ORAU TEAM

Dose Reconstruction

Project for NIOSH

Oak Ridge Associated Universities I Dade Moeller I MJW Technical Services

Page 1 of 35

DOE Review Release 05/30/2013

Document Title:

Weldon Spring Plant – Occupational 

Environmental Dose

Document Number: ORAUT-TKBS-0028-4

Revision: 01

Effective Date: 05/17/2013

Type of Document: TBD

Supersedes: Revision 00 

Subject Expert(s): David P. Harrison, Bryce L. Rich, Leo G. Faust, Billy P. Smith, Robert L. Morris, and 

Lori J. Arent

Approval: Signature on File Approval Date: 05/14/2013

David P. Harrison, Document Owner

Concurrence: Signature on File Concurrence Date: 05/15/2013

John M. Byrne, Objective 1 Manager

Concurrence: Signature on File Concurrence Date: 05/15/2013

Edward F. Maher, Objective 3 Manager

Concurrence: Vickie S. Short Signature on File for Concurrence Date: 05/15/2013

Kate Kimpan, Project Director

Approval: Signature on File Approval Date: 05/17/2013

Stuart L. Hinnefeld, Director DCAS

New Total Rewrite Revision Page Change

FOR DOCUMENTS MARKED AS A TOTAL REWRITE, REVISION, OR PAGE CHANGE, REPLACE THE PRIOR 

REVISION AND DISCARD / DESTROY ALL COPIES OF THE PRIOR REVISION.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 2 of 35

PUBLICATION RECORD

EFFECTIVE 

DATE

REVISION 

NUMBER DESCRIPTION

06/28/2005 00 First approved issue of new technical basis document for the Weldon 

Spring Plant – Occupational Environmental Dose. Incorporates 

formal internal and NIOSH review comments. Training is not 

required. Initiated by Robert Meyer.

05/17/2013 01 Revision initiated to revise the TBD as a result of completion of 

Advisory Board Work Group issues. Included information in Section 

4.2.2.1 about the drying of the raffinate pits and its potential for 

resuspension of pit radionuclide content. Included factors for 

calculation of recycled uranium contaminant activity based on ppb or 

pCi uranium. Revised and implemented according to ORAUTPROC-0031, Rev. 02. Added a table for maximum sitewide median 

intake values to comply with PROC-0031, and also added a table of 

annual median intake values for the WSCP, WSRP, and WSQ. 

Replaced introductory text with updated template language in 

Section 4.1. Revised Section 4.1.1, Purpose, and Section 4.1.2, 

Scope. Revised Sections 4.2.1 and 4.2.2 to more specifically target

the radionuclides of concern and source terms that contribute to 95% 

of the potential internal dose. Revised the approach to determination 

of annual intake of radionuclides (Section 4.2.3.1) during the 

operational period to optimize the use of available site-specific 

monitoring data. Added a table of annual median values for 

occupational external dose to be used as surrogates for onsite 

ambient dose during the operational period. Added Section 4.4 as a 

summary of environmental doses for use by dose reconstructors and 

provided tabulated inhalation intakes and ambient dose default 

values. Incorporates formal internal and NIOSH review comments. 

Constitutes a total rewrite of the document. Training required: As 

determined by the Objective Manager. Initiated by David P. 

Harrison. 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 3 of 35

TABLE OF CONTENTS

SECTION TITLE

Acronyms and Abbreviations..................................................................................................................

PAGE

5

4.1 Introduction .................................................................................................................................7

4.1.1 Purpose...........................................................................................................................8

4.1.2 Scope..............................................................................................................................8

4.2 Internal Dose from Onsite Atmospheric Radionuclide Concentrations .......................................9

4.2.1 Radionuclides of Concern ...............................................................................................9

4.2.1.1 Airborne Particulate Radionuclides ..................................................................9

4.2.1.2 Radon...............................................................................................................9

4.2.2 Source Terms for Airborne Radionuclides ......................................................................9

4.2.2.1 Source Terms During Operational Period (1957 to 1966)................................9

4.2.2.2 Source Terms During Monitoring and Remediation Period (1975 to 

Present)..........................................................................................................11

4.2.3 Annual Intake of Radionuclides.....................................................................................11

4.2.3.1 Intakes During Operational Period (1957 to 1966).........................................11

4.2.3.2 Intakes During Monitoring and Remediation Periods (1975 to Present) ........16

4.3 External Exposure to Onsite Atmospheric Radionuclide Concentrations .................................23

4.3.1 Ambient Exposure During Operational Period (1957 to 1966)......................................23

4.3.2 Ambient Exposure During Monitoring and Remediation Periods (1975 to 

Present).........................................................................................................................24

4.3.3 Organ Dose Conversion Factor ....................................................................................27

4.4 Summary Environmental Dose Default Values.........................................................................27

4.5 Attributions and Annotations .....................................................................................................28

References ...........................................................................................................................................29

Glossary................................................................................................................................................34

LIST OF TABLES

TABLE TITLE

4-1 Annual median intakes for WSCP, WSRP, AND WSQ.............................................................

PAGE

20

4-2 Maximum sitewide (WSCP, WSQ, and WSRP) annual median intakes...................................22

4-3 Median values for occupational external gamma dose.............................................................23

4-4 Estimated ambient onsite doses ...............................................................................................24

4-5 Estimated maximum sitewide ambient dose at WSP................................................................27
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 4 of 35

LIST OF FIGURES

FIGURE TITLE

4-1 Map showing perimeter sampling locations and processing facilities.......................................

PAGE

14

4-2 Map showing the WSP layout with a 600-m radius circle superimposed to 

demonstrate the distance from the plant center to the perimeter .............................................15

4-3 Air particulate, radon, and gamma monitoring stations in WSCP and WSRP ..........................18

4-4 Air particulate, radon, and gamma monitoring stations in WSQ ...............................................19

4-5 Topographic map and locations of gamma exposure rate measurements for WSQ ................26
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 5 of 35

ACRONYMS AND ABBREVIATIONS

Bq becquerel

CFR Code of Federal Regulations

Ci curie

cm centimeter

DOE U.S. Department of Energy

DOL U.S. Department of Labor

dps disintegrations per second

DR dose reconstructor

EEOICPA Energy Employees Occupational Illness Compensation Program Act of 2000

ft feet

g gram

hr hour

ICRP International Commission on Radiological Protection

m meter

mrem millirem

MCW Mallinckrodt Chemical Works

MT metric ton

NIOSH National Institute for Occupational Safety and Health

NLCO National Lead Company of Ohio, Inc.

ORAU Oak Ridge Associated Universities

pCi picocurie

POC probability of causation

ppb parts per billion

s second

SRDB Ref ID Site Research Database Reference Identification (number)

TBD technical basis document

U.S.C. United States Code

WLM working level month

WSCP Weldon Spring Chemical Plant

WSP Weldon Spring Plant

WSQ Weldon Spring Quarry

WSRP Weldon Spring Raffinate Pits

yr year

μCi microcurie

μm micrometer
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 6 of 35

μR microroentgen

§ section or sections
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 7 of 35

4.1 INTRODUCTION

Technical basis documents and site profile documents are not official determinations made by the 

National Institute for Occupational Safety and Health (NIOSH) but are rather general working 

documents that provide historical background information and guidance to assist in the preparation of 

dose reconstructions at particular sites or categories of sites. They will be revised in the event 

additional relevant information is obtained about the affected site(s). These documents may be used 

to assist NIOSH staff in the completion of the individual work required for each dose reconstruction.

In this document the word “facility” is used as a general term for an area, building, or group of 

buildings that served a specific purpose at a site. It does not necessarily connote an “atomic weapons 

employer facility” or a “Department of Energy [DOE] facility” as defined in the Energy Employees 

Occupational Illness Compensation Program Act [EEOICPA; 42 U.S.C. § 7384l(5) and (12)]. 

EEOICPA defines a DOE facility as “any building, structure, or premise, including the grounds upon 

which such building, structure, or premise is located ... in which operations are, or have been, 

conducted by, or on behalf of, the Department of Energy (except for buildings, structures, premises, 

grounds, or operations ... pertaining to the Naval Nuclear Propulsion Program)” [42 U.S.C. § 

7384l(12)]. Accordingly, except for the exclusion for the Naval Nuclear Propulsion Program noted 

above, any facility that performs or performed DOE operations of any nature whatsoever is a DOE 

facility encompassed by EEOICPA.

For employees of DOE or its contractors with cancer, the DOE facility definition only determines 

eligibility for a dose reconstruction, which is a prerequisite to a compensation decision (except for 

members of the Special Exposure Cohort). The compensation decision for cancer claimants is based 

on a section of the statute entitled “Exposure in the Performance of Duty.” That provision [42 U.S.C. § 

7384n(b)] says that an individual with cancer “shall be determined to have sustained that cancer in the 

performance of duty for purposes of the compensation program if, and only if, the cancer ... was at 

least as likely as not related to employment at the facility [where the employee worked], as 

determined in accordance with the POC [probability of causation1

The statute also includes a definition of a DOE facility that excludes “buildings, structures, premises, 

grounds, or operations covered by Executive Order No. 12344, dated February 1, 1982 (42 U.S.C. 

7158 note), pertaining to the Naval Nuclear Propulsion Program” [42 U.S.C. § 7384l(12)]. While this 

definition excludes Naval Nuclear Propulsion Facilities from being covered under the Act, the section 

of EEOICPA that deals with the compensation decision for covered employees with cancer [i.e., 42 

U.S.C. § 7384n(b), entitled “Exposure in the Performance of Duty”] does not contain such an 

exclusion. Therefore, the statute requires NIOSH to include all occupationally-derived radiation 

exposures at covered facilities in its dose reconstructions for employees at DOE facilities, including 

radiation exposures related to the Naval Nuclear Propulsion Program. As a result, all internal and 

external occupational radiation exposures are considered valid for inclusion in a dose reconstruction. 

No efforts are made to determine the eligibility of any fraction of total measured exposure for inclusion 

in dose reconstruction. NIOSH, however, does not consider the following exposures to be 

occupationally derived (NIOSH 2010a):

] guidelines established under 

subsection (c) ...” [42 U.S.C. § 7384n(b)]. Neither the statute nor the probability of causation 

guidelines (nor the dose reconstruction regulation, 42 C.F.R. Pt. 82) restrict the “performance of duty” 

referred to in 42 U.S.C. § 7384n(b) to nuclear weapons work (NIOSH 2010a).

• Background radiation, including radiation from naturally occurring radon present in 

conventional structures

• Radiation from X-rays received in the diagnosis of injuries or illnesses or for therapeutic 

reasons

 1 The U.S. Department of Labor (DOL) is ultimately responsible under the EEOICPA for determining the POC.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 8 of 35

4.1.1

The purpose of this technical basis document (TBD) is to describe the potential occupational 

environmental dose to Weldon Spring Plant (WSP) workers. Occupational environmental exposure 

refers to exposures workers received while on the site but outside facilities from elevated ambient 

radiation, from facility effluent releases to the environment, and from resuspension of radionuclides in 

soils. Effluent releases can result in internal and external exposures by inhalation of airborne 

radionuclides and by submersion in an effluent. This TBD provides estimated annual intakes for 

inhalation exposure and estimated doses as a result of submersion and ambient exposure at WSP.

Purpose

4.1.2

The periods for which this TBD evaluates environmental doses are those during which DOE or its 

predecessor agencies (the U.S. Atomic Energy Commission until 1975 and the Energy Research and 

Development Administration until 1979) had contractors on some or all of the WSP. The WSP 

consisted of the Weldon Spring Chemical Plant (WSCP), the Weldon Spring Raffinate Pits (WSRP), 

and the Weldon Spring Quarry (WSQ). These include the operational period (1957 to 1966) and the 

monitoring and remediation periods (1975 to 2002). After remediation was complete, long-term 

surveillance and maintenance by DOE commenced. The monitoring period, from 1975 through 1984, 

applies only to the raffinate pits and quarry areas because DOE did not assume control of the 

chemical plant until 1985. The WS Quarry was initially transferred from the Army to the AEC in 1958. 

There is some potential applicability of shutdown operations in 1967 before transfer to the 

U.S. Department of Defense in December 1967. The raffinate pits and the quarry were not 

transferred to the Army. From 1968 to early 1969 decontamination and dismantling operations 

commenced to support the herbicide production. However, the defoliant project was canceled in 

February 1969 whereupon the chemical plant entered a care and custody status by the Army. The 

AEC didn’t have any contractors at the WS Raffinate Pits or the WS Quarry until August 1975 for 

environmental monitoring. From 1969 to 1981 the status of the site did not change, and from 1981 to 

1985 the site was placed in caretaker status. The WS Chemical Plant was transferred from the Army 

to the DOE in 1985, and remediation efforts began in 1985. EEOICPA does not cover the period 

when the WSP site was under control of the Army, and, therefore, this TBD does not cover that 

period.

Scope

To summarize, there were five periods in the history of the WSP:

• Operational: 1957 to 1966;

• Transfer to the U.S. Army: 1967 to 1974;

• Environmental monitoring: 1975 to 1985;

• Remediation: 1985 to 2002; and

• Long-term surveillance and maintenance: 2002 to present.

Workers at the WSCP received environmental doses during the operational period as a result of stack 

effluents from buildings, contamination of soil as a result of stack releases, and onsite storage of ore 

concentrates. Workers at the WSQ received environmental doses during the same period as a result 

of resuspension from contaminated rubble and soil being placed in, or already in, the disposal area. 

During the remediation period, workers received occupational doses from contaminated soils and 

structures at the WSQ, the WSCP, and the WSRP during excavation of contaminated sludges and 

soils, demolition and removal of contaminated structures, and placement of contaminated media in 

the onsite disposal facility in the WSRP (see Part 2 of this Site Profile, ORAUT 2013a).

Section 4.2 contains information for estimation of internal environmental dose and includes 

discussions of airborne particulate and radon concentrations at WSCP, WSRP, and WSQ. 

Section 4.3 contains information for estimation of external environmental dose. Section 4.4 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 9 of 35

summarizes the tables that provide environmental dose default values for use by dose reconstructors 

(DRs).

4.2 INTERNAL DOSE FROM ONSITE ATMOSPHERIC RADIONUCLIDE 

CONCENTRATIONS

This section describes internal exposure due to the intake of radionuclides. Section 4.2.1 identifies 

the radionuclides of concern. Section 4.2.2 describes specific sources of various radionuclides in the 

outdoor environment. Section 4.2.3 presents the methods that were used to calculate activity intakes 

of radioactivity in the form of air particulates and radon. Section 4.4 provides tabulated values for 

maximum sitewide median inhalation intakes of radioactive air particulates and radon at WSCP, 

WSRP, and WSQ.

4.2.1

The radionuclides of concern are defined as those contributing to 95% of the potential internal dose.

Radionuclides of Concern

4.2.1.1 Airborne Particulate Radionuclides

The occupational environmental airborne particulate radionuclides of concern for dose reconstruction 

are the naturally occurring isotopes of uranium (234U, 235U, and 238U) and their decay products 

(primarily 230Th and 226Ra) and isotopes of natural thorium and their decay products. Part 5 of this 

Site Profile (ORAUT 2012) provides additional details for the internal deposition of these radionuclides 

of concern.

4.2.1.2 Radon

Three radon isotopes are generated during the decay of 235U, 238U, and 232Th: 219Rn, 222Rn, and 220Rn, 

respectively. The risks associated with 219Rn due to its extremely short half-life (4 seconds) and small 

amount of precursor radium (due to the limited amount of 235U WSP processed) were insignificant in 

comparison with those from 222Rn and 220Rn, and are not relevant. Therefore, this TBD considers the 

inhalation intakes for these two isotopes to be potentially significant, as discussed in more detail 

below.

4.2.2

4.2.2.1 Source Terms During Operational Period (1957 to 1966)

Source Terms for Airborne Radionuclides

Uranium and thorium were released from the WSCP process building stacks during the operational 

period. No stack monitoring data have been found. Perimeter monitoring data are available in WSP 

environmental reports and a materials balance study (Harris 1986, pp. 10, 33) and form the basis of 

the estimates of uranium and thorium intake rates. The reported atmospheric discharges from the 

materials balance study were engineering estimates that were derived from airflows and other 

process factors (see Part 2 of this Site Profile, ORAUT 2013a). The estimated amount of uranium 

activity that was emitted from the operating plants ranged between approximately 1 and 5 Ci/yr.

An estimate of radon release based on the amount of processed uranium during the operational 

period ranged from 12 to 34 Ci/yr (Meshkov et al. 1986, pp. 47–48), assuming (1) 5,000 to 14,500 MT 

of uranium materials were processed per year, (2) 70% of this was elemental uranium, (3) radium 

activity was 1% of the uranium activity (believed to be an upper end estimate), (4) radon was in 

equilibrium with radium, and (5) all radon was released through the stack during processing.
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No raw ores were processed at WSP. Only ore concentrations (yellowcake) and other highly refined 

uranium and thorium compounds were processed. The ore concentrates at Weldon Spring were a 

relatively small source of radon because most of the radium, the radon precursor, in the ore was 

removed in the milling process, which occurred elsewhere.

According to the review of source emissions by Meshkov et al. (1986), only a fraction of radon (about 

20%) is released when attached to solid particles, such as those that occur in uranium ore 

concentrates. However, the digestion phase of the refining process would have released the trapped 

radon during the operational period. Off-gases that contained radon isotopes from this process were 

conveyed to the acid recovery plant at the WSCP. The discharge from the acid recovery plant was 

the primary source of radon emission.

During the operational period, drums of uranium ore concentrate (yellowcake) were emptied into the 

hopper at the top of the receiving and sampling building (ORAUT 2013a). Dust was collected in three 

large collectors, each with its own stack, and either repackaged and shipped off the site or 

reprocessed. In the refinery plant process, uranium-laden dust was generated during material 

transfers, denitration, reduction and hydrofluorination, and conversion to solid metal. Impurities that 

were generated in the purification process before denitration were bled off in liquid form in the 

raffinate, which was pumped to the pits. The denitration process was the dustiest part of the 

operation. Therefore, point sources of uranium emissions from stacks existed during this period. 

Stack monitoring concentration data for the operational period are not available to NIOSH.

Meshkov et al. (1986, p. 47) assumed that activity concentrations of 230Th, 226Ra, and 210Pb in uranium 

ore concentrates were 5%, 1%, and 1%, respectively, of that of 238U. However, specific isotopic 

characterization of raffinates at Weldon Spring indicates that the uranium mill processes that 

produced the yellowcake concentrates that was used at both Fernald and WSP effectively removed 

the radium but were not effective in removing thorium, specifically 230Th. Therefore, this TBD 

assumes activity ratios for 230Th, 226Ra, and 210Pb in uranium ore concentrate of 80%, 1%, and 1%, 

respectively, of that of 238U (Mason 1958, Sears 1975 p. 143, Sears 1976 p. 4). 

Impurities that were generated in the uranyl-nitrate purification process were bled off in the raffinate, 

which was pumped to raffinate pits. The raffinate contained a variety of radionuclides, including 

thorium and radium (Author unknown, 1967, pp. 10–11). Wastes in the raffinate pits were not a 

significant source of airborne radionuclides, particulate or gaseous, during the operational period, 

primarily due to the presence of water in the pits. It is unlikely that a significant portion of the 

sediments became sufficiently dry to be considered a source term during this period, even though two 

decades later Bechtel (1984a, p. 14) reported that Pits 1 and 2 could become dry during the summer 

months. NLCO (1977, p. 18) stated:

The transport of radiological contamination by air is not considered a problem at the 

site. Good ground cover exists and the raffinate pits are either covered with water or 

remain moist due to the balance between precipitation and evaporation in the area. 

Even in times of prolonged dry weather, the inherent consistency of the raffinate 

material contained in the pits precludes drying.

If the raffinate pits had been dry, resuspension from the pits should be reflected in the boundary 

station air sampling results (NIOSH 2012a). As discussed below in Section 4.2.3.1, perimeter 

monitoring data were extrapolated to the central portion of the plant for use in occupational 

environmental intake rate calculation.

Wastes that were disposed of in the WSQ during the operational period presented a diffuse source of 

particulate emissions to the air as a result of entrainment of contaminated, wind-exposed surface soil 

or rubble. Radon-222 and 220Rn (from 226Ra and 224Ra, respectively) in the quarry also presented a 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 11 of 35

diffuse source of airborne radionuclides. Before 1963, the quarry contained only drummed thorium 

wastes that were probably submerged (Author unknown 1967, pp. 17–19) and not a significant source 

of radon because water is an effective barrier to radon release. Each 25-cm increase in the depth of 

a water column reduces the 222Rn concentration by approximately 50% (Usman, Spitz, and Weisman 

2005). The attenuation of 220Rn flux is expected to be even larger due to the shorter half-life of 220Rn. 

Therefore, the radon release before 1963 is negligibly small. In 1963 and 1964, an estimated 

38,000 m3 of uranium- and radium-contaminated rubble, equipment, and soil were placed in the 

quarry after demolition of the Mallinckrodt Destrehan Street site. A majority of this waste was not 

submerged and was a potential source of radon exposure (Author unknown 1967, pp. 17–20). The 

emission rate from the quarry is assumed to be the same from 1963 until it was measured during the 

monitoring and remediation period.

Recycled Uranium

The DR should assume as favorable to claimants that all of the uranium WSP processed after 1961 

was recycled uranium. This assumption is consistent with that in Ohio Field Office Recycled Uranium 

Recovery Project Report (DOE 2000, p. 118), which assumed in lieu of better information that all 

uranium receipts at WSP after 1961 were recycled uranium. 

Contaminant radionuclides in recycled uranium that could be dosimetrically significant are plutonium 

(assume 239Pu), neptunium (237Np), and technetium (99Tc). For the periods that included recycled 

uranium, the DR should consider the factors in Table 5-11 of the Technical Basis Document for the 

Fernald Environmental Management Project (FEMP) – Occupational Internal Dose (ORAUT 2004). 

These factors, when multiplied by the calculated uranium gram-value intake, result in the activity per 

gram of uranium of the contaminants at levels of 100 ppb 239Pu, 3,500 ppb 237Np, and 9,000 ppb 99Tc. 

For example, 1 ppb-Pu/U equals 1 × 10-9 gPu/gU. For 239Pu the conversion factor is 62.89 pCi Pu/gU 

per ppb, for 237Np the factor is 0.714 pCi Np/gU per ppb, and for 99Tc the factor is 17.15 pCi Tc/gU per 

ppb.

4.2.2.2 Source Terms During Monitoring and Remediation Period (1975 to Present)

During the monitoring (1975 to 1985), remediation (1985 to 2002), and long-term surveillance and 

maintenance (2002 to present) periods, diffuse (i.e., non-point-source) emissions predominated as the 

source of radionuclides to the air at the WSCP, WSRP, and WSQ. Annual environmental monitoring 

reports provided estimates of air concentrations of particulate radionuclides and of radon at the 

WSCP and WSQ beginning in 1981. These estimates reflect emissions during the later monitoring 

period and throughout remediation activities.

4.2.3

Descriptions of particle size and absorption type are not available for radionuclides of concern. DRs 

should assume that the default aerosol size is 5-μm activity median aerodynamic diameter. In 

addition, DRs should base the selection of dose factors on the absorption type that yields the highest 

dose to the organ of interest. Calculated annual intakes are based on a 2,400-m3

/yr inhalation rate 

(ICRP 1994) based on an hourly breathing rate of 1.2 m3 for light activity and a 2,000-hour work year. 

Environmental intakes from ingestion are considered to be negligibly small. Intakes can be scaled to 

a different rate or to consider partial year exposures.

Annual Intake of Radionuclides

4.2.3.1 Intakes During Operational Period (1957 to 1966)

This TBD analysis used the available perimeter monitoring data to calculate estimated intakes of 

radioactive airborne particulates and radon according to the methods described in this section.
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Airborne Particulate Radionuclides

Uranium air concentration measurements at the WSP perimeter from 1959 through 1965 were 

evaluated. The perimeter data were converted to units of becquerels per cubic meter, and the 

average airborne particulate concentrations are presented in ORAUT (2013b). The original data were 

reported in units of “special uranium microcuries,” which is a modification of the “special curie” as 

defined in DOE 2009 and stated in the glossary section of this technical basis document. Converting 

to units of becquerel, the special uranium μCi is multiplied by 3.7 × 104 Bq/μCi and by a factor of 2.024 

to report total uranium activity. Refer to ORAUT (2012) for an expanded discussion of the use of the 

special uranium microcurie at WSP. Other radionuclides were not measured.

Perimeter monitoring data were extrapolated to the central portion of the plant for use in occupational 

environmental intake rate calculation. The extrapolation was based on the ratio of the calculated 

concentration at two different locations of interest using the Pasquill-Gifford equation for Gaussian 

plume atmospheric dispersion:

2 2

2 2

1 1

exp 2 2 y z y z

χ( x,y ) y H

Qπσ σ u σ σ

   

= −+          

(4-1)

where:

χ(x,y) = ground-level concentration at point (x,y) (Bq/m3

).

x = downwind distance on plume centerline (m). In this case the calculation is done at 

100 m and 750 m.

y = crosswind distance (m). In this case, y = 0 m.

Q = emission rate (Bq/s), which is set to unity in this case.

σy, σz = horizontal and vertical standard deviations of the contaminant concentration in the 

plume (m). At 100 m, σy = 17.6 and σz = 10.9. At 750 m, σy = 109 and σz = 80.

u = mean wind speed at level of plume centerline (m/s), which in this case is an annual 

average of 4.6 m/s.

H = effective release height (m), which is assumed to be 10 m to represent the stack of a 

large one-story industrial building.

The values of σy and σz can be determined from graphic presentations or from equations the U.S. 

Nuclear Regulatory Commission uses in computer programs such as RACHET2, which was done in 

this case. The equations are presented in Napier and Ramsdell (2005).

The wind speed of 4.6 m/s was based on the average wind frequency data from Lambert Field in St. 

Louis for the period from 1961 through 1990 (ISCO 2009). The same data were used to select an 

atmospheric stability class. Stability class B was selected for this analysis to represent a relatively 

turbulent flow that would increase the dilution between the center of the plant and the plant perimeter 

where the measurements were made. Stability class B is characterized as an unstable or turbulent 

atmosphere with surface wind speed in the range of 3 to 5 m/s and moderate incoming solar radiation. 

The only stability class that would be more turbulent – and therefore more favorable to the claimant –

would be class A, but the wind frequency data do not support that choice.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 13 of 35

The distances for the location of the perimeter monitoring and the onsite worker were based on 

inspection of a map of WSP sampling locations near the fence line (see Figure 4-1). Figure 4-1 does 

not include a distance scale, but Figure 4-2 includes a distance scale and a circle superimposed near 

the fence line. The radius of the circle is nominally 600 m, so this value was considered to represent

the distance from the release point to the sampling location. Further inspection shows that the 

processing area is on the east side of the plant, and a better representation of the greatest distance 

from the center of the processing area to a point on the perimeter is 750 m. The value of 100 m for 

the exposed worker location is based on the limitations of the atmospheric dispersion model and is 

because it is likely to be a reasonable average estimate of the distance of any individual on the 

ground from a stack on the roof of a process building.

When Equation 4-1 is solved for a unit emission rate at both 100 m and 750 m, the ratio of results 

defines a dilution factor that can be used to extrapolate the data that were measured at the perimeter 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 14 of 35

Figure 4-1. Map showing perimeter sampling locations and processing facilities (lacking distance 

scale).

to the concentration outdoors in the processing area. The calculated dilution factor is 30. For 

example, a measured air concentration of 0.01 Bq/m3 at the perimeter can be extrapolated to a 

concentration of 0.3 Bq/m3 near the center of the operating area of the plant.

Thorium intake for years when it was processed can be estimated by scaling the annual uranium and 

thorium mass throughput rates and apportioning that fraction of the intake rate to thorium instead of 

uranium. This is justified by the fact that the similar (or the same) processing facilities and 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 15 of 35

Figure 4-2. Map showing the WSP layout with a 600-m radius 

circle superimposed to demonstrate the distance from the plant 

center to the perimeter.

environmental controls were used for both uranium and thorium operations; therefore, a portion of the 

environmental release could be expected to be thorium.

The measured perimeter air concentration data for the WSCP and WSQ can be found in quarterly and 

semiannual environmental monitoring reports (MCW 1961a, p. 36, 53–54; 1961b, p. 6; 1961c, pp. 9,

11; 1962a, p. 14; 1962b, p. 44, p. 65; 1962c, pp. 85–86; 1964a, pp. 9, 12; 1964b, pp. 10–11; 1965, 

pp. 13–14; 1966, pp. 10–11), and in the summary report by Meshkov et al. (1986, pp. 101, 103–104). 

In some instances, the same data were reported in more than one document; in those cases the 

contemporary environmental reports were preferred as the primary data source. Intake rates can be 

calculated based on the extrapolated air concentrations and an assumed breathing rate of 1.2 m3

/hr

for 2,000 hr/yr. 

For 1957 and 1958 at the WSCP, for which measurements are not available, this analysis assumed

that perimeter air concentrations were the same as the measured concentrations in 1959, the 

operational year with the highest measured perimeter concentrations. This is considered an 

overestimate for the first 2 years, when uranium receipts were lower than those during the main 

production years (1960 to 1964; see ORAUT 2013a).
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 16 of 35

Radon

Measured ground-level air concentrations of radon during the operational period were not reported in 

the available references, but Meshkov et al. (1986) estimated an annual release rate of 222Rn in the 

range of 12 to 34 Ci. This radon was released from the acid recovery building stack. Using the radon 

intake calculation as stated in ORAUT (2013b), an annual 222Rn intake of 12.4 WLM/year is assigned 

to personnel working at the Weldon Spring Site during the operational period (NIOSH 2012b). This 

TBD analysis estimated radon concentrations for the WSQ during the operational period from 

measurements in the vicinity from 1977 through 1982 (Weidner and Boback 1982, p. 50; Bechtel 

1983a, p. 25; 1983b, pp. 24, 27; Meshkov et al. 1986, p. 101). This approach is justified because the 

activities of 226Ra and 224Ra are not significantly depleted in the quarry over time due to limited 

leaching and continuous production of these isotopes from precursors in the waste. These years 

reasonably represent radon emanations for the WSQ during the years of operation of the plant. 

These measurements were applied to the period from 1963 to 1966 only. Before that, drummed 

thorium waste was most likely submerged and no significant source of radon existed.

A similar estimate for 220Rn release from the WSCP during the operational period was not made. 

Harris (1986, p. 86) states, “Natural thorium was typically received in either a nitrate or oxide form.” In 

addition, Harris (pp. 23, p. 28) indicates that the amount of processed thorium material ranged from a 

low of 0.05% of the processed natural uranium in 1964 to a high of 5.4% in 1965. Assuming 

concentrated thorium feed (i.e., 70% thorium) and secular equilibrium between 232Th, 224Ra, and 

220Rn, the 220Rn release could approach 70% of the 222Rn release. The estimated dose attributable to 

220Rn and its progeny is insignificant in relation to 222Rn and its progeny because 222Rn progeny have 

a higher estimated equilibrium factor and higher associated dose factors than the 220Rn thoron 

progeny (MK-Ferguson 2001a, pp. 31–35).

4.2.3.2 Intakes During Monitoring and Remediation Periods (1975 to Present)

After 1974, air monitoring occurred in the WSRP and WSQ areas. Measurements of radon in air were 

reported in annual reports beginning with a monitoring report for 1979 and 1980 (Weidner and Boback 

1982, pp. 28–30, 33, 50), which were specific to the raffinate pits and quarry. In October 1985, the 

radon monitoring program was expanded to include the WSCP (Bechtel 1986, pp. 34–35), which 

transferred back to DOE at that time. Air particulate monitoring was added beginning in 1987 at the 

WSCP and WSRP (MK-Ferguson 1988, pp. 77–83) and beginning in 1989 at the WSQ (MK-Ferguson 

1990a, pp. 125–133). Air sampling data from the annual monitoring reports from 1979 to 2000, when 

remediation was nearly complete, were the basis for the following estimates of air concentrations and 

intakes at the WSRP, WSCP, and WSQ for periods after 1974.

Airborne Particulate Radionuclides

Airborne particulate results were reported at the WSCP and WSRP beginning in 1987 and at the 

WSQ beginning in 1989 (MK-Ferguson 1988, pp. 77–83; 1989a, pp. 90–92; 1990a, pp. 125–133; 

1991, pp. 131–135; 1992a, pp. 98–101; 1993, pp. 128–132; 1994, pp. 106–111; 1995, pp. 104–108; 

1996, pp. 96–99; 1997, pp. 92–97; 1998a, pp. 78–81; 1999, pp. 86–90; 2000, pp. 81–85; 2001b, pp.

79–83).

ORAUT (2013b) lists air monitoring data for airborne particulate radionuclides during the monitoring 

and remediation periods. The data are reported as gross alpha rather than uranium. Because more 

than 99% of the material WSP received was natural uranium, it is assumed that the gross alpha data 

represents the natural uranium concentration. Figures 4-3 and 4-4 show the locations of monitoring 

stations for the WSRP and WSCP and for the WSQ, respectively. Radioactive air particulates were 

not monitored before the beginning of remediation activities at the site in 1985. In 1987 and 1988, 

monitoring of particulates at a few perimeter locations for the WSRP and WSCP, and in 1989 at the 

WSQ, indicated that measured gross alpha concentrations were statistically indistinguishable from 

background (MK-Ferguson 1988, p. 81; 1989a, p. 92; and 1990a, p. 133). Therefore, the 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 17 of 35

concentrations in for 1987 and 1989 at the WSRP and WSCP and in 1989 at the WSQ are zero. 

Because all areas of the WSP were essentially undisturbed between 1975 and the beginning of 

remediation activities in 1985, this analysis assumed that radioactive air particulate concentrations 

before 1987 were the same as those measured in 1987 through 1989; therefore, ORAUT (2013b) lists 

particulate concentrations from 1975 through 1986 as insignificant.

From 1989 to 2000, concentrations of radioactive air particulates were measured and reported at 

locations identified in Figures 4-3 and 4-4, even though many of the concentrations were statistically 

indistinguishable from background. The measurements occurred at perimeter locations for the 

WSRP, WSCP, and WSQ. These perimeter data were extrapolated to represent concentrations at 

the center of operating area using the method described in Section 4.2.3.1. Therefore, the measured 

perimeter concentrations of airborne particulate radionuclides were multiplied by a factor of 30 to 

represent the average onsite airborne concentrations in ORAUT (2013b).

Section 4.2.1.1 identifies the radionuclides of concern as the naturally occurring isotopes of uranium 

(

234U, 235U, and 238U) and their decay products (primarily 230Th and 226Ra) as potentially significant 

isotopes of concern during the remediation period. However, air concentrations of these isotopes 

were measured in terms of gross alpha concentrations at the WSP for most years of interest. The 

lack of refinement is probably because (1) the radionuclides of interest are alpha emitters, and (2) the 

perimeter data for the WSRP, WSCP, and WSQ, representing all that are available for air particulates, 

seldom showed air concentration measurements higher than those at offsite background monitoring 

stations. Some isotope-specific data appear in annual reports in the late 1990s but, because the ratio 

of isotopes probably would be highly variable by location due to the variability in isotopic composition 

of the contaminated soil, the utility of these data is limited. Since over 99% of the material received at 

WSP was natural uranium, gross alpha activity is assumed to be natural uranium represented as 

100% 234U.

Air particulate monitoring ended at the end of 2000 for all WSP areas because radioactive waste 

handling activities were essentially complete and no critical receptor air monitoring data had 

demonstrated a dose to the public of greater than 1 mrem (MK-Ferguson 2001b, pp. 95, 230–237). 

The Weldon Spring Site remediation was effectively complete in 2002. The site has since been 

transferred for long-term surveillance and maintenance. A formal review of the remedial action has 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 18 of 35

Figure 4-3. Air particulate (P), radon (R), and gamma (G) 

monitoring stations in WSCP and WSRP.

found that the remedies are “protective of human health and the environment” (DOE 2006). 

Therefore, all environmental doses are zero beginning in 2002.

ORAUT (2013b) lists estimated annual gross alpha activity intakes of airborne particulate 

radionuclides (Bq/yr) (represented as 100% 234U) between 1975 and 2002. The table does not 

include estimates for the WSCP from 1975 to 1984 because this facility did not transfer from the Army 

to DOE until 1985. The intakes were obtained by multiplying the 234U concentrations (Bq/m3

) by an 

assumed inhalation rate of 2,400 m3

/yr. Table 4-1 lists the annual median intakes for the three WSP 

sites WSCP, WSRP, and WSQ. Table 4-2 lists the maximum sitewide median 234U intakes for the 

remediation period. These intakes correspond to the highest value, by year, for the WSCP, WSRP, 

and WSQ.

Radon

Radon measurements in the raffinate pit area in the late 1970s and early 1980s (before remediation) 

averaged 34 ±37 Bq/m3

, which indicates the pits were not a major source of radon (Meshkov et al. 

1986, p. 101). This value is limiting for the operational period because the amount of 226Ra in the pits 

was at its maximum at the end of operations and it would not have decayed or leached out of the pits 

significantly before the measurements were made.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 19 of 35

During the monitoring and remediation periods, outdoor radon was measured at the WSCP, WSRP, 

and WSQ (Weidner and Boback 1982, pp. 28–30, 33, 50; Bechtel 1983a, pp. 22–25; 1983b, 

Figure 4-4. Air particulate (P), radon (R), and gamma (G) monitoring stations in WSQ.

pp. 22-27; 1984a, pp. 23–26; 1985a, pp. 24–48; 1986, pp. 34–41; MK-Ferguson 1987, p. 58–63; 

1988, pp. 66–73; 1989b, pp. 143–147; 1989a, pp. 80–84; 1990b, pp. 8–17; 1990a, pp. 110–119; 

1991, pp. 105, 115–127; 1992a, pp. 75–90; 1992b, pp. 276–277, 431; 1993, pp. 114–124; 1994, pp. 

92–103; 1995, pp. 87–10; 1996, pp. 75–91; 1997, pp. 70–88; 1998a, pp. 58–73; 1998b, pp. 32–36; 

1999, pp. 67–82; 2000, pp. 63–78; 2001b, pp. 64–76). At the WSCP, only perimeter measurements 

occurred except in 1999 and 2000, when some measurements occurred inside the perimeter where 

the disposal cell received much of the remediation wastes.

At the WSRP, radon measurements occurred at the perimeter monitoring stations between 1985 and 

2000, at one location inside the perimeter during 1985 and 1986, and at several interior locations 

during the years of active remediation (1998 to 2000). This TBD assumes the average measured 

radon concentrations at the perimeter stations were underestimates of the average radon 

concentration over the WSCP and WSRP onsite areas during the remediation period. Therefore, just 

as for particulates, the measured concentrations were multiplied by 30 to provide an average net 

radon concentration for each of the two areas (WSCP and WSRP). ORAUT (2013b) lists the derived 

concentrations, which include contributions of radon from naturally occurring 226Ra and 228Ra. These 

concentrations reflect total radon (222Rn and 220Rn) as measured by F-type alpha track detectors.

Measurements in the quarry area in the late 1970s and early 1980s (before remediation) averaged 

24 ±15 Bq/m3

, which indicates the quarry was not a major source of radon (Meshkov et al. 1986, 

p. 101).
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 20 of 35

At the WSQ, radon measurements occurred only at the perimeter monitoring stations except in 1989, 

when monitors were placed inside the perimeter down to the quarry floor. The ratio of the average 

perimeter radon concentration to the average interior concentration was 30. This is a significant 

increase, but the interior of the quarry is fairly inaccessible, with a quick drop in elevation and an 

abundance of vegetation. Therefore, this TBD assumes that the perimeter concentrations are 

reasonably representative of exposure concentrations except during the active removal of the quarry 

bulk waste in 1993, 1994, and 1995. This TBD assumes the radon concentration during this period of 

active remediation to be 30 times the concentration measured at the perimeter (ORAUT 2013b).

The TBD analysis used Equation 4-2 to convert the radon concentrations into intake values for 

periods outside the operational period from 1957 through 1966. The WLM/yr intake per Bq/m3 for 

222Rn is calculated from:

 222 4

3

0 3 2000 9 54 10

3700 170

WLM / yr . Rn . Bq / m× − = = ×

× (4-2) 

 

The annual median radon intake values for the WSCP, WSRP, and WSQ are listed in Table 4-1. 

Table 4-2 lists maximum sitewide median intakes across WSP, represented in IREP as lognormal 

distributions with a geometric standard deviation of 3. 

The purpose of Table 4-1 is to give the WSP worker an estimate of their annual intake for various 

radionuclides for the three sites at WSP: the chemical plant, the raffinate pits, and the quarry. This 

table also can be used by the DR to determine environmental internal doses specific to the worker’s 

work site. The purpose of Table 4-2 is to give the DR the maximum median intake for a specific year 

for use in determining the energy employee’s dose. Table 4-2 would most likely be used by the DR 

since the calculated dose would be favorable to the claimant and it expedites processing the dose 

reconstruction.

Table 4-1. Annual median intakes for WSCP, WSRP, and WSQ.

Year

WSRP

U-234a

Bq/y

WSRP

radonb

WLM/y

WSCP

U-234 

Bq/y

WSCP

Th-230 

Bq/y

WSCP

natural 

thorium Bq/y

WSCP

radon 

WLM/y

WSQ

U-234 

Bq/y

WSQ

radon 

WLM/y

1957 0.00E+00e 0.00E+00e 6.78E+02 5.43E+02 0.00E+00 1.24E+01h 0.00E+00f 0.00E+00f

1958 0.00E+00e 0.00E+00e 6.78E+02 5.43E+02 0.00E+00 1.24E+01h 0.00E+00f 0.00E+00f

1959 0.00E+00e 0.00E+00e 6.78E+02 5.43E+02 0.00E+00 1.24E+01h 0.00E+00f 0.00E+00f

1960 0.00E+00e 0.00E+00e 1.38E+03 1.11E+03 0.00E+00 1.24E+01h 0.00E+00f 0.00E+00f

1961 0.00E+00e 0.00E+00e 2.37E+03 1.90E+03 0.00E+00 1.24E+01h 3.47E+00 0.00E+00f

1962 0.00E+00e 0.00E+00e 5.85E+02 4.68E+02 0.00E+00 1.24E+01h 2.36E+00 0.00E+00f

1963 0.00E+00e 0.00E+00e 1.06E+03 8.49E+02 0.00E+00 1.24E+01h 2.56E+00 1.24E+01h

1964 0.00E+00e 0.00E+00e 8.11E+02 6.49E+02 6.28E-01 1.24E+01h 5.90E+00 1.24E+01h

1965 0.00E+00e 0.00E+00e 4.42E+02 3.54E+02 1.17E+01 1.24E+01h 3.93E+01 1.24E+01h

1966 0.00E+00e 0.00E+00e 4.42E+02 3.54E+02 3.82E+01 1.24E+01h 3.93E+01 1.24E+01h

1967 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1968 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1969 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1970 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1971 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1972 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1973 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1974 0.00E+00c 0.00E+00c 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00c 0.00E+00c

1975 0.00E+00e 4.06E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 1.90E-02

1976 0.00E+00e 4.06E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 1.90E-02
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 21 of 35

Year

WSRP

U-234a

Bq/y

WSRP

radonb

WLM/y

WSCP

U-234 

Bq/y

WSCP

Th-230 

Bq/y

WSCP

natural 

thorium Bq/y

WSCP

radon 

WLM/y

WSQ

U-234 

Bq/y

WSQ

radon 

WLM/y

1977 0.00E+00e 5.79E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 1.93E-02

1978 0.00E+00e 5.79E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 1.93E-02

1979 0.00E+00e 1.06E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 1.06E-02

1980 0.00E+00e 6.56E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 1.74E-02

1981 0.00E+00e 4.30E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 2.22E-02

1982 0.00E+00e 8.69E-03 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 2.53E-02

1982 0.00E+00e 1.00E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 2.10E-02

1984 0.00E+00e 1.72E-02 0.00E+00d 0.00E+00d 0.00E+00d 0.00E+00d 3.93E+01 2.38E-02

1985 0.00E+00e 1.14E-02 3.28E+00 2.62E+00 0.00E+00g 2.15E-01 3.93E+01 2.38E-02

1986 0.00E+00e 1.62E-02 3.28E+00 2.62E+00 0.00E+00g 3.29E-01 3.93E+01 2.29E-02

1987 0.00E+00 1.34E-02 3.28E+00 2.62E+00 0.00E+00g 4.29E-01 3.93E+01 4.29E-02

1988 0.00E+00 2.10E-02 3.28E+00 2.62E+00 0.00E+00g 5.87E-01 0.00E+00 6.49E-02

1989 0.00E+00 1.57E-02 3.28E+00 2.62E+00 0.00E+00g 5.44E-01 0.00E+00 4.10E-02

1990 1.20E-01 9.54E-03 3.28E+00 2.62E+00 0.00E+00g 3.43E-01 0.00E+00 3.34E-02

1991 6.00E-02 1.05E-02 1.98E+00 1.58E+00 0.00E+00g 2.86E-01 0.00E+00 2.86E-02

1992 4.68E-02 1.05E-02 1.48E+00 1.18E+00 0.00E+00g 2.29E-01 0.00E+00 2.58E-02

1993 5.52E-02 4.77E-03 1.66E+00 1.32E+00 0.00E+00g 1.06E-01 0.00E+00 5.82E-02

1994 6.48E-02 1.34E-02 2.27E+00 1.81E+00 0.00E+00g 2.43E-01 0.00E+00 1.62E-01

1995 5.64E-02 1.62E-02 1.84E+00 1.47E+00 0.00E+00g 3.15E-01 0.00E+00 5.53E-02

1996 7.44E-02 2.72E-02 2.12E+00 1.70E+00 0.00E+00g 3.86E-01 0.00E+00 1.24E-02

1997 9.00E-02 6.20E-02 1.98E+00 1.58E+00 0.00E+00g 3.15E-01 0.00E+00 1.05E-02

1998 1.04E-01 1.10E-02 2.77E+00 2.22E+00 0.00E+00g 1.86E-01 0.00E+00 7.06E-03

1999 9.24E-02 1.76E-02 2.74E+00 2.19E+00 0.00E+00g 3.58E-01 0.00E+00 1.62E-02

2000 4.92E-02 9.54E-03 1.84E+00 1.47E+00 0.00E+00g 3.72E-01 0.00E+00 1.24E-02

2001 4.92E-02 9.54E-03 1.84E+00 1.47E+00 0.00E+00g 3.72E-01 0.00E+00 1.24E-02

2002–

present

0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00g 0.00E+00 0.00E+00 0.00E+00

a. Data are reported as gross alpha rather than uranium. Because more than 99% of the material WSP received was 

natural uranium, it is assumed that the gross alpha data represents the natural uranium concentration and is 

represented as 100% 234U.

b. Radon refers to both Rn-220 and Rn-222 and includes natural background contribution.

c. There were no AEC contractors onsite during this period. National Lead of Ohio began environmental monitoring at the 

raffinate pits and the quarry in August 1975.

d. Controlled by the Department of the Army.

e. There is no significant airborne concentration expected since the source term is small and the pits are covered with 

water.

f. Prior to 1963 the quarry contained only drummed waste which was typically submerged in water and was therefore 

negligible.

g. No source term for natural thorium.

h. Assumed radon intake value for the operational period at the Weldon Spring Site.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 22 of 35

Table 4-2. Maximum sitewide (WSCP, WSQ, and 

WSRP) annual median intakes.

Year

U-234a

Bq/yr

Th-230 

Bq/yr

Natural

thorium

Bq/yr

Radonb

WLM/yr

1957 6.78E+02 5.43E+02 0.00E+00 1.24E+01

1958 6.78E+02 5.43E+02 0.00E+00 1.24E+01

1959 6.78E+02 5.43E+02 0.00E+00 1.24E+01

1960 1.38E+03 1.11E+03 0.00E+00 1.24E+01

1961 2.37E+03 1.90E+03 0.00E+00 1.24E+01

1962 5.85E+02 4.68E+02 0.00E+00 1.24E+01

1963 1.06E+03 8.49E+02 0.00E+00 1.24E+01

1964 8.11E+02 6.49E+02 6.28E-01 1.24E+01

1965 4.42E+02 3.54E+02 1.17E+01 1.24E+01

1966 4.42E+02 3.54E+02 3.82E+01 1.24E+01

1967–1974 0.00E+00c 0.00E+00c 0.00E+00c 0.00E+00c

1975 3.93E+01 0.00E+00d 0.00E+00d 4.06E-02

1976 3.93E+01 0.00E+00d 0.00E+00d 4.06E-02

1977 3.93E+01 0.00E+00d 0.00E+00d 5.79E-02

1978 3.93E+01 0.00E+00d 0.00E+00d 5.79E-02

1979 3.93E+01 0.00E+00d 0.00E+00d 1.06E-02

1980 3.93E+01 0.00E+00d 0.00E+00d 6.56E-02

1981 3.93E+01 0.00E+00d 0.00E+00d 4.30E-02

1982 3.93E+01 0.00E+00d 0.00E+00d 2.53E-02

1982 3.93E+01 0.00E+00d 0.00E+00d 2.10E-02

1984 3.93E+01 0.00E+00d 0.00E+00d 2.38E-02

1985 3.93E+01 2.62E+00 0.00E+00e 2.15E-01

1986 3.93E+01 2.62E+00 0.00E+00e 3.29E-01

1987 3.93E+01 2.62E+00 0.00E+00e 4.29E-01

1988 3.28E+00 2.62E+00 0.00E+00e 5.87E-01

1989 3.28E+00 2.62E+00 0.00E+00e 5.44E-01

1990 3.28E+00 2.62E+00 0.00E+00e 3.43E-01

1991 1.98E+00 1.58E+00 0.00E+00e 2.86E-01

1992 1.48E+00 1.18E+00 0.00E+00e 2.29E-01

1993 1.66E+00 1.32E+00 0.00E+00e 1.06E-01

1994 2.27E+00 1.81E+00 0.00E+00e 2.43E-01

1995 1.84E+00 1.47E+00 0.00E+00e 3.15E-01

1996 2.12E+00 1.70E+00 0.00E+00e 3.86E-01

1997 1.98E+00 1.58E+00 0.00E+00e 3.15E-01

1998 2.77E+00 2.22E+00 0.00E+00e 1.86E-01

1999 2.74E+00 2.19E+00 0.00E+00e 3.58E-01

2000 1.84E+00 1.47E+00 0.00E+00e 3.72E-01

2001 1.84E+00 1.47E+00 0.00E+00e 3.72E-01

2002 and 

beyond

0.00E+00 0.00E+00 0.00E+00e 0.00E+00

a. Data are reported as gross alpha rather than uranium. Because 

more than 99% of the material WSP received was natural 

uranium, it is assumed that the gross alpha data represents the 

natural uranium concentration and is represented as 100% 234U.

b. Radon refers to both Rn-220 and Rn-222 and includes natural

background contribution.

c. The WSCP was not a covered facility under EEOICPA and there 

were no AEC contractors at the WSRP and WSQ during this 

period.

d. Controlled by the U.S. Army.

e. No source term for natural thorium.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 23 of 35

4.3 EXTERNAL EXPOSURE TO ONSITE ATMOSPHERIC RADIONUCLIDE 

CONCENTRATIONS

External ambient exposure at the WSP is a result of gamma and X-ray radiation from radionuclides in 

the ore concentrate that were stored on the site during the operational period and from radionuclides 

in the raffinate pits and quarry.

A 1975 aerial radiological survey of the WSP (Jobst 1976, p. 32) indicated that for most of the site the 

normal terrestrial gamma exposure rate was 3 to 6 μR/hr at 1 m above ground level and the average 

cosmic exposure rate was approximately 4 μR/hr. For continuous exposure over a year, this 

represents an annual ambient dose of 61 to 88 mrem/yr. However, the aerial survey found elevated 

terrestrial exposures over the raffinate pits and the quarry, indicating the presence of manmade 

changes from the natural radioisotopes (NIOSH 2010b, pp. 61–62). Section 4.3.1 identifies ambient 

exposures during the operations period, and Section 4.3.2 provides ambient exposures during the 

monitoring and remediation period.

4.3.1

Available documents do not contain monitoring data that described the ambient exposure rate at the 

WSP during the operational period. During this period, ambient dose rates in excess of natural 

background radiation would have been due primarily to gamma radiation from short-lived decay 

products of 238U in the vicinity of the storage pad for the drums that contained the ore concentrate 

(Meshkov et al. 1986, p. 46). Exposure to radionuclides that accumulated in the raffinate pits and 

quarry would be mitigated somewhat by the shielding and physical barrier that was provided by water 

that covered the pits entirely and some of the waste in the quarry for much of the year.

Ambient Exposure During Operational Period (1957 to 1966)

Weldon Spring employees who worked in radiological areas were monitored, and their exposures are 

accounted for in their normal dosimetry results. Because all employees in operational areas were 

required to wear film dosimeters, there would not be unmonitored employees subject to exposure in 

those areas (NIOSH 2010b, pp. 61–64). Because no site-specific ambient exposure data for the 

WSCP has been discovered for the operational period, DRs should consider applying the 50thpercentile value of the occupational external dose for monitored workers during the operational period

as favorable to claimants as stated in Table 4-3. Potential ambient environmental dose for 

unmonitored workers, such as nonbadged administrative personnel, is bounded by the 50th-percentile 

value of the data for monitored individuals. There are no median values listed for the year 1967 since 

there were no measured external doses found associated with the pool of Weldon Spring claimants.

Table 4-3. Median values for occupational external 

gamma dose.

Year

50th-percentile gamma

(mrem)a

1957 161

1958 81

1959 78

1960 126

1961 136

1962 139

1963 220

1964 187

1965 151

1966 123

a. Calculated as the 50th-percentile value of a lognormal 

distribution in accordance with Battelle-TIB-5000 (BMI 

2007).
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 24 of 35

4.3.2

Between 1982 and 2000, ambient exposure was monitored using thermoluminescent dosimeters at 

many perimeter locations around the WSCP, the WSRP, and the WSQ (Bechtel 1983a, pp. 26–27; 

1984a, pp. 27–28; 1985a, pp. 28–30; 1986, pp. 40–44; MK-Ferguson 1987, pp. 64–66, 58–61; 1988, 

pp. 73–76; 1989b, pp. 147–149; 1989a, pp. 85–90; 1990a, pp. 119–125; 1991, pp. 127–131; 1992a, 

pp. 90–98; 1992b, pp. 276–277, 432; 1993, pp. 125–128; 1994, pp. 103–106; 1995, pp. 100–104; 

1996, pp. 92–95; 1997, pp. 89–92; 1998a, pp. 74–78; 1998b, pp. 32–36; 1999, pp. 82–86; 2000, pp. 

78–81; 2001b, pp. 76–79). In 1986, locations in the WSCP and the WSRP were monitored, but the 

results did not indicate a significant difference in exposure rate from the perimeter stations. 

Figures 4-3 and 4-4 show the locations of monitoring stations.

Ambient Exposure During Monitoring and Remediation Periods (1975 to Present)

Reported ambient exposure values included background except for 1985, when an average 

background rate of 99 mrem/yr was subtracted from the total measured values at the monitoring 

stations. Many of the reported values for 1985 were zero, representing a net value (exposure rate 

minus background rate) of either zero or less than zero. To use these numbers for 1985, the TBD 

analysis added the background value of 99 to the reported net value. Therefore, the average ambient 

exposures for 1985 might be a slight overestimate due to the addition of background to a zero value 

that actually might have been less than zero.

Ambient exposure rates in excess of natural background radiation exposure rates existed before

remediation in areas of the WSP that are close to waste in the raffinate pits or quarry, as recognized 

in Jobst (1976, p. 32–33). Based on the results of the aerial survey, gamma radiation exposure rate 

isopleths that were drawn in the immediate vicinity of the plant and centered on the raffinate pits 

indicated exposure rates that ranged from 116 to 164 microroentgen per hour (μR/hr) with decreasing 

levels from 11.8 to 31.8 μR/hr at approximately 1,000 ft from the pits. These measurements represent 

terrestrial radiation only. The average cosmic exposure rate of 4 μR/hr should be added to the 

isopleths to compute the total exposure rate for personnel within the site boundary (Jobst 1976, p. 

32).

A comprehensive radiological survey of the WSRP in 1982 and 1983 (Bechtel 1984b, p. 22) indicated 

an average onsite gamma exposure rate of 23 μR/hr for that site, which gives a dose rate of 

approximately 200 mrem/yr for continuous exposure (8,760 hr/yr). This is higher than the perimeter 

monitors reported for the WSRP before remediation. A comparison of the average survey-based 

value (201 mrem/yr) to the average perimeter value in 1983 of 88 mrem/yr (Bechtel 1984a, p. 27) 

suggests the area inside the WSRP perimeter is more appropriately characterized by an exposure 

rate approximately twice the average perimeter values. The modified ambient dose rate in Table 4-4

represents twice the average perimeter values for 1984 through 2000, and is recommended for 

environmental dose reconstruction. From 2000 to the present, after the completion of remediation of 

most of the chemical plant area (MK-Ferguson 2001b, p.79), the measured dose rate result is 

included in Table 4-4 without factoring. For 1975 through 1983, the value of 201 mrem/yr in Table 4-4

is the average survey value for 1982 to 1983 from Bechtel (1984b, p. 22), as it is considered the best 

value to use for those years.

Table 4-4. Estimated ambient onsite doses.

a

Year

WSRP average

(mrem/yr)b

WSCP average

(mrem/yr)c

WSQ average

(mrem/yr)d

Background

average (mrem/yr)

1957–1966 (e) (e) Not significant 69

1975–1979 201 (f) 97 69

1980 201 (f) 97 69

1981 201 (f) 97 69

1982 201 (f) 85 69

1983 201 (f) 95 72
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 25 of 35

Year

WSRP average

(mrem/yr)b

WSCP average

(mrem/yr)c

WSQ average

(mrem/yr)d

Background

average (mrem/yr)

1984 245 (f) 127 110

1985 228 199 123 114

1986 183 157 97 82

1987 139 145 95 78

1988 120 126 73 58

1989 131 140 81 64

1990 127 133 77 59

1991 140 150 84 67

1992 135 137 73 67

1993 116 125 67 56

1994 118 122 65 55

1995 144 140 66 62

1996 165 135 62 60

1997 186 135 61 66

1998 139 126 57 57

1999 123 124 55 55

2000 63 111 48 52

2001 63g 111g 48g 52

2002–present 0 0 0 0

a. Based on 8,760 hr/yr exposure; includes contributions from natural background.

b. From 1984 to 2000, average value is twice the average of the measured values at perimeter locations for the 

WSRP.

c. Before 2001, average value is twice the average of the measured values at perimeter locations for the WSCP.

d. Values are the average of the measured values at perimeter locations for the WSQ.

e. Apply the 50th-percentile occupational external dose from Table 4-3 or evaluate on a case-by-case basis. 

Workers assigned to these areas were monitored; ambient dose was accounted for as part of their 

occupational dose.

f. WSCP did not transfer to DOE until 1985.

g. Not monitored after 2000; assumed equal to average for 2000 for respective location.

A similar radiological survey of the WSQ in 1984 and 1985, before remediation occurred, indicated 

gamma exposure rates that ranged from 8 μR/hr (similar to the overall area background rate) to 

286 μR/hr over the quarry floor, where contamination was greatest (Bechtel 1985b, p. 29). This single 

maximum result is provided to indicate the upper measured exposure rate in the quarry. The survey 

report stated that characterization of the WSQ was “extremely difficult because of the rough terrain,” 

and that “the area was densely vegetated” (Bechtel 1985b). Figure 4-5 includes a topographic map of 

the WSQ area, along with locations of gamma exposure rate measurements. The survey included 

many of the relatively inaccessible areas of the quarry, where significant exposure was unlikely except 

during excavation of quarry bulk wastes. Therefore, the perimeter exposure rates in Table 4-4 are 

appropriate for estimating exposures except during the excavation period, which occurred during most 

of 1993, 1994, and 1995 (MK-Ferguson 1994, pp. 44–45; 1995, p. 48; 1996, pp. 50–51). For 

Table 4-4, the average value as presented in annual environmental reports is considered the best 

value for dose reconstruction.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 26 of 35

Figure 4-5. Topographic map and locations of gamma 

exposure rate measurements for WSQ (Bechtel 1985b, pp. 

14, 17).

A 1987 radiologic characterization of the WSCP and WSRP (Marutzky, Colby, and Cahn 1988, 

pp. 159–168) used portable scintillation counters to record external radiation, in counts per minute, at 

880 locations across the WSRP and WSCP; correlation with a pressurized ionization chamber 

allowed estimates of exposure rate in μR/hr. Exposure rates ranged from 9 to 287 μR/hr (at 1 m), 

which corresponds to a dose rate between 79 and 2,500 mrem/yr for continuous exposure for 

8,760 hr/yr. Fewer than 10% of the 880 surveyed locations had exposure rates of 15 μR/hr or greater. 

Assuming 10% of the locations were at 85 μR/hr and the remaining 90% were at approximately 

11 μR/hr produces an average exposure rate of approximately 18 μR/hr. This is a reasonable 

assumption for the WSCP area because few of the exposure rates over 15 μR/hr exceed 20 μR/hr, 

and many of the contaminated areas were probably not those in which occupational exposures would 

normally have occurred. The elevated exposure rates were in the areas around the buildings, onsite 

dump areas, the Ash Pond, and drainages of Frog Pond, but it is not possible to sort out exposure

rates as a function of location in the reports. An exposure rate of 18 μR/hr represents an annual dose 

of 158 mrem/yr for continuous exposure. In 1987, the reported WSCP perimeter exposure rate was 

72 mrem/yr. Therefore, the TBD analysis assumed that, until remediation of the WSCP was 

essentially complete in 2000, the average onsite exposure rate was approximately twice the 

measured perimeter rate. Table 4-4 lists values reflecting this assumption.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 27 of 35

Measured exposure rates are not available for 1975 through 1981 for the WSQ or for 1975 through 

1982 for the WSRP. It is reasonably assumed that the average of the exposure rates from 1982 

through 1989 for the WSQ and from 1983 through 1989 for the WSRP adequately represent these 

earlier years, when the entire site was essentially undisturbed. Table 4-4 lists these averaged rates. 

Table 4-5 lists sitewide maximum external exposure rates for WSP during the remediation period.

Table 4-5. Estimated maximum sitewide 

ambient dose at WSP.

a,b

Year

Maximum for WSRP, 

WSCP, and WSQ (mrem/yr)

1957–1966 (c)

1975–1983 201

1984 245

1985 228

1986 183

1987 145

1988 126

1989 140

1990 133

1991 150

1992 137

1993 125

1994 172

1995 144

1996 165

1997 186

1998 139

1999 124

2000 111

2001 111d

2002–present 0

a. Maximum of annual recommended average value for 

each area (from Table 4-4).

b. Based on 8,760-hr/yr exposure.

c. Apply the 50th-percentile occupational external dose 

from Table 4-3 or evaluate on a case-by-case basis.

d. Not monitored after 2000; assumed to be equal to the 

sitewide maximum for the WSP for 2000.

4.3.3

The measured photon dose is used with the dose conversion factors (DCFs) to calculate annual 

organ doses of interest using the external dose reconstruction implementation guidelines (NIOSH 

2007) for an isotropic exposure geometry. For the operational period (1957–1966) and initial cleanup 

period (1967–1969), the exposure (R)-to-organ dose conversion factor is used. For the period 1975–

1983, the ambient dose equivalent-to-organ dose conversion factor is used. For the period after 

1983, the exposure (R)-to-organ dose conversion factor is used.

Organ Dose Conversion Factor

4.4 SUMMARY ENVIRONMENTAL DOSE DEFAULT VALUES

This section summarizes the tables that list the recommended default values for inhalation intakes 

and ambient dose. Section 4.2.2.1 presents the recycled uranium contaminants and their conversion 

factors to be applied to uranium activity after 1961. Table 4-1 presents the annual median intake 

values for the WSCP, WSRP, and WSQ. Maximum sitewide estimated median inhalation intakes of 

radioactive air particulates and radon are shown in Table 4-2. For external environmental dose, Table 
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 28 of 35

4-3 presents the 50th-percentile values for occupational external dose which should be applied for 

unmonitored workers during the operational period, Table 4-4 presents estimated average ambient 

onsite doses for WSRP, WSCP, and WSQ, and Table 4-5 provides the maximum sitewide estimates 

of ambient dose. DRs should consider the naturally occurring isotopes of uranium (234U, 235U, and 

238U) and their decay products (primarily 230Th and 226Ra) when calculating and assigning doses to 

unmonitored workers from the occupational environmental isotopic air species.

4.5 ATTRIBUTIONS AND ANNOTATIONS

All information requiring identification was addressed via references integrated into the reference 

section of this document.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 29 of 35

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GLOSSARY

alpha particles

See alpha radiation.

alpha radiation

Positively charged particle emitted from the nuclei of some radioactive elements. An alpha 

particle consists of two neutrons and two protons (a helium nucleus) and has an electrostatic 

charge of +2.

becquerel (Bq)

International System unit of radioactivity equal to 1 disintegration per second; 1 curie equals 

37 billion (3.7 × 1010) Bq.

beta radiation

Charged particle emitted from some radioactive elements with a mass equal to 1/1,837 that of 

a proton. A negatively charged beta particle is identical to an electron. A positively charged 

beta particle is a positron.

curie (Ci)

Traditional unit of radioactivity equal to 37 billion (3.7 × 1010) becquerels, which is 

approximately equal to the activity of 1 gram of pure 226Ra.

exposure

(1) In general, the act of being exposed to ionizing radiation. See acute exposure and chronic 

exposure. (2) Measure of the ionization produced by X- and gamma-ray photons in air in units 

of roentgens.

gamma radiation

Electromagnetic radiation (photons) of short wavelength and high energy (10 kiloelectron-volts 

to 9 megaelectron-volts) that originates in atomic nuclei and accompanies many nuclear 

reactions (e.g., fission, radioactive decay, and neutron capture). Gamma photons are identical 

to X-ray photons of high energy; the difference is that X-rays do not originate in the nucleus.

gamma ray, particle, or photon

See gamma radiation.

ionizing radiation

Radiation of high enough energy to remove an electron from a struck atom and leave behind a 

positively charged ion. High enough doses of ionizing radiation can cause cellular damage. 

Ionizing particles include alpha particles, beta particles, gamma rays, X-rays, neutrons, 

high-speed electrons, high-speed protons, photoelectrons, Compton electrons, 

positron/negatron pairs from photon radiation, and scattered nuclei from fast neutrons. See 

alpha radiation, beta radiation, gamma radiation, neutron radiation, photon radiation, and X-ray 

radiation.

isotope

One of two or more atoms of a particular element that have the same number of protons 

(atomic number) but different numbers of neutrons in their nuclei (e.g., 234U, 235U, and 238U). 

Isotopes have very nearly the same chemical properties. See element.
Document No. ORAUT-TKBS-0028-4 Revision No. 01 Effective Date: 05/17/2013 Page 35 of 35

neutron radiation

Radiation that consists of free neutrons unattached to other subatomic particles emitted from a 

decaying radionuclide. Neutron radiation can cause further fission in fissionable material such 

as the chain reactions in nuclear reactors, and nonradioactive nuclides can become 

radioactive by absorbing free neutrons.

nuclide

Stable or unstable isotope of any element. Nuclide relates to the atomic mass, which is the 

sum of the number of protons and neutrons in the nucleus of an atom. A radionuclide is an 

unstable nuclide.

photon radiation

Electromagnetic radiation that consists of quanta of energy (photons) from radiofrequency 

waves to gamma rays.

radiation

Subatomic particles and electromagnetic rays (photons) with kinetic energy that interact with 

matter through various mechanisms that involve energy transfer. See ionizing radiation.

radioactivity

Property possessed by some elements (e.g., uranium) or isotopes (e.g., 14C) of spontaneously 

emitting energetic particles (electrons or alpha particles) by the disintegration of their atomic 

nuclei. See radionuclide.

radionuclide

Radioactive nuclide. See radioactivity and nuclide.

raffinate

Waste from uranium or thorium extraction as well as solids from the neutralization of this 

waste.

rem

Traditional unit of radiation dose equivalent that indicates the biological damage caused by 

radiation equivalent to that caused by 1 rad of high-penetration X-rays multiplied by a quality 

factor. The sievert is the International System unit; 1 rem equals 0.01 sievert. The word 

derives from roentgen equivalent in man; rem is also the plural.

special uranium microcurie

The sum of 3.7 × 104 dps from 238U, 3.7 × 104 dps from 234U, and 9 × 102 dps from 235U.

thermoluminescent dosimeter

Device for measuring radiation dose that consists of a holder containing solid chips of material 

that, when heated, release the stored energy as light. The measurement of this light provides 

a measurement of absorbed dose.

X-ray radiation

Electromagnetic radiation (photons) produced by bombardment of atoms by accelerated 

particles. X-rays are produced by various mechanisms including bremsstrahlung and electron 

shell transitions within atoms (characteristic X-rays). Once formed, there is no difference 

between X-rays and gamma rays, but gamma photons originate inside the nucleus of an atom.