Final Report



### History and Basis of NESHAPs and Subpart W

Prepared by

S. Cohen & Associates 1608 Spring Hill Road, Suite 400 Vienna, VA 22182

Under

Contract Number EP-D-05-002 Work Assignment No. 4-11, Task 4

Prepared for

U.S. Environmental Protection Agency

Office of Radiation and Indoor Air

1200 Pennsylvania Avenue, N.W. Washington, DC 20460

Reid J. Rosnick

Work Assignment Manager

September 25, 2008In accordance with the Quality Assurance Project Plan: Technical and Regulatory Support to Develop a Rulemaking to Modify the NESHAP Subpart W Standard for Radon Emissions from Operating Uranium Mills (40 CFR 61.25) , this document has been reviewed and approved by the following individuals:

Work Assignment Task Manager: ________________________ Date: __ 09/25/2008

__ Harry Pettengill

Project Manager: ________________________ Date: __ 09/25/2008

__ Abe Zeitoun

Corporate Quality Assurance Mgr: ________________________ Date: __ 09/25/2008

__ Gregory Beronja

Work Assignment QA Manager: ________________________ Date: __ 09/25/2008

__ Stephen Ostrow

WA 4-11, Task 4 – NESHAPs History i SC&A – September 25, 2008

### TABLE OF CONTENTS

1.0 Introduction ......................................................................................................................... 1

2.0 Background on the Developmen t of Radionuclide NESHAPS .......................................... 1

2.1 The 1977 Amendments to the Clean Air Act .......................................................... 2

2.2 Regulatory Activities between 1979 and 1987 ....................................................... 2

2.3 Regulatory Activities between 1987 and 1989 ....................................................... 4

2.4 1989 Radionuclide NESHAPs Reconsideration Rulemaking ................................. 4

3.0 Basis for the Subpart W Risk Assessment .......................................................................... 5

3.1 Existing Impoundments .......................................................................................... 5

3.2 New Impoundments ................................................................................................ 6

4.0 Comparison of the NESHAPs Risk Assessment with Current Risk Assessment Approaches .......................................................................................................................... 7

5.0 Conclusions ....................................................................................................................... 10

6.0 References ......................................................................................................................... 10

WA 4-11, Task 4 – NESHAPs History ii SC&A – September 25, 2008

### 1.0 INTRODUCTION

On December 15, 1989, the Environmental Protecti on Agency’s (EPA) Office of Radiation and Indoor Air (ORIA) promulgated a National Emission Standard for Hazardous Air Pollutant (NESHAP) for radon emissions from operati ng uranium mill tailings (Subpart W). Section 112(q) of the Clean Air Act (CAA), as amended, requires the EPA to review, and if appropriate, revise or update the Subpart W standa rd on a timely basis (10-year interval). To date, EPA has not revisited this standard since its promulgation and now desires to do so. The purpose of this work assignment is to provide essential technical a nd regulatory support necessary for EPA to review the technical ba sis on which the standard was based and the decision-making process that was used to de termine the requirement s of the standard. Furthermore, this effort will assist the EPA in determining the appropriateness of the standard for this type of pollutant, and to decide if modification of Subpart W is warranted.

The facilities covered by Subpa rt W are uranium mills licensed and regulated by the U.S. Nuclear Regulatory Commission (NRC) or its Agreement States. There are two separate standards outlined in Subpart W. The first stat es that existing sources must ensure emissions from tailings impoundments not exceed 20 pCi/m 2 -sec of radon-222 (Rn-222). The second prescribes a work practice speci fying one of two types of imp oundment structures that new sources must construct to handle tailings during operations. The work practice also applies to operations at existing sources once their existi ng impoundments can no lo nger accept additional tailings. As part of these two standards, Subpa rt W also requires that existing sources file an annual report of the facility's emissions.

The standard as promulgated was a health-based standard. It is important to review how the initial standard was developed and to ascertain if it is still valid. Furthermore, it needs to be determined if the standard requires revision to satisfy the requirements in CAA Section 112(d), which requires a technology-based standard. It is also important to determine if this type of standard is appropriate fo r this type of pollutant.

The reports collected for this revi ew include the original risk a ssessment material used by EPA to develop the Subpart W standard, including the final rulemaking package for Subpart W (FR 1989), the background information document (BID) for the Subpart W rulemaking (EPA 1989, Volumes 1 and 2), and the economic impact analysis for the Subpart W rulemaking (EPA 1989, Volume 3). This regulatory information was ev aluated and compared and contrasted to current risk assessment modeling methodologies. The pu rpose of this report is to illuminate the differences, if any, and detail what impact this information would have on the original radon risk standard as provided in Subpart W.



### 2.0 BACKGROUND ON THE DEVE LOPMENT OF RADIONUCLIDE

NESHAPS

In the following subsections, we present a brief history of the development of environmental radiation protection standards by the EPA, with particular emphasis on the development of

radionuclide NESHAPs.

WA 4-11, Task 4 – NESHAPs History 1 SC&A – September 25, 20082.1 The 1977 Amendments to the Clean Air Act

On January 13, 1977, the EPA established environm ental protection standards for nuclear power operations pursuant to its authority under the Atomic Energy Act (AEA) (FR 1977). The standards, Title 40, Part 190, of the Code of Federal Regulations (40 CFR 190), which covered

all licensed facilities that are part of the uranium fuel cycle, established an annual limit of exposure and the requirement that licensees keep all exposures “as low as reasonably achievable” (ALARA). Because of the uncertainties associated w ith the risk of inhaled radon, the standards exempted Rn-222 from the annual limit.

After the promulgation of 40 CF R 190, the 1977 amendments to the Clean Air Act (CAA) were passed. These amendments included the requir ement that the Administrator of the EPA

determine whether or not radionuclides s hould be regulated under the Act.

In December of 1979, the Agency published its determination in the Federal Register (FR 1979) that radionuclides constitute a hazardous air polluta nt within the meaning of Section 112(a)(1).

As was stated in the Federal Register , radionuclides are known to cause cancer and genetic defects, and contribute to air po llution that may be anticipate d to result in an increase in mortality or an increase in serious irreversible or incapacitating reversible illness. The Agency further determined that the risks posed by emi ssions of radionuclides into the ambient air warranted regulation, and listed radionuclides as a hazardous air pollutant under Section 112.

Section 112(b)(1)(B) requires the Administrator to establish NESHAPs as a “level which (in the judgment of the Administrator) provides an ample ma rgin of safety to protect the public health” or find that they are no t hazardous and delist them.

2.2 Regulatory Activities between 1979 and 1987

To support the development of radionuclide NESHAPs, the Agency developed a BID to characterize “source categories” of facilities that emit radionuclides into ambient air (EPA 1979). For each source category, information needed to characterize the exposure of the public was developed. This included characterization of the facilities included in the source category (numbers, locations, proximity of nearby indivi duals); radionuclide source terms [curie/year (Ci/y)] release rates by radionuclide, solubility class, and particle size); release poin t data (stack height, volumetric flow, area size); and effluent controls (type, efficiency). Doses to nearby individuals and regional populations caused by releases from e ither actual of model facilities were estimated using the computer codes AIRDOSE-EPA and DARTAB.

In 1983, the EPA proposed radionuclide NESHAPs for four source categories based on the results reported in a new BID (EPA 1983). The four source categories for which NESHAPs were proposed were Department of Energy (DOE) a nd Non-NRC-Licensed Federal Facilities, NRCLicensed Facilities, Elemental Phosphorus Plants , and Underground Uranium Mines. For all of the other source categories that it had considered in its BID (i.e., coal-fired boilers, the phosphate industry, other extraction industries, uranium fu el-cycle facilities, ur anium mill tailings, highlevel waste disposal, and low-energy accelerator s), the Agency found that NESHAPs were not necessary. In reaching this conclusion, the EP A found that (1) the levels of radionuclide emissions did not cause a significant dose to nearby individuals or the regional populations,

WA 4-11, Task 4 – NESHAPs History 2 SC&A – September 25, 2008(2) the costs of additional effluent controls were not cost effective, or (3) existing regulations

under other authorities were sufficient to keep emissions at an acceptable level.

During the public comment period on the proposed NESHAPs, the Agency completed its rulemaking efforts under the Uranium Mill Tailings Remedial Control Act (UMTRCA) to establish standards (40 CFR 192) for the disposal of uranium m ill tailings. With respect to the emission of Rn-222, the UMTRCA standards esta blished a design standard calling for a Rn-222 flux rate of no more than 20 pCi/m 2 -sec.

In February of 1984, the Sierra Club sued the EP A in the U.S. District Court for Northern California (Sierra Club v. Ruckelshaus, No. 84-0656) (EPA 1989), demanding that the Agency promulgate final NESHAPs or delist radionuclides as a hazardous air pollut ant. The court sided

with the Sierra Club and ordere d the EPA to promulgate final regulations. In October of 1984, the EPA withdrew the proposed NESHAPs for El emental Phosphorus Plants, DOE-Facilities, and NRC-Licensed Facilities, finding that existing cont rol practices protected the public health with an ample margin of safety (FR 1984). The EPA also withdrew the NESHAP for Underground Uranium Mines, but stated its intention to pr omulgate a different standard, and published an Advance Notice of Proposed Rulemaking (ANPR) to solicit additional information on control methods. It also published an ANPR for licensed uranium mills. Finally, the Federal Register notice affirmed the decision not to regulate the other source categories identified in the proposed rule, with the exception that it was doing furt her studies of phosphogypsum stacks to see if a

standard was needed.

In December of 1984, the District Court for Northern California found the EPA's action withdrawing the NESHAPs to be in contempt of its order. Given the ru ling, the EPA issued the final BID (EPA 1984) and promulgated final st andards for Elemental Phosphorus Plants, DOEFacilities, and NRC-Licensed Facilities in Fe bruary of 1985 (FR 1985a), and a work practice standard for Underground Uran ium Mines in April (FR 1985b).

The Environmental Defense Fund (EDF), the Natural Resources Defense Council (NRDC), and the Sierra Club (SC) filed court petitions seeking review of th e October 1984 final decision not to regulate the source categorie s identified above, the Februa ry 1985 NESHAPs, and the April 1985 NESHAP. The American Mining Congress (AMC ) also filed a petiti on seeking judicial

review of the NESHAP fo r underground uranium mines.

On September 24, 1986, the Agency issued a final NESHAP for Operating Uranium Mill Tailings, establishing an emission standard of 20 pCi/m 2 -sec for Rn-222 and a work practice standard requiring that new ta ilings be disposed of in small impoundments or by continuous disposal. The justifications for the work practices included the fact that while large impoundments did not pose an unacc eptable risk during ac tive operations, the cyclical nature of the uranium milling industry could lead to prolonged periods of plant stand-by and the risk that the tailing impoundments could experience signifi cant drying with the resulting increase in Rn-222 emissions. Furthermore, the two acceptabl e work practices were believed to actually save the industry the signifi cant costs of constructing and cl osing large impoundments before they were completely filled. With the promulgation of the NESHAP for Operating Uranium Mill

WA 4-11, Task 4 – NESHAPs History 3 SC&A – September 25, 2008Tailings, releases of radionuclides to air during operations and tailings disposal at uranium mills were covered by three EPA regulations, 40 CFR 190, 40 CFR 192, and 40 CFR 61, Subpart W.

In November of 1986, the AMC and the EDF filed petitions challenging the NESHAP for operating uranium mill tailings.

2.3 Regulatory Activities between 1987 and 1989

While the petitions filed by th e EDF, NRDC, SC, and AMC were still before the courts, a decision by the U.S. District Court for the Dist rict of Columbia in NRDC v. EPA (FR 1989), found that the Administrator had impermissibly c onsidered costs and tech nological feasibility in promulgating the NESHAP for Vinyl Chloride. Th e court outlined a two-step decision process that it would find acceptable, first establishing a st andard based solely on an acceptable level of risk, and then considering additi onal factors, such as costs to establish the “ample margin of safety.” Given the Court's decision, the Agency reviewed how it had conducted all its NESHAP rulemakings and requested that the Court gr ant it a voluntary remand for its radionuclide NESHAPs. As part of an agreement with th e Court and the NRDC, the Agency agreed to reconsider all issues that were currently being litigated, and it agreed that it would explicitly

consider the need for a NESHAP for two additional source categories; radon from phosphogypsum stacks and radon from DOE facilities. The subsequent reconsideration became

know as the radionuclide NESHAP s reconsideration rulemaking.

2.4 1989 Radionuclide NESHAPs Reconsideration Rulemaking

In the radionuclide NESHAPs rec onsideration rulemaking, the Admini strator relied on a “bright line” approach for determining whether or not a source category required a NESHAP. Namely, no NESHAP was required if all individuals exposed to the ra dionuclide emissions from the facilities in the source category were at a life-time cancer ri sk of less than 1 in 1,000,000, and less than 1 fatal cancer per year was estimated to be incurred in the population. For source categories that did not meet th is “bright line” exclus ion, a two-step multi-factor approach to setting the emission standards was adopted.

The first step established a presumptivel y acceptable emissions level corresponding to a maximum individual risk (MIR) of about 1 in 10,000 life-time cancer risk, with the vast majority of exposed individuals at a lifetime risk lo wer than 1 in 1,000,000, and with the total fatal cancers per year in the exposed populat ion of less than 1. If the baseline emissions from a source category met these criteria, they were presumptivel y adequately safe. If they did not meet these criteria, then the Administrator was compelled by his non-discretionary duty to provide adequate safety to determine an emission limit that woul d correspond to risks that were adequately safe.

After baseline emissions were determined to be ade quately safe, or an adequately safe alternative limit defined, the analysis moved to the second st ep, where reduced risks for alternative emission limits were evaluated, along with the technological feasibility and cost s estimated to be associated with reaching lower levels. In the tw o-step approach, the Administrator retained the

discretion to decide whether or not the NESHAP should be set at these lower limits.

WA 4-11, Task 4 – NESHAPs History 4 SC&A – September 25, 2008As with previous radionuclide NESHAPs, expo sures were estimated using a combination of actual site data and model or representative faci lities and computer models. For all radionuclides other than Rn-222, the CAP88 computer code , which included updates to AIRDOSE-EPA and DARTAB, and the addition of RADRISK, was used to calculate total effective dose equivalent and lifetime fatal cancer risk, a nd the distribution of risks in the exposed populations. For Rn-222, the CAP88 computer code s were used to established ambient concentrations (pCi/m 3 ) in

each of the sectors in a 0-80 km radius of the s ource. The concentration within each sector was then converted to working level months (WLMs), based on a 0.70 equilibrium fraction between Rn-222 and its decay products, and a respiration rate appropriate to members of the general public. Using risk factors derived from human epidemiological studies, the WLM exposure data

were converted to risks.

Of the NESHAPs promulgated in 1989, thos e for Phosphogypsum Stacks (Subpart R), Radon from DOE Facilities (Subpart Q), and Operati ng Uranium Mills Tailings Disposal (Subpart T) are the most relevant for comparison with Subpart W, in that they all address the emission of Rn-222 from relatively large area sources. Furt hermore, the basic post-disposal Rn-222 emission limit is consistent at 20 pCi/m 2 -s. Regarding the operational pha se, no standard was deemed to be necessary for phosphogypsum stacks, since the la rge ponds that cover most to the top of the stacks and are part of the plants normal operatio n to control Rn-222 emissions to an acceptable level. For DOE facilities, there is no operational pha se, as all these site are simply storage sites for radon-emitting wastes that were generated in the past (most as part of the Manhattan Project). The NESHAP for disposal of uranium mill tailings (Subpart T) was determined to be necessary by the Administrator to assure th at the tailings did not remain unreclaimed for long periods of time, as was possible under the UMTRCA sta ndard (40 CFR 192). Additionally, the design standard of the UMTRCA regulations were enhanced by the requirement that the 20 pCi/m 2 -sec Rn-222 design standard be demonstrated to have been achieved by post-disposal radon monitoring.



### 3.0 BASIS FOR THE SUBPART W RISK ASSESSMENT

3.1 Existing Impoundments

As noted previously, the NESHAP for operating uranium mill tailings addressed both existing and future tailings impoundments. For the existing impoundments, the radon emissions and estimated risks were developed using site-specific data for each of the 12 mills that were operating or operable at the time the assessment was made. These data included the average radium-226 (Ra-226) content of the tailings; the overall dimensions and areas of the impoundments (developed from licensing data and ar eal photographs); areas of dry (unsaturated) tailings; the existing populations within 5 km of the centers of the impoundments (identified by field enumeration); 5–80 km populations derived fr om U.S. Census tract data; meteorological data (joint frequency distribut ions) from nearby weather stati ons; mixing heights; and annual precipitation rates.

The CAP88 codes were used to estimate airborne concentrations based on the calculated Rn-222 source term for each facility. Radon-222 source terms were estimated on the assumption that a Rn-222 flux of 1 pCi/m 2 -sec results for each 1 pCi/g Ra-226 in the tailings and the areas of dried

WA 4-11, Task 4 – NESHAPs History 5 SC&A – September 25, 2008tailings at each site. The radon flux rate of 1 pCi/m 2 -sec per pCi/g Ra-226 was derived based on both theoretical radon diffusion equations and the available radon emissions measurements.

For each sector in the 0–80 km grid around each facility, the estimated Rn-222 airborne

concentration was converted to cumulative WLMs assuming a 0.70 equilibrium fraction between radon and its decay products, an average respirati on rate appropriate for members of the general public, and the assumption of continuous exposur e over a 70-year lifetime. Using a risk

coefficient of 760 fatalities/10 6 WLM, lifetime risk, fatal can cers per year, and the risk

distribution were calculated for the exposed population.

The baseline risk assessment for existing uranium tailings showed MIR of 3×10 -5 , with 0.0043 committed cancers in the 2 million persons living with in 80 km of the mills. The distribution of the cancer risk showed that 240 pe rsons were at risks between 1×10 -5 and 1×10 -4 , and 60,000

were at risks between 1×10 -6 and 1×10 -5 . The remainder of the population of about 2 million

were at a risk of less than 1×10 -6 . Based on these findings, the EPA concluded that baseline risks were acceptable.

The decision on an ample margin of safety considered all of the risk da ta presented above plus costs, scientific uncertainty, and the technical f easibility of control tec hnology necessary to lower emissions from operating uranium mill tailings pile s. As the risks from existing emissions were very low, the EPA determined that an emission standard of 20 pCi/m 2 -sec, which represented current emissions, was all that was necessary to provide the ample margin of safety. The necessity for the standard was explained by the ne ed to assure that mills continued the current control practice of keeping tai lings wet and/or cove red. Finally, in order to assure that groundwater was not adversely affected by contin ued operation of existing piles that were not synthetically lined or clay lined, the NESHAP ended the exemption to the requirements of 40 CFR 192.32(a), which protects wate r supplies from contamination.

3.2 New Impoundments

The risk assessment for new mill tailings im poundments was based on a set of model mills, defined so that the impact of alternative dispos al strategies could be evaluated. For the purpose of estimating the risks, the model mills were ch aracterized to reflect operating mills, and the dispersion modeling and population exposures were based on the arid conditions and sparse population density that charac terize existing impoundments in the southwestern states.

The results of the modeling exer cise indicated an MIR of 1.6×10 -4 , a fatal cancer incidence of 0.014 per year, and only 200 persons at a risk greater than 1×10 -4 . Given the numerous uncertainties in establishing the parameters fo r the risk assessment and in modeling actual emissions and exposures, the Administrator found that the baseline emissions for new tailings impoundments met the criteria for presumptively safe.

The decision on an ample margin of safety for ne w tailings considered two alternatives to the baseline of one large impoundment; phased dis posal using a series of small impoundments and continuous disposal. The evaluatio n of these alternatives showed a modest reduction in the MIR and the number of fatal cancers per year, but a si gnificant increase in the number of individuals

at a lifetime risk of less than 1×10 -6 . The costs estimated for the two alternatives showed that

WA 4-11, Task 4 – NESHAPs History 6 SC&A – September 25, 2008phased disposal would lead to an incremental cost of $6.3 million, while continuous disposal was believed to actually result in a modest cost saving of $1 million.

Given the large uncertainties associated with th e risk and economic assessments performed for the new tailing impoundments, and considering the boom and bust cycles that the uranium industry has experienced, the Administrator dete rmined that a work practice standard was necessary to prevent the risks fr om increasing if an impoundment we re allowed to become dry. Finally, although continuous disposal showed slightly lower over-a ll risks and costs than phased disposal, the Administrator r ecognized that it was not a pr oven technology for disposal of uranium mills tailings. Therefore, he determined that the work practice standard should allow for either phased disposal (limited to 40-acre impoundments, with a maximum of 2 impoundments open at any one time) or continuous disposal.



### 4.0 COMPARISON OF THE NESHAP S RISK ASSESSMENT WITH

CURRENT RISK ASSE SSMENT APPROACHES

Since it is neither feasible nor practical to dire ctly measure the exposure of individuals in the 0– 80-km area surrounding an emission source, risk assessments rely on modeling exposures. The essential elements in assessing the risk from a source emitting Rn-222 to the ambient air are as

follows:

• The source term (Ci/y)

• The dispersion of the Rn-222 from the source to the receptor

• The ingrowth and depletion of the short-lived Rn-222 decay products from the source to the receptor

• The location of the receptors within the assessment area

• The duration of the receptors' exposures

• The fatal cancer risk/unit of exposure (risk/cumulative WLM)

The following paragraphs discuss how each of these elements were derived for the risk assessments performed in support of the Subpart W rulemaking and suggest where different values might be used if the assessments were performed now.

The source terms for existing impoundment s were based on radon flux rates (pCi/m 2 ), Ra-226 concentrations in the tailings, a nd the areas of unsaturated taili ngs exposed at each site. The radon flux rate that was used, 1 pCi/m 2 Rn-222/pCi/g Ra-226, was se lected based on theoretical

diffusion rates from thick sources. As diffusion rates depend on the porosity of the matrix and its moisture content, the specific rate that was selected was chosen to reflect site conditions that pertain in the southwestern part of the count ry where the industry is concentrated. The

concentrations of Ra-226 in the tailings reflect measurement data , while the areas of unsaturated tailings were estimated based on both photogr aphs of the impoundments and information

WA 4-11, Task 4 – NESHAPs History 7 SC&A – September 25, 2008supplied by the industry during the public comment period. Given that the NESHAP imposed an annual requirement for the facilities to measur e and report their Rn-222 emissions, it should now be possible to develop the source term for each m ill based on measurement data. If this approach were to be taken, it would be necessary to know the configuration of the impoundment during each measurement period.

The dispersion of the Rn-222 from the tailings impoundments to the recepto rs in the assessment area were estimated using the AIRDOSE-EP A model in the CAP88 assessment code. AIRDOSE-EPA uses a Gaussian plume dispersion m odel to calculate air concentrations at the locations of the receptors. The model uses mete orological data (in the form of joint frequency distributions of wind speed and direction by stab ility class), annual prec ipitation rate, and lid height supplied by the user, and it accounts fo r removal from the plume by dry deposition and scavenging. The model allows for the source to be characterized as either a point source or an area source, and allows the user to input the eff ective release height. Fo r the risk assessments, impoundments were characterized as area sources with an effective re lease height of 1 meter. As on-site meteorological data were not available, joint frequency data representing long-term averages were obtained from the nearest weathe r station. Annual precip itation rates and lid heights were site-specific.

While the EPA has developed a number of disper sion models, including some that are more sophisticated than the AIRDOSE-EPA model, the AIRDOSE-EPA model is preferred for assessments involving radionuclides. When its pr edicted concentrations have been benchmarked against measured values, it has demonstrated goo d agreement; in fact, it has often surpassed the performance of more “sophisticated” models.

The ingrowth and decay of the Rn-222 decay products is very important to estimating the risks from Rn-222 exposure. When the Rn-222 emanates from the tailings, the fraction of its shortlived decay products is zero, as th ey are retained in the tailings matrix. However, their ingrowth begins immediately, and theoretically could reach 100% (total equilibrium) at some distance. As a practical matter, 100% ingrowth is unlikely to ever be atta ined, due to dry deposition and scavenging during plume transport. For the Subp art W assessments, the equilibrium fraction of decay products was set at 0.70. The equilibrium fraction of 0.70 is appropriate for distances beyond approximately 15,000 meters from the impoundme nts (where the majority of the exposed populations are located) and assume s that an individual spends 75% of their time indoors. For

individuals nearer to the im poundments than 15,000 meters, the assumption of a 0.70 equilibrium

fractions will over-state thei r exposure and resulting risk.

Since the NESHAP Subpart W was promulgated, th ere has been a great deal of work done to better characterize the appropriate equilibrium fraction for asse ssing exposure to Rn-222. In general, these studies suggest a somewhat lo wer fraction than was used in the Subpart W assessments, which would have the effect of lowering the estimated risks (UNSCEAR 2000).

The locations of the receptors in the 80-km a ssessment area around each site were determined in one of two ways. For the 0–5 km radius, actual s ite visits were conducted, and the populations in each of 16 directions were determined for distances of 0.5, 1.0, 1.5, 2.0, 2.5, and 5.0 km. For distances between 5 and 80 km, incr ements of 5 km and 10 km were used, and U.S. Census tract

data were used to estimate the population in each sector.

WA 4-11, Task 4 – NESHAPs History 8 SC&A – September 25, 2008Locating the nearby receptors by actual enumera tion is seldom possible when conducting risk assessments. Generally, the best that can be done is to identify nearby sectors where persons are presumed to reside. Using the U.S. Census tr act data to populate the 5–80 km assessment grid, while not perfect, as it pl aces all of the tract's population at the centroid of the tract, is as accurate a means of calculating colle ctive exposure as we have.

For the NESHAPs risk assessment, individuals in the population are presumed to experience a constant level of exposure over a 70-year period (i.e., lifetime). While the Agency has often been criticized for making this assumption, it ha s repeatedly found that it is appropriate for evaluating radiation risks where age at exposure is an important factor in the over-all risk.

The final step in the assessment of the risks fr om Rn-222 released from operating uranium mill tailings impoundments is to corr elate the exposures with risk. For almost all radionuclide risk assessments, the risk is based on dosimetry m odels. However, for Rn-222, it is based on epidemiology. Specifically, based largely on wo rk presented by the Nation Council on Radiation Protection (NCRP 1984) and the International Commission on Radiological Protection (ICRP 1977), the NESHAP used a risk of 760 fatal cancers/10 6 cumulative WLM (reflecting a risk

coefficient of 7.6×10 -4 /WLM).

As with the equilibrium fraction, considerable additional studies have been conducted to determine the appropriate risk coefficient for Rn-222. EPA’s current recommended risk

coefficient is 5.38×10 -4 per WLM. This value is based primarily on the Na tional Academy of Sciences Report BEIR VI (NAS 1999). The EPA r ecommended risk coefficient is reported in

Section VI of “EPA Assessment of Risks from Radon in Homes,” EPA 402-R-03-003, June 2003. Table 10 of that report, reproduced below, provi des a more detailed breakdown of the risks.

Table 10: Estimates of risk per WLM by sm oking category and gender for a stationary population in which 53% of males and 41% of females are ES (Aut hors note: In this table, ES refers to ever smoked and NS refers to never smoked).

Gender Smoking Category Risk per WLM a (10-4) Expected Life Span (years)

Male ES

NS

ES and NS 10.6

1.74

6.40 71.5

72.8

72.1

Female ES

NS

ES and NS 8.81

1.61

4.39 78.0

79.4

78.8

Male & Female ES

NS

ES and NS 9.68

1.67

5.38 74.2

76.4

75.4

a Based on 1990 adult (ages greater than or equal to 19 y) ever smoked prevalence data (58.7 males and 42.3

females are ES) and assumption that 37% males and 36% females or children (ages < 18y) will become ES).

If the risk assessments for Subpart W were done t oday, the over-all risks th at would be estimated would likely be somewhat lowe r than those estimated in 1989.

WA 4-11, Task 4 – NESHAPs History 9 SC&A – September 25, 2008

### 5.0 CONCLUSIONS

The risk assessments that were performed for the NESHAP for Operating Uranium Mill Tailings

were based on the best data and sc ience that were available at the time. While it is unlikely that the over-all risk profile would change signifi cantly if the assessments were redone today,

additional data and new scientific findings have become availabl e. Most significantly, measured emissions data should be available, and the current scientific cons ensus on both equilibrium

fractions and the radon risk coefficien t could be used in the assessment.



### 6.0 REFERENCES

40 CFR 61, Title 40, Part 61: National Emission Standards for Hazardous Air Pollutants, Subpart W: National Emissions Standards for Radon Emissions from Operating Mill Tailing s.

40 CFR 190, Title 40, Part 190: Environmental Radiati on Protection Standards for Nuclear Power Operations

.

40 CFR 192, Title 40, Part 192: Health and Environmenta l Protections Standards for Uranium and Thorium Mill Tailings

.

NAS (National Academy of Sciences) 1999. Biological Effects of Ionizi ng Radiation (BEIR) VI: The Health Effects of Exposure to Indoor Radon . National Academy of Sciences, National

Research Council. 1999.

EPA (Environmental Protection Agency) 1979. Radiological Impacts C aused by Emission of

Radionuclides into Air in the United States , EPA 520/7-79-006, Office of Radiation Programs, Environmental Protection Agency, Washington DC. August 1979.

EPA (Environmental Protection Agency) 1983. Draft Report, Background Information Document Proposed Standards for Radionuclides , EPA 520/1-83-001, Office of Radiation Programs, Environmental Protection Agency, Washington DC. March 1983.

EPA (Environmental Protection Agency) 1984. Final Background Information Document Proposed Standards for Radionuclides , EPA 520/1-84-022-1, Office of Radiation Programs, Environmental Protection Agency, Washington DC. October 1984.

EPA (Environmental Protection Agency) 1986. Final Rule for Radon-222 Emissions From Licensed Uranium Mill Tailings Background Information Document , EPA 520/1-86-009, Office of Radiation Programs, Environmental Pr otection Agency, Washington DC. August 1986.

EPA (Environmental Protection Agency) 1989. Risk Assessment Methodology Environmental Impact Statement NESHAPS for Radionuclides Background Information Document , Volumes 1– 3, EPA 520/1-89-005, Office of Radiation Prog rams, Environmental Protection Agency, Washington DC. September 1989.

WA 4-11, Task 4 – NESHAPs History 10 SC&A – September 25, 2008WA 4-11, Task 4 – NESHAPs History 11 SC&A – September 25, 2008 EPA (Environmental Protection Agency) 2003. EPA Assessment of Risks from Radon in Homes

, EPA 402-R-03-003, June 2003.

FR (Federal Register) 1977. EPA established environmental protection standards for nuclear power operations pursuant to it s authority under the Atomic Energy Act (AEA). Volume 42, page 2858. January 13, 1977.

FR (Federal Register) 1979. EPA determination that radionuclides constitute a hazardous air pollutant within the meaning of Section 112(a)(1). Volume 44, page 78738. December 27, 1979.

FR (Federal Register) 1984. EPA withdrew the proposed NESHAPs for Elemental Phosphorus Plants, DOE-Facilities, and NRC-Licensed Facilities. Volume 49, page 43906. October 23,

1984.

FR (Federal Register) 1985a. EPA promulgated final standards for Elemental Phosphorus Plants, DOE-Facilities, and NRC-Licensed Facilities . Volume 50, page 7280. February 8, 1985.

FR (Federal Register) 1985b. EPA establishe d a work practice sta ndard for Underground Uranium Mines. Volume 50, page 15385. April 17, 1985.

FR (Federal Register) 1989. Fi nal rulemaking package for Subpart W. Volume 54, page 51679. December 15, 1989.

ICRP (International Commission on Radiological Protection) 1977. Recommendations of the International Commission on Radiological Protection , ICRP Publication 26, Ann. ICRP, 1, (1), Pergamon Press, 1977.

NCRP (National Council on Radiation Protection and Measurements) 1984. Evaluation and Occupational and Environmental Exposures to Radon and Recommendations , NCRP Report No. 78, Washington, DC.

UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) 2000. United Nations Scientific Committee on the Effect s of Atomic Radiation Report to the General Assembly , with Scientific Annexes. United Nations. New York 2000.