,,,, Fiadisrion

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# Final

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# Radon

# - Emissions

# from 

# LicensedUranium

# Mill Tailings



# BackgroundInformation Document40 CFR Part 61 National Emission Standards for HarzardousAir 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. 20460Figures Tables 

### vi 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.onof Risk Coefficients 2.4 Estimating the Risks 2.4.1 Exposure 2.4.2 Risk Esti.rnation

References

3. RADON-222 SOURCES, ENVIRONMENTALTRANSPORT,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 EstimatesCONTENTS (cantinued)

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 PopulationWithin 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 fromNew 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 TechniquesCONTENTS (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 PracticesApplicable 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. SUMMARYAND 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-1FIGURES
Page Number

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 penetrationwith 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 impoundmentFIGURES (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 themodel 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

viiTABLES



### Number Page

2-1 

### Annual exposure equivalent (WLM) 

### as a function of age formembers 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-222progeny 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 thepopulation living within 0 

### to 5 

### km from the centroid of tailings impoundments of active and standbymills in 1983 4-36
Estimate of thepopulation livingwithin 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 frommaximum 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 6-5TABLES (continued)
Page Number

6-4 Summary of nationwidehealth 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 (thousandsof dollars per hectare) of attenuating radon-222 as a function of thiclcness (metersof 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 frommodel singlecell tailings impoundments 7-22

Estimated costs for a model single-cell tailings impoundment 7-23 Average radon-222 emission rate formodel 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 amodel 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 7-40TABLES (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 impoundmentwith final cover applied at 0, 20, and 40years after reaching capacity 8-4
Emissions and costs for model phased-disposal impoundments 8-5 Comparison of estimated death formodel 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 8-12Chapter 1: INTRODUCTION

This Background Information Document supports theAgencyss 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 ProtectionAgency (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 (42FR 2858), EPA issued Environmental Radiation Protection Standards for Nuclear Power Operations. These standards,promulgated in Title 40, Code of Federal Regulations Part 190 (40CFR 190), limit the total individual radiationdose due to emissions fromuranium fuel-cycle facilities, including licensed uranium mills. At the time 40 CFR 190was 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,theAgency exempted radon-222 from control under 40 CFR 190.

On September 30, 1983, theAgency issued standards under the Uranium Mill Tailings Radiation control Act (uMTRCA) (40CFR 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 standardswere promulgated, the Agency stated that it would issue
an Advance Notice of Proposed Rulemakingwith respect to control of radon-222 emissions from uranium tailings piles during the operationalperiod of a uranium mill.
On April 6,1983, standards for NRC licensees were proposed under the Clean Air Act (48FR 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 CleanAir Act standard-s,it was noted that radon-222 emitted from operating uranium mills and their actively used tailings piles were no'tsubject to any current orproposed 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 theAgency is considering emissions standards for licensed uraniummills and solicited information in the following areas:

o Radon-222 emission rates from uranium mills and associated tailings piles

o Local and regional impactsdue 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'suitprovision of theAct, 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. Thismotion 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 forpublic 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 (51FR 6382-6387). Subsequent to the announcement of the proposed rule, a public hearing was held on March 25, 1986 in Denver, Colorado (51FR 8205) and a second commentperiod 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 themethods 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 controlmethods are estimated. 

### A comparison of work practices, costs,and effectiveness is presented in Chapter 8.

Information for this studywas compiled from the technical literature,previous studies by EPA and the Nuclear Regulatory Commission, comments resulting from rulemaking notices, and discussionswith industry representatives. Comments received during the public comment period were incorporated into this final document as appropriate. No significant change in the technical informationwas made except for the Agency's revision of the risk factors associatedwith radon-222 exposure. These risk factorswere 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 informationwas corrected and the discussion of interim cover was revised.

1.3 Other EPA StandardsAffecting UraniumMills

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 ConservationAct. This Act requires that standards for nonradioactive hazards frcm uranium byproduct materials be consistent with standardspromulgated 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 inactiveuranium processing sites on January 5, 1983 (48 FR 590) under UMTRCA. For inactivemills, the standard specified in 40 CFR 192.02 requires that controls:
(a)Be effective forup 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 squaremeter 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 (48FR 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 themill 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 20picocuries per square meter per second

(pCi/m sj aftermill 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 concentrationsto 3 x 10- pCi/ml (30pCi/liter) in restric ed areas (i.e.,areas within the mill property) and 

# -6 3 

### x LO pCi/ml (3pCi/liter) in unrestricted areas. These concentrationsare 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 (50FR 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 constructionof tailings impoundments tomkni.mizeground-water contamination. In addition, States inspect tailing impoundment dams to ensure that they are built and maintained to minimi.zesafety 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-earlicensing
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

Themethodology 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-222progeny (radon-222decay 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-222progeny, 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.tingradiation 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-ingoperations enters the general environment from stockpiled ore and mill exhaust systems and through waste materials frommilling 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 themost important sources of cancer risk. Members of the decay chainwith 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.

Theprincipal 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 themoist 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 radiationpasses 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 theoreticalmodels, 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-222decay products to which people are exposed rather than
on the dose absorbed by the lung.Figure2-1. Radon-222 decay series.

2-3inqrowth 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-lifedecay products is eventually obtained. At secular equilibrium, the activities of radon-222 and of all its short-half-lifedecay 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 thepotential alpha energy from those decayproducts actually present to the potential alpha energy thatwould be present at complete equilibrium. As radon-222 and its decay products are transported by thewind, the equilibrium fraction increases with distance from the tailings pile, and at great distances, approaches the theoretical maximum value of one; however, depletionprocesses, 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 (inChapter 6),themodel uses the calculated effective equilibrium fraction at selected distances. from a tailings pile (seeTable 2-4 presented later in this chapter). For estimating population exposures, a population-distanceweighted effective equilibrium fractionwould 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'forcalculating 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-zinqExposures to .theGeneral Pooulation Vis-a-vis Undcrqround Miners
Although considerable progress has been made in modeling the deposition of particulatematerial in the lung (Ha82,Ja80, JaBL), adequate characterization of the bronchial 'ose delivered by alpha particles from inhaled radon-222progeny attached to dust particles is not yet possible. Knowledge is still lacking concerning the kinds of cells inwhich 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-222progeny 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-222progeny 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-222progeny.
Exposures to radon-222 decay products under working conditionsare commonly reported in a special unit called the working level (WL). One working level is any concentration of shorthalf-life radon-222progeny having 1.3 x 105 MeV per liter of potential alpha energy (FRC67). (AWL is also equivalent to approximately 100pCi/liter of radon-222 in secular equilibrium with its short-lived decay products.) This unit was developed because the concentration of specific radon-222progeny 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-222progeny for a working month of 170hours. Inasmuch as the results of epidemiological studies are expressed in units of WL and WLM, comparable estimates of 'exposurewere developed for members of the general population exposed to radon-222progeny, 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 hoursper day, 7 days a week), the average amount of air inhaled per minute (minute volume) is less in this group than that for amine worker when periods ofsj.eepi.nyand res'c:i.nii are talcen into account (EPA79, 'Th82)

, The radcn-.222progeny 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 (anddose) in the conducting airways of the lung is proportional to ventilation rate (quantity inhaled)has also been recommendedby 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-222model,however,
assumes an inhalation rate of 20 iitersper minute formine workers,which corresponds to 8 hours of light activity per day

(ICRP81j. 

### his may be appropriate for nuclear workers: however, studies of themetabolic rate of mine workers clearly show that they are not engaged in light activity only (Sp56,ICRP75, NASA73j. Therefore, 30 liters appears to be amore realistic estimate of the averageminute volume for this groyp. Based on this minute volume, a mine worker inhales 3,6x 10 cubic meters in a working year of 2000 hours LgCRP79). One working level of radon-322progeny 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
oneworking level is 7.5 

### x 20- joules.
According to the ICRP Task Group repor$ on reference man (ICRP75),an i.nhaledair volume of 2.3 x 10 liters per day is4 assumed for adultmales 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 formembers of the adult gopulation. This average volume resuits,in 

## - an intake of 8-04x 10 cubic meters of air and 1-67x 1.0 " joules per year 

### of inhaled potential alpha energy from a continuous exposure of an adult member of the population 

### .toone working 3.evel. of ra-don-222progeny for 365.25 days. Al'khoilghit 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 647Uwould 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 (seeTable 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 smallerbronchial area of children as compared with that of adults more than offsets their lower per-minute volume; therefore, for a given concentration of radon-222progeny, 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 informationwas 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 (2.08x 10- joulesper cubicmeter)

Age of generalpopulation (Years)

0-2 3-5 6-11 12-15 16-19 20-22 23 or more Exposure Equivalent (WLM)

Lifetime Average 31

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., formine 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 1980NAS BEIR-3 Report (NAS80)contains a review of epidemiological studies on mine workers and develops an age specific absolute riskmodel. 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, reanalyzesmany 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 aminimum inductionperiod, is a crucial factor in numerical risk estimates. For radiation-induced leukemia and bone cancer,theperiod 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, amodel is needed to project the risk beyond the period of direct observation. As discussed in the 1980NAS 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, inwhich it is assumed that the observed percent age increase of the baseline cancer risk per unit exposure (ordose) 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 65years 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 cancermortality, which peaks inmales at about age 75but is relatively constant in femalesuntil age 95 (NCHS73,NCHS83) (see Figure 2-3). The age-specificmortality 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 riskmodel can adequately account for the temporalpattern of cancer deaths observed in underground mine workers,whereas absolute risk projectionmodels fail to do so.

### AGEinYEARS
Figure 2-2. U.S. lung cancer mortality by age--1970 and 1980.2-3-2 The EPA Relative Risk b!odel

Since 1978,theAgency has based risk estimates dae to inhaled radon-222progeny on a linear dose-respor~sefunction,a relative risk projection mocJ.el, and a .ni.n-L.mum induction period of 10 years. Lifetime risks are projected on "theassumption 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 "toproject this risk 

### over a full life span.
The EPA model has been described in detail (EPA79,El79). A review of thismodel in light of themore recent information described herein revealed that the major assumptions, linear response, and relative risk projection have been affirmed. The A-bomb survivordata 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). TheUNSCEAR,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 McNeilllsana1ys.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 cancermo:rtalityrate per WLM. Thisvalue is based an the exce.ssiiiortality caused by lun~ cancer among exposed mine workers of varl-ousEges, many of whom smoked. Therefore, it represents 

### an avezage value for a mixed population of smokers, former smokers, arnd nnr;snolcers 'i'l?is assumptionmay tend to inflate the risk estimate (asdiscussed 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-arsi.r!?o were exposed to radon-222progeny, This study is unique 

### in that most of theminers were exposed to less than 100 WL1.I and tlhe risks to smokers and nonsmokerswere considered separately, The nbgoiute risks of the two groups were similar, 20 fatalitiesper 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 forthe smoking and nonsmoking miners, relative riskswere not. Nonsmokers have a much Lower baseline incidence of lung cancer mortality than smokers, This resulted in a relative risk coefficient fornonsmoking 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 ofmine 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-222progeny 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-222progeny 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. TheA-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 specificdata 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 survivordata 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 estimatedminimum 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 (casesper 10 inductionperiod 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 35years 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 riskmodels 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 consistentwith the incidence of excess lung
cancer observed in groups of underground mine workers than any of the othermodels 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 (whichwould 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 simpleproportional 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 arebased 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-222progeny, 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 cancerweighting 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.

TheUnited 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 Fagalitiesper 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 Th82 1CRP 150-450 Working 30 years ICRP8l lifetime 

# uNscT&y 200-450 Lifetime 40years UNSCEAR77 NCRP 130 Lifetime Lifetime NCRP84

(a)The number of fatalitiesper million-person WLM listed for EPA and NAS BEZR-3 differs fr&m those previouslypublished by6EPA [860 fatalitiesper LO PWLm and 850 fatalitiesper LO PWLSII, respectively (EPA83a)because the increased exposure equivalent applicable to childhood has now been included. Risk estimates forvarious sources of radon-222 in the environment have not changed because all were calculated in a life table analysisyielding 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 forbreathing rate (and other factors). For comparison purposes, thevalues in parentheses express the risk in more customary form, 

### inwhich a continuous exposure to 1 WL for a year corresponds to 51-6W1X.

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

(d)Assumes risk diminishes exponentially with a 20-year halftime.National Council on Radiation Protection and Measurements

TheNational 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 interestbecause, 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-yearhalf-life and, therefore, exposures occurring early in lifepresent 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 JapaneseA-bomb survivors (followingtheminimum latent period) would have decreased during theperiod 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 coefficientmay 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 estimatesmay be slightly high because they represent relative risks based on adult males, many of whom smoked. The actual riskmay 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 InformationDocument for Underground iiraniuxMines (EPA85),EPA averaged the estimates of BEIR-3, the EPA model, and.the AECB to est.ablishan upper bound of the range. The lower bound of the rangewas established, by averaging the UNSCEAR and ICRP estimates, The Agency chose not to include the NCRP estimate in its determination of the lowerbound 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.ustratethe breadth of much of current scientifi-copinion.

The lower limit of the range of relative risk coefficients, 1.2percent per WLM, is similar to that derived by the Ad Hoc Working Group to Develop RadioepidemiologicalTables,which also used 1.2percent per WUM (NIK85). Some other estimates based only on U.S. and Czech miner data average 1 percent per WLpa

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


# .
A possible 0.5 percent per WLM 1.ower bound of risk mentioned by the Environmental Prot.ecticnAgency 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 WTdor less,however, is usually 2.4 times ormore 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 ironminers 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-matedthe relati-verisk coefficient in these Swedish miners was 3-6percent 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 indwellings 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,theEPA is increasing theupper limit of its estimated range of relative risk coefficients. To estimate the risk due toexposure toradon-222 progeny, theEPA 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 thenearest whole number.

These changes are in agreementwith the recommendations of theRadiation Advisory Committee of the Science Advisory Board of EPA (SAB85)which recommended thatEPA use a risk coefficient range of 1 to 4 percent per WLM,as they believed thatboth overestimations of exposure and the effectof random error could have biased the risk coefficientsdownward, 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 aprecision that does not exist. In response to these recommendations,EPA used risk coefficients of 1 to 4percent per WLM. These risk coefficientswere obtained by rounding off the coefficients discussed above. Thebasis for these relative risk coefficientswas reviewed for this final report,but no changeswere made and the risk estimates are based
on 1 and 4percent per WWII,

Itmay be noted here that using a 1% to 4% relative risk per WLM with theWLM Exposure Equivalent defi-nedearlier is numerically the same as using a 0.6% to 2.4% relative risk per WLM with the conventional WM, (seetable 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 (WLper pCi/liter) (WL) ~Ci/l) (fe )

For individuals and regional populations, emission data and meteorological data are used with theAIRDOS-EPA model (74079)tc calculate air concentrations of radon-222; for national populations, emission data and meteorologica1 data are used with the NOAA Trajectory DispersionModel (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 ingrowthmod-elof 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 inminutes (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 1h (oneair change per hour) in combinationwith 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 equilibriumwith the radon-222 in theventilation 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 75percent of his orher 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 19,550meters.

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 riskTable 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 (tabulatedto 3 decimal places to facilitate comparisons) presume: a 3.5m/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 forventilation air with 100 percent equilibrium between radon-222 and its decay products; and an effective equilibrium fractionbased on 75 percent of time indoors and 25 percent of time outdoors.projections for lifetime exposurebased 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-222progeny 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 estimateswere based on the 1970 life table (NCHS75)and the 1970 mortality data (NCXS73). For this document the basis for calculationhas been changed to the recently available 1980 life table (NCHS85)and 1980mortality data (NCHS83).
Although this change provides risk estimatesmore appropriate for the l980s, the increase in the life span reflected in the iife table and,more significantly,the increase in lung cancer mortality (Figures2-2 and 2-3) have caused an appreciable upward change in the risk estimate. Lifetime risk estimatesmade using the relative risk projectionwith 1980 vital statistics are about 50% greater than thosemade 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% increaseper 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-222progeny (1980Life Table, 1980Mortality Data)

Lifetime risk of lung cancer Radon-222 progeny 4 percent increase lpercent 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 tomaximum 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 1percent 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 alsoused 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 fraction of 0.7. National an~lualcollective 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.REFERENCES

Archer V, E., Radford E, P.,and Axelson 0, wFactorsin Exposure-Response Relationships of Radon Daughter Injury*'!in: Conference/Workshop on Lung Cancer Epidemiology and Industrial Applications of Sputum Cytology, Colorado School of Mines, Golden, Colorado, pp. 324-367, 1979.
Bunger B., Cook J,R.,and Barrick M. K., "LifeTable Methodology for Evaluating Radiation Risk: An Application Based on Occupational Exposure", Health Physics 40, 439-455, 1981.

Chameaud J.,Masse R., and Lafuma J., "Influence of Radon Daughter Exposure at Low Doses on Occurrence of Lung Cancer in Rats",Radiat. Prot. Dos. 

### 1,385-388, 1984.

Chameaud J., Masse R.,Morin M., and Lafuma J., "Lung Cancer Inductionby Radon Daughters in RatsM,in: Occupational Radiation Safety in Mining,Vol. 1, H. Stocker, editor, CanadianNuclear Assoc., Toronto, Canada,pp. 350-353, 1985.

Cook J. R., Bunger B. M., and Barrick M. K., "A Computer Code for Cohort Analysis of Increased Risk of Death (CAIRD)",Technical Report 520/4-78-12, Office of Radiation Programs,USEPA,Washington, D.C., 1978. Edling C., Kling H., and Axelson,O:,"Radon in Homes

## - A Possible Cause of Lung Cancer", In: Lung Cancer and Radon Daughter Exposure in Mines and Dwellings. Linkoping University Medical DissertationsNo. 157, by Christer Edling, Department of Occupational Medicine, Linkoping University, Linkoping,Sweden,pp. 123-149, 1983. Edling C., Wingren G., and Axelson O., "Radon Daughter Exposure in Dwellings and Lung Cancer", in: Indoor Air,Volume 2: Radon, Passive Smoking,Particulates and Housing Epidemiology, B. Berglund, T. Lindvall and 3. Sundell, editors, Swedish Council for Building Research, Stockholm,Sweden,pp. 29-34, 1984.Ellett W. H. and Nelson N. S., "EnvironmentalHazards From Radon Daughter Radiation", in: Conference/ Workshop on Lung Cancer Epidemiology and Industrial Applications of Sputum Cytology, Colorado School of Nines Press,Golden, Colorado,pp. i14-148, 1979.

Ellett W. H. and Nelson N. S., "Epidemiologyand Risk Assessment: Tests of Models for Lung Cancer Induction, in: indoor Air and Human Healthw,R. B. Gammage and S. 

### V. Kaye, editors,Lewis Publishers, Inc.,Chelsea, Michigan, pp. 79-107, 1985.

Environmental ProtectionAgency, "Indoor Radiation Exposure Due to Radium-226 in Florida Phosphate Lands", EPA 520-4-78-013, Office of Radiation Programs,USEPA, Washington,D. C., revised printing,July 1979.
Environmental ProtectionAgency, "Final Environmental Impact Statement for Remedial Action Standards for Inactive Uranium Processing Sites (40CFR 192), Volume I",EPA 520/4-82-013-1, Office of Radiation Programs, USEPA, Washington, D.C., 1982.

EPA83a Environmental ProtectionAgency, "Final Environmental Impact Statement for Standards for the Control of Byproduct Materials from Uranium Ore Processing (40 CFR 192), Volume I",EPA 520/1- 83-008-1,Office of Radiation Programs,USEPA,Washington, D.C., 1983.

EPA83b Environmental ProtectionAgency, "Final Environmental Impact Statement for Standards for the Control of Byproduct Materials From Uranium Ore Processing (40CFR 192), Volume IIw,p. A.2-33, EPA 520/1-83-008-2, Office of Radiation Programs,USEPA,Washington, D.C., 1983.

EPA84 Environmental ProtectionAgency, "Radionuclides Background Information Document for Final Rules,Volume I",EPA 520/1-84- 022-1,Office of Radiation Programs, USEPA, Washington, D.C. 1984.

EPA85 Environmental ProtectionAgency, "Background Information Document--Standard forRadon-222 Emissions fromUnderground Uranium Minesw, EPA 502/1-85-010, Office of Radiation Programs,USEPA,Washington, D.C. 1985.

Ev69 Evans R., "EngineersGuide to the Elementary Behavior of Radon Daughtersi', Health Physics,

### 17,229-252, 1969.Federal Radiation Council, "Radiation Guidance for Federal Agencies,Memorandum for the President", July 21, 1967, 32 FR 113.83, 84,August 1, 1967.
Harley N. H. and Pasternack B. S., "Environmental.Radon DaughterAlpha Dose Factors in a Five-Lobed Human Lungt\ Health Physics,

### 42,789-799, 1982.

Hofmann W. and Steinhausler F., "Dose Calculations for Infants and Youths Due to the Inhalation of Radon and Its Decay Products in the Normal Environmentiv, in: Proceedings of the 4th International Congress of the International Radiation ProtectionAssociation, Paris, 2 497-500, 1977. 

## -, Hofmann,W. "Cellular Lung Dosimetry for Inhaled Radon Decay Products as a Base forRadiation-Induced Lung Cancer Risk Assessment", Radiat. Environ. Biophys., =:95-112 (1982)


# .
Howe G. R., "Presentation at the Society for EpidemiologicalResearchw,19th Annual Meeting, Chapel Hill,North Carolina, June 18-21, 1985.

International Commission on Radiological Protection, "Report of the Task Group on Reference Man", LCRP Publ. 23, Pergamon Press,New York, 1975.
International Commission on Radiological Protection, MRecommendationsof the International Commission on Radiological Protection", ICRP Publ. 26,Ann. ICRP, i

(I),Pergamon Press, 1977.

International Commission on Radiological Protection, ivLimits for Intakes of Radionuclides by Workers", IIGRP Publication 30, Part 1,Ann. ICRP,2 (3/4), Pergamon Press,New York, 1979.

International Commission on Radiological Protection, "Limits for Inhalation of Radon Daughters by Workersw, ICRP Publication 32,Ann. ICRP,

### 6,Pergamon Press, 1981.

JacobiW. and Eisfeld K., "Dose to Tissue and Effective Dose Equivalent by Inhalation of Radon-222 and Radon-220 and Their Short-Lived Daughterss\ GGFS Report S-626, Gesellschaftfur Strahlen und Unweltforschung mbH, Munich, 1980.JaEl JamesA. C,, Jacobi W. and Steinhausler F,, "Respiratory Tract Dosimetry of Radon and Thoron Daughters: The State-of-the-Artand ~mplicationsfor Epidemiology and Radiology", in: Proceedings of the International Conference on Hazards in Mining: Control, Measurement, and Medical Aspects, October 4-9, 1981, Golden, Colorado, editor Manual Gomez, Society of Mining Engineers,New York,pp. 42-54, 1981.

Ja85 JacobiW., ParetzkeH. G. and Schindel F., "LungCancer Risk Assessment ofRadon-Exposed Miners on the Basis of
a ProportionalHazard Model", in: Occupational Radiation Safety in Mining,Volume 1,H. Stocker, editor, Canadian Nuclear Association, Toronto, Ontario, Canada,pp. 17-24, 1985.

Ka82 Kato H. and SchullW. J., "Studiesof theMortality of A-bomb Survivors, 7. Mortality, 1950-1978: Part I", Cancer Mortality,Rad. Research, 90,395-432, 1982.

(Also published by the Radiation Effect Research Foundation as: RERF TR 12-80, Life Span Study Report 9. Part 1.)

Lu71 Lundin F. E. Jr.,Wagoner J. K. and Archer V. E., "Radon Daughter Exposure and Respiratory Cancer, Quantitative and Temporal Aspects", JointMonograph No. 1,U.S. Public Health Service,U.S. Department of Health,Education and Welfare, Washington, D.C., 1972.

Mc78 McDowell E. M., McLaughlin J. S.,Merenyi D. K., Kieffer R. P.,Harris C. C., and Trump B. F., "The Respiratory Epithelium V. Histogenesis of Lung Carcinomas in Humans'" J. Natl. Cancer Inst., 6l, 587-606, 1978.

Mc83 McDowell E. M. and Trump B. F., "Histogenesis of Preneoplastic and Neoplastic Lesions in TracheobronchialEpitheliumi',Surv. Synth. Path. Res., 2,235-279,1983. 

### -
Mo76 Moeller D. W. and Underhill D. W., ":FinalReport on Study of the Effects of Building Materials on Population Dose Equivalent",School of Public Health, Harvard University, Boston, Massachusetts, December 1976.Moore K. E., Baes C. P, 111,McDoweTl-Boyer I,. M., Watson A. P.,Hoffman F. O., Pleasant J, G., and Miller C. W., "AIRDOS-GPA: A Computerized Methodology for Estimating Environmental Concentrations and Doses to Man fromAirborne Releases of Radionuclidesw, ORNL-5532,Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1979.

Muller J.,Wheeler W. C., Gentleman J. F., Suranyi G., and Kusiak R. A., "Study of Mortality of Ontario Miners, 1955-1977, Part I",Ontario Ministry of Labor, Ontario, Canada,May 1983.

National Academy of Sciences

## - National Research Council, "The Effects of Populations0' Exposures to Low Levels of IonizingRadiationw,Report of the Committee on the Biological Effects of Ionizing Radiations (BEIRReport),NAS,Washington,D.C., 1972.
National Academy of Sciences

## - National Research Council, "The Effects of Populations of Exposures to Low Levels of IonizingRadiation: 198OV,Committee on the Biological Effects of IonizingRadiation (BEIR-3 Report), NAS,Washington, D.C., 1980.

National Aeronautics and SpaceAdministration, "BioastronauticsData Book",NASA SP-3006, 2nd Edition, J. R. Parker and V. R. West 

## - editors,NASA, Washington,D.C., 1973.

National Center forHealth Statistics, "PublicUse Tape,Vital Statistics

## - Mortality, Cause of Death Summary

## - 1970",PB80- 133333,NTIS, Washington, B.C., 1973.

National Center for Health Statistics, "U.S. Decennial Life Tables for 1969-1971,Volume 1,No. I", DHEW PublicationNo. (HRA) 75-1150. U.S. Department of Health, Education and Welfare,USPHS, NCHS,Rockville, Maryland, 1985.

National Center for Health Statistics, "PublicUse Tape,Vital Statistics

## - Mortality, Cause of Death Summary

## - 1980",PB83-261578,NTIS, Washington,D.C., 1983.National Center for Health Statistics, "U.S.Decennial Life Tables for 1979-1981,Volume 1,No. 1, 'United States Life Tablesw,PHs PubiicaticnNo. 85-1150-1, Department of Health and Human Services,USPHS,NCKS, Hyattsville, Maryland, 1985.

National Council on Radiation Protection and Measurements, "Evaluationof occupational and Environmental Exposures to Radon and Recommendations", NCRP Report No. 78,NCRPM,Washington, D.C., 1984.

National Institutes of Health, "Reportof the National Institutes of Health Ad Hoc Working Group to Develop RadioepidemiologicalTables",NIH Publication No. 85-2748,U,S. Department of Health and Human Services, NIX, Bethesda,Maryland, 1985.

National Institute for Occupational Safety and Health, "Evaluation of Epidemiologic Studies Examining the Lung Cancer Mortality of Underground.Miners",National Institute for Occupational Safety and Health, CDC, Cincinnati,Ohio,May 9,1985. Nuclear Regulatory Commission, Draft Generic Environmental Impact Statement on Uranium Milling, Volume 11,NUREG-0511,USNRC,Washington, D.C., 1979.
Oakley D,T.< "NaturalRadiation Exposure in the United States",ORP/SID 72-1,USEPA, Washington, D.C., 1972.

Porstendorfer J., Wicke A., and Schraub A., "The Influence of Exhalation,Ventilation, and Deposition ProcessesUpon the Concentration of Radon, Thoron and Their Decay Products in Room Ai.rw,Health Physics,

### 2, 465-473, 1978,

Prentice R. La,Yoshimoto Y., and Mason M. W., "Relationshipof Cigarette Smoking and Radiation Exposure to Cancer Mortality in Hiroshima and Nagasakiv1, J. Nat. Cancer Inst,, 79,611-622, 1983.

Kadford E. P.,and Renard K. G. St. Cl., '%Lung Cancer in Swedish Iron Miners Exposed to Low Doses of Radon Daughters",N. Gngl. 5.Ned., 31Q, 1485-1494, 1984.
Radford, E,P, "RadonDaughters and Lung Cancer". N. Engl. J. Med., =:1610-1611 (1985)..$A138 5 Science Advisory Board, "Letter from the Radiation Advisory Committee of the Science Advi.soryBoard of EPA to Lee M. Tl?ornas, Admi.nistrator of EPA, dated November 5, 1985", on the subject of EPA radon risk estimates.
Sp56 Spector W. S., editor, "Ra.ndbookof BioLogical Data, Table 314,Energy Cost,Work: Man", W, B. Sanders Go,, Philadelphia, 1956.
St85 Steinhausler F., and Kofmann W,, "inherent Dosimetric and Epidemiological Uncertainties Associated with Lung Cancer Risk Assessment in Mining Populations", in: Occupational Radiation Safety in Mining, Volume 1,He Stocker, editor, Canadian Nuclear Association, Toronto, Ontario, Canada, pp. 327-334, 1985.

Th82 Thomas D. C., and McNeill K. G., "Risk Estimates for the Health Effects of Alpha Radiationw,Report INFO-0081, Atomic Energy Control Board, Ottawa, Canada, 1.982,

UNSCEAR77 United Nations Scientific Committee on the Effects of Atomic Radiation, "Sources and Effects of Ionizing Radiationw,Report to the General Assembly, with Annexes, UN publication E. 77 IX.i., United Nations, New Uork, 1977.

Wh83 Whitemore A. S. and McMillar A., "Lung Cancer Mortality Among U,S.Uranium Miners: k ReappraisaTli, Technical Report No. 68,Department of Statisticsi Stanford. University, California, 1983.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 concentrationsof 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 99.3percent 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-219and radon-220) occur from the decay of uranium-235 and thorium-232,but these isotopeshave 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 90percent 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 leftbehind and disposed of with themill waste (tailings). These tailingswill remain radioactive for hundreds of thousands of years.
Radon-222 is the only member of 'thedecay 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) themineral matrix that contains its parent, radium-226. The subsequent radioactive decay of radon-222 produces a series of solid radioactive products called "radonprogeny.!! 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 inwater 51 cms in 100 grams at 0°C

8.5 cm3 in 100 grams at 60°C

Half-1ife 3.824 days
Decay modes and energy

ci 5.4897 MeV

Y 0.512 MeV

(a) Source: ChemicalEngineer's Handbook,Perry,J. H. (editor), McGraw-Hill Book Co., New York,New York, 1983,and Chart of the Nuclides, KnollsAtomic Power Laboratory,Operatedby 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 amile,however, the contribution of radon-222 concentrations from themills and tailings piles is indistinguishable from natural background (NRCBl). Some uranium-238, 1-2 ppm, is present inmost soils; therefore, radon-222 is emitted constantly from the Earth's surface (NRC81). It is estimated that 120million 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 licensedmills currently contributes about 140,000Ci/y (PEI85).

3.3 Sources of Radon-222 Emissions in theMillinq 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 uraniummetal, 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 tailingspiles are sources of radon-222 at operational uraniummills, 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 comparisonwith 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 advectivemechanisms. 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 releaseper 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 currentlymined contain an average of about 0.1 percent uranium. When uranium ore lies underground, only a very small fraction (ifany) of the radon-222 it producesescapes 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 ismined 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 atmosphereby diffusive and advectivemechanisms. Both the increased surface area of the particles and increased porosity resulting from themilling 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 themill feed is of uniform grade,which is necessary to achievemaximum efficiency in themill circuit. Blending may be performed at either the mine or themill. Ore is stored in stockpiles on ore pads at themill site. The stockpiles provide sufficient feed for a continuous supply to themill. Ore received from themine often has a high moisture content; however, the dry climate typical of themajor uranium districts
causes rapid drying. For this reason, some ore storagepiles are sprayed with water to maintain theirmoisture content and to reduce dusting.
Storage pads typically cover several acres and provide enough ore storage to feed themill for one or two months of operation, Ore usually is not kept 

### on the storagepad 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 themill site than would be if themill were operating at full capacity. The ore residence time in storagepiles 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 themass of a pile. The piles vary in shape among different mills, but they are frequently conical, oblong,
or wedge-shaped. A maximum height of 10m (30 ft) and 45-degree sloping sides are common. Thevolume and surface area of a typical pile have been estimated to be 8000

### m and 2500m 

### , respectively (Th82). 

### missions of radon-222 from stockpiles areconsidered 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 severalweeks, a nearly constant radon-222 flux (emissionrate) 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 (undersizedmaterial) 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. Thesebins provide a fine-ore storage capacityup 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-orebins to the grinding circuit, where rod and ball mills or semiautogenousmills are used to reduce the ore size further. Occasionally,the ore is roasted before it is sent to the grinding circuit to reducemoisture before grinding, to increase the solubility of othervaluable constituents (e.g., vanadium), or to improve the physical characteristics of the
ore. The ores are ground dry and then slurriedwith 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 coarserparticles 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, semiautogenousgrinding is being used increesingly inplace of dry crushing orball and rod mill grinding operations, which may be run wet or dry. The semiautogenous grinder performs the ore sizing functionof 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 theprocess of transferring and dumping the ore into themill feed area, The
ore is typically reduced to sizes of less than 40 cm,which is the relaxation diameter for rad0n-~22~diffusion from orepieces with diffusion coefficientsof 10-

### cm /s; therefore, radon-222 escapes readily from the pores of the orewhen 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 14cmparticles 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 smallerparticle 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 shortmilling time (lessthan 24 hours) does notpermit significant formationof 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 (12percent or Less)

(NRCBO)and is thepredominant Leach process in theUnited States. A flowdiagram of the acid leach/solvent extraction process is shown in Figure 3-3,


### The leaching circuit consists of a series of 

### mechanically agitated tankshaving a total ore residence time of approximately 7

### hours. ThepH in the tanks ismaintained between 0.5 and 2.0 

### by adding.sulfuricacid. The free acid concentration is from 1 to 90 

### grams of acid per liter during the contactperiod (NRC80). Acid leaching is carried out at atmospheric pressure and slightly above room temperature.
After leaching,thepregnant leach solution is separated from the tailing solids in a countercurrent decantation (CCD) 

### circuit. The sands and slimes are pumped to a tailingspond 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 (10to 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 solutionby the addition of gaseous ammonia (NH ), sodium hydroxide (NaOH),hydrogen peroxide (H 02),or ma3nesia (MgO)in several stagesunder controlled $H. Most mills use gaseous ammonia. Theprecipitated 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 0.1percent 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 200mesh (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.

### CRUSHINGAND

WET GRINDING 

# I

SODIUMCHLORATE TAILINGSPOND (TAILINGSSANDAND SLIMES,

I 

### LIQUIDWASTES)

COUNTERCURRENT

SOLVENT EXTRACTION FURTHER P 

### ROCESSING

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

### CRUSHINGAND GRINDING

WET GRINDING

FLOCCULANT COUNTERCURRENT FILTRATION TAILINGS

10

### GRINDING 

### AND LEACHING

Y

### ELLOWCAKE

Figure 3-4. Simplified flowdiagram of the alkaline leach-caustic precipitation process.Dry tailings from an acid leach mill are typically composed of 20 to 37 percent slimesby weight (NRCBO). Tailings are discharged from themill as a slurry at an average ratio,by weight, of about l:l (solidsto 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 concentrationsof radium-226 present. The fine slimes fraction contains the majority of radium-226 in the tailings (upto 80 percent) (NRC80). The sands fraction contains radium-226 in concentrationsranging from 26 to 100pCi/gram (NRC80),and the tailings liquid (raffinate) contains 1.7 to 35,000pCi/liter of radium-226 and 50 to 250,000 pCi/liter of thor.ium-230 (EPA83).

Themethods 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. Themore porous sands are deposited away from the center of thepile and are therefore typically drier than the slimes,which are usually saturated with moisture of actually covered with standingprocess fluids.
Except for a small percentage used for backfill in underground mines, virtually all tailings are disposed of in impoundments. Disposal is below grade inmined-out or excavated pits and above grade behind dams. Themajority of the tailing impoundmentsat licensed mills are above grade. Currently,new dams are constructed of earthen material, whereas in the past they were constructed of tailings sands. Impoundment sizesvary 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 earthenmaterial,but
some (atsix 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 (40CFR Part 440) and rely on evaporation.Constrrrcting impoundments with earthen embankments or below grade is thepreferred method at new milling operations or for new impoundments at existing mills because they inherently have greater short-termand 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 ratesvary in different areas and over time. A qualitative illustration of the variation in radon-222 emissions over the Life of amilling 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 themill. Radon-222 and radium-226both 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). Itwould 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 variationsmake 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 lmeter deep). This work has largely been carried out in support of the Uranium Mill Tailings Remedial Action Program (UMTRAP). Although these calculationswere developed for inactivemill 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 atthe surface of the source t 2 (pCi/ms);R is ttre speeific activity of radium-226 inore 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 fraction of source, dimensionless:



### -6 

### h is the radon-222 decay constant (2.1 x 10 /s): D is the effective diffusion coefficient 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.onwithin 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~uetersrequired 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 orevile 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 10m 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 diffusioncoefficient = 0.05 ci~ /s 104Rp~ (hD) 112 281 x 0.2'~ 1.6 (2.1x x $ 0.05)1/2
4 2 2 10 cm /m 2 291 pCi Rn.-222/m s

The ore pad would have the €ollowitlgcalculated 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~rlssioxisare:

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~yoperation. Hence, the ore does not refease large quantities of radoil-222 in the lnill circuit unless tlie radoil--222that previously emanated from the
ore was not released completely dirrir~gstorage. handlirlg, and crusb.lngand grinding.

Most milling emissions of radon222 occur during the transferrit1q and d~lmpingof 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-222emissions frunl mi.l.liilg

1800 tiday 

### x 310 daysjy 

### x 2200 Lb/t X 0.001 ib '7 U 0 libore 

### 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&eproduct 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.emissions Prom Tahlitlgs Disp.~._l, 3.4.3 The large area occupied by tailings impound~rrentuaE1d 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 willdepend
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-ffusionequation to estimate radon-222 flux may be used. Where specific iftformation is not available. a simplified relationship of 1pci ~n-222fms per pci ~a-226/gof 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 10m (30 ft)deep.

Emission estimates made by usinq diffusioqEquation 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/cm3



### -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 f4x 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 thedry
area and seconds per year.

Emissions estimate based on specificflux of 2 1 pCi ~n-222/m s per pCi Ra-Z26/g

The simplified calculation based on a specificflux of 1 pCi Rn-222/m s per pCi Ra-226/g yields a similar but higher emission estimate inthis example case.
In almost all cases, the tailings impoundlnents are byfar 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 isthe 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 estimating, at various locations. its concentration and the corresponding exposure to its decay products inunits ofWLW 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.
TheAIRDOS-EPA code uses a modified Gaussian plume equation to estimate airborne dispersion. Calculations are site-specific and require the joint frequencydistribution of wind direction, windspeed, and atmospheric stability. The accuracy of these projections decreaseswith distance; therefore, calculationswith thismethod are limited to regional areas (e.g., less than 80 km from the source). Thevalues 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-222progeny 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 dispersionmodel developed by the National Oceanic and Atmospheric Administration (Tr79)were used to estimate the national impact of radon-222 emissions. Themodel yields radon-222 concentrations in the air (inpicocuries/ 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 thatworking 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 tomeasure 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-222present in the ambient air and typically have short sample collection periods (i.e., minutes). Concentrating samplers use amedium 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 constructionvary 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 (onthe 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 concentratingmedium. Their physical dimensions and the quantity of charcoal used to collect a radon-222 samplevary 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 sampleby 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 (nomatter 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-keVpeak 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 theAIRDOS-EPA and DARTAB Computer Codesw, ORNL-5720,Oak Ridge National Laboratory, Oak Ridge, Tennessee,March 1981.

EPA79 U.S. Environmental Protection Agency, "IndoorRadiation 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.

EPA83 U.S. Environmental ProtectionAgency, "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 ProtectionAgency, "Draft Document-Estimates of Population Distributionsand TailingsAreas 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 forUranium Milling Operations",PNL for U.S. Nuclear Regulatory Commission, Washington, D.C., NUREG/CR-4088 June 1985.

Me71 Merritt, R. C., "The Extractive Metallurgy of Uraniumu, prepared under contract with the United StatesAtomic Energy Commission, 1971.

M079 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 HazardousWaste", 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 forU.S. Environmental ProtectionAgency, Office of Radiation Programs,June 1985 (revisedNovember 1985).

ThomasV. W.,Nielson K. K., and Mauch M. L., "Radon and Aerosol Release From Open PitUranium 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.ctiveMaterials"',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 additionalmills have been licensed,but either have never been constructed or have never operated. Only 4 of the 26 licensed facilitieswere operating; 16 were on standby status,and 6 were being or have been decommissioned. Themills on standby status
are being maintained,but they are not processing uranium ore. When the demand for uranium increases, these standbymills 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 themid-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 uraniummills were prepared aspart 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 impoundmentswere taken from a 1984 survey that BattelleTable4-1- ting statusandcapacityof li ed wnventional 

# =@? uranimmills asofAugust 4, 1986

State Mill Owner 

### (-@=at* 

# Op"tw capacity status (tons/day)(')

Colorado Canon City Uravan

NewMexico L-Bar Churcbrock Bluewater Quivira Gmts
SoutbDakota Edgemnt

Texas

Utah Panna Maria Conquista Fay

### mint

WhiteMesa La Sal Moab ShootaringCanyon

Ford Shemod 

### cotter Corp. UmetcoMinerals

Sohio/Kennecott United Nuclear Anaconda K€XT-Md;ee Hmestzke

Chevron Conoco/Pioneer Won

UmetcaMinemls Riohlgm Atlas PlateauResources

DawnMining WestemNuclear standby s-Y Decormnissioning(dl ~ssioning (d) ~ssion~ (dl s-4re) Active

Active kdssioned Dedssioned

Active(f) Active(g) s-Y s-YMenlorial 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-iationPrograms to augment t'ne available data base (EPA85)-

A sunliatary of current cai?ditionsand the extent of 'tailings impoundments and evaporationponds 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.tienand Umetco Minerals (Union Carbide) in Canon City and Uravan (seeFigure 4-2)- A third mill, PioneerNuclearisproposed SanMiguel mill in San Miguel County,was licensed but never constructed. The license for this mill 

### is under litigation (NRC84).

The Cotter Corporation, a subsidi.aryof Comvlonwealth Edison, operates a two-stage acid leachmill at Canon City, Colorado, which recoversuranium and vanadium. A small alkaline leachmill 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 rangesbetween 0,23and 0.35 percent U308 (NRC84). Themi~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.ndmentthat covers 34 ha (84acresj 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 (77acres) 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

(7acres), of which I.. 8 ?].a(4.5acres) is dry (EPA85). The tailings disct~argeinto the pond is moved al.ong the perimeter during operations to keep the tailings wet and even18 distributed. This impoundmentnow 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 oEcurrent uranium mill tailings impoundment areas and radium-226 content

fC) 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. pondsTable 4-2. Summary of current uranium milltailings 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

AtlasMoab

Plateau Resources Shootaring
Washington Dawn Mining Ford 1-2$3 Ford 400 0000 0 0000 0 0 0 0 NNNN m iiid N -3 NN -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 mmmm mlm* 0044w
0Table 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 CityMill 

## @ Urnetco Minerals Uravan Mill

Figure 4-2. Location of millsinColoradoA,Lg-ha (3:L-acre)secoildary impo-undmentcontain-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 operationshas been constructed adjacent to themain impoundment. Approximately 0.4ha (1acre) 

### is covered with ponded solution, 0,4ha (1acre) consists of exposed saturated tailings, and about 12 ha (30acres) 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 decommissioningwaste 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 impoundmentswere $15,800,000 and $7,200,000, respectively (DOE82).

Canon City is located about 3.2 km (2mi) north of themill site. The area immediately surrounding the mill site is unpopulated, and the land is used primarily for livestock grazing

(DOE82). The nearest residents are 184people who live between 2 and 3 km (1.2 and 1.9mi) 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 (8mi/h) (DOE82).

Uravan Mill

Umetco Mineral" uranium mill in Uravan, Colorado, an area of rugged canyons and mesas, is 80 km (50mi) south of Grand Junction. Uranium,vanadium, and radium-226 recovery operations
were begun 

### at this site 

### in 2.915. Themill has been on standby status sinceNovember 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.

Themill uses a hot,highly oxidizing, two-stage acid leach to recover uranium and vanadium. During milling operations, ore has been received frommore 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 mesasaboveUrnvan. Impoilndments 1 and 2 are adjacent and overlapping and actua-llyconstitute 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 slimeswere carried to the interiorwith the tailings solution.
Impoundments 1 and 2 cover a combined area of 27 ha (66 acres) and have a maximum dam height of 46m (155 ft) (EPA85, DOE82). Impoundment 3 covers 13 ha (32 acres), and the dike is about 33

### m (110ft) 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 (37acres). 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 tailingsponds at closure. The SX ponds cover 15 ha

(36 acres) (NRC84)


# . The general area is sparselypopulated. 

### A recent survey indicates 349 people living from 2 to 5 km (1.2 to 3.0mi) away from themain tailings impoundments. The survey showed nobody livingwithin 0-5km (0.3mi) of these impoundments,but 147people lived 0-5to 1.0 km (0.3 to 0.6mi) distant (PNL84).
The climate at Uravan is semiarid, with only about 25 cm (LO inches) of precipitation a year. Evaporation is about 142 om (56inches) per year (EFA83b).

The five licensed mills located inNew Mexico are operated by Sohio/Kennecott Minerals,United Nuclear Corporation,Anaconda

(Atlantic Richfield), Kerr-McGee Corp. (Quivira Mining), and Homestake Mining Co. (seeFigure 4-3). Two additionalmills, 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 (44mi) west of Albuquerque and 16 km (10mi) north of Laguna,New Mexico. Ore is obtained from an underground mine in the Jackpile sandstone formation. The acid-leachmill began operations in 1976,but has been on standby status sinceMay 1981

(NRC84). The ore processing capacity of themill 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 0.30percent U O8 and averages 0.225percent (NRC84). Size reduction is aacomplishedby semiautogenousgrinding.

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 thatwas 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 solutionwas maintained about 60m (200 ft) from the dam crest. A light-track pressure dozer was used to construct raiseswith the sand tailings. The total impoundmentarea covers 72 ha (180acres), 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'ns solution (EPA85). The impoundment consists kg of about 1.6 

### x 10 tons of tailings. Themaximum height of the dam is 15m (50 ft) (NRC80). The facilitywas dgsigned to provide an ultimate storage capacity of 7.5 

### x LO tons of tailings (Jo80). The tailings are reported to contain 500pCi/g of radium-226 (EPA83b).
Durinq operations,ore is stockpiled at themill 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 2.5mi) away and 129 livebetween 4 and 5 km (2-5and 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 ofmills in New Mexico.United Nuclear Corporation'sChurchrock 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 0.381percent U308 (averageis 0.12percent) in a sandstone matrix. Fresh water for mill operations is obtained from underground mines. Themill has been on standby status since 1982.

The tailings impoundment is formed by a dam built from native clays and compacted coarse tailings. Ithas 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). Themaximum depth of tailings is about 15

### m (50 ft)6 The storage capacity of the pond is about 10

### x 10

### m (365x 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 (1.25mi) and 77 living within 3 km (1.9mi) (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 (93x 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 1percent 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 contaminatedby 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 (10mi) northwest of Grants, New Mexico. The site is in a small valley characterizedby
an undulating, relatively level surface with gentle swales and small rounded hills (DOE82). Themill was originally constructed in 1953 and operated until 1982,when it went to standby status. Since 1953,themilling operations have gone through severalmajor 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 2avebeen initiated at this mill.

The mill sitehas three tailings impoundments. Carbonate tailings from early operationswere deposited in
an area immediately northwest of themill 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 inwhat 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 (24acres), and in 1977 was covered with about 0.8

### m (2.5 ft) of native soil (DOE82).

Themain 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

(60ft) high at the south end and 6m (20 ft) high at the north end (DOE82). Tailings are discharged along the southergpart of the dam. This impoundment contains 25 

### x 10 tons of tailings (NRC84).

There are also 162 acres of evaporationponds 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 themain pond (NM85): however, it has also been estimated to average 620pCi/g (EPA83a).

The area around the Bluewater Mill 's sparsely populated. A 1983 survey indicated 907people living within 5 km (3.1mi) of themill (PNL84). Of this total, 142 lived within 3 km (1.9mi.). No one lives within 2 km (1.2 mi.) of the mill (PNL84)



## . Annual precipitation averages 22 cm (8.8 inches)--mostas rain,but some as snow. Wind is channeled through the valley in a westerly direction. The site is in the !!southwestmountains" climatological subdivision of New Mexico.
Quivira Mill

Kerr McGeelsQuivira mill has been on standby status since February 1985. The largest acid leach mill in the United States, its current capacity is 6350 t (7000tons) of ore per day (NCR84). The Quivira mill is in a flat area of the Grants Mineral Belt about 40 km (25mi) north of Grants,New Mexico. The mill began operation in 1958with a capacity of 3270 t of

(3600tons) sandstone ore per day.

All of the tailings from the mill are contained in two main impoundments, (Tailings impoundmentsNos. 1 and 2a) and two ancillary impoundments (2band 2c), Impoundment No. 1 was the most recently active area for tailings deposition. It extends southeasterly from the mill for about 1370m (4500 ft); its greatest width is about 820m (2700ft), and the outside berm ranges from 8 to 27 m (25to 90 ft) above ground level (COE82). An earthen starter dike was used al.ongwith the ~rpstrearr:me.thod of tailings disposal. 'Tailingswere 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 theberm, 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. ImpoundmentNo. L covers 108 ha (269 acres) and contains a liquid covered area of about 6 ha (14acres) (EPA85). Approximately 76 ha (191acres) are dry and the remaining 26 ha

(64acres) remain saturated (EPA85).
Tailings ImpoundmentNo. 2a covers about 42 ha (105acres) and is west of and contiguous with Pond No. 1 (EPA85). ImpoundmentsNos. 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 undergroundmine. Tailings set aside for use as backfillare contained in ImpoundmentNo. 2b, Heap leached tail-ingsare contained in impoundmentNo. 2c. Impoundments 2b and 2c cover 11 and 12 ha (28and 30 acres), respectively. Although no water is currentlyponded 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 620pCi./g of radium-226 (EPA83bjThe Quivira mill uses 15 evaporation ponds in its water management system. Theseponds currently cover a total.of 149 ha

(372acres) (EPA85). Of this total surface area, 107 ha (268acres) are covered with solution, 4 ha (10acres) are wet, and 38 ha (95 acres) are dry (EPA85). Some tailings soli.dsare carried with the liquid solution and are deposited in these evaporation ponds.

The area surrounding themill is sparselypopulated. 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 (1.2and 1.9 mi.) from the impoundment (PNL84). Precipitation averages 22 cm (8.8 in.) per year (DOE82). Local winds are channeled by thevalley, and gusts can exceed 80 km (50 mi) per hour.

Homestake Mill

Homestake Mining Company's mill is 16 km (10mi) 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. Themill has been on standby status since mid-1985. The ore grademilled at Homestake has ranged from 0.05 to 0.30percent U308 (NRC84).

Themill site is relatively flat and covers about 600ha (1500acres). 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 (8acres), of this tailings impoundmenthas 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-baseprism that rises above the flat ground surface (DOE82). It has a surface area of 82 ha (205acres) (including the sides) and is about 26 m (85ft) 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 tailingsdischarge. 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 (63acres)

(EPA85). Homestakemaintains 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 centerlinemethod of construction. A mobile cyclone is used to separate the sands and slimes. Decanted pond liquid is recycled back to themill. Surfacewater sprays and chemical treatmentsare 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 (1mi) of the mill. Homestake's 1982 license renewal application and the 1983 survey both indicated no population within 1 km (0.6mi). The 1983 survey indicated that 190 people live between 1and 2 km (0.6 to 1.2 mi.) from the impoundment (PNL84). The survey counted a population of 396 people within 5 km (3.1mi.) 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 characterizedby low precipitation [22 cm (8.8 in.)/y average), sunny days (75to 80percent), low humidity, wind gusts to 80 kilometersper hour (50 mph), and moderate temperatureswith 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 additionalmill, 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 PannaMaria Uranium Project of Chevron Resources Company is located in South Texas about 160 km (100mi) northwest of Corpus Christi and 10 km (6 mi) north of Karnes City. Themill processes about 2600 tons per day of a mixture of sandy clay oreaveraging 0.05 percent U 0 (Ma85). This facility,which
uses semi-autogeneousgrln8ing followedby 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 50ha (124acres); 14 ha (36 acres) consist of dry, exposed beach, and about 27ha (68 acres) are covered with tailings solution6(EPA85). The impoundment contains approximately 3.3 

### x 10 tons of tailings (NRC84). Itwas 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 6m (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 isperiodicallymoved around theperimeter of the impoundment. An exposed beach of coarse tailings forms along the dike and the tailings solution gathers in the centerportion 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 thewest (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 [69,000t (76,000tons) at capacity] is stockpiled on the pad.

A 1983 survey of population in the area indicated 453 people livingwithin 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/PioneerNuclear 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 (seeFigure 4-5) are owned 

### by Atlas Minerals, Plateau Resources, Ltd.,Umetco Minerals, and.

### Rio Algom Corporation.

Umetcq White Mesa Mill 

## ---
TheUmetco Mi.neralsWhite Mesa mill,which is about 8 km (5mi.) south of Blanding,Utah,began operating in July 1980. Thismill 

### is currently active. Semi-autogenousgrinding, acid-leaching, and solvent-extractionare used to process ores containing about 0.13 percent U O8 (NRC84). The capacity of themill is 1800 t (2000tons) 8f ore per day (NRC84). Approximately 500,000 t (550,000tons) of tailings are contained in three cells of a proposed six-celldisposal system. The cells contain 19, 24, and 21

### ha (48,61,and 53 acres) of tailings for a total of 64ha (162 acres) (EPA85). A total of 22 ha (56 acres) is covered by solution, 5 ha (13acres) are saturated,and 42 ha (106acres) 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 (30mi) 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, Themill's designed throughput is 700 t (750tons) of ore per day.

Over 1.6

### x 106 t (1.8x 106 tons) of tailings have been generated at this mill (NRC84). The tailings are contained in two unlined tailings impoundments retained by natural soil embankmentsplaced across a drainage course, one immediately upstream of the other (NRC84). The lower impoundmenthas been in
use since 1972, the upper since 1976. The total area of tailings is 30 ha (75acres) (EPA85). Approximately 6 ha (16acres) are covered with solution, 3 ha (7acres) 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 SalMill 

## @ Atlas Minerals Moab Mill 

## @ Plateau Resources, Ltd. Shootaring Canyon Mill

Figure 4-5. Location of millsinUtah.A 1983 survey of the population in the area indicated no inhabitants living within 0-3km (0,3mi,) of the tailings impoundment (PNL8.1). Eight inhabitantswere reported to live between 0.5 and 1.0 kn (0.3 and 0-6 mi) from 'he impoundment,and 105people between 1 and 2 km (0.6 and 1,2mi) from the impoundment (PNL84)

, Moab Kill

The Atlas CorporationMill is located on the Colorado River in a Long, narrow valley of a mountairlous area about 5 km (3mi,) northwest of MoaS, Utah, Themill, which began operations in October 1.956,is on standby status, Thismill. 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 frommultiple 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 impoundmentwith the tailings solution. The impoundmentsstotal surface area is 60ha (147acres (EPA85). Of the total area, 22 ha (54acres) are covered by ponded solution, 2 ha (4acres) are saturated,and 36 ha (90acres) are exposed dry tailings (incl.udingthe 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 (8and 10 x 106 tons) of tailings are contained in this impoundment (DOE82,NRC84)-

The radium-226 content of the tailingshas 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 tailingspire (PNL84). The same survey indicated no people l-ivingwithin 1.0 km (0-6 mi) and 9 people within 1and 2 km (0.6and 1.2 mi) from the impoundment, The survey also indicated that 2319 people were living between 3 and 5 km (1.8and 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 ameans of minimizing dusting, the dried tailings are sometimeswetted 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 fromApril to October 1982 and is currently on standby status. The capacity of themill is 725 t (800tons) 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 97,000tons of surface mined ore is stockpiled on site when themill is running at capacity (Ee85). The primary mill circuit involves semi-autogenousgrinding 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 shortperiod 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 (7acres), and about 0.8 ha

(2acres) 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 171people living within 4 and 5 km (2.4 and 3.1mi) of the tailings impoundment (PNL84).

Washington has two licensed conventionalmills, owned by Dawn Mining (NewmontMining/Midnight Mines) and Western Nuclear, Inc. (PhelpsDodge) (seeFigure 4-6). Another mill, owned by Joy Mining Company,was licensed,but was never fully operational. This lattermill 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 inWashington.Dawn Mining Mi1.L.

The Dawn Mining Mill,which is near Ford,Washington, about 72 km (45mi) 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 purchaseprogram. Themill 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 themill is 550 t (600 tons) of
ore per day, Themill circuit incorporates a two-stage agitation acid leach process followed by ion exchange and precipitation of uranium with ammonia, TheMidnight mining open-pit mine produces ore between 0.10 and 0.25percent U 0 (NRC84). During operations, a 1-year supply of ore 1183,000t (212,300 tons)] was maintained on a 6-ha (14-acre) stockpile at themill site

(DOE82).

The tailings generated by tbe DawnMill are contained in four separate impoundments, three of which are above grade, unlined, and constructedbehind earthen dams. These three impoundments have been filled to capacity and are inacgive. ImpoundmentNos, 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). ImpoundmentNo, 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 (95acres), all of which is dry (EPA85). ImpoundmentNo. 4 is an excavated, below-grade, lined (Kypalon)pond covering 11ha (28acres). Seven hectares (17acres) are covered by solution and 4 ha (11acres) are 

### dry (EPB95)- The tailings are covered with water to a depth of 1-2to 1.5 m (4to 5 ft). The radium-226 content of the DawnMill tailings is reported to be 240pCi/g (EPA86).

The community of Ford is located within 3.2 km (2mi) of the tailings irnpoundments. in 1983 approximately 411 people were living within 5 km (3.1mi.) of the tailings impoundments (PNL84). No one lived within 0.5 km (0,3mi) and 3 people Lived within 0-5and 1.0 km (0.3 and 0.6mi). Ninety-three people lived within l and. 2 km (0.6and 1.2 mi) and 157 lived within 2 and 3 km (1.2and 1.9mi) 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 (50in) (EPA83b).Western Nuclear Sherwood Mi.11

Western NucleartsSherwood uranium mill is located in eastern Washington about 64 km (40mi) northwest of Spokane. Ore taken from a nearby surfacemine 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

(94acres) (EPA85). Of this total, 7 ha (18acres) are covered with tailings solution, 28 ha (70acres) are dry, and the remainder is saturated (EPA85). Tailings slurry from themill was neutralizedwith lime before being pumped to the Hypalon-lined impoundment. Tailings solution decanted from the impoundmentwas 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 (10to 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 PathfinderMines Corp. (formerlyLucky Mc Corp.) Gas Hills Mill is located in the Gas Hills region of Fremond County, Wyoming, about 40 km (25mi.) 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. Themill uses an acid-leach process and
was the first in the United States to incorporate themoving-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 HillsMill 

## @ Western Nuclear, Inc Split Rock Mill 

## @ Umetco Gas HillsMill 

## (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~earCorp. Gas HillsMill 

## @ Exxon Corp. Highland Mill

Figure 4-7. Location of millsinWyoming.Company- owned open-pit 8ni.ni.n.y opefati.ons, Located L."So 3 km (lto 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 0.21percent 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 sitemakes 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 lRm (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 (21acres) 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 tailings 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 1m (3it)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.earPsSplit Rock Mill is located 3-2km (2miles) north of Jeffrey City,Wyoming. Thismill began operation in 1957 and has been on standby status since June 1981. When running at capacity,themill produced 935 tons of yellowcakeper year (Bo85)- Maximum throughputwas about 1700 tons of ore per day (NRC84). The ore grade has ranged from 0.15 to 0.30percent U 0 in the past and is expected to range from 0-05to 0.13 Bercent in the future (NRC84)


# . Milling operations involve semi-autogenousgrinding, an acid leach, and solvent extraction. Themill 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,ailingsimpoundmenthas a surface area of 62 ha

(156acres), and the maximum depth is about 29 m (95 ft)(EPA85, B085). Currently, 38 ha (94acres) 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 100pCi/g (99.5

## + 42 pCi/g) (Bo85). Radium-226 values in the sands and slimeswere 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 fluxmeasurements,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 threepeople lived between 0.5 and 1.0km (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 2.5mi), and 176 people within 4 and 5 km (2.5and 3.1 mi) (PNL84).TheUmetco minerals Gas Bills Mill is located in the southeastern portion af the Wind River Basin of Wyoming. The rni.11 is about 95km (60mi) west of Casper in an area of rolling hiL1s interspersed with relatively flat areas. Themill 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. Themill began operation in early 1960with 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 facilitywaskept in operation. During milling operations, a 2-month stockpile of ore ismaintained at the mill (Wo85). This amounts to 85,800tons when themil1 is operating at capacity.
During the anticipated t~tal active life of the project (1960to 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 themill" original above-grade tailings impoundmenthas 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

(25acres), 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 6ha (14acres) (EPA85). Themaximum height of the embankment of the original above-grade tailings impoundment (and expansions) is about 14 m (45 ft). This impoundmenthas a surface area of 6& ha (151acrgs), all of which is dry, and contains 5.8 

### x 10 t (6.4x 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 threeponds with a combined surface area of 8 ha (20acres).

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 livingwithin 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 reclamationplan, Umetcc is committed to provide a uniform cover of 0.3 m (1ft) 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, thebasic materials needed for the reclamationprogram will cost about $3,800,000.

Umetco also operates a heap leach facility in themill area at its Gas Hill site. The water used in the process [1.7 liters/s (27gal/min)] is taken from a nearby tailings area, and U O8 is recovered fromhigh-grade leach liquorby a solvent-extractionprocess. 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-pitmining operations in the Powder River area of Converse County, Wyoming, about 72 km (45miles) 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 them.ill on 

### an 8-ha (20-acre)pad; approximately 66,000 tons are currently on hand (Me85). Themill is currently operating at about 20percent of its capacity and is milling stockpiled ore. It is likely that themill 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 (121acres), of which 18 ha (45acres) are covered with tailings solution and 21 ha (53acres) are dry tailings beaches

(Me85). A portion, 13 ha (32acres), of the pile has been covered with 30 cm (Ifoot) 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 420pCijg (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 PathfinderMines Corporation Shirley Basin Uranium Mill is located in an area of plains and rolling hills about 72 km (45mi) south of Casper,Wyoming. The mill,which began operation in 1971, uses semiautogenousgrinding, leaching, and ion exchange. Currentmill capacity is 1600 t (1800tons) of ore per day (NRC84). Themill is currently active and has a throughput of 900 t (990tons) 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 18m (60 ft) high. The surface area of the tailings impoundment is lo ha (261acres), of which 72 ha (179 acres) are covered with ponded tailings solution (EPA85). Twenty-four hectares (60acres& are dry beaches. The impoundment contains 5.8 x 106 t (6.4x 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 (2.9and 2-5mi) from the i~~poundrnent, were the cnLy inhabitants within 5 km (3.1 mi) (PNL84). Minerals ExplorationMill

TheMinerals Exploration Company" sweetwater Mill is located within the Red Desert portion of Wyoming's Great Divide Basin, about 64 km (40mi) northwest of Rawiins. Themill, 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 (3000tons) 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 fluxmade on the tailings solids ranged from 90 to 100 pCi/m s (Hi85).



### A 1983 survey indicated no population living within 5 km (3.1mi.) of the tailings impoundment (PNL84). The annual precipitation in the area is 15 to 20 cm (6to 8 in.), and annual evaporation is 102 to 178 cm (40to 70 in.) (EPA83).

4.3 PopulationWithin 5 km (3.1mi) of Existina Tailinqs Impoundments



### A 1983 estimate indicated that 12,824persons lived within 5 km (3.1mi) from the centroid of the tailings impoundments at the active and standby sites (PNL84). No one lived within 0.5 km

(0.3mi), whereas 173 people lived between 0.5 and 1 km (0.6and 1.2 mi). Nobody lived within 5 km (3.1mi) of four of these mills, all of which were in Wyoming. A summary of this informationby state and by mill ispresented 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 (3.1mi) of these tailings impoundments. This more recent survey,which was based on interpretation of aerial photographs, indicated that no one lived within 5 km (3.1mi) of six of these tailings impoundments. The results of this later survey are presented in Table 4-4.T&Le 4-3. Estimateof thep0pulatic:n livingwivrbin 0 to5kinfrcm centroid of tail.ings .hpm&nent.s of a&j.ve and standbymillsin 1.983

# 'w

Colorado cotter 0 Umetco 0

NewMexico Sohio 0 United

Nuclear 0 Anaconda 0 Kerr-Mae 0 Hamestake 0

Texas Chevron 0

Utah Vmetco 0 RioAlgam 0 Atlas 0 Plateau

Resources 0 Washhqton Dawn 0 Western

Nuclear 0

WyanW Paathf jnder (GasHills) 0 Western

Nuclear 0 Ihietco 0 RockyMt. 0

Energy PaWfinder

(Shi-r1ey Basin) 0 Minerals 0

Exp.Table 4-4. :stL?ate of theppulation livhgtrfiihin0to 5km

### fron.tl'e centroidof L?il!inqs imp~mchnents of active 31ds'~%n&y "d11sin 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

(GasEiil1.s) 0 Westen1

Nucleax 0 Umetco 0 RG€QMt.

mewY 0 Pathfhder (Shj.rl.ey Basin) 0 Minerais

&p


## . 0

Total 0 12 569 833 4826 '5243 11,433Andrew R. E., "UraniumMills Program, Department of Social and Health Services, State of Washingtonv, Correspondencewith PEI Associates, Inc.,December 1984.
Bogden G., Western Nuclear, Inc., Correspondencewith 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 IndustryNot Viable in 1984,Determines DOE'S Harrington",November 1985.
Environmental ProtectionAgency, "Regulatory Impact Analysis of Environmental Standards for Uranium Mill Tailings at Active Sites",EPA 520/1-82-023,March 1983.

Environmental ProtectionAgency, "Final Environmental Statement for Standards for the Control of Byproduct Materials from Uranium Ore Processing (40CFR 192)",

(EPA 520/1-83-008-l),Office of Radiation Programs, Washington, D.C,, September 1983.

U.S. Environmental ProtectionAgency, "Draft Document-Estimatesof Population Distributions and Tailings Areas Around Licensed Uranium Mill Sitesw", Office of Radiation Programs,November 1985.

Environmental ProtectionAgency, "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., "Correspondencewith 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, Correspondencewith 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.

PacificNorthwest Laboratory. Estimated Population Near Uranium Tailings. (PNL-4959). January 1984.

Simchuk G. 

### J., PathfinderMines 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 (UnionCarbide), Correspondence with PEI Associates, Inc., February 1985.Chapter 5: INDUSTRYRADON-222 EMISSION ESTIMATES

5.1 Introduction

This chapterpresents 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 evaporationpond 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 arebased on an assumed emission rase that equals the specific flux of 1pCi radon-222/m s per pCi radium-226/g tailings for dry tailings times the dry area. Ithas been assumed that tailings that are either saturatedwith 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 1pCi 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 impoundmentmust be known. The surface area of existing tailings impoundmentshas 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, EPAFsOffice 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 resultsof a survey the EPA conducted of 22 uranium mill sites in 1985, This surveyproduced 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 informationwas also compiled for evaporationponds, These estimates of tailings areas were used as the basis for estimating radon-222 emissions in this report (SeeTable 4-2 in Chapter 4). This tabulation includes a listing,by state, of each known tailings impoundment and evaporationpond 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 impoundmentand evaporation pond area is 1570 ha (3882 acres), over 50 percent of which is dry. Only fourmills 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.

Emissionswere estimated for two conditions: current water-cover conditions (asof 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 evaporationponds. In the esti ates of radon-222 emissions, a 

# Y specific flux of 1pCi 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 calculationwas used to estimate emissions from dry areas:
2 kCi Rn-222/y = dry area,m2 x 1pCi 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 inT&ie 5-1, Summaryof radon-222 missions from w~iUn .milltailings s

cxrrent lxlrrrnt conditio wnditio After 

## %) wing (f

adored) (flux= 1)

Colorado CotterCop. 

### m-jmury Secondary

Umetw Iitpunc3ments 1& 2 ~un&ent 3 Sludgepile Evaporationpond

NewMexico Sohio LrBar

United Nuclear QIUrchrmk

Anaconda Bluewater I Bluewater 2 Bluewater 3 Evaporationponds

Kerr-McGee Quiviral Quivira 2a Quivira 2b Quivira 2c Evaporationponds

Hamestake Homestake 1 Homestake 2

ms Chewoi? Pm MariaTable 5-1. S of radon-222 emissions fromuranim milltailings impomIhnents (continued)

Radon-222 emissions (kCi/y)

Cuncmt Current wndition wnditio After Owner/lmpoundment (flux= 1) (factored)



# m Uinetco WhiteMesa 1 WhiteMesa 2 miteMesa 3

RioAlgom

Atlas Moab

Plateau Resources ShootariyCanyon

Western Nuclear Shemood Evaporationpond warning Pathfinder Gas Hills 1 Gas Hills2 Gas Hills3 Gas Hills4

Western Nuclear SplitRock

Umetco Gas Hills A-9 Pit Leachpile Zvapratj.on pondsTable 5-1. Sununaryof radon-222 emissions frmuranium mill tailings~unhents (continued)

Radon-222 emissions (kCi/y)

Cuncent Current conditio wnditio After Owner/Inpmndtment (flux= 1) ?a) (factored)

RockyMountainEnergy BearCreek

Pathfinder ShirleyBasin
Minerals Exploration Sweetwater

Totals 129 137 238

2 (a) Based on a specific fluxof 1pCiRn-222/m sperpCiRa-226per 

### gramof tailings fordryareasanda fluxof zeroforponded and wet areas.

2 (b) Specific fluxof 0.3pCim-222/111 s

### perpCiRa5226pergramof tailings forwet tailings

### area, 1pciRn-222/m sperpCiRa-226 per

### gramof tailings fordryarea,

### and zero forpond& areas.thepreceding 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 recommendedby NRC (NRC85) when specific data are lacking,alternative methods of flux estimation are available. One alternativemethod is to assume that2the radon-222 flux from dry areas is 1 pCi radon-222/m per pCi radium-226/g; zero fromgonded 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 thismethod of calculation indicate 137 kCi/y, as shown in Table 5-1.

Other alternative methods of estimating radon-222 emissions require site-specificdata. 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 forponded and saturated areas resulted in a conservative (high) estimate of radon-222 emissions. Total emissions estimated by using the assumed specific fluxwere about twice as high as thosemade using site-specific information. The site-specific informationwas 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 allowmore accurate calculation of emissionsbased on site-specific tailings characteris$ics; therefore,the specific flux (IpCi radon-222/m s per pci radium-226/g) for dry areas and zero for ponded and saturated areaswere used in this report. The emission estimatespresented herein may be conservative compared with estimates made by other means, but insufficient specific data are available to draw any definite conclusions.REFERENCES

EPA83 Environmental ProtectionAgency, "Final Environmental impact Statement for Standards for the Control by Byproduct Material fromUranium Ore Processingn,EPA 520/l-83-008-1, Office of Radiation Programs, U.S. EPA, Washington, D.C.,September 1983.

EPA85 Environmental ProtectionAgency, "Estimates of Population Distribution and TailingsAreas Around Licensed Uranium Mill Sites (Draft)" Office of Radiation Programs, Las Vegas Facility, Las Vegas, Nevada, 1985.

NRC80 Nuclear Regulatory Commission, "Final Generic Environmental Impact Statement onUranium MillingN, NUREG-0706, September 1980.

NRC85 Nuclear Regulatory Commission, "Methods for Estimating Radioactive and Toxic Airborne Source Terms forUranium 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 RISKASSESSMENT

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 futureby assuming that net? tailings impoundmentswill 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 exposurewere 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.TheAIRDOS-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 themaximum 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 (personWTA) for the population in the assessment area by a computerizedmethodology known as AIRDOS-EPA (~079).An effective equilibrium fraction of 0-7is presumed because little collective exposure takes place near themill.

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 sectorby the population in that sector. The parameters used in theAIRDOS-EPA code are shown in Table 6-2. An approximate emission height of 1meter was assumed in all cases. Meteorological parameters from selected weather stationswere used for each mill. Included in this table are the resulting exposure for that mill based on the emission rate and the population near themill. 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 estimateswere then multiplied by l520/760 or 380/760 to adjust to the risk coefficients of 4 and 1 gercent, respectively (1520and 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 (partiallywet 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 byproductmaterials. 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 riskof fatal. lung

### cancer frommaxdexposure foran individual livingnear tailingskpoundment

Maxh lifetime ~istance (a) State Millowner risktoindividual(b) meters

Colorado Cotter Umetco

NewMexico Kerr-MGee 1E-2 (2E-3) 2500 Anaconda 2E-2 (5E-3) 1500 UnitedNuclear 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 PlateauRes.
Washington Dawn 3E-3 (GE-4) 750 WesternNuclear 2E-4 (5E-5) 4500
WYomj-~ Minerals Exploration 4~-G (9~-7) 30000 Pathfinder Gas Hills 2E-3 (6E-4) 2500 ShirleyBasin 9E-5 (2E-5) 15000 RockyMt. 9E-5 (2E-5) 15000 Umetco 1E-4 (3E-5) 15000 WesternNuclear 2E-3 (5E-4) 750

(a) Distance fromcenter of a homogenous circularequivalent impoundment.
(b) Thevalueginthe firstcolmisbased on a riskfactorof 1520 deaths/lO pergon WLM, and thevalues inwenthesesarebased on 380 deaths/lO personWLM.Table 6-2. AIRCOS-EPA code inputs and estimatedrisks

ADDEcode inputs Approximate Atmospheric Ambient impOWent 

# m Precipitation t~rature area I3?aths/yeara State C0l'F-Y depth (m) 

### (WY) (

### c) (ha) 0-5Ian 5-80lon

Colorado Cotter mtco

NewMexico Kerr-Ma Anaconda UnitedNuclear Harnestake Sohio

5- I Texas Chevron
C Utah Umetco RiaAlgam Atlas PlateauRe. Washington Dawn WesternNuclear



### 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 ShirleyBasin 700 29.6 6 20 

### - 4.63-3 RockyMt. 700 35.4 6 20 

## - 3.7'0-3 Umetco 700 33.9 6 80 

## - 2.23-3 WesternNuclear 700 28.0 6 20 1.4E-3 5.23-4

(a) Based on 760deathsper lo6personWLM.
(b)Zeropopulation inthe 0-5 Ianregion.Table 6-3. S of regional healtheffects fromexisting tailingswundments

Conditionof Esnissions

### (a) Cdttedfatalcancers pervear(b) tailinqs (kCiLy) 0-5km 5-80

### km 0-80km

Current 129 0.3 (0.1) 1.6 (0.4) 1.8 (0.5)

2 

### (a)Based onradon-222 fluxof 1pCi/m 

### perpCi ofRa-226

### pergram of tailings.
(b)Values6in firstcolumn arebased on 1520deathsdueto lungcancer 

### per 10 person

# q. The values inparenthesesarebased on 380deaths

### per 10 personWLM.Radon-222 released from mills can be transportedbeyond 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. Themodel yields radon-222 concentrations

(inpicocuries 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 distancesbeyond the 80-km regional limit for a total population of 200million persons. Thismodel
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 deathsx 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 cancersper year(a)

(a)Values in firsg column are based on 1520 deaths due to lung cancer per 10 person WLM.6 Thevalues in parentheses are based on 380 deaths per LO person WLM.Tine es.timatedhealth effect:: 

### from existing impoundments is shown in ?'able6-5, 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 ianpoundmentswill 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. Smmaqof fatalcancers Crm cuz~ent tailingsimpoundments

Condition Fatalcancers

### aeryear(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 firstcolmarebased on 1520deathsduetolungcancer per 10person6TCCM. Thevalues 

### inparentheses arebased on 380 deathsper 10personWIM.REFERENCES

Bu81 Bunger B., Cook J. R., and Barrick M. K., "LifeTable Methodology for Evaluating Radiation Risk: An Application Based on Occupational Exposure",Health Physics 40, 439-455, 1981.

EPA83 Environmental ProtectionAgency, "Final Environmental Impact Statement for Standards for the Control of Byproduct Materials fromUranium 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 onUranium 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 tailingsdisposal 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 concernedwith 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 controlledmost 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 continuousdisposal 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 asmeans 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 uraniummills.

7.1 Description of Control Pract*

The most effectiveway of controlling radon-222 emissions is to cover the radium-bearing tailings with an impervious material. Earth and water are the cover materialsmost commonly used and are effective in reducing radon-222 emissions. These
covermaterials retard the movement of radon-222 long enough for it to decay in the covermaterial; 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 earthand 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~roiiqhearth is a complex phenomenon affected by processes such as molecular diffusion, described mathematically by Pi.ck0slaw. 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 inthe 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 emissionsby about 90percent. In Figure 7-1 the earth types are categorized by their "half-value layerw (HVL). The HVL is that thickness of
covermaterial (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 smallerdiffusion 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 covermaterials 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 covermaterial is ease of excavation and the type of excavating equipment used. In general, themore 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 theWestern 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 costswould add approximately 30percent to the direct charges.EARTHTYPE 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)

7-4Table 7-1. Percentage reduction inradon-222 emissions attainedby applyingvarious types of earthcover

Depthof earthcover (m)

Earth

### type(a) HVL(m) 0.5 1.0 2.0 3.0

(a)~ee Figure 7-1.Table 7-2, Summyofunit costs forestimating mercosts(a)

Task Unit cost ($) Grading,self-propelledscraper,1000-fthaul
Excavati.on,elevatingscraper,5000-fthaul 2-4 6/& Compaction,vibrating l.OO/yd3

Excavation, front-endloader,truck-loaded 0.84/yi3 Hading,12-yd dq truck, 2-mile roundtrip 2.35/yd3 Fencing,6-ft,aluminizedsteel 11.3O/linear ft
Riprap,machine-placedslopeprotection 2L.oo/~~~

BO~CX~~) ban?-?-m gravel 6.60/yd3

(a)EuildingConstructionCost Eats 1985,R. S. Means Co., Ic. 

## , 43rdAnnualmitian, 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 (asshown 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 thevariation 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 64percent reduction (from 280 to 100 pCi/m s) is $5.2 x lo0 (50ha 

### x $105,00O/~a= $5,250,000)with a fairlydry 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.ngthe 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 ormore. These sloped areas represent about 8percent 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 feasiblepractice.

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 themill water recirculation rate (ifany), evaporation and precipitation rates, impoundment construction and slope, phreatic levels,ground-water contaminationpotential,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 (10CFR 40,Appendix A). These strict ground-water contamination standardswill frequently determine the type of impoundment design and degree of water covermaintained in an active area. An impoundment liner and ground-watermonitoring programs willbe required for new installations.Table 7-3. Earthmwing andplacement costs (thousandsofdollarsperhectare)(a)of attenuating radon-222 as a functionof thickness (metersofdifferent soils) and

### typeofearth

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) Costbasis: $7.00/in ($5.35/yd ) of soil covermaterial; includes excavating ($0.84/yd )

### ,hauling
3 3 ($2.35/~a )

### ,spreading (sL.~G/Y~ )

## ,andcarpacting ($1.00/yd3)

### , in1.985 dollars.
(') SeeFigure 7-1.
2 (') Based on initial radon-222 emissionrateof 280pCi/m s.Effectiveness arid Cost

Ths diffusion coefficient of water is very low (1.1x cm /s), about one-thousandth of that of soil with a 9percent 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 1meter, 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-226per gram of taiiings compared with a dry tailings flux of about 1pCi/m s per pCi of radium-226per gram, or a radon-222 reduction efficiency of about 98percent (PEI85). Emission estimates of zero are frequentlyused forponded 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. Continuedmonitoring is required to determine if any seepage is occurring through the dam or sides, and ground-water samplesmay be required periodically as a check for contamination.

7.1.3 Water Sprayinq

Water (ortailings 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 diffusionof radon-222 through the tailings; however, ground-water .contaminationmay 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 increaseswith increasing moisture content up to about 5 to 10weight percent moisture and then remains fairly constant. Thus, if water is applied to a very dry beach area, radon-222 emissionsmay initially increase because of a larger emanation coefficient. As themoisture increases, however, the diffusion coefficientwill 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 lowmoisture levels, a larger emanation coefficientmay outweigh the effects of a lower diffusion coefficient and result in increased emissions at lowmoisture 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 highmoisture levels.

7.1.. 4 0t.herControl Techniques

Several other radon-222 control techni-queshave been evaluated. Although none of thesemethods has been applied on a large scale, they are described briefly here as part of this Background InformationDocument.
Ssthetic Covers

.. - Synthetic material, such as polyethylene sheet, can reduce radon-222 emissions if carefullyplaced 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 onportions 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 covermaterial were subsequent.1~ applied. ?'heoverall. 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 installingpolyethylege 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 thedry 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,roltechniquebecause such systems exhibitvery low rad.on-222 diffusion coefficients, The Pacific Northwest Laboratory (PNL) has investigated controlling the release of radon-222 through use of asphalt emulsi-oncovers for several.years for DOG" Vraniurn Mill TailingsRemedial.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 systemshave 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 impoundmentsmay 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 evaluationswould 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 earthenmaterial should be available as a final cover of new uranium mill tailings impoundments that are constructed below or partially below grade; such a supplywould 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 inactivemill 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 disposalmethod, 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 contaminationmay 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 (precursorsof 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.

Themajor 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 90percent were attained,radium-226 concentrations in tailings would still be in the range of 30 to 60pCi/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 forproducing 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 systemwith a 1-meter earth cover over it, soil (tailings) cementwould 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 subsidewith.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 ismuch less than that of surfacedisposal. Radon-222 releases 

### to the atmospherewould 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 emissionsbut that does not meet the requirements of final reclamation. Standards for final reclamation include rsquirements for reducing average radon-222 emissions to 20pCi/m s and for long-term (1000y) 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 (1ft) 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 (atcapacity, standby, or active) and the type of construction (dams constructed of coarse tailings, earth dams, or below-grade lined impoundments) control the extent towhich interim cover could be applied. Interim cover could be applied immediately tomost dry areas of existing impoundments

(excludingdams). 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 standbyperiods, 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 furtherwould 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 (percentageof capacity),and the operational practices used to construct the impoundment. In addition, a source of cover material must be obtained and a techniquemust 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 covermaterial. Metal gratings or timbersmay 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, 11have sand tailings dams and are above ground, 22 have earthen dams and are above ground (4of 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 20pCi/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 tailingsbeach areas
are continuously being formed. Covering the currently dry beach areas, excluding dams,with 1meter 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.

7-15The 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
coverwould 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 overflowpipe leading to an adjacent evaporation pond and/or for recycling to the mill. The use of water coverwould require maintaining sufficient freeboard to prevent overflow and themonitoring 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-lingoperations,new tailings impoundmentswould 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 estimatespresented in this section. The cost of enough e2rth (8%moisture) to attenuate the radon-222 flux to 20pCi/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 theTable 7-4. Benefitsandwstsof alteaativesthatapplyearthcover toexistingtailingsimpoun&ents

Alternative Radon-22 2 emissions Avoided 

### fa Cost(b)

(kCi/~) cancers/y

Current After 0-80km National

Ceaseuseof current h- 129 8 1.7(0.5) 2.9(0.7) 660 poun&&s, allowtodry andapply finalcover. Covercurrentdryareas 129 69 0.8(0.2) 1.5(0.4) 63 with l m ofearth.

6

(a)Values arebased on 1520 deaths dueto lungcancerper 12 personWLM. The values 

### inparenthesesarebased on 380deathsper 10 personWLM.
(b)Total cost,includingindirepcharges. Final cover includes earth rewiredtoachieve 20pCi/m s,regradingsandtailings damsto 5:1 (H:V) slop,ripraponsides,

### andgravel on topof ~unc3ments (1985dollars).currently dry areas, excluding dams and evaporationponds, with a meter of earth achieves a .theoreticalestimatgd reduction in emissions of 46 percent at a cost of $63 x 10 (1985dollars) and prevents from 0.6 to 2.36cancersper year (basedon 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 94percent can2be achieved by applying sugficient cover to achieve 20 pCi/m s; thiswould cost $660

### x 10 (1985dollars) 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,tin time only. It does not reflect reapplicationsof interim cover required after restarting of operations at specific sites or changes in emissions due to interim cover deterioration. Annual maintenance costs thatwould
occur over time are also not included.

7.3 Control PracticesApplicable to New Tailinss Im~oundments New tailings-disposal impoundmentsat uraniummills can be designed to incorporate radon-222 controlmeasures. 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 NRCpspreference, 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 (40CFR 190 and 192 and LO CFR 40) for prevention of ground-water contamination and airborne particulate emissions. New impoundmentswill 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, itwill 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 impoundmentwas 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 uraniummill 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

(116acres), 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 impoundmenthas 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 (TypeB soil, 8 percent moisture as shown in Figure 7-1). Total emissionsduring 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, dependingmainly 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 ($4.15x 10 for earth
cover and $1.9 

### x 10 for gravel cap). The partially above-gradedesign is identical to the below-grade design except that 6m (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 = 

### 1800t/d 

### x 310d/y 

### x 15y = 

### 8.4

### x

## lo6 t 

### 6 3 

### TAILINGS VOLUME = 

### 8.4 x

## lo6 t 

### + 1.6 t/m3 = 

### 5.25 

### x 10 in


### FINALTAILINGS SURFACEAREA = 

### 47 ha 

### (116acres)
DIAGRAMS

### ARE NOT TO SCALE.

Figure 7-3. Size and layout of themodel single-cell tailings impoundment.

7-20Figure 7-4. Estimated radon-222 emissions from a model single-cell tailings impoundment.

### Table 7-5. Average radon-222 emission rat frommodel 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 impoundmentwith 15-year life and 5-year drying-outperiod. Emissions are based on 280psi 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. Esthtedcosts foramodel sinyle--@+1 tailings jJlW5~~1.&en'r.

costs ($

### x lo6)

Item &1ow grade

Excavation Syntheticliner (30-mil) Gradinq Drainaqe system 

### Damconstruction Cover (3-m) Gravel cap (0.5-m) Ripraponslopes Partially abovegrade(b)

Subtotaldire@)cost 31.31 Indirect cost 10.02

Total cost 41.33 2s.71

(a)Below-gradeinpundments

### areconstrudedsothatthetop of the finalcover is

### atgrade.

(b)Fiftypercentb1owqiadeand 50percent abuvegrade.
(') Indirect costsareestimated tobe 32percent ofdirect costs,7,3.i Phasee-Df~sgosal Tailipczs I~~~o~~ndment

Inphased-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 cellswould 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 interferingwith 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. UmetcossWhite 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-outperiod (about 5years 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. Thisimpoundment 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 (atthe 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 0.7kCi/y is lower than that for a single cell impoundment (1.2kCi/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-dingphased-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 (similarto 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 themill tailings generated during a 15-year operational period. As an example, a below-grade, phased-disposal impoundment utilizing three cells was investigated.

### GRADELEVEL

### FOR DE DESIGN

SECTIONA-A

NOTES:

TAILINGSCAPACITY PER CELL = 1800 t/d x 310d/y 

### x 15y

### + 6 

### CELLS = 1.4

### x lo6 

### t/CELL 5 3 

### TAILINGSVOLUME PER CELL = 1.4x lo6 

### t/CELL t 1.6 t/rn3 = 8.75

### x 10 

### rn 

### /CELL

FINALTAILINGSSURFACEAREA = 8.6 

### ha/CELL (21.3

### acre/CEL~)

DIAGRAM IS

### NOT TOSCALE

Figure 7-5. Sizeand layout of model phased-disposal impoundment.RADIUM CONCENTRATION

## - 280pCi 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 

# ::

00 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 rateformodel 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 coveredwith 3m of earth

0.33 coveredwith3m of earth

(a)For new mdel impoundmentwith 15yr. lifeand 5yr. dryingperidfor each cell. ?&$ssions hsedon 280 pCi Ra-226/g and specific fluxof l pCi Rn-222/m sper pCi Ra-22G/g of tailingswhen dry.
(b' Assumes a 5-y drying-out period foreach celland irmnediate cover of 3m of earth.Table 7-8. Estimated costs for amodel phased disposal impoundment(a) 6 ($x 10 )

Item Belowwade Partially abovemade 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

Damcontruction 

## - - 1.27 7.61

Cover (3m) 0.76 4.57 0.76 4.57
Riprap on slopes 

## - - 0.32 1.91 (0.5m)

Gravel cap (0.5-m) 0.37 2.21 0.39 2.34
Evaporationpond 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 impoundmentsare construct& so that the top of the final cover is atgrade. Partially above-grade impoundment is 6m below gradeand 6 m above grade.

(b) Indirect costs are estimated tobe 32percent of direct costs.Comparecl v;it.h 'chi: rdesiyi of the p)re\iioui;?y~-di.scu.?st?d phased-disposal impo~rr:drnc'rrtwith s:i.-,cel:l.s,the ti- I.

-.6-2

?---Q~ i..i.i,A impoundment i.sconceptual1.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-cellimpoundment is somewha% l.ess than that of a six-cell impoundment some redi~ctionsin cost and emi.ssionsare effec'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.onalpilase o:€a three-cell iinpoundment is 0, 62 kC.i./y, compared with 0.6'7kCi/y for six eel-ls, and during the post-operational phase, the emissj.ons are 0,3l and 0.33 kCi/y, respective1y,

Water c<?nbe removed from the tailings slurry prior to disposal. The relatively dry, dewatered (25to 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-eachingprocesses do not generally recycle water, and larger evaporation ponds with anci.l:larypiping and pumpi-ngsystems 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 fil.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 :filterplugging or bi-nding. Corror;ion-resistant iiiateri.a?.swou2.d be requi-redi.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.ummills in the TJni.tedStates: 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,Oha (10acres) of tailings were to be exposed at any one time, Tl!e clay car, .:J;I.; tobe 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 .trenchand fil.1.type operation. Tailings were to be thickened to 60percent 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-ingsdisposal operation consisted of bel-ow-gradeburial 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 760m (250by 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 6.4m (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 572,000m, or 57,200m 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 .ina 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 itminimizes the excavation cost as well as the cost of dam construction.GRPDE L BELW-GRADE

+77m4 SECTION A-A

GRADE L OELW-GRAN

TAILINGS 

# u

SECTION B-8
NOTES:

TAILINGS CAPACITY PER TRENCH = 1800 

### tfd x 110dfyx 15y r 10TRENCHES = 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 (14.9 ~C~~JTRENCH) DIAGRAM ISMOT TO SCALE

Figure 7-7, Sizeand layout of themodel continuous-disposal impoundment.

7-32Emissions 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-cellmodel 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 4ha (10acres) 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 0.30kCi/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 tobe 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 alternativewould cost about $37.4 

### x 10


# .Table 7-9. Estimatedradon-222 emission rates formodel single-cell, phased disposal,and continuous-disposaltailings impmdments Averaqe emissionrate (kCi/y~(~) operational phase Post-operationalphase

Singlecell

Phaseddisposal 1.2(b) 4.2 uncovered
0.30 coveredwith 3m of earth

Continuous disposal 0.5 (single-cell) 0.7(b) 0.33 coveredwith 3m ofearth

Continuous disposal 0.5 (trenched) 0.30 coveredwith 3m of earth

0.36 coveredwith 3m of

### earth

(a)Fornewmodel impundmentswith 15-y operational life*ions based
on 280pCi Ra-226/q and specific fluxof 1piRn-222/m sperpCi Ra-226/g of tailingswhendry.
(b) Includes 5-'y drying-outperiod.RADIUM CONCENTRATION

## - 280pCi 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:

00 5 10 15 20 YEAR

Figure 7-8. Estimated radon-222 emissions from a mcdel continuous-disposal impoundment.

### RADIUM CONCENTRATION

## - 280pCi 

### Ra-226/g 

### 2 SPECIFIC FLUX

## - 1 

### pCi Rn-222/m s per



## .--- pCi Ra-22619 FORDRY AREAS 3 

# .

-7 U Y 

# -

0 20 0 

### 5 

### 10 15 

### YEAR

Figure 7-9. Estimated radon-222 emissions from a model continuous/single-cell disposal impoundment.Table 7-10. Estimatd costs fora6m@~l continuous disposal irnpunchnent ($x 10 ) Partially above-arade

Item

Excavation(b) Syntheticliner

(30-mil) Gradjng n3mconstruction Cover (3-m) Riprap on slopes Gravel cap (0.5-m) Evaporationpond Vacuum filter Below-grade trenchdesign Single-cell Trench design design

Subtotal direct cost 41.03

Indirect cost(C) 13.13

Totalcost 54.16

(a)In 1985dollars.

(b)Below-grade inpundments areconstkcted sothatthe top of the final

cover is atgrade. Partially above-grade design is 6 m deep and 6m above qrade.
(') indirectcosts areestimated tobe 32percent of direct costs.r "7

~4 ~>ummary of..Iia0on-222 Control Practices

A summary of the radon-222 emissions from new model impoundments servi-ngan 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-ightlylarger.

The final column of Tabie 7-11 presents cumulative emissions over various time periods. Emissions over these different timeperiods are the sum of those from the operational phase of an impoundment as well as those occurring after final
cover (ifapplicable). All iypoundmentswith 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 ad a U
3 a

WO 

## 5
m om m

N P X 3 W h ii .a w C a UO Y m .Ad rd 71 WU ?? rim 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' meN 

## ,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 Cma, 

# " 232 

## 2 2% U d al .i > alo El U u 0 dalU Udl U MO 

### "35
0 m .r( Z" 3Table7-12. smmry of estimatedcostsfognewmodel tailings iltpundment (1985$ X 10)

Continuous-disposal Partially Sinqle-cell Phased-disnosal abovemadePartially Partially SingleBelow grade above grade Pelowgrade above grade Belowgrade cell Trench

V I -. C 0 Direct cost 31.3 22.5 36.2 31.5 41.0 28.3 46.2

Indirectcost 10.0 7.2 11.6 10.0 13.1 9.1 1.4.8

Totalcost 41.3 29.7 47.8 41.5 54.1 37.4 61.0Baker 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 onUranium Mill TailingsManagement, 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 theThickened DischargeMethod 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/rARYAND COMPP~RiSONOF 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-tsare 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.tmany mills. TI-iis nominal 50 ha (125ac) impoundment (actual1.y 47 ha or 3.26 acres) has a 15year active life. The surface area is 80percent 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 onwhen the impoundment is covered to compiy with Federal and/or state :regulations, For il.liis'trativepurposes time periods of 0,20,and 40years 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'tis d:~ffereilt. The longer the cover cost it; pos*poxled, the sma%?.erthe no% present value. A summary of radon-222 emissions and costs fc;r s?-nglecell 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 sincenothing is done for 4.0years after the impoundment is full. and dry (GOyears from start). In Base Case 11 no cover is applied for 20years after the impoundment is full and dry (40years 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 20years sooner. Covering the impoundment as soon aspossible after it is full reduces radon-222 exii.ssions still. further and increases the net present valrle cost by a.bn?.%t $2,500,000when compared with Rase Case I.

(") Net present value = current cost 

### x [i.,/(14- 0.05)") at a 5 percent discount rate and where n

# - years 

### in which cost is incurred.Table 8-1. missionandcost comparison for singlecell impoundment with final coverappliedat 0,20,and 40yearsafterreaching capacity

Work practice Curmiiative Nmr radon-222 emissions (kCil costg(a) 0-20y 20-40y 40-60y 0-60y ($10)

Cover 40yearsafter 25 83 83 191 33.9

full

## -BaseCase I Cover 20yearsafter 25 83 6 114 34.6

full

## -BaseCase I1 Cover

### when full 25 6 6 37 36.4

(a)At 5percentdiscountrate.The risks incurred by leaving a model impoundment uncovered
can be estimated from the radon-222 emission ra'teand assuming the model impoundmenthas an impact in proportion to that of the current licensed mills as shownbelow:

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 impoundmentsand a nationwide fatal cancer rate of 2.34 committed fatal cancers per year (basedon 760 deaths per million person WLM), deaths at other emission rates can be estimated.

For the single cell model impoundments deaths and benefits (deathsavoided) were estimated for a 60-yearperiod as shown in Table 8-2. Benefits are determined by comparing with the Base Case I, i.e., not covering for 40years. 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 arevery similar and the NPV for the 40-acre/cell impoundment is about $1,500,000less than the 20 acre/cell design.

Committed fatal cancers for the model phased disposal impoundmentswere 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. Comparisonof estimateddeathsandbenefits fora single

cell model i.rpundhnent with finalcoverappliedat 0, 20,and 40years after reachingcapacity

Benefits,

Workpractice Nationwidedeaths,(a)

0-60y 0-60y

BaseCase I

## -Cover40years
after full

BaseCase I1

# -Cover 20years
after full

Coverwhen full

(a)Basedon 760deaths

### permillion personWLM.Table 8-3. Emissions and costs formodel 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 5percent discount rate.Table 8-4. Corprisonof estimateddeath formodel
phased-disposal impoundments

Nationwidedeaths,(a)
Work practices 0-60

### y

20acre

## - 6 celldesign

40acre

## - 3cell design

(a)Based on 760deaths

### permillionpersonWIM.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 impoundmentwith 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-yearperiod are 24 kCi. Based on this emission rate, committed fatal cancers from this work practice at amodel impoundment amount to 0.4 over a 60-yearperiod. 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 impoundmentwith 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 cumulativehealth 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. Emissionsandcostofmodelbelow-grade

### trenchtype
continuousdisposal impoundment

Cumulativeradon-222emissions (kCi1

0-20

### y 20-40

### y 40-60

### y 0-60

### y NPV cost(a) ($

### x 107

(a)At 5percent discountrate.Table 8-6. Ccrmparisonof workpractices for

### newmodel tailircJs

### -ts

radon-222 emissions (Mi) NmT of

### work Gn~nnitted ~ractice @ 5%

, fatalcancers(a) Work practice

1. Single cellmered 25 6 6 37 36.4 0.6 whenN1(20

### y

to fromstart)

10 2. Phaseddisposal 13 7 7 27 36.1 20-acrecells

3. Phased disposal 40-acrecells

4. Continuous dis- 10 7 7 24 43.3 0.4 posal (trench

### type)

6 (a)Nationwide,basedon 760deaths110 person WIM. Assuaesmodel plant isataverage locationof existingmills.When compared with an uncovered single-cell impoundment, all the work practices yield similarbenefits 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 8-8present a comparison between the alternative work practices and a base case single cell impoundment uncovered for 40years 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-yearperiod when alternative work practices are used.Table 8-7. Camparisonof costandbenefitsbetween model Base Case 

### Iandnew work practices

Work practice DifferenceinNPCT 

### Deaths frombase6case avoided(a) ($X 10 ) 0-60

### y

Base Case I Singlecellcovered40

### y after full (60

### y fromstart)

L. Single cellcoveredwhen full (20

### yfrom start)

2. Phaseddisposal 20-acrecells 2.2 3.0

3. Phaseddisposal 40-acre cells 0.7 3.1

4. Continuous disposal (trench-type) 9.4 3.1

(a)Nationwidebasis.Table 8-8. Conparison of cost andbenefitsbetweenmcdel Base Case I1and

### newworkpractices

Workpractice Difference inNPV Deaths frombasepse avoided(a) ($ X 10) 0-60 y

Base Case 11 Singlecellcovered 20y afterfull (40y from

### start)

1. Singlecell coveredwhen full (20

### y fromstart)

2. Phased disposal 20-acre cells 1.5 1.6

3. Phaseddisposal 40-acre cells 

## - 1.7

4. Continuous disposal (trench-type) 8.7 1.7

(a)Nationwidebasis.APPENDIX A

DIAGRAMS OF URANIUM MILL SITES AND TAILINGS IMPOUNDMENTSDiagrams 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 WZ

## .. COWCZb046 UUOACCESS ROAD

L-BAR TAILINGS

IMPOUNDMENT 

# '-,

WATER COVERED TAILINGS -

SOH10 MILL CEBOLLETA, NM DATE: 10/5/85

MINE BUllDiNGS 

## 00 

### 8- 

## 2 

# -

8-

ul

0-

# -
2z r CL3G 

# s * d-lrul ut-m 3-1 ZUW 

# -. zrm CL W W CL

## .. +uw mu-+- WW4 x7nIURFACE WATER

### N

0 1
ROCKY MT. ENERGY MILL BEAR CREEK, WY DATE: 9113/85 BEAR CREEK

### TAILINGS 

# /IMPOUNDMENTMILL

### BUILDINGS



### PATHFINDER SHIRLEY BASINMILL SHIRLEY BASIN, WY DATE: 9/f3/85APPENDIX 

### B

COST ESTIMATES FOR EXISTING AND MODEL NEW URANIUM MILL TAILINGS IMPOUNDMENTSAppendix B: COST' EST'IMAT'ESFOR EXISTING AND MODEL NEW URANIUM MILL TAILINGS IMPOUNDMENTS

l'hisAppendix presents the approach, assumptions,and bases used to generate the cost estimates of Chapter 7. For existing impoundments,themost recent available site-specific information was used to estimate the cost of interim control and final reclamationmeasures. For new tailings impoundments, model impoundmentswere 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 lmeter 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'tslopeswas also incl.uded. In'terimcontrol 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 20pCi/m s and to place the impoundment in a state of permanent, long-term stability.Table B-1. Indirect cost factorsused intheastestimation of uraniummilltailings impundments

Indirectwst 

### item

Rqineerjxgand design Imance Performancebond Permits Overhead andprofit Contingencyatwnceptual stage

Total Percentaqe Range valuewed

Source: "Means SiteWork CostData 1985," 4thAnnual Edition, R.S=Nm Co., Inc.No credits for earth covers that ma.y have previously been placed for interim controlmeasures were considered to be of help in achieving final reclamation. Final reclamation was assumed to be possible immediately after an impoundmenthad dried. No cost for attaining dry-out was assumed. The measures taken and the costs of final reclamationdepend on the type of impoundmentand 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 (sourceof 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 slopesTearthen coverwith 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 slopeswould 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 uraniummill tailings impoundments: single-cell,phased-disposal, continuous-disposal,and continuous/single-cell disposal impoundments. Costs of the first three types of impoundmentswere estimated for below-grade placement of tailings and for partially below-gradeplacement, Only partially (50percent) below-grade placement of tailings was considered for themodel 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 6meters of tailings below grade and 6 meters above-grade (inthe 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 themodel 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, 15meters 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 9meters above grade. Each type of impoundment has a 30-mil synthetic liner and a drainage system to facilitate dewatering when the impoundmenthas 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 thepartialky 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 themodel 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 themodel single-cell impoundment,an evaporationpond is included in the cost estimate of phased-disposal impoundments. The impoundment surface area available for evaporation is much smaller; therefore, an evaporationpond is required. The estimate includesboth the cost of construction and the cost of closure of the evaporationpond at the end of themill% life.

Excavation to a depth of 6 meters for the partially below-grade phased-disposal impoundmentdoes not provide sufficient earth to construct the dam and to place a 3-meter earth cover over the tailings. Thus, the costs of obtainingadaitionai 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 partial18beiaw-grade pkgsed disposal impoundments are $47.8x 3.0 and $41-5

### x LO

(1905dollars), 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 trencheswould 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 hmediateplacement of the cover. The estimate includes the cost of a vacuum filter to dewater the tailings. An evaporationpond (largerthan 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 impoundmentdam. 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 forplacement 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 evaporationpond and vacuum filter are still required because the tailings must be dewatered.DOE82 Department ofEneergy, "Ym:minggled ilranitx~riTai:.incjs Studyge, DOE/ DP-0011, Office of Defense Wa"steand Bypri~dti~ts Management, Washington.,I).C,

### , June 30, 1-982.

EPAB5 U,S. Environmental Protection Agency, "Draft Document-Estimates of Population Distributions and TailingsAreas Around Licensed Uranium Mill Sites"',Office of Rad.iati.on Programs, November 1985.

NRCB0 Nuclear Regulatory Commission, Q'FiiiaTGeneric ." Environmental impact Sta.'cementon tiraniurn Miliingn,NUREG-0706, Septex:ber 1980,

NRC84 Nuclear Regulatory Commission, IYDirectoryand, 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 OPTION2. 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 theproposed 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 coverwould be about 1 foot or 1meter in depth

(dependingon the selected option). If and when the impoundment returned to active use, tailingswould be dumped on top of the earth cover. Other methods of reducing radon-222 emissions includewater cover,an8 synthetic or asphalt covers. Maintaining a water cover causespotential ground water and,at some sites,dam stabilityproblems. If a mill is on standby, water coverwill be difficult tomaintain 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 tailingsdisposal 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 impoundmentwas not used again. This option is thereforebeing reevaluated to better
assess its practicability,effectiveness and cost.Chapter 2: TECHNICAL ISSUES

2.1 Introduction

Interim earthen covers of 0.3 or 1m having 8percent moisture content theoretically reduce radon-222 emissions by about 37 and 62percent,respectively. The actual effectiveness of such interim covershas never been demonstrated on licensed tailings impoundments. Additionally, while use of earthen covers is a demonstrated control technology at inactive uraniummill 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. Thereforethe 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 characteristicsof the impoundments impact the potential use of interim cover. Site-specific characteristics such as evaporation rates,dam construction, phreatic level, availability of covermaterial, presence of liners, expected length of standby periods, remaining capacity and expected mill lifemust be considered on a siteby sitebasis.

Uraniummill tailings are deposited as a slurry in tailings impoundments. Threemajor types of impoundments currently exist: thosewhere coarse tailings are used as dam construction material (11impoundmentsrepresenting 32 percent of total tailings area): those using earthen dams (22 impoundments representing 65percent of the total area); and below-grade impoundments (5 impoundmentsrepresenting 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 determininghow much time is required to allow an impoundment to dry sufficiently before interim cover can be applied. For example, some tailings impoundmentsare located in arid areas (i.e.,New Mexico) relativelywet 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 settingsvary 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 Mariaimpoundment in Texas would require a longer drying period because of the impermeablebase thatwould inhibit dewatering by seepage and the relatively high rainfall rate. There are also several operational aspects thatmust 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 dependsmainly on its moisture content and depth, and the homogeneity and integrity of the cover layer. The effectiveness of an earth coverwas estimated in the Draft BID by using diffusion equations which take into account the covermaterial and tailings density, porosity, specific gravity and moisture content,and by assuming theseproperties do not vary throughout the cover or tailings, or with time. These idealized conditionswould 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 thisvariation 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 6percent, 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 soilswith a higher silt and clay content will retain more moisture much longer than a sandy soil.

In addition to the covermaterial'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 covereffectiveness with moisture content.

### The combiriation of 

### surface drying, erosion, and loss of integrity reduces the interim cover" effectiveness. This loss in effectivenesswould 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 effectivenesscanbe offset by frequent maintenance of the earth cover, as discussed under OperationalAspects.

2.3 

### ADDlicability of Interim Cover
Limitations regarding theplacement 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. Tailingsmust be dry in order to support earthmoving equipment and the cover itself. Tailingsare dewatered and dried by seepage from the impoundmentand by evaporation. (Thetime required to achieve sufficientdryness is discussed in Section 2.4.) The tops of tailings impoundmentsare essentially flat, and if thoroughly dry,would pose no difficulty to placement of interim cover. However, 11 impoundmentsat 6

### mill sites are constructed with damsmade of coarse tailings (Type1 impoundments). The outer faces of these dams are steep (approximately2.5:1, H:V). Placement of interim
cover on these damswould be difficultbecause 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 thephreatic 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, itwould be very difficult to compact covermaterial placed on such a slope. Uncompacted material would be subject tomore 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.
31percent of the total sloped area is at onemajor impoundment (Homestake),that is a 4 sided structure,with steep slopes (2to 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 damswould have to be extended and their
use uninterrupted during application of interim cover.



### It would be necessary toprovide drainage between the 'tailingsand the earthen cover to allow any seepage through the dam to escape without building up a hydrostatichead 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-222migration,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,

### 1year for example, Heavy equipment could access most of the area at that time. Other sites having lower evaporation,more rainfall/snowfall and/or lesspermeable 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 recommendationduring 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 impoundmentsmake up 11percent of currently dry areas.

Issue of lost capacity ismore important on these impoundmentsbecause 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, severalmills use evaporationponds for water management. Decantwater from the tailings impoundments and oftenmine pump-out water and seepage from the tailings impoundment ispumped to these evaporation ponds. Some tailings slimes and dissolved radium-226 are carried along with thewater 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 standbyperiods; 2) the quantity of tailings present and their contribution to the site's source term are not accurately known; 3) 

### these ponds will eventuallybe 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 complicationsassociatedwith 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 remainuncovered. 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 (asspecified 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 capacitywill 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 ofplacing tailings in impoundments is to discharge from severalpoints around theperimeter or tomove the dischargepoint around theperimeter; in either case interim
coverwould 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 5years).

The useful life of an interim cover is limited by return to active status atwhich time the earthen cover is covered with new tailings. In the current evaluation, impoundments would become active sometimebetween 1990 and 1995 and a second application of interim coverwould be made in the year 2000.

Itwas initially assumed for the base case that an inactive impoundmentwould remain uncovered for 40 years. This appears unrealistic and a shorter time period of no more than 20 years ismore 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
coverper year.

One important aspect regarding interim cover is the issue of lost capacity. An interim cover of 1meter 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 impoundmentswould have no remaining capacity if interim cover were applied, while otherswould 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. bstcapacityassmiatedwitha singleapplicationof ir@rim
cover (0.9

### rn) overtheentire impm&ent innonagreement states (1000tons)

Mill

White Mesa La Sal Mod5 ShootaringCanyon GasHills (Pathfinder) SplitRock GasHills (UMGIYT)) 

### BearCreek Shirley Basin Sweetwater Licensed Quantityof interim Current quantity cover

## - 0.91meter 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)NRCUraniumFieldOffice, Denver,Colorado,April 1986. informationon remainingcapacityof inpm&ents inagreement stateswasnot 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