,,,, 

Fiadisrion 

,-,,-, -" 

Final Rule for 

Radon - Emissions from 

Licensed Uranium Mill 

Tailings 

Background Information 

Document 

40 CFR Part 61 

National Emission Standards 

for Harzardous Air Pollutants 

EPA 520/1-86-009 

BACKGROUND INFORMATION DOCUMENT 

STANDARD FOR RADON-222 EMISSIONS 

FROM LICENSED URANIUM MILL TAILINGS 

August 15, 1986 

U.S. Environmental Protection Agency 

Office of Radiation Programs 

Washington, D.C. 20460 

Figures 

Tables 

v i 

viii 

1. INTRODUCTION 

1.1 History of Standard Development 

1.2 Content 

1.3 Other EPA Standards Affecting Uranium Mills 

1.4 Other Regulations Affecting Uranium Mills 

2. ESTIMATING THE RISK DUE TO EXPOSURE TO RADON-222 DECAY 

PRODUCTS 

2.1 Introduction 

2.2 Radon-222 Exposure Pathways 

2.2.1 Physical Considerations 

2.2.2 Characterizing Exposures to the 

General Population Vis-a-vis 

Underground Miners 

2.3 Health Risk From Exposure to Radon-222 Decay 

Products 

2.3.1 Risk Models 

2.3.2 The EPA Relative Risk Model 

2.3.3 Comparison of Risk Estimates 

2.3.4 Selecti.on of Risk Coefficients 

2.4 Estimating the Risks 

2.4.1 Exposure 

2.4.2 Risk Esti.rnation 

References 

3. RADON-222 SOURCES, ENVIRONMENTAL TRANSPORT, AND RISK 

ESTIMATES 

3.1 Introduction 

3.2 Origin and Properties of Radon-222 

3.3 Sources of Radon-222 Emissions in the Milling 

Process 

3.4 Characterization of Emissions 

3.4.1 Ore Handling and Preparation 

3.4.2 Mill Emissions 

3.4.3 Emissions From Tailings Disposal 

3.5 Transport and Risk Assessment 

3.5.1 Air Dispersion Estimates 

3.5.2 Risk Estimates 
CONTENTS (cant inued) 

3.6 Measurement of Radon-222 3-22 

3.6.1 Ambient Air Samplers 3-23 

3.6.2 Concentrating Samplers That Measure 

Radon-222 Emanation From Surfaces 3-23 

References 3-25 

4. INDUSTRY DESCRIPTION 4-1 

4.1 overview 

4.2 site-Specific Characteristics 

4.2.1 Colorado 

4.2.2 New Mexico 

4.2.3 Texas 

4.2.4 Utah 

4.2.5 Washington 

4.2.6 Wyoming 

4.3 Population Within 5 km (3.1 mi) of Existing 

Tailings Impoundments 

References 4-38 

5. INDUSTRY RADON-222 EMISSION ESTIMATES 5-1 

5.1 Introduction 

5.2 Estimating Emissions 

References 

6. BASELINE INDUSTRY RISK ASSESSMENT 

6.1 Introduction 6-1 

6.2 Risk Estimates 6-1 

6.2.1 Nearby Individuals 6-1 

6.2.2 Regional Population 6-2 

6.2.3 National 6-6 

6.2.4 Risks from New Tailings Impoundments 6-8 

References 6-10 

7. RADON-222 CONTROL TECHNIQUES 7-1 

7.1 Description of Control Practices 

7.1.1 Earth Covers 

7.1.2 Water Cover 

7.1.3 Water Spraying 

7.1.4 Other Control Techniques 
CONTENTS (continued) 

7.2 Control Practices Applicable to Existing 

Tailings Impoundments 

7.2.1 Interim Controls 

7.2.2 Final Reclamation 

7.2.3 Comparison of Interim and Final 

Controls 

7.3 Control Practices Applicable to New Tailings 

Impoundments 

7.3.1 Single Cell Tailings Impoundment 

7.3.2 Phased Disposal Tailings Impoundment 

7.3.3 Continuous Disposal 

7.4 Summary of Radon-222 Control Practices 

References 7-41 

8. SUMMARY AND COMPARISON OF WORK PRACTICES 8-1 

8.1 Single-Cell Impoundments 

8.2 Phased Disposal 

8.3 Continuous Disposal 

8.4 Comparison of Work Practices 

Appendices 

A - Diagrams of Uranium Mill Sites and Tailings Impoundments A- 1 

B - Cost Estimates for Existing and Model New Uranium 

Mill Tailings Impoundments B-1 

C - Evaluation of Interim Cover as a Control Option C-1 
FIGURES 

Number Page 

2-1 

2 -2 

3-1 

Radon-222 decay series 

U.S. lung cancer mortality by age--1970 

Uranium-238 decay chain and half-lives of principal 

radionuclides 

Schematic illustration of the radon sources at a 

uranium mill 

Simplified flow diagram of the acid leach process 

Simplified flow diagram of the alkaline leach-caustic precipitation process 

Qualitative illustration of radon-222 emissions from 

licensed uranium milling process 

Effect of ore pile depth on hyperbolic tangent term 

in radon-222 flux equation 

Approximate locations of licensed conventional 

uranium mills 

Location of mills in Colorado 

Locatioh of mills in New Mexico 

Location of mills in Texas 

Location of mills in Utah 

Location of mills in Washington 

Location of mills in Wyoming 

Changes in radon-222 penetration with earth cover 

thickness 

Radon emanation coefficients for tailings samples 

Size and layout of the model single cell tailings 

impoundment 

Estimated radon-222 emissions from a model singlecell tailings impoundment 
FIGURES (continued) 

Number Page 

7-5 Size and layout of model phased-disposal impoundment 7-26 

7-6 Estimated radon-222 emissions from a model phaseddisposal impoundment 7-27 

7-7 Size and layout of the model continuous-disposal 

impoundment 7-32 

7-8 Estimated radon-222 emissions from a model continuousdisposal impoundment 7-35 

7-9 Estimated radon-222 emissions from a model continuous 

single-cell disposal impoundment 7-36 

vii 
TABLES 

Number Page 

2-1 Annual exposure equivalent (WLM) as a function of age 

for members of the general public continuously 

exposed to radon progency 2-7 

Age-dependent risk coefficients and minimum induction 

period for lung cancer due to inhaling radon-222 

progeny 2-12 

Estimated risk from exposure to radon-222 progeny 2-15 

Radon-222 decay product equilibrium fraction at 

selected distances from the center of a tailings 

impoundment 2-20 

Lifetime risk for lifetime exposure to a given level 

of radon-222 progeny 2-22 

Properties of radon-222 3-3 

Operating status and capacity of licensed conventional 

uranium mills as of August 4, 1986 4-2 

Summary of current uranium mill tailings impoundment 

areas and radium-226 content 4-6 

Estimate of the population living within 0 to 5 km 

from the centroid of tailings impoundments of 

active and standby mills in 1983 4-36 

Estimate of the population living within 0 to 5 km 

from the centroid of tailings impoundments of 

active and standby mills in 1985 4-37 

Summary of radon-222 emissions from uranium mill 

tailings impoundments 5-3 

Estimated risk of fatal lung cancer from maximum exposure for an individual living near tailings 

impoundment 6-3 

AIRDOS-EPA code inputs and estimated risks 6-4 

Summary of regional health effects from existing 

tailings impoundments 6-5 
TABLES (continued) 

Number Page 

6-4 Summary of nationwide health effects for tailings 

impoundments 6-7 

Summary of fatal cancers from current tailings 

impoundments 6-9 

Percent reduction in radon-222 emissions attained by 

applying various types of earth cover 7-5 

Summary of unit costs for estimating earth cover costs 7-6 

Earth moving and placement costs (thousands of dollars 

per hectare) of attenuating radon-222 as a function 

of thiclcness (meters of different soils) and type of 

earth 7-8 

Benefits and Cost of alternatives that apply 

earth cover to existing tailings impoundments 7-17 

Average radon-222 emission rate from model singlecell tailings impoundments 7-22 

Estimated costs for a model single-cell tailings 

impoundment 7-23 

Average radon-222 emission rate for model singlece11 and phased-disposal tailings impoundments 7-28 

Estimated costs for a model phased-disposal impoundment 7-33 

Estimated radon-222 emission rates for model 

single-cell, phased-disposal, and continuousdisposal tailings impoundments 7-34 

Estimated costs for a model continuous-disposal 

impoundment 7-37 

Summary of estimated radon-222 emissions from new 

model tailings impoundments 7-39 

Summary of estimated costs for new model tailings 

impoundment 7-40 
TABLES (continued) 

Number 

8-2. 

Page 

Emission and cost comparison for single cell impoundment with final cover applied at 0, 20, and 

40 years after reaching capacity 8-2 

Comparison of estimated deaths and benefits for a 

single cell model impoundment with final cover applied at 0, 20, and 40 years after reaching capacity 8-4 

Emissions and costs for model phased-disposal impoundments 8-5 

Comparison of estimated death for model phaseddisposal impoundments 8-6 

Emissions and cost of model below-grade trench type 

continuous disposal impoundment 8-8 

Comparison of work practices for new model tailings 

impoundments 8-9 

Comparison of cost and benefits between model Base 

Case I and new work practices 8-11 

Comparison of cost and benefits between model Base 

Case II and new work practices 8-12 
Chapter 1: INTRODUCTION 

This Background Information Document supports the Agencyss 

final rule on radon-222 emissions from licensed uranium milling 

activities. It is an integrated risk assessment that provides 

the scientific basis for this action. Although the U.S. 

Environmental Protection Agency (EPA) has considered radon-222 in 

several regulatory actions, no specific emission standard for 

this radionuclide has yet been promulgated for operating licensed 

uranium mills. 

1.1 History of Standard Development 

On January 13, 1977 (42 FR 2858), EPA issued Environmental 

Radiation Protection Standards for Nuclear Power Operations. 

These standards, promulgated in Title 40, Code of Federal 

Regulations Part 190 (40 CFR 190), limit the total individual 

radiation dose due to emissions from uranium fuel-cycle 

facilities, including licensed uranium mills. At the time 40 CFR 

190 was promulgated, considerable uncertainty existed regarding 

the public health impact of levels of radon-222 in the air and 

the best method for managing new man-made sources of this 

radionuclide. Therefore, the Agency exempted radon-222 from 

control under 40 CFR 190. 

On September 30, 1983, the Agency issued standards under the 

Uranium Mill Tailings Radiation control Act (uMTRCA) (40 CFR 192, 

Subparts D and E) for the management of tailings at locations 

licensed by the Nuclear Regulatory Commission (NRC) or the States 

under Title I1 of the UMTRCA, These standards do not 

specifically limit radon-222 emissions until after closure of a 

facility; however, they require as low as reasonably achievable 

(ALARn) procedures for radon-222 control, and the NRC does 

consider ALARA procedures in licensing a mill. When the UMTRCA 

standards were promulgated, the Agency stated that it would issue 

an Advance Notice of Proposed Rulemaking with respect to control 

of radon-222 emissions from uranium tailings piles during the 

operational period of a uranium mill. 

On April 6, 1983, standards for NRC licensees were proposed 

under the Clean Air Act (48 FR 15076, April 6, 1983); however, 

uranium fuel-cycle facilities, which included operating uranium 

mills, were excluded because these sources are subject to EPA1s 

40 CFR Part 190 standard. 
During the comment period for the Clean Air Act standard-s, it was 

noted that radon-222 emitted from operating uranium mills and 

their actively used tailings piles were no't subject to any 

current or proposed EPA standards, and that such emissions could 

pose significant risks. 

On October 31, 1984, EPA published an Advance Notice of 

Proposed Rulemaking in the Federal Resister, 49 FR 43916, for 

radon-222 emissions from licensed uranium mills. The notice 

stated that the Agency is considering emissions standards for 

licensed uranium mills and solicited information in the following 

areas: 

o Radon-222 emission rates from uranium mills and 

associated tailings piles 

o Local and regional impacts due to emissions of 

radon-222 from uranium mills and associated tailings 

piles prior to permanent disposal 

o Applicable radon-222 control options and strategies, 

including work practices 

o Feasibility and cost of radon-222 control options and 

strategies 

o Methods of determining compliance with a work practice 

type of standard to control radon-222 emissions 

o Impact of radon-222 controls on the uranium industry 

Pursuant to the citizens'suit provision of the Act, the 

U.S. District Court for the Northern District of California 

directed EPA to promulgate standards for other sources of 

radionuclide emissions, which could include radon-222 emissions 

from licensed uranium.mills. Thus, discussions between EPA and 

the Sierra Club regarding a schedule for developing a standard 

led to an agreement to submit a schedule for the promulgation of 

a standard in one year rather than having the Court establish a 

schedule. This motion was submitted to the Court on August 5, 

1985, and the Court ordered the EPA to issue final standards for 

radon-222 emissions from licensed uranium mills and mill tailings 

impoundments by May 1, 1986. This date was later moved to August 

15, 1986 to allow additional time for public comment. 

The EPA then issued the proposed rulemaking for "National 

Emission Standards for Hazardous Air Pollutants; Standards for 

Radon-222 Emissions from Licensed Uranium Mill Tailings," on 

February 21, 1986 (51 FR 6382-6387). Subsequent to the 

announcement of the proposed rule, a public hearing was held on 

March 25, 1986 in Denver, Colorado (51 FR 8205) and a second 

comment period was held open until April 28, 1986. 
1.2 Content 

The health effects of radon-222 and the risk assessment 

procedure are summarized in Chapter 2. The incidence of lung 

cancer and resulting deaths among miners exposed to radon-222 are 

described, and the range of risk factors is presented. 

The sources of radon-222 in uranium milling and the factors 

affecting the rate of radon-222 emissions are described in 

Chapter 3. This chapter also includes a general description of 

EPA's risk-estimating procedure, along with the methods of 

measuring radon-222. 

A description of each licensed mill, its associated tailings 

impoundments, and its estimated milling production rates are 

contained in Chapter 4. Estimates of radon-222 emissions from 

the existing tailings impoundments are presented in Chapter 5. 

The baseline industry risk assessment for individuals and 

regional and national populations and the control techniques and 

work practices that can be used to reduce radon-222 emissions are 

described in Chapters 6 and 7 respectively. The resulting 

emissions after application of these control methods are 

estimated. A comparison of work practices, costs, and 

effectiveness is presented in Chapter 8. 

Information for this study was compiled from the technical 

literature, previous studies by EPA and the Nuclear Regulatory 

Commission, comments resulting from rulemaking notices, and 

discussions with industry representatives. Comments received 

during the public comment period were incorporated into this 

final document as appropriate. No significant change in the 

technical information was made except for the Agency's revision 

of the risk factors associated with radon-222 exposure. These 

risk factors were increased from a range of 250-1000 deaths per 

million person working level months to a range of 380-1520 deaths 

per million person working level month. In addition, mill 

site-specific information was corrected and the discussion of 

interim cover was revised. 

1.3 Other EPA Standards Affecting Uranium Mills 

On December 3, 1982, EPA issued guidelines under the Clean 

Water Act for effluent limitations for New Source Performance 

Standards for wastewater discharges from the mining and dressing 

of uranium, radium, and vanadium ores (40 CFR Part 440, 47 FR 

54598). These effluent guidelines cover discharges of both 

radioactive and nonradioactive materials to surface waters from 

uranium byproduct materials. 
The EPA promulgated 40 CFR Part 261, Subpart F 

--Groundwater Protection--on July 26, 1932 (47 FR 32274) 

under the Solid Waste Disposal Act (SWDA) as amended by the 

Resource Recovery and Conservation Act. This Act requires 

that standards for nonradioactive hazards frcm uranium 

byproduct materials be consistent with standards promulgated 

under SWDA for such hazards. The Act also requires that the 

NRC establish general requirements that are, insofar as 

possible, at least comparable to requirements applying to 

the possession, transfer, and disposal of similar hazardous 

material regulated by EPA under the SWDA. 

The 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) under UMTRCA. For inactive mills, the standard 

specified in 40 CFR 192.02 requires that controls: 

(a) Be effective for up to one thousand years, to the 

extent reasonably achievable, and, in any case, 

for at least 200 years, and, 

(b) Provide reasonable assurance that releases of 

radon-222 frcm residual radioactive material to 

the atmosphere will not: 

(1) Exceed an average release rate of 20 

picocuries per square meter per second, or 

(2) Increase the annual average concentration of 

radon-222 in air at or above any location 

outside the disposal site by more than 

one-half picocurie per iiter. " 

This standard was later amended under Section 84 of the 

Atomic Energy Act of 1954 to include standards for 

radionuclides during and after processing of uranium ore 

sites (48 FR 45946, October 7, 1983). These regulations in 

40 CFR 192.30 specify concentration limits and construction 

standards for surface impoundments to ensure ground-water 

protection. In addition, Part 192.32 addresses radon-222 at 

active mills in a generic manner by requiring the mill owner 

to "make every effort to maintain radiation doses from 

radon-222 emissions from surface impoundments of uranium 

byproduct materials as far below the Federal Radiation 

Protection Guides as is practicable at each licensed site." 
This standard also specifies that radon-222 missions 

are limited to 20 picocuries per square meter per second 

(pCi/m sj after mill closure. This limitation does not 

apply to sites that contain a radium-226 concentration from 

mill tailings that does not exceed the background level by 

Inore than 5 pCi per gram over the top 15 cm of soil and 

15 pCi per gram over each successive 15-cm layer of soil 

below the top 15 cm. 

1.4 Other ~equlations Affecting Uranium Mills 

All uranium mills are licensed by the NRC or by States 

that enforce the NRC regulations, and are subject to the 

regulations contained in 10 CFR 20, Specific standards 

pertaining to radon-222 limit atmospheric radon-222 

concentrations to 3 x 10- pCi/ml (30 pCi/liter) in 

restric ed areas (i.e., areas within the mill property) and -6 3 x LO pCi/ml (3 pCi/liter) in unrestricted areas. 

These concentrations are approximately equivalent to 

-third and one-thirtieth of a working level, ?" respectively. The NRC has also recently issued 

amendments to its regulations governing uranium mill 

tailings disposal (LOO CFR Part 40) as published on October 

16, 1985 (50 FR 41852). These amendments conform to the EPA 

regulations for tailings disposal. 

The NRC has entered into agreement with a number of 

States to provide enforcement of tlie NRC regulations. These 

States are referred to as "Agreement States," The Agreement 

States that have uran fgy. mills are Colorado, New Mexico, 

Texas, and Washington 

State regulations pertain to the construction of 

tailings impoundments to mkni.mize ground-water 

contamination. In addition, States inspect tailing 

impoundment dams to ensure that they are built and 

maintained to minimi.ze safety problems. 

(a) A working level is defined in Chapter 2. The 

relationship between radon-222 and working levels 

depends on the degree of equilibrium between radon-222 

and its decay products. 

(b) Utah also is an Agreement State in nucl-ear licensing 

areas other than uranium milling. New Mexico returned 

licensing authority to the NRC on May 1, 1986. 

Chapter 2: ESTIMnTING THE RISK DUE TO EXPOSURE 

TO RADON-222 DECAY PRODUCTS 

2.1 Introduction 

The methodology the EPA uses to estimate the exposure and 

the health detriment (i.e., lung cancer) due to radon-222 in the 

general environment is described in this chapter. Radon-222 

exposure pathways are explained, the EPA risk model is described, 

estimates of risks due to radon-222 progeny (radon-222 decay 

products) made by various scientific groups are compared, and the 

risk coefficients to be used in this risk assessment are 

selected. Earlier studies have shown that a degree of 

uncertainty exists in all risk estimates (EPA84); therefore, EPA 

uses more than a single coefficient to indicate the range of this 

uncertainty. 

The occurrence of radiation-induced cancer is infrequent 

compared with the current incidence of all cancers. Even among 

heavily irradiated populations (e.q., some of the uranium mine 

workers in epidemiologic studies), the precision and accuracy of 

the estimate of the number of lung cancers resulting from 

radiation is uncertain because of the small sampling segment and 

because the data vary greatly. Also, the small sampling of 

exposed populations has not been followed for their full 

Lifetime; therefore, information on the ultimate effects of their 

exposure is limited. 

Only human epidemiological data are used to derive risk 

estimates for effects of exposure to radon-222 progeny, but 

animal studies support the risk estimates. In a series of 

studies performed with rats, French investigators have shown a 

dose-effect relationship similar to that obtained in surveys of 

uranium miners (Ch84, 85). In these studies, the risk per 

working level month at 20 cumulative working level months (CWLM) 

is about four times greater than at 3000 or more CWLM (Ch84, 

85). The lowest exposure studied to date, 20 CWLM, which is 

about 10 times the background exposure, doubled the incidence of 

lung cancer in the rats (Ch84, 85). 

When considered in light of experiments with animals and 

various theories of carcinogenesis and mutagenesis, the 

observational data on cancers related to human exposure to 

radiation are subject to a number of interpretations. These 

various interpretations lead to differing estimates of radiation 

risks by both individual radiation scientists and expert advisory 

groups. Readers should bear in mind that estima.ting radiation 

risks is not a mature science and that the evaluation of the risk 

due to radon-222 decay products (progeny) will change as 

additional information becomes available. 
Nevertheless, a substantial data base is available for use in 

developing risk estimates, and the Agency believes these 

estimates can be used in the development of regulatory 

requirements. 

2.2.1 Phvsical Considerations 

Radon-222 from uranium mill-ing operations enters the general 

environment from stockpiled ore and mill exhaust systems and 

through waste materials from milling operations. The half-life 

of radon-222 is 3.8 days; therefore, when it is released into the 

atmosphere, some atoms of gaseous radon-222 can travel thousands 

of miles through the atmosphere before they decay. As shown in 

Figure 2-1, the radon-222 decay process involves seven principal 

decay products before the radon-222 becomes nonradioactive lead. 

The first four short-half-life radioactive decay products of 

radon-222 are the most important sources of cancer risk. 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 inhaled and generally present much smaller 

risks. 

The principal short-half-life products of radon-222 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 in diameter. When inhaled, these small particles have 

a good chance of sticking to the moist epithelial lining of the 

bronchi. Most inhaled particles are eventually cleared (removed) 

from the bronchi by mucus, but not quickly enough to keep the 

bronchial epithelium from being exposed to alpha particles from 

the decay of polonium-218 and polonium-214. This hi.ghLy ionizing 

radiation passes through and delivers radiation doses to several 

types of lung cells. 

Adequate characterization cannot be made of the exact doses 

delivered to cells that eventually become cancerous. Knowledge 

of the deposition pattern of the radioactive particles in the 

lung is hased on theoretical models, and the distances from the 

radioactive particles to cells that are susceptible can only he 

assumed. Further, some disagreement exists about the types of 

bronchial cells in which cancer originates. Therefore, EPA 

estimates of lung cancer risk are based on the amount of inhaled 

radon-222 decay products to which people are exposed rather than 

on the dose absorbed by the lung. 
Figure 2-1. Radon-222 decay series. 

2-3 
inqrowth of Radon-222 Decay Products 

At the point where radon-222 diffuses out of the tailings 

pile surface, the concentration of associated radon-222 decay 

products is zero because those decay products generated prior to 

diffusion from the surface have been captured in the tailings or 

cover. As soon as radon-222 is airborne, ingrowth of decay 

products commences and secular equilibrium between the radon-222 

and the short half-life decay products is eventually obtained. 

At secular equilibrium, the activities of radon-222 and of all 

its short-half-life decay products are equal, and the alpha 

activity per unit of radon-222 concentration is at its maximum. 

As a means of accounting for the incomplete equilibrium before 

this state is reached, the "equilibrium fraction" is defined 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-222 and its decay 

products are transported by the wind, the equilibrium fraction 

increases with distance from the tailings pile, and at great 

distances, approaches the theoretical maximum value of one; 

however, depletion processes, such as dry deposition and 

precipitation scavenging, selectively remove decay products (but 

not radon), so complete equilibrium of the short-lived decay 

products with the radon-222 is seldom, if ever, reached. 

When radon-222 and its decay products enter a structure, the 

building ventilation rate is the principal factor affecting the 

indoor equilibrium fraction. The equilibrium fraction can also 

be affected by other considerations, however, such as the indoor 

surface-to-volume ratio and the dust loading in indoor air 

(P078). 

In estimating the exposures oE nearby individuals to 

radon-222 decay products (in Chapter 6), the model uses the 

calculated effective equilibrium fraction at selected distances. 

from a tailings pile (see Table 2-4 presented later in this 

chapter). For estimating population exposures, a 

population-distance weighted effective equilibrium fraction would 

be appropriate, but it is impractical to calculate this 

fraction. Indoor exposure is the dominant form of exposure due 

to radon-222 [Americans spend about 75 percent of their time 

indoors (M076, Oa72)], and the indoor effective equilibrium 

fraction does not depend greatly on the distance from the 

tailings pile. In this assessment, an effective equilibrium 

fraction of 70 percent is assumed'for calculating the exposure of 

populations because most of the affected individuals are at some 

distance from the tailings pile (see Section 2.4.1). 
2-2.2 Characgeri-zinq Exposures to .the General Pooulation 

Vis-a-vis Undcrqround Miners 

Although considerable progress has been made in modeling the 

deposition of particulate material in the lung (Ha82, Ja80, 

JaBL), adequate characterization of the bronchial 'ose delivered 

by alpha particles from inhaled radon-222 progeny attached to 

dust particles is not yet possible. Knowledge is still lacking 

concerning the kinds of cells in which bronchial cancer is 

initiated (Mc78, Mc83) and the depth of these cells in the 

bronchial epithelium. Current estimates of the exposure dose of 

inhaled radon-222 progeny actually causing radiogenic cancer are 

based on average doses, which may or may not be relevant (E185). 

Until more reliable estimates of the bronchial dose become 

available, following the precedents set in the 1972 and 1980 

National Academy of Sciences reports appears to be a prudent 

approach (NAS72, NASBO). Therefore, the EPA estimates the risk 

due to radon-222 progeny on the basis of exposure rather than 

dose per se. This is called the epidemiological approach; i.e., 

risk is estimated on the basis of observed cancers after 

occupational exposure to radon-222 progeny. 

Exposures to radon-222 decay products under working 

conditions are commonly reported in a special unit called the 

working level (WL). One working level is any concentration of 

short half-life radon-222 progeny having 1.3 x 105 MeV per liter 

of potential alpha energy (FRC67). (A WL is also equivalent to 

approximately 100 pCi/liter of radon-222 in secular equilibrium 

with its short-lived decay products.) This unit was developed 

because the concentration of specific radon-222 progeny depends 

on ventilation rates and other factors. A working level month 

(WLM) is the unit used to characterize a mine worker's exposure 

to one working Level of radon-222 progeny for a working month of 

170 hours. Inasmuch as the results of epidemiological studies 

are expressed in units of WL and WLM, comparable estimates of 

'exposure were developed for members of the general population 

exposed to radon-222 progeny, as explained in the following 

paragraphs. 

For a given concentration of radon-222 progeny, the amount 

of potential alpha energy a member of the general population 

inhales in a month is more than the amount a mine worker receives 

in a working month. Although members of the general population 

are exposed longer (up to 24 hours per day, 7 days a week), the 

average amount of air inhaled per minute (minute volume) is less 

in this group than that for a mine worker when periods of 
sj.eepi.ny and res'c:i.nii are talcen into account (EPA79, 'Th82) , The 

radcn-.222 progeny exposure of a mine worker can be compared with 

that of a member of the gerieral population by considering the 

amount of potential. alpha energy each inhales per year (Ev69)- 

That radon daughter deposition (and dose) in the conducting 

airways of the lung is proportional to ventilation rate (quantity 

inhaled) has also been recommended by other investigators (Ra85, 

~1082) . 

The EPA assumes that a mine worker inhales 30 liters per 

minute (averaged over a work day). This average corresponds to 

about 4 hours of light activity and 4 hours of moderately heavy 

work per day (XCR875)- The new ICRP radon-222 model, however, 

assumes an inhalation rate of 20 iiters per minute for mine 

workers, which corresponds to 8 hours of light activity per day 

(ICRP81j. his may be appropriate for nuclear workers: however, 

studies of the metabolic rate of mine workers clearly show that 

they are not engaged in light activity only (Sp56, ICRP75, 

NASA73j. Therefore, 30 liters appears to be a more realistic 

estimate of the average minute volume for this groyp. Based on 

this minute volume, a mine worker inhales 3,6 x 10 cubic 

meters in a working year of 2000 hours LgCRP79). One working 

level of radon-322 progeny is 2.08 x 10 joules per cubic 

meter (1-3 x 10 MeV per liter); therefore, in a working year, 

the potential alpha energy inh9led by a mine worker exposed to 

one working level is 7.5 x 20- joules. 

According to the ICRP Task Group repor$ on reference man 

(ICRP75), an i.nhaled air volume of 2.3 x 10 liters per day is4 

assumed for adult males in the general population and 2.1 x4i0 

liters per day for adult females, or an average of 2.2 x 10 

liters per day for members of the adult gopulation. This average 

volume resuits,in - an intake of 8-04 x 10 cubic meters of air 

and 1-67 x 1.0 " joules per year of inhaled potential alpha 

energy from a continuous exposure of an adult member of the 

population .to one working 3.evel. of ra-don-222 progeny for 

365.25 days. 

Al'khoilgh it may be technically inappropriate to quantify the 

amount of potential alpha particle energy inhaled by a member of 

the general population in working level months, continuous 

exposure to 1 ML corresponds to about the same inhaled potential 

alpha energy as 27 647U would to a miner, Eience, for an adult 

member of the general population, a one working level 

concentration of radon proqeny results in a 27 WLFl annual 

exposure equivalent (see Table 2-1). As stated earlier, an 

occupancy factor of 0.75 is assumed for indoor exposure: thus, an 

indoor exposure to one WL results in an annual exposure 

equivalent of 20 WLM (EPA79) in terms of the amount of potential 

alpha energy actually inhaled. 
The smaller bronchial area of children as compared with that 

of adults more than offsets their lower per-minute volume; 

therefore, for a given concentration of radon-222 progeny, the 

dose to children" bronchi is greater. This problem has been 

addressed in a paper by Wofmann and Steinhausler (Ho77), in which 

they estimate that doses received during childhood are about 50 

percent greater than adult doses. This information was used to 

prepare Table 2-1, which lists the age-dependent potential 

exposure eguival n used in the risk assessment described in the 

next subsection.iai The larger effective exposure to children 

relative to that to adults increases the estimated mortality due 

to lifetime exposure from birth by about 20 percent. 

Table 2-1. Annual exposure equivalent (WLM) as a 

function of age for members of the general public 

continuously exposed tg radon progeny at one working 

level (2.08 x 10- joules per cubic meter) 

Age of 

general population 

(Years) 

0-2 

3-5 

6-11 

12-15 

16-19 

20-22 

23 or more 

Exposure 

Equivalent 

(WLM) 

Lifetime Average 3 1 

2.3 Health Risk From ExDosure to Radon-222 Decav Products 

2.3.1 Risk Models 

A wealth of data indicates that radon-222 exposure of the 

bronchial epithelium of underground mine workers causes an 

increase in bronchial lung cancer among both smokers and 

nonsmokers. Among recent reviews (ICRP81, NA580, NCRP84, 

N105H85, Th82), two are of particular interest. 

(a) The assumptions on minute volume, etc., for mine workers 

and the' general population just described are the same as those 

used in the preparation of the EPA report entitled "Indoor 

Radiation Exposure Due to Radium-226 in Florida Phosphate Landsw 

(EPA79) and Final Environmental Impact Statements (EPA82, 83a). 
The 1980 NAS BEIR-3 Report (NAS80) contains a review of 

epidemiological studies on mine workers and develops an age 

specific absolute risk model. A lengthy report entitled "Risk 

Estimates for the Health Effects of Alpha Radiation," which was 

prepared by D. C. Thomas and X. C. McNeil for the Atomic Energy 

Control Board (AECB) of Canada, reanalyzes many of these 

epidemiological studies in a consistent fashion so that the 

modeling assumptions are the same for all of the data sets and 

develops a relative risk coefficient which fits most studies 

(Th82) . 

The manner in which radiogenic lung cancers are distributed 

in time, after a minimum induction period, is a crucial factor in 

numerical risk estimates. For radiation-induced leukemia and 

bone cancer, the period of risk expression is relatively brief; 

most occur within 25 years of exposure. For other 

radiation-induced cancers (including lung cancer), however, it 

appears that people are at risk for the remainder of their lives 

(NAS80). None of the epideniological studies of underground mine 

workers provides information on lifetime expression; indeed, most 

of the study populations are still alive and still at risk, 

Lifetime risks cannot be estimated only on the basis of 

observations to date; therefore, a model is needed to project the 

risk beyond the period of direct observation. As discussed in 

the 1980 NAS BEIR report, there are two basic models of risk 

projection: (1) the absolute risk projection model, in which it 

is assumed that the observed annual numerical excess cancer risk 

per unit exposure (or dose) continues throughout life; and (2) 

the relative risk projection model, in which it is assumed that 

the observed percent age increase of the baseline cancer risk per 

unit exposure (or dose) is constant with time (NAS8O). 

In the case of lung cancer and most other solid cancers, a 

relative risk model leads to larger estimated risks than the 

absolute risk model because of the generally increasing incidence 

of such cancers with increasing age. The number of lung cancer 

deaths that occurred in the U.S. population as a function of age 

in 1970 and in 1980 is shown in Figure 2-2. The decrease in the 

number oE deaths for ages greater than 65 years is due in part to 

depletion of the population by competing risks, and in part to a 

decrease in the age-specific incidence of lung cancer mortality, 

which peaks in males at about age 75 but is relatively constant 

in females until age 95 (NCHS73, NCHS83) (see Figure 2-3). The 

age-specific mortality of underground mine workers dying of 

radiogenic lung cancer shows the same pattern of death as a 

function of age as the general male population (Ra84, E185). In 

a recent review (E185), it was shown that a relative risk model 

can adequately account for the temporal pattern of cancer deaths 

observed in underground mine workers, whereas absolute risk 

projection models fail to do so. 
AGE in YEARS 

Figure 2-2. U.S. lung cancer mortality by age--1970 and 1980. 

2 -3 -2 The EPA Relative Risk b!odel 

Since 1978, the Agency has based risk estimates dae to 

inhaled radon-222 progeny on a linear dose-respor~se function, a 

relative risk projection mocJ.el, and a .ni.n-L.mum induction period 

of 10 years. Lifetime risks are projected on "the assumption 

that exposure to 1 WLM increases the age-specific risk, of l.ung 

cancer by 3 percent over the age-specific rate in the U.S. 

population as a whole (EPA79). The life table anaLysis 

described in Bu8l and EPA84 is used "to project this risk over a 

full life span. 

The EPA model has been described in detail (EPA79, El79). 

A review of this model in light of the more recent information 

described herein revealed that the major assumptions, linear 

response, and relative risk projection have been affirmed. The 

A-bomb survivor data clearly indicate that the absolute risk of 

radiogenic lung cancer has continued to increase among these 

survivors, whereas their relative risk has remained reasonably 

constant (Ka82). The UNSCEAR, the ICRP, and the 1980 NAS 

Committee have continued to use a linear dose response to 

estimate the risk of lung cancer d.ue to inhaled radon-222 

progeny. Thomas and McNeillls ana1ys.i~ (Th8?) indicates that 

the use of linearity is not unduly conservative and actus.iiy may 

underestimate the risk at law doses. The i.980 NAS BEZR 

Committee reached a similar conclusion (NASBO). 

A major limitation of earlier EPA risk estimates is the 

uncertainty in the relative risk coefficient used, 3 percent 

increase in the age-specific lung cancer mo:rtality rate per 

WLM. This value is based an the exce.ss iiiortality caused by lun~ 

cancer among exposed mine workers of varl-ous Eges, many of whom 

smoked. Therefore, it represents an avezage value for a mixed 

population of smokers, former smokers, arnd nnr;snolcers 'i'l?is 

assumption may tend to inflate the risk estimate (as discussed 

herein) because smoking was more prevalent anicing some groups of 

mine workers studied than it is amcnq the U,S, general 

population today. 

En a recent paper, Radforci and Renard (Ra84j r.cpcir..ted on 

the results of a long-term study of Swedisi~ irsn rcii.i-ars i.r!?o were 

exposed to radon-222 progeny, This study is unique in that most 

of the miners were exposed to less than 100 WL1.I and tlhe risks to 

smokers and nonsmokers were considered separately, The nbgoiute 

risks of the two groups were similar, 20 fatalities per I0 

person-year WLM for smokers compared with 16 fatalities for 

nonsmokers. The total number of lung cancer fatalities for 

nonsmokers is small; therefore, the estimate of 16 fatalities is 

not too reliable. Although absolute risks were comparable for 
the smoking and nonsmoking miners, relative risks were not. 

Nonsmokers have a much Lower baseline incidence of lung cancer 

mortality than smokers, This resulted in a relative risk 

coefficient for nonsmoking exposed miners relative to unexposed 

nonsmokers that was about four times larger than the relative 

risk coefficient for exposed smokers. This larger relative risk 

does not, however, fully compensate for the lower baseline 

incidence of lung cancer mortality among nonsmokers, Therefore, 

this study indicates that a relative risk coefficient derived 

from data on miners maybe biased high when applied to the 

population as a whole. Further follow-up of this and other 

groups of mine workers may provide more reliable data on the 

risk to nonsmokers, and EPA expects to incorporate separate 

consideration of smokers and nonsmokers into its analyses as 

more data become available. 

Although occupational exposures to pollutants other than 

radon-222 progeny are probably not important factors in the 

observed lung cancer risk for underground mine workers (E179, 

Th82, Mu83, Raga), the use of occupational risk data to estimate 

the risk of a general population is far from optimal, as it 

provides no information on the effect of radon-222 progeny 

exposures to children and women. Although the assumption has 

continued that the risk per unit exposure during childhood is no 

more effective than that occurring to adults, this assumption 

may not be correct. The A-bomb survivor data indicate that, in 

general, the risk resulting from childhood exposure to low 

linear energy transfer (LET) radiation is greater than that 

resulting from adult exposure, and this greater risk continues 

for at least 33 years (Ka92). As yet, however, no specific data 

pertaining to the effect of age at irradiation on lung cancer 

have been published (Ka82). Another limitation of the data for 

underground mine workers is the absence of women in the studied 

populations, The A-bomb survivor data indicate that women are 

about as sensitive as men to radiogenic lung cancer, even though 

they tend to smoke less as a group (Pr83). These data are not 

conclusive, however. 
2,3.3 Comparison of Risk Estimates 

National Academv of Sciences BEIR-3 

Several estimates of the risk due to radon-222 progeny have 

been published since the EPA model was developed. One of 

particular interest was developed by the National Academy of 

Sciences BEIR Committee (NASBO). The BEIR-3 Committee formulated 

an age-dependent absolute risk model with increasing risk for 

older age groups. Estimates of the risk per WLM for various ages 

and the estimated minimum induction period for lung cancer after 

exposure (NAS80, pp. 325 and 327, respectively) are summarized in 

Table 2-2. These have been used to calculate the lifetime risk 

of lung cancer mortality due to lifetime exposure of persons in 

the general population. 

Table 2-2. Age-dependent risk coefficients and minimum induction 

period for lung cancer due to inhaling radon-222 progeny (NAS80) 

Age at 

diagnosis 

(years) 

0-15 

16-36 

36-50 

51-64 

65 or more 

Excess lung cangers Minimum 

(cases per 10 induction period 

person-year WLM) (years) 

This was done by means of the same life table analysis that was 

used to calculate other EPA risk estimates (Bu81). 
The zero risk shown in Table 2-2 for those under 35 years of 

age at diagnosis does not mean that no harm occurs; rather, it 

means that the risk is not expressed until the person is more 

than 35 years old, i.e., only after the minimum induction 

period. The sequence of increasing risk with age shown in this 

table is not unlike the increase in lung cancer with age observed 

in unexposed populations; therefore, the pattern of excess risk 

over time is similar to that found by the use of a relative risk 

projection model. 

Atomic Enerqy Control Board of Canada 

In their recently conducted thorough analysis of the 

incidence of lung cancer among uranium mine workers for the 

Atomic Energy Control Board (AECB) of Canada, Thomas and McNeill 

tested a number of risk models on all of the epidemiological 

studies that contained enough data to define a dose-response 

function (Th82). They concluded that lung cancer per WLM among 

males increased 2.3 percent and that a relative risk projection 

model was more consistent with the incidence of excess lung 

cancer observed in groups of underground mine workers than any of 

the other models they tested. This is the only analysis that 

treated each data set in consistent fashion and used, to the 

extent possible, modern epidemiological techniques such as 

controlling for age at exposure and duration of foilowup. 

The estimate for lifetime exposure to ~anadian males is 830 

fatalities per million person W~;M (Th82). For presentation in 

Table 2-3, this estimate has been adjusted to 600 fatalities per 

million person WLM (which would be the appropriate estimate for 

the U.S. 1970 general population) by determining the "best 

estimate" risk (see p. 114 in Th82). This estimate was then 

multiplied by the ratio of lung cancers caused by radon-222 in 

the U.S. 1970 general popuLation to lung cancers in the U.S. 1970 

male population as calculated in the EPA model. The 1978 

reference life tables for Canadian males and U.S. males are quite 

similar; therefore, the simple proportional relationship of 

general populatior deaths to male deaths should give a reasonable 

estimate. 
International Commission on_fiadiolocii~~~Pro"cc&b 

The International Commission on Radiological Protection 

(SCRP) has made risk estimates for occupational exposure of 

working adults (ZCRPBL). The larger ICRP estimate (shown in 

Table 2-3) is based on an epidemiological approach; i.e., the 

exposure to mine workers in WLM and the risk per WLM observed in 

epidemiological studies of underground mine workers. The ICRP 

epidemiological approach assumes an average expression period of 

30 years for lung cancer. Children, who have a much longer 

average expression period, are excluded from this estimate. The 

ICRP has not explicitly projected the risk to mine workers beyond 

the years of observation, even though most of the mine workers on 

whom these estimates are based are still alive and continue to 

die of lung cancer. 

The smaller of the two ICRP estimates listed in Table 2-3 is 

based on their dosimetric approach. These estimates are in the 

lower part of the range shown for the ICRP estimate in Table 

2-3. In the dosimetric approach, the ICRP assumes that the risk 

per rad for lung tissue is 0.12 of the risk of cancer and genetic 

damage after whole-body exposure (ICRP77). For exposure to 

radon-222 progeny, the ICRP divides this factor of 0.12 into two 

equal parts. A weighting factor of 0.06 is used to assess the 

risk from a high dose to bronchial tissue, where radiogenic lung 

cancer is observed in exposed underground mine workers. The 

other half of the lung cancer weighting factor, another 0.06 of 

the total body risk, is used to assess the risk to the pulmonary 

region, which receives a comparatively small dose from radon-222 

progeny and where human lung cancer is seldom, if ever, observed. 

The United Nations Scientific Committee on the Effects of 

Atomic Radiation (UNSCEAR) estimate shown in Table 2-3 is for a 

general population and assumes an expression time of 40 years 

(UNSCEAR77). Like the ICRP, UNSCEAR did not make use of an 

explicit projection of risk of fatal lung cancer over a full 

lifetime. 
Table 2-3. Estimated risk from exposures to radon-222 progeny 

Organization Fagalities per Exposure Expression Reference 

10 person WLM period period 

EPA (a) 760 (460) (b) Lifetime Lifetime EPA84 

NAS BBJ~-3 (a) 730 (440) (') Lifetime Lifetime NAS8O 

AECB 600 (300) (b) Lifetime Lifetime Th8 2 

1CRP 150-450 Working 30 years ICRP8l 

lifetime 

uNscT&y 200-450 Lifetime 40 years UNSCEAR77 

NCRP 130 Lifetime Lifetime NCRP84 

(a) The number of fatalities per million-person WLM listed for 

EPA and NAS BEZR-3 differs fr&m those previously published 

by6EPA [860 fatalities per LO PWLm and 850 fatalities per 

LO PWLSII, respectively (EPA83a) because the increased 

exposure equivalent applicable to childhood has now been 

included. Risk estimates for various sources of radon-222 

in the environment have not changed because all were 

calculated in a life table analysis yielding deaths per 

100,000 exposed rather than deaths per 10 PWLN. 

(b) The EPA and AECB estimates of risk for the general 

population are based on an exposure equivalent, corrected 

for breathing rate (and other factors). For comparison 

purposes, the values in parentheses express the risk in more 

customary form, in which a continuous exposure to 1 WL for a 

year corresponds to 51-6 W1X. 

-j Adjusted for the 1970 U,S. general population; see text. 

(d) Assumes risk diminishes exponentially with a 20-year 

halftime. 
National Council on Radiation Protection and Measurements 

The National Council on Radiation Protection and 

Neasurements (NCRP) risk estimate in Table 2-3 is based on an 

analysis by Harley and Pasternack (Ha82). This estimate is of 

particular interest because, like the EPA and AECB estimates, it 

is based on a life table analysis of the lifetime risk from 

lifetime exposure (NCRP84). This estimate uses an absolute risk 

projection model with a relatively low risk coefficient, 10 cases 

per 10 person WLM per year at risk, which is the smallest of 

those listed by the NAS BEIR-3 Committee (cf. Table 2-2). 

Moreover, they have assumed that the risk of lung cancer after 

irradiation decreases exponentially with a 20-year half-life and, 

therefore, exposures occurring early in life present very little 

risk. 

The NCRP assumption of a 20-year half-life for radiation 

injury reduces the estimated lifetime risk by about a factor of 

2.5. Without this assumption, the NCRP risk estimate would be 

the same as the midpoint of the UNSCEAR estimate (325 fatalities 

per million person WLM). The assumed decrease in risk used by 

NCRP is questionable. If lung cancer risk decreased over time 

with a 20-year half-life, the excess lung cancer observed in 

Japanese A-bomb survivors (following the minimum latent period) 

would have decreased during the period this group has been 

followed (1950-1982); but to the contrary, their absolute lung 

cancer risk has increased markedly (Ka82). 

Comparison of Estimates 

Good agreement exists among the EPA, NAS (BEIR-3), and the 

AECB estimates listed in Table 2-3. Each of these estimates is 

based on lifetime exposure and lifetime expression of the 

incurred risk.. Conversely, the three lower risk estimates shown 

in Table 2-3 either do not explicitly include these conditions or 

they include other modifying factors. Nevertheless, Table 2-3 

indicates a divergence, by a factor of about 6, in risk estimates 

for exposure to radon-222 progeny. Thus, the use of a single 

risk coefficient may not be appropriate, as it could give the 

impression that the risk is well known when obviously it is not. 

The EPA, BEIR-3, and AECB estimates may be slightly high because 

they represent relative risks based on adult males, many of whom 

smoked. The actual risk may be smaller for a population that 

includes adult females, children, and nonsmokers. The UNSCEAR 

and ICRP estimates are probably low because they represent 

absolute risk estimates that do not completely take into account 

the duration of the exposure and/or the duration of the risk 

during a lifetime. The NCRP estimate is likely to be very low, 

as a low risk coefficient was used in an absolute risk model, and 

it was assumed that the risk decreases exponentially after the 

exposure. 
To estimate the range of reasonable risks from exposure to 

radon-222 progeny for use in the Background Information Document 

for Underground iiraniux Mines (EPA85), EPA averaged the estimates 

of BEIR-3, the EPA model, and. the AECB to est.ablish an upper 

bound of the range. The lower bound of the range was established, 

by averaging the UNSCEAR and ICRP estimates, The Agency chose 

not to include the NCRP estimate in its determination of the 

lower bound because this estimate used an absolute risk 

projection model with a relatively low-risk coefficient. 

Therefore, the ETA chose relative risk coefficients of 1.2 

percent per WLM and 2.8 percent per CaLM (300 to 700 fatalities 

per million-person WZM) as reasonable estimates for the possible 

range of effects from inhaling radon-222 progeny for a full life 

time. Although these two risk estimates do not encompass the 

full range of uncertainty, they appeared to ill.ustrate the 

breadth of much of current scientifi-c opinion. 

The lower limit of the range of relative risk coefficients, 

1.2 percent per WLM, is similar to that derived by the Ad Hoc 

Working Group to Develop Radioepidemiological Tables, which also 

used 1.2 percent per WUM (NIK85). Some other estimates based 

only on U.S. and Czech miner data average 1 percent per WLpa 

(Ja35) or 1.1 percent per WLM (S.tS5) . 

A possible 0.5 percent per WLM 1.ower bound of risk mentioned 

by the Environmental Prot.ecticn Agency Radiation Advisory 

Committee (SAB85) appears too low. Estimates of this magnitude 

of risk are usually based on data from the entire cohort of U.S. 

white uranium miners (Tb82, Wh83, Ja85, St85). The risk of 

exposure of 600 cumulative WTd or less, however, is usually 2.4 

times or more higher than the risk for the entire cohort (Lu71., 

Ar79, ThRZj, For "cis reason, the 0.5 percent per WLM relative 

risk coefficient was not used, 

The upper limit is lower than what might be justified by 

some current reports. Although the Swedi.sl-i iron miners study 

(Ka84) suggested a rather high relative risk coefficient, this is 

a comparatively small study, In 1985, the National Institute of 

Occupational Safety and Xealth esti-mated the relati-ve risk 

coefficient in these Swedish miners was 3-6 percent per WLX 

(NIOSK85). In the same year, a report on 8500 Sa-skatchewan 

uranium miners (Ho85) estimated a relative risk of 3.3 percent 

per WLM, in addition, a small study was made of persons exposed 

to different levels of radon--222 daughters and smoking in 
dwellings on the Swedish island of Oeland (Ed.83, 84). Data from 

this study could justify a relative risk coefficient of about 3.6 

percent per WLM. 

These three studies indicate a relative risk coefficient 

greater than 3 percent per WLM; therefore, the EPA is increasing 

the upper limit of its estimated range of relative risk 

coefficients. To estimate the risk due to exposure to radon-222 

progeny, the EPA will use the range of relative risk coefficients 

of 1 to 4 percent per WLM. These risk coefficients were obtained 

by rounding off the coefficients listed above to the nearest 

whole number. 

These changes are in agreement with the recommendations of 

the Radiation Advisory Committee of the Science Advisory Board of 

EPA (SAB85) which recommended that EPA use a risk coefficient 

range of 1 to 4 percent per WLM, as they believed that both 

overestimations of exposure and the effect of random error could 

have biased the risk coefficients downward, and a risk 

coefficient of 4% was recommended as an upper bound. The 

Committee also recommended use of single-digit risk coefficients 

to avoid the suggestion of a precision that does not exist. In 

response to these recommendations, EPA used risk coefficients of 

1 to 4 percent per WLM. These risk coefficients were obtained by 

rounding off the coefficients discussed above. The basis for 

these relative risk coefficients was reviewed for this final 

report, but no changes were made and the risk estimates are based 

on 1 and 4 percent per WWII, 

It may be noted here that using a 1% to 4% relative risk per 

WLM with the WLM Exposure Equivalent defi-ned earlier is 

numerically the same as using a 0.6% to 2.4% relative risk per 

WLM with the conventional WM, (see table 2-3). 

2.4 gtimatinq the Risks 

2.4.1 Exposure 

The exposure to radon-222 progeny at a site of interest is 

based on the calculated radon-222 concentration and the 

calculated radon-222 progeny equilibrium fraction: 

Radon progeny Radon Radon progeny - 9.84 x 

concentration -. conc. x equil. &ction x (WL per pCi/liter) 

(WL) ~Ci/l) (fe ) 

For individuals and regional populations, emission data and 

meteorological data are used with the AIRDOS-EPA model (74079) tc 

calculate air concentrations of radon-222; for national 

populations, emission data and meteorologica1 data are used with 

the NOAA Trajectory Dispersion Model (NRC79). 
Calculations of radon-222 progeny equilibrium fractions are 

based on distance from a source and the time required to reach 

the exposure site. By using the ingrowth mod-el of Evans (Ev69) 

and the potential alpha energy data of UNSCEAR (UNSCEAR77), the 

outdoor equilibrium fraction can be calculated by the expression: 

where t is the travel time in minutes (distance/transport 

velocity). 

The indoor equilibrium fraction presumes that those decay 

products associated with the radon-222 reletife also enter the 

building and that a ventilation rate of 1 h (one air change 

per hour) in combination with indoor removal processes (e.g., 

deposition onto room surfaces) produces an indoor equilibrium 

fraction of 0.35 when there are no decay products in the 

ventilation air and 0.70 when the decay products are in 

equilibrium with the radon-222 in the ventilation air (EPA83b). 

A simple linear interpolation is used to obtain the indoor 

equilibrium fraction: 

in = 0.35 (1 + fe out) *e 

If one further assumes that a person spends 75 percent of 

his or her time indoors and the remaining 25 percent outdoors at 

the same location, the effective equilibrium fraction is given 

by: 

eff = 0.75 fe in + 0.25 fe Out = 0.2625 + 0.5125 fe out 

e 

An example of the case for a 3.5 m/s windspeed and various 

distances from the source is given in Table 2-4. Removal 

processes outdoors were assumed to limit the equilibrium 

fraction to 0.85, which corresponds to an indoor equilibrium 

fraction of 0.65 and an effective fraction of 0.70. Table 

2-4 shows that this limit is reached at a distance of 

19,550 meters. 

2.4.2 Risk Estimation 

After the exposure equivalent has been calculated, the risk 

can be estimated for an individual or a population. 

Individual 

Individual risks are calculated by using the life table 

methodology described by Bunger et al. (Bu81). Relative risk 
Table 2-4. Radon-222 decay product equilibrium fraction at 

selected di$gmces from the center of a 80 ha. tailings 

impoundment 

Distance out in eff 

(m) 

fe e fe 

0 

100 

150 

200 

250 

300 

400 

500 

600 

800 

1,000 

1,500 

2,000 

2,500 

3,000 

4, GOO 

5,000 

6,000 

8,000 

10,000 

15,000 

19,550 

(a) Calculations (tabulated to 3 decimal places to facilitate 

comparisons) presume: a 3.5 m/s windspeed for the outdoor 

equilibrium fraction; an indoor equilibrium fraction of 0.35 

for no radon-222 decay products in the ventilation air and 

0.70 for ventilation air with 100 percent equilibrium between 

radon-222 and its decay products; and an effective 

equilibrium fraction based on 75 percent of time indoors and 

25 percent of time outdoors. 
projections for lifetime exposure based on coefficients of 1.0 

percent and 4.0 percent per WLM for the radiation-induced 

increase &n iung cancer yield rounded-ofg estimates of 380 

deaths/lO person WLM and 1520 deatlzs/lO person WLM, 

respectively when using updated age specific mortality and the 

1980 iife table data. These risk grojections compare to the 

estimate of 250 and 1000 deaths/10 person WLM used in the 

Draft Background Information Document which were based on the 

1970 life tables. The updated estimates used in this final 

document are based on the same risk coefficients but yield higher 

death rates since there are more people in each age category and 

there is a higher total incidence of lung cancer. 

These risk coefficients can be used in the CAIRD Code (Co78) 

to calculate the risk from any exposure to radon-222 progeny 

across any time period. Usually, the lifetime risk from lifetime 

exposure at a constant level is calculated. The age-specific 

differences in exposure equivalent listed in Table 2-1 are 

included in calculations of the lifetime risk. 

One of the characteristics of the life table based 

calculations is that the same risk coefficients will yield 

different estimates of life time risk when different life tables 

are used. This is particularly true of relative risk projections 

when both the life table and the age-specific mortality data in 

the calculation may be changed. Prior ORP relative risk 

estimates were based on the 1970 life table (NCHS75) and the 1970 

mortality data (NCXS73). For this document the basis for 

calculation has been changed to the recently available 1980 life 

table (NCHS85) and 1980 mortality data (NCHS83). 

Although this change provides risk estimates more 

appropriate for the l980s, the increase in the life span 

reflected in the iife table and, more significantly, the increase 

in lung cancer mortality (Figures 2-2 and 2-3) have caused an 

appreciable upward change in the risk estimate. Lifetime risk 

estimates made using the relative risk projection with 1980 vital 

statistics are about 50% greater than those made earlier using 

the 1970 vital statistics. Thus, the updated estimates used in 

this final document are based on the same risk coefficients (1% 

and 4% increase per WLM), but yield highter numerical risks since 

there are more people in each age catagory and there is a higher 

rate of lund cancer mortality for each age. 

Results of representative calculations of lifetime risk 

using 1980 data are given in Table 2-5. 
Table 2-5. Lifetime risk for Lifetime exposure to a given 

level of radcn-222 progeny 

(1980 Life Table, 1980 Mortality Data) 

Lifetime risk of lung cancer 

Radon-222 progeny 4 percent increase l percent increase 

concentration (WL) per WLM per WLM 

The lifetime risk estimates shown in Table 2-5 are for lifetime 

exposure at a constant level of radon-222 progeny. These risk 

estimates were used with WL exposures th$ifwere calculated by 

using radon-222 concentrations and an f determined as 

shown in Table 2-4 to estimate the riskg of fatal lung cancer 

due to maximum exposure of individuals living nearest the 

tailings impoundments (Table 6-1). 

Lifetime risk factors for selected concentrations of 

radon-222 in air with relative risk coefficients of l percent 

and 4 percent per WLM are shown in Table 2-6 in a manner similar 

to Table 2-5. 

Table 2-6. Lifetime risk for lifetime exposure to a given 

level of radon-222 in air 

Lifetime risk of lunq cancer 

concentratio s 

=?a, 

4 percent increase 1 percent increase 

(pCi/l) (WL) per WJiM per wLM 

(a) At equilibrium fraction of 0.7. 
Collective (population) risks for the region are calculated 

from the annual collective exposure (person WtM) for the 

population in the assessment area by a computerized methodology 

known as AIRDOS-EPR (Mo79). An effective equilibrium fraction 

of 0.7 is presumed because little collective exposure takes 

place near the source. 

Formally, the annual collective exposure, SE, can be 

defined as: 

where SE is the collective exposure (person WLM). E is the 

exposure level (WLM), and n(E) is the population density at 

exposure level E (person/ WLM). 

Practically, however, the collective exposure is 

calculated by dividing the assessment area into cells and then 

calculating the population, Ni (persons). and the arulual 

exposure, Ei (WLM). for each one. The collective exposure is 

then calculated by the following expression: 

where the summation is carried out over all the cells. 

Customarily. the regional population exposure is limited to 

persons within 80 km of the source. 

The same risk factors used for the individual risk 

calculations (4 percent increase per WLM or 1 percent increase 

per WLM) are also used to calculate the population risk. 

National 

Radon-222 released from a source can be transported beyond 

the 80-km regional cutoff. A trajecto~y dispersion model 

developed by NOAA (NRC79) has been used to estimate the 

national impact of radon-222 releases from a source. This 

model calculates the average radon-222 exposure to the U.S. 

population from unit releases at four typical uranium mining 

and milling sites. The model yields radon-222 concentrations 

(in picocuries per liter) in air, which are then converted to 

decay product exposures by assuming an effective equilibrium 

f raction of 0.7. National an~lual collective exposures 

(person-WLM) are calculated for distances beyond the 80-km 

regional limit. The exposures and risks are calculated for a 

total population of 200 million persons. 
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the Biological Effects of Ionizing Radiation (BEIR-3 

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J. R. Parker and V. R. West - editors, NASA, 

Washington, D.C., 1973. 

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Chapter 3: RADON-222 SOURCES, ENVIRONMENTAL TRANSPORT, AND 

RISK ESTIMATES 

3.1 Introduction 

This chapter presents the physical and chemical properties 

of radon-222, where and how it is emitted from the uranium 

milling process, and how it is transported through the 

environment. Also presented are the methods used to model the 

dispersion of the radon-222 and a description of how the health 

risks associated with these emissions are estimated. 

3.2 Oriqin and Properties of Radon-222 

Uranium ore contains both uranium and its decay products, 

including significant concentrations of radium-226. Radon-222 is 

a naturally occurring radioactive gaseous element that is formed 

by the radioactive decay of radium-226. Radium-226 is a 

long-lived (1620-year half-life) decay product of the uranium-238 

series. In nature, uranium is about 99.3 percent uranium-238; 

thus, it is the decay products of uranium-238 (shown in Figure 

3-1) that govern the radioactive content of the ore (NRC81). 

Other isotopes of radon (radon-219 and radon-220) occur from the 

decay of uranium-235 and thorium-232, but these isotopes have 

short half-lives of 3.96 and 55.6 seconds, respectively, and have 

little environmental impact due to the short half-lives of the 

decay products, Important properties of radon-222 are presented 

in Table 3-1 for information purposes only. 

Mined uranium ore is milled to extract the uranium-238, 

Milling removes about 90 percent of the uranium-238 from the 

ore. The remaining uranium-238 and essentially all other 

radioactive elements (including thorium-230) present in the ore 

are left behind and disposed of with the mill waste (tailings). 

These tailings will remain radioactive for hundreds of thousands 

of years. 

Radon-222 is the only member of 'the decay chain that is a 

gas, It is a noble gas and therefore does not usually combine 

with other elements to form nongaseous compounds. As a gas, 

radon-222 is released to the atmosphere if it escapes (emanates 

from) the mineral matrix that contains its parent, radium-226. 

The subsequent radioactive decay of radon-222 produces a series 

of solid radioactive products called "radon progeny.!! If 

radon-222 is airborne at the time of its decay, these radon 

progeny become attached to dust particles in the air and can be 

inhaled and deposited in the lungs (NRC8l). 
y - years 

d - days 

m - minutes 

s - seconds 

Figure 3-1. Uranium-238 decay chain and half-lives or 

principal radionuclides. 
Table 3-1. Properties of radon-222 (a) 

Property Value 

Atomic number 86 

Atomic weight 222 

Boiling point -62°C 

Melting point -71°C 

Density 9.73 grams/liter 

Solubility in water 51 cms in 100 grams at 0°C 

8.5 cm3 in 100 grams at 60°C 

Half -1if e 3.824 days 

Decay modes and energy 

ci 5.4897 MeV 

Y 0.512 MeV 

(a) Source: Chemical Engineer's Handbook, Perry, J. H. (editor), 

McGraw-Hill Book Co., New York, New York, 1983, and Chart of the 

Nuclides, Knolls Atomic Power Laboratory, Operated by General 

Electric Co. for U.S. Dept. of Energy, 12th Edition, April 1977. 
Radon-222 that enters the atmosphere can be transported over 

great distances, At distances beyond about a mile, however, the 

contribution of radon-222 concentrations from the mills and 

tailings piles is indistinguishable from natural background 

(NRCBl). Some uranium-238, 1-2 ppm, is present in most soils; 

therefore, radon-222 is emitted constantly from the Earth's 

surface (NRC81). It is estimated that 120 million Ci/y of 

radon-222 is emitted from undisturbed soil and an additional 3 

million Ci/y is emitted from tilled soil (NRC81). In comparison, 

uranium tailings disposal at licensed mills currently contributes 

about 140,000 Ci/y (PEI85). 

3.3 Sources of Radon-222 Emissions in the Millinq Process 

Uranium ore is processed in mills to recover and concentrate 

uranium to an intermediate, semirefined product often called 

"yellowcake." This yellowcake is sent to separate refining 

facilities that produce uranium metal, UO , or UF6. 

Conventional uranium milling involves a sgries of unit 

operations, including ore handling and preparation, extraction, 

concentration and precipitation, product preparation, and 

tailings disposal. 

Ore stockpiles, crushing and grinding operations, the 

extraction circuit, and tailings piles are sources of radon-222 

at operational uranium mills, as illustrated in Figure 3-2. 

Other sources, such as contaminated former ore storage areas, 

also release radon-222, These sources, however, are 

comparatively small in comparison with tailings and of such 

uncertainty in size, source strength, and frequency of occurrence 

that they are omitted from the present analyses. 

Radon-222 releases can be characterized as total-release 

events or continual, diffusion-limited releases. Thick or deep 

sources, such as ore storage piles and mill tailings 

impoundments, that remain undisturbed for extended periods of 

time release radon-222 by diffusive and advective mechanisms. 

Accordingly, the radon-222 emission is often characterized by a 

mathematical diffusion expression of the radon-222 flux. 

Conversely, sources that rapidly release radon-222 during a 

mechanical disturbance, such as the crushing and grinding 

operation, are best characterized by a radon-222 release per unit 

mass; e.g., picocuries of radon-222 per picocuries radium-226 

present. This release can then be expressed in terms of the 

amount of U 0 produced by the mill. 3 8 

The domestic uranium ores currently mined contain an average 

of about 0.1 percent uranium. When uranium ore lies underground, 

only a very small fraction (if any) of the radon-222 it produces 

escapes to the atmosphere. Radon-222 has a half-life of only 

3.8 days; therefore, most of the radon-222 that is generated more 

than a few meters below the surface decays into nongaseous 

radionuclides before it can migrate through the soil pore space 

(the air space between soil particles) and escape into the 

atmosphere. When uranium ore is mined and milled, however, the 

handling and grinding operations liberate radon-222 contained in 

the pores in the ore. Milling of the ore to sand-sized particles 

also allows a greater portion of the radon-222 that forms in the 

tailings to be released into the atmosphere by diffusive and 

advective mechanisms. Both the increased surface area of the 

particles and increased porosity resulting from the milling 

process cause an increase in the portion of radon-222 that 

escapes to the atmosphere. 

Ore Handlinq and Preparation 

Ore handling and preparation include ore blending, storage, 

crushing, fine ore storage, and grinding. Ore blending ensures 

that the mill feed is of uniform grade, which is necessary to 

achieve maximum efficiency in the mill circuit. Blending may be 

performed at either the mine or the mill. Ore is stored in 

stockpiles on ore pads at the mill site. The stockpiles provide 

sufficient feed for a continuous supply to the mill. Ore 

received from the mine often has a high moisture content; 

however, the dry climate typical of the major uranium districts 

causes rapid drying. For this reason, some ore storage piles are 

sprayed with water to maintain their moisture content and to 

reduce dusting. 

Storage pads typically cover several acres and provide 

enough ore storage to feed the mill for one or two months of 

operation, Ore usually is not kept on the storage pad when the 

mills are on standby status. Similarly, when operations are 

reduced because of a depressed economy, as they currently are, a 

lesser quantity of ore is stockpiled at the mill site than would 

be if the mill were operating at full capacity. The ore 

residence time in storage piles varied from 4 to 180 days, with a 

mean and standard deviation of 87 72 days, at seven mills 

surveyed in Wyoming (Th82). 

The number of piles can be estimated by the product of the 

mill feed rate (weight/day) and the stockpile residence time 

(days) divided by the mass of a pile. The piles vary in shape 

among different mills, but they are frequently conical, oblong, 

or wedge-shaped. A maximum height of 10 m (30 ft) and 45-degree 

sloping sides are common. The volume and surface area of a 

typical pile have been estimated to be 8000 m and 2500 m , respectively (Th82). missions of radon-222 from stockpiles are 
considered to emanate from an infinitely deep or thick source 

from all surfaces, even though some parts may be shallow or 

thin. The resulting high radon-222 emission estimate for some of 

the pile areas is justified by the variable sizes, shapes, and 

other characteristics of ore stockpiles. 

Stockpiles initially emit no radon-222 because all of the 

emanated radon-222 stored in the pores of the ore was released as 

the ore was mined and transported to the stockpiles. As new 

radon-222 emanates into the pore space of the ore, the 

interstitial radon-222 levels and the escaping radon-222 flux 

increase. After several weeks, a nearly constant radon-222 flux 

(emission rate) is attained. 

Crushing is the first stage of size reduction and involves 

the use of impact and/or gyratory crushers. Crushing typically 

reduces mine run ore to between minus 3/4 inch and minus 1-1/2 

inch size (Me71). Fine ores (undersized material) bypass the 

crushing circuit and are conveyed directly to fine-ore storage 

bins. Air exhaust hoods with dust collectors are located on 

crushers and screens and at transfer points to minimize 

particulate emissions, and air is exhausted to the atmosphere via 

vents. The dust collectors do not capture radon-222 emanating 

from the ore during these processes, and it is vented to the 

atmosphere. Crushing plant capacities range from 70 to 320 tons 

per hour (NRC80) . Crushed and undersized ore is stored in cylindrical fine-ore 

bins about 7 to 10 m (25 to 35 feet) in diameter. These bins 

provide a fine-ore storage capacity up to double the rated daily 

milling capacity (NRC80). Radon-222 that emanates from the fine 

ore in storage is vented to the atmosphere. 

Belt-type feeders convey the ore from the crushing circuit 

and fine-ore bins to the grinding circuit, where rod and ball 

mills or semiautogenous mills are used to reduce the ore size 

further. Occasionally, the ore is roasted before it is sent to 

the grinding circuit to reduce moisture before grinding, to 

increase the solubility of other valuable constituents (e.g., 

vanadium), or to improve the physical characteristics of the 

ore. The ores are ground dry and then slurried with water or 

wet-ground to yield a pulp density of 50 to 65 percent solids 

(NRC80). Classifiers, thickeners, cyclones, or screens are used 

to size the ore, and coarser particles are returned for further 

grinding. One mill uses an alkaline leaching process, which 

requires the ore be ground much finer (200-mesh) than for acid 

leaching (28-mesh) . 
Wet, semiautogenous grinding is being used increesingly in place of dry crushing or ball and rod mill grinding 

operations, which may be run wet or dry. The semiautogenous 

grinder performs the ore sizing function of these operations and 

reduces or eliminates dry ore handling. 

The total release of radon-222 from the dumping, crushing, 

and extraction processes occurs mostly during the process of 

transferring and dumping the ore into the mill feed area, The 

ore is typically reduced to sizes of less than 40 cm, which is 

the relaxation diameter for rad0n-~22~diffusion from ore pieces 

with diffusion coefficients of 10- cm /s; therefore, 

radon-222 escapes readily from the pores of the ore when it is 

handled and results in the total release of accumulated 

radon-222. During the remainder of the short milling process, 

little additional radon-222 escapes from the pre for release. 

Hard-rock uranium ores are an exception, in tQat they have very 

10br~di~fusion coefficients for radon-222 (10- to 

LO cm /s). The 4 to 14cm particles of these ores can 

significantly reduce radon-222 releases; hence, the sharp 

one-time release is less and is delayed until the ore is ground 

to smaller particle sizes during milling. 

Extraction 

Hydrometallurgical leaching techniques are used to recover 

uranium from the ground ore slurry. Little radon-222 is released 

from the extraction process because the radon-222 contained in 

the ore is released during initial ore handling and size 

reduction steps and the relatively short milling time (less than 

24 hours) does not permit significant formation of new 

radon-222. The extraction process uses sulfuric acid or an 

alkaline carbonate solution for lixivation. Acid leaching is 

preferred for ores with low lime content (12 percent or Less) 

(NRCBO) and is the predominant Leach process in the United 

States. A flow diagram of the acid leach/solvent extraction 

process is shown in Figure 3-3, 

The leaching circuit consists of a series of mechanically 

agitated tanks having a total ore residence time of approximately 

7 hours. The pH in the tanks is maintained between 0.5 and 2.0 

by adding.sulfuric acid. The free acid concentration is from 1 

to 90 grams of acid per liter during the contact period (NRC80). 

Acid leaching is carried out at atmospheric pressure and slightly 

above room temperature. 

After leaching, the pregnant leach solution is separated 

from the tailing solids in a countercurrent decantation (CCD) 

circuit. The sands and slimes are pumped to a tailings pond for 

disposal. 
Alkaline Leaching, which is best suited to ores with high 

lime content, may be used in combination with ion exchange or 

caustic precipitation to concentrate and purify uranium, A flow 

diagram of the alkaline leach/caustic precipitation process is 

shown in Figure 3-4. 

The are slurry is leached in a two-stage system (pressure 

leaching followed by atmospheric leaching). The leach solution 

contains sodium carbonate (40 to 50 grams per liter) and sodium 

bicarbonate (10 to 20 grams per liter). Circular tanks are used 

and air is added to oxidize the uranium to the hexavalent state. 

Residence time varies from 21 to 33 hours. The pregnant leach 

solution is separated from the tailings in a series of CCD 

filtrations. 

Concentration and Precipitation 

Three techniques are used to concentrate uranium from the 

pregnant leach solution: ion exchange, solvent extraction, and 

the Eluex process, which is a combination of ion exchange and 

solvent extraction. Uranium that has been concentrated by one of 

these methods is precipitated from the solution by the addition 

of gaseous ammonia (NH ), sodium hydroxide (NaOH), hydrogen 

peroxide (H 02), or ma3nesia (MgO) in several stages under 

controlled $H. Most mills use gaseous ammonia. The precipitated 

uranium is dewatered in thickeners and then filtered and washed 

in drum, plate, or frame filters. At this point, the resulting 

filter cake still oontains considerable moisture. 

Product Preparation 

The uranium filter cake (yellowcake) is dried in a 

continuous steam-heated dryer or in a multiple-hearth dryer. The 

dried yellowcake is crushed and screened to the required size and 

packaged in 55-gallon drums for shipment. Some radon-222 

emanates from this operation and is vented to the atmosphere. 

With the exception of the uranium extracted during milling, 

the dry weight of the tailings represents the total dry weight of 

the processed ore. Ore contains only about 0.1 percent uranium; 

therefore, the tailings consist of 99.9 percent of the ore, 

including all the radioactive decay products. The tailings 

discharge is composed of three fractions: (1) the sands, which 

consist of solids greater than 200 mesh (74 mm); (2) the slimes, 

which consist of solids less than 200-mesh; and (3) the liquid 

solution containing milling reagents and dissolved ore solids. 
CRUSHING AND 

WET 

GRINDING I 

SODIUM CHLORATE 

TAILINGS POND 

(TAILINGS SAND AND SLIMES, 

I LIQUID WASTES) 

COUNTER CURRENT 

SOLVENT 

EXTRACTION FURTHER 

P ROCESSING 

Figure 3-3. Simplified flow diagram of the acid leach process. 
CRUSHING AND 

GRINDING 

WET 

GRINDING 

FLOCCULANT COUNTERCURRENT 

FILTRATION TAILINGS 

10 GRINDING 

AND LEACHING 

Y ELLOWCAKE 

Figure 3-4. Simplified flow diagram of the alkaline 

leach-caustic precipitation process. 
Dry tailings from an acid leach mill are typically composed of 20 

to 37 percent slimes by weight (NRCBO). Tailings are discharged 

from the mill as a slurry at an average ratio, by weight, of 

about l:l (solids to liquids) and are sent to an impoundment, 

where the tailings settle. 

About TO percent of the uranium-238 and virtually all of the 

other radionuclides in the ore are contained in the tailings. 

Tailings represent the largest and longest lasting source of 

radon-222 emissions from licensed conventional uranium mills 

because of the large exposed area and the significant 

concentrations of radium-226 present. The fine slimes fraction 

contains the majority of radium-226 in the tailings (up to 80 

percent) (NRC80). The sands fraction contains radium-226 in 

concentrations ranging from 26 to 100 pCi/gram (NRC80), and the 

tailings liquid (raffinate) contains 1.7 to 35,000 pCi/liter of 

radium-226 and 50 to 250,000 pCi/liter of thor.ium-230 (EPA83). 

The methods used to construct and fill tailings impoundments 

causes segregation of the slimes and sands. During spigoting, 

the sands are deposited on the perimeter of the impoundment and 

the slimes are carried to the central portions of the impoundment 

with the raffinate. The more porous sands are deposited away 

from the center of the pile and are therefore typically drier 

than the slimes, which are usually saturated with moisture of 

actually covered with standing process fluids. 

Except for a small percentage used for backfill in 

underground mines, virtually all tailings are disposed of in 

impoundments. Disposal is below grade in mined-out or excavated 

pits and above grade behind dams. The majority of the tailing 

impoundments at licensed mills are above grade. Currently, new 

dams are constructed of earthen material, whereas in the past 

they were constructed of tailings sands. Impoundment sizes vary 

from 10 to about 121 ha (25 to 300 acres) (EPA85). 

Site topography dictates the general shape of above-grade 

surface impoundments. One-sided, two-sided. and three-sided dams 

are constructed across valleys and along hillsides. Dams 

constructed on relatively flat terrain, where the tailings cannot 

be contained by the natural topography, are four-sided. 

Embankments are generally constructed of earthen material, but 

some (at six mills) are constructed of the snad fraction of the 

tailings. 

The water level in a tailings impoundment is controlled 

through the use of decant towers, pumps, or siphons to recycle 

the water or to transfer it to evaporation ponds for proper 

maintenance of freeboard. Most mills operate with zero liquid 

discharge (40 CFR Part 440) and rely on evaporation. 
Constrrrcting impoundments with earthen embankments or below 

grade is the preferred method at new milling operations or for 

new impoundments at existing mills because they inherently have 

greater short-term and long-term stability. In addition, 

tailings disposed of below grade are typically covered with 

raffinate, which effectively controls dusting and reduces 

radon-222 emissions during the mill" active Life. 

Radon-222 is emitted from all exposed tailings in 

impoundments. Emission rates vary in different areas and over 

time. A qualitative illustration of the variation in radon-222 

emissions over the Life of a milling operation is shown in Figure 

3-5. These emissions occur during the licensed phase of mill 

operations and continue for hundreds of thousands of years after 

closure of the mill. Radon-222 and radium-226 both have much 

shorter half-lives than their precursor thorium-230; therefore, 

their radioactivity remains the same as that for thorium-230 

(EPA83). The radon-222 emissions decrease only as the 

thorium-230, which has a half life of 77,000 years, decreases 

(EPA83). It would require about 265,000 years for the radon-222 

emissions to be reduced to 10 percent of its initial value 

(EPA83). If control techniques are not imposed, the radon-222 

emissions will remain relatively constant, on a year-to-year 

basis for many tens of thousands of years. 

3.4 Characterization of Emissions 

The amount of radon-222 emitted from ore storage piles, 

milling circuits, evaporation ponds, and tailings impoundments 

depends on a number of highly variable factors, such as ore 

grade, emanation fraction, porosity, moisture, temperature, and 

barometric pressure. These factors, in turn, vary between 

milling sites, between locations on the same site, and with time 

(PEI85). These variations make it difficult to assess the 

radon-222 emission rate. For these reasons, mathematical models 

typically have been used to estimate average radon-222 emissions 

on a theoretical basis. A few systematic measurements have been 

made of radon-222 emissions from licensed uranium mills and 

tailings piles, and studies have demonstrated good agreement 

between actual measurements and estimates based on mathematical 

models (EPA83) . 

Considerable research has been conducted to develop and 

refine ways of calculating average radon-222 flux from infinitely 

thiclc or deep sources (i.e., at least l meter deep). This work 

has largely been carried out in support of the Uranium Mill 

Tailings Remedial Action Program (UMTRAP). Although these 

calculations were developed for inactive mill tailings piles, 

they are directly applicable to ore storage piles and tailings 

impoundments at Licensed mills. 
TIME, years 

Figure 3-5. Qualitative illustration of radon-222 emissions 

fr~m licensed uranium milling process. 
A one- dirnensitsnal. steady-state, radoia- 222 diffusion 

equation bas been develuued for sources (e.~.. ore piles and 

tailings) that are more iban several meteis ihick (~i82, Fr84) 

The equation is: 

where J is the radon-222 flux at the surface of the source 

t 

2 (pCi/m s); R is ttre speeif ic activity of radium-226 in ore 

or tailings equal to 2812 x uranium ore grade in percent 

3 (pCi/y): p is tire bulk dry density of source (g/cm ): E is 

the radon- 222 emanating f raction of source, dimensionless: 

- 6 h is the radon-222 decay constant (2.1 x 10 /s): D is the 

effective diffusion coef f icient for radon-222. equal to 

- 

L bulk radon diffusion coefficient/porosity De/p (em /s); and 

p is the porosity, equal to 1- (bulk density/speclfic 

gravity). 

For piles that are less than a few meters thick, 

Equation 3-1 should be multiplied by a hyperbolic tangent 

function that varies with depth or thickness (T), as shown 

in Figure 3-6. With the exception of the radon-222 decay 

constant. these parameters can vary sigtlificantly from 

location to 1ocati.on within the source, both horizontally 

and with depth, in a given ore pile or tailings 

impoundmeltt. Except for the decay constant and bulk 

density. these parameters are difficult to measure. They 

are based on the physical characteristics of the source 

materials, whictl vary over time (e.g.. radium-226 content 

may decrease over the life of the mill as ore grade 

decl.i.nes). seasonally. or with changing mill operation 

(e.g., moisture content changes seasonally and with changes 

in mill operations and directly affects the emanation and 

diffusion coefficients). 

2 A radon-222 release rate of 1 pCi Rn-222/m s per pCi 

of Ha--226 per gram of tailings is used in this backgcound 

report because oE emission rate variations and the lack of 

specific information required to use the more detailed 

mathematical equations (NRCUO) (Ha85). Using an average, 

specific flux does not take into account site-specific 

conditions suctt as moisture, porosity. and emanation 

coefficients. It is useful for estimating industry-wide 

emissions. however. and is consistent with previous EPA 

studies (EPA83). In the following sections, a model mill 

handling 1800 t/day of ore with 0.1 percent U308 will be 

used to illustrate radon- 222 emission calculations. 

Assumptions are made for the para~ueters required to 

calculate emissions with the diffusion equations, and for 

2 comparison a specific flux of 1 pCi Rn-ZZZ/m s per pCi of 

Ha-22G/g is also used to estimate emissions. 
DEPTH, em 

rigure 3-6. Effect of ore vile depth on hyperbolic tangent 

tern in radon-222 flux equation (Ha85). 
Stockpiles are blettded to the average or optitni~m feed grade 

upon entry to the mill. Emissions cat1 be based on the average 

radium-226 content. as both the initial total radon-222 release 

and the longer-term. diffusion-cotltrolled radon-222 releases vary 

Ziirearly with radium-226 eontent. The radium--226 content is 

typically estimated from ore grades, assuming secular equilibrium 

between the uranium-238 and the radium-226. 

Ore storage piles are typically more than 3 meters deep. 

Thus, Equation 3-1 can be used to estimate radon-222 emissiotls if 

the various values are known. OK a specific flux of 1 yCi 

Rn-222/m s per pCi Ra-226 per gram of ore can be used. 

As an example. consider the ore pad at a hypothetical mill 

with the following parameters: 

4 2 

area of ore pile = 6 acres or 2.4 x 10 m 

depth of ore pile = 3m minimum 

Ra-226 concentration = 2812 x 0.1 U308 = 

281 pCi/g 

emanating power of ore = 0.2 

3 density = 1.6 g/cm 

2 diffusion coefficient = 0.05 ci~ /s 

104Rp~ (hD) 112 

281 x 0.2'~ 1.6 (2.1 x x $ 0.05) 1/2 

4 2 2 10 cm /m 

2 291 pCi Rn.-222/m s 

The ore pad would have the €ollowitlg calculated radon-222 

emissions: 
2 Or if a speci.fie flux of 1. pb:i Rn~ 222/rr! i; per pili. Ela-226 j.8 

assumed, the estimated ea~rlssioxis are: 

The tlrronghyut is relatively large (sever:al thousand tons 

per day): tilerefore. the residence time of ore in the RliP.1 is 

Less than one day. This short residence time. means that little 

new radon- 222 is fourmeal in the millii~y operation. Hence, the ore 

does not refease large quantities of radoil-222 in the lnill 

circuit unless tlie radoil--222 that previously emanated from the 

ore was not released completely dirrir~g storage. handlirlg, and 

crusb.lng and grinding. 

Most milling emissions of radon222 occur during the 

transferrit1q and d~lmping of the o?:e into tire inill feed area 

because the ore has usually been reduced to sizes of less than 40 

cm, which allow trapped cadoai- 222 to escape. Emissions from 

dumping, ecnshirrg, and grinding can be estimated by assuming LO 

percent of the radon is released, as shown here: 

i klterrratiare1.y. an average emissiui~ factor t3f 3.8 x 10 pciilb 

TJ308 may be used to estimate RII-222 emissions frunl mi.l.liilg 

1800 tiday x 310 daysjy x 2200 Lb/t X 0.001 ib 

'7 U 0 lib ore x 3.8 x 10 pCi/Lb U,O x 3 8 , D 

- 1.2 CiipCi = 47 Ci/g 

Radon-222 emission:: from the leaching and extraetioil 

processes of the mill circuit are very low because these are Wet 

processes artd most of the radon222 in the ore was already 

!:eleased during storage and handling prior to milling. Emissions 

from packagitrq the yt?'LIowca&e product are also 1.o~. as very 

little (less than 0.1. peccent) of the radium-226 that pa:oduces 

the radon-222 remains in the yellowcake. 
3.4.3 emissions Prom Tahlitlgs Disp.~._l, 

The large area occupied by tailings impound~rrentu aE1d th.e 

extent of the exposed surface area make these impoutldments the 

major potential source of radon-222. Taili.ngs include the barren 

crushed ore material plus process solutions. These tailings 

consist of mixtures of sand and slimes (coarse and fine 

tailings). Evaporatioll ponds used to contain excess liquid from 

tailings impoundments also coiltain suspended and dissolved 

tailings and are included in this analysis. The size of these 

ponds was documented in a recent report (EPR85). Tailings solids 

are assumed to be carried with the process liquids and deposited 

oil the bottoms of these ponds. If exposed. these solids are 

assumed to emit radon-222 at the same specific flux as tailings 

impoundments. 

The procedure for estimating cadon-222 emissions will depend 

on the amount of site-specific information available. If 

site-specific information on the radium-226 conceIItrati0n. 

moisture content. porosity, density. and emanating power are 

known, the di-ffusion equation to estimate radon-222 flux may be 

used. Where specific iftformation is not available. a simplified 

relationship of 1 pci ~n-222fm s per pci ~a-226/g of tailings may 

be used to estimate emissions from dry areas of tailings 

impoundments (wet and ponded areas are not assumed to emit 

radon-222). Rn example of the calculatiot~ used to estimate 

radon-222 emissions from tailings by both calculation procedures 

is presented here for a 50-ha (120-acre) impoundment. Of the 

total area. 50 percent consists of saturated or liquid-covered 

tailings and 50 percent is dry. The tailings solids i.n the 

impoundment are 10 m (30 ft) deep. 

Emission estimates made by usinq diffusioq Equation 3-2 

L/Z Radon-222 flux J = IO'R~E (hD) 

R = 281 pCi Ra-226/g of tailings 

E = 0.2 (based on measurement: varies from -0.1 to 

-0.4) 

p = density = 1.6 gm/cm 3 

- 6 h = z.rxro /S 

D = diffusion coefficient for tailings 

2 5 = 0,07 exp (4mp - 4m - 4m ) 

where m is the moisture saturatio~l fraction (-0.35), p is the 

3 porosity (1-p/g), and g is the specific gravi.ty (-2.7 g/cm j. 
D = 0.07 exp f4 x 0.35 x (0.407)~ - 4 x 

5 0.35 - 4 x (0.35) 1 

2 = 0.0~13 cm /s - 6 

J = 281 X 0.2 X 1.5 (2.1 X 10 X 

422 0.0213) x 10 em /m 

2 = 190 pCi/m s 

Total. annual emissions are determined by multiplying J by the dry 

area and seconds per year. 

Emissions estimate based on specific flux of 

2 1 pCi ~n-222/m s per pCi Ra-Z26/g 

The simplified calculation based on a specific flux of 1 pCi 

Rn-222/m s per pCi Ra-226/g yields a similar but higher emission 

estimate in this example case. 

In almost all cases, the tailings impoundlnents are by far 

the largest source of radon-222 emissions. For mills on standby, 

the tailings impoul~dmei>ts account for practically all the 

radon-222 emissions. The tailings impoundment. which is the most 

significant source of radon-222 emissions from the mill site, 

accounts for about 80 percent of the total radon-222 emissions at 

an active licensed mill and practically 100 percent at an 

inactive or standby licensed mill. 

3.5 Transport and Risk Assessment 

Two separate steps are required to estimate the health 

impact of a specific source of radon-222: (I) determining itsdispersi.on and est imating, at various locations. its 

concentration and the corresponding exposure to its decay 

products in units of WLW and (2) calculating the risk. 
3.5.1 Air Dispersion Estimates 

EPA uses the AZRDOS-EPA code (Mo79, BaBl) to analyze the 

transport of radionuclide emissions into air from a specific 

source. This analysis estimates radionuclide concentrations in 

air at various distances from the source. 

The AIRDOS-EPA code uses a modified Gaussian plume equation 

to estimate airborne dispersion. Calculations are site-specific 

and require the joint frequency distribution of wind direction, 

windspeed, and atmospheric stability. The accuracy of these 

projections decreases with distance; therefore, calculations with 

this method are limited to regional areas (e.g., less than 80 km 

from the source). The values calculated represent annual 

averages because diurnal or seasonal variations are included in 

the joint frequency distribution. Calculations of working-level 

exposures for the inhalation of radon-222 progeny are then made 

based on estimates of radon-222 concentrations in air. 

Radon-222 emitted from tailings impoundments can be 

transported beyond the 80-km regional area. Results from a 

trajectory dispersion model developed by the National Oceanic and 

Atmospheric Administration (Tr79) were used to estimate the 

national impact of radon-222 emissions. The model yields 

radon-222 concentrations in the air (in picocuries/ liter), which 

are converted to decay product concentrations and expressed in 

terms of working levels. 

3.5.2 Risk Estimates 

After the exposure to radon-222 decay products has been 

estimated in terms of working level months for a specific source 

by means of the environmental transport code, the risk of fatal 

lung cancer is calculated using the risk factors discussed in 

Chapter 2. The risk is scaled up to the total population risk by 

multiplying by the population exposed to that working level over 

a lifetime. 

3.6 Measurement of Radon-222 

Although all radon-222 emission levels in this report 

represent calcuLated estimates, it is possible to make direct 

measurements on specific sources. Radon-222 measurement 

methodologies are discussed in the following subsections. 

Ambient samplers are generally used to measure radon-222 

emissions; however, some concentrating samplers are also used. 

The latter operate in a grab or continuous mode and sample 

radon-222'as it emanates from a source. Ambient gas samplers 

measure the accumulation of radon-222 present in the ambient air 

and typically have short sample collection periods (i.e., 

minutes). Concentrating samplers use a medium such as activated 

charcoal to adsorb radon-222. Sample collection periods for 

concentrating samplers are typically 24 to 72 hours. 
The most common type of ambient air sampler for the 

collection of radon-222 grab samples is the accumulator can. 

Accumulator can design and construction vary widely; however, all 

accumulator cans are constructed with an open-ended container 

fitted with a sampling port for periodic withdrawal of radon-222 

air samples. During collection of a radon-222 sample, the open 

end of the container is sealed to the sample medium (e.g., 

tail-ings) by simple insertion, caulking, or the use of permanent 

fixtures. After an adequate length of time (on the order of 

minutes) has been allowed for the radon-222 to accumulate in the 

container, a fixed air volume is withdrawn from the container 

through the sampling port and the alpha activity is counted. 

Another type of ambient sampler, which operates continuously 

rather than collecting grab samples, uses the same sampling 

procedure as the accumulator can except air is pumped through the 

can at a rate equivalent to one air volume per sampling period. 

The air is pumped through a filtered inlet to a calibrated 

scintillation cell and alpha activity is counted continuously. 

3.6.2 Concentratinq Samplers That Measure Radon-222 Emanation 

From Surfaces 

There are two types of concentrating samplers equipped with 

activated charcoal to adsorb radon-222. These include the 

passive charcoal canister samplers and the active, 

circulating-air test sampler. The charcoal canisters, which are 

available in a variety of sizes, are placed directly on the soil 

or tailings surface, exposed for 24 to 72 hours, and use 

activated charcoal as the concentrating medium. Their physical 

dimensions and the quantity of charcoal used to collect a 

radon-222 sample vary widely (Ni84). 

Selection of a specific charcoal sampler depends on the 

particu3ar application. Large-area samplers (e.g., greater than 

1000 em ) improve the representativeness of the sample by 

sampling a larger area, but small samplers are more economical 

and logistically simpler. 

The circulating-pir test samgler covers a much larger area 

than the canisters (i.e., 9290 cm (Ni84). It is a continuous, 

active sampler in which air is circulated across the soil or 

tailings surface enclosed by the sampler, and continues through a 

sectian of corrugated tubing containing the activated charcoal. 

The tubing is sectioned into two halves, which, allows for the 

detection of any carryover. The sampler is typically operated 

for 24 hours at a flow rate of about 2 liters per minute. The 

circulating-air test sampler is a cumbersome technique and is 

less effective than charcoal canisters considering cost and labor 

(Y083). 
Activated charcoal used for the collection of radon-222 is 

sealed in an air-tight container and set aside for a few hours to 

allow the short-lived redon daughters to come to equilibrium 

(Yo83). The amount of radon adsorbed by the activated charcoal 

(no matter which concentrating sampler is used) is quantified by 

gamma-ray spectroscopy of the charcoal using a NaI(T1) crystal or 

germanium diode and multichannel analyzer. Typically the 

Bismuth-214 609-keV peak is used to determine radon-222 activity, 

but other Bismuth-214 or Lead-214 peaks could by used. 
REFERENCES 

Ba8l Baes C. F. IT1 and Sharp R. D., "A Directory of 

Parameters Used in a Series of Assessment Applications 

of the AIRDOS-EPA and DARTAB Computer Codesw, 

ORNL-5720, Oak Ridge National Laboratory, Oak Ridge, 

Tennessee, March 1981. 

EPA7 9 U.S. Environmental Protection Agency, "Indoor Radiation 

Exposure Due to Radium-226 in Florida Phosphate Landsv, 

EPA 520/4-78-013, Office of Radiation Programs, U.S. 

EPA, Washington, D.C., July 1979. 

EPA8 3 U.S. Environmental Protection Agency, "Final 

Environmental Impact Statement for Standards for the 

Control of Byproduct Material From Uranium Ore 

Processingv, EPA 520/1-83-008-1, Office of Radiation 

Programs, U.S. EPA, Washington, D.C., September 1983. 

EPA85 U.S. Environmental Protection Agency, "Draft 

Document-Estimates of Population Distributions and 

Tailings Areas Around Licensed Uranium Mill Sites", 

Office of Radiation Programs, U.S. EPA, Washington, 

D.C., November 1985. 

Freeman H. D., and Hartley J. N., "Predicting Radon 

Flux From Uranium Mill Tailings", in: Sixth Symposium 

on Uranium Mill Tailings Management, Fort Collins, 

Colorado, February 1-3, 1984. 

Hartley J. N., Glissmeyer J. A., and Mill 0. F., 

"Methods for Estimating Radioactive and Toxic Airborne 

Source Terms for Uranium Milling Operations", PNL for 

U.S. Nuclear Regulatory Commission, Washington, D.C., 

NUREG/CR-4088 June 1985. 

Me7 1 Merritt, R. C., "The Extractive Metallurgy of Uraniumu, 

prepared under contract with the United States Atomic 

Energy Commission, 1971. 

M07 9 Moore R. E., Baes C. P. 1x1, McDowell-Boyer L. M., 

Watson A. P., Hoffman F. O., Pleasant J. C,, and Miller 

C. W., "AIRDOS-EPA: A Computerized Methodology for 

Estimating Environmental Concentrations and Dose to Man 

From Airborne Releases of Radionuciidesu, EPA 

520/1-79-009, Office of Radiation Programs, U.S. EPA, 

Washington, D.C., December 1979. 
Nielson K. X,, et al,, "Radon Emanation Characteristics 

of Uranium Mill Tailings", in: Symposium on Uranium 

Mill Tailings Management, Fort Collins, Colorado, 

December 9-10, 1982, 

Neilson K. K. and Rogers V. C., "Radon Flux Measurement 

Methodologies, Management of Uranium Mill Tailings, 

Low-Level Waste and Hazardous Waste", in: Proceedings 

of the Sixth Symposium, Colorado State University, Fort 

Collins, Colorado, February 1-3, 1984. 

Nuclear Regulatory Commission, '"Final Generic 

Environmental Impact Statement on Uranium Milling", 

NUREG-0706, September 1980. 

Nuclear Regulatory Commission, "MILDOS - A Computer 

Program for Calculating Environmental Radiation Doses 

From Uranium Recovery Operations", NUREG/CR-2011, 

PNL-3767, prepared by Pacific Northwest Laboratory, 

Battelle Memorial Institute for the U.S. Nuclear 

Regulatory Commission, April 1981. 

PEI Associates, Inc., **Radon-222 Emissions and Control 

Practices for Licensed Uranium Mills and Their 

Associated Tailings Piles", prepared for U.S. 

Environmental Protection Agency, Office of Radiation 

Programs, June 1985 (revised November 1985). 

Thomas V. W., Nielson K. K., and Mauch M. L., "Radon 

and Aerosol Release From Open Pit Uranium Mining", 

NUREG/CR-2407, Nuclear Regulatory Commission, 1982. 

Travis C. C., Watson A, P., McDowell-Boyer L. M., 

Cotter S. J., Randolph M, L., and Fiedls D. E., A 

"Radiological Assessment of Radon-222 Released From 

Uranium Mills and Other Natural and Technologically 

Enhanced Sourcesu, ORNL/NUREG-55, Oak Ridge National 

Laboratory, Oak Ridge, Tennessee, 1979. 

Young J. A., et al. "Recommended Procedures for 

Measuring Radon Fluxes From Disposal Sites of Residual 

Radioa.ctive Materials"', NUREG/CR-3166, PNL-4597, March 

1983. 

Chapter 4 : INDUSTRY DESCRIPTION 

4.1 Overview 

In January 1986, the conventional uranium milling industry 

in the United States consisted of 26 licensed facilities. Three 

additional mills have been licensed, but either have never been 

constructed or have never operated. Only 4 of the 26 licensed 

facilities were operating; 16 were on standby status, and 6 were 

being or have been decommissioned. The mills on standby status 

are being maintained, but they are not processing uranium ore. 

When the demand for uranium increases, these standby mills could 

resume milling. The decommissioned mills have been dismantled 

and have been removed off site or disposed of on site; therefore, 

these mills will never resume operations. Their associated 

tailings impoundments are either being reclaimed or there are 

plans to reclaim them. The current operational status and 

capacity of each licensed conventional mill are shown in Table 

4-1. 

The Secretary of Energy has determined that the domestic 

uranium mining and milling industries were not viable in 1984 

(ELP85). In 1984, the annual domestic uranium production was the 

lowest since the mid-l95O1s, and employment was down 75 percent 

from 1981 to 1984 (ELP85). 

4.2 Site-Specific Characteristics 

The licensed conventional uranium mills are in Colorado, New 

Mexico, South Dakota, Texas, Utah, Washington, and Wyoming. 

Their approximate locations are shown in Figure 4-1. Brief, 

site-specific summaries of all the active or standby conventional 

uranium mills were prepared as part of this document and are 

presented in this section. As described in Chapter 3, the 

tailings disposal operations represent the largest source of 

radon-222 emissions; therefore, the summaries focus largely on 

these operations. 

The site summaries were compiled from data contained in 

other EPA, NRC, and DOE documents. A recent EPA report (EPA85) 

entitled "Estimates of Population Distributions and Tailings 

Areas Around Licensed Uranium Mill Sites" was the source of the 

measurements of the surface areas of impoundments. The 

populations in the 0- to 5-km range around the tailings 

impoundments were taken from a 1984 survey that Battelle 
Table 4-1- ting status and capacity of li ed wnventional =@? uranim mills as of August 4, 1986 

State Mill Owner 

(-@=at* Op"tw capacity 

status (tons/day) (') 

Colorado Canon City 

Uravan 

New Mexico L-Bar 

Churcbrock 

Bluewater 

Quivira 

Gmts 

Soutb Dakota Edgemnt 

Texas 

Utah 

Panna Maria 

Conquista 

Fay mint 

White Mesa 

La Sal 

Moab 

Shootaring Canyon 

Ford 

Shemod 

cotter Corp. 

Umetco Minerals 

Sohio/Kennecott 

United Nuclear 

Anaconda 

K€XT-Md;ee 

Hmestzke 

Chevron 

Conoco/Pioneer 

Won 

Umetca Minemls 

Rio hlgm 

Atlas 

Plateau Resources 

Dawn Mining 

Westem Nuclear 

standby 

s-Y 

Decormnissioning (dl 

~ssioning (d) 

~ssion~ (dl 

Active s-4re) 

Active 

kdssioned 

Dedssioned 

Active (f) 

Active (g) 

s-Y 

s-Y 


Menlorial Institute conducted for :he EPA (PNL,84) . In addition, 

color aerial photographs of each active and standby mill site 

were provided by the office of Rad-iation Programs to augment t'ne 

available data base (EPA85)- 

A sunliatary of current cai?ditions and the extent of 'tailings 

impoundments and evaporation ponds at these sites is presented in 

Table 4-2, Diagrams of each mill site are included in 

Appendix A. Additional details regarding these mills and the 

impoundments are provided in the following text under the 

appropriate state, 

4.2.1 Colorado 

The two Licensed uranium mills located in Colorado are 

operated by Cotter Corpora.tien and Umetco Minerals (Union 

Carbide) in Canon City and Uravan (see Figure 4-2)- A third 

mill, Pioneer Nuclearis proposed San Miguel mill in San Miguel 

County, was licensed but never constructed. The license for this 

mill is under litigation (NRC84). 

The Cotter Corporation, a subsidi.ary of Comvlonwealth Edison, 

operates a two-stage acid leach mill at Canon City, Colorado, 

which recovers uranium and vanadium. A small alkaline leach mill 

also was operated on this site from 1968 until its 

decommissioning in 1979. The existing mill, which began 

operations in September 1979, has a capacity of 1.200 tons of ore 

per day. The ore grade ranges between 0,23 and 0.35 percent 

U308 (NRC84). The mi~i has been, on stand.by status since 

February 1985. 

Tailings generated since September 1979 have been placed in 

an above-grade clay- and membrane-lined impou.ndment that covers 

34 ha (84 acresj and has earthen embankments (EPA85). Plans call 

for the dam to be raised to its ultimate height of 35 m 

(I15 feet) in one additional stage, The tailings solution 

currently covers 31 ha (77 acres) and varies in depth from less 

than 0.3 to more than 6 in (<I. to >%0 fee.tj (EPA85, Mc85). 

Currently, the area of exposed tailings beach covers 3 ha 

(7 acres), of which I.. 8 ?].a (4.5 acres) is dry (EPA85). The 

tailings disct~arge into the pond is moved al.ong the perimeter 

during operations to keep the tailings wet and even18 

distributed. This impoundment now con-ains 0,9 x 10 tons of 

tailings and has a capacity of 14 x IOk ions (NRC84). The 

tailings are reported, to contain 780 pCi/y of radium-226 

(EPA83aj. 
Table 4-2. Summary oE current uranium mill tailings impoundment areas 

and radium-226 content 

f C) Average 

Type of Surface area(acres) ~a-226(~) 

Owner/Impoundment impoundment (a) status (b) Total Ponded Wet Dry pCi/g) 

Colorado 

Cotter Corp. 

Primary 

Secondary 

Umetco 

Ijravan 1 & 2 

Uravan 3 

Sludge pile 

Evap. pond 

0 

I 

m New Mexico 

Sohio 

United Nuclear 

Churchrock 

Anaconda 

Bluewater 1 

Bluewater 2 

Bluewater 3 

Evap. ponds 

Kerr-McGee 

Quivira 1 

Quivira 2a 

Quivira 2b 

Quivira 2c 

Evap. ponds 
Table 4-2. Summary of current uranium mill tailings impoundment areas 

and radium-226 content (continued) 

(c) Average 

Type of Surface area(acres1 ~a-226(~) 

Owner/Impoundment impoundment (a) status (b) Total Ponded Wet Dry pCi/p) 

Homestake 

Homestake 1 

Homestake 2 

Texas 

Chevron 

Panna Maria 

- Utah 

f Umetco I 

q White Mesa 1 

White Mesa 2 

White Mesa 3 

Rio Algom 

Rio Algom 1 

Rio Algom 2 

Atlas 

Moab 

Plateau Resources 

Shootaring 

Washington 

Dawn Mining 

Ford 1-2 $3 

Ford 4 
0 0 0000 0 0000 0 0 0 0 NNNN m iiid N -3 N N -3 4 -s -3 .-f mmmm .;r V1. 

P.2 rl 4 in in ti 1 1 NNNN N NLNN N N 

N -2 M 

VI 

w 5 VI ic 3 .. 0 i~ aa .i .. ZhS. u a mmm m mlm* 0044w 

0 
Table 4-2. Summary of current uranium mill tailings impoundment areas 

and radium-226 content (continued) 

(c) Average 

Type of Surface area(acres) ~a-226(~) 

Owner/Impoundment impoundment (a) status (b) Total Ponded Wet Dry pCi/g) 

Minerals Exploration 

Sweetwater 2/SL 

Totals 3882 1282 457 2140 - 

(a) Type of impoundment; 1 = dam constructed of coarse tailings; 2 = earthen dam; 3 = below grade; 

SL = synthetic liner; CL = clay liner, 

" I (b) Status of impoundment; A = active; S = standby (will be used when operations resume); C = filled to LD capacity (will not be used again). 

(c) Source: EPA85 

(d) Source: EPA83 

(ef Source: EPA86 
@ Cotter Corp. 

Canon City Mill 

@ Urnetco Minerals 

Uravan Mill 

Figure 4-2. Location of mills in Colorado 
A, Lg-ha (3:L-acre) secoildary impo-undment contain-i.ng 

1.5 x 10 tons commingled tailings (defense-related tailings 

generated under Atomic Energy Commission contracts commingled 

with tailings generated under commercial contracts) generated in 

pre-1979 operations has been constructed adjacent to the main 

impoundment. Approximately 0.4 ha (1 acre) is covered with 

ponded solution, 0,4 ha (1 acre) consists of exposed saturated 

tailings, and about 12 ha (30 acres) are dry (EPA85). These 

impoundments are actually two cells of one large impoundment. 

The secondary impoundment also is used for disposal of 

nontailings solid waste generated on site and will be used for 

disposal of decommissioning waste during closure operations 

(DOE82). The old tailings have not been covered, but they have 

been furrowed to control dusting. The costs for constructing the 

main and secondary impoundments were $15,800,000 and $7,200,000, 

respectively (DOE82). 

Canon City is located about 3.2 km (2 mi) north of the mill 

site. The area immediately surrounding the mill site is 

unpopulated, and the land is used primarily for livestock grazing 

(DOE82). The nearest residents are 184 people who live between 

2 and 3 km (1.2 and 1.9 mi) from the impoundment (PNL84) . A 1983 

survey indicated 5933 people lived within 5 km (3.1 mi) of the 

tailings impoundment (PNL84). 

The climate in the area is semiarid and temperate; average 

annual precipitation is 30 cm (12 in.) (DOE82). Windspeeds are 

variable, with a mean of 13 km/h (8 mi/h) (DOE82). 

Uravan Mill 

Umetco Mineral" uranium mill in Uravan, Colorado, an area 

of rugged canyons and mesas, is 80 km (50 mi) south of Grand 

Junction. Uranium, vanadium, and radium-226 recovery operations 

were begun at this site in 2.915. The mill has been on standby 

status since November 1984 and will likely be on standby for at 

least 2 years and possibly permanently (Kr85). The existing 

tailings disposal facilities have reached their maximum capacity, 

and a new disposal area must be planned and approved before mill 

operations are restarted (Kr85). The capacity of this mill is 

1300 tons of ore per day. 

The mill uses a hot, highly oxidizing, two-stage acid leach 

to recover uranium and vanadium. During milling operations, ore 

has been received from more than 200 mines in the Uravan mineral 

belt. Tailings have been generated under AEC, Army, and 

commercial contracts and have been commingled and digposed of on 

site. The impoundments contain an estimated 10 x 10 tons of 

tailings. These tailings impoundments are situated on mesas 
above Urnvan. Impoilndments 1 and 2 are adjacent and overlapping 

and actua-lly constitute just one impound.ment. The impoundments 

are constructed behind dikes of coarse tailings on the outward 

face and contained by the native terrain on the inward side. 

Tailings were discharged to the impoundments from spigots 

situated around. the berm. Gravity settling deposited the sands 

near the dike, and slimes were carried to the interior with the 

tailings solution. 

Impoundments 1 and 2 cover a combined area of 27 ha 

(66 acres) and have a maximum dam height of 46 m (155 ft) (EPA85, 

DOE82). Impoundment 3 covers 13 ha (32 acres), and the dike is 

about 33 m (110 ft) high. Eight other impoundments, which either 

contain tailings or have been constructed of tailings, were 

mainly used for evaporation. These eight impoundments cover 

15 ha (37 acres). The radium-226 content of the Uravan tailings 

has been reported to be 480 pCi/gram (EPA83b). 

The Uravan operation uses several other ponds in its water 

management system. Six solvent extraction (SX) raffinate 

evaporation/seepage ponds receive barren solution from the 

vanadium SX section. Residue in these ponds will be placed in 

the tailings ponds at closure. The SX ponds cover 15 ha 

(36 acres) (NRC84) . 

The general area is sparsely populated. A recent survey 

indicates 349 people living from 2 to 5 km (1.2 to 3.0 mi) away 

from the main tailings impoundments. The survey showed nobody 

living within 0-5 km (0.3 mi) of these impoundments, but 

147 people lived 0-5 to 1.0 km (0.3 to 0.6 mi) distant (PNL84). 

The climate at Uravan is semiarid, with only about 25 cm 

(LO inches) of precipitation a year. Evaporation is about 142 om 

(56 inches) per year (EFA83b). 

The five licensed mills located in New Mexico are operated 

by Sohio/Kennecott Minerals, United Nuclear Corporation, Anaconda 

(Atlantic Richfield), Kerr-McGee Corp. (Quivira Mining), and 

Homestake Mining Co. (see Figure 4-3). Two additional mills, 

Bokum Resources Corporation and Gulf Minerals, were licensed but 

have never operated, 
The Sohio/Kennecott L-Bar Uranium Mill is located near 

Seboyeta in Cibola county, in an area of hilly terrain about 

71 km (44 mi) west of Albuquerque and 16 km (10 mi) north of 

Laguna, New Mexico. Ore is obtained from an underground mine in 

the Jackpile sandstone formation. The acid-leach mill began 

operations in 1976, but has been on standby status since May 1981 

(NRC84). The ore processing capacity of the mill is 1650 tons 

per day. Ore reserves are adequate to provide for 10 to 15 years 

of operation. The ore grade varies from 0.05 to 0.30 percent 

U O8 and averages 0.225 percent (NRC84). Size reduction is 

aacomplished by semiautogenous grinding. 

Mill tailings are contained in a single tailings 

impoundment. The L-Bar tailings dam was one of the last dams 

permitted in the industry in which the upstream construction 

method was used (Jo80). The tailings impoundment is built above 

grade with an earthen starter dam to the west that keys into 

natural topography on the north and south. A smaller saddle dam 

is constructed to the east. Tailings have been discharged to the 

impoundment from a single pipe that was moved along the dam. 

Coarse sands settled near the dike, whereas slimes deposited in 

the interior area. Water was decanted and pumped back to the 

mill. During operations, the ed.ge of the tailings solution was 

maintained about 60 m (200 ft) from the dam crest. A light-track 

pressure dozer was used to construct raises with the sand 

tailings. The total impoundment area covers 72 ha (180 acres), 

about 51.2 ha (128 acres) of which are covered with tailings 

(NRC84). Approximately 11.2 ha (28 acres) of the tailings are 

covered with tail'n s solution (EPA85). The impoundment consists kg of about 1.6 x 10 tons of tailings. The maximum height of the 

dam is 15 m (50 ft) (NRC80). The facility was dgsigned to 

provide an ultimate storage capacity of 7.5 x LO tons of 

tailings (Jo80). The tailings are reported to contain 500 pCi/g 

of radium-226 (EPA83b). 

Durinq operations, ore is stockpiled at the mill on an ore 

pad and apron feeder. Since the plane went on standby status in 

1981, no ore has been stored on these areas, but a short supply 

has been stored north of the tailings area (NM85). 

The surrounding area is sparsely populated. A 1983 survey 

indicated no population residing within a 3-km (1.9-mi) radius of 

the tailings impoundment (PNL84). Reportedly 42 people live 

between 3 and 4 km (1.8 and 2.5 mi) away and 129 live between 

4 and 5 km (2 -5 and 3.1 mi) (PNL84). 
@) Sohio 

L-Bar Mill 

@ United Nuclear Corp. 

Churchrock Mill 

@ Anaconda Minerals Co. 

Bluewater Mill 

@ Kerr-McGee Nuclear Corp. 

Quivara Mill 

@ Homestake Mining Co 

Homestake Mill 

Figure 4-3. Location of mills in New Mexico. 
United Nuclear Corporation's Churchrock Mill is located 

32 km (20 mi) northeast of Gallup, New Mexico, on an 

alluvial plain situated near an arroyo. The mill, which 

opened in 1977, is designed to use acid-leach extraction to 

process about 4000 tons of ore per day from the 

company-owned underground mines. The ore contains 0.035 to 

0.381 percent U308 (average is 0.12 percent) in a 

sandstone matrix. Fresh water for mill operations is 

obtained from underground mines. The mill has been on 

standby status since 1982. 

The tailings impoundment is formed by a dam built from 

native clays and compacted coarse tailings. It has three 

compartments separated by earthen embankments. The total 

surface area of tailings is 59 ha (148 acres) (EPA85). The 

surface area of liquid on the tailings impoundment is 3 ha 

(7 acres). The maximum depth of tailings is about 15 m 

(50 ft)6 The storage capacity of the pond is about 

10 x 10 m (365 x 10 ft ) (NRC84). The tailings are 

reported to contain 290 pCi/g of radium-226 (EPA83b). 

The area around the mill is sparsely populated. The 

1983 population survey indicated 25 people residing within 

2 km (1.25 mi) and 77 living within 3 km (1.9 mi) (PNL84). 

The survey also indicated a total of 213 ~eo~le livina 

within 5 km (3.1 mi) of the mill, but none w2thin 1 k& 

(0.6 mi) (PNL84) . 

in July 1979, a break in the tailings dam caused about 

350 x 106 liters (93 x 106 gal) of effluent and 1100 tons of 

tailings to spill on or into nearby soil and streams 

(NRC84). This spill resulted in the release of almost all 

of the impounded liquid, but less than 1 percent of the 

solids. The streams carried the spilled tailings into the 

Rio Puerco River, which flows through Navajo grazing lands, 

and finally into Arizona. The mill was closed from July 

1979 until the fall of 1979 while measures were taken to 

clean up the streams contaminated by the spill. The cleanup 

of the streams has been completed. The mill has been 

inactive since 1982, and corrective action to clean up the 

contaminated groundwater is continuing (NRC84). 
Bluewater Nil1 

Anaconda" Bluewater Uranium Mill is located in the 

Grants Mineral Belt about 16 km (10 mi) northwest of Grants, 

New Mexico. The site is in a small valley characterized by 

an undulating, relatively level surface with gentle swales 

and small rounded hills (DOE82). The mill was originally 

constructed in 1953 and operated until 1982, when it went to 

standby status. Since 1953, the milling operations have 

gone through several major modifications. Capacity has been 

expanded to 6000 tons of ore (0.2 percent U 0 ) 

(NRC84). Production has been under both AE?! 81956 to 1970) 

and commercial contracts. Througg 1981, the Bluewater mill 

had processed more than 23.5 x 10 tons of ore ranging 

from 0.06 to 0.60 percent U O8 (DOE82). Some 

decommissioning activities 2ave been initiated at this 

mill. 

The mill site has three tailings impoundments. 

Carbonate tailings from early operations were deposited in 

an area immediately northwest of the mill in a flat-lying 

impoundment (No. 2) covering about 19 ha (47 acres) 

(DOE82). This inactive impoundment has been covered with 

native soil to an average depth of 0.8 m (2.5 ft) (DOE82). 

Other tailings from the early carbonate processing were 

emplaced in what is now the main tailings impoundment far 

acid tailings (No. I). A third tailings impoundment, the 

north area acid pile, is situated immediately northwest of 

the main pond. it covers 10 ha (24 acres), and in 1977 was 

covered with about 0.8 m (2.5 ft) of native soil (DOE82). 

The main impoundment (No. 1), which was put in 

operation in 1956, covers 96 ha (239 acres) (EPA85). It is 

currently dry. The dam surrounding the pond is constructed 

of compacted natural soils and alluvium and is about 18 m 

(60 ft) high at the south end and 6 m (20 ft) high at the 

north end (DOE82). Tailings are discharged along the 

southerg part of the dam. This impoundment contains 

25 x 10 tons of tailings (NRC84). 

There are also 162 acres of evaporation ponds in the 

mill water management circuit. Currently, 97 acres are 

covered with solution, 17 acres are exposed and wet, and 

48 acres are exposed and dry jEPA85). Some tailings solids 

are carried with the water to these evaporation ponds where 

they remain after the solution evaporates, 
The specific activity of radium-226 in the old taiiings has 

been reported to be 520 pCi/gram and 280 pCi/gram in the taiiings 

in the main pond (NM85): however, it has also been estimated to 

average 620 pCi/g (EPA83a). 

The area around the Bluewater Mill 's sparsely populated. A 

1983 survey indicated 907 people living within 5 km (3.1 mi) of 

the mill (PNL84). Of this total, 142 lived within 3 km 

(1.9 mi.). No one lives within 2 km (1.2 mi.) of the mill 

(PNL84) . 

Annual precipitation averages 22 cm (8.8 inches)--most as 

rain, but some as snow. Wind is channeled through the valley in 

a westerly direction. The site is in the !!southwest mountains" 

climatological subdivision of New Mexico. 

Quivira Mill 

Kerr McGeels Quivira mill has been on standby status since 

February 1985. The largest acid leach mill in the United States, 

its current capacity is 6350 t (7000 tons) of ore per day 

(NCR84). The Quivira mill is in a flat area of the Grants 

Mineral Belt about 40 km (25 mi) north of Grants, New Mexico. 

The mill began operation in 1958 with a capacity of 3270 t of 

(3600 tons) sandstone ore per day. 

All of the tailings from the mill are contained in two main 

impoundments, (Tailings impoundments Nos. 1 and 2a) and two 

ancillary impoundments (2b and 2c), Impoundment No. 1 was the 

most recently active area for tailings deposition. It extends 

southeasterly from the mill for about 1370 m (4500 ft); its 

greatest width is about 820 m (2700 ft), and the outside berm 

ranges from 8 to 27 m (25 to 90 ft) above ground level (COE82). 

An earthen starter dike was used al.ong with the ~rpstrearr: me.thod 

of tailings disposal. 'Tailings were discharged to the pond from 

multiple spigots located along the crest at 9-rn (30-ft) 

intervals. The bulk of the sands is deposited on a beach inside 

the berm, and the slimes and liquid flow into the central 

depression to form a lake (DOE82). The operator maintains a 

150-m (500-ft) wide beach and a 1.5 m (5 ft) freeboard during 

operation. Impoundment No. L covers 108 ha (269 acres) and 

contains a liquid covered area of about 6 ha (14 acres) (EPA85). 

Approximately 76 ha (191 acres) are dry and the remaining 26 ha 

(64 acres) remain saturated (EPA85). 

Tailings Impoundment No. 2a covers about 42 ha (105 acres) 

and is west of and contiguous with Pond No. 1 (EPA85). 

Impoundments Nos. l and 2a have been in use si&ce 2.958. These 

two impoundments contain approximately 26 x 10 tons of 

tailings. Some tailings are used as backfill in a nearby 

underground mine. Tailings set aside for use as backfill 
are contained in Impoundment No. 2b, Heap leached tail-ings are 

contained in impoundment No. 2c. Impoundments 2b and 2c cover 

11 and 12 ha (28 and 30 acres), respectively. Although no water 

is currently ponded in either of these impoundments, l to 1-5 ha 

(3 or 4 acres) of each are saturated (EPA85). The tailings are 

reported to contain 620 pCi./g of radium-226 (EPA83bjThe Quivira mill uses 15 evaporation ponds in its water 

management system. These ponds currently cover a total. of 149 ha 

(372 acres) (EPA85). Of this total surface area, 107 ha 

(268 acres) are covered with solution, 4 ha (10 acres) are wet, 

and 38 ha (95 acres) are dry (EPA85). Some tailings soli.ds are 

carried with the liquid solution and are deposited in these 

evaporation ponds. 

The area surrounding the mill is sparsely populated. The 

1983 population survey indicated only one person living within 

5 km (3.1 mi) of the mill (PNL84), and that person lived between 

2 and 3 km (1.2 and 1.9 mi.) from the impoundment (PNL84). 

Precipitation averages 22 cm (8.8 in.) per year (DOE82). 

Local winds are channeled by the valley, and gusts can exceed 

80 km (50 mi) per hour. 

Homestake Mill 

Homestake Mining Company's mill is 16 km (10 mi) northwest 

of Grants, New Mexico. The mill began production in 1958. Since 

its beginning, its capacity has been increased from 675 t 

(742 tons) to its present 3200 t (3400 tons) of ore per day 

(DOE82). The Womestake Mill uses the alkaline leach process. 

The mill has been on standby status since mid-1985. The ore 

grade milled at Homestake has ranged from 0.05 to 0.30 percent 

U308 (NRC84). 

The mill site is relatively flat and covers about 600 ha 

(1500 acres). Two tailings impoundments, one on standby and the 

other inactive, are located on site. The inactive impoundment 

contains tailings generaged between 1258 and 1962 under AEC 

contracts. The 1.1 x 10 t (1.2 x 10 tons) of AEC tailings 

cover about 18 ha (44 acres) and are contained within an 8-m 

(25-ft) high earthen embankment (DOE82). There currently is 

1.6 ha (4 acres) of ponded water on the impoundment (GPA85). 

Approximately 20 percent, 3.2 ha (8 acres), of this tailings 

impoundment has been covered with a meter of contaminated soil 

excavated from an area affected by a past spill from the active 

impoundment (DOE82). Efforts have been made to revegetate the 

impoundment to reduce dusting. 
The active impoundment contains about 20 x lo6 tons of 

commingled tailings (DOE82). The impoundment is shaped like a 

large rectangular-base prism that rises above the flat ground 

surface (DOE82). It has a surface area of 82 ha (205 acres) 

(including the sides) and is about 26 m (85 ft) high. The slopes 

of the four sides are about 2:l (h:v). The top of the 

impoundment is divided into two cells which are used alternately 

for tailings discharge. Most of the interior of both cells is 

covered with tailings solution, The total surface area of the 

ponded fluid in these two cells is about 25 ha (63 acres) 

(EPA85). Homestake maintains a 15-m (50-ft) beach and 1.5-m 

(5-ft) freeboard. The embankments are constructed of coarse 

tailings (sands) built up by the centerline method of 

construction. A mobile cyclone is used to separate the sands and 

slimes. Decanted pond liquid is recycled back to the mill. 

Surface water sprays and chemical treatments are applied to the 

embankment faces to inhibit dusting. The tailings are reported 

to contain 385 pCi/g of radium-226 (EPA83b). 

Residential areas are located within 1.6 km (1 mi) of the 

mill. Homestake's 1982 license renewal application and the 1983 

survey both indicated no population within 1 km (0.6 mi). The 

1983 survey indicated that 190 people live between 1 and 2 km 

(0.6 to 1.2 mi.) from the impoundment (PNL84). The survey 

counted a population of 396 people within 5 km (3.1 mi.) of the 

mill (PNL84). Homestake has purchased additional land adjacent 

to the mill site to provide a 0.8-km (0.5-mi.) buffer zone 

(DOE82). 

The site" climate is characterized by low precipitation 

[22 cm (8.8 in.)/y average), sunny days (75 to 80 percent), low 

humidity, wind gusts to 80 kilometers per hour (50 mph), and 

moderate temperatures with large diurnal and annual fluctuations 

(DOE82)- 

The three licensed mills in Texas are owned by Chevron 

Resources, Conoco-Pioneer, and Exxon Minerals. Their locations 

are indicated in Figure 4-4. One additional mill, Anaconda 

Minerals Rhode Branch Mill, was licensed in 1982, but was never 

constructed. Only the Panna Maria Mill is described herein, as 

the others are being decommissioned. 

Panna Maria Mill 

The Panna Maria Uranium Project of Chevron Resources Company 

is located in South Texas about 160 km (100 mi) northwest of 

Corpus Christi and 10 km (6 mi) north of Karnes City. The mill 

processes about 2600 tons per day of a mixture of sandy clay ore 
averaging 0.05 percent U 0 (Ma85). This facility, which 

uses semi-autogeneous grln8ing followed by acid leaching, began 

operation in January 1979 and has been on standby status since 

June 1985 (Ma85). 

Tailings are contained in a single above-ground impoundment 

contained by earthen dikes. Material for the dikes was excavated 

from the area beneath the impoundment. The tailings area covers 

50 ha (124 acres); 14 ha (36 acres) consist of dry, exposed 

beach, and about 27 ha (68 acres) are covered with tailings 

solution6(EPA85). The impoundment contains approximately 

3.3 x 10 tons of tailings (NRC84). It was designed to contain 

all the tailings projected to be generated over the life of the 

mill. The maximum height of the earthen dam surrounding the pile 

is 19 m (62 ft), the crest width is 6 m (20 ft), and the 

downstream slope is 3:l (h:v) (Ki80). Designed maximum storage 

of tailings in this impoundment is 10 x lo3 tons) (Ki80)3 The 

average density of the tailings is 1.2 t/m (0.04 ton/ft ), 

and the specific gravity is 2.55 (Ki80). 

During operations, the tailings discharge to the impoundment 

is periodically moved around the perimeter of the impoundment. 

An exposed beach of coarse tailings forms along the dike and the 

tailings solution gathers in the center portion of the pond. The 

depth of the solution varies from an average of 1.5 m (5 ft) on 

the e3st side to 5 to 6 m (15 to 20 ft) on the west (Ma85). 

The radon-222 flux from the tailings has not been measured. 

The radium-226 content of the tailings is estimated to be 

196 pCi/g. 

The ore pad at this facility covers approximately 12 ha 

(30 acres). During normal operations, a 1-month supply of ore 

[69,000 t (76,000 tons) at capacity] is stockpiled on the pad. 

A 1983 survey of population in the area indicated 453 people 

living within 5 km (3.1 mi) of the tailings impoundment, 

12 people within 1 km (0.6 mi), 42 people within 1 and 2 km 

(0.6 and 1.25 mi), and 33 people within 2 and 3 km (1.25 and 1.9 

mi) (PNL84). 

The average annual rainfall at the location of the 

impoundment is 76 cm (30 in.), and the net annual evaporation is 

89 cm (35 in.). 
a Conoco/Pioneer Nuclear 

Conquista Project 

@ Chevron Resources Co. 

Panna Maria Mill 

@ Exxon Minerals 

Ray Point 

Figure 4-4. Location of mills in Texas. 
Tbe fou.r Licensed mills located in Utah (see Figure 4-5) are 

owned by Atlas Minerals, Plateau Resources, Ltd., Umetco 

Minerals, and. Rio Algom Corporation. 

--- Umetcq White Mesa Mill 

The Umetco Mi.nerals White Mesa mill, which is about 8 km 

(5 mi.) south of Blanding, Utah, began operating in July 1980. 

This mill is currently active. Semi-autogenous grinding, 

acid-leaching, and solvent-extraction are used to process ores 

containing about 0.13 percent U O8 (NRC84). The capacity of 

the mill is 1800 t (2000 tons) 8f ore per day (NRC84). 

Approximately 500,000 t (550,000 tons) of tailings are 

contained in three cells of a proposed six-cell disposal system. 

The cells contain 19, 24, and 21 ha (48, 61, and 53 acres) of 

tailings for a total of 64 ha (162 acres) (EPA85). A total of 

22 ha (56 acres) is covered by solution, 5 ha (13 acres) are 

saturated, and 42 ha (106 acres) are dry (EPA85). The proposed 

system was planned to feature simultaneous construction, 

operation, closure, and reclamation. The tailings impoundments 

are ilned vith synthetic liners. The tailings are reported to 

contain 350 pCi/g of radium-226 (EPA83b). 

A 1983 population survey indicated no people living within a 

4-krn (25-mi) radius of the tailings impoundment (PNL84). The 

same survey indicated eight people living between 4 and 5 km 

(2-5 and 3.1 mi) of the tailings disposal area (PNL84). 

Rio Alqom Mill 

The Rio Algom Mill is near La Sai, Utah, about 48 km (30 mi) 

southeast of Moab, This mill is currently active and has been in 

operation since 1971. Ore obtained from adjacent underground 

mining operations is processed by alkaline leaching and ion 

exchange, The mill's designed throughput is 700 t (750 tons) of 

ore per day. 

Over 1.6 x 106 t (1.8 x 106 tons) of tailings have been 

generated at this mill (NRC84). The tailings are contained in 

two unlined tailings impoundments retained by natural soil 

embankments placed across a drainage course, one immediately 

upstream of the other (NRC84). The lower impoundment has been in 

use since 1972, the upper since 1976. The total area of tailings 

is 30 ha (75 acres) (EPA85). Approximately 6 ha (16 acres) are 

covered with solution, 3 ha (7 acres) are saturated, and 21 ha 

(53 acres) are dry (EPA85). The tailings are reported to contain 

560 pCi/g of radium-226 (EPA83b) . 
@ Umetco Minerals 

White Mesa Mill 

@ Rio Algom Corp. 

La Sal Mill 

@ Atlas Minerals 

Moab Mill 

@ Plateau Resources, Ltd. 

Shootaring Canyon Mill 

Figure 4-5. Location of mills in Utah. 
A 1983 survey of the population in the area indicated no 

inhabitants living within 0-3 km (0,3 mi,) of the tailings 

impoundment (PNL8.1). Eight inhabitants were reported to live 

between 0.5 and 1.0 kn (0.3 and 0-6 mi) from 'he impoundment, and 

105 people between 1 and 2 km (0.6 and 1,2 mi) from the 

impoundment (PNL84) , 

Moab Kill 

The Atlas Corporation Mill is located on the Colorado River 

in a Long, narrow valley of a mountairlous area about 5 km (3 mi,) 

northwest of MoaS, Utah, The mill, which began operations in 

October 1.956, is on standby status, This mill. has combined acid 

and alkaline circuits, which give it greater flexibility in 

handling a variety of ores (DOE82), Uranium has been produced 

for sale to both government and commercial buyers. Capacity of 

the mill is 1980 tons of ore per day (NRC84). 

Prior to 1977, mill tailings were discharged to the Colorado 

River (NRC84). Since that time, all tailings have been placed in 

a single tailings impoundment. The dam has been constructed 

mainly of coarse tailings. Tailings 're discharged from multiple 

spigots around the perimeter of the dam. The coarse sand is 

deposited on and near the dam, whereas the fines are carried to 

the interior of the impoundment with the tailings solution. The 

impoundmentss total surface area is 60 ha (147 acres (EPA85). Of 

the total area, 22 ha (54 acres) are covered by ponded solution, 

2 ha (4 acres) are saturated, and 36 ha (90 acres) are exposed 

dry tailings (incl.uding the dams) (EPA85) . Because the 

impoundment is on a sloping surface, its height varies from 6 to 

abaut 36 m (20 to about 120 ft) above ground (DOE82). Between 

7 and 9 x 106 t (8 and 10 x 106 tons) of tailings are contained 

in this impoundment (DOE82, NRC84)- 

The radium-226 content of the tailings has been reported to 

be 540 pCi/gram (EPA83). Ore grade ranges from 0.20 to 

0.25 percent U O8 (NRC84). 

Moab is the only nearby incorporated community, A 

1983 survey indicated a total population of 2361 within a 5-km 

(3.3.-mi) radius of the tailings pire (PNL84). The same survey 

indicated no people l-iving within 1.0 km (0-6 mi) and 9 people 

within 1 and 2 km (0.6 and 1.2 mi) from the impoundment, The 

survey also indicated that 2319 people were living between 3 and 

5 km (1.8 and 3. l mi) of the mill (PNL84), 
The climate at the site is semiarid, Annual precipitation 

is 20 cm (8 inches), and the annual evaporation rate is 163 cm 

(64 inches) (EPA83). As a means of minimizing dusting, the dried 

tailings are sometimes wetted with sprinklers and/or a chemical 

dust suppressant, such as Coherex (DOE82). Windspeeds usually 

are quite low (DOE821 

-- Plateau Resources Kill 

The Plateau Resources Shootaring Canyon Mill is located near 

~anksville, Utah. This mill was operational only from April to 

October 1982 and is currently on standby status. The capacity of 

the mill is 725 t (800 tons) per day (NRC84). The average ore 

grade is 0.15 percent U308, ranging from 0.07 to 0.24 percent 

(NRC84). An average of approximately 97,000 tons of surface 

mined ore is stockpiled on site when the mill is running at 

capacity (Ee85). The primary mill circuit involves 

semi-autogenous grinding of the sandstone ores, followed by a 

sulfuric acid leach. Tailings are disposed of in a planned, 

phased disposal system. An earthen dam has been constructed 

across the valley. Behind the earthen dam, berms have been 

constructed to form six cells for tailings disposal. Because of 

the short period of operation, only one cell contains a 

significant quantity of tailings. Two other cells contain only 

minor quantities, and the other three cells contain none. The 

area of the tailings is only 3 ha (7 acres), and about 0.8 ha 

(2 acres) of these are covered with water (EPA85). Plateau 

Resources has taken steps to stabilize this impoundment 

temporarily by inducing water evaporation and placing a 0.3-m 

(I-ft) cover of local soil over 1.2 ha (3 acres) of the tailings 

to limit windblown dust. This interim stabilization process will 

be completed in approximately 3 years. Radon-222 flux from the 

tailings has not been measured. 

The area around the mill is sparsely populated; no 

inhabitants live within a 4-km (2.4-mi.) radius (PNL84)- The 

1983 survey indicated 171 people living within 4 and 5 km 

(2.4 and 3.1 mi) of the tailings impoundment (PNL84). 

Washington has two licensed conventional mills, owned by 

Dawn Mining (Newmont Mining/Midnight Mines) and Western Nuclear, 

Inc. (Phelps Dodge) (see Figure 4-6). Another mill, owned by Joy 

Mining Company, was licensed, but was never fully operational. 

This latter mill is not typical as it processed a bog material on 

a leach pad. Only 820 t (900 tons) of tailings (heap leached bog 

material) was generated. It is reported that this residue has a 

low radium-226 content (WA86). The license for this mill was 

suspended in June 1985. 
@ Dawn Mining Co. 

Ford Mill 

@) Western Nuclear, Inc. 

Sherwood Mill 

Figure 4-6. Location of mills in Washington. 
Dawn Mining Mi1.L. 

The Dawn Mining Mill, which is near Ford, Washington, about 

72 km (45 mi) northwest of Spokane, is jointly owned by Newmont 

Mining Corporation and Midnight Mines, Inc, It began operations 

in 1957 and operated through 1964 under the AEC concentrate 

purchase program. The mill was shut down and rehabilitated 

between 1965 and 1969, it operated between 1969 and 1982, but 

has been inactive and on standby status since 1982. 

The production capacity of the mill is 550 t (600 tons) of 

ore per day, The mill circuit incorporates a two-stage agitation 

acid leach process followed by ion exchange and precipitation of 

uranium with ammonia, The Midnight mining open-pit mine produces 

ore between 0.10 and 0.25 percent U 0 (NRC84). During 

operations, a 1-year supply of ore 1183,000 t (212,300 tons) ] was 

maintained on a 6-ha (14-acre) stockpile at the mill site 

(DOE82). 

The tailings generated by tbe Dawn Mill are contained in 

four separate impoundments, three of which are above grade, 

unlined, and constructed behind earthen dams. These three 

impoundments have been filled to capacity and are inacgive. 

Impoundment Nos, 1 and 2 contain an estimated 1.2 x lo tons of 

tailings from government contract production. They have been 

covered with about 0.61 m (2 ft) of sandy soil and wood chips for 

dust control and interim stabilization (DOE82, Ag84). 

Impoundment No, 3, which contains about 1.6 x 10 tons of 

tailings, has also been covered with sandy soil and wood chips. 

These three impoundments have a surface area of 38 ha (95 acres), 

all of which is dry (EPA85). Impoundment No. 4 is an excavated, 

below-grade, lined (Kypalon) pond covering 11 ha (28 acres). 

Seven hectares (17 acres) are covered by solution and 4 ha 

(11 acres) are dry (EPB95)- The tailings are covered with water 

to a depth of 1-2 to 1.5 m (4 to 5 ft). The radium-226 content 

of the Dawn Mill tailings is reported to be 240 pCi/g (EPA86). 

The community of Ford is located within 3.2 km (2 mi) of the 

tailings irnpoundments. in 1983 approximately 411 people were 

living within 5 km (3.1 mi.) of the tailings impoundments 

(PNL84). No one lived within 0.5 km (0,3 mi) and 3 people Lived 

within 0-5 and 1.0 km (0.3 and 0.6 mi). Ninety-three people 

lived within l and. 2 km (0.6 and 1.2 mi) and 157 lived within 

2 and 3 km (1.2 and 1 .9 mi) of the impoundments (PNL84) . The area's topography is characterized by rolling hills. 

The average annual precipitation is 30 to 46 cm (12 to 18 in); 

annual evaporation is about 127 cm (50 in) (EPA83b). 
Western Nuclear Sherwood Mi.11 

Western Nuclearts Sherwood uranium mill is located in 

eastern Washington about 64 km (40 mi) northwest of Spokane. Ore 

taken from a nearby surface mine has averaged 0.05 to 0.09 

percent U 0 (EPA83). This mining and milling operation, 3 8 which began in 1978, has been inactive and on standby status 

since July 1984, 

The tailings generated by acid leaching at the Western 

Nuclear Mill have been placed in a single above-grade impoundment 

behind an earthen dam. The area covered by tailings is 38 ha 

(94 acres) (EPA85). Of this total, 7 ha (18 acres) are covered 

with tailings solution, 28 ha (70 acres) are dry, and the 

remainder is saturated (EPA85). Tailings slurry from the mill 

was neutralized with lime before being pumped to the 

Hypalon-lined impoundment. Tailings solution decanted from the 

impoundment was pumped to a 16-acre evaporation pond situated 

immediately upstream of the tailings impoundment. The current 

am unt of tailings under management is estimated to be (1.6 x R 10 tons) (NRC84). The tailings are reported to contain 

200 pCi/g of radium-226 (EPA83). 

The area is sparsely populated. A 1983 survey indicated 

49 people living between 3 and 5 km (1.9 and 3.1 mi) away from 

the tailings impoundment (PNL84). This survey also indicated 

that no one was living within 3 km (1.9 mi) of the impoundment. 

Annual precipitation is 25 to 38 cm (10 to 15 in.), and annual 

evaporation is about 127 cm (50 in.) (EPA83b). 

As shown in Figure 4-7, nine mills are located in Wyoming. 

Three of these have been decommissioned, two are active, and four 

are on standby status. Descriptions of the active and standby 

mills are presented in the following subsections. 

Pathfinder Gas Hills Mu 

The Pathfinder Mines Corp. (formerly Lucky Mc Corp.) Gas 

Hills Mill is located in the Gas Hills region of Fremond County, 

Wyoming, about 40 km (25 mi.) northeast of Jeffrey City. 

This mill first began producing yellowcake in 1958 with a 

nominal ore-processing capacity of 850 t (935 tons) per day. 

Since then, the capacity has been expanded to about 2273 t (2500 

tons) of ore per day. The mill uses an acid-leach process and 

was the first in the United States to incorporate the moving-bed, 

ion-exchange technique originally developed in South Africa. It 

is also the only domestic uranium mill that uses anion exchange 

for concentration of uranium from the feed solution. 
@ Pathfinder Mines Corp. 

Gas Hills Mill 

@ Western Nuclear, Inc 

Split Rock Mill 

@ Umetco 

Gas Hills Mill 

(4) Rocky Mountain Energy 

Bear Creek Mill 

@ Pathfinder Mines Corp. 

Shirley Basin Mill 

Minerals Explorati~on Co. 

Sweetwater Mill 

a Petrotornics 

Shirley Basin Flil~l~ 

Americnn Nucl~ear Corp. 

Gas Hills Mill 

@ Exxon Corp. 

Highland Mill 

Figure 4-7. Location of mills in Wyoming. 
Company- owned open-pit 8ni.ni.n.y opefati.ons, Located L. "So 

3 km (l to 2 mi) from the mill, supply 90 percent of the ore: the 

remaining LO percent i.s produced at Pathfindei" Big Eagle Mi.ne 

near Jeffrey City. The ore grade has averaged 0.21 percent U 0 3 8 

in past operations and is expected to average 0.11 percent in the 

future (Haas). Although mines adjacent to the mill also could 

provide fresh water for ore processing, the availability of hot 

[57'~ (13s0~)1 well water at the site makes it advantageous, from 

a process standpoint, to use well water in the mill and to treat 

mine water for discharge. 

The tailings retention system consists of four tailings 

impoundmetlts having surface areas of 50. 22, 4. and 36 ha (124, 

54. 22 and 89 acres) (EPA85) The impoundments are situated 

sequentially in the head of a draw north-northeast of the mill 

and are dug into an underlying sltale formation. The clay core 

dams are keyed into the shale. The average tailings depth is now 

12 m (40 ft) and is expected to increase to lR m (60 ft) by the 

end of the projected inillitrg operation in 1996 (Ha85). Water is 

sprayed over 8 ha (19 acres) of the dry tailings during warm 

weather to control dust (Ka85). Dry beaches account for 69 ha 

(172 acres) of the total, whereas 38 ha (96 acres) are covered 

with tailings solution. The remaining 8 ha (21 acres) of exposed 

tailings are saturated with solution (EPA85). The current amount 

of tailings under management is 11.5 x lo6 tons) (Wa85). 

The radium-226 activity for the solid tailings. combined 

sands. and slimes is about 160 pCi/q (Ka85). An earlier EPR 

report estimated the radium-226 content at 420 pCi/g (EPA83b). 

The radium-226 activity of the taili ngs liquid is approximately 

200 pCi/liter (Wa85). 

The Pathfinder Gas Mills Mill is in a remote Location away 

from permanent habitation. The nearest residence is 

appruximately 19 km (1.2 mi) away (Ha85). A 1983 survey also 

indicates no population within a 5--km /%mi) radius of the 

tailings piles (PNL84). 

In 1963 a flood at the mill. site resulted in the release of 

8.7 x liters (2.3 x lo7 gal) of impounded tailings solution 

to the enviro~tment. As a result of this incident, the tailiilgs 

impoundment was enlarged to its current capacity. The existing 

system. with a ininimum of 1 m (3 it) of freeboard. is estimated 

8 to provide 12.6 x 10 liters (3.3 x 10' gal) of einergenroy 

storage. 
Wess_kern Nu-clear Split Rock Mi.ll 

Western Nuc3.earPs Split Rock Mill is located 3-2 km 

(2 miles) north of Jeffrey City, Wyoming. This mill began 

operation in 1957 and has been on standby status since June 

1981. When running at capacity, the mill produced 935 tons of 

yellowcake per year (Bo85)- Maximum throughput was about 

1700 tons of ore per day (NRC84). The ore grade has ranged from 

0.15 to 0.30 percent U 0 in the past and is expected to 

range from 0-05 to 0.13 Bercent in the future (NRC84) . Milling 

operations involve semi-autogenous grinding, an acid leach, and 

solvent extraction. The mill usually stockpiles 2000 to 

5000 tons of ore when it is operating. Two 8-m (25-ft) diameter 

bins are used to store fine ore. 

The tailings generated by the Split Rock Millare contained 

in a single tailings impoundment that is enclosed by an earthen 

dam. The t,ailings impoundment has a surface area of 62 ha 

(156 acres), and the maximum depth is about 29 m (95 ft)(EPA85, 

B085). Currently, 38 ha (94 acres) of the impoundment are 

covered by tailings solution (EPA85). There are 17 ha (43 acres) 

of dry tailings in the impoundment (EPA85). Tailings are 

discharged from the crest of the dam; the point of discharge is 

periodically moved along with the crest. Western Nuclear uses a 

sprinkler system to control dusting from the pond during 

nonfreezing months. Wind fences, chemical sprays, and vggetation 

seeding are also used to control dusting. About 12 x 10 tons 

of commingled tailings are under management (NRC84). 

The average radium-226 concentration of the tailings is 

approximately 100 pCi/g (99.5 + 42 pCi/g) (Bo85). Radium-226 

values in the sands and slimes were determined to be 63 pCi/g and 

87 pCi/g, respectively (Bo85). Western Nuclear has used charcoal 

canisters to measure radon-222 flux from the tailings. The 

avera e flux measurements, made in 1977-1978, were 2 i 1.1 9' pCi/m s (Bo85). An earlier EPA report indicated that 430 pCi/g 

of radium-226 was present in the tailings (EPA83b). 

A 1983 population survey indicated that three people lived 

between 0.5 and 1.0 km (0-3 and 0.6 mi) from the tailings 

impoundment (PNL84). This survey further indicated that 

30 people resided wit'nin 2 and 3 km (1.2 and 1.9 mi) of the 

tailings impoundment, 697 people within 3 and 4 km (1.9 and 

2.5 mi), and 176 people within 4 and 5 km (2.5 and 3.1 mi) 

(PNL84). 
The Umetco minerals Gas Bills Mill is located in the 

southeastern portion af the Wind River Basin of Wyoming. The 

rni.11 is about 95 km (60 mi) west of Casper in an area of rolling 

hiL1s interspersed with relatively flat areas. The mill is 

currently on standby status. 

An acid-leach system (RIP-Eluex system) is used to recover 

uranium. Recycled solution from the impoundment system is used 

to wash sands after sand-slime separation. Additional pond 

decant solution is used for tailings dilution. The mill began 

operation in early 1960 with a capacity of about 1100 tons per 

day; in January 1980, the capacity was increased to 1400 tons per 

day. In June 1983, milling of mined ore was temporarily 

curtailed, and only the heap leach facility waskept in 

operation. During milling operations, a 2-month stockpile of ore 

is maintained at the mill (Wo85). This amounts to 85,800 tons 

when the mil1 is operating at capacity. 

During the anticipated t~tal active life of the project 

(1960 to 1986), about 13 x 10 tons of mill tailings will have 

begn produced, The retention capacity [7.6 x 10 t (8.4 x 

10 tons)] of the mill" original above-grade tailings 

impoundment has been reached, and since January 1980, tailings 

have been discharged to a gepleted open-pit mine (A-9 Pit), which 

has a capacity of 2.5 x 10 tons. This has an area of 10 ha 

(25 acres), is clay-lined on the bottom, and has an in-pit 

dewatering system. The A-9 Pit has an exposed dry tailings beach 

area of about 6 ha (14 acres) (EPA85). The maximum height of the 

embankment of the original above-grade tailings impoundment (and 

expansions) is about 14 m (45 ft). This impoundment has a 

surface area of 6& ha (151 acrgs), all of which is dry, and 

contains 5.8 x 10 t (6.4 x 10 tons) of commingled tailings 

(EPA85, Wo85). The inactive tailings area, which has not been 

used since January 1980, is currently in a preliminary phase of 

reclamation. The inactive impoundment has been covered with an 

average thickness of 1.2 m (4 feet) of overburden (Wo85). The 

tailings are reported to contain 310 pCi/g of radium-226 

(EPA83b). The evaporation area consists of three ponds with a 

combined surface area of 8 ha (20 acres). 

An EPA report estimates the radium-226 content of the 

tailings to be 310 pCi/g (EPA83b). No measurements of radon-222 

flux from the tailings impoundment have been made at this site 

(Wo85) . 
The area is sparsely populated. A 1983 survey indicated no 

people living within a 5-km (3-mi) radius of the tailings 

impoundment (PNL84). Average annual precipitation is 25 cm 

(10 in.), and evaporation is 17 cm (42 inches) (EPA83b). 

Under the current reclamation plan, Umetcc is committed to 

provide a uniform cover of 0.3 m (1 ft) of clay and 2-6 m 

(8.5 ft) of overburden gver the egtire tailings area, This will 

require about 210,000 m Q7.3 x 10 fg ) of clay, at a cost of 

$1,129,000, and 1.8 x 10 m (65 x 10 ft ) of overburden, 

at a cost of $1,840,000 (NRC84). When the cost of revegetation 

is added, the basic materials needed for the reclamation program 

will cost about $3,800,000. 

Umetco also operates a heap leach facility in the mill area 

at its Gas Hill site. The water used in the process 

[1.7 liters/s (27 gal/min)] is taken from a nearby tailings area, 

and U O8 is recovered from high-grade leach liquor by a 

solvent-extraction process. The organic phase is pumped to the 

mill circuit. Heap leach pads cover about 9 ha (22 acres) at 

this site (EPA85). 

Rockv Mountain Enerqy Mill 

Rocky Mountain Energy's Bear Creek Mill is part of a uranium 

project that includes open-pit mining operations in the Powder 

River area of Converse County, Wyoming, about 72 km (45 miles) 

northeast of Casper. The operation, which was dedicated in 

September 1977, has a capacity of 2000 tons of ore per day 

(NRC84). The U 0 content of the ore ranges from less than 

0.1 to 1.0 perc2n@ (NRC84). Ore is stockpiled at the m.ill on an 

8-ha (20-acre) pad; approximately 66,000 tons are currently on 

hand (Me85). The mill is currently operating at about 20 percent 

of its capacity and is milling stockpiled ore. It is likely that 

the mill will go to standby status sometime during the second 

quarter of 1986. 

Mill tailings are contained in a single tailings impoundmen?. 

enclosed by an earthen dam. The surface area of tailings is 

48 ha (121 acres), of which 18 ha (45 acres) are covered with 

tailings solution and 21 ha (53 acres) are dry tailings beaches 

(Me85). A portion, 13 ha (32 acres), of the pile has been 

covered with 30 cm (I foot) of soil to control fugitive dust 

(Me85). 
No measurements of radon-222 flux from tailings have been 

made at this site, The radium-226 content of the Bear Creek 

tailings is reported to be 420 pCijg (EPA83b). 

A 1983 survey indicated no one living within a 5-km (3.1-mi) 

radius of the tailings pile (PNL84). The annual precipitation in 

the area is about 30 cm (12 in.), and annual evaporation is 102 

cm (40 in.) (EPA83). 

Pathfinder Shirlev Basin 

The Pathfinder Mines Corporation Shirley Basin Uranium Mill 

is located in an area of plains and rolling hills about 72 km 

(45 mi) south of Casper, Wyoming. The mill, which began 

operation in 1971, uses semiautogenous grinding, leaching, and 

ion exchange. Current mill capacity is 1600 t (1800 tons) of ore 

per day (NRC84). The mill is currently active and has a 

throughput of 900 t (990 tons) per day (Si85). Operations are 

projected to continue through 1994. 

Tailings are contained in a single onsite tailings 

impoundment that is contained above grade by a single-sided 

earthen retention dam 18 m (60 ft) high. The surface area of the 

tailings impoundment is lo ha (261 acres), of which 72 ha 

(179 acres) are covered with ponded tailings solution (EPA85). 

Twenty-four hectares (60 acres& are dry beaches. The impoundment 

contains 5.8 x 106 t (6.4 x 10 tons) of tailings (NRC85). The 

tailings are reported to contain 540 pCi/g of radium-226 

(EPA83b). 

A 1983 survey of the population in the vicinity of the 

Pathfinder Shirley Basin Mill indicated no inhabitants living 

within 3 km (1.9 mi.) of the tailings impoundment (PNL84). Six 

people, who lived between 3 and 4 km (2.9 and 2-5 mi) from the 

i~~poundrnent, were the cnLy inhabitants within 5 km (3.1 mi) 

(PNL84). 

Minerals Exploration Mill 

The Minerals Exploration Company" sweetwater Mill is 

located within the Red Desert portion of Wyoming's Great Divide 

Basin, about 64 km (40 mi) northwest of Rawiins. The mill, which 

began operations in early 1981, has been inactive since November 

1981 and is currently on standby status. The capacity of the 

mill is 2700 t (3000 tons) pew day, The average ore grade 

processed to date has been 0.03 percent U308 (Hi85). 
All tailings have been placed in a single tailings 

impoundment. It is a lined (synthetic) impoundment that is 

partially below grade and has earthen embankments. The total 

surface area of the tailings is 15 ha (37 acres) (EPA85). With 

the exception of a 3-ha (7-acre) delta at the tailings discharge 

point, the tailings arg covered bx tailings solution. 

Approximately 0.9 x 10 t (1 x 10 tons) of tailings have 

been generated and are contained in this impoundment. Plans call 

for a second cell to be constructed to the north of the existing 

cell if additional capacity is required. The Sweetwater tailings 

disposal system is a phased-disposal facility that has gone 

through several iterations during development. The impoundment 

was originally designed to be square, below-grade, and divided 

into four cells. The Minerals Exploration Company reports that 

measurements of radoy-222 flux made on the tailings solids ranged 

from 90 to 100 pCi/m s (Hi85). 

A 1983 survey indicated no population living within 5 km 

(3.1 mi.) of the tailings impoundment (PNL84). The annual 

precipitation in the area is 15 to 20 cm (6 to 8 in.), and annual 

evaporation is 102 to 178 cm (40 to 70 in.) (EPA83). 

4.3 Population Within 5 km (3.1 mi) of Existina Tailinqs 

Impoundments 

A 1983 estimate indicated that 12,824 persons lived within 

5 km (3.1 mi) from the centroid of the tailings impoundments at 

the active and standby sites (PNL84). No one lived within 0.5 km 

(0.3 mi), whereas 173 people lived between 0.5 and 1 km (0.6 and 

1.2 mi). Nobody lived within 5 km (3.1 mi) of four of these 

mills, all of which were in Wyoming. A summary of this 

information by state and by mill is presented in Table 4-3. By 

comparison, a population survey conducted by EPA in 1985 showed 

that there were 11,483 people living within 5 km (3.1 mi) of 

these tailings impoundments. This more recent survey, which was 

based on interpretation of aerial photographs, indicated that no 

one lived within 5 km (3.1 mi) of six of these tailings 

impoundments. The results of this later survey are presented in 

Table 4-4. 
T&Le 4-3. Estimate of the p0pulatic:n living wivrbin 0 to 5 kin frcm 

centroid of tail.ings .hpm&nent.s of a&j.ve and standby mills in 1.983 'w 

Colorado 

cotter 0 

Umetco 0 

New Mexico 

Sohio 0 

United 

Nuclear 0 

Anaconda 0 

Kerr-Mae 0 

Hamestake 0 

Texas 

Chevron 0 

Utah 

Vmetco 0 

Rio Algam 0 

Atlas 0 

Plateau 

Resources 0 

Washhqton 

Dawn 0 

Western 

Nuclear 0 

WyanW Paathf jnder 

(Gas Hills) 0 

Western 

Nuclear 0 

Ihietco 0 

Rocky Mt. 0 

Energy 

PaWf inder 

(Shi-r1ey 

Basin) 0 

Minerals 0 

Exp. 
Table 4-4. :stL?ate of the ppulation livhg trfiihin 0 to 5 km fron. tl'e 

centroid of L?il!inqs imp~mchnents of active 31d s'~%n&y "d11s in 1985 t.: 

State/Owner 0.0-0.5 0.5-1.0 1.0-2.0 2.0-3.0 3.0-4 -0 4.0-5.0 Total 

Colorado 

Cotter 0 

Vmetco 0 

New Mexico 

Sohio 0 

united 

Nuclear 0 

Anaconda 0 

Kern-Mae 0 

Romes'cake 0 

Texas 

Chevron. 0 

urn 

Lhnetco 0 

Ri.0 Algm 0 

Atlas 0 

Plateau 

Resources 0 

Washington 

mwn 0 

Westem 

Nucileav 0 

Wyoming 

Pathfinder 

(Gas Eiil1.s) 0 

Westen1 

Nucleax 0 

Umetco 0 

RG€Q Mt. 

mewY 0 

Pathf hder 

(Shj.rl.ey 

Basin) 0 

Mi nerais 

&p . 0 

Total 0 12 569 833 4826 '5243 11,433 
Andrew R. E., "Uranium Mills Program, Department of 

Social and Health Services, State of Washingtonv, 

Correspondence with PEI Associates, Inc., December 

1984. 

Bogden G., Western Nuclear, Inc., Correspondence with 

PEI Associates, Inc., January 1985. 

Department of Energy, Office of Defense Waste and 

Byproducts Management, "Commingled Uranium Tailings 

Study," DOE/DP-0011, Washington, D.C., June 30, 1982. 

Department of Energy, "United States Mining and Milling 

Industrytv, DOE/2-0028, May 1984. 

Electric Light and Power, "Uranium Industry Not Viable 

in 1984, Determines DOE'S Harrington", November 1985. 

Environmental Protection Agency, "Regulatory Impact 

Analysis of Environmental Standards for Uranium Mill 

Tailings at Active Sites", EPA 520/1-82-023, March 

1983. 

Environmental Protection Agency, "Final Environmental 

Statement for Standards for the Control of Byproduct 

Materials from Uranium Ore Processing (40 CFR 192)", 

(EPA 520/1-83-008-l), Office of Radiation Programs, 

Washington, D.C,, September 1983. 

U.S. Environmental Protection Agency, "Draft 

Document-Estimates of Population Distributions and 

Tailings Areas Around Licensed Uranium Mill Sitesw", 

Office of Radiation Programs, November 1985. 

Environmental Protection Agency, "Technical information 

submitted by letter dated January 27, 1986 from T. R 

Strong, Head, Radiation Control Section, State of 

Washington, Department of Social and Health Services, 

Olympia, Washington to Sheldon Meyers, Acting 

Directorw, Office of Radiation Programs, U.S. EPA. 

Gerdemann F. W., "Correspondence with PEI Associates, 

Incaw', Plateau Resources Limited, January 1985. 
Hardgrove T., Pathfinder Mines Corporation, 

Correspondence with PEI Associates, Inc,, January 

1985. 

Hill c., Minerals Exploration Company, Correspondence 

with PEI Associates, Inc., January 1985. 

Johnson T. D., Sohio Western Mining Company Tailings 

Dam, in: First International Conference on Uranium 

Mine Disposal, C. 0. Brawer, editor, Society of Mining 

Engineers of AIME, New York, 1980. 

King K. and Lavander R., Design and Construction of 

Uranium Disposal Facilities for the Panna Maria 

Project, Texas, Presented at First International 

Conference on uranium Mine Waste Disposal, Vancouver 

British Columbia, May 19, 1980. 

Kray E., State of Colorado, Correspondence with PEI 

Associates, Inc., January 1985. 

Manka M., Cheveron Resources Company, Panna Mana 

Project, Correspondence with PEI Associates, Inc., 

February 1985. 

McClusky J., Cotter Corporation, Correspondence with 

PEI Associates, Inc., February 1985. 

Medlock R., Bear Creek Uranium, Correspondence with PEI 

Associates, Inc., February 1985. 

State of New Mexico, Radiation Protection Bureau, 

Correspondence with PET Associates, Inc., January 

1985, 

Nuclear Regulatory Commission, Final Generic 

Environmental Impact Statement on Uranuim Milling, 

NUREG-0706, September 1980. 

Nuclear Regulatory Commission, Office of State 

Programs, Directory and Profile of Licensed 

Uranium-Recovery Facilities, (NREG/CR-2869), 

Washington, D.C., March 1984. 

Pacific Northwest Laboratory. Estimated Population 

Near Uranium Tailings. (PNL-4959). January 1984. 

Simchuk G. J., Pathfinder Mines Corporation, 

Correspondence with PEI Associates, Inc., February 

1985. 
State of Washington, Department of Social and Health 

Services, Uranium Mills Program, Correspondence with 

PEI Associates, Inc. January 1986. 

Wong T., Umetco (Union Carbide), Correspondence with 

PEI Associates, Inc., February 1985. 
Chapter 5: INDUSTRY RADON-222 EMISSION ESTIMATES 

5.1 Introduction 

This chapter presents a discussion of the methodology used 

to estimate the quantity of radon-222 emitted from tailings 

impoundments and evaporation ponds at licensed uranium mills. As 

mentioned in Chapter 3, ore storage and milling operations emit 

relatively low amounts of radon-222 compared with the amounts 

emitted by tailings impoundments. Mills that are on standby 

generate almost no radon-222 other than that from their tailings 

impoundments. The quantity of radon-222 emitted annually from 

each site is estimated both for current conditions (i.e., 

fraction of tailings area with current water cover) and for 

anticipated future conditions (i.e., dry tailings). Water cover 

and tailings moisture content have a major influence in 

controlling the amount of radon-222 that is released; therefore, 

dry conditions must be considered in the determination of the 

potential maximum amount of radon-222 that could be emitted 

(i.e:, future conditions). Emissions are estimated for each 

taillngs impoundment and evaporation pond at each licensed 

uranium mill except the six mills that have already initiated 

decommissioning activities and are subject to other Federal 

standards. 

5.2 Estimatins Emissions 

Estimates of radon-222 emissions are based on an assumed 

emission rase that equals the specific flux of 1 pCi 

radon-222/m s per pCi radium-226/g tailings for dry tailings 

times the dry area. It has been assumed that tailings that are 

either saturated with or covered by tailings solution do not emit 

radon-222. These assumptions were applied to the site-specific 

data to estimate emissions. 

2 For the specific flux of 1 pCi radon-222/m s per pCi 

radium-226/g to be used, both the dry surface area and the 

radium-226 concentration of the tailings impoundment must be 

known. The surface area of existing tailings impoundments has 

been documented previously (EPA83, NRC80). The uranium industry, 

however, has changed significantly since the compilation of these 

earlier data bases, as demonstrated by the drop in uranium 

production (and thus tailings generation), the initiation of 

decommissioning activities at six mills, and the drying of 

tailings impoundments at others because they are not in use. To 

obtain an updated data base, EPAFs Office of Radiation Programs 

completed a study entitled "Estimates of Population Distribution 

and Tailings Areas Around Licensed Uranium Mill Sitesw (EPA85). 

As discussed in Chapter 4, this document summarizes the results 
of a survey the EPA conducted of 22 uranium mill sites in 1985, 

This survey produced estimates of the total surface area of the 

tailings impoundments, which includes the area covered by 

tailings solution, the saturated area, and the dry surface area 

of tailings. The same information was also compiled for 

evaporation ponds, These estimates of tailings areas were used 

as the basis for estimating radon-222 emissions in this report 

(See Table 4-2 in Chapter 4). This tabulation includes a 

listing, by state, of each known tailings impoundment and 

evaporation pond at the licensed mills. The type of impoundment 

is also identified, i.e., earthen dam, sand tailings dam, or 

below-grade impoundment. The status of each impoundment (active, 

standby, or at capacity) is shown, and estimates of the average 

radium-226 content in the tailings are listed for each mill. The 

total impoundment and evaporation pond area is 1570 ha (3882 

acres), over 50 percent of which is dry. Only four mills with 

seven tailings impoundments are currently active; 32 tailings 

impoundments are on a standby basis or have been filled to 

capacity. 

Concentrations of radium-226 present in tailings vary from 

site to site. The EPA% Final Environmental Impact Statement for 

Standards for the Control of Byproduct Materials from Uranium Ore 

Processing listed radium-226 concentrations in tailings for each 

licensed mill (EPA83). These values were used in this report to 

estimate emissions of radon-222. 

Emissions were estimated for two conditions: current 

water-cover conditions (as of late summer of 1985) and after 

drying. Under current conditions, it was assumed that radon-222 

was emitted only from dry areas of the tailings impoundments or 

evaporation ponds. In the esti ates of radon-222 emissions, a Y specific flux of 1 pCi Rn-222/m's per pCi of Ra-226 per gram of 

tailings was used for dry tailings and a specific flux of zero, 

for ponded and saturated tailings. As discussed in Chapter 3, 

this assumed specific flux calculation has been previously 

documented and used (NRC80, EPA83). This average conservative 

flux, which provides an approximate estimate of emissions, is 

useful when the many other factors affecting the flux, such as 

tailings moisture content, diffusion factors, and emanation 

coefficients, are not well known. The following calculation was 

used to estimate emissions from dry areas: 

2 kCi Rn-222/y = dry area, m2 x 1 pCi Rn-222/m s per pCi 

The radium-226 concentration in picocuries/gram of tailings is 

shown in Table 5-1. For estimates of emissions after drying, the 

total tailings area was substituted for the dry tailings area in 
T&ie 5-1, Summary of radon-222 missions from w~iUn 

.mill tailings s 

cxrrent lxlrrrnt 

conditio wnditio After 

(flux = 1) ( f adored) %) wing 

Colorado 

Cotter Cop. 

m-jmury 

Secondary 

Umetw 

Iitpunc3ments 1 & 2 

~un&ent 3

Sludge pile 

Evaporation pond 

New Mexico 

Sohio 

LrBar 

United Nuclear 

QIUrchrmk 

Anaconda 

Bluewater I 

Bluewater 2 

Bluewater 3 

Evaporation ponds 

Kerr-McGee 

Quivira l 

Quivira 2a 

Quivira 2b 

Quivira 2c 

Evaporation ponds 

Hamestake 

Homestake 1 

Homestake 2 

ms 

Chewoi? 

Pm Maria 
Table 5-1. S of radon-222 emissions from uranim 

mill tailings impomIhnents (continued) 

Radon-222 emissions (kCi/y) 

Cuncmt Current 

wndition wnditio After 

Owner/lmpoundment (flux = 1) (factored) 

m 

Uinetco 

White Mesa 1 

White Mesa 2 

mite Mesa 3 

Rio Algom 

Atlas 

Moab 

Plateau Resources 

Shootariy Canyon 

Western Nuclear 

Shemood 

Evaporation pond 

warning 

Pathfinder 

Gas Hills 1 

Gas Hills 2 

Gas Hills 3 

Gas Hills 4 

Western Nuclear 

Split Rock 

Umetco 

Gas Hills 

A-9 Pit 

Leach pile 

Zvapratj.on ponds 
Table 5-1. Sununary of radon-222 emissions frm uranium 

mill tailings ~unhents (continued) 

Radon-222 emissions (kCi/y) 

Cuncent Current 

conditio wnditio After 

Owner/Inpmndtment (flux = 1) ?a) (factored) 

Rocky Mountain Energy 

Bear Creek 

Pathfinder 

Shirley Basin 

Minerals Exploration 

Sweetwater 

Totals 129 137 238 

(a) 2 Based on a specific flux of 1 pCi Rn-222/m s per pCi Ra-226 per 

gram of tailings for dry areas and a flux of zero for ponded and 

wet areas. 

2 (b) Specific flux of 0.3 pCi m-222/111 s per pCi Ra5226 per gram of 

tailings for wet tailings area, 1 pci Rn-222/m s per pCi Ra-226 

per gram of tailings for dry area, and zero for pond& areas. 
the preceding calculation. The results of the calculations for 

impoundments at each mill considered in this report are presented 

in Table 5-i. Total radon-222 emissions are estimated to be 129 

kCi/y under current conditions and to rise to about 238 kCi/y 

after all the areas have dried. 

2 Although a specific flux of 1 pCi radon-222/m s per pCi 

radium-226/g tailings is commonly used and recommended by NRC 

(NRC85) when specific data are lacking, alternative methods of 

flux estimation are available. One alternative method is to 

assume that2the radon-222 flux from dry areas is 1 pCi 

radon-222/m per pCi radium-226/g; zero from gonded areas, as 

previously discussed; and 0.3 pCi radon-222/m per pCi 

radium-226/g for saturated areas instead of zero (NRCBO). 

Estimates of radon-222 emissions made by using this method of 

calculation indicate 137 kCi/y, as shown in Table 5-1. 

Other alternative methods of estimating radon-222 emissions 

require site-specific data. As discussed in Chapter 3, 

information on radium-226 and on the moisture content, porosity, 

density, and emanating power of tailings can be substituted into 

the diffusion equation to estimate a site-specific flux for 

each area of a tailings impoundment. An attempt was made to 

complete such an estimate for each mill in a recent study 

(PEI85). That stydy indicated that using a specific flux of 

1 pCi radon-222/m s per pCi radium-226/g tailings for dry areas 

and zero for ponded and saturated areas resulted in a 

conservative (high) estimate of radon-222 emissions. Total 

emissions estimated by using the assumed specific flux were about 

twice as high as those made using site-specific information. 

The site-specific information was based on a number of 

assumptions, however, as not all of the necessary tailings data 

are currently available at licensed mill sites. Also, estimating 

radon-222 emissions from tailings after drying would, require 

additional assumptions regarding their physical characteristics. 

The current data base is not sufficient to allow more accurate 

calculation of emissionsbased on site-specific tailings 

characteris$ics; therefore, the specific flux (I pCi 

radon-222/m s per pci radium-226/g) for dry areas and zero for 

ponded and saturated areas were used in this report. The 

emission estimates presented herein may be conservative compared 

with estimates made by other means, but insufficient specific 

data are available to draw any definite conclusions. 
REFERENCES 

EPA8 3 Environmental Protection Agency, "Final Environmental 

impact Statement for Standards for the Control by 

Byproduct Material from Uranium Ore Processingn, EPA 

520/l-83-008-1, Office of Radiation Programs, U.S. EPA, 

Washington, D.C., September 1983. 

EPA8 5 Environmental Protection Agency, "Estimates of 

Population Distribution and Tailings Areas Around 

Licensed Uranium Mill Sites (Draft)" Office of 

Radiation Programs, Las Vegas Facility, Las Vegas, 

Nevada, 1985. 

NRC8 0 Nuclear Regulatory Commission, "Final Generic 

Environmental Impact Statement on Uranium MillingN, 

NUREG-0706, September 1980. 

NRC85 Nuclear Regulatory Commission, "Methods for Estimating 

Radioactive and Toxic Airborne Source Terms for Uranium 

Milling OperationsM, NUREG/CR-4088, June 1985. 

PEI85 PEI Associates, Inc., "Radon-222 Emissions and Control 

Practices for Licensed Uranium Mills and Their 

Associated Tailings Pilesw, EPA Contract 68-02-3878, 

June 1985. 

Chapter 6: BASELINE INDUSTRY RISK ASSESSMENT 

6.1 Introduction 

This chapter contains an assessment of the risks of fatal 

lung cancer caused by radon-222 emissions from uranium tailings 

impoundments. Two measures of risk are presented: risks to 

nearby individuals and risks to the total population. The first 

measure refers to the estimated increased lifetime risk imposed 

upon individuals who spend their entire lifetime at a location 

near a tailings impoundment, where the predicted radon-222 

concentrations are highest. ~isks to nearby individuals are 

expressed as a probability, i.e., 0.001 (l/lOOO) or 1.E-3, This 

means that the increased chance of lung cancer in an exposed 

person's lifetime is 1 in 1000. Estimates of risks to nearby 

individuals must be interpreted cautiously, as few people 

generally spend their whole lives at such locations. The second 

measure, risks to the total population, refers to all people 

exposed to radon-222 emissions from all of the licensed uranium 

mill tailings impoundments. Expressed in terms of the number of 

fatal cancer cases caused by the amount of radon-222 emitted 

annually, this provides a measure of the overall public health 

impact. 

An epidemiological approach is used to estimate risks which 

are based on relative risk from exposures to radon-222 expressed 

in working level months (WLM). The WLM is in turn related to a 

concentration of radon-222 decay products, expressed in 

picocuries/liter. Risks are directly proportional to emissions; 

therefore, one can estimate the deaths due to radon-222 in the 

future by assuming that net? tailings impoundments will be 

located in the same general area of existing impoundments. 

6.2 Risk Estimates 

6.2.1 Nearby Individuals 

Individual risks are calculated by using the life table 

methodology described by Bunger et al. (Bu81). The relative 

risk projections used for lifetime exposure were based cn 

relative risk coefficients of l and 4 percent per WLM for the 

radiation-induced increase in lung cancer. See discussion in 

Section 2.3. 
The AIRDOS-EPA and DARTAB codes and an assumed radon-222 

decay product equilibrium fraction determined as shown in 'Table 

2-4 were used to estimate the increased chance of lung cancer 

for individuals living near a tailings impoundment and receiving 

the maximum exposure. Results are shown in Table 6-1. The 

maximum risk of 2 percent (2E-2) occurs at Anaconda, New Mexico 

at a distance of 1.5 km from the center of the impoundment. 

6.2.2 Reqional Population 

~ollective (population) risks for the region are calculated 

from the annual collective exposure (person WTA) for the 

population in the assessment area by a computerized methodology 

known as AIRDOS-EPA (~079). An effective equilibrium fraction 

of 0-7 is presumed because little collective exposure takes 

place near the mill. 

In this study, population data in the 0- to 5-km and 5- to 

80-km regions around each mill were obtained from an earlier 

detailed study by EPA and are summarized in Chapter 4 (EPA83). 

Collective exposure calculations expressed in person WM were 

performed for each mill by multipiying the estimated 

concentration in each annular sector by the population in that 

sector. The parameters used in the AIRDOS-EPA code are shown in 

Table 6-2. An approximate emission height of 1 meter was 

assumed in all cases. Meteorological parameters from selected 

weather stations were used for each mill. Included in this 

table are the resulting exposure for that mill based on the 

emission rate and the population near the mill. Estimates of 

the number of fatal cancers corresponding to this exposure were 

ma e by using a risk factor of 3 percent (760 deaths per 2 10 person WLM). These estimates were then multiplied by 

l520/760 or 380/760 to adjust to the risk coefficients of 4 and 

1 gercent, respectively (1520 and 380 deaths per 

10 person WLM). A summary of the estimated fatal cancers due 

to radon-222 from existing tailings impoundments is shown in 

Table 6-3 under the current (partially wet and partially dry) 

conditions and under entirely dry conditions. 

These estimated health effects for the 20 mills considered 

compare favorably with the previous EPA study (EPA83) for 

uranium byproduct materials. In the earlier study, a model 

plant approach was used at 26 sites, and 0.38 and 2.1 deaths 

were estimated for the 0-5 km and 5-80 km regions, respectively, 

for post-operational (dry) conditions (Page 6-14 in EPA83). 
Table 6-1. Estimated risk of fatal. lung cancer from maxd exposure 

for an individual living near tailings kpoundment 

Maxh lifetime ~istance (a) 

State Mill owner risk to individual (b) meters 

Colorado Cotter 

Umetco 

New Mexico Kerr-MGee 1E-2 (2E-3) 2500 

Anaconda 2E-2 (5E-3) 1500 

United Nuclear 2E-3 (4E-4) 1500 

Homestake GE-3 (lE-3) 1500 

Sohio 7E-4 (2E-4) 3500 

Texas Cnevron 2E-3 (4E-4) 750 

Utah Umetco 

RioAlgom 

Atlas 

Plateau Res. 

Washington Dawn 3E-3 (GE-4) 750 

Western Nuclear 2E-4 (5E-5) 4500 

WYomj-~ Minerals Exploration 4~-G (9~-7) 30000 

Pathfinder 

Gas Hills 2E-3 (6E-4) 2500 

Shirley Basin 9E-5 (2E-5) 15000 

Rocky Mt. 9E-5 (2E-5) 15000 

Umetco 1E-4 (3E-5) 15000 

Western Nuclear 2E-3 (5E-4) 750 

(a) Distance from center of a homogenous circular equivalent 

impoundment. 

(b) The valuegin the first colm is based on a risk factor of 1520 

deaths/lO pergon WLM, and the values in wentheses are based on 

380 deaths/lO person WLM. 
Table 6-2. AIRCOS-EPA code inputs and estimated risks 

ADDE code inputs Approximate 

Atmospheric 

m 

Ambient impOWent 

Precipitation t~rature area I3?aths/yeara 

State C0l'F-Y depth (m) (WY) ( c) (ha) 0-5 Ian 5-80 lon 

Colorado Cotter 

mtco 

New Mexico Kerr-Ma 

Anaconda 

United Nuclear 

Harnestake 

Sohio 

5- 

I Texas Chevron C 

Utah Umetco 

RiaAlgam 

Atlas 

Plateau Re. 

Washington Dawn 

Western Nuclear 

YYw Minerals Explora- 700 27.3 6 3 - 8.33-5 

tion 

Pathfinder 

Gas Hills 700 28.0 6 70 1.93-3 2.93-3 

Shirley Basin 700 29.6 6 20 - 4.63-3 

Rocky Mt. 700 35.4 6 20 - 3.7'0-3 

Umetco 700 33.9 6 80 - 2.23-3 

Western Nuclear 700 28.0 6 20 1.4E-3 5.23-4 

(a) Based on 760 deaths per lo6 person WLM. 

(b) Zero population in the 0-5 Ian region. 
Table 6-3. S of regional health effects from existing 

tailings wundments 

Condition of Esnissions (a) Cdtted fatal cancers per vear (b) 

tailinqs (kCiLy) 

0-5 km 5-80 km 0-80 km 

Current 129 0.3 (0.1) 1.6 (0.4) 1.8 (0.5) 

2 (a) Based on radon-222 flux of 1 pCi/m per pCi of Ra-226 per gram 

of tailings. 

(b) Values6in first column are based on 1520 deaths due to lung cancer 

per 10 person q. The values in parentheses are based on 

380 deaths per 10 person WLM. 
Radon-222 released from mills can be transported beyond the 

80-km regional cutoff. A trajectory dispersion model developed 

by NORE4 (NRC79) has been used to estimate the national impact of 

radon-222 releases. The model yields radon-222 concentrations 

(in picocuries per Liter) in air, which are then converted to 

decay product exposures by assuming an effective equilibrium 

fraction of 0.7. National annual collective exposures (person 

WLM) are calculated for distances beyond the 80-km regional 

limit for a total population of 200 million persons. This model 

was used in a previous EPA study on byproduct material from 

uranium ore processing (EPA83). Inasmuch as all mills are still 

in the same location, the results of this earlier study were 

used. to estimate current national health effects by ratioing the 

estimated deaths to the current emission estimates and adjusting 

for the revised risk factor ranges The calculations are shown 

below and summarized in Table 6-4 ra) 

2.47 deaths x 129 kCi/y x ,1520 = 3.1 deaths/y 

202.7 kCi/y 760 

- 2.47 deaths x 129 kCi/y x 380 = 0.8 death/y 

202.7 kCi/y 760 

For the dry tailings condition with emissions of 238 kCi/y, 

the corresponding values are 5.8 and 1.4 deaths per year. 

fd) The 2.47 deaths from emissions of 202.7 kCi/y are from 

EPAk i983 report and were based on a risk of 760 deaths 

per 10 person WLM. 
Table 6-4. Summary of health effects beyond the 80-km region 

from tailings impoundments 

Condition of 

tailinqs 

Current 

All dry 

Emissions 

(kCi/y) 

Committed fatal 

cancers per year (a) 

(a) Values in firsg column are based on 1520 deaths due to lung 

cancer per 10 person WLM.6 The values in parentheses are 

based on 380 deaths per LO person WLM. 
Tine es.timated health effect:: from existing impoundments is 

shown in ?'able 6-5, This summary shows that about 3 fatal 

cancers per year can be attributed to tailings impoundments in 

their i:urrent conditions, and this cou1.d increase to 6 deaths 

per year if the impoundments d.ried and emissions increased, 

Radon-222 emissions will not increase yreatly until the 

current impoundments reach capacity and new impoundments are 

built. The need for new impoundments is directly related to 

industry growth. The health effects caused by new impoundments 

may be estimated by assuming a direct. proportion of effects to 

emissions. This procedure assumes that new ianpoundments will be 

located in the same geographical area as the existing 

impoundments and will have the same impact on surrounding 

populations. Emissions from model new tailings impoundments are 

estimated in Chapter 7 and will vary with the design and work 

practice 'used. 
Table 6-5. Smmaq of fatal cancers Crm 

cuz~ent tailings impoundments 

Condition Fatal cancers aer year (3) 

of tailhqs 

0-5 km 5-80 km National Total 

Current 0.3 (0.1) 1.6 (0.4) 3.1 (0.8) 4.9 (1,2) 

Dry 0.4 (0.1) 2.9 (0.7) 5.7 (1.4) 9.0 (2.3) 

(a) Values &n first colm are based on 1520 deaths due to lung cancer 

per 10 person6TCCM. The values in parentheses are based on 380 

deaths per 10 person WIM. 
REFERENCES 

Bu8 1 Bunger B., Cook J. R., and Barrick M. K., "Life Table 

Methodology for Evaluating Radiation Risk: An 

Application Based on Occupational Exposure", Health 

Physics 40, 439-455, 1981. 

EPA83 Environmental Protection Agency, "Final Environmental 

Impact Statement for Standards for the Control of 

Byproduct Materials from Uranium Ore Processing (40 

CPR l92), Volume I", EPA 520/1-83-0'08-1, Office of 

Radiation Programs, USEPA, Washington, D.C., 1983. 

M079 Moore R. E., Baes C. F. 111, McDowell-Boyer L. M., 

Watson A. P., Hoffman F. O., Pleasant J. C., and 

Miller C. W., ilAIRDOS-EPA: A Computerized Methodology 

for Estimating Environmental Concentrations and Doses 

to Man from Airborne Releases of Radionuclidesv, 

ORNL-5532, Oak Ridge National Laboratory, Oak Ridge, 

Tennessee, 1979. 

NRC79 Nuclear Regulatory commission, "Draft Generic 

Environmental Impact Statement on Uranium Milling, 

Volume II", NUREG-0511, USNRC, Washington, D.C., 1979. 
Chapter 7: RAL1ON-222 CONTROL, TECHNIQUES 

The reduction of radon-222 emissions at licensed uranium 

mill sites is accomplished most effectively by reducing the 

emissions from the tailings disposal area. Radon-222 emissions 

from the balance of the milling circuit are relatively small and 

are not easily controlled. At mills that are not operating and 

are on a standby basis, almost all of the radon-222 emissions 

come from the tailings disposal area. 

This chapter is concerned with control techniques that can 

be applied to licensed uranium mill tailings impoundments to 

reduce radon-222 emissions. A general discussion of radon-222 

control techniques is followed by more detailed discussion of 

controls for existing and new impoundments. 

Radon-222 emissions from uranium mill tailings can be 

controlled most easily by keeping the tailings covered with 

water or by covering them with earthen material. At new 

tailings impoundments, phased disposal of the tailings or 

continuous disposal by dewatering and immediate covering 

represent systematic ways of controlling radon-222 emissions 

using water or earth covers. Extraction of radium-226 from the 

tailings, chemical fixation, and sintering of tailings have been 

explored as means of reducing radon-222 emissions, but they have 

not been applied on a large scale and they appear to be too 

costly for general application (NRCBO). 

The applicability and effectiveness of control techniques 

depend primarily on the design of the mill tailings disposal 

area and the mill's operating schedule. Thus, the control 

techniques can be broadly classified as applicable to 

(I) existing tailings disposal areas at existing uranium mills, 

and (2) new tailings disposal areas at either new or existing 

uranium mills. 

7.1 Description of Control Pract* 

The most effective way of controlling radon-222 emissions 

is to cover the radium-bearing tailings with an impervious 

material. Earth and water are the cover materials most commonly 

used and are effective in reducing radon-222 emissions. These 

cover materials retard the movement of radon-222 long enough for 

it to decay in the cover material; thus, the decay products 

remain in the cover. 
Covering the deied beach area with earthen materials has 

been used to cunteol dust and radon--222 emissions at inactive 

tailings impoundments. The depth of earth required for a given 

amount of coaitrol varies with the type of earth and the rate at 

which radon-222 emanates from the bare tailings. 

F:artb cover restricts the diffusion of radon-222 long 

enough so that it will decay in the cover material. Radon-222 

diffusion ti~roiiqh earth is a complex phenomenon affected by 

processes such as molecular diffusion, described mathematically 

by Pi.ck0s law. These complex diffusion parameters have been 

evaluated by Rogers and Nielson (Ro81). They determined that 

diffusion depends greatly on the porosity and moisture content 

of the medium through which it occurs. Ideally, the diffusion 

coefficient should be measured experimentally for a given earth 

cover at its ambient moisture content and expected compaction 

level. This coefficiettt can. however, be estimated based on 

the moistuce content and porosity of the material. Clay soils 

have superior moisture retention (9 to 12 percent moisture) and 

are best for coveting tailings: clay soils are found in the 

uranium milling regions of Colorado. New Mexico. Utah. and 

Wyoming (Ro81). 

Cover thickness may be calculated by using the same 

diffusion equations that apply to emissions from uncovered 

tailjnqs as shown in the following equations (Ra84): 

2 where Jc is the flux through cover (pCi/m sj: St is the flux 

2 through tailings (pCiim s); bc is (h/~~)"~; g is the radon-222 

decay constant (2.1 x LQ-'~/s): Dc is the diffusion coefficient 

5 of cover. 0.07 exp I-4(m-mp2 + m )I; m is the moisture 

saturation fraction EO.01 M(l/p - l/gL M is the moisture 

content of cover material (percent dry weight): p is the bulk 

3 3 density (g/em ); g is the specific gravity (g/cm ): p is the 

porosity (I - p/gt; and x is the depth of cover matecial (em). c 

This simplified equation assumes that the physical 

parameters of the cover material, such as its density, specific 

gravity. moisture content, and porosity, are similar to those 

of the tailings. and that the tailings are sufficiently thick 

so that other terms approach a value of one. The flux through 

the cover material may be estimated by substituting values for 

the cover depth and the uncovered tailings flux. 
Effectiveness and Cost 

The approximate effectiveness of various types of earth 

cover in reducing radon-222 emissions is shown in Figure 

7-1. The application of almost any type of earth will 

initially achieve a rapid decrease in radon-222 emissions. 

One meter's depth of high-moisture-content earth such as 

clay will reduce radon-222 emissions by about 90 percent. 

In Figure 7-1 the earth types are categorized by their 

"half-value layerw (HVL). The HVL is that thickness of 

cover material (earth) that reduces the radon-222 flux to 

one-half its uncovered value. High-moisture content earth 

provides greater radon-222 emission reduction because of its 

smaller diffusion coefficients and its lower HVL values. 

The approximate reduction in radon-222 emissions achieved by 

applying selected types of earth at Q.5m, lm, 2m, and 

3 meter depths is shown in Table 7-1. 

In practice, earthen cover designs must take into 

account uncertainties in the measurements of the properties 

of the specific cover materials used, the tailings to be 

covered, and especially the predicted long-term values of 

equilibrium moisture content for the specific location. 

Predicting long-term moisture content requires specific 

knowledge of the earthen cover to be used and the climatic 

conditions (Ha84, Ge84). Proper consideration of these 

factors at the design stage help ensure that radon-222 

emissions remain constant over the long term. In predicting 

reductions in radon-222 flux, uncertainty increases when the 

required radon-222 emission limit is very low. 

The cost of applying earth covers varies widely with 

location of the tailings impoundment, its layout, and 

availability of earth. Costs also depend on the size and 

topography of the disposal site, its surroundings, the 

amount of earth required, and the hauling distance. Another 

factor affecting the costs of cover material is ease of 

excavation and the type of excavating equipment used. In 

general, the more difficult the excavation, the more 

elaborate and expensive the equipment is and the higher the 

cost. The availability of such materials as clay will also 

affect costs. Large deposits of bentonite and similar clays 

are found in Wyoming and Utah, and smaller deposits are 

found in all the Western States. If the necessary materials 

are readily available locally, no incremental costs would be 

incurred; if they must be purchased or hauled, costs could 

increase 'significantly. Cost factors for earth cover 

application are given in Table 7-2, and more detailed cost 

factors are presented in Appendix B. These are direct 

costs, and they do not include indirect costs such as 

engineering design and permit costs, insurance, or a 

contingency. Indirect costs would add approximately 

30 percent to the direct charges. 
EARTH TYPE HVL (mj % MOISTURE 

90 A SANDY SOIL 

6 SOIL 

C SOIL 

0 1 2 3 4 5 6 7 

EARTH COVER THICKNESS (meters) 

Figure 7-1. Changes in radon-222 penetration with earth 

cover thickness. (adapted from FPA53) 

7-4 
Table 7-1. Percentage reduction in radon-222 emissions attained by 

applying various types of earth cover 

Depth of earth cover (m) 

Earth type (a) HVL(m) 0.5 1.0 2.0 3.0 

(a)~ee Figure 7-1. 
Table 7-2, Summy of unit costs for estimating mer costs (a) 

Task Unit cost ($) 

Grading, self-propelled scraper, 1000-ft haul 

Excavati.on, elevating scraper, 5000-ft haul 2 -4 6/& 

Compaction, vibrating l.OO/yd 3 

Excavation, front-end loader, truck-loaded 0. 84/yi3 

Hading, 12-yd dq truck, 2-mile round trip 2. 35/yd3 

Fencing, 6-ft, aluminized steel 11.3O/linear ft 

Riprap, machine-placed slope protection 2 L.oo/~~~ 

BO~CX~~) ban?-?-m gravel 6.60/yd3 

(a) Euilding Construction Cost Eats 1985, R. S. Means Co., Ic. , 43rd Annual mitian, 1984. 
Based on the cost factors and the required earth thickness 

shown in Figure 7-1, the resulting total costs per hectare for 

earth cover can be estimated (as shown in Table 7-3) for 

selected emission or flux ievels and a bare tailings radon-222 

emission rate of 280 pCi/m s. These costs only take into 

account the earth moving and placement costs; they do not 

include any indirect charges or final closure costs, such as 

riprap or reclaiming borrow pits. They are presented to show 

the variation in costs among the different types of soil. 

For a model 50-ha (124-acre) tailings impoundment, the 

approximate direct earth moving sost to achieve p 64 percent 

reduction (from 280 to 100 pCi/m s) is $5.2 x lo0 (50 ha x 

$105,00O/~a = $5,250,000) with a fairly dry type A earth and 

$1.4 x 10 for a more moist type D earth. 

Earth cover is applied to dry tailings with conventional 

earth-moving equipment and engineering practices, However, some 

areas, especially the sloped sides of dams constructed of coarse 

tailings, may be difficult to cover without recontouri.ng the 

pile. Dams constructed of coarse tailings are located at six 

mill sites, mainly in New Mexico. The slope of the sides of 

these dams is 2:l or steeper. Some of these dams have heights 

of 100 ft or more. These sloped areas represent about 8 percent 

of the total tailings area. At least one site, Uravan in 

Colorado, has applied a partial earth cover to the sloped sides 

of dams constructed of tailings, which would indicate that this 

is a feasible practice. 

7.1.2 Water Cover 

Maintaining a water cover over tailings reduces radon-222 

emissions. The degree of radon-222 control increases slightly 

with the depth of the water. Factors affecting this practice 

include the mill water recirculation rate (if any), evaporation 

and precipitation rates, impoundment construction and slope, 

phreatic levels, ground-water contamination potential, and dike 

or dam stability. Some above-ground tailings impoundments 

minimize the depth of water to reduce seepage and possible 

ground-water contamination by draining the water through an 

overflow pipe to a separate evaporation pond. All uranium mill 

surface impoundments are subject to ground-water concentration 

standards as specified in 40 CPR Subpart D 192.32 and 

incorporated in NRC criteria for tailings impoundments (10 CFR 

40, Appendix A). These strict ground-water contamination 

standards will frequently determine the type of impoundment 

design and degree of water cover maintained in an active area. 

An impoundment liner and ground-water monitoring programs willbe required for new installations. 
Table 7-3. Earth mwing and placement costs (thousands of dollars per hectare) (a) of attenuating 

radon-222 as a function of thickness (meters of different soils) and type of earth 

Earth ,,(b) 

Final 31UX(c) 

(@i/m S) Cost Thickness Cost Thickness Cost Thickness Cost Thickness Cost Thickness 

200 34 0.49 25 0.36 17 0.24 10 0.15 4 0.06 

3 3 3 (a) Cost basis: $7.00/in ($5.35/yd ) of soil cover material; includes excavating ($0.84/yd ) , hauling 

3 3 ($2.35/~a ) , spreading (sL.~G/Y~ ) , and carpacting ($1. 00/yd3) , in 1.985 dollars. 

(') See Figure 7-1. 

2 (') Based on initial radon-222 emission rate of 280 pCi/m s. 
Effectiveness arid Cost 

Ths diffusion coefficient of water is very low (1.1 x 

cm /s), about one-thousandth of that of soil with a 

9 percent moisture content. Thus, water is an effective barrier 

for radon-222. In shallow areas, the release of radon-222 

dissolved in water is increased by thermal gradients and wave 

motion, and emissions approach those of saturated tailings. 

Increased radium-226 content in the water reduces its overall 

effectiveness in controlling radon-222 because the solution also 

releases radon-222. For a water depth less than 1 meter, the 

flux rate is similar to that of saturated tailings and may be 

estimated by Equation 3-1 as presented in Section 3. 

Water-covezed tailings have a radon-222 flux of about 

0.02 pCi/m s per pCi of radium-226 per gram of taiiings 

compared with a dry tailings flux of about 1 pCi/m s per pCi 

of radium-226 per gram, or a radon-222 reduction efficiency of 

about 98 percent (PEI85). Emission estimates of zero are 

frequently used for ponded and saturated areas, and that 

assumption is used throughout this report (Ha85) (EPA83). 

If a pond is initially designed and built to maintain a 

water cover, there is no added cost for this form of radon-222 

control. Continued monitoring is required to determine if any 

seepage is occurring through the dam or sides, and ground-water 

samples may be required periodically as a check for 

contamination. 

7.1.3 Water Sprayinq 

Water (or tailings liquid) sprays can be used to maintain a 

higher level of moisture in the tailings beach areas. This 

reduces fugitive dust emissions and may reduce the diffusion of 

radon-222 through the tailings; however, ground-water 

.contamination may be increased at some sites. The effectiveness 

of this method varies with the moisture content of the 

tailings. As shown in Figure 7-2, the radon-222 emanation 

coefficient initially increases with increasing moisture content 

up to about 5 to 10 weight percent moisture and then remains 

fairly constant. Thus, if water is applied to a very dry beach 

area, radon-222 emissions may initially increase because of a 

larger emanation coefficient. As the moisture increases, 

however, the diffusion coefficient will decrease. These 

mechanisms (both affecting radon-222 emissions) "compete" at low 

moisture levels. Whereas some reports (NRC80) estimate that 

wetting can achieve an overall radon-222 reduction of 20 

percent, others (ST82) have stated that by wetting tailings at 

low moisture levels, a larger emanation coefficient may outweigh 

the effects of a lower diffusion coefficient and result in 

increased emissions at low moisture contents. The overall 
- 

0 0.2 0.4 0.6 0 .pl l .O 

MOISTURE SATURATION, m 

Figure 7-2. Radon emanation coefficients for tailings samples 

(Ro84). 
feasibility of wetting to achieve significant radon-222 

reductions is questionable, especially in arid regions, because 

large quantities of Liquid are required to maintain high moisture 

levels. 

7.1.. 4 0t.her Control Techniques 

Several other radon-222 control techni-ques have been 

evaluated. Although none of these methods has been applied on a 

large scale, they are described briefly here as part of this 

Background Information Document. 

.. 

Ssthetic - Covers 

Synthetic material, such as polyethylene sheet, can reduce 

radon-222 emissions if carefully placed on dry bgackj areas and 

sealed. Diffusion coefficients of less than 10 cm /s have 

been measured for synthetic materials (RoSI.) . Such covering 

could he used on portions of the tailings on a temporary basis 

and then removecj. or covered with fresh tailings. Such a barrier 

also would aid, at Least temporarily, in the control of radon-222 

if a soil cover material were subsequent.1~ applied. ?'he overall. 

effectiveness of synthetic covers is not known because leaks 

occur around the edges and at seams and breaks. Synthetic covers 

have a limited :Life, especially in d.ry, silnny, windy areas, and 

will not provide a long-term barrier to radon-222. The cost of 2 installing polyethylege material. is about $O,Ol/ft per mil of 

thickness or $0.50/ft" for 50 mil material, which is equivalent 

to about $53 ,800/ha ($Z1,750/acre) , 

Chemical stabilization sprays that form coatings on the dry 

tailings are effective for controlling dust, but they are not 

useful for suppressing radon-222 because they do not provide an 

impermeable cover. 

Asphalt cover systems have been proposed as a radon-222 

cont,rol technique because such systems exhibit very low rad.on-222 

diffusion coefficients, The Pacific Northwest Laboratory (PNL) 

has investigated controlling the release of radon-222 through use 

of asphalt emulsi-on covers for several. years for DOG" Vraniurn 

Mill Tailings Remedial. Action Project (UMTRAP), Results nave 

shown asphalt emulsion cover systems to be effective at 

substantially reducing radon-222 emissions, and field tests 

indicate that such systems have the properties necessary for 

long-",rm'effectiveness and stability. Of the various types of 

asphalt cover systems that were researched, an asphalt emulsion 

admix seal was found to be the most effective (Ka84, Ba84). 
Costs of applying a full-scale asphalt cover were estimated 

to be $24,20/m ($20.23/yd) in 1981 dollars or $lB0,000/acre 

(Ba84). These cost estimates are probably applicable to 

relatively flat sites. Existing uranium mill tailings 

impoundments may have to be regraded before these techniques 

could be applied. Cover protection, in the form of gravel or 

revegetation, above an earthen cover applied over the asphalt 

radon-222 barrier to protect it may also have to be considered. 

Asphalt cover systems could prove to be economically competitive 

with earthen covers at some existing sites. Site-specific 

evaluations would have to be performed that analyzed the amount 

of earth required as well as its availability and cost versus the 

cost of applying an asphalt cover system. An ample supply of 

earthen material should be available as a final cover of new 

uranium mill tailings impoundments that are constructed below or 

partially below grade; such a supply would probably make an 

asphalt cover system economically unattractive. 

Thermal Stabilization 

Thermal stabilization is a process in which tailings are 

sintered at high temperatures. The Los Alamos National 

Laboratory has conducted a series of tests on tailings from four 

different inactive mill sitesowhere ta&lings were sintered at 

temperatures ranging from 500 to 1200 C (Dr81). 

The results show that thermal stabilization effectively 

prevented the release (emanation) of radon-222 from tailings. 

The authors note, however, 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 with 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. 

Gamma radiation is still released after sintering; 

therefore, protection against the misuse of sintered tailings 

would be required. Although the potential health risk from 

external gamma radiation is not as great as that from the 

radon-222 decay products, it can produce unacceptably high 

exposure levels in and around occupied buildings. Also, the 

potential for ground-water contamination may require the use of 

liners in a disposal area. 
Chemical Processinq 

The Los Alamos National Laboratory has also studied various 

chemical processes for the extraction of thorium-230 and 

radium-226 (precursors of radon-222) from the tailings along with 

other minerals (Wm81). After their removal from the tailings, 

the thorium-230 and radium-226 can be concentrated and fixed in a 

matrix such as asphalt or concrete. This greatly reduces the 

volume of these radioactive materials and permits disposal with a 

higher degree of isolation than economically achievable with 

tailings. 

The major question regarding chemical extraction is whether 

it reduces the thorium-230 and radium-226 values in the stripped 

tailings to safe levels. If processing efficiencies of 80 

percent to 90 percent were attained, radium-226 concentrations in 

tailings would still be in the range of 30 to 60 pCi/g. Thus, 

careful disposal of the stripped tailings would still be required 

to prevent misuse. Another disadvantage of chemical processing 

is the high cost, although some of the costs might be recovered 

from the sale of other minerals recovered in the process (Th81). 

Soil Cement Covers 

A mixture of soil and portland cement, called soil cement, 

is widely used for stabilizing and conditioning soils (PC79). 

The aggregate sizes of tailings appear suitable for producing 

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 likely provide reasonable resistance 

to erosion and intrusion, could be expected to reduce radon-222 

releases, and would shield against penetrating radiation. The 

costs are expected to be comparable to those of thick earth 

covers. 

The long-term performance of soil cement is unknown, 

especially as tailings impoundments 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 for radon-222 control has not been 

evaluated. 

Deep-Mine Disposal 

Disposal of tailings in worked-out deep mines offers several 

advantages and disadvantages compared with surface disposal 

options. The probability of intrusion into and misuse of 

tailings in a deep mine is much less than that of surface 
disposal. Radon-222 releases to the atmosphere would be reduced, 

as would erosion and external radiation. This method, however, 

has potential for ground-water contamination problems. Also, it 

could be costly, depending on the mine location and the controls 

required to guard against potential ground-water contamination. 

7.2 Control Practices Applicable to Existinq Tailinqs 

Impoundments 

Control practices that are applicable to existing tailings 

impoundments are limited to application of earthen covers, or 

possibly asphalt mixtures, to dry areas, and maintaining or 

expanding the area of tailings covered by water (if it were 

determined that ground-water impacts would not result). Either 

interim (i.e., short-term) or final (i.e., long-term) controls 

could be applied. Interim control is the application of a cover 

that reduces radon-222 emissions but that does not meet the 

requirements of final reclamation. Standards for final 

reclamation include rsquirements for reducing average radon-222 

emissions to 20 pCi/m s and for long-term (1000 y) stability 

and protection against misuse. 

7.2.1 Interim Controls 

Application of an interim earthen cover on the dry portions 

of tailings impoundments could reduce radon-222 emissions over 

the period of licensed operation and prior to final reclamation. 

For example, a 0.3 m (1 ft) or 1 m (3.3 ft) thick earth cover 

having 8 percent moisture content would theoretically reduce 

radon-222 emissions by about 25 and 62 percent, respectively 

(Table 7-1). There are many unknowns regarding the 

effectiveness, applicability, timing, and operational aspects of 

interim cover. These items are discussed below and more fully in 

Appendix C. 

The operational status (at capacity, standby, or active) and 

the type of construction (dams constructed of coarse tailings, 

earth dams, or below-grade lined impoundments) control the extent 

to which interim cover could be applied. Interim cover could be 

applied immediately to most dry areas of existing impoundments 

(excluding dams). Currently, about 50 percent of the total area 

of existing impoundments is dry (Table 4-2). Ten existing 

impoundments have been filled to capacity. These impoundments 

represent about 14 percent of the total area and about 25 percent 

of the total area that is currently dry (the dry areas are the 

major sources of radon-222 emissions as discussed in Chapter 3). 

Impoundments that are at capacity could be covered immediately 

because they have already dried and because they will never be 

used again for tailings disposal. 
Site characteristics that control or prohibit the 

applicability of interim cover include impoundment design and 

construction; dam height; stability; phreatic level; 

permeability; site water balance; evaporation rates; presence and 

location of movement monitors, monitor wells or piezometers; and 

availability of suitable earth cover material. Operating factors 

such as expected uranium production rate, length and number of 

standby periods, impoundment capacity, and expected mill life 

also affect the applicability of interim cover. 

At active impoundments, only those areas that are not to be 

used further would be covered. Which areas could be covered are 

a function of expected mill life and quantity of tailings, the 

size of tailings impoundment, the level of tailings generated 

(percentage of capacity), and the operational practices used to 

construct the impoundment. In addition, a source of cover 

material must be obtained and a technique must be developed for 

hauling, dumping, spreading and compacting the earth cover onto 

the beach area. Limited access to the tailings area and the 

stability of the dam would affect the size of the equipment that 

can be used to transport and spread the cover material. Metal 

gratings or timbers may be required to distribute vehicle wheel 

loads on the dike or dried beach area to facilitate the use of 

earthmoving equipment. These site-specific factors would 

increase earthmoving costs. 

Of the existing tailings impoundments, 11 have sand tailings 

dams and are above ground, 22 have earthen dams and are above 

ground (4 of these are lined), and 5 are below grade and lined. 

Currently, all tailings impoundments at licensed mills must limit 

radon-222 to as low as reasonably achievable (ALARA) levels, as 

specified in 40 CFR 192. Work practices or emission limits are 

not specified, however. Mills that are on standby and have begun 

or are about to begin the decommissioning process will evsntually 

cover the tailings areas and reduce emissions to 20 pCi/m s as 

required by Federal regulations. Mills that wish to retain their 

operating licenses do not have to begin their final 

decommissioning process, but they could take some interim actions 

to minimize radon-222 emissions. Interim cover as a means of 

reducing radon-222 emissions to air from operational tailings 

impoundments is difficult to apply as new tailings beach areas 

are continuously being formed. 

Covering the currently dry beach areas, excluding dams, with 

1 meter of earth and maintaining the current water cover on the 

ponded and wet beach areas would reduce radon-222 emiss o s from 

129 kCi/y to about 69 gCi/y, a reduction of 46 percent, tar at a 

cost of about $63 x 10 (1985 dollars). Additional details 

regarding the applicability, timing, and operational aspects of 

interim cover are discussed in Appendix C. 

(a) Based on soil with 7.5 percent moisture content. 

7-15 
The feasibility of maintaining water cover is Limited 

because of potential site-specific factors such as seepage, 

ground-water contamination, and dam stability problems, For an, 

existing above-ground tailings impoundment, many si.te-specific 

factors cannot be readily changed, and the feasibility of water 

cover is limited, mainly because of dike stability and seepage. 

Also, during extended standby periods, maintaining the water 

cover would be difficult, especially in arid areas. Ideally, the 

impoundment would be lined and constructed to allow approximately 

a 1-meter depth of water cover and have an overflow pipe leading 

to an adjacent evaporation pond and/or for recycling to the 

mill. The use of water cover would require maintaining 

sufficient freeboard to prevent overflow and the monitoring of 

ground water. Eight impoundments are lined, representing 

11 percent of the total tailings area and 9 percent of the dry 

exposed tailings areas. Five of these impoundments are below 

grade. The water cover on these lined impoundments could be 

increased to reduce radon-222 emissions from the 200 acres of dry 

tailings that they currently contain. The potential for 

increased ground-water contamination, however, would limit the 

use of this radon-222 control option. 

7.2.2 Final Reclamation 

If a11 existing impoundments were allowed to dry, 2nd were 

covered with enough earth to achieve a flux of 20 pCi/m s, the 

total radon-222 emissiong would be reduced to 8 kCi/y. The cost 

would be about $660 x 10 . For ongoing mil-ling operations, new 

tailings impoundments would be built and work practices would be 

instituted to reduce emissions. 

Bringing existing impoundments to final reclamation entails 

substantially more effort than effecting interim control 

measures. After the sand tailings dams have dried, they are 

recontoured to 5:1 (H:V) slopes for long-term stability. Earth 

dams were not recontoured in the cost estimates presented in this 

section. The cost of enough e2rth (8% moisture) to attenuate 

the radon-222 flux to 20 pCi/m s is placed over the tailings. 

The earthen cap is covered with gravel to protect the top 

surface, and the riprap is used to protect earth-covered side 

slopes from erosion. The cost estimate also includes reclaiming 

the on-site borrow pits that are assumed to be the source of 

earthen cover material. 

7.2.3 Comparison of Interim and Final Controls 

Estimates of the reduction in emissions, the avoided fatal 

cancers, and the costs of applying earth cover to achieve various 

control alternatives are summarized in Table 7-4, Covering the 
Table 7-4. Benefits and wsts of alteaatives that apply earth cover 

to existing tailings impoun&ents 

Alternative 

Radon-2 2 2 

emissions Avoided fa Cost (b) 

(kCi/~) cancers/y 

Current After 0-80 km National 

Cease use of current h- 129 8 1.7(0.5) 2.9(0.7) 660 

poun&&s, allow to dry 

and apply final cover. 

Cover current dry areas 12 9 69 0.8(0.2) 1.5(0.4) 63 

with l m of earth. 

6 (a) Values are based on 1520 deaths due to lung cancer per 12 person WLM. 

The values in parentheses are based on 380 deaths per 10 person WLM. 

(b) Total cost, including indirep charges. Final cover includes earth 

rewired to achieve 20 pCi/m s, regrading sand tailings dams to 

5: 1 (H:V) slop, riprap on sides, and gravel on top of ~unc3ments 

(1985 dollars). 
currently dry areas, excluding dams and evaporation ponds, with a 

meter of earth achieves a .theoretical estimatgd reduction in 

emissions of 46 percent at a cost of $63 x 10 (1985 dollars) 

and prevents from 0.6 to 2.36cancers per year (based on a range 

of 380 to 1520 deaths per 10 person WM). Total avoided 

cancers are the sum of avoided cancers in the 0-80 km region and 

the national (i. e. , outside the 0-80 km region) . An estimated 

emission reduction of 94 percent can2be achieved by applying 

sugficient cover to achieve 20 pCi/m s; this would cost $660 x 

10 (1985 dollars) and prevent from 1.2 to 4.6 cancers each 

year. (These cost estimates are for the control practice only 

and do not include the cost of establishing new impoundments. In 

addition, these estimates have not been discounted.) This 

comparison shows one pcin,t in time only. It does not reflect 

reapplications of interim cover required after restarting of 

operations at specific sites or changes in emissions due to 

interim cover deterioration. Annual maintenance costs that would 

occur over time are also not included. 

7.3 Control Practices Applicable to New Tailinss Im~oundments 

New tailings-disposal impoundments at uranium mills can be 

designed to incorporate radon-222 control measures. Three 

different kinds of new model impoundments are considered: 

single-cell, phased disposal, and continuous disposal of 

dewatered tailings. Descriptions of radon-222 emissions and 

estimated costs of the three types of new model tailings 

impoundments are presented in the following sections. 

Below-grade impoundments are the NRCps preference, as this 

method minimizes potential for windblown emissions and water 

erosion and eliminates the potential for dam failure (NRCBO). 

Although below-grade disposal is preferable, well-designed and 

operated above-grade tailings impoundments can also provide 

adequate safety and be licensed by the NRC. 

7.3.1 Sinqle-Cell Tailinqs Impoundment 

New tailings disposal areas must conform with Federal 

regulations (40 CFR 190 and 192 and LO CFR 40) for prevention of 

ground-water contamination and airborne particulate emissions. 

New impoundments will also be designed to facilitate final 

closure as required by current Federal Standards. New tailings 

areas will have synthetic liners, will probably be built below or 

partially below grade, and will have earthen dams or 

embankments. A means for dewatering the tailings at closure also 

should be incorporated. This basic layout is amenable to 

maintaining a water cover over nearly the entire tailings area 

during the operational phase and standby periods; therefore, it 
will maintain a very low level of radon-222 emissions. The 

drainage system can be used to accelerate dewatering of the 

tailings when the impoundment is full. 

Effectiveness and Cost 

A model single-cell impoundment was used to estimate 

radon-222 emissions and the effectiveness of single-cell tailings 

impoundments. The basic design and layout of this impoundment 

are consistent with previous uranium mill tailings studies. The 

impoundment is a square sloping pit containing a 12-meter depth 

of tailings and having a final tailings surface area of 47 ha 

(116 acres), as shown in Figure 7-3. A synthetic liner is placed 

along the sides and bottom. It handles about 2000 tons/day of 

tailings over a 15-year active period. During operation, 20 

percent of the surface area is assumed to be dry beach and the 

remainder is assumed to be water-covered. Cover material is 

applied after the impoundment has reached capacity or is not 

going to be used further and the tailings have dried. Emissions 

average 0.8 kCi/y during the operational 15-year life and 

increase after drying begins, as shown in Figure 7-4 and 

Table 7-5. 

Emissions are constant at approximately 4.2 kCi/y after the 

tailings are dry. If an earth cover is applied after drying, 

emissions can be reduced (as shown in Figure 7-4 and Table 7-5) 

to about 0.30 kCi/y with 3 meters of earth (Type B soil, 8 

percent moisture as shown in Figure 7-1). Total emissions during 

the 5-year drying period amount to 12.5 kCi. 

The approximate costs for constructing a new single-cell 

impoundment are shown in Table 7-6 for a below-grade design and a 

partially above-grade design. The cost of a new impoundment 

would vary widely, depending mainly on the site-specific 

topography and the ease of excavation. The total cgst for a 

below grade impoundment is approximat&ly $41.3 x lg , including 

a final cover cost gf about $6.0 x 10 ($4.15 x 10 for earth 

cover and $1.9 x 10 for gravel cap). The partially 

above-grade design is identical to the below-grade design except 

that 6 m (19.6 ft) of tailings are below grade and 6 m (19.6 ft) 

are above grade and surrounded by an earthen dam. This design is 

less costly because of the savings result&ng from decreased 

excavation. The cost is about $29.7 x610 . Final closure 

costs are slightly higher at $7.8 x 10 , as riprap is required 

on the sides of the dam. 
VEL FOR 

IMPOUNDMENT 

SECTION A-A 

TAILINGS CAPACITY = 1800 t/d x 310 d/y x 15 y = 8.4 x lo6 t 

6 3 TAILINGS VOLUME = 8.4 x lo6 t + 1.6 t/m3 = 5.25 x 10 in 

FINAL TAILINGS SURFACE AREA = 47 ha (116 acres) 

DIAGRAMS ARE NOT TO SCALE. 

Figure 7-3. Size and layout of the model single-cell tailings impoundment. 

7-20 
Figure 7-4. Estimated radon-222 emissions from a model 

single-cell tailings impoundment. 
Table 7-5. Average radon-222 emission rat 

from model sinqle-cell tailinqs impoundments ?a) 

Time period Emissions (kCi/y) 

Year 0-15 

Year 15-20 

Year >20 

0.8 

2.5 

4.2 uncovered 

0.3 with 3 meters 

of earth 

(a) For 47-ha new model impoundment with 15-year life 

and 5-year drying-out period. Emissions are based 

on 280 psi Ra-226/g and a specific flux of 1 pCi 

Rn-222/m s per pCi Ra-226/g of tailings when dry. 
Table 7-6. Esthted costs for a model sinyle--@+1 tailings 

jJlW5~~1.&en'r. 

costs ($ x lo6) 

Item &1ow grade 

Excavation 

Synthetic liner (30-mil) 

Gradinq 

Drainaqe system 

Dam construction 

Cover (3-m) 

Gravel cap (0.5-m) 

Riprap on slopes 

Partially 

above grade (b) 

Subtotal dire @) cost 

31.31 

Indirect cost 10.02 

Total cost 41.33 2s. 71 

(a) Below-grade inpundments are construded so that the top of the 

final cover is at grade. 

(b) Fifty percent b1ow qiade and 50 percent abuve grade. 

(') Indirect costs are estimated to be 32 percent of direct costs, 
7,3.i Phasee-Df~sgosal Tailipczs I~~~o~~ndment 

In phased-disposal systems, a tailings area is partitioned 

into sections or cells that are used independently of other 

sections. After a cell has been filled, it can be dewatered, 

dried, and covered while another section is in use. In practice, 

one or two lined cells would be constructed initially. Tailings 

are pumped to the first cell until it is filled and then pumped 

to the second cell while the first cell is dewatered and allowed 

to dry. After the first cell has dried, it would be covered with 

earth obtained from the cells excavation. This process continues 

sequentially. This system reduces emissions at any given time, 

as a cell can be covered after use without interfering with the 

operation of subsequent cells. Standby periods do not present as 

great a problem and construction of new cells can easily be 

postponed. Less total tailings surface area is thus uncovered at 

any one time compared with operation of the model single-cell 

impoundment, which is uncovered until mill closure aria the 

impoundment dries. 

Several existing mills have either proposed or implemented 

phased-disposal systems. At the Plateau Resources Shootaring 

Canyon Mill in Utah, an earthen dam has been constructed across a 

valley. Behind this dam, earthen beams have been constructed to 

form six cells for tailings disposal. Currently, only one cell 

contains a significant quantity of tailings. Umetcoss White Mesa 

Mill, also in Utah, uses a phased tailings disposal system 

designed to feature simultaneous construction, operation, and 

reclamation. Three cells of a proposed six-cell system have been 

constructed. These impoundments are lined with either clay or 

synthetic liners. Minerals Exploration" Sweetwater Mill also 

has a planned phased-disposal system. One cell of a proposed 

multicell impoundment system has been constructed. This system 

has gone through several iterations during development. 

Originally, it was designed to consist of four square, 

below-grade cells. 

Effectiveness and Cost 

Phased disposal is effective in reducing radon-222 emissions 

because tailings are assumed to be completely covered with water 

during cell operation and, finally, with soil. Only during the 

drying-out period (about 5 years for each cell) do any radon-222 

emissions occur, and these are from a relatively small area. 

During mill standby periods, a water cover could be maintained on 

the operational cell. For extended standby periods, the cell 

could be dewatered and an earth or synthetic cover applied. To 

estimate radon-222 emissions, a model phased-disposal impoundment 

comparable to the model single-cell impoundment was used. This 
impoundment consists of six cells, and each cell ho1.d~ one-sixth 

of the mill tailings generated during a 15-year operational 

period (i.e., 2 years worth of tailings). Each cell is square 

with a tailings depth of 12 meters and a trapezoidal cross 

section, as shown in Figyre 7-5. The total tailings surface area 

at capacity is 86,260 m per cell. 

Emissions from a cell during operation are zero because the 

cell is covered with water. After the first cell reaches 

capacity, it is dewatered and begins a 5-year drying period. 

Over this period, radon-222 emissions gradually increase up to a 

rate of about 0.8 kCi/y, at which time the cell is dry and soil 

cover is applied. Meanwhile, the second cell has begun drying 

and also contributing emissions. Emissions thus increase at 

2.5-year intervals as the cells reach capacity and begin their 

drying out periods. The emission rates occurring after 3 meters 

of earth cover have been applied to dry cells are shown in Figure 

7-6. Earth cover of the first cell is not started until after 

7.5 years have elapsed. After the final 5-year drying period for 

the last cell is complete (at the 20th year), this cell is also 

covered and emissions are then constant at 0.33 kCi/y. 

Total emissions during the 20-year operating life of this 

impoundment are 13.5 kCi. Average radon-222 emission rates are 

shown in Table 7-7. During the operational phase, the average 

emission rate of 0.7 kCi/y is lower than that for a single cell 

impoundment (1.2 kCi/y). In the post-operational period, 

emissions from a phased-disposal impoundment are much lower than 

those from uncovered single-cell impoundments and equivalent to 

those from single-cell impoundments with the same respective 

earth cover. 

Estimated costs of buil-ding phased-disposal impoundments are 

shown in Table 7-8. The total cost. of below-grade phased 

disposal, at $47.88 x LOG, is greater than the cost of a 

single-cell impoundment with similar earth cover, but the costs 

are incurred over a 20-y period. This cost is based on a 12-m 

tailings depth (similar to the model single-cell impoundment). 

An evaporation pond is included as part of the phased-disposal 

system. The cost for a p rtially above-grade phased-disposal i: sygtem is about $6.9 x 10 per cell, or a total of $41.5 x 

10 . The decreased cost of excavation is partially offset by 

the dam construction cost and the riprap on the sides. 

Numerous variations in the model phased-disposal impoundment 

are conceivable. An impoundment could be designed to include any 

number of cells, each capable of containing an equal amount of 

the mill tailings generated during a 15-year operational period. 

As an example, a below-grade, phased-disposal impoundment 

utilizing three cells was investigated. 
GRADE LEVEL FOR 

DE DESIGN 

SECTION A-A 

NOTES: 

TAILINGS CAPACITY PER CELL = 1800 t/d x 310d/y x 15y + 6 CELLS = 1.4 x lo6 t/CELL 

5 3 TAILINGS VOLUME PER CELL = 1.4 x lo6 t/CELL t 1.6 t/rn3 = 8.75 x 10 rn /CELL 

FINAL TAILINGS SURFACE AREA = 8.6 ha/CELL (21.3 acre/CEL~) 

DIAGRAM IS NOT TO SCALE 

Figure 7-5. Size and layout of model phased-disposal impoundment. 
RADIUM CONCENTRATION - 280 pCi Ra-226/g 

2 SPECIFIC FLUX - 1 pCi Rn-222/m s per 

- pCi Ra-226/g FOR DRY AREAS 

-. h 3 

.,- 

U 

- Y 

v, 

Z - 0 

- 2 

E 

W 

N 

N 

N 

I 

Z 

0 

1 :: 

0 

0 5 10 15 2 0 

YEAR 

Figure 7-6. Estimated radon-222 emissions from a model 

phased-disposal impoundment. 
Table 7-7. Average radon-222 emission rate for model singlecell and phased-disposal tailings impoundments 

Average emission rate (kCi/y) (a) 

Operational phase (b) Post-operational phase 

Single-cell 1.2 

Phased-diswsal 0.7 

4.2 Uncovered 

0.30 covered with 3 m of earth 

0.33 covered with 3 m of earth 

(a) For new mdel impoundment with 15 yr. life and 5 yr. drying perid for 

each cell. ?&$ssions hsed on 280 pCi Ra-226/g and specific flux of 

l pCi Rn-222/m s per pCi Ra-22G/g of tailings when dry. 

(b' Assumes a 5-y drying-out period for each cell and irmnediate cover of 

3m of earth. 
Table 7-8. Estimated costs for a model phased disposal impoundment (a) 

6 ($ x 10 ) 

Item 

Below wade Partially above made 

One cell A11 cells One cell All cells 

SynEhetic liner 0.57 3.40 0.57 3.40 

(30-mil) 

Grading 0.07 0.45 0.07 0.45 

Drainage system 0.07 0.40 0.07 0.40 

Dam contruction - - 1.27 7.61 

Cover (3 m) 0.76 4.57 0.76 4.57 

Riprap on slopes - - 0.32 1.91 

(0.5 m) 

Gravel cap (0.5-m) 0.37 2.21 0.39 2.34 

Evaporation pond 0.52 3.09 0.52 3.09 

Subtotal direct 6.04 36.20 5.25 31.47 

cost 

Indirect cost (b) 1.93 11.58 1.68 10.07 

Total cost 7.97 47.78 6.93 41.54 

(a) Below-grade impoundments are construct& so that the top of the 

final cover is at grade. Partially above-grade impoundment is 

6 m below grade and 6 m above grade. 

(b) Indirect costs are estimated to be 32 percent of direct costs. 
Comparecl v;it.h 'chi: rdesiyi of the p)re\iioui;?y~-di.scu.?st?d 

phased-disposal impo~rr:drnc'rrt with s:i.-, cel:l.s, the ti- I. -. 6-2 ?---Q~ i..i.i,A 

impoundment i.s conceptual1.y i.rle?n"r!;cai except that each. cell s 

cxpacity is now doubl.ed. liecause the total surface area of a .A" ~hree-cell impoundment is somewha% l.ess than that of a six-cell 

impoundment some redi~ctions in cost and emi.ssions are ef f ec'ted a 

The estimated cost of a below-ggade, phased-disposal impoungment, 

with three cells is $46.50 x 10 , compared with $47.88 x 10 

foir six cells. The average radon-222 emission rate during .the 

operati.onal pilase o:€ a three-cell iinpoundment is 0, 62 kC.i./y, 

compared with 0.6'7 kCi/y for six eel-ls, and during the 

post-operational phase, the emissj.ons are 0,3l and 0.33 kCi/y, 

respective1 y , 

Water c<?n be removed from the tailings slurry prior to 

disposal. The relatively dry, dewatered (25 to 30% moisture) 

tailings can be placedand covered with soil almost immediately. 

No extended drying phase is necessary. Ground-water problems 

would also be reduced. Implementation of a dewatering system 

would require added planning, design, and modification of current 

designs. Acid-based 1-eaching processes do not generally recycle 

water, and larger evaporation ponds with anci.l:lary piping and 

pumpi-ng systems would be required to handle the liquid removed 

from the tailings, 

n ~ailings dewatering systems have been used successfully at 

noilferrous ore henefi.ci.at:i.on mi!.ls ii? the United States and 

Canada (Ro78) . Various f il.t:ering systems, such as rotary, 

vacuum, and belt filters, are available and could be adapted to a 

uranium tailings dewatering system, Experimental studies would 

be required for a specific- , ore to determine the filter media and 

dewatering properties of the sand and slime fracti.ons. The 

typical mi.ll. ore griiiding ci1:cul.t may have to be modified to 

permit efficient dewatering and to prevent :filter plugging or 

bi-nding. Corror;ion-resistant iiiateri.a?.s wou2.d be requi-red i.n any 

tailings dewatering system because of the highly-corrosive 

solutions that must be handled. Although it is used in some 

foreign countries, continuous tailings dewaterinq is not 

practiced at any urai?i.um mills in the TJni.ted States: however, it 

has been proposed for several sites. In a planned installation 

in the Eastern United States, tailings were to be dewatered by a 

belt fi.lter system and trucked to a tailings disposai area, where 

a 0.3-m (1-ft) clay cap would be applied (Ma83) . An active 

working edge of 100 rn (300 ft) was allowed for spreading, but no 

more than 4,O ha (10 acres) of tailings were to be exposed at any 

one time, Tl!e clay car, .:J;I.; to be covered with 0.2 m (8 inches) 

of gravel and ahout 2.7 m (8 ft) of random fiil. Additional 

random fill and ovorburdcn fro9 3 ~~~lrface mi.ni.!lg aperation i~jere 

to complete the taiiincjr c:?>r!?r. 
At least three uranium mills have proposed the use of 

continuous disposal systems. Anaconda submitted conceptual plans 

of such a tailings disposal system prior to the downturn of the 

uranium market. However, the plans were never implemented. The 

system was to be a .trench and fil.1. type operation. Tailings were 

to be thickened to 60 percent solids prior to pumping to 91-m 

(300-ft) by 2300-m (7500-ft) trenches excavated to a depth of 

15 to 22 m (50 to 70 ft). The tailings were then to be covered 

with 5 m (16 ft) of earthen material. Pioneer Uravan, Inc., 

submitted plans to build the San Miguel Mill using continuous 

tailings disposal at Slick Rock, Colorado (NRC81). The mill has 

not been constructed. The planned tail-ings disposal operation 

consisted of bel-ow-grade burial of belt-filtered tailings in a 

series of 10 trenches. Excess water was to be transferred to two 

evaporation ponds. Each trench would measure 76 by 760 m (250 by 

2500 ft) and be 9 to 11 m (3n to 35 ft) below grade. Tailings 

would be transferred from the mill to the trench via conveyor. 

Six to 6.4 m (20 to 21 ft) of earth cover would be placed over 

the tailings. Excavation, filling, and covering would be carried 

out simultaneously. Umetco Minerals proposed a continuous 

disposal system that would be located on a mesa adjacent to the 

Uravan, Colorado, mill. The existing impoundments at this site 

have been filled to capacity. 

Effectiveness and Cost 

Continuous disposal is an effective means of reducing 

radon-222 emissions, especially during the operational life of a 

uranium mill. Dewatered tailings are placed in trenches and 

covered with soil shortly after placement, which eliminates the 

drying period associated with other tailings disposal 

techniques. The model continuous-disposal impoundment consists 

of a series of 10 trenches, each having the capacity for 

one-tenth of the volume of tailings generated over the 15-y life 

of the model mill. Each trench has sloping sides and contains a 

12-m depth of tailings. A 6-m berm separates the trenches to 

allow for tailings placement. R diagram of the model 

continuous-disposal impoundment is shown in Figure 7-5. The 

total tailings surface area at capacity is 572,000 m, or 57,200 m 

per trench. 

Another alternative method of continuous disposal of uranium 

mill tailings entails a combination of two previously discussed 

methods, Continuous/single-ceII disposal involves placement of 

dewatered tailings in a single large impoundment as opposed to 

placement .in a series of trenches. The size of tlie impoundment 

would be comparable to that required for the single-cell 

impoundment. A partially below-grade continuous/single-cell 

disposal impoundment is also considered because it minimizes the 

excavation cost as well as the cost of dam construction. 
GRPDE L 

BELW-GRADE 

+77m4 

SECTION A-A 

GRADE L 

OELW-GRAN 

u TAILINGS 

SECTION B-8 

NOTES: 

TAILINGS CAPACITY PER TRENCH = 1800 t fd x 110 dfy x 15y r 10 TRENCHES = 8.4 x la5 f 

3 5 3 TAILINGS VOLUME PER TRENCH = 8.4 x lo5 t 4 1.6 t/m = 5.25 x 10 m 

FINAL TAILINGS SURFACE AREA = 5.72 ha/TRENCH (1 4.9 ~C~~JTRENCH) 

DIAGRAM IS MOT TO SCALE 

Figure 7-7, Size and layout of the model continuous-disposal impoundment. 

7-32 
Emissions from continuous-disposal impoundments during 

operation are low. Elimination of the drying-out period, which 

is responsible for the majority of the operational radon-222 

emissions associated with the other model disposal impoundments, 

substantially reduces emissions from continuous-disposal 

impoundments. This is evident in Table 7-9, which shows the 

average emission rates for continuous-disposal and the 

single-cell model impoundments. 

Figures 7-8 and 7-9 show the radon-222 emission rates for 

the model continuous-disposal impoundments of single-cell and 

trench designs, respectively. It has been assumed that 4 ha 

(10 acres) of dewatered tailings are uncovered at any point in 

time over the 15-y life because of the normal short interval 

between placement and covering of tailings. At year 15, when the 

impoundment is at capacity, the final 4 ha of tailings are 

covered. The final emission rates, 0.36 kCi/y or 0.30 kCi/y, are 

similar to the other model impoundments. The estimated costs for 

continuous disposal, shown in Table 7-10, include an evaporation 

pond for the liquid removed from the tailings and a vacuum filter 

system. The cost of a below-grade impoundment is estimated to be 

about $54.2 x 10 , and the cost of a partkally above-grade 

trench design system, at about $61.0 x 10 . A design 

consisting of a single large impoundment partially above grade 

could reduce the large dam construction cost inherent in bgilding 

10 trenches. This alternative would cost about $37.4 x 10 . 
Table 7-9. Estimated radon-222 emission rates for model single-cell, 

phased disposal, and continuous-disposal tailings impmdments 

Averaqe emission rate (kCi/y~(~) 

operational phase Post-operational phase 

Single cell 

Phased disposal 

1.2 (b) 4.2 uncovered 

0.3 0 covered with 3m 

of earth 

Continuous disposal 0.5 

(single-cell) 

0.7 (b) 0.33 covered with 3m 

of earth 

Continuous disposal 0.5 

(trenched) 

0.30 covered with 3m 

of earth 

0.36 covered with 3m 

of earth 

(a) For new model impundments with 15-y operational life *ions based 

on 280 pCi Ra-226/q and specific flux of 1 pi Rn-222/m s per pCi 

Ra-226/g of tailings when dry. 

(b) Includes 5-'y drying-out period. 
RADIUM CONCENTRATION - 280 pCi Ra-226/g 

2 

SPECIFIC FLUX - 1 pCi Rn-222/m s per 

pCi Ra-22619 FOR DRY AREAS 

.---. 

-. % 3 .FU 

- Y 

v, 

Z 

- 0 

ln - 2 

5 

N 

N 

N 

I 

Z 

0 

n 

4 1 P: 

0 

0 5 10 15 20 

YEAR 

Figure 7-8. Estimated radon-222 emissions from a 

mcdel continuous-disposal impoundment. 
RADIUM CONCENTRATION - 280 pCi Ra-226/g 

2 

SPECIFIC FLUX - 1 pCi Rn-222/m s per 

.--- pCi Ra-22619 FOR DRY AREAS 

. 3 -7 

U 

- Y 

0 

0 5 10 15 20 

YEAR 

Figure 7-9. Estimated radon-222 emissions from a model 

continuous/single-cell disposal impoundment. 
Table 7-10. Estimatd costs for a6m@~l continuous disposal irnpunchnent 

($ x 10 ) 

Partially above-arade 

Item 

Excavation (b) 

Synthetic liner 

(30-mil) 

Gradjng 

n3m construction 

Cover (3-m) 

Riprap on slopes 

Gravel cap (0.5-m) 

Evaporation pond 

Vacuum filter 

Below-grade 

trench design 

Single-cell Trench 

design design 

Subtotal direct cost 41.03 

Indirect cost (C) 13.13 

Total cost 54.16 

(a) In 1985 dollars. 

(b) Below-grade inpundments are constkcted so that the top of the final 

cover is at grade. Partially above-grade design is 6 m deep and 6 m 

above qrade. 

(') indirect costs are estimated to be 32 percent of direct costs. 
r "7 ~ 4 ~>ummary of..Iia0on-222 Control Practices 

A summary of the radon-222 emissions from new model 

impoundments servi-ng an 1800 t/day mill is presented in Table 

7-9, Three types of emissions are presented: operational, 

post-operational, and total emissions. The emissions from a 

model single-cell impoundment represent those with and without 

final cover to provide a perspective on the emission reductions. 

Operational emissions are those that occur during the 

operating 15 yr, life of the mill plus those due to the 

impoundment's 5 yr. drying-out period, if applicable. For 

determination of the average operational emission rates 

presented, the total amount of emitted radon-222 was calculated 

and divided by the appropriate 20 or 15 yr. lifetime. Emission 

rates for the active and drying-out periods of phased- and 

continuous-disposal impoundments are not presented because these 

values vary with time. Tailings are being dried at various 

points in time in a phased-disposal system, and no 

5 yr.drying-out period is required for continuous disposal. 

Post-operational emissions occur at the end of an 

impoundment's drying-out period. After the 15-y operational 

period and the 5-y drying-out period of a single-cell 

impoundment, radon-222 emissions increase to 4.2 kCi/y with no 

cover. After compliance with Federal requirements, the emission 

rate reduces to 0.3 kCi/y. The post-operational emission rates 

for the model. imp~undments~with final cover meet the Federal 

emission Limit of 20 pCi/m s. The emission rate for 

continuous disposal (trench design) with final cover is slightly 

higher than the others because the tailings surface area is 

sl-ightly larger. 

The final column of Tabie 7-11 presents cumulative 

emissions over various time periods. Emissions over these 

different time periods are the sum of those from the operational 

phase of an impoundment as well as those occurring after final 

cover (if applicable). All iypoundments with final cover meet 

an emission limit of 20 pCi/m s; therefore, variations in 

emissions from the various covered impoundments are due to 

different operational emissions and small differences in the 

tailings surface areas. 

Cost estimates for constructing new model tailings 

impoundments are summarized in Table 7-12. The partgally 

above-grade single-cell impoundinent cost, $29.7 x 10 , is the 

lowest cost alternative, but most of the costs are incurred 

during initial construction. Its completely belgw-grade 

counterpart costs are estimated to be $41.3 x 10 . The 

difference is largely due to increased excavation costs. Phased 

and continuous disposal impoundments are more costly, but the 

costs are spread out over the Life of the impoundment. 
m a, Y 

m 5 n M 

E 

C- r 

E 

.ri 

d M u v. 3 

a d a 

U 3 a 

WO 

5 

m 

om m N P 

X 

3 W h 

ii w .a 

C a 

UO Y m .Ad rd 71 

WU ?? 

ri m 

uu 5 z 

(UU U Y 

a~ m m m a, 

umu 

mE:w C 

E:z -? 8 0 *(a \DUC 1N a 3 

a, N 0 

mI 0 04' 

me N ,3~ P.2 U Y 

ma al me, 

mm a, C> Uu 5 Uz 

m 

0 WI 2.2* U OY 

m aa a, U mC UMU 

.i am a, om d $ N3 

a ~m a OM u mm 

$3 d 

a, .A 

u m m 5m 

0 rld C ma, " 232 2 2% 

U 

d al 

.i > 

alo 

El U u 

0 

dalU 

Ud l 

U MO 

"35 

0 m .r( 

Z" 3 
Table 7-12. smmry of estimated costs fog new model tailings iltpundment 

(1985 $ X 10 ) 

Continuous-disposal 

Partially 

Sinqle-cell Phased-disnosal above madePartially Partially SingleBelow grade above grade Pelow grade above grade Below grade cell Trench 

V 

I -. C 

0 Direct cost 31.3 22.5 36.2 31.5 41.0 28.3 46.2 

Indirect cost 10.0 7.2 11.6 10.0 13.1 9.1 1.4.8 

Total cost 41.3 29.7 47.8 41.5 54.1 37.4 61.0 
Baker E. G., Hartley J, N., Freeman H, D,, Gates T. 

E., Nelson D. A, and Dunning R. L., "Asphalt Emulsion 

Radon ~arrier Systems for Uranium Mill Tailings - An 

Overview of the Technology", DOE/UMT-0214, PNL-4840, 

March 1984. 

Dreesen D. R., Williams J. M., and Cokal E. J., 

"Thermal Stabilization of Uranium Mill Tailings", in: 

Proceedings of the Fourth Symposium on Uranium Mill 

Tailings Management, Fort Collins, Colorado, October 

1981. 

Environmental Protection Agency, "Final Environmental 

Impact Statement for Standards for the Control of 

Byproduct Material from Uranium Ore Processing", EPA 

520/1-83-008-1, Office of Radiation Programs, U.S. 

EPA, Washington, D.C., September 1983. 

Gee G. W., Nielson K. K, and Rogers V. C., "Predicting 

Long-Term Moisture Contents of Earthen Covers at 

Uranium Mill Tailings Sites", DOE/UMT-0220, PNL-5047, 

September 1984. 

Hartley J. N., Gee G. W., Baker E. G., and Freeman H. 

D., "1981 Radon-222 Barrier Field Test at Grand 

Junction Uranium Mill Tailings Pile", DOE/UMT-0213, 

PNL-4539, April 1983. 

Hartley J. N., and Gee G. W., "Uranium Mill Tailings 

Remedial Action Technology", in: Proceedings of the 

Second Annual Hazardous Materials Management 

Conference, Philadelphia, Pennsylvania, June 1984. 

Hartley J. N., Glissmeyer J. A., and Hill 0. F., 

"Methods for Estimating Radioactive and Toxic Airborne 

Source Terms for Uranium Milling Operations", 

NUREG/CR-4088, Nuclear Regulatory Commission, 

Washington, D.C., June 1985. 

Marline Uranium Corp. and Union Carbide Corp, "An 

Evaluation of Uranium Development in Pittsylvania 

County, Virginia", October 15, 1983, Section E.3. 

Nuclear Regulatory Commission, "Final Generic 

Environmental Impact Statement on Uranium Millingw, 

NUREG-0706, September 1980. 
Nuclear Regulatory Commission, "Environmental 

Assessment Related to the Operation of San Miguel 

Uranium Project" NUREG-0'723, January 1981. 

Portland Cement Assn., "Soil-Cement Construction 

Handbook", ER003.095, Skokie, Ill. 1979. 

PEI Associates, Tnc,, "Radon-222 Emissions and Control 

Practices for Licensed Uranium Mills and Their 

Associated Tailings Piles", EPA Contract No. 

68-02-3878, June 1985. 

Robinsky E. I., "Tailing Disposal by the Thickened 

Discharge Method for Improved Economy and 

Environmental Controlw, in: Volume 2, Proceedings of 

the Second international Tailing Symposium, Denver, 

Colorado, May 1978. 

Rogers V, C., and Nielson K. K., "A Handbook for the 

Determination of Radon-222 Attenuation Through Cover 

Materials", NUREG/CR-2340, Nuclear Regulatory 

Commission, Washington, D.C., December 1981. 

Rogers V. C., Nielson K. K., and Kalkwarf D. R., Radon 

"Attenuation Handbook for Uranium Mill Tailings Cover 

Designv, NUREG/CR-3533, 1984. 

Strong K. P. and Levins D. M., "Effect of Moisture 

Content on Radon Emanation from Uranium Ore and 

Tailingsv, Health Physics, 42, 27-32, January 1982. 

Thode E. F. and Dreesen D. R., "Technico-Economic 

Analysis of Uranium Mill Tailings Conditioning 

Alternatives", in: Proceedings of the Fourth 

Symposium on Uranium Mill Tailings Management, Fort 

Collins, Colorado, October 1981. 

Williams J. M., Cokal E. J., and Dreesen D. R., 

"Removal of Radioactivity and Mineral Values from 

Uranium Nil1 Tailings1', in: Proceedings of the Fourth 

Symposium on Uranium Mill Tailings Management, Fort 

Collins, Colorado, October 1981. 
Chapter 8: SUm4/iA/rARY AND COMPP~RiSON OF WORK PRACTICES 

A number of alternatives are available to reduce radon-222 

emissions and subsequent risks from tailings disposal, Both 

ti.ming and the disposal method effect emissions. The control 

alternatives, their emissions, costs, and potential benefi-ts are 

presented in this chapter on a comparable basis by using the 

model tailings impoundment described in Chapter 7. 

The base case assumes disposal of tailings in a single cell 

impoundment si.mil.ar to current practice a.t many mills. TI-iis 

nominal 50 ha (125 ac) impoundment (actual1.y 47 ha or 3.26 acres) 

has a 15 year active life. The surface area is 80 percent wet 

or ponded during this active period and average radon-222 

emissions are 0.8 k Ci/y. Emissions then increase during a 

5-year drying period to 4.2 kCi/y. Emissions after this time 

depend on when the impoundment is covered to compiy with Federal 

and/or state :regulations, For il.liis'trative purposes time 

periods of 0, 20, and 40 years are used before final cover is 

applied. The total cost for constructing and s'ventually 

covering a single cell impoundment is the same, but since the 

final cover is applied at different times in,tbis example, the 

net present vaiue of this cos't is d:~ffereilt. The longer 

the cover cost it; pos*poxled, the sma%?.er the no% present value. 

A summary of radon-222 emissions and costs fc;r s?-ngle cell 

impoundments are presented. in Table 8-1. 

In Base Case 1 the impoundment is dry and uncovered for 

40 years. Chis example case yields the nighest emissisns and 

least cost since nothing is done for 4.0 years after the 

impoundment is full. and dry (GO years from start). In Base 

Case 11 no cover is applied for 20 years after the impoundment 

is full and dry (40 years from start). Initially emissions are 

the same a.s the first example, but greatiy r:educed during the 

40- "i 60-year period since final earth cover is appli.ed, Costs 

are increased by $700,000 since the cover cast is incurred 

20 years sooner. Covering the impoundment as soon as possible 

after it is full reduces radon-222 exii.ssions still. further and 

increases the net present valrle cost by a.bn?.%t $2,500,000 when 

compared with Rase Case I. 

(") Net present value = current cost x [i.,/ (1 4- 0.05) ") at a 

5 percent discount rate and where n - years in which cost 

is incurred. 
Table 8-1. mission and cost comparison for single cell impoundment 

with final cover applied at 0, 20, and 40 years after reaching capacity 

Work practice 

Curmiiative Nmr 

radon-222 emissions (kCil costg (a) 

0-20 y 20-40 y 40-60 y 0-60 y ($10 ) 

Cover 40 years after 25 83 83 19 1 33.9 

full - Base Case I 

Cover 20 years after 25 83 6 114 34.6 

full - Base Case I1 

Cover when full 25 6 6 37 36.4 

(a) At 5 percent discount rate. 
The risks incurred by leaving a model impoundment uncovered 

can be estimated from the radon-222 emission ra'te and assuming 

the model impoundment has an impact in proportion to that of the 

current licensed mills as shown below: 

Risks from model = nationwide risks emissions from 

impoundment total emissions model impoundment 

Based on the current estimated emission rate of 138 kCi/y 

from licensed mill impoundments and a nationwide fatal cancer 

rate of 2.34 committed fatal cancers per year (based on 

760 deaths per million person WLM), deaths at other emission 

rates can be estimated. 

For the single cell model impoundments deaths and benefits 

(deaths avoided) were estimated for a 60-year period as shown in 

Table 8-2. Benefits are determined by comparing with the Base 

Case I, i.e., not covering for 40 years. When compared with the 

cover in 20 years case, the benefits of covering immediately 

when full are reduced to 1.3 deaths avoided over a 60-year 

period. 

8.2 Phased Disposal 

Phased disposal provides a means of reducing emissions 

since the smaller areas involved in each cell at any given time 

are easier to keep flooded during operation and standby 

periods. Also, during the drying phase less tailings are 

exposed. Two model phased disposal impoundments with the same 

capacity as the large single cell impoundment were characterized 

to estimate emissions, cost, and potential benefits. A 6-cell, 

20-acre-per-cell, and a 3-cell, 40-acre-per-cell impoundment 

were used as models. Average emissions during a 20-year 

operational period are 0.7 and 0.6 kCi/y for the 20 acre and 

40-acre cell size, respectively. Average radon-222 emissions 

after being completely covered with earth are similar at 0.33 

and 0.31 kCi/y for the 20-acre and 40-acre cells, respectively. 

The total costs of a 6-cell, 20-acre-per-cell design and a 

3-cell, 40 acre cell design are similar but the net present 

value for the 40-acre-per-cell design is less since some costs 

are postponed compared with the 20-acre-per-cell design. 

The emissions and cost data for below grade phased disposal 

model impoundments are summarized in Table 8-3. Radon-222 

emissions are very similar and the NPV for the 40-acre/cell 

impoundment is about $1,500,000 less than the 20 acre/cell 

design. 

Committed fatal cancers for the model phased disposal 

impoundments were also estimated as shown in Table 8-4. Only a 

very slight difference in estimated deaths is seen, and this 

would be expected since emissions are very similar. 
Table 8-2. Comparison of estimated deaths and benefits for a single 

cell model i.rpundhnent with final cover applied at 0, 20, and 40 years 

after reaching capacity 

Benefits, 

Work practice 

Nationwide deaths, (a) 

0-60 y 0-60 y 

Base Case I - Cover 40 years 

after full 

Base Case I1 - Cover 20 years 

after full 

Cover when full 

(a) Based on 760 deaths per million person WLM. 
Table 8-3. Emissions and costs for model phased disposal impoundments 

NW 

Radon-222 emissions (kCi) costs (a) 

Work practice 6 0-20 y 20-40 y 40-60 y 0-60 y ($ x 10 ) 

(a) At 5 percent discount rate. 
Table 8-4. Corprison of estimated death for model 

phased-disposal impoundments 

Nationwide deaths, (a) 

Work practices 0-60 y 

20 acre - 6 cell design 

40 acre - 3 cell design 

(a) Based on 760 deaths per million person WIM. 
8.3 wtinuous Disposal 

Dewatering and continuously covering tailings is an 

attractive but untried method for tailings disposal in this 

country. By exposing only a relatively small beach area, 

radon-222 emissions are reduced during operation and a long 

drying period is not required prior to final cover. A model 

continuous disposal below-grade, trench type impoundment with 

the same capacity as the single cell conventional impoundment 

was used to estimate emissions and cost. Average emissions 

during the operational period are 0.5 kCi/y and drop to 

0.36 kCi/y after the final beach area is covered at the 15-year 

point. As shown in Table 8-5, cumulative emissions over a 

60-year period are 24 kCi. Based on this emission rate, 

committed fatal cancers from this work practice at a model 

impoundment amount to 0.4 over a 60-year period. Assuming that 

costs are incurred at the beginning of each of three 5-year 

periods, the net present vaLu& cost for a below-grade trench 

impoundment is about $43 x TO . 

8.4 Comparison of Work Practices 

Work practices for new model tailings impoundments are 

summarized in Table 8-6 in order to compare their radon-222 

emissions, net present value cost, and the resulting health 

effects attributed to each model impoundment. The single-cell 

impoundment with cover applied when dry has the highest 

emissions during its operating life and thus, the highest 

cumulative emissions. This higher emission rate results in a 

higher health risk. Phased disposal yields lower emissions 

during the operating period and thus lower cumulative 

emissions. Costs are similar to the single-cell impoundment and 

cumulative health effects are lower. Continuous-disposal 

emissions are very similar to phased disposal and health effects 

are thus also similar. Net pgesent value costs for this trench 

type of disposal are $43 x 10 ; higher than single-cell or 

phased-disposal alternatives. 
Table 8-5. Emissions and cost of model below-grade trench type 

continuous disposal impoundment 

Cumulative radon-222 emissions (kCi1 

0-20 y 20-40 y 40-60 y 0-60 y NPV cost(a) 

($ x 107 

(a) At 5 percent discount rate. 
Table 8-6. Ccrmparison of work practices for new model tailircJs -ts 

radon-222 emissions (Mi) NmT of work Gn~nnitted 

~ractice @ 5% , fatal cancers (a) 

Work practice 

1. Single cell mered 25 6 6 37 36.4 0.6 

when N1 (20 y to from start) 

10 

2. Phased disposal 13 7 7 27 36.1 

20-acre cells 

3. Phased disposal 

40-acre cells 

4. Continuous dis- 10 7 7 24 43.3 0.4 

posal (trenchtype) 

6 (a) Nationwide, based on 760 deaths110 person WIM. Assuaes model plant is at average location of 

existing mills. 
When compared with an uncovered single-cell impoundment, 

all the work practices yield similar benefits in the form of 

avoided deaths. Costs of these alternative work practices are 

also si~ilar except for continuous disposal which is about 

$9 x lo higher. Tables 8-7 and 8-8 present a comparison 

between the alternative work practices and a base case single 

cell impoundment uncovered for 40 years and also 20 years 

respectively. Depending on the base case selected, benefits of 

about 1.4 to 2.8 deaths avoided can be realized for a model 

impoundment over a 60-year period when alternative work 

practices are used. 
Table 8-7. Camparison of cost and benefits between model 

Base Case I and new work practices 

Work practice 

Difference in NPCT Deaths 

from base6case avoided (a) 

($ X 10 ) 0-60 y 

Base Case I 

Single cell covered 40 y 

after full (60 y from start) 

L. Single cell covered when 

full (20 y from start) 

2. Phased disposal 20-acre cells 2.2 3.0 

3. Phased disposal 40-acre cells 0.7 3.1 

4. Continuous disposal (trench-type) 9.4 3.1 

(a) Nationwide basis. 
Table 8-8. Conparison of cost and benefits between mcdel 

Base Case I1 and new work practices 

Work practice 

Difference in NPV Deaths 

from basepse avoided(a) 

($ X 10 ) 0-60 y 

Base Case 11 

Single cell covered 20 y 

after full (40 y from start) 

1. Single cell covered when 

full (20 y from start) 

2. Phased disposal 20-acre cells 1.5 1.6 

3. Phased disposal 40-acre cells - 1.7 

4. Continuous disposal (trench-type) 8.7 1.7 

(a) Nationwide basis. 
APPENDIX A 

DIAGRAMS OF URANIUM MILL SITES AND 

TAILINGS IMPOUNDMENTS 
Diagrams of each of the 20 licensed uranium mill sites that 

were included in this evaluation are presented in this 

appendix. These diagrams were adapted from aerial photographs 

taken by the Office of Radiation Programs. The diagrams are 

presented to show the relative location of the tailings 

impoundments, mill structures, and other important site 

features. Approximate scales and the dates of the aerial 

photograph are indicated on each diagram. 
EO Urn 

m 

a -1 

CLS-N 

ob-F- u-1 

urn 

CL 

W Z .. COW 

CZb046 UUO 

ACCESS ROAD 

L-BAR TAILINGS 

IMPOUNDMENT '-, 

WATER COVERED 

TAILINGS - 

SOH10 MILL 

CEBOLLETA, NM 

DATE: 10/5/85 

MINE 

BUllDiNGS 

0 
0 

8- 2 - 

8- 

ul 

0- 

- 

2z 

r 

CL3G 

s * 

d-lrul 

ut-m 

3-1 

ZUW 

zrm 

-. 

CL W W CL .. +uw 

mu-+- 

WW4 x7n 
IURFACE 

WATER 
N 

0 

1 

ROCKY MT. ENERGY MILL 

BEAR CREEK, WY 

DATE: 911 3/85 

BEAR CREEK TAILINGS / IMPOUNDMENT 
MILL BUILDINGS 

PATHFINDER SHIRLEY BASIN MILL 

SHIRLEY BASIN, WY 

DATE: 9/f 3/85 

APPENDIX B 

COST ESTIMATES FOR EXISTING AND MODEL 

NEW URANIUM MILL TAILINGS IMPOUNDMENTS 
Appendix B: COST' EST'IMAT'ES FOR EXISTING AND MODEL NEW URANIUM 

MILL TAILINGS IMPOUNDMENTS 

l'his Appendix presents the approach, assumptions, and bases 

used to generate the cost estimates of Chapter 7. For existing 

impoundments, the most recent available site-specific 

information was used to estimate the cost of interim control and 

final reclamation measures. For new tailings impoundments, 

model impoundments were designed, which formed the basis of the 

cost estimate. 

All costs are presented in 1985 dollars, which have not 

been discounted. Both direct and indirect costs are included. 

In general, direct costs represent labor, equipment, and 

material costs. A total of 32 percent was added to this figure 

to cover indirect cost items such as engineering, insurance, 

contingency, etc, Table B-1 presents information on the 

indirect cost factors used in preparation of the cost estimates. 

B-1 Existinq Impoundments 

Detailed data on each existing site were obtained from 

various sources (DOE82, EPA85, NRC84, PEI85). Two types of work 

practice control measures were considered for control of 

radon-222 from existing uranium mill tailings impoundments: 

interim control and final reclamation. 

Xnterim Control 

Interim control involved placing l meter of earth on the 

surface of all dry tailings areas of an impoundment. For sand 

tailings dams, the amount of soil required to cover the 

embankmen't slopes was also incl.uded. In'terim control is 

considered a temporary measure; therefore, neither the costs of 

reclamation of the source of cover soil (borrow pits) nor the 

costs of im oundment tjrosion control were included. A unit cost 13 of $4,35/yd ($7,00/m ) was used to estimate the cost of 

placing the interim cover, This includes the direct costs of 

excavation, hauling, spreading, and compacting the cover. 

Final Reclamation 

Measures for effecting final reclamation of existing 

uranium mill tailings impoundmznts are those required to reduce 

the radon-222 flux to 20 pCi/m s and to place the impoundment 

in a state of permanent, long-term stability. 
Table B-1. Indirect cost factors used in the ast estimation of 

uranium mill tailings impundments 

Indirect wst item 

Rqineerjxg and design 

Imance 

Performance bond 

Permits 

Overhead and prof it 

Contingency at wnceptual stage 

Total 

Percentaqe 

Range value wed 

Source: "Means Site Work Cost Data 1985," 4th Annual Edition, R.S= Nm 

Co., Inc. 
No credits for earth covers that ma.y have previously been 

placed for interim control measures were considered to be of 

help in achieving final reclamation. Final reclamation was 

assumed to be possible immediately after an impoundment had 

dried. No cost for attaining dry-out was assumed. The 

measures taken and the costs of final reclamation depend on 

the type of impoundment and its size. 

An estimate of the cost of covering each impoundment 

with 3ufficient earth to reduce the radon-222 flux to 20 

pCi/m s was based on the radium-226 concentration of the 

tailings. Costs of reclaiming a borrow pit (source of the 

earth for cover) and placing an 18-inch thick gravel cap on 

top also were included for each impoundment. For 

impoundments that are constructed of sand tailings dams, the 

costs for regrading slopes to 5:1(H:V) and protection of the 

slopesT earthen cover with 18 inches of riprap were also 

included. For these cost estimates, it was assumed that the 

slopes of each dam constructed of tailings originally had 

l:1 (H:V) slopes. These slopes would be reshaped to 5:1 

(H:V) before placement of the cover and riprap. As 

discussed earlier, indirect costs were then added to the 

direct costs to obtain the total cost of final reclamation 

of existing impoundments. 

B.2 New Tailinqs Impoundments 

Four types of model impoundments were defined for 

estimation of the costs of constructing new uranium mill 

tailings impoundments: single-cell, phased-disposal, 

continuous-disposal, and continuous/single-cell disposal 

impoundments. Costs of the first three types of 

impoundments were estimated for below-grade placement of 

tailings and for partially below-grade placement, Only 

partially (50 percent) below-grade placement of tailings was 

considered for the model continuous/single-cell disposal 

impoundment. 

Each model impoundment was assumed to have 2:1 (H:V) 

interior sloping sides, to contain a 3.2-meter depth of 

tailings, and to have 6 meters of tailings below grade and 6 

meters above-grade (in the case of the partially below-grade 

impoundment). This arrangement ensures the comparability of 

the cost estimates for the various impoundments. Each model 

impoundment is designed or sized to handle the production 

output of the model mill over its615-year life (NRC80), 

which is estimated go ge 8.4 x 10 t of tailings with a 

volume of 5.25 x 10 m . 
Sinqle-Cell Imooundments 

The single-cell impoundments are large, square 

impoundments. For the below-grade impoundment, 15 meters of 

earth is excavated so that the final level of the 

impoundment, which will contain a 12 meter depth of tailings 

and be covered with 3 meters of earth, is at grade. For the 

partially below-grade single-cell impoundment, a depth of 6 

meters of tailings is below-grade; therefore, the top of the 

impoundment after final cover is 9 meters above grade. Each 

type of impoundment has a 30-mil synthetic liner and a 

drainage system to facilitate dewatering when the 

impoundment has reached capacity. For the partially 

below-grade impoundments, embankments are constructed from 

the excavated material, which is also used for the final 

cover. The embankments are 9 meters high, have a 6-meter 

berm, and have interior and exterior slopes of 2:l and 5:1, 

respectively. The exterior of the embankment is covered 

with riprap for erosion protection. An 18-inch gravel cap 

is placed atop the final cover of each type of impoundment 

for protection. The total estimated costs for the 

below-grade and the partialky below grade skngle-cell 

impoundments are $41.3 x 10 and $29.7 x 10 (1985 

dollars), respectively. The difference is largely due to 

the additional excavation required for a below-grade 

impoundment. 

Phased D~SDOS~~ Impoundments 

The phased-disposal impoundment consists of a series of 

small impoundments or cells that are constructed 

sequentially, filled, and brought to final reclamation over 

the life of the model mill. The six cells are similar in 

design to the single-cell impoundment, but the capacity of 

each is just one-sixth of the total tailings quantity. 

Unlike the model single-cell impoundment, an 

evaporation pond is included in the cost estimate of 

phased-disposal impoundments. The impoundment surface area 

available for evaporation is much smaller; therefore, an 

evaporation pond is required. The estimate includes both 

the cost of construction and the cost of closure of the 

evaporation pond at the end of the mill% life. 

Excavation to a depth of 6 meters for the partially 

below-grade phased-disposal impoundment does not provide 

sufficient earth to construct the dam and to place a 3-meter 

earth cover over the tailings. Thus, the costs of obtaining 
adaitionai earth and rociaiminc; a borrow pit are included in 

the cost of the dam cnnstructioal. The total estimated costs 

for the below-yrade and the partial18 beiaw-grade pkgsed 

disposal impoundments are $47.8 x 3.0 and $41-5 x LO 

(1905 dollars), respectively. 

Continuous Disposal. Impa~in~~ment~ 

A series of LO rectangular trenches are included in the 

model continuous-disposal impoundments. As in phased 

disposal, the trenches would be constructed sequentially, 

filled, and covered over the life of the model mill. Unlike 

phased disposal, however, the tailings are dewatered to 

allow fur almost hmediate placement of the cover. The 

estimate includes the cost of a vacuum filter to dewater the 

tailings. An evaporation pond (larger than that required 

for the phased-disposal model) is also needed. The tailings 

are dewatered prior to disposal; therefore, no drainage 

system is necessary. 

The volume excavated is insufficient to meet the earth 

requirements for the partially below-grade 

continuous-disposal impoundment dam. The shortfall is made 

up by hauling earth from a borrow pit, which is later 

reclaimed. These costs are included in that of the dam 

construction, The total estimated costs far the below-grade 

and the partially below-grage continuous-digposal 

impoundments are $54.2 x 10 and $61.0 x 10 (1985 

dollars), respectively. 

Conti.nuous/~inql~e, <:ell Disposal 1m~oundmen.t 

The design of the conti.nuous/single-cel.1 disposal 

l,,~~ndment 7-1"-'3 includes a single, partially below-grade 

impoundment for placement of dewatered tailings, as opposed 

to a series uf trenches, Such a design substantially lowers 

the estimated cost of the dam construction, as it eliminates 

individual embankments between trenches and the negd to haul 

in additional earth. The total cost of $37.4 x 10 (9985 

dollars) is essentially the same as that estimated for the 

partially below-grade single-cell impoundment except that an 

evaporation pond and vacuum filter are still required 

because the tailings must be dewatered. 
DOE82 Department ofEneergy, "Ym:minggled ilranitx~ri Tai:.incjs 

Studyge, DOE/ DP-0011, Office of Defense Wa"ste and 

Bypri~dti~ts Management, Washington., I). C, , June 30, 

1-982. 

EPAB5 U,S. Environmental Protection Agency, "Draft 

Document-Estimates of Population Distributions and 

Tailings Areas Around Licensed Uranium Mill 

Sites"', Off ice of Rad.iati.on Programs, November 

1985. 

NRCB 0 Nuclear Regulatory Commission, Q'FiiiaT Generic ." Environmental impact Sta.'cement on tiraniurn 

Miliingn, NUREG-0706, Septex:ber 1980, 

NRC84 Nuclear Regulatory Commission, IYDirectory and, 

Profile of Licensed Uranium-Recovery Facilities", 

Office of State Programs, NUREG/CR-2869, 

Washington, D.C., Karch 1984. 

PI3185 PEI Associates, Znc,, '?Radon-222 Emissions and 

Control Practices for Licensed Uranium Mills and 

Their Associated Tailings Piles, Final Reportn, 

prepared for the U. S. Environmental Protection 

Agency, Office of Radiation Programs, Document No. 

PEI 3642-6, June 1985 (revised l<c:vemher 1965), 

APPENDIX C 

EVALUATION OF INTERIM COVER 

AS A CONTROL OPTION 
2. Technical Issues 

2.1 Introduction 

2.2 Effectiveness of Interim Cover 

2.3 Applicability of Interim Cover 

2.4 Timing of Interim Cover 

2.5 Operational Aspects 
Chapter 1: INTRODUCTION 

The use of an earthen cover on the dry portion of inactive 

tailings impoundments can potentially reduce radon-222 emissions 

by restricting the diffusion of this gas long enough to allow 

decay. In developing the background information for the proposed 

standard, the option of using a temporary or interim earthen 

cover evolved as a possible work practice standard. This cover 

would be placed on dry portions of impoundments that are not in 

use. The cover would be about 1 foot or 1 meter in depth 

(depending on the selected option). If and when the impoundment 

returned to active use, tailings would be dumped on top of the 

earth cover. Other methods of reducing radon-222 emissions 

include water cover, an8 synthetic or asphalt covers. 

Maintaining a water cover causes potential ground water and, at 

some sites, dam stability problems. If a mill is on standby, 

water cover will be difficult to maintain due to evaporation. 

Synthetic or asphalt covers have not been evaluated over longer 

time periods on a large scale and their true effectiveness is not 

known. Thus, only a limited number of viable options are 

available for reducing radon-222 emissions from existing tailings 

impoundments, namely: 

Apply a relatively shallow earthen (interim) cover 

over the dry areas when the impoundments are not in use 

(i.e., standby). 

Discontinue tailings disposal in current impoundments 

and apply final cover per existing standards. 

Various schedules can be used with either of these options as 

described in the Federal Register Notice of February 21, 1986. 

An analysis of these alternatives for reducing radon-222 

indicated that the application of an interim earthen cover 

appeared to be a cost effective option if an impoundment was not 

used again. This option is therefore being reevaluated to better 

assess its practicability, effectiveness and cost. 
Chapter 2: TECHNICAL ISSUES 

2.1 Introduction 

Interim earthen covers of 0.3 or 1 m having 8 percent 

moisture content theoretically reduce radon-222 emissions by 

about 37 and 62 percent, respectively. The actual effectiveness 

of such interim covers has never been demonstrated on licensed 

tailings impoundments. Additionally, while use of earthen covers 

is a demonstrated control technology at inactive uranium mill 

tailings sites, it has never been used on a short term basis to 

limit radon-222 emissions from licensed tailings impoundments on 

active or standby status. Therefore the evaluation of interim 

cover is based on best engineering judgment and not practical 

experience. However, the use of thick (3 m) earth covers to 

control radon-222 and provide long-term stabilization of inactive 

tailings piles is demonstrated technology. The evaluation of 

interim cover, particularly estimation of its effectiveness in 

controlling radon-222, is based on research conducted under the 

UMTRCA program. 

Several characteristics of the impoundments impact the 

potential use of interim cover. Site-specific characteristics 

such as evaporation rates, dam construction, phreatic level, 

availability of cover material, presence of liners, expected 

length of standby periods, remaining capacity and expected mill 

life must be considered on a site by site basis. 

Uranium mill tailings are deposited as a slurry in tailings 

impoundments. Three major types of impoundments currently 

exist: those where coarse tailings are used as dam construction 

material (11 impoundments representing 32 percent of total 

tailings area): those using earthen dams (22 impoundments 

representing 65 percent of the total area); and below-grade 

impoundments (5 impoundments representing about 3 percent of the 

total). As discussed in later sections, impoundment construction 

affects the applicability of interim cover. Additionally, 

climate plays an important role in determining how much time is 

required to allow an impoundment to dry sufficiently before 

interim cover can be applied. For example, some tailings 

impoundments are located in arid areas (i.e., New Mexico) 

relatively wet areas (i.e., Texas, Washington) and areas that 

experience severe winter weather (i.e., Wyoming). The geology 

beneath an impoundment also impacts the time required for 

drying. The geologic settings vary from porous underlayments 

(sandy soils of New Mexico) to relatively impermeable bases (clay 

foundations in Texas). For example, impoundments in New Mexico 

would dry'relatively quickly because of seepage through the 

bottcm coupled with high evaporation rates while the Panna Maria 
impoundment in Texas would require a longer drying period because 

of the impermeable base that would inhibit dewatering by seepage 

and the relatively high rainfall rate. There are also several 

operational aspects that must be evaluated when considering 

interim cover. For example, annual maintenance, periodic 

inspections, enforcement, and loss of capacity must be included 

in the evaluation. Each of these items are discussed in the 

following sections. 

2.2 ~ffectiveness of Interim Cover 

The effectiveness of any earthen cover depends mainly on its 

moisture content and depth, and the homogeneity and integrity of 

the cover layer. The effectiveness of an earth cover was 

estimated in the Draft BID by using diffusion equations which 

take into account the cover material and tailings density, 

porosity, specific gravity and moisture content, and by assuming 

these properties do not vary throughout the cover or tailings, or 

with time. These idealized conditions would not typically be 

achieved in practice and the actual effectiveness would probably 

be less than the calculated effectiveness. The applicability of 

the basic diffusion equation to relatively shallow earth covers, 

such as 0.3 m, is also questionable. 

The key variable effecting the effectiveness of an earthen 

cover of given depth in controlling radon-222 is its moisture 

content. An example of this variation is shown in Figure 2-1. 

For a 1-meter depth of cover with 12 percent moisture, about 

20 percent of the radon-222 released from the tailings surface 

would still emanate from the cover. If the cover material dries 

out to 6 percent, about 47 percent of the radon-222 from the 

tailings would emanate from the cover. Thus, the emissions 

increased by a factor of 2.35 (47/20) or the effectiveness 

decreased by about 33 percent. Similar losses in effectiveness 

are evident for all depths of earth cover. However, a thicker 

cover will not dry out as completely or quickly as a thin cover, 

and soils with a higher silt and clay content will retain more 

moisture much longer than a sandy soil. 

In addition to the cover material's moisture content, the 

overall integrity of the cover must be maintained in order to 

reduce radon-222 emanations. Wind and rain erode an earth cover, 

thus reducing its depth and subsequent effectiveness. In 

addition, cracks from freeze-thaw cycles, subsidence, or 

burrowing animals decrease a shallow cover's effectiveness. When 

final reclamation is implemented, gravel, rip-rap, or vegetation 

cover, and additional grading and runoff control are included to 

decrease erosion and ensure the long-term integrity of the 

cover. These items are not included in interim earth covers 

since, by definition, they are not designed as long-term control 

techniques. 
0.90 

MOISTURE CONTENT OF TAILING IS 8% 

0.80 

0.70 

0.60 

0.50 

1 METER DEPTH 

0.40 

0.30 

0.20 

0.10 

0 

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 

EARTH COVER MOISTURE CONTENT, % by weight 

Figure 2-1. Variation in earth cover effectiveness with moisture content. 
The combiriation of surface drying, erosion, and loss of 

integrity reduces the interim cover" effectiveness. This loss 

in effectiveness would be especially evident in a shallow cover 

of only 0.3 m. The exact decrease in effectiveness is not known 

and cannot be calculated readily since these factors are highly 

variable and site-specific. The loss in effectiveness can be 

offset by frequent maintenance of the earth cover, as discussed 

under Operational Aspects. 

2.3 ADDlicability of Interim Cover 

Limitations regarding the placement of interim cover are 

associated with physical conditions of the tailings. The water 

content of the tailing and the slope of the surface are 

controlling factors. Tailings must be dry in order to support 

earthmoving equipment and the cover itself. Tailings are 

dewatered and dried by seepage from the impoundment and by 

evaporation. (The time required to achieve sufficient dryness is 

discussed in Section 2.4.) The tops of tailings impoundments are 

essentially flat, and if thoroughly dry, would pose no 

difficulty to placement of interim cover. However, 

11 impoundments at 6 mill sites are constructed with dams made of 

coarse tailings (Type 1 impoundments). The outer faces of these 

dams are steep (approximately 2.5:1, H:V). Placement of interim 

cover on these dams would be difficult because of the steep 

slope. In addition, seepage through the dams could cause 

instability and slumping of the interim cover. Conversely, the 

interim cover could cause the phreatic surface to rise in the dam 

by inhibiting seepage through the dam. This occurrence could 

cause a decrease in the stability of the dam itself. 

In evaluating the applicability of interim cover, three 

distinct situations currently exist on tailings impoundments. 

These conditions and how they affect the applicability of interim 

cover are addressed below. 

Interim Cover on Dams Constructed of Tailinas 

The faces of these dams are at a slope of about 2.5:l (H:V), 

it probably would not be possible to apply and maintain 

interim cover to these steep areas without recontouring the 

impoundment. Recontouring would result in a significant 

loss of storage capacity. Additionally, it would be very 

difficult to compact cover material placed on such a slope. 

Uncompacted material would be subject to more rapid wind and 

water erosion. 

These slopes (300 acres, total) represent 8 percent of total 

area and 15 percent of currently dry areas. 
20 percent of this sloped area is at impoundments that have 

been filled to capacity (Uravan). These impoundments would 

more logically apply final cover. 

12 percent of this sloped area is at impoundments at sites 

that have indicated decommissioning will begin soon (L-Bar 

and Churchrock). These impoundments would more logically 

apply final cover. 

31 percent of the total sloped area is at one major 

impoundment (Homestake), that is a 4 sided structure, with 

steep slopes (2 to 2.5:1) that would be most difficult to 

place interim cover on without recontouring. 

Coarse tailings are reported to have lower Ra-226 content 

than the slimes. Therefore, these areas have a lower source 

term than the tops of the impoundments. 

Piezometers and movement benchmarks used to monitor the 

stability of these dams would have to be extended and their 

use uninterrupted during application of interim cover. 

It would be necessary to provide drainage between the 

'tailings and the earthen cover to allow any seepage through 

the dam to escape without building up a hydrostatic head 

that could cause dam failure. Seepage through these dams is 

inherent to their design and must be maintained. A drainage 

system, such as a blanket drain, would also provide a 

permeable path for radon-222 migration, making at least the 

lower portion of the cover less effective. 

Interim Cover on Tops of Unlined Type 1 and Type 2 Impoundments 

Tops of Type 1 and 2 unlined impoundments account for 75 

percent of the total tailings area. 

Current dry areas on top of these piles equal 

44 percent of the total and 73 percent of the currently dry 

areas. 

These areas are flat and if thoroughly dry, interim cover 

could be placed easily. 

The length of time required for drying prior to placement of 

cover is site-specific and will vary depending on 

impoundment design, climate, and hydrogeology. Some 

impoyndments, particularly those in climates characterized 

by high net evaporation and permeable soils (e.g., New 

Mexico) would dry sufficiently in a relatively short time, 
1 year for example, Heavy equipment could access most of 

the area at that time. Other sites having lower 

evaporation, more rainfall/snowfall and/or less permeable 

soils that limit seepage could require considerably longer 

to dewater and dry (5 to PO years for example). 

Placement of 0.3-meter cover on these dry areas is 

demonstrated technology and is an NRC recommendation during 

standby to control windblown tailings. 

Interim Cover on Lined Type 2 and TvDe 3 Im~oundments 

Tops of lined impoundments represent 14 percent of the total 

area. 

Dry areas on lined impoundments make up 11 percent of 

currently dry areas. 

Issue of lost capacity is more important on these 

impoundments because their construction cost is greater. 

The dry out period will be longer than in unlined piles 

because seepage is limited. 

Evaporation Ponds 

In addition to tailings impoundments, several mills use 

evaporation ponds for water management. Decant water from the 

tailings impoundments and often mine pump-out water and seepage 

from the tailings impoundment is pumped to these evaporation 

ponds. Some tailings slimes and dissolved radium-226 are carried 

along with the water and are deposited in these ponds. Upon 

drying, these solids emit radon-222. Interim cover was applied 

to dry areas of evaporation ponds in the Draft BID. In the 

current evaluation, interim cover is not applied to evaporation 

ponds because: 1) these ponds receive water from sources other 

than tailings impoundments and would need to remain in service 

during standby periods; 2) the quantity of tailings present and 

their contribution to the site's source term are not accurately 

known; 3) these ponds will eventually be excavated and the 

material placed on the tailings impoundments prior to 

reclamation; and 4) these ponds are lined to prevent seepage. 

Movement of heavy equipment on these ponds could destroy the 

integrity of the liners. 

Summary of Applicability 

Because of the significant uncertainties and perceived 

difficulties and complications associated with the application of 
interim cover to the outward faces of dams constructed of coarse 

tailings, in addition to the relatively lower source term of 

these areas, the current evaluation of interim cover assumes that 

these slopes remain uncovered. All other tailings surfaces can 

be covered as soon as they are dry enough to support earthmoving 

equipment and the cover itself, In this evaluation of interim 

cover, it is assumed that dry areas of evaporation ponds are not 

covered for the reasons stated above. 

2.4 Timinq of Interim Cover 

The evaluation of interim cover includes several 

assumptions that are based on best engineering judgment, 

regarding the timing of interim cover applications (i.e., when 

can interim cover be applied). The assumptions are specified 

below: 

Dry areas (as specified in Table 4-2 of the BID) of tailings 

impoundments that are on standby status or that have been 

filled to capacity can be covered immediately. 

Wet and ponded areas of tailings impoundments that are on 

standby status or that have been filled to capacity will 

dewater and dry over a 5-year period, at which time it is 

assumed interim cover could be applied. 

Interim cover is not applied to operating impoundments. The 

method of placing tailings in impoundments is to discharge 

from several points around the perimeter or to move the 

discharge point around the perimeter; in either case interim 

cover would not be compatible with these operations. These 

impoundments receive interim cover when they go to standby 

status (i.e., dry areas covered immediately, wet and ponded 

areas covered in 5 years). 

The useful life of an interim cover is limited by return to 

active status at which time the earthen cover is covered 

with new tailings. In the current evaluation, impoundments 

would become active sometime between 1990 and 1995 and a 

second application of interim cover would be made in the 

year 2000. 

It was initially assumed for the base case that an inactive 

impoundment would remain uncovered for 40 years. This 

appears unrealistic and a shorter time period of no more 

than 20 years is more representative. 
2.5 Operational. Aspects 

The effectiveness of an unmaintained interim cover in 

limiting the escape of radon-222 can be expected to deteriorate 

with time. The rate of deterioration is highly site-specific. 

It depends upon many variables such as frequency and intensity of 

precipitation and wind, characteristics of the interim cover 

(e.g., moisture content, type of soil, compaction, grade, etc.), 

and drainage basin considerations (e.g., run-on and run-off). To 

prevent or minimize deterioration of interim covers, maintenance 

practices would be employed. Annual maintenance would include 

periodic regrading or placement of additional cover material, 

Additionally, periodic inspections of the interim cover system 

would be required to ensure its integrity. Such expenses are 

estimated to be 5 percent of the capital cost of the interim 

cover per year. 

One important aspect regarding interim cover is the issue of 

lost capacity. An interim cover of 1 meter applied over a 

tailings impoundment that is on standby status results in a loss 

of tailings capacity equal to the cover volume. If interim cover 

is applied more than once (i.e., a covered impoundment goes from 

standby to operational status and back to standby), the effect of 

lost capacity is multiplied. Information received from the NRC 

on the capacity of existing piles and the capacity loss 

associated with an application of interim cover is presented in 

Table 2-1. Some impoundments would have no remaining capacity if 

interim cover were applied, while others would lose as little as 

9 percent of their remaining capacity. Information on the 

remaining capacity at other sites is not currently available. 
Table 2-1. bst capacity assmiated with a single application of ir@rim 

cover (0.9 rn) over the entire impm&ent in nonagreement states 

(1000 tons) 

Mill 

White Mesa 

La Sal 

Mod5 

Shootaring Canyon 

Gas Hills (Pathfinder) 

Split Rock 

Gas Hills (UMGIYT)) 

Bear Creek 

Shirley Basin 

Sweetwater 

Licensed Quantity of interim 

Current quantity cover - 0.91 meter thick 

tailings of tailings (% of remaining capacity) 

1,500 

2,954 

10, 600 

174 

11,762 

7,700 

9, GOO 

4,100 

6,800 

3,900 

(a) NRC Uranium Field Office, Denver, Colorado, April 1986. information on 

remaining capacity of inpm&ents in agreement states was not available. 
REFERENCES FOR CHAPTER 2 

ORNL 83 Oak Ridge National Laboratory, "Guidance for Disposal 

of Uranium Mill Tailings: Long-Term Stabilization of 

Earthen Cover Materials," Prepared for U.S. Nuclear 

Regulatory Commission, NUREG/CR-~~~~, ORNL/TM-8685. 

October 1983. 

C-13 

*U. S. GOVERNHENT PRINTING OFFICE 1986; 621-735160533