rock cover. There is no
maintenance and inspection of the pile. A fence is installed to form
an exclusion area 0.5 kilometer wide all around the disposed tailings.
The borrow pit is reclaimed as described in Section B.2. The costs for
this method are shown in Table B-4.
Method ET3
For this method the edges of the square tailings pile are graded
to a 5:1 (H:V) slope. The entire tailings area is covered with 3
meters of earth obtained nearby or locally. After covering, the slopes
are covered with rock, and the tailings are landscaped. No fence is
necessary. The borrow pit is reclaimed as described in Section B.2.
The costs for this option are listed in Table B-5.
B-10
-------
Table B-2. Reclamation Costs for a Borrow Pit on Flat Terrain^3'
(198L dollars in millions)
2
7
20
Size of
Tailings Pile
million tons
5:1 slope
8:1 slope
million tons
5 : 1 slope
8: 1 slope
million tons
5 : 1 slope
8:1 s lope
Cover Thickness on Tailings Pi
0 . 5 me t e r 1 me t e r
0.18 0.28
0.28
0.22 0.39
0.40
0.34 0.64
0.67
3 meters
0.69
0.73
0.95
1.05
1.42
1.59
le
5 meters
1.06
1.10
1.29
1.42.
2.18
2.45
(a)
Where it is assumed that 15 cm of topsoil were stripped and saved,
the four side walls of the pit were graded to an 8:1 slope, the top soil
was replaced, and the area revegetated. The size and depth of the pit
varied, depending on the amount of soil needed to cover the tailings;
however, in no case was the borrow pit excavated deeper than 12 meters.
B-ll
-------
Table B-3. Disposal Cost Summary: Method ETl
(1981 dollars in millions)
Size of Pile (MT)
Task 2 7 20
Grading slopes 0.06 0.64 2.37
Excavating, hauling, spreading
and compacting cover material 0.69 0.92 1.63
Excavating pit -
Placing liner - - -
Excavating, hauling, spreading,
and compacting tailings - - -
Fencing
Landscaping
Placing rock cover
Reclaiming borrow pit
Maintain for 100 years
Contingency, overhead and profit
TOTAL
Composite Unit Costs:
$/MT Tailings
fc/MT U308
0.49
0.38
-
0.18
1.47
0.65
3.92
1.96
2,107
0.52
0.50
-
0.22
1.91
0.94
5.65
0.81
868
0.60
0.92
-
0.34
3.39
1.85
11.10
0.56
597
B-12
-------
Method ET4
The sides of the tailings piles are graded to a 8:1 (H:V) slope,
after which the entire area is covered to a 3-meter depth with earth
obtained nearby or locally. The slopes are covered with 0.5 meter rock
cover, and the earth-covered tailings are landscaped. No fence is
needed. The borrow pit is reclaimed as described in Section B.2. The
costs for this option are presented in Table B-6.
Method ET5
The edges of the tailings piles are contoured to a slope of 8:1
(H:V). The entire area is then covered with 5 meters of earth obtained
nearby. The slopes are covered with a 0.5-meter thick rock cover, and
the earth-covered tailings are landscaped. No fence is necessary. The
borrow pit is reclaimed as described in Section B.2. The costs for
this option are presented in Table B-7.
Method ET6
The sides of the tailings piles are graded to a 5:1 (H:V) slope.
The entire area is then covered with 1 meter of earth obtained nearby,
after which a 0.5-meter rock cover is added to the entire area. A
fence is installed to form an exclusion area 0.5 kilometer wide all
around the disposed tailings. The borrow pit is reclaimed as described
in Section B.2. The costs for this method are listed in Table B-8.
Method ET7
This disposal method provides for below surface level disposal of
the tailings, with a 3-meter earth cover over the tailings and a
1-meter clay liner below the tailings. For the 2-million-ton pile, a
366-meter square pit is excavated to a 12-meter depth adjacent to the
pile. The bottom of the pit is assumed to be above the groundwater
table. The pit is lined with 1 meter of purchased clay hauled 3.2
kilometers. The tailings are moved into the pit with scrapers, after
which they are covered with 3 meters of the excavated earth. The
disposal area is landscaped. The area covered by excess excavated
earth is restored.
The disposal pit for the 7-million ton pile is 614 meters square
by 15 meters deep, and the pit for the 20-million-ton pile is 1,047
meters square by 15 meters deep. Both pits are assumed to be above the
groundwater table. Because of the large sizes, hauling by trucks for
an average off-road distance of 3.2 kilometers is assumed. The
disposal method and landscaping are similar to those of the 2-million
ton-case. The costs for this method are summarized in Table B-9.
B-13
-------
Table B-4. Disposal Cost Summary: Method ET2
(1981 dollars in millions)
Task
Size of Pile (MT)
20
Grading Slopes
Excavating, hauling, spreading
and compacting cover material
Excavating pit
Placing liner
Excavating, hauling, spreading,
and compacting tailings
Fenc ing
Landscaping
Placing rock cover
Reclaiming borrow pit
Contingency, overhead and profit
TOTAL
Composite Unit Costs
$/MT Tailings
U30
0.06
1.38
3.79
0.64
1.84
6.96
1.90 0.99
2,037 1,069
2.37
3.26
0.54
0.36
0.54
0.28
0.63
0.57
0.41
1.95
0.39
1.16
0.66
0.73
4.32
0.64
2.40
14.38
0.72
773
B-14
-------
Table B-5. Disposal Cost Summary: Method ET3
(1981 dollars in millions)
Task
Size of Pile (MT)
20
Grading slopes
Excavating, hauling, spreading
and compacting cover material
Excavating pit
Placing liner
Excavating, hauling, spreading,
and compacting tailings
Fencing
Landscaping
Placing rock cover
Reclaiming borrow pit
Contingency, overhead and profit
TOTAL
Composite Unit Costs:
$/MT Tailings
U30g
0.06
4.15
0.36
0.54
0.69
1.16
6.94
0.64
5.51
0.41
1.95
0.95
1.89
11.35
2.37
9.79
0.73
4.32
1.42
3.72
22.34
3.47 1.62 1.12
3,730 1,743 1,201
B-15
-------
Table B-6. Disposal Cost Summary: Method ET4
(1981 dollars in millions)
Task
Size of Pile (MX)
20
Grading slopes
Excavating, hauling, spreading,
and compacting cover material
Excavating pit
Placing liner
Excavating, hauling, spreading,
and compacting tailings
Fencing
Landscaping
Placing rock cover
Reclaiming borrow pit
Contingency, overhead and profit
TOTALS
Composite Unit Costs:
fc/MT Tailings
$/MT U30g
0.09
4.29
0.36
0.88
0.73
1.27
7.62
1.04
5.90
0.41
3.20
1.05
2.32
13.92
3.80
11.08
0.73
7.15
1.59
4_.87_
29.22
3.81 1.99 1.46
4,096 2,138 1,571
B-16
-------
Table B-7. Disposal Cost Summary: Method ET5
(1981 dollars in millions)
Task
Size of Pile (MT)
20
Grading slopes
Excavating, hauling, spreading,
and compacting cover material
Excavating pit
Placing liner
Excavating, hauling, spreading,
and compacting tailings
Fencing
Landscaping
Placing rock cover
Reclaiming borrow pit
Contingency, overhead and profit
TOTALS
Composite Unit Costs:
$/MT Tailings
fc/MT U30g
0.09
6.94
1.04
9.84
3.84
18.46
0.94
0.88
1.10
1.99
11.94
1.09
3.20
1.42
3.32
19.91
1.91
7.15
2.45
6.76
40.57
5.97 2.84 2.03
6,418 3,058 2,186
B-17
-------
New Tailings Piles
Method Nil
This method is the same as the base case in the NRC analysis
(NRC80). An initial square basin would be formed by building low
earthen embankments along each side of 947 meters length at the
centerline. The mill tailings would be slurried into the basin, and as
the basin filled, the coarse fraction of the tailings (sands) would be
used to raise and broaden the embankments. The final dimensions of the
embankments would be 10 meters high and 13 meters wide at the top.
When the mill ceases operations, no specific control measures for
disposal would be used. The cost for this option is listed in
Table B-10 and consists only of preparation of the initial basin.
Method NT2
This method is similar to ETl, since both use a thin earth cover
on the tailings and rely on institutional controls to prevent misuse.
A pit is excavated close to the mill and measures 930 meters square by
2 meters deep. Embankments are constructed along each side, 947 meters
long, 10 meters high, and 13 meters wide at the top. The pit is lined
with 1 meter of clay obtained locally. Tailings are pumped directly
into the pit during operation of the mill. It is assumed that water
from the pond will be recycled to the mill, thereby negating the need
for an evaporation pond.
At the end of mill life, the embankments are excavated and placed
on top of the tailings to a depth of 0.5 meter. The slopes of the
covered tailings are graded to 5:1 (H:V). The entire area is
landscaped. A fence is placed around the disposal area and provides a
0.5-kilometer exclusion zone. The site is maintained for 100 years by
irrigation of the vegetative cover and inspection and repair of the
earth cover and fence. Costs are shown in Table B-10.
Method NT3
This method is similar to ET2, since both use a 1-meter earth
cover and a 0.5-meter rock cover on the slopes. A pit is prepared and
used in the same manner to that described for method NT2.
At the end of mill life, the embankments are excavated and placed
on top of the tailings to a depth of 1 meter. The slopes of the
disposed tailings are graded to 5:1 (H:V) and then covered with rock to
a depth of 0.5 meter. The top of the disposed tailings area (that part
not covered with rock) is landscaped. A fence is contructed at a
distance of 0.5 kilometer from the edge of the disposed tailings all
around the site. The costs are listed in Table B-10.
B-18
-------
Method NT4
This method is similar to ET3, since both use a 3-meter earth
cover and a 0.5-meter rock cover on the slopes. A pit is excavated,
prepared, and used in the same manner as that described for method NT2.
At the end of mill life, the embankments are excavated and placed
on top of the tailings. Additional earth cover is obtained from a
nearby borrow pit so that the final earth cover over the tailings is 3
meters deep. The slopes of the covered tailings are graded to 5:1
(H:V) and are covered with a 0.5-meter rock cover. The top of the
earth-covered tailings is landscaped. The borrow pit is reclaimed.
The costs are listed in Table B-10.
Method NTS
This method is somewhat similar to the staged or phased disposal
method described by the NRC's GEIS (NRC80). This method uses 6 pits,
each 300 meters square and 13 meters deep. Two pits are constructed
initially and lined with 1 meter of clay. Tailings are pumped to the
first pit until it is full and then pumped to the second pit. When the
first pit is sufficiently dry, the third or fourth pit is excavated,
and the excavated earth is used to cover the first pit to a depth of 3
meters up to the original ground contour. This process continues
sequentially until the end of mill life. An evaporation pond is needed
in this method. Costs for this pond are taken from the NRC GEIS and
corrected for inflation.
At the end of mill life there will likely be four completed pits,
which are covered with 3 meters of earth to the original ground contour
and 2 uncovered pits. When sufficiently dry, these last two pits are
covered with 3 meters of excavated earth to the original ground
contour. The disposed tailings area is landscaped. The areas covered
by the evaporation pond and excess excavated earth are restored. The
costs for this method are presented in Table B-10.
Method NT6
This method is the same as Alternative 7 in the NRC GEIS (NRC80).
The tailings are pumped to the edge of a depleted mine pit, where the
sands (coarse fraction) and slimes (fine fraction) are separated. The
sands are washed, dried, and deposited in the mine pit. The slimes are
partially dried, mixed with cement, and deposited in the mine pit where
the cement and fine slurry would harden. The cost for this method is
listed in Table B-10.
Method NT7
This method is similar to ET5, since both use a 5-meter earth
cover and a 0.5-meter rock cover on the slopes. A pit is excavated,
prepared, and used in the same manner as that described for method NT2.
B-19
-------
At the end of mill life, the embankments are excavated and placed
on top of the tailings. Additional earth cover is obtained from a
nearby borrow pit so that the final earth cover over the tailings is
5 meters deep. The slopes of the covered tailings are graded to 8:1
(H:V) and are covered with a 0.5-meter rock cover. The top of the
earth-covered tailings is landscaped. The borrow pit is reclaimed.
The costs are listed in Table B-10.
Table B-8. Disposal Cost Summary: Method ET6
(1981 dollars in millions)
Task
Size of Pile (MT)
Grading slopes
Excavating, hauling, spreading,
and compacting cover material
Excavating pit
Placing liner
Excavating, hauling, spreading,
and compacting tailings
Fencing
Landscaping
Placing rock cover
Reclaiming borrow pit
Contingency, overhead and profit
TOTALS
Composite Unit Costs:
$/MT Tailings
$/MT U308
0.05
1.37
0.54
12.79
0.64
1.82
0.57
17.37
2.35
3.24
0.66
8.34
0.35
2.14
11.05
0.39
2.90
20.25
0.64
5.40
32.54
6.40 2.48 1.63
6,875 2,668 1,749
B-20
-------
Table B-9. Disposal Cost Summary: Method ET7
(1981 dollars in millions)
Task
Size of Pile (MT)
20
Grading slopes
Excavating, hauling, spreading,
and compacting cover material
Excavating pit
Placing liner
Excavating, hauling, spreading,
and compacting tailings
Fenc ing
Landscaping
Placing rock cover
Reclaiming borrow pit
Contingency, overhead and profit
TOTAL
Composite Unit Costs:
$/MT Tailings
$/MT U308
1.08
3.82
1.55
3.70
0.10
2.06
12.31
2.94
14.70
4.37
14.09
0.28
7.28
43.66
8.55
42.75
12.69
40.97
0.81
21.20
126.92
6.16 6.24 6.35
6,617 6,705 6,822
B-21
-------
Table B-10.
Disposal Cost Summary: Methods NT1 Through NT6
(1981 dollars in millions)
Disposal Method
(For 8.4-Million-Ton Pile)
Task
NT1
NT2
NT 3
NT4
NT5
NT6
NT7
Excavate pit and construct
embankments
Placing liner
Grading slopes
Spreading and compacting
cover material
Fencing
Landscaping
Placing rock cover
Reclaiming borrow pit
Maintain for 100 years
Other costs
Contingency, overhead,
and profit
TOTAL
Composite Unit Costs:
$/MT Tailings
U308
0.96 4.67 4.67 4.67 I8.61
-------
REFERENCES
DG81 "Dodge Guide to Public Works and Heavy Construction Cost,"
Annual Edition No. 13, McGraw-Hill, 1981.
Me82 "Building Construction Cost Data," 1982, Robert Snow Means
Co., Inc., 100 Construction Plaza, Duxbury, Mass.
NRC80 Nuclear Regulatory Commission, "Final Generic Environmental
Impact Statement on Uranium Milling," NUREG-0706, Washington,
D.C., September 1980.
PE82 PEDCO Environmental, Inc., "Evaluation of Costs to Control
Fugitive Dust from Tailings at Active Uranium Mills," EPA
Contract No. 68-02-3173, Task No. 053, USEPA, Washington,
D.C., March 1982.
B-23
-------
APPENDIX C
HEALTH BASIS FOR HAZARD ASSESSMENT
-------
Appendix C: HEALTH BASIS FOR HAZARD ASSESSMENT
CONTENTS
Page
Introduction C-5
C.I Risk Models for Stochastic Effects C-5
C.I.I The.RADRISK Code C-6
C.2 Risk Estimates for Inhaled Radon and Radon-Daughters (Radon
Decay Products C-9
C.2.1 Risk of Lung Cancer from Inhaling Radon Decay Products C-9
C.3 Risk Factors per Unit Exposure C-13
C.4 Risks from Toxic Materials, Nonstochastic Effects C-13
C.4.1 Estimates of Chronic Toxicity in Humans C-22
C.4.2 Estimates of Chronic Toxicity in Animals and Plants ... C-22
References C-24
TABLES
C-l Risk Parameters for Cancers Considered C-7
C-2 Genetic Risk Parameters C-8
C-3 Lifetime Risk of Excess Cancer in a Cohort of 100,000 for
Continuous Exposure to Lead-210 C-14
C-4 Lifetime Risk of Excess Cancer in a Cohort of 100,000 for
Continuous Exposure to Polonium-210 C-15
C-5 Lifetime Risk of Excess Cancer in a Cohort of 100,000 for
Continuous Exposure to Radium-226 C-16
C-6 Lifetime Risk of Excess Cancer in a Cohort of 100,000 for
Continuous Exposure to Thorium-230 C-17
C-7 Lifetime Risk of Excess Cancer in a Cohort of 100,000 for
Continuous Exposure to Uranium-234 C-18
C-3
-------
CONTENTS (Continued)
Page
C-8 Lifetime Risk of Excess Cancer in a Cohort of 100,000 for
Continuous Exposure to Uranium-238 C-19
C-9 30-Year Genetic Dose Commitment C-20
C-10 Selected Potentially Toxic Substances Associated with Uranium
Mill Tailings C-22
C-ll Daily Intake Levels of Selected Elements Estimated to be
Toxic C-23
FIGURES
C-l Excess Fatal Lung Cancer in Various Miner Groups by
Cumulative Exposure C-10
C-4
-------
Appendix C: HEALTH BASIS FOR HAZARD ASSESSMENT
I ntroduction
Inhalation or ingestion of radionuclides or toxic chemicals can
have adverse effects on human and animal health. The adverse effects
can be separated, generally, into stochastic and nonstochastLc.
Stochastic effects are those in which the probability of the effect is
proportional to the exposure level, but the severity of the effect is
independent of exposure. Nonstochastic effects are those in which the
severity of the effect is proportional to the exposure level and there
is usually a threshold level of exposure below which no effect is
observed.
Low levels of radiation exposure, such as that associated with
inhalation or ingestion of radionuclides transported into the
environment from tailings piles, generally produce stochastic effects.
Radiation from radionuclide particles deposited on the ground may also
expose people causing stochastic effects. Ingestion or inhalation of
toxic chemicals from tailings piles would cause nonstochastic effects.
For purposes of this analysis, only stochastic effects (e.g.,
cancer and inherited abnormalities) will be considered in the case of
ionizing radiation exposure and only nonstochastic (e.g., acute and
chronic poisoning) in the case of exposure to toxic elements.
C. 1 Risk ModeJ.s for_S_tochastic Ef fec^s
There are two kinds of risks from the low levels of ionizing
radiation characteristic of exposures to radionuclides released into
the environment. The most important of these is cancer, which is fatal
at least half the time. The other risk is the induction of hereditary
effects in descendants of exposed persons; the severity ranges from
fatal to inconsequential. As mentioned above, we assume that at low
levels of exposure the risk of cancer and hereditary effects is in
proportion to the dose received, and that the severity of any induced
effect is independent of the dose level. That is, while the
probability of a given type of cancer occurring increases with dose,
such a cancer induced at one dose is equally as debilitating as that
same type of cancer induced at another dose. For these effects, we
assume that there is no completely risk-free level of radiation
exposure.
C-5
-------
The risks and effects on health from low-level ionizing radiation
were reviewed for EPA by the National Academy of Sciences in reports
published in 1972 and in 1980 (NAS72a, NASBOb). We have used these
studies and others to estimate the risks associated with the radiation
doses calculated in this report.
exposed individuals;" these people are located at the point of highest
lifetime risk. The risk to the individual is the risk of premature
death from cancer due to the radiation dose received. The risk
calculation considers all important radionuclides, pathways, and organs
of the body.
The risk to an individual can be subdivided and related to other
parameters. For example, we can determine which part of the risk is
committed by radionuclides moving through a specific pathway or which
organ is at highest risk. This information is helpful when deciding
which control strategies will be the most effective.
The risk to populations can also be estimated; that is, the number
of future effects on health that are committed for each year that the
source operates. The risks are associated with doses delivered to
people over a time period which is longer than the average individual's
lifespan. The dose is not necessarily delivered to people during the
years of release because radionuclides with long half-lives may take a
long time to move through environmental pathways to people.
Like the individual lifetime risk, the total risk to populations
can be subdivided and related to other parameters, such as organ,
radionuclide, or exposure pathway.
The genetic risk is the risk to future generations associated with
the dose equivalent to the gonads of both exposed parents over the
first 30 years of their lives. We calculate the total genetic risk for
the same population for which we calculate the collective potential
fatal cancer risk.
C.1.1 The RADRISK Code
The estimates of cancer and genetic risk are calculated using a
computer code called RADRISK. In RADRISK, the group assumed to be at
risk by the code is a hypothetical cohort of 100,000 people, all born
simultaneously and subject to the same risks throughout their lives.
Each member is assumed to be exposed at a constant rate to a unit
concentration of radionuclides. For each radionuclide and for each
pathway, the code calculates the number of premature deaths Hue to
radiation and the number of years of life lost due to these deaths.
When radionuclides are inhaled, they enter the lung, and the ICRP
Task Group lung model is used to predict where in the lung they go and
C-6
-------
Table C-l. Risk parameters for cancers considered (Su81)
Risk Factor
Latency
Cancer (years)
Leukemia
Bone
Lung
Breast
Liver
Stomach
Pancreas
Lower Large
Intestine
Kidneys
Bladder
Upper Large
Intestine
Small Intestine
Ovaries
Testes
Spleen
Uterus
Thymus
Thyro id
2
5
10
15
15
15
15
15
15
15
15
15
15
15
15
15
15
2
Low-LET radiation
Plateau (deaths/106 rad
(Drears) person-years at risk)
25
30
110
HO
110
110
110
110
110
110
110
110
110
110
110
110
110
45
2.3
0.2
3.0
2.3
0.9
0.5
0.7
0.4
0.2
0.2
0.2
0.1
O.L
0.1
0.1
0.1
0.1
0.4**
High-LET radiation
(deaths/106 rad
person-years at risk)
46
4
30
2.3
9
5
7
4
2
2
2
1
1
1
1
1
1
0.4**
Number of premature
deaths in cohort from
chronic 1 mrad/y exposure*
0. 326
0.031
0.608
0.399
0.154
0.087
0.121
0.069
0.035
0.035
0.035
0.017
0.017
0.017
0.017
0.017
0.017
0.085
*Low-LET
**0.04 for 131]; anc} longer-lived radio iodine.
C-7
-------
how fast they are removed to other parts of the body. Depending on
size and solubility class, there is removal of some of this material to
the gastrointestinal (Gl) tract and absorption by the blood. A GI
tract model is used to estimate how much of the material reaching the
tract is absorbed by the blood.
After absorption by the blood, radionuclides are distributed among
the organs according to uptake and metabolic information supplied to
RADRISK. Dose rates are calculated with the help of models that
simulate the biological processes involved when radionuclides enter and
leave organs.
Cancers do not appear immediately after exposure. There is a
latent period before the cancers are observed; the length, usually
years, varies with the type of cancer. Thereafter, there is a
specified period when there is a finite probability of cancer, a
"plateau" period, and it also varies with the type of cancer. Table
C-l lists the risk parameters used in RADRISK.
Lifetime probabilities for many types of cancer, in many organs,
are followed and risks calculated. At the same time, competing risks
unrelated to the radiation exposure are accounted for. The RADRISK
code does this; however, we do not yet understand how accurate these
calculations are. In particular, cancer risks and metabolic parameters
are uncertain, and since relative risk estimates are not available for
all radiation-induced cancers, only an absolute risk estimate is made.
We believe risks are accurate to an order of magnitude only and should
never be reported to more than one significant figure.
Inherited abnormalities (genetic effects), as noted above, do not
occur in those exposed to radiation but in their progeny. The genetic
risk coefficient used in RADRISK is:
Table C-2. Genetic Risk Parameters
First All
Generation Generations
Risks per one million live- 0.04 0.2
births per mrad low-LET
radiation
A more detailed description of RADRISK can be found in
ORNL/TM-7745, "Estimates of Health Risk from Exposure to Radioactive
Pollutants" (Su81).
C-8
-------
^•2 Risk Estimates f_or Inhaled Radon . an«J T^dcm^aughters__(Radon_ Dec_ay
Produ c t s )
An estimate of the health risk from inhaling radon and its
short-lived daughters has been done separately for both historic and
technical reasons.
The history of the health impact of exposure to radon and its
short-lived daughters has its roots in the past, before the discovery
of x-rays or identification of radioactivity. The units of exposure,
Working Level (WL) , Working Level Month (WLM) , are unusual and do not
fit into the RADRISK computer code. The risk of radon, radon-daughter
exposure has been calculated independently of the RADRISK program
calculations for this analysis.
C . 2 . 1 Risk of Lung Cane e r _f_rom _In_ha Li ng_ Radp n Dej^ay^ Produc t_s
The high incidence of lung cancer mortality among underground
miners is well documented (EPA79a, Ar79, Ar81). Uranium miners are
particularly affected, but lead, iron, and zinc miners exposed to
relatively low levels of radon decay products also show an increased
lung cancer mortality that correlates with exposure to radon decay
products. The type of lung cancer most frequently observed, moreover,
is relatively uncommon in the general population.
Risk estimates for the general public based on these studies of
miners are far from precise. First, and most important, the relatively
small number of miners at risk injects considerable statistical
uncertainty into estimating the number of excess lung cancer cases (see
Figure C-l) . Second, although the cumulative lifetime exposure in
contaminated buildings can be comparable to that of some miners, most
of the miners studied were exposed to much higher levels of radon decay
products than usually occur in the general environment. Third, the
exposure levels are uncertain. Fourth, significant demographic
differences exist between miners and members of the general public — the
miners were healthy males over 14 years old, many of whom smoked.
However, information from the studies of miners can provide useful
estimates, if not precise predictions, of the risks to the general
population from radon decay products. ^ *•'
Since the miners being studied have not all died, their eventual
excess lung cancers must be projected from current data by using
mathematical models. There are two ways to use the observed frequency
of lung cancer deaths among the exposed miners to estimate the risk
from inhaling radon decay products over a person's lifetime. One,
"indoor Radiation Exposure Due to Radium-226 in Florida
Phosphate Lands" (EPA 79a) for greater detail of such an analysis.
C-9
-------
80
70
DC
LU
> 60
o
0
o
o"
i 5°
LU
0
z
0 40
z
D
% 30
CO
ATTRIBUT
NJ
O
10
0
>
—
"
—
—
—
c
A
Jt
<
-i-
|
A(
>
>
t
A
i
> R°
I
<
*\
4
\
}
i
O
1
—
__
—
—
—
—
0 CZECH -URANIUM
Q SWEDEN - LEAD, ZINC (A), IRON (R.J)
^ A UNITED STATES -URANIUM
A CANADA -URANIUM —
X 95% CONFIDENCE LIMITS
I
1 1 1
0 100 200 300 400 500 600
CUMULATIVE WORKING LEVEL MONTHS
700
Figure C-l. EXCESS FATAL LUNG CANCER IN VARIOUS MINER GROUPS
BY CUMULATIVE EXPOSURE (Ar79).
C-LO
-------
commonly called the relative risk model, yields the percent increase in
the normal incidence of cancer per unit of exposure. The other, called
the absolute risk model, yields the absolute numerical increase in
cancers per unit of exposure. In the relative risk model, it is
assumed that the increased risk is proportional to the age-dependent
natural incidence of the disease for each year an individual remains
alive following exposure. In the absolute risk model, it is assumed
that the added risk is independent of natural incidence, i.e., the risk
is constant each year an individual remains alive following exposure.
As a basis for calculating estimates using the relative risk
model, we conclude that a 3-percent increase in the number of lung
cancer deaths per WLM is consistent with data from the studies of
underground miners. However, because of the differences between adult
male miners and the general population (EPA79a), we estimate that the
risk to the general population may be as low as 1 percent or as high as
5 percent. To develop absolute risk estimates in earlier reports, we
used the estimate of 10 lung cancer deaths per WLM for 1 million
person-years at risk reported by the National Academy of sciences
(NAS76). In a 1978 paper, Land and Norman (La78) reported that in
Japanese A-bomb survivors, radiation-induced lung cancers had a
temporal distribution of occurrence similar to naturally-occurring
cancers of the same site. Further, they concluded the cumulative
distribution of radiation-induced lung cancer across time after
exposure was consistant with a relative risk model of cancer incidence
or with an age-specific absolute risk model.
In a paper at the same symposium, Smith and Doll (Sm78) reported
the risk of cancer developing at most "heavily irradiated" sites in
ankylosing spondylitic patients treated with x-rays was directly
proportional to the risk of a tumor in the absence of radiation; in
other words, a relative-risk-like response. In the most recent report
on the Japanese A-bomb survivors, Kato and Schull (Ka82) reiterated the
observation that radiation-induced lung cancer develops only after the
survivors attain the age at which this cancer normally develops. The
evidence in these three reports of external radiation exposure points
to relative-risk or age-specific absolute risk models as being
appropriate for radiation-induced lung cancer.
Recent information from China provides similar evidence for
exposure to radon, radon daughters. Shi-quan and Xiao-ou (Sh82) have
reported that in Chinese tin miners exposed to radon and its daughters,
ths lung cancers developed at the age at which lung cancer normally
develops. Those who started mining at age 8 or 9 had an
induction-latent period about 10 years longer than those who started
mining at age 19 or 20. Here, again, a simple absolute risk model will
not fit the observations.
In view of these observations that a simple absolute risk model is
inappropriate for estimating the risk of lung cancer due to radon
C-ll
-------
daughter exposure, a simple absolute risk estimate was not calculated.
A prior comparison of risks calculated using a relative model and the
age-specific absolute risk model from BEIR III (NASSOb) showed them to
be numerically similar (860 cases/10" person-WLM versus 850
cases/106 person-WLM) (RPC80). Because of the similarly in risk
estimates, only relative risk estimates for radon daughter exposures
are used in this document.
Unless we state otherwise, we estimate excess cancer fatalities,
i.e., those caused by elevated radiation levels that are in addition to
those from other causes.
To estimate the total number of lung cancer deaths from increased
levels of radon in the environment, we have used a Life-table analysis
of the additional risk due to radiation exposure (Bu81). This analysis
uses the risk coefficients just discussed. It also takes into account
the length of time a person is exposed and the number of years a person
survives other potential causes of death based on 1970 U.S. death rate
statistics. The result is expressed as the number of premature lung
cancer deaths that would occur due to lifetime radiation exposure of
100,000 persons. We assume, further, that injury caused by alpha
radiation is not repairable, so that exposed persons remain at risk for
the balance of their lifetimes.
Using the relative risk model, we estimate that a person exposed
to 0.01 WL (.27 WLM/y) over a lifetime incurs a 1.7 percent (1 in 60)
additional chance of contracting a fatal lung cancer. This estimate
was made assuming children are no more sensitive than adults. IE
exposure to radon decay products during childhood carries a three times
greater risk, this estimated lifetime relative risk would increase by
about 50 percent (EPA79a). Using a similar lifetable analysis and an
absolute risk model, we would have estimated that a person exposed to
0.01 WL over a lifetime incurs a 0.7 percent (1 in 140) additional
chance of contracting a fatal lung cancer. Again, equal child and
adult sensitivities are assumed (EPA79a). For comparison, a lifetable
analysis for the same population not exposed to excess radiation yields
a 2.9 percent chance of lung cancer death.
Even though, under either of these models, the risk of
radon-induced lung cancer varies with age, it is sometimes convenient:
to express these risks on an average annual basis. We have calculated
a person's average annual risk from a lifetime of exposure by dividing
the lifetime risk estimates given above by an average lifespan of 71
years.^1' Based on the risk model and assumptions just described for
(1) Note that this is not the same as applying the risk coefficient for
71 years, since the lifetable analysis accounts for other causes of
death.
C-12
-------
lifetime exposure, we estimate an average of 2.4 lung cancer deaths per
year for each 100 person-working-levels of such exposure. "Person-
working-levels" is the population's collective exposure; that is, the
number of people times the average concentration of radon decay
products (in working levels) to which they are exposed.
For the entire U.S. population, the estimated number of cancers is
large using the relative risk model, but this estimate does not hold
for all locations because the lung cancer rate varies considerably in
different parts of the country. Therefore, we can base our relative
risk estimate for each source on the lung cancer death rate for the
State in which the source is located. Lung cancer death rates are
lower than the national average in several of the States, so at some
localities the relative risk is lower than at others.
Radiation risk can also be stated in terms of years of life lost
due to cancer death. In the relative risk model, the distribution of
ages at which lung cancer caused by radiation occurs is the same as
that for all lung cancer in the general population. Since lung cancer
occurs most frequently in people over 70 years of age, the years of
life lost per fatal lung cancer—14.5 years on the average—is less
than for many other fatal cancers. The absolute risk model wrongly
assumes that lung cancer fatalities occur at a uniform r-ate throughout
life and, therefore, each fatality reduces the lifespan by a larger
amount—an average of 24.6 years.
Because we used recent population data, our assessments are for
current conditions. If the population lifestyle, medical knowledge,
and other patterns of living affecting mortality remain unchanged, then
these rates of lung cancer death could persist for the indefinite
future. We have not attempted to assess the effects of future change,
which may either increase or decrease our risk estimates. It is
prudent, we believe, to assume that estimated risks based on current
data could persist over the indefinite future.
C. 3 Risk Factors per Unit__Exp_osure
Risk factors computed in the RADRISK program or in the radon risk
program for unit exposure are listed in Tables C-2 through C-9.
C.4 RjJ?^s_Fr_om Toxic Materials, Nojistochastic^ Effects
Toxic materials have been considered in this analysis if they are
in substantially greater concentration in the source than in native
rocks or soils or in a relatively mobile form (anionic or cationic).
Materials that are harmful to livestock and plants as well as those
potentially affecting humans directly have been included. Evaluating
the potential risks from nonradioactive toxic substances requires
C-13
-------
Table C-3. Lifetime Risk of Excess Cancer in a Cohort
of 100,000 from Continuous Exposure to 21°Pb
Inhalation (1 pCi/y)
Organ
Red Marrow
Endos teum
Pulmonary Lung
Breast
Liver
Stomach Wall
Pancreas
Lower Large
Intestine Wall
Kidneys
Bladder Wall
Upper Large
Intestine Wall
Small Intestine
Wall
Ovaries
Testes
Spleen
Uterus
Thymus
Thyroid
0.3 ym
J.6E-4
1.8E-4
2.0E-6
4.5E- o
3.4E-4
7.3E-9
l.OE-5
6.8E-8
3.8E-5
1. 5E-6
l.OE-8
2.1E-9
1.5E-6
1.5E-6
1.7E-6
1.5E-6
1.5E-6
l.OE-6
Particle Size
7.75 urn
4.1E-4
2.1E-4
3.8E-7
5.0E-6
3.9E-4
1.4E-8
1.1E-5
5.3E-7
4.1E-5
1.6E-6
5.9E-8
5.1E-9
1.6E-6
1.6E-6
1.6E-6
1.6E-6
1.6E-6
1.2E-6
54.2 ym
3.9E-4
2.0E-5
1.8E-7
4.9E-6
3.8E-4
1.4E-8
1.1E-5
6.0E-7
3.9E-5
1.6E-6
6.6E-8
5.5E-9
1.6E-6
1.6E-6
1.5E-6
1.6E-6
1.6E-6
1.1E-6
Ingest ion
(1 pCi/y)
1.3E-4
6.4E-4
3.6E-8
1.6E-6
1.2E-4
1.6E-8
3.6E-6
1.2E-6
1.3E-5
5.0E-7
1.3E-7
7.8E-9
5.1E-7
5.1E-7
4.9E-7
5.1E-7
5.1E-7
3.6E-7
Ground
Deposition
(1 pCi/cm2)
1.3E-3
1.4E-4
l.OE-3
9.1E-4
2.0E-4
1.3E-4
1.1E-4
5.6E-5
4.9E-5
3.5E-5
3.5E-5
1.5E-5
3.0E-5
4.6E-5
2.1E-5
6.4E-6
2.5E-5
2.0E-4
TOTAL
9.5E-4
1.1E-3
l.OE-3
3.4E-4
4.3E-3
C-14
-------
Table C-4. Lifetime Risk of Excess Cancer in a Cohort
of 100,000 from Continuous Exposure to Polonium-210
Inhalation (1 pCi/y)
Organ
Red Marrow
Endosteum
Pulmonary Lung
Breast
Liver
Stomach Wall
Pancreas
Lower Large
Intestine Wall
Kidneys
Bladder Wall
Upper Large
Intestine Wall
Small Intestine
Wall
Ovaries
Testes
Spleen
Uterus
Thymus
Thyroid
0. 3 jj m
2.6E-4
5.6E-6
4.1E-2
1.6E-5
1.9E-4
8.2E-8
4.8E-5
2.6E-6
2.4E-4
6.8E-6
4.3E-7
3.7E-8
6.8E-6
6.8E-6
2.1E-4
6.8E-6
6.8E-6
3.3E-6
Particle Size
7. 75 jjm
3.8E-4
8.1E-6
5.9E-3
2.3E-5
2.7E-4
1.6E-7
6.9E-5
5.2E-6
3.5E-4
9.8E-6
8.6E-7
7.3E-8
9.8E-6
9.8E-6
3.0E-4
9.8E-6
9.8E-6
4.8E-6
54.2 pm
3.6E-4
7.6E-6
1.4E-3
2.1E-5
2.6E-4
1.7E-7
6.5E-5
5.5E-6
3.3E-4
9.2E-6
9.2E-7
7.8E-8
9.2E-6
9.2E-6
2.4E-4
9.2E-6
9.2E-6
4.5E-6
Ingest ion
(1 pCi/y)
1.8E-4
3.8E-6
7.0E-12
l.OE-5
1.3E-4
2.0E-7
3.2E-5
6.2E-6
1.6E-4
4.6E-6
l.OE-6
8.8E-8
4.6E-6
4.6E-6
1.4E-4
4.6E-6
4.6E-6
2.2E-6
Ground
Deposition
(1 pCi/cm2)
3.1E-6
3.1E-7
5.1E-6
3.6E-6
1.2E-6
6.9E-7
9.1E-7
4.1E-7
2.9E-7
2.7E-7
2.7E-7
1.2E-7
8.0E-8
1.5E-7
1.6E-7
1.1E-7
l.OE-7
5.6E-7
TOTAL
4.2E-2
7.4E-3
2.8E-4
6.9E-4
1.7E-5
C-15
-------
Table C-5. Lifetime Risk of Excess Cancer in a Cohort
of 100,000 from Continuous Exposure to Radium-226
Organ
Red Marrow
Endosteum
Pulmonary Lung
Breast
Liver
Stomach Wall
Pancreas
Lower Large
Intestine Wall
Kidneys
Bladder Wall
Upper Large
Intestine Wall
Small Intestine
Wall
Ovaries
Testes
Spleen
Uterus
Thymus
Thyroid
Inhalation (
Particle
7.75 Urn
8.9E-4
3.6E-4
7.2E-3
1.7E-5
5.8E-5
2.6E-7
4.8E-5
1.1E-5
1.3E-5
6.9E-6
1.3E-6
1.1E-7
6.9E-6
6.9E-6
6.4E-6
6.9E-6
6.9E-6
3.6E-6
1 pCi/y)
Size
54.2 pm
8.6E-4
3.4E-4
1.8E-3
1.6E-5
5.6E-5
2.6E-7
4.6E-5
1.2E-5
1.2E-5
6.6E-6
1.3E-6
1.1E-7
6.6E-6
6.6E-6
6.2E-6
6.6E-6
6.6E-6
3.4E-6
Ingestion
(1 ECi/y)
5.9E-4
2.4E-4
7.0E-7
1.1E-5
3.8E-5
2.5E-7
3.2E-5
1.3E-5
8.5E-6
4.5E-6
1.5E-6
1.1E-7
4.5E-6
4.5E-6
4.2E-6
4. 5E-6
4.5E-6
2.3E-6
Ground
Deposition
(1 pCi/cra2)
3.9E-3
4.0E-4
4.5E-3
3.0E-3
l.OE-3
4.8E-4
5.9E-4
3.2E-4
2.1E-4
1.9E-4
2.1E-4
l.OE-4
7.6E-5
1.8E-4
1.1E-4
8.1E-5
1.1E-4
7.1E-4
TOTAL 8.7E-3 3.1E-3 9.6E-4 1.6E-2
C-16
-------
Table C-6. Lifetime Risk of Excess Cancer in a Cohort
of 100,000 from Continuous Exposure to
Organ
Red Marrow
Endosteum
Pulmonary Lung
Breast
Liver
Stomach Wall
Pancreas
Lower Large
Intestine Wall
Kidneys
Bladder Wall
Upper Large
Intestine Wall
Small Intestine
Wall
Ovaries
Testes
Spleen
Uterus
Thymus
Thyroid
TOTAL
Inhalation
Particle
7.75 pm
2.3E-2
1.6E-2
6.6E-2
8.0E-6
1.5E-4
1.7E-7
2.4E-5
6.0E-6
6.9E-6
3.5E-6
l.OE-6
8.5E-8
3.5E-6
3.5E-6
3.5E-6
3.5E-6
3.5E-6
1.8E-6
1.1E-1
(1 pCi/y)
Size
54.2 jjm
1. 5E-2
1.1E-2
1.6E-2
5.2E-6
9.7E-5
1.8E-7
1.6E-5
6.2E-6
4.5E-6
2.3E-6
l.OE-6
8.8E-8
2.3E-6
2.3E-6
2.3E-6
2.3E-6
2.3E-6
1.1E-6
4.2E-2
Ingestion
. Jl_PCi6l>_ -
2.4E-4
1.7E-4
3.7E-10
8.4E-8
1.6E-6
1.8E-7
2.5E-7
6.3E-6
7.3E-8
3.6E-8
l.OE-6
8.9E-8
3.6E-8
3.6E-8
3.6E-8
3.6E-8
3.6E-8
1.8E-8
4.2E-4
Ground
Deposition
(1 pCi/cm2)
2.9E-4
3.0E-5
2.7E-4
2.5E-4
5.3E-5
3.1E-5
3.3E-5
1.9E-5
1.2E-5
9.9E-6
l.OE-5
4.9E-6
4.7E-6
1.3E-5
5.7E-6
3.0E-6
5.4E-6
4.6E-5
1.1E-3
C-17
-------
Table C-7. Lifetime Risk of Excess Cancer in a Cohort
of 100,000 from Continuous Exposure to
Organ
Red Marrow
Endos teum
Pulmonary Lung
Breast
Liver
Stomach Wall
Pancreas
Lower Large
Intestine Wall
Kidneys
Bladder Wall
Upper Large
Intestine Wall
Small Intestine
Wall
Ovaries
Testes
Spleen
Uterus
Thymu s
Thyroid
Inhalation
Particl
7.75 ym
2.4E-5
1.6E-5
6.7E-2
1.3E-7
4.7E-7
2.0E-7
3.6E-7
6.1E-6
1.1E-5
5.7E-8
l.OE-6
9.1E-8
5.2E-8
5.2E-8
5.2E-8
5.2E-8
5.2E-8
2.7E-8
i (1 pCi/y)
.e Size
54.2 pm
1.6E-5
1.1E-5
1.6E-2
8.4E-8
3.2E-7
2.0E-7
2.5E-7
6.3E-6
7.5E-6
3.9E-8
1.1E-6
9.2E-8
3.6E-8
3.6E-8
3.6E-8
3.6E-8
3.6E-8
1.8E-8
Ingest ion
.(1 pCi/y)
2.3E-4
1.5E-4
1.7E-6
1.2E-6
4.5E-6
4.2E-7
3.5E-6
5.3E-6
1.1E-4
5.5E-7
9.5E-7
1.2E-7
5.0E-7
5.0E-7
5.0E-7
5.0E-7
5.0E-7
2.5E-7
Ground
Deposition
(1 pCi/cm2)
1.4E-4
1.5E-5
1 . 1E-4
1 . 9E-4
1.6E-5
1.3E-5
1.4E-5
l.OE-5
3.4E-6
2.8E-6
2.8E-6
1.4E-6
1.9E-6
9.6E-6
1.9E-6
7.6E-7
1 . 6E-6
1.6E-5
TOTAL 6.7E-2 1.6E-2 5.1E-4 5.4E-4
C-18
-------
Table C-8. Lifetime Risk of Excess Cancer in a Cohort
of 100,000 from Continuous Exposure to
Org_an
Red Marrow
Endos teum
Pulmonary Lung
Breast
Liver
Stomach Wall
Pancreas
Lower Large
Intestine Wall
Kidneys
Bladder Wall
Upper Large
Intestine Wall
Small Intestine
Wall
Ovaries
Testes
Spleen
Uterus
Thymus
Thyroid
TOTAL
Inhalation
Particle
7.75 p m
2.0E-5
1.3E-5
6.1E-2
2.7E-7
5.1E-7
2.9E-7
3.8E-7
9.2E-6
9.8E-6
5.4E-8
1.5E-6
1.3E-7
4.8E-8
4.7E-8
5.4E-8
5.0E-8
5.9E-8
5.6E-8
6.1E-2
(1 pCi/y)
Size
54. 2 jj tn
1.4E-5
9.0E-6
1.5E-2
1.2E-7
3.0E-7
2.1E-7
2.4E-7
7.0E-6
6.7E-6
3.6E-8
1.1E-6
9.6E-8
3.1E-8
3.1E-8
3.4E-8
3.3E-8
3.5E-8
2.6E-8
1.5E-2
Ingestion
(1 pCi/y)
1.9E-4
1.3E-4
1.5E-6
1.2E-6
3.9E-6
3.7E-7
3.2E-6
5.1E-6
9.5E-5
4.9E-7
8.7E-7
1.1E-7
4.3E-7
4.3E-7
4. 5E-7
4. 5E-7
4.5E-7
2.7E-7
4.3E-4
Ground
Deposition
(1 pCi/cm?)
7.6E-5
8.3E-6
5.2E-5
1.3E-4
4.6E-6
6.3E-6
7.0E-6
5.8E-6
l.OE-6
7.4E-7
7.9E-7
3.6E-7
9.2E-7
6.8E-6
8.0E-7
1.3E-7
5.3E-7
6.0E-6
3.1E-4
C-19
-------
Table C-9. 30-Year Genetic Dose Commitment
(mrad)
Organ
Ovary
LOW-LET
High-LET
Testis
LOW-LET
High-LET
Ovary
LOW-LET
High-LET
Testis
LOW-LET
High-LET
Ovary
LOW-LET
High-LET
Testis
LOW-LET
High-LET
Lead-
210
9.6E-5
2.5E-4
9.4E-5
2.5E-4
9.3E-5
2.4E-4
9.1E-5
2.4E-4
3.1E-5
7.8E-5
2.9E-5
7.8E-5
Polonium-
210
(7.75
1.6E-9
1.7E-3
5.9E-10
1.7E-3
(54.2
1.6E-9
1.6E-3
5.6E-10
1.6E-3
1.3E-9
7.8E-4
3.2E-10
7.8E-4
Radium-
226
INHALATION
m particle
7.1E-5
1.2E-3
3.9E-5
1.2E-3
m particle
7.1E-5
1.2E-3
3.7E-5
1.1E-3
INGESTION
6.2E-5
7.6-6
2.7E-5
7.1E-4
Rad ium-
230
size)
2.0E-6
5.8E-4
1.8E-6
5.8E-4
size)
1.4E-6
3.8E-4
1.2E-6
3.8E-4
2.0E-7
6.2E-5
2.4E-8
6.2E-6
Thorium-
234
1.8E-7
8.8E-6
2.4E-8
8.8E-6
1.8E-7
6.0E-6
1.7E-8
6.0E-6
3.7E-5
8.6E-5
2.2E-7
8.6E-5
Uranium-
238
6.7E-6
7.3R-6
5.0E-6
7.4E-6
2.6E-6
5.1E--6
1.9E-6
5.1E--6
1.5E-5
7.2E-5
1.4E-5
7.2E-5
GROUND DEPOSITION
Ovary
Testis
4.0E-2
7.9E-2
1 . 4E-4
2.6E-4
1.3E-1
3.1E-1
8.1E-3
2.3E-2
3.2E-3
1.7E-2
1.6E-3
1.2E-2
020
-------
different methods from those used for radioactive substances.vD As
noted earlier, with nonradioactive toxic materials, the type of effect
varies with the material; the severity of the effect—but not its
probability of occurring—increases with the dose. Moreover, because
the body can detoxify some materials or repair the effects small doses,
often no toxic effects occur below a threshold dose.
We cannot construct a numerical risk assessment for nonradioactive
toxic substances because we do not have enough information. We can,
however, qualitatively describe risks of toxic substances in terms of
their likelihood of reaching people (or animals, or agricultural
products), concentrations at which they may be harmful, and their toxic
effects. No acute effects—death in minutes or hours—are expected at
concentrations addressed in this analysis. Severe sickness, or death
within days to weeks, from the use of highly contaminated water is
possible, but unlikely.
Chronic toxicity from the continuous consumption of contaminants
at low concentrations could be a problem. Toxic substances can
accumulate slowly in tissues, causing symptoms only after some minimum
amount has accumulated. Such symptoms of chronic toxicity develop
slowly, over months or years.
An extensive section in the EIS for inactive sites (EPA82-83) was
devoted to toxicity of elements found in uranium mill tailings and
tailings ponds and problems associated with them. Only an abreviated
discussion will be presented here. For the more detailed discussion,
the EIS for remedial action at inactive sites should be consulted.
At active uranium milling sites, inorganic toxic elements are
expected to be the major cause of concern (see Table C-10).
Organic chemicals used in processing ore are recycled and only
fugitive releases to tailings ponds might occur. The principal
organics associated with uranium milling are kerosene, di
(2-ethylhexyl) phosphoric acid (EHPA), tributyl phosphate, tertiary
amines (e.g., almine-336) and isodecanol (NRC80).
Although the organic chemicals used in uranium milling are not
expected to be released with mill tailings to any appreciable extent,
background levels in surface and ground water should be established for
both inorganic and organic potential pollutants. Both inorganic
chemicals and some organic chemicals may be transported long distances
so local levels in water may reflect distant industrial sources of
pollution rather than mill operations.
'•I'Many nonradioactive substances can induce cancer in experimental
animals (Go77, Ve78). However, for nonradioactive substances found in
uranium mill tailings, we do not feel that dose-response relationships
adequate for estimating such risks for oral intake have been developed.
C-21
-------
Table C-10. Selected Potentially Toxic Substances
Associated with Uranium Mill Tailings
Arsenic
Barium
Boron
Cadmium
Chromium
Copper
Cyanide
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Nitrates
Radium
Selenium
Silver
Thorium
Uranium
Vanadium
C.4.1. Estimates of Chronic Toxicity _in_Humans
Data reviewed by the National Academy of Sciences showed that for
elements essential to human nutrition, there is a margin of safety
between the amount required for good nutritiion and the amount which is
toxic. The margin of safety may be narrow; e.g., 10 times the daily
recommended intake of arsenic is toxic; or wide, e.g., 1,000 times the
daily recommended intake of chromium is toxic (NASSOa). Table C-ll
lists selected substances found in uranium mill tailings and estimated
toxic levels. Note that these estimates are derived from a number of
sources of data and are not adjusted for chemical form of the element,
age or sex of subject, or any other factors. The estimates should be
viewed as very broad estimates of where toxicity might be expected.
C.4.2 .E^t.yiiate_s__o£_ Chronic Toxicit_y _in Animals and Plants
Although there is potential for causing acute toxic conditions to
develop in plants or animals if tailings pond water or other highly
contaminated standing water is used for plants or animals, this is
considered unlikely to occur. Induction of chronic toxicity in plants
or animals by using contaminated surface water, or more likely,
contaminated groundwater is deemed more plausible.
Maintaining water quality no worse than levels specified in the
interim primary (EPA76) or secondary (EPA79b) drinking water
regulations would also protect plants and animals in most cases.
However, these limits may not be adequate to protect dairy cattle, and
C-22
-------
not all possible contaminants would be covered. Likewise, not all
elements potentially toxic to plants would be covered. For a more
extended discussion of elements toxic to plants and animals, the
National Academy of Sciences 1972 publication, "Water Quality
Criteria," (NAS72b) can be consulted.
Table Oil. Daily Intake Levels of Selected Elements
Estimated to be Toxic (NASSOa, EPA82)
Ratio of Toxic
Intake to Adult
Element _Re
-------
REFERENCES
Ar79 Archer V.E., "Factors in Exposure Response Relationships of
Radon Daughter Injury," in Proceedings of the Mine Safety and
Health Administration Workshop on Lung Cancer Epidemiology and
Industrial Applications of Sputum Cytology, November 14-16,
1978, Colorado School of Mines Press, Golden, Colorado, 1979.
Ar81 Archer V.E., "Health Concerns in Uranium Mining and Milling,"
J. Occup. Med. 23:502, 1981.
Bu81 Bunger B.M., Cook J.R. and Barrick M.K., "Life Table
Methodology for Evaluating Radiation Risk: An Application Based
on Occupational Exposures," in Health Physics, 40:439-455,
1981.
EPA76 Environmental Protection Agency, "National Interim Primary
Drinking Water Regulations," EPA-570/0-76-003, Office of Water
Supply, USEPA, Washington, D.C., 1976.
EPA79a Environmental Protection Agency, "Indoor Radiation Exposure
Due to Radium-226 in Florida Phosphate Lands," EPA
520/6-78-013, Office of Radiation Programs, Washington, B.C.,
July 1979.
EPA79b Environmental Protection Agency, "National Secondary Drinking
Water Regulations," Federal Register 44:42195-42202, 1979.
EPA82-83 Environmental Protection Agency, "Final Environmental Impact
Statement for Remedial Action Standards for Inactive Uranium
Processing Sites (40 CFR 192)," EPA, Office of Radiation
Programs, Washington, D.C.,1982.
Go77 Goyer R.A. and Mehlman M.A., editors, "Advances in Modern
Toxicology," Vol. 2: Toxicology of Trace Elements, John Wiley
& Sons, New York, 1977.
Ka82 Kato H. and Schull W.J., "Studies of the Mortality of A-Bomb
Survivors. 7. Mortality, 1950-1978: Part 1. Cancer
Mortality." Radiat. Res. 90:395-432 (1982).
La78 Land C.E. and Norman J.E. , "Latent Periods of Radiogenic
Cancers Occurring Among Japanese A-Bomb Survivors," pp. 29-47
in Late Biological Effects of Ionizing Radiation, Volume I,
IAEA, Vienna, 1978.
C-24
-------
REFERENCES (Continued)
NAS72b
NAS76
NAS72a National Academy of Sciences, The Effects on Populations of
Exposure to Low Levels of Ionizing Radiation, Report of the
Advisory Committee on the Biological Effects of Ionizing
Radiation, PB-239 735/AS, HAS, National Technical Information
Service, Springfield, Virginia, 1972.
National Academy of Sciences, "Water Quality Criteria,"
EPA-R3-73-033, USEPA, Washington, D.C. 1972.
National Academy of Sciences, "Health Effects of Alpha
Emitting Particles in the Respiratory Tract," Report of Ad Hoc
Committee on "Hot Particles" of the Advisory Committee on the
Biological Effects of Ionizing Radiations, EPA Contract No.
68-01-2230, EPA 520/4-76-013, USEPA, Washington, D.C. October
1976.
NASSOa National Academy of Sciences, "Drinking Water and Health,"
Volume 3, NAS, National Academy Press, Washington, D.C., 1980.
NASSOb National Academy of Sciences, "The Effects on Population of
Exposure to Low Levels of Ionizing Radiation," Committee on
the Biological Effects of Ionizing Radiations, NAS, National
Academy Press, Washington, D.C., 1980.
NRC80 Nuclear Regulatory Commission, "Final Generic Environmental
Impact Statement on Uranium Milling," NUREG-0706, Office of
Nuclear Material Safety and Safeguards, USNRC, Washington,
D.C., 1980.
RPC80 Radiation Policy Council, "Report of the Task Force on Radon
in Structures," RPC-80-002, U.S. Radiation Policy Council,
Washington, 1980.
Sh82 Shi-quan S. and Xiao-on Y., "Induction-Latent Period and
Temporal Aspects of Miner Lung Cancer," unpublished report (in
English), 1982.
Sm78 Smith P.G. and Doll R., "Age- and Time-Dependent Changes in
the Rates of Radiation-Induced Cancers in Patients with
Ankylosing Spondylitis Following a Single Course of X-ray
Treatment," pp. 205-218 in: Late Biological Effects of
Ionizing Radiation, Volume I., IAEA, Vienna, 1978.
Su81 Sullivan R.E., et al., "Estimates of Health Risk from Exposure
to Radioactive Pollutants," ORNL/TM-7745, Oak Ridge National
Laboratory, Oak Ridge, Tennessee, 1981.
C-25
-------
REFERENCES (Continued)
Ve78 Venugopal B. and Luckey T.D., "Metal Toxicity in Mammals,"
Volume 2, Chemical Toxicity of Metals and Metaloids, Plenum
Press, New York, 1978.
C-26
-------
APPENDIX D
WATER MANAGEMENT AT URANIUM ORE PROCESSING SITES
-------
APPENDIX D: WATER MANAGEMENT AT URANIUM ORE PROCESSING SITES
CONTENTS
D. 1 Introduction D-5
D.2 Uranium Recovery Processes D-6
D. 3 Contaminants in Uranium Waste D-6
D.4 Water Use and Retention at Operating Mills D-7
D.5 Design of Tailings Impoundments D-8
D.6 Clay and Synthetic Liners D-8
D. 7 Groundwater Monitoring Results D-10
D.7.1 Introduction D-10
D.7.2 Constituents Available for Seepage D-10
D.7.3 The Neutralization Zone D-ll
D.7.4 Monitoring Groundwater Contamination D-ll
D.8 Controls of Toxic Materials to Groundwater D-14
D.9 Summary D-15
References D-17
D-3
-------
APPENDIX D: WATER MANAGEMENT AT URANIUM ORE PROCESSING SITES
Operating uranium mills produce effluents containing radioactivity
and toxic materials which are potential contaminants to groundwater.
Large amounts of tailings effluents placed in unlined evaporation ponds
on permeable soil at existing mill sites have seeped into the sandstone
bedrock that contains groundwater. Investigations of the altered
bedrock along the seepage pathways show attenuation of most of the
radionuclides and some of the toxic elements during the neutralization
phase of the leachate. Some of the highly mobile and soluble heavy
metals, (Mo, V, Mn, Pb, As, and Se) have migrated beyond the
neutralization zone into the groundwater. The presence of diagnostic
chemical species related to seepage plumes and higher-than-normal
concentrations of toxic materials above groundwater background levels
disclose the presence of tailings contaminants in the groundwaters
close to the uranium mills.
The characteristics of seepage migration are site specific and
controlled by the relatively complex hydrogeology of the typical
uranium mill site. No satisfactory method exists to abate or predict
contaminant movement from these unlined tailings ponds.
Using synthetic liners, clay liners, or a combination of both in
the tailings pond seems to be the most effective method of confining
mill tailings effluents.. The type of liner used is usually determined
by the nature of the waste and conditions of the site. Both clay and
synthetic liners are similar in cost. Synthetic liners are more
impervious but are subject to tear or puncture. Clay liners, properly
designed with structural integrity, can provide an even tighter seal by
the precipitation of solids into pore spaces as a result of neutraliza-
tion reactions attending the interaction of acid waste water and the
liner materials.
D. 1 _In_t rodu c_t_ion.
The water used in the recovery of uranium ore at operating mills
contains toxic materials that must be effectively managed to prevent
potential surface water or groundwater contamination. It has been
D-5
-------
estimated that as much as 85 percent of the mill tailings effluents are
lost to groundwater during the mill's operation (Ja79). Thus,
confining water during the mill operating phase is critical in
controlling the amount of contaminants available for potential
pollution.
Mill tailings effluents discharged to unlined evaporation ponds
have resulted in seepage loss of some of the contaminants to
groundwater during the operation phase of the mills. Tailings pond
seepage has been detected in the groundwater at a number of sites. The
maximum distance of migration reported at one site was 1.5 miles
(UI80). Within a few years after the mill closes, tailings ponds will
evaporate in the arid to semi-arid climate of western United States;
this leaves a tailings pile vulnerable to wind and water erosion.
Over the past several years, there have been a number of core hole
borings and water monitoring investigations to better understand and
develop methods to mitigate the migration from uranium tailings
impoundments. These site-specific studies on the extent and travel
rates of seepage plumes have identified the radionuclides and toxic
material attenuated by the geologic media and have contributed to the
understanding of the physicochemical factors involved. The task
remains to mitigate the migration of highly mobile contaminants that
pollute the groundwater. Emphasis presently is placed on the
confinement and retention of effluents in the tailings ponds by
synthetic liners, clay liners, or a combination of both; however, some
natural media may be impervious to seepage. Future technology directed
toward changing the chemistry of tailings pond effluents may help
contain the mobile toxic materials that contaminate groundwater.
D.2 Uranium Recovery Processes
There are two basic conventional processes for recovering uranium
from the ore: the acid-leach process and the alkaline-leach process.
The acid-leach process is used when the ore contains less than 12
percent limestone and generally accounts for 80 percent of the uranium
recovery. The alkaline-leach process is used on the remaining 20
percent of the ore milled. Both processes involve an initial dry
crushing and grinding, then water is introduced as the ore is wet
ground to a pulp density of 50 to 65 percent solids. Water consumption
at this step is reduced by recirculating the water.
A leaching process removes the uranium from the crushed ore, with
sulfuric acid as the leaching agent in the acid-leach process; a mixed
sodium carbonate-sodium bicarbonate solution is the leaching agent in
the alkaline-leach process (NRCSOa). After ore leaching is completed,
the "pregnant" leach liquor containing the dissolved uranium is removed
from the tailings solids by a counter current decantation (CCD)
circuit. The leach solution is sent to a solvent extraction for
further processing, and the remaining solids are washed and pumped as a
D-6
-------
slurry to the tailings ponds. Water in the tailings ponds generally is
characterized by total dissolved solids in the range of 12,000 to
90,000 mg/L with an abundance of dissolved radionuc1 ides and heavy
metals. The pH of the water averages about 1.8 for mills using the
acid-leach process and about 10.2 for mills that use the alkaline-leach
process.
The acid-leach and alkaline-leach processes have considerable
chemical differences. A larger fraction of thorium is solubilized in
the acid-leach process, but the thorium is precipitated in the tailings
pond when the acidity is reduced. In addition to variations in the
chemical composition from the milling process used, other variations
exist from differences in the composition of the ores related to their
origin.
D.3 Contaminants _in_Uranium Waste
The waste from the milling operations of uranium ore contains all
the toxic contaminants present in the original ore, about 10 percent of
the uranium not recovered in the process, and a variety of chemicals
used in the extraction process. The nature of the contaminants vary in
relation to the source of the ore and the type of process used.
Radionuc lides reported include uranium, thorium, and ra~dium, and toxic
materials include arsenic, lead, molybdenum, and selenium. Other
elements and parameters reported include iron, manganese, sulfate,
chloride, total dissolved substances (TDS), and acidity index (pH).
Many levels of toxic materials are more than two orders of magnitude
above EPA drinking water standards. Additional heavy metals and
chemicals existing in uranium mill wastewater which are locally
important, include Sb, Be, Cd, Cr, Cu, Ni, Zn, V, Mn, Al, and ammonia.
The solid portion of the tailings is comprised of particles
ranging in size from coarse sands to fine slimes. Quartz and feldspar
comprise the major portion of the sands, while fines contain
appreciable amounts of clay minerals, gypsum, calcite, and barite in
addition to quartz and feldspar (Dr81). In both the acid process and
the alkaline process, the residual uranium and radium content of slimes
(fines) is about twice that of sands; this is undoubtedly due to the
greater concentration of sorptive minerals, e.g., clay minerals, in the
slimes. In the acid-leach process, about 95 percent of the thorium in
the original ore remains in the solid tailings waste. Less than one
percent of the radium is dissolved in the liquids. Even more of the
thorium and radium remains in the solid waste from the alkaline-leach
process.
Radon gas is released as a daughter radionuclide from the decay of
radium-226, which is largely retained in the solid waste. Because
radon is chemically inert, it migrates by diffusion from the tailings
pile to the atmosphere. Radon emissions rates have been calculated at
between 200 to 900 pCi/m^s. Uncontaminated soils average about
^s by comparison. Standing water and entrapped water in the
D-7
-------
tailings pile inhibit the release of radon gas so that calculated
release rates cited may be high.
D.4 Water Use and _Retention at Operating Mills
Water conservation is a necessity in the mining and milling
operations of most uranium mills. Mine waters are treated to recover
uranium and/or to remove radium, heavy metals, and suspended solids.
The treated mine waters are used at the mill as feed water or
discharged to the watershed. Currently, only the Uravan, Colorado,
mill discharges treated waters as surface water. Water used in the
mill is cycled to an impoundment along with the tailings for disposal
by evaporation and/or treatment and discharge. Water solution decanted
from the ponds in the impoundment system may be recycled to the mill,
decreasing fresh water usage. When mines are dry or too far from the
mill to permit use of groundwater infiltration into the mine, the mill
derives water from wells or, in rarer instances, from surface streams.
The quantity of water used in milling is variable and depends on
the process used and the degree of recycling. The acid-leach process
requires greater amounts of fresh water than mills using the
alkaline-leach process. Fresh water is usually required in acid leach
mills for ore grinding, leaching (as steam), counter current
decantation washing, and precipitation (Ja79). The alkaline-leach
process normally employs a mixed sodium carbonate-sodium bicarbonate
leach solution in the grinding circuit with fresh water used for
post-leaching filtration and second-stage precipitation (Ja79). The
waste streams from the milling process are partially or totally
segregated for disposal, especially if recycling from the impoundment
system is practiced. Segregation and disposal in separate ponds allow
reuse of less contaminated wastes while providing for containment of
liquid wastes which contain high concentrations of contaminants.
D . 5 Des ign of
The predominant method of disposal of all solid and liquid wastes
generated in the uranium mill today is impoundment of the wastes in a
tailings retention system. This system consists of an earthen dam or
embankment and an evaporation basin or pond behind the dam. The dam is
built in the best location for effluent control. The evaporation basin
on the upstream side of the dam is lined with a clay blanket to prevent
seepage loss to the. underlying soil. As much natural runoff as
possible is diverted from the evaporation basin by siting the
impoundment to minimize the upstream catchment area or in the
construction of ditches to direct the water around the impoundment.
The NRC has issued Regulatory Guide 3.11, "Design, Construction,
and Inspection of Embankment Retention Systems for Uranium Mills" which.
provides the design goals for tailings impoundments (NRC77). The
design takes into consideration the protection of the embankment
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retention systems from the Probable Maximum Flood (PMF). The PMF is
defined as the flood that may be expected from the most severe
combination of critical meteorologic and hydrologic conditions that are
reasonably possible in the region (NRC77). The regulatory guide lists
appropriate guidance for determining the Probable Maximum Flood.
Methods for estimating return intervals of paleofloods in the
particular acute semiarid regions have been described by Kochel and
Baker (Ko82).
D.6 Clay and Synthetic Liners
In the early days of uranium milling, not much attention was given
to the protection of the subsurface hydrogeologic environment. Most of
the mill wastes generated before 1977 are stored in unlined tailings
ponds, and some of these have leaked. Most waste disposal sites are
located in hydrogeologic environments that consist of nonindurated
and/or indurated sediments that were deposited in fluvial
environments. Buried river deposits are coarse grained and difficult
to detect because of their braided, band-like occurrence in such
terrain. High seepage rates of migrating solutions can take place if
such formations occur beneath an unlined uranium mill tailings
evaporation pond.
Since groundwater monitoring was initiated in 1977, seepage from
tailings ponds has been detected in groundwater from a number of sites,
with migration as much as 1.5 miles at one of the sites (UI80). The
seepage plumes were traced by one or more of several chemical
parameters found in the seepage water, particularly sulfate and total
dissolved solids. In some cases, this monitoring effort has identified
contamination problems which require the use of recovery wells to
return contaminated water from seepage plumes back to lined tailings
ponds. (UI80).
The technology of pond liners is a relatively recent development.
Generally speaking, synthetic liners are used for evaporation ponds of
mine waters or less contaminated effluents, and thicker clay liners are
used in tailings ponds. Synthetic liners of polyvinyl chloride (PVC),
chlorinated polyethylene (CPE), and hypalon (synthetic rubber) used at
uranium mills are less permeable (10~10 cm/s) than clay liners, but
costs are generally higher (Ja79). Synthetic liners, however, are
subject to loss of seal by puncture or tearing during installation and
are probably less suited to withstand the long-term effects of the
chemical environment.
Clay liners, in addition to having structural stability, are
effective in sealing ponds because of their layered structure and their
high sorptive properties. The desorption of Na+ from montmorillonite
in the mill tailings of the Grants Mineral Belt has been described as
being desirable because pollutants are probably being adsorbed in their
place on this clay mineral (Lo32). Leaching of clay into liner pores
(caused by precipitation) can also increase the impermeability of the
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clay liner; this enhances the long-term stability of the clay liners
(Pe82). Natural clays treated with polymeric materials have also been
shown to improve the sealing properties of clay, and permeabilities as
small as 10~6 to 10"^ cm/s have been achieved (Ja79).
The uncertainty of maintaining an acceptable level of
environmental control with unlined tailings ponds warrants the use of
clay liners or other acceptable liners that meet the licensing
requirements. The need for properly constructed clay liners is thus a
major cost consideration in constructing new uranium mills.
D.7 Groundwater Monitoring Results
D.7.1 Introduction
Before 1977 most mill, wastes were stored in unlined tailings
ponds. Seepage from these ponds has contaminated groundwater. The
characteristics of seepage movement are site specific, and a number of
methods can identify the pathways and extent of pollution to
groundwater. Some of the data that were collected at uranium mill
disposal sites are incomplete, and some were collected by methods that
are not state of the art. The most reliable method of characterizing
groundwater contamination is by identifying the chemicals in tailings
ponds that are also in groundwater above background levels.
The methods used to delineate the migration path of the seepage
plume and the actual groundwater monitoring results at the active mill
tailings sites are reviewed in the next section.
D.7. 2 Composition of Tailings JPonds
The dissolved radionuclides of primary concern within most
tailings ponds include radium-226, thorium-230, uraniutn-238, lead-210,
and polonium-210. Heavy metals found in varying quantities among the
uranium mill sites include molybdenum, arsenic, selenium, lead, iron,
chromium, manganese, magnesium, cobalt, nickel, barium, vanadium, and
copper. Toxic heavy metals are higher in concentration in acid mill
waste than in alkaline mill waste. Anions of toxic heavy metals are
generally more soluble and, thus, potentially more hazardous than the
cationic species of the same element which can be precipitated with
lime or sulfide. Major anions formed by heavy metals in tailings ponds
include species of arsenic, chromium, molybdenum, uranium, and
vanadium. Inorganic anions, notably sulfate, nitrate, and chloride,
are present in significant quantities in acid leach mill wastes. Other
inorganic anions found in minor amounts In most wastewater include
sulfide, cyanide, fluoride, and total dissolved solids (Ja79). Light
elements in tailings ponds include potassium, sodium, aluminum,
beryllium, calcium, magnesium, and titanium.
While organics are widely used in the extraction process, most of
these chemicals are removed, and quantities of organic compounds in
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mill liquid wastes are low. Typical concentrations of total organic
carbon in acid mill waste range from 6 to 24 mg/L in acid mill waste
and 1 to 450 mg/L in alkaline mill waste; oil and grease is generally
1 mg/L in acid mill waste and 3 mg/L in alkaline mill waste; MBAS
surfactants average 0.5 mg/L in acid mill waste and 0.02 mg/L in
alkaline mill waste; phenol is less than 0.2 mg/L for both types of
wastes (Ja79). The pH of the waters in the tailings ponds averages
about 1.8 for mills using the acid-leach process and about 10.2 for
mills using the alkaline extraction process.
D.7.3 The Neu tralizat ion _Zone
The acid seepage plumes are normally neutralized by carbonate
minerals in the bedrock within a few hundred yards of most tailings
ponds. At a distance of a few hundred yards, the total dissolved
substances can be expected to range from 5,000 to 10,000 mg/L, as
contrasted to the 25,000-35,000 mg/L found in normal tailings pond
water (UI80). The pH change gradually increases to that of the normal
groundwater, and minerals are precipitated that are not generally
native to the bedrock in this same distance of transport.
Several investigators have attempted to characterize the
transition zone between the mill tailings pond water and the point
where it becomes indistinguishable from native groundwater. A recent
investigation describes the interaction between the seepage from the
tailings ponds and the natural soils by thermodynamic principles; this
interaction is based on minerals identified as precipitates and
dissolved minerals (Ma82). Gypsum precipitation, for example, results
when calcite comes in contact with sulfuric acid; carbon dioxide gas is
produced and the calcium reacts with the sulfate to produce gypsum.
Barium will also precipitate as BaSO^ and in the process remove
radium from solution (Ma82). Conclusions drawn, however, are almost
entirely on solid-phase data, and the liquid-phase chemistry is ignored.
Another line of investigation utilizes an analytical
hydrogeochemical model based upon acid consumption-neutralization front
movement. In this mode'l it is possible to identify and characterize
zones within migrating plumes of tailings-derived water by the chemical
characteristics of the water (Sh82). An investigation of the seepage
from an unlined mill tailings pond in the Wyoming Gas Hills district
describes radionuclide retention within the first 40 to 60 cm beneath
the pond. The neutralization zone to an 11-meter depth is delineated
by typical gypsum precipitation and carbonate removal and increases to
the 8.2 pH background level (Er82).
The foregoing investigations describe the retention of certain
radioactive and toxic materials attending the neutralization of mill
pond seepage and the nature of transition zones. Of major concern is
determining what portion of the seepage has gone beyond the
neutralization zone to become part of groundwater contamination. This
is best determined by groundwater monitoring.
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D.7.4 Monitoring^ Groundwa te r Contaminat ion
Several groundwater monitoring investigations of uranium mill
sites have disclosed chemical pollutants above background levels that
are attributed to seepage from unlined mill tailings ponds. A
description of these site-specific monitoring findings follows.
Canon City, Colorado
Before 1979, the Cotter Corporation near Canon City, Colorado,
used the alkaline-leach process and disposed of mill tailings wastes in
a series of unlined tailings ponds. The seepage waste is typical of
both the alkaline and acidic types and is described as concentrated
sodium sulfate waters with high levels of molybdenum, selenium, and
emitters of radiation (UI80).
Concentrations of molybdenum at levels of 16.7 mg/L at a well
approximately 8000 feet from the Cotter tailings pond, within an
isoconcentration delineated zone, are evidence of pollution from a
point source in the tailings pond. The maximum background level of
molybdenum in the vicinity of the mill is 1.1 mg/L, and the Drinking
Water Standard for molybdenum is 0.05 mg/L (JI80).
A Soil Conservation Reservoir near the tailings pond (3000 feet)
has elevated levels of sodium, sulfate, radionuclides, and selenium (in
addition to elevated levels of molybdenum) which appear to be related
to the seepage effluents from the pond. The complex nature of the
hydrogeology around the Cotter Mill, however, makes migration pathways
difficult to interpret for engineering corrective measures.
Ford, Washington
The Dawn Mining Company mill near Ford, Washington, has acid-leach
process effluent seepage from existing unlined tailings ponds that has
contaminated the groundwater beneath the site. Sulfate is the primary
tracer of the contamination plume that is easily traced through the
highly permeable sand and gravel glacial sediments to an underlying
glacial lake, derived clay stratum. At the impervious clay stratum, a
groundwater mound gradient is created that causes discharge in a
direction approximately 0.5 miles west of the tailings pond to a nearby
surface stream (UI80). Uranium concentration in the seepage emergence
zone is 0.06 mg/L, whereas uranium in springs not affected by the
tailings pond is 0.004 mg/L. However, the only contaminant in the
seepage emergence zone that exceeds Drinking Water Standards is
nitrate, which occurs in levels of 35 mg/L and is three and one-half
times the maximum permissible concentration specified. Sulfate,
manganese, and total dissolved solids occur in excess of "recommended"
limits for drinking'water. Pump-back systems are being considered as
engineering control measures to control the pollution.
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Gas_ Ji i 1 l^s , Wyoming
The Union Carbide Gas Hills, Wyoming, uranium mill near Riverton,
Wyoming, has contributed groundwater contaminants from an unlined
tailings disposal pond containing acid-leach process effluents. Water
quality in the water-bearing horizons of the Wind River Formation used
as background indicator wells barely exceeds the Drinking Water
Standards for total dissolved solids, sulfate, selenium, and radium-226
(UI80).
Monitoring wells around the mill tailings pond indicate that
migration of contaminants is occurring in the upper alluvial layer and
middle sandy layer of the Wind River Formation which has a thickness of
400 feet.
Typical water contamination from a monitoring well to a depth of
140 feet and at a distance of 700 feet from the disposal pond indicate
the following: sulfate 2932 mg/L, with 250 mg/L the irrigation
standard; selenium 0.26 mg/L, with 0.01 mg/L the irrigation standard;
total dissolved solids 5760, with 250 mg/L the irrigation standard;
nitrate 150 mg/L, with 10 mg/L the irrigation standard; aluminum
59 mg/L, with 20 mg/L the irrigation standard; manganese 7 mg/L, with
0.05 mg/L the irrigation standard; chloride 893 mg/L, with 250 mg/L the
irrigation standard (NRCSOb). More monitoring wells would be required
to determine how far the seepage has migrated because of the complex
hydrogeologic conditions and the interpretation of data required.
Jefferson City, Wyoming
Groundwater has been contaminated by the acid-leach effluent
seepage from the Western Nuclear, Inc., Split Rock uranium mill near
Jefferson City, Wyoming. The unlined tailings pond leaked contaminants
into the underlying Split Rock Formation comprised of fine-grained
sandstone having a hydraulic conductivity of 1.4 x 10~2 to 1 x 10~^
cm/s (UI80). Groundwater degradation occurs beyond the site boundary
in the direction of Jefferson City.
Arsenic contamination has been detected up to 2900 feet from the
tailings pond. A chemical analysis of sediments shows a decrease in
contaminants with depth and distance from the tailings pond. Due to
high levels of iron and manganese in the tailings pond (300 mg/L and 17
mg/L respectively), it appears that oxyhydroxides of these elements are
readily formed and coprecipitate other heavy metals under governing
chemical conditions in the host media. The sorption of cationic
species by clay minerals as well as change in redox potential (Eh) and
pH are other factors that control the migration distance of
contaminants. Arsenic is the exception with the media effecting less
control on its migration.
D-13
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Fremont County,
The Federal American Partners mill tailings pond located in the
Gas Hills area of Fremont County, Wyoming, has leaked seepage to
groundwater beneath the site. The unlined tailings pond is situated on
weathered sandstone of the Wind River Formation. The acid-leach
effluents have migrated approximately 3200 feet with chloride, sulfate,
nitrogens lead, and total dissolved solids found above background
levels (UI80). Isoconcentration maps delineate the direction of
migration of the contaminants with test data from 27 monitoring wells
ranging in depth from 20 to 105 feet. Seepage migration appears to be
confined to the deeper aquifer. Buried stream channels in the area
could constitute zones of higher hydraulic conductivity so that
groundwater migration could become greater without corrective action.
La Sal, Utah
The Rio Algom Corporation's Lisbon Valley mill tailings pond near
La Sal, Utah, has seeped alkaline-leach process effluents to a perched
groundwater mound in the vicinity of the tailings pond (UI80). The
unlined pond is located on a thin layer of terrestrial deposits (10 feet
or less) that overlie the Dakota-Burro Canyon sandstones. Contami-
nation is restricted to the Dakota-Burro Canyon Formation with Drinking
Water Standards exceeded approximately 1500 ft. away from the tailings
ponds (UI80) . Conclusions regarding the migration are based on
isoconcentration maps for alkalinity (CO^) , chloride, nitrate sodium,
sulfate, boron, total uranium, and radium-226. A major northwesterly-
trending fault present near the site (3,000 ft. away) may influence the
movement of the seepage plume at the site.
Mi_l£n, _New_Mexic_o
The Homestake uranium mill near Milan, New Mexico, has sustained
440 m-Vd or 6 percent seepage loss of alkaline-leach process
effluents discharged to unlined tailings ponds (Ja79). The seepage has
penetrated the highly permeable and saturated alluvium which blankets
(up to 75 feet thick) the more massive, less permeable Chinli Formation
bedrock of shale and sandstone (Pi81). A mound of contaminated
groundwater underlies the tailings ponds, and elevated levels of
uranium, radium, selenium, and nitrate-nitrogen, in excess of New
Mexico Drinking Water Standards, have been found in surrounding wells
used as drinking water by nearby residents (Pi81).
Selenium ranges up to 2.0 mg/L (limit is 0.05 mg/L) ;
nitrate-nitrogen, up to 14.1 mg/L (limit is 10.0 mg/L); uranium, up to
5 mg/L (limit is 0.5 mg/L); radium-226, up to 9.5 picocuries/L (limit
is 5.0 picocuries/L). Background levels and preoperational levels of
selenium, nitrate, and sulfate have also at times exceeded New Mexico
Drinking Water Standards. Such variations and potential faults beneath
the tailings piles have made it difficult to determine the extent of
D-14
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contamination. Homestake is attempting to mitigate the groundwater
pollution by pumping contaminated alluvial groundwaters back to
tailings ponds and injecting better quality waters into the alluvium
(Pi81). Some monitoring wells show water quality deterioration while
others show improvement (UNHP80). The monitoring program in a complex
hydrogeologic setting is compounded by potential faults which makes an
assessment of the situation exceptionally difficult.
D.8 Ccmtro1 of Toxic Materials to Groundwater
Monitoring investigations of the migration pathways from unlined
mill tailings pond have determined that radionuclides and some of the
toxic heavy metals are attenuated within a few feet of the tailing pond
but that some toxic heavy metals are highly mobile and have
contaminated the groundwater. The mobile species include molybdenum,
selenium, chlorine, sulfate, nitrate, arsenic, lead, and vanadium.
Under existing hydrogeologic conditions and the chemical makeup of the
seepage from the tailings pond, this condition prevails unless
protective controls are utilized. Controls that exist to prevent
groundwater contamination include, (a) complete containment by
impervious seals (clay or synthetic liners), and/or (b) altering the
chemistry of tailings pond effluents.
Clay and synthetic liners were mentioned earlier and are probably
the most positive long-term controls for containment of both the
acid-leach and alkaline-leach process effluents in tailings ponds. The
long-term stability of earthen materials or clay liners in contact with
acid tailings solutions has received extensive study by Pacific
Northwest Laboratory (PNL) under NRC contract (Pe82). The highly acid
condition of the acid-leach tailing effluents (1.8 pH) leach some of
the clay. However, by laboratory testing the PNL investigation
disclosed that materials that contained over 30 percent clay showed a
decrease in permeability with time (Pe82).
The decreases in permeability for a number of clay materials
considered were attributed to pore plugging resulting from the
precipitation of minerals and solids. X-ray diffraction and
geochemical predictions confirm that gypsum, jarosite, and other
minerals precipitate after tailings solution reacts with the earth
material comprising the liners (Pe82). To ensure that the initial
permeability of the liner is minimized, the liner should be compacted
to at least 90 percent of its maximum capacity as determined by a
standard Proctor test (Pe82). A one-meter clay liner compacted with a
calcium carbonate content of 4 percent or greater could be expected to
impede the pH front advance into the surrounding geologic materials for
hundreds of years and to neutralize the total acidity of a typical
tailings pond (Pe82).
D-15
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The concept of altering the chemistry of the uranium mill
wastewater by precipitation to control the removal of toxic materials
in tailings ponds has been investigated by the Environmental Protection
Agency. This study was performed for both acid and alkaline waste
streams and considered a number of processes. The most promising
finding is the combining of acid waste streams with alkaline waste
streams to precipitate metals that occur as anions (We80). Mobile
metals, such as Mo and V, present in anionic form as molybdates and
vanadates, are effectively removed from solution at a pH range of 5.8
to 6.1 achieved by mixing the acid and alkaline mill waste at a 5:3
ratio by volume (We80). Other metals largely removed at this pH
include iron, aluminum, chromium, and nickel. However, few alkaline-
process mills and acid-process mills are located close enough to
accomplish this mixing.
D-16
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REFERENCES
Dr81 DressenD.R., Williams J.M., and Cokal E.J., 1981, "Thermal
Stabilization of Uranium Mill Tailings Management," Colorado
State University, Oct. 26-27, 1981.
Er82 Erikson R.L. and Sherwood D.R., "Interaction of Acidic
Leachate with Soil Materials at Lucky McPathfinder Mill, Gas
Hills, Wyoming," Symposium on Uranium Mill Tailings
Management, Fort Collins, Colorado, Dec. 9-10, 1982.
Ja79 Jackson B., Coleman W., Murray C., and Scinto L.,
"Environmental Study on Uranium Mills," TRW Report for EPA,
Contract 68-03-2560, 1979.
Ko82 Kochel C.R. and Baker V.R., 1982, "Paleoflood Hydrology,"
Science, Vol. 215, No. 4531.
Lo82 Longmire P. and Brookins D., "Trace Metals, Major Elements,
and Radionuclide Migration in Groundwater from an Acid
Leaching Uranium Tailings in the Grants Mineral Belt, N.M.,"
Symposium on Uranium Mill Tailings Management, Fort Collins,
Colorado, Dec. 9-10, 1982.
Ma82 Markos G. and Bush K.J., 1982, "Thermodynamic Calculations and
Phase Diagrams Evaluating Tailings-Soil-Water Interactions,"
Symposium on Uranium Mill Tailings Management, Fort Collins,
Colorado, Dec. 9-10, 1982.
NRC77 Nuclear Regulatory Commission, "Design, Construction and
Inspection of Embankment Retention Systems for Uranium Mills,"
Regulatory Guide 3.11, NRC, Washington, D.C., 1977.
NRCSOa Nuclear Regulatory Commission, "Final Generic Environmental
Impact Statement on Uranium Milling," NUREG-0706, Vol. 1, 2,
3, NRC, Washington, D.C., 1980.
NRCSOb Nuclear Regulatory Commission, "Radiological Effluent and
Environmental Monitoring at Uranium Mills," Regulatory Guide
4.14, NRC, Washington, D.C., 1980.
Pe82 Peterson S.R., Erikson R.L., and Gee G.W., "The Long-Term
Stability of Earthen Materials in Contact with Acidic Tailings
Solutions," Pacific Northwest Laboratory, NUREG/CR-2946,
PNL-4463, 1982.
D-17
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REFERENCES (Continued)
Pi81 Pierce J.A., "Groundwater Contamination at the United
Nuclear-Homestake Partners Uranium Mill," State of New Mexico,
Environmental Improvement Division Report of 23 April 1981.
Sh82 Shepherd T.A. and Brown S.E., "A Generic Model of Contaminant
Migration from Uranium Tailings Impoundments," Symposium on
Uranium Mill Tailings Management, Fort Collins, Colorado, Dec.
9-10, 1982.
UI80 University of Idaho, "Overview of Ground Water Contamination
Associated with Six Operating Uranium Mills in the United
States," Mineral Resources Waste Management Team, University
of Idaho, Dec. 30, 1980.
UNHP80 United Nuclear-Homestake Partners, "Review of the Broadview
Acres Injection System at UNHP Mill near Milan, N.M.,"
Hydro-Engineering Contract, 1980.
We80 Werthman P.M. and Bainbridge K.L., "An Investigation of
Uranium Mill Wastewater Treatment," Environmental Protection
Agency, Contract 68-01-4845, 1980.
D-18
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA Report 520/1-82-022
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Draft Environmental Impact Statement for Standards
for the Control of Byproduct Materials from Uranium
Ore Processing (40 CFR 192)
5. REPORT DATE
March 1983
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
U.S. Environmental Protection Agency
Office of Radiation Programs (ANR-460), Washington, DC
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The Environmental Protection Agency is proposing health and environmental
protection standards for control of uranium and thorium tailings during ore
processing operations and for final disposal. These standards would apply to
tailings licensed by the U.S. Nuclear Regulatory Commission and the States
under Title II of the Uranium Mill Tailings Radiation Control Act of 1978 (Public
Law 95-604). This Draft Environmental Impact Statement examines health, environ-
mental, technical, and cost considerations and other factors important to developing
the proposed standards.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
uranium mill tailings
radioactive waste disposal
radon
radium
hazardous constituents
Uranium Mill Tailings Radiation Control Ac|t
Resource Conservation and Recovery Act
thorium
18. DISTRIBUTION STATEMENT
Release Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
230
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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United States
Environmental Protection
A96nCV ANR 458
Official Business
Penalty for Private Use
$300
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