Draft

Advisory Board on Radiation and Worker Health

National Institute for Occupational Safety and Health

Metals and Controls Corp. Exposure Pathway Evaluation 

Contract No. 75D30119C04183

Document No. SCA-TR-2021-SEC004, Revision 0

Prepared by

Rose Gogliotti, MS

SC&A, Inc.

2200 Wilson Blvd., Suite 300

Arlington, VA 22201-3324

October 25, 2021

DISCLAIMER

This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A for use in discussions with the National Institute for 

Occupational Safety and Health (NIOSH) and the Advisory Board on Radiation and Worker 

Health (ABRWH), including its Working Groups or Subcommittees. Documents produced by 

SC&A, such as memorandum, white paper, draft or working documents are not final NIOSH or 

ABRWH products or positions, unless specifically marked as such. This document prepared by 

SC&A represents its preliminary evaluation on technical issues.

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SC&A, Inc. technical support for the Advisory Board on Radiation and Worker Health’s 

review of NIOSH dose reconstruction program

Document title Metals and Controls Corp. Exposure Pathway Evaluation

Document number SCA-TR-2021-SEC004

Revision number 0 (Draft)

Supersedes NA

Effective date October 25, 2021

Task manager Rose Gogliotti, MS [signature on file]

Project manager Bob Barton, CHP [signature on file]

Document reviewer(s) Bob Barton, CHP [signature on file]

John Mauro, PhD, CHP [signature on file]

Record of revisions

Revision number Effective date Description of revision

0 (Draft) 10/25/2021 Initial issue
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Table of Contents

List of Tables................................................................................................................... 4

List of Figures.................................................................................................................. 4

Abbreviations and Acronyms........................................................................................... 5

1 Introduction and Background.................................................................................... 7

2 External Dose ........................................................................................................... 7

3 Subsurface Models ................................................................................................... 8

3.1 Subsurface inside pathway ................................................................................ 8

3.2 Subsurface outside pathway ............................................................................ 15

3.3 Subsurface occupancy..................................................................................... 18

3.4 Dust loading for subsurface activities............................................................... 19

4 Roof and Overhead ................................................................................................ 19

4.1 Data supporting the intake model..................................................................... 20

4.2 Concerns expressed by M&C Work Group ...................................................... 21

4.3 External exposures from roof and overhead pathway ...................................... 22

5 Welding................................................................................................................... 22

5.1 Data supporting welding intake model ............................................................. 23

5.2 Concerns raised by work group and SC&A...................................................... 23

5.3 External exposures from welding ..................................................................... 24

6 HVAC Maintenance ................................................................................................ 24

6.1 Data supporting the intake model..................................................................... 25

6.2 External exposures from HVAC maintenance.................................................. 25

7 Remaining Exposures............................................................................................. 26

7.1 Data source...................................................................................................... 27

7.2 External dose from remaining period ............................................................... 27

8 Conclusions and Recommendations ...................................................................... 28

9 References ............................................................................................................. 29

Attachment A: Building 10 Pipes Remediation.............................................................. 32
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List of Tables

Table 1. Summary of Weston (1996a) drainage pipe sampling data............................. 11

Table 2. Data sources used for outside subsurface modeling....................................... 17

List of Figures

Figure 1. Areas in Building 10 identified from characterization surveys as being affected

...................................................................................................................................... 10

Figure 2. Approximate drainage pipe locations within Building 10 and total uranium 

concentrations............................................................................................................... 11

Figure A-1. Building 10 removed drain lines.................................................................. 32

Figure A-2. Remediated drain lines............................................................................... 33

Figure A-3. Drain lines left in place in affected areas .................................................... 34
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Abbreviations and Acronyms

ABRWH Advisory Board on Radiation and Worker Health 

AWE Atomic Weapons Employer 

D&D decontamination and decommissioning 

DCF dose conversion factor 

dpm disintegrations per minute 

dpm/100 cm2 disintegrations per minute per 100 square centimeters

DR dose reconstruction 

EEOICPA Energy Employees Occupational Illness Compensation Program Act

EPA U.S. Environmental Protection Agency 

ER evaluation report 

FGR Federal Guidance Report

g gram 

GM geometric mean

GSD geometric standard deviation

h hour 

HFIR High Flux Isotope Reactor 

HVAC heating, ventilation, and air conditioning

keV kiloelectron volt

m meters

m2 square meter

m3 cubic meter

m3

/h cubic meters per hour 

M&C Metals and Controls Corporation 

μCi microcurie

μg microgram

mR milliroentgen

mrad millirad

mrad/h millirad per hour

mrem millirem

mrem/yr millirem per year

NIOSH National Institute for Occupational Safety and Health
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ORAUT Oak Ridge Associated Universities Team

pCi/g picocurie per gram 

RF resuspension factor

SEC Special Exposure Cohort 

SRDB Site Research Database

TBD technical basis document

TI Texas Instruments

U uranium 

WG Work Group 
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1 Introduction and Background

At its March 18, 2021, meeting, the Metals and Controls Corp (M&C) Work Group (WG) tasked 

SC&A to review each of the exposure models the National Institute for Occupational Safety and 

Health (NIOSH) presented in its January 21, 2021, paper, “Response to Comments from the 

Metals and Controls Corp. Work Group Meeting held on September 2, 2020” (NIOSH, 2021a).

The paper lays out six exposure pathways that have been developed over many iterations in 

support of the evaluation of Special Exposure Cohort (SEC) Petition SEC-00236. These 

pathways include the following (numbers are assigned by SC&A for the purposes of discussion 

in this report):

1. Subsurface Inside

2. Subsurface Outside

3. Roof and Overhead

4. Welding

5. HVAC Maintenance

6. Remaining (nonmaintenance) 

All M&C workers, irrespective of their job titles, will be assigned maintenance workers doses 

because it is unclear which workers were involved in various maintenance activities. Each of 

these pathways have internal and external exposure risks to uranium and thorium.

2 External Dose

In the SEC-00236 petition evaluation report (ER), NIOSH (2017a) proposed using dosimetry 

data from 1967, the last year of operations (Landauer, 1965–1974), to bound doses to workers. In 

this analysis, NIOSH calculated the 95th percentile of measured external doses to be 150 

millirem per year (mrem/yr) (12.5 mrem/month). SC&A’s (2018a) review of the ER identified a 

number of issues related to this calculation and how the data were being applied. NIOSH revised 

its approach in the September 12, 2018, M&C SEC issues matrix (NIOSH, 2018b) and derived a 

beta skin dose of 12 mrem/month and a penetrating dose of 4 mrem/month. 

SC&A reviewed the NIOSH revised modeling in the matrix and agreed with the penetrating dose 

modeled. SC&A modeled beta doses and had a modestly different interpretation of beta 

dosimetry results. SC&A calculated a similar but lower dose of 9.7 mrem/month. The difference 

is modest; therefore, SC&A believes this concern is not worth pursuing further. 

NIOSH’s (2021a) approach mirrors the method presented in the September 12, 2018, M&C SEC 

issues matrix (NIOSH, 2018b). NIOSH proposes assigning the quarterly geometric mean (GM)

gamma dose rate of 12 mrem/quarter (4 mrem/month) and the quarterly GM skin dose rate of 36 

mrem/quarter (12 mrem/month), both with a geometric standard deviation (GSD) equal to the 

default value of 5 in Battelle-TBD-6000, revision 1, “Site Profiles for Atomic Weapons 

Employers that Worked Uranium Metals” (NIOSH, 2011). NIOSH proposes to assume a 

claimant-favorable gamma energy of 100 percent 30–250 kilo-electronvolts (keV) and electron 

energy of 100 percent >15 keV. The paper continues:
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These dose rates will be applied to the maintenance work exposures [pathways 1 

through 5] with no adjustments for source-term depletion because of the potential 

for the maintenance area environments (e.g., inside clogged drains, rafters) to be 

less impacted by environmental reduction factors and routine cleaning. For all 

non-maintenance work exposures [pathway 6], source-term depletion adjustments 

will be considered (per the guidance in ORAUT-OTIB-0070) to determine the 

non-maintenance exposure rates throughout the residual period [[NIOSH,] 2012]. 

[NIOSH, 2021a, p. 15] 

SC&A’s evaluation of each pathway discussed in the subsequent sections of this report includes 

an evaluation of the applicability of the NIOSH external dose modeling to the corresponding

exposure scenario.

3 Subsurface Models

Two of the six modeled exposure pathways involve subsurface work. NIOSH (2021a, p. 14) 

indicates that “NIOSH will assume an occupancy rate of two months per year for subsurface 

work (2000 hours per year x 2/12 {fraction of year} = 333.33 hours per year).” In other words, 

NIOSH intends to assume a single subsurface model per individual, and “If the subsurface 

location (e.g., inside or outside) cannot be determined, the most claimant-favorable work 

location will be assigned” (p. 14). 

3.1 Subsurface inside pathway

The first pathway, “subsurface inside,” is used by NIOSH to model exposures caused by workers 

accessing materials below the concrete slab inside Building 10 and, to a lesser degree, Building 

4. These exposures may have been caused by: 

• workers snaking clogged pipes 

• workers removing and replacing subsurface pipes 

• repurposing work that required breaking the concrete slab to modify the foundation for 

equipment 

• work inside trenches

NIOSH modeled this pathway by assuming workers are exposed to the 95th percentile of the 

sampled uranium results from inside the pipes in Building 10 (6,888 picocuries per gram 

(pCi/g)), dust loading is equal to the 95th percentile Mound air sampling, and workers spent 

2 months a year performing these activities. Table 4 of NIOSH (2021a) provides an example of 

the doses calculated in the subsurface inside pathway. SC&A was able to replicate the calculated

annual committed effective doses in table 4, as shown in example 3-1. Ingestion doses were 

calculated using guidance from OCAS-TIB-009 (2004). SC&A is providing this example to 

establish SC&A understood the assumptions NIOSH was using to calculate doses from this 

exposure pathway. Organ doses rather than committed effective doses are assigned in dose 

reconstructions (DRs) performed under the Energy Employees Occupational Illness 

Compensation Program Act (EEOICPA). 
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Example 3-1: Annual uranium intakes and committed effective doses from subsurface 

inside Building 10 pathway

UU iiiihaaaa. iiiiiiaaiiii = [UU 95iih PPiiPPPPiiiiiiiiaaii] ∗ ddddddii aallaaddiiiill ∗ iiiihaaaa. PPaaiiii ∗ llPPPPddooaaiiPPoo ffaaPPiillPP 

6.9 ∗ 10−9 μCi

ug ∗ 212 μ

ll

mm3 ∗

1.2 mm3

hllddPP ∗

333.33 hllddPPdd

ooiiaaPP

= 5.85 ∗ 10−4μCCii

IIiihaaaa. CCllmmmmiiiiiiiidd EEffffiiPPiiiiffii DDllddii = 5.85 ∗ 10−4μCCii ∗

2.52 ∗ 104mmPPiimm

μCCii

= 14.7 mmPPiimm/ooiiaaPP

UU iiiilliiddiiiillii iiiiiiaaiiii = iiiilliiddiiiillii PPaaiiii ∗ [UU 95iih PPiiPPPPiiiiiiiiaaii] ∗ llPPPPddooaaiiPPoo ffaaPPiillPP

50,000 μg

8 hour workday ∗ 6.9 ∗ 10−9 μCiug ∗

333.33 hllddPPdd

ooiiaaPP

= 1.43 ∗ 10−2μCCii

IIiilliiddii. CCllmmmmiiiiiiiidd EEffffiiPPiiiiffii DDllddii = 1.43 ∗ 10−2μCCii ∗

1.81 ∗ 102mmPPiimm

μCCii

= 2.6 mmPPiimm/ooiiaaPP

CCllmmmmiiiiiiiidd EEffffiiPPiiiiffii DDllddii = 14.7

mmPPiimm

ooiiaaPP

+ 2.6

mmPPiimm

ooiiaaPP = 17.3 mmPPiimm/ooiiaaPP

Using the same approach as shown in example 3-1 for uranium exposure, NIOSH will assign a 

thorium committed effective dose of approximately 29 mrem. Thorium exposures are 

specifically discussed in section 3.1.2 of this report.

3.1.1 Data supporting intake model

The data used to quantify the concentration of uranium in the pipes originates from a 1995 

Weston study to characterize the drain lines for remediation (Weston, 1996a). The subsurface 

work environment inside Building 10 was characterized by 20 sediment samples that were 

collected and analyzed for isotopic uranium before remediation. According to Weston (1996a), 

historical information and a pilot survey of the drainage lines were used to predict how material 

was expected to flow through the pipes. The 13 sampling locations within Building 10 were 

selected based on this information. At each sampling location, the concrete above the pipe was 

removed and the soil was excavated just below the pipe level. A section of the pipe was cut and 

opened, and a sample of the sediment/pipe residues/buildup was collected and submitted for 

isotopic analysis. When multiple pipes were found at the sampling location, samples from each 

pipe were taken. Field personnel observed the fraction of the pipe that was obstructed. 

Figure 1 shows a diagram of a Building 10 with designations of the areas of interest assigned in 

remediation. Notably, only a small section of the building (as illustrated in the site map 

thumbnail in bottom right corner of figure 1) was determined to be an area of interested of 

concern for remediation. Figure 2 shows an overlay of the locations of piping within the building 

according to how they were remediated following the initial sampling and subsequent surveys. 

The blue, diagonally striped sections (designated “Priority 1”) show sections of piping that was 
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removed. The red, gridded sections (“Priority 2”) show areas of the pipe that were remediated by 

flushing the pipes, then left in place. The green, horizontally striped sections (“Priority 3”) show 

the areas of pipe that were sampled from but left in place with no subsequent remediation 

performed. The remainder of pipes in the building that were not designated as in an affected area 

were also left in place because they were not believed to be contaminated. Attachment A gives 

the original Weston diagrams used to create figure 2, with highlighted areas of interest. 

Figure 1. Areas in Building 10 identified from characterization surveys as being affected

Source: Weston (1996b), figure 4, PDF p. 15. 
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Figure 2. Approximate drainage pipe locations within Building 10 and total uranium 

concentrations

Source: Aggregate of Weston (1996b), figures 4 (PDF p. 15), 5.3 (PDF p. 175), 5.4 (PDF p. 176), and 5.5 

(PDF p. 178). 

Table 1 shows the results of the Weston (1996a) sampling. Analysis of the sampling data shows 

that 11 of the 20 samples identified total activity concentrations of below 200 pCi/g, and 17 of 

the 20 samples identified activity concentrations of below 850 pCi/g. The 95th percentile value 

obtained from the study was larger than all but two of the hundreds of isotopic samples taken 

across the entire site. 

Table 1. Summary of Weston (1996a) drainage pipe sampling data

Parameter Concentration of total uranium (pCi/g)

95th percentile 6,887.84

50th percentile 185.82

Minimum 9.75

Maximum 53,224.7

Other that the 1995 Weston drainage line survey (Weston, 1996a), additional drainage line 

samples were conducted on the priority 2 and priority 3 drainage lines in subsequent 

characterization efforts. Since these samples were conducted on pipes already deemed to be 
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lower activity lines, SC&A believes it is appropriate to omit including these samples as a means 

of bounding materials in the pipes. Inclusion of these additional results would bias the sample 

results low. SC&A is unaware of any other samples with reported isotopics from within the 

Building 10 drainage lines. 

3.1.2 Thorium assumption

Unlike the other exposure models for M&C that have thorium and/or gross alpha measurements, 

the subsurface Building 10 model is supported by only uranium data. There are no thorium or 

gross alpha measurements in the pipes. NIOSH’s (2021a) response paper also suggests that it can 

bound Building 10 subsurface thorium exposures by assuming the subsurface pipes contained 

equivalent amounts by weight of natural uranium and thorium-232 (NIOSH, 2021a, p. 11): 

Since the specific activity of natural uranium is 6.83E5 pCi/g [NIOSH 2006], the 

95th percentile concentration (6,888 pCi/g) corresponds to approximately 1% 

natural uranium by weight in the sediment. Therefore, NIOSH can assume the 

Building 10 subsurface sediments were contaminated with 1% of the specific 

activity of thorium-232 (1.1 E5 pCi/g) per gram of sediment. Using this approach, 

NIOSH calculated a concentration of 1,109 pCi/g and will use it to bound thorium 

exposures [NIOSH 2019, PDF p. 8]. 

SC&A (2020b) evaluated this approach most recently in July 2020 and presented two alternative 

approaches to model thorium concentrations using outdoor data. The WG discussed this review 

during the September 2, 2020, WG teleconference meeting (M&C WG, 2020). The thorium 

doses from SC&A’s alternative approaches bracket the doses expected from NIOSH’s thorium

model. At that time, WG members expressed concerns that the outdoor data ratios of thorium to 

uranium are not representative of the ratios inside Building 10 pipes.

SC&A acknowledges that there is limited information about the time periods and types of waste 

that are associated with the outdoor contamination such that is difficult to establish with a high 

degree of precision a relationship between the activities seen outside and those found in the pipes 

within Building 10. The NIOSH approach avoids establishing this relationship by assuming 

equivalent amounts of uranium and thorium. SC&A also acknowledges that it is clear from 

multiple reports and inventory information (ASTRA, 1962) that uranium operations far exceeded 

thorium operations. SC&A believes there is no evidence that suggests that equal weights of 

thorium should be expected when uranium is present; however, there is not sufficient 

information to establish that it could not be that high. It is reasonable to conclude that it is 

unlikely that thorium weights would be greater than uranium weights. Therefore, given the 

uncertainties associated with the thorium-to-uranium ratios present on site and the fact that we 

cannot rule out a 1:1 mass ratio of uranium to thorium, the NIOSH approach is claimant 

favorable.

3.1.2.1 Concerns expressed by work group and petitioners

The petitioners and M&C WG have raised concerns about how representative the results of the 

1995 drainage survey are of potential exposures experienced by maintenance workers throughout 

the residual period. These concerns included the possibility that materials within the pipes were 

diluted by water and solids flowing through the pipes throughout the residual period. They also 
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include the possibility that materials were removed from the pipes by snaking and pipe 

replacement that altered the distribution within the drainage system. 

SC&A acknowledges that there are uncertainties that impact the materials found in the

subsurface environment at M&C. These uncertainties include but are not limited to how often the 

subsurface pipes were used, the flow rate of the pipes, the typical pH of the materials moving 

through the pipes, and how often and where the materials in the pipes were disturbed. With 

currently available information, it is not possible to succinctly quantify possible dilutions caused

by these actions. However, SC&A believes it is reasonable to assume it is a non-zero number. 

Similarly, it is not possible to quantify what exact concentrations of material were in the pipes 

accessed by maintenance workers during each individual extraction. SC&A believes it is 

possible to bound the exposures workers may have received in any given year, such that no 

worker received a higher dose in the aggregate over the course of a year. In NIOSH’s initial 

white paper on subsurface exposures (NIOSH, 2018a), NIOSH indicated that the geometric mean 

of the subsurface data would be used to quantify activities within the pipes. At that time, SC&A 

expressed concerns based on a similar justification as the petitioner, and NIOSH increased the 

value to the upper 95th percentile (NIOSH, 2018c, 2018d). SC&A believes the upper 95th 

percentile is bounding for the following reasons: 

• Building 10 was a large building (over 15,000 square feet). Only a fraction of the 

subterranean pipes under Building 10 were identified as possibly affected

(i.e., contaminated). Figure 1 shows the footprint inside Building 10 that the affected 

areas were believed to cover. Figure 2 shows the footprint of pipes identified to be 

potentially contaminated. These were the only pipes sampled from during the Weston 

1995 study (Weston, 1996a). The rest of the building’s subterranean pipes were not 

sampled. From that study and subsequent efforts, Weston determined that roughly a third 

of the originally sampled pipes needed no remediation of any kind, and they were left in 

place (shown in green boxes with horizontal stripes in figure 2). 

• The NIOSH model assumes that all materials below the concrete slab in Building 10 have 

an activity concentration equal to the upper 95th percentile activity concentration inside 

the pipes. This means NIOSH will assume every worker, every time they access any part 

of the subterranean environment, encounters only the 95th percentile for the duration of 

the exposure. 

– All material in all pipes within Building 10 is assumed to be contaminated at the 

upper 95th percentile. As shown in figure 1 of the SC&A (2020a) roadmap, most 

of the samples taken to quantify the activities are orders of magnitude lower that 

the 95th percentile that NIOSH intends to apply. 

– All soils below the slab are assumed to be at the same activity concentration. In 

effect, this assumes that the pipes leaked to a degree that the material inside the 

pipes and the soils surrounding those pipes have the same levels of contamination.

In reality, the soils surrounding the pipes were most likely contaminated to a 

lesser degree than the materials in the pipes. Most pipes were identified to be 

“2 to 3 feet (ft) below facility grade” (Weston, 1996b, PDF p. 171). The volume 

of the soils surrounding the pipes is substantially greater than the materials in the 
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pipes such that any digging activity would dilute the airborne activities. The only 

soil sample that SC&A is aware of inside Building 10 was taken from the soils 

surrounding the pipe where the fuel pin was found. Inside that cast iron pipe that 

had the fuel pin, the total uranium concentration was found to be 53,000 pCi/g 

(i.e., around 10 percent pure natural uranium). The soils surrounding that pipe 

were found to have a total uranium concentration of 2,000 pCi/g (Weston, 1996a). 

Although this is a single data point, it lends credence to the notion that it is 

conservative to assume equal levels of contamination. 

SC&A believes the impacts of the conservativeness of the assumptions applied to the model are

greater than the impacts of the uncertainties associated with material dilution and extraction. 

Taken in combination, SC&A believes that the methods and assumptions used by NIOSH 

(2021a) to reconstruct internal doses to M&C workers involved in subsurface maintenance and 

repurposing activity in Building 10 during the residual period are scientifically sound and 

claimant favorable. 

For perspective, it is also important to consider comparable dose reconstruction situations for 

residual periods at other Atomic Weapons Employer (AWE) sites. SC&A examined several 

AWE SEC discussions to identify situations in which little or no usable data are available from 

the end of operations and residual data taken many years into residual operations were deemed 

acceptable. In SC&A’s opinion, the most comparable scenario occurred for Linde Ceramics 

regarding the reconstruction of internal dose for periodic entry into subsurface utility tunnels. In 

this case, the residual period1

 not already covered by an SEC was 1970 through mid-2006. 

Surface survey contamination data taken in 2001 (specifically, surface external beta 

measurements) were used to develop a 95th percentile surface contamination in the tunnels. This, 

along with typical breathing rates (1.2 cubic meters per hour (m3/h)), a resuspension factor 

(10-6 per meter (m-1)), and an occupancy factor (50 percent exposure time to maintenance 

workers), was used to develop acceptable bounding intakes. It is notable that these derived 

intakes were used for the entire evaluated period without correction for degradation over time 

(~31 years between 1970 and 2001). 

1 The Linde Ceramics residual period is characterized by two distinct time periods: (1) the decontamination and 

decommissioning (D&D) and renovation period (1954–1969) and (2) the remaining residual period (1970–2006). 

SEC-00107 was granted for the D&D and renovation period (1954–1969).

Another comparable dose reconstruction methodology for AWE sites during the residual period 

was used for Chapman Valve. At this site, two residual periods exist: May 1, 1949, through 

December 31, 1949, and January 1, 1991, through December 31, 1993. No usable air sampling 

data were available for the residual periods, so intakes were derived using survey results taken in 

1992. Specifically, the highest of 30 direct reading alpha measurements were used with a 

resuspension factor of 10-6 m-1, breathing rate of 1.2 m3/h, and an exposure time of 2,000 hours. 

The resulting intake was applied for the entire period from 1949 through 1993. No adjustments 

were made to the intake rate due to degradation over time (over 40 years). 
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3.1.3 External dose rate

NIOSH proposes assigning a quarterly GM gamma dose rate of 12 mrem/quarter 

(4 mrem/month) and a quarterly GM skin dose rate of 36 mrem/quarter (12 mrem/month), both 

with a GSD equal to the Battelle-TBD-6000 default value of 5 (NIOSH, 2011). To benchmark 

this value against the potential magnitude of the doses from exposures to materials inside pipes, 

SC&A examined data on the highest levels of residual radioactive contamination found in the 

available documents. Weston (1996a) listed the activity concentrations of the three naturally 

occurring uranium isotopes in the sediment or pipe scale in 22 pipes at 15 locations inside 

Buildings 4 and 10, along with the volume of contaminated material in each pipe. Since some of 

these pipes were leaking and could have potentially contaminated the surrounding soil, SC&A

assumed that a worker stood during the entire work year on soil contaminated to an infinite depth 

with the same isotopic concentrations as one of the sampled materials. Such a hypothetical 

scenario bounds the exposures that workers may have experienced when excavating and opening 

these drainpipes during the residual period. 

In performing the analyses, SC&A assumed that the uranium-235 (U-235) and U-238 in the soil 

were in full equilibrium with their short-lived progeny and calculated the effective dose and skin 

dose from a year of standing on contaminated soil, using the dose coefficients for exposure to 

soil contaminated to an infinite depth tabulated in Federal Guidance Report (FGR) No. 12 (EPA,

1993). SC&A ranked the effective doses and skin doses corresponding to each of the 22 

sampling locations, along with the cumulative volumes of pipe scale or sediment in each pipe, 

and calculated the dose corresponding to 95 percent of the cumulative volume by linear 

interpolation. In this manner, SC&A derived 95th percentile annual doses of 153 mrem effective 

dose and 390 mrem skin dose. Assuming the same worker was involved in subsurface activities 

for 2 month per year, the bounding annual penetrating and skin dose to such a hypothetical 

worker would be 153*2/12 = 25.5 mrem/yr (NIOSH’s model assumes 8 mrem/yr) and 

390*2/12 = 65 mrem/yr (NIOSH’s model assumes 24 mrem/yr), respectively. 

Finding 1: Building 10 subsurface external exposures not bounded

SC&A finds that NIOSH’s proposed external dose rate assumptions are inconsistent with the 

contamination levels assumed for the subsurface of Building 10. SC&A’s independent 

calculations suggest dose rates from the modeled pathway are expected to be substantially 

greater. NIOSH’s 2017 SEC ER proposed using the 95th percentile dosimetry values (with 

adjustments for missed dose) of 200 mrem/year (16.7 mrem/month). SC&A believes it is more 

appropriate to assign elevated subsurface exposures inside Building 10 using the 95th percentile 

of the dosimetry with occupancy adjustments.

3.2 Subsurface outside pathway

Remediation activities at M&C identified that the soils surrounding Building 10, the burial 

grounds, and other outdoor areas were contaminated. It is also known that on at least two 

occasions during the residual period, workers excavated the soil in these areas. According to the 

worker interviews, smaller scale soil penetrations may have also occurred.

To model subsurface exposures, NIOSH will use the upper 95th percentile value (117.86 pCi/g 

for the dose calculations for uranium and 87.5 pCi/g for thorium) from outside soil sampling, a 

dust loading equal to the 95th percentile Mound air sampling, and the assumption that 
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maintenance workers spent 2 months a year performing these activities. Table 4 of NIOSH 

(2021a) provides an example of the doses calculated in the subsurface outside pathway. SC&A 

was able to replicate the calculated annual committed effective doses in table 4, as shown in 

example 3-2. SC&A is providing this example to establish SC&A understood the assumptions 

NIOSH was using to calculate doses from this exposure pathway. Organ doses rather than 

committed effective doses are assigned in DRs performed under EEOICPA. 

Example 3-2: Annual uranium intakes and committed effective doses from subsurface 

outside pathway

UU iiiih. iiiiiiaaiiii = [UU iiii ddlliiaa] ∗ ddddddii aallaaddiiiill ∗ iiiihaaaaaaiiiillii PPaaiiii ∗ llPPPPddooaaiiPPoo ffaaPPiillPP

1.18 ∗ 10−10 μCi

ug ∗ 212 μ

ll

mm3 ∗

1.2 mm3

hllddPP ∗

333.33 hllddPPdd

ooiiaaPP

= 1.00 ∗ 10−5μCCii

IIiihaaaa. CCllmmmmiiiiiiiidd EEffffiiPPiiiiffii DDllddii = 1.00 ∗ 10−5μCCii ∗

2.52 ∗ 104 mmPPiimm

μCCii

= 0.25 mmPPiimm/ooiiaaPP

ddPPaaiiiiddmm iiiilliiddiiiillii iiiiiiaaiiii = iiiilliiddiiiillii PPaaiiii ∗ [UU iiii ddlliiaa] ∗ llPPPPddooaaiiPPoo ffaaPPiillPP

50,000 μg

8 hour workday ∗ 1.18 ∗ 10−10 μCiμg ∗

333.33 hllddPPdd

ooiiaaPP

= 2.46 ∗ 10−4μCCii

IIiilliiddii. CCllmmmmiiiiiiiidd EEffffiiPPiiiiffii DDllddii = 2.46 ∗ 10−4μCCii ∗

1.81 ∗ 102mmPPiimm

μCCii

= 4.44 ∗ 10−2 mmPPiimm/ooiiaaPP

CCllmmmmiiiiiiiidd EEffffiiPPiiiiffii DDllddii = 0.25

mmPPiimm

ooiiaaPP

+ 4.44 ∗ 10−2 mmPPiimm

ooiiaaPP

= 0.3 mmPPiimm/ooiiaaPP

Thorium exposures are calculated in a similar fashion by replacing uranium values with 

applicable thorium values. This results in a committed effective dose equivalent of 2.3 mrem/yr.

3.2.1 Data supporting model

Considerable surface and subsurface soil data were collected in many outdoor areas in the 1980s 

by the NRC and again in the1990s in support of license termination. NIOSH’s October 24, 2018, 

white paper indicates that 2,391 soil samples were collected prior to remediation, 1,629 samples 

were analyzed for gross alpha, and 762 samples were collected for uranium and thorium and 

analyzed using isotopic identification (NIOSH, 2018d, p. 8). SC&A received a copy of the 

NIOSH spreadsheet used to analyze the isotopic data in November 2018. The data supporting the 

outdoors subsurface characterization comes from several data sources, as shown in table 2. 
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Table 2. Data sources used for outside subsurface modeling

SRDB Ref. ID Outside location

94371 Building 10 perimeter

94371 Burial Area

164755 Burial Area

161141 Stockade and Rail Spur

161141 Building 10 perimeter and zirconium burn area

165968 Metals Recovery Area

3.2.2 Concerns expressed by work group

In a January 12, 2021, email (Beach, 2021), WG members raised the concern that the “Debris 

buried in the burial site was not representative of radioactive materials (U and Th) handled 

throughout the AWE operational period (1952-67), but was a selective sample of those materials, 

largely from 1958-1961.” NIOSH responded to this concern and similar concerns raised in the 

September 2020 meeting (M&C WG, 2020) in a memorandum dated February 8, 2021 (NIOSH, 

2021b). SC&A agrees with the WG members’ concern that the data from the waste and 

associated contamination in the burial grounds are representative of only a subset of the work 

performed during operations. The wastes do not capture the entirety of the operations period. 

However, SC&A does not believe this represents a DR infeasibility. Although the data do not 

represent all of the operations period, they do represent the remaining source term on site 

throughout the residual period. The burial grounds data are not being used to characterize the 

work from the AWE operational period (SEC-00149 was granted January 9, 2010, to cover AWE 

operations at M&C). The burial grounds sampling data represent material that was on site and 

thus potentially excavated during the residual period. Thus, SC&A believes it is appropriate to 

include the data when modeling exposures during the residual period. NIOSH has elected to not 

use any outdoor data to quantify thorium concentrations inside Building 10; therefore, there is no 

need to qualify the representativeness of thorium-to-uranium ratios obtained from these data. 

The January 2021 WG email also raised the concern that the burial ground data may not be 

representative of the exposures experienced by workers because there were known disturbances 

during the residual period. There are two known major soil disturbances to the burial grounds: 

(1) soil grading in 1968 following the construction of Building 12 and (2) the installation of the 

compressed airline in 1980.

Although the exact date is not known, the soil grading in 1968 (Texas Instruments Incorporated

(TI), 1994, PDF p. 35) took place early in the residual period, which extends from January 1, 

1968, through March 21, 1997 (SEC-00149). Any materials dispersed in 1968 throughout the site 

would be the same materials that workers were exposed to during the remainder of the residual 

period. SC&A believes that, because this disturbance happened early in the residual period, soil 

sampling from the burial area in the 1980s and 1990s is representative of potential exposures 

encountered by maintenance workers.

The installation of the compressed airline between Buildings 11 and 12 was done in 

August 1980. This airline was installed below grade and required a trench to be dug, part of 
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which dug through a section of the burial site. According to a 1981 NRC inspection report (NRC, 

1981, PDF p. 128), the area that was dug up was “slightly contaminated” and “a trained health 

physicist, surveyed the material dug up and placed any contaminated materials into 55 gallon 

drums. Eleven 55 gallon drums were sent to the Barnwell, South Carolina, burial site on 

October 31, 1981.” The remaining soils were reburied on the eastern edge of the developed 

portion of the site. This area was later surveyed during remediation, but levels of radioactivity 

detected were below applicable NRC release criteria and thus it did not require remediation (TI, 

1996, PDF p. 33). Based on these accounts, only a small amount of contaminated material was 

removed from the site. The burial ground is large in comparison to the small amount of material 

displaced by the trench. SC&A does not believe that this removal altered the distribution of the 

materials in the burial grounds significantly enough to make later surveys not representative of 

the earlier exposure potential.

3.2.3 External dose rate 

NIOSH proposes assigning a quarterly GM gamma dose rate of 12 mrem/quarter 

(4 mrem/month) and a quarterly GM skin dose rate of 36 mrem/quarter (12 mrem/month), both 

with a GSD equal to the Battelle-TBD-6000 default value of 5 (NIOSH, 2011). To benchmark 

this value against the known activities in the outside subsurface environment, SC&A calculated

external dose rates from the burial grounds, which have the highest activities identified outside at 

M&C. 

SC&A determined the dose rates to a worker in an excavated area at the burial ground by first 

calculating the weighted average concentrations of radionuclides reported by Sowell (1985) for 

core samples collected at 28 locations for which core sample data were reported at two or more 

depths. SC&A then calculated the dose rates that would be experienced by a worker exposed to 

an infinite layer of soil contaminated at the concentrations equal to those of the core samples, 

again using the FGR 12 external dose coefficients. Assuming the 95th percentile of these 28 

results and that a worker was exposed for 333.33 hours/year, their annual effective dose from 

this pathway would have been approximately 3.5 mrem. This dose is less than half of the NIOSH 

suggested value of 8 mrem per year. Therefore, SC&A finds the NIOSH assumptions to be 

bounding and claimant favorable when applied to the outside subsurface pathway. 

3.3 Subsurface occupancy

NIOSH (2021a, p. 14) indicates that:

NIOSH will assume an occupancy rate of two months per year for subsurface 

work (2000 hours per year x 2/12 {fraction of year} = 333.33 hours per year). If 

the subsurface work area (e.g., inside or outside) cannot be determined, the most 

claimant-favorable work location will be assigned. 

In other words, NIOSH intends to assume a single subsurface model per individual. NIOSH will 

choose a model based on the subsurface work area scenario that the DR determines to be the 

most likely the energy employee experienced: If the exposure location (e.g., inside or outside) 

cannot be determined, the most claimant-favorable work location will be assigned. When 

considering the wealth of evidence at the site, SC&A questions the decision to limit occupancy 

to either inside or outside. SC&A has not seen evidence that justifies the assumption that workers 
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who performed surface work inside did not also participate in outdoor excavations and vice 

versa. 

Observation 1

SC&A reviewed the claimant interviews and does not believe that there is sufficient evidence to 

limit any individual’s subsurface exposures to a single subsurface scenario. The interviews 

indicate that, irrespective of an individual’s job title, they may have been asked to complete any 

task on site. SC&A believes that means an individual could have participated in both indoor and 

outdoor subsurface scenarios within a year.

3.4 Dust loading for subsurface activities

NIOSH indicates it will use a dust loading of 212 micrograms per cubic meter (μg/m3

)for 

subsurface work that originates from air sampling data collected during remediation activities at 

Mound. The applicability of this value to use at M&C to represent both indoor and outdoor dust 

loads will be evaluated in a separate SC&A review document.

4 Roof and Overhead

It is known from the worker interviews and petitioner statements that the roof and overhead areas 

inside Building 10 required frequent maintenance during the residual period. Since these

maintenance-related activities could have potentially removed materials with the highest 

concentrations, NIOSH will use the 95th percentile removable contamination level of

8.99 disintegrations per minute per 100 square centimeters (dpm/100 cm2

), a resuspension factor 

(RF) of 10-4 per meter (m), and a breathing rate of 1.2 m3/h and will assume maintenance 

workers spent 1 month a year (166.67 hours) performing these activities. Table 4 of NIOSH 

(2021a) provides an example of the doses calculated in the roof and overhead pathway. SC&A 

was able to replicate the calculated annual committed effective doses in table 4, as shown in 

example 4-1 for uranium. SC&A is providing this example to establish SC&A understood the 

assumptions NIOSH was using to calculate doses from this exposure pathway. Organ doses 

rather than committed effective doses are assigned in DRs performed under EEOICPA. 

Example 4-1: Annual uranium intakes and committed effective doses from roof and 

overhead pathway

UU iiiih. iiiiiiaaiiii = PPiimmllffaarraaii aaaaoohaa ∗ RRRR ∗ llPPPPddooaaiiPPoo ffaaPPiillPP ∗ iiiihaaaaaaiiiillii PPaaiiii

8.994 ddoomm

100PPmm2 ∗ μCCii

2,220,000 ddoomm ∗

10,000 PPmm2

mm2 ∗

10−4

mm ∗

167.67 hllddPPdd

ooiiaaPP ∗ 1.2

mm3

h

= 8.15 ∗ 10−6 μCCii/ooiiaaPP

UU iiiih. ddllddii = 8.15 ∗ 10−6 μCCii/ooiiaaPP ∗

2.52 ∗ 104mmPPiimm

μCCii = 0.2 mmPPiimm/ooiiaaPP

ddPPaaiiiiddmm iiiilliiddiiiillii iiiiiiaaiiii = iiiilliiddiiiillii PPaaiiii ∗ PPiimmllffaarraaii aaaaoohaa ∗ llPPPPddooaaiiPPoo ffaaPPiillPP

10−4 mm2

hllddPP ∗ 89.94 ddoomm

100PPmm2 ∗ μCCii2220,000 ddoomm ∗

10000PPmm2

mm2 ∗

48 hllddPPdd

ooiiaaPP

= 1.94 ∗ 10−5 μCCii/ooiiaaPP
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U ingestion dose = 1.94 ∗ 10−5 μCCii

ooiiaaPP ∗

1.81 ∗ 102mmPPiimm

μCCii = 1.23 ∗ 10−3 mmPPiimm/ooiiaaPP

iiiihaaaaaaiiiillii ddllddii + iiiilliiddiiiillii ddllddii = 0.20

mmPPiimm

ooiiaaPP

+ 1.23 ∗ 10−3 mmPPiimm

ooiiaaPP

= 0.21 mmPPiimm/ooiiaaPP

Thorium doses are calculated by replacing the uranium dose conversion factors (DCFs) with 

thorium DCFs and result in a committed dose calculation of less than 1 mrem. Since the results 

are gross alpha, NIOSH will assign the most claimant-favorable mixture of thorium or uranium. 

4.1 Data supporting the intake model

NIOSH used 285 grid average alpha survey data to quantify the removable contamination found 

in the roof and overhead areas. These surveys were completed in 1982 in support of license 

termination at M&C. According to NIOSH’s (2021a) response paper (p. 12): 

Ten of these survey results are from the walls and ceiling of the Unclad Fuel 

Manufacturing Area . . . and 275 are from the Clad Fuel Manufacturing Area on 

the ceiling, pipes, buss ducts, wall, and columns (1.5 meters high to ceiling), and 

the roof near the ventilation exhaust ducts. These surveys were performed by 

M&C and verified by NRC inspectors [[NRC & TI, 1982–1983], PDF pp. 70–72, 

75–83, 140–141]. 

It is worth noting these surveys were completed before the positive temperature coefficient 

powder explosion that is believed to have occurred in the late 1980s or early 1990s. Therefore, 

the subsequent cleanup activities reported by an interviewee (NIOSH, 2017b, PDF pp. 9–10) did 

not impact the readings. These results were from direct probe measurements; therefore, NIOSH 

indicated it will assume that 10 percent of the measured activity was associated with removable 

activity per the guidance in ORAUT-OTIB-0070 (NIOSH, 2012). 

NIOSH provided SC&A with the NIOSH calculation files supporting its assessment in 

November 2018. SC&C reviewed the files and found that, in general, the direct probe grid 

averages were as described by NIOSH. SC&A noted that eight of the grid averages were 

reported as direct alpha measurements from the bus ducts when they actually represent

removable alpha measurements from the bus ducts. Although these data are still relevant, it is 

inappropriate to treat the data as a direct measurement instead of removable contamination. 

Complicating the calculation, NIOSH identified the minimum in the dataset from these swipe

data (1.7 dpm/100 cm2

) and used it to replace all reported zeros instead of the higher minimum 

(3.65 dpm/100 cm2). Correcting for these minor errors, SC&A calculated a removable 

contamination GM of 1.34 dpm/100 cm2 with a GSD of 2.98. This is very similar to the GM of 

1.09 dpm/100 cm2 with a GSD of 3.61 dpm/100 cm2 calculated by NIOSH. Because the GSD

calculated by NIOSH was higher, the NIOSH-calculated 95th percentile, 8.99 dpm/100 cm2, is 

greater than the SC&A-calculated value of 8.06 dpm/100 cm2. These differences are modest, and 

the NIOSH value is larger, so SC&A determined that these differences and minor errors have no 

adverse effect on the roof and overhead dose reconstruction pathway. 
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4.2 Concerns expressed by M&C Work Group

While evaluating the SEC petition, M&C Work Group members raised questions about the 

representativeness of the data in terms of where and over what time period the data were 

collected. In particular, one Advisory Board on Radiation and Worker Health member asked 

whether some of the measurements were collected on the roof outdoors, where weathering would 

remove the contamination and thus reduce their representativeness with respect to exposures to 

workers performing maintenance indoors in the rafters and upper levels close to the ceiling. 

SC&A revisited the file of reports and correspondence associated with the M&C request for 

termination of NRC License SNM-23 (NRC & TI, 1982–1983). These documents present 

measurements of direct alpha, removable alpha, and beta/gamma radioactivity and are the 

primary reference NIOSH used to support characterization on the roof and overhead models. 

Most of the direct measurements used in modeling were indoor measurements done on the 

ceiling and other overhead areas and thus were not impacted by outdoor weather, but some of the

measurements were also outdoors on the roof. Direct measurements were taken by 

representatives of TI at 45° increments from 0.5-, 1.0-, and 2-meter distances on the roof around 

the exhaust from the high-efficiency filter system. Additionally, TI representatives took direct 

measurements on the roof around the exhaust from the fuel manufacturing area at distances of 1, 

2, and 4 meters. SC&A believes the point of discharge of the exhaust system is the most logical 

pathway for material to deposit on the roof. In its original 1982 report requesting license 

termination, TI indicated: 

No cleaning prior to measuring for radioactivity was performed on the roof of 

Building 10 as the regular monitoring of the two exhausts from the fuel 

manufacturing area have always showed essentially background radioactivity in 

the air being discharged. [NRC & TI, 1982–1983, PDF p. 60] 

Therefore, the data represent the radiological condition as they were at the time of the 

measurements. This also provides some evidence that the site was regularly monitoring roof 

areas for contamination during the residual period. Following the application for license 

termination, the site was audited by the NRC inspectors from August 31- September 2, 1982. 

The inspection involved two regional NRC inspectors who each spent 32 hours inspecting the 

site. At the conclusion on the inspection, they noted that “Fixed and removable contamination 

levels measured during the inspection are comparable to those in the licensee’s close-out survey” 

(NRC & TI, 1982–1983, PDF p. 20]. This provides further reassurance that the survey results 

were confirmed by regulators in 1982. 

A total of 40 direct measurements were performed on the roof by TI. Assuming 10 percent 

removable contamination, SC&A calculates a GM of 2.6 dpm/100 cm2

 and a 95th percentile of 

29.0 dpm/100 cm2, roughly double the amount modeled by NIOSH for the aggregate roof and 

overhead model. Since the roof is subject the weather, it would be reasonable to assume source 

term depletion occurred over the roughly 14 years of the residual period between monitoring, 

assuming zero contribution from activities related to the High Flux Isotope Reactor (HFIR) 

during the residual period. SC&A notes that the direct alpha roof measurements suggest that at 

least some portions of the roof had more contamination than the overhead areas. These 

differences are small but suggest that the roof at the upper 95th percentile is not bounded by the 

combined roof and overhead model. Despite this, the resulting doses from a roof only model are 
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still small (<1 mrem in 1982). If another pathway were created, the occupancy factor would have 

to be reduced, which would further reduce the doses. 

4.3 External exposures from roof and overhead pathway

NIOSH proposes assigning a quarterly GM gamma dose rate of 12 mrem/quarter 

(4 mrem/month) and a quarterly GM skin dose rate of 36 mrem/quarter (12 mrem/month), both 

with a GSD equal to the Battelle-TBD-6000 default value of 5 (NIOSH, 2011). For the roof and 

overhead pathway, NIOSH intends to assume 1 month of occupancy, so an annual penetrating

dose of 4 mrem and a skin dose of 12 mrem will be assigned for this pathway. NIOSH proposes 

assuming a claimant-favorable gamma energy of 100 percent 30–250 keV and electron energy of 

100 percent >15 keV with no source term depletion. 

As a check, SC&A modeled doses from exposure to the roof activities, which had the highest 

dose rates identified by surveying. SC&A calculated the 95th percentile of these direct alpha

readings to be 186 dpm/100 cm2 (18,600 dpm per square meter (dpm/m2

)). Assuming the 

contamination to be due to natural uranium in equilibrium with its short-lived progeny, SC&A 

applied the DCF of 3.94×10-10 milliroentgen (mR)/h per dpm(α)/m2 listed in Battelle-TBD-6000, 

revision 1 (NIOSH, 2011, table 3.10), to obtain an exposure rate of 7.33×10-6 mR/h, which is 

undetectable in the presence of natural background. Assuming an exposure duration of 

166.67 hours/year, SC&A derived an annual exposure of 0.001 mR, which is far below the 

minimum exposure that needs to be considered in a DR. The corresponding beta skin dose rate, 

based on the DCF of 3.82×10-8 millirad per hour (mrad/h) per dpm(α)/m2 listed by NIOSH 

(2011a, table 3.10), is 0.12 mrad/year, which is below the 1 mrem/year threshold for radiation 

doses that need to be addressed by a DR. This suggests the proposed NIOSH assumptions for 

external dose bound the likely exposures during the roof and overhead work. 

5 Welding

It is known from petitioner statements that welding activities inside and on the roof of 

Building 10 occurred during the residual period. Since these maintenance-related activities could 

have potentially suspended materials with the highest concentrations, NIOSH will assume that

100 percent of the 95th percentile direct measurement roof and overhead contamination is 

removable (89.94 dpm/100 cm2

). NIOSH indicates it will assume all workers spent 48 hours a 

year performing these activities and apply a resuspension factor of 10-3/m. Table 4 of NIOSH 

(2021a) gives an example of the doses calculated in the welding pathway. SC&A was able to 

replicate the calculated annual committed effective doses in table 4, as shown in example 5-1. 

SC&A is providing this example to establish SC&A understood the assumptions NIOSH was 

using to calculate doses from this exposure pathway. Organ doses rather than committed 

effective doses are assigned in DRs performed under EEOICPA.

Example 5-1: Annual uranium intakes and committed effective doses from welding

pathway

UU iiiih. iiiiiiaaiiii = PPiimmllffaarraaii aaaaoohaa ∗ RRRR ∗ llPPPPddooaaiiPPoo ffaaPPiillPP ∗ iiiihaaaaaaiiiillii PPaaiiii
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89.94 ddoomm

100PPmm2 ∗ μCCii2,220,000 ddoomm ∗

10,000 PPmm2

mm2 ∗

10−3

mm ∗

48 hllddPPdd

ooiiaaPP ∗ 1.2

mm3

h

= 2.33 ∗ 10−4 μCCii/ooiiaaPP

UU iiiihaaaaaaiiiillii ddllddii = 2.33 ∗ 10−4 μCCii/ooiiaaPP ∗

2.52 ∗ 104 mmPPiimm

μCCii = 5.88 mmPPiimm/ooiiaaPP

ddPPaaiiiiddmm iiiilliiddiiiillii iiiiiiaaiiii = iiiilliiddiiiillii PPaaiiii ∗ PPiimmllffaarraaii aaaaoohaa ∗ RRRR ∗ llPPPPddooaaiiPPoo ffaaPPiillPP

10−4 mm2

hllddPP ∗ 89.94 ddoomm100 PPmm2 ∗ μCCii2,220,000 ddoomm ∗

10,000 PPmm2

mm2 ∗

48 hllddPPdd

ooiiaaPP

= 1.94 ∗ 10−5 μCCii/ooiiaaPP

UU iiiilliiddiiiillii ddllddii = 1.94 ∗ 10−5 μCCii/ooiiaaPP ∗

1.81 ∗ 102mmPPiimm

μCCii = 3.52 ∗ 10−3 mmPPiimm/ooiiaaPP

iiiihaaaaaaiiiillii ddllddii + iiiilliiddiiiillii ddllddii = 5.88

mmPPiimm

ooiiaaPP

+ 3.52 ∗ 10−3 mmPPiimm

ooiiaaPP

= 5.88 mmPPiimm/ooiiaaPP

Thorium doses are calculated by replacing the uranium DCFs with thorium DCFs, resulting in a 

committed dose calculation of 17 mrem per year. Since the data used to support the model come 

from direct measurements of gross alpha, NIOSH will assign the most claimant-favorable 

mixture of thorium or uranium. 

5.1 Data supporting welding intake model

The data supporting the welding pathway are identical to the data used in the roof and overhead 

model previously evaluated in section 4.1; however, NIOSH assumes 100 percent of 

contamination is removable (rather than 10 percent assumed in the roof and overhead model). 

These data are equally applicable to the welding scenario because welding would have occurred 

in the same areas as the roof and overhead work. 

5.2 Concerns raised by work group and SC&A

According to NIOSH (2021a, p. 13), 

NIOSH modeled exposures for the entire overhead area uniformly using a 10-4

resuspension factor. NIOSH is aware that good work practice requires clean bare 

metal before welding, which can include wire brushing and grinding. NIOSH 

believes this weld-preparation work to be the portion of the welding task capable 

of generating the highest airborne concentration. Also, NUREG-1400 [NRC 

1993] Section 1.2.3 indicates that a dispersibility factor of 10 should be used to 

model intakes involving grinding operations. Therefore, NIOSH will increase the 

resuspension factor and apply a value of 10-3 to the 95th-percentile total 

contamination level. 

SC&A raised a concern (finding 2) in its 2019 (SC&A, 2019a) and 2020 (SC&A, 2020b) 

reviews of welding and thorium activities that a resuspension factor of 10-3/m may not be 
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adequate to represent the dust generated by grinding and wire brushing to prepare a surface for 

welding. The work group members echoed this concern during the September 2, 2020, M&C 

Work Group meeting (M&C WG, 2020). To date, this issue has not been resolved. SC&A agrees 

that this is a “TBD issue” rather than an SEC issue.

5.3 External exposures from welding

The external exposure potential from welding is comparable to the roof and overhead pathway 

SC&A evaluated in section 4.3 of this report, with shorter occupancy times. Due to the heat and 

nonradiological hazards associated with welding, it is reasonable to assume personal protective 

equipment was used that would have provided shielding, though no reduction in dose rate is 

assumed for this pathway. External doses from welding activities are believed to be below the 

threshold for inclusion in a DR. 

NIOSH proposes assigning a quarterly GM gamma dose rate of 12 mrem/quarter 

(4 mrem/month) and a quarterly GM skin dose rate of 36 mrem/quarter (12 mrem/month), both 

with a GSD equal to the Battelle-TBD-6000 default value of 5 (NIOSH, 2011). For the welding 

pathway, for which NIOSH intends to assume 48 hours of occupancy, an annual penetrating dose 

of approximately 1 mrem and a skin dose of 3.5 mrem will be assigned. This is larger than the 

SC&A-modeled external doses; therefore, SC&A believes the NIOSH model is bounding for the 

welding exposure pathway. 

6 HVAC Maintenance

To model heating, ventilation and air conditioning (HVAC) maintenance exposures, NIOSH 

assumes that 1 hour per year is required for performing these activities. Table 4 of NIOSH 

(2021a) provides an example of the doses calculated in the subsurface outside pathway. Using 

the calculation in example 6-1, SC&A was initially unable to replicate the calculated annual 

committed effective doses given in table 4. SC&A contacted NIOSH regarding this discrepancy 

and discovered NIOSH inadvertently used a 48-hour/year occupancy rather than the intended 

1 hour per year in their calculations. NIOSH confirmed 1 hour per year was the intended 

occupancy factor. Thus, the HVAC values in table 4 were 48 times larger than intended. 

Example 6-1: Annual uranium intakes and committed effective doses from HVAC 

maintenance

[ddPPaaiiiiddmm iiddiiiimmaaiiiidd] = aaaaoohaa ddddPPffaaPPii ∗ RRRR ∗ Dust Loading in Building 10

12.3 dpm

100 cm2 ∗

10,000 PPmm2

mm2 ∗

10−5

mm ∗ mm3100 μll

= 1.23 ∗ 10−4ddoomm/ μll

UU iiiihaaaa. iiiiiiaaiiii = [UU iiddiiiimmaaiiiidd] ∗ Dust Loading in vent ∗ inhal. rate ∗ occupancy factor 

1.23 ∗ 10−4ddoomm

ddll ∗

100,000 μll

mm3 ∗ 1.2

mm3

hllddPP ∗

1 hllddPP

ooiiaaPP = 14.76 ddoomm/ooiiaaPP

14.76 ddoomm/ooiiaaPP ∗ μCCii

2,220,000 ddoomm ∗

2.52 ∗ 104 mmPPiimm

μCCii = 0.168 mmPPiimm/ooiiaaPP
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UU iiiilliiddiiiillii iiiiiiaaiiii = iiiilliiddiiiillii PPaaiiii ∗ UU ddddPPffaaPPii aaPPiiiiffiiiioo ∗ llPPPPddooaaiiPPoo ffaaPPiillPP

50,000 μg

8 hour workday ∗

1.23 ∗ 10−4ddoomm

μll ∗ μCCii2,220,000 ddoomm ∗

1 hllddPP

ooiiaaPP

= 3.46 ∗ 10−7μCCii

2.46 ∗ 10−4μCCii ∗

1.81 ∗ 102mmPPiimm

μCCii = 6.27 ∗ 10−5 mmPPiimm/ooiiaaPP

iiiihaaaaaaiiiillii ddllddii + iiiilliiddiiiillii ddllddii = 0.168

mmPPiimm

ooiiaaPP

+ 6.27 ∗ 10−5 mmPPiimm

ooiiaaPP

= 0.168 mmPPiimm/ooiiaaPP

6.1 Data supporting the intake model

NIOSH (2021a, p. 13) indicates that NIOSH will use “7,765 gross-alpha swipe data collected at 

the end of AWE operations in 1966 and 1968.” These samples were taken near the end of 

operations inside Building 10 and represent removable contamination found at the site during 

operations. At the end of the AWE operations period, the non-HFIR areas were cleaned and 

released for use. This cleaning would be expected to reduce the contamination during the 

residual period 

Limited sampling results exist during the residual period that can be clearly linked to non-HFIR

activities prior to the 1982 site characterization associated with license termination. In January 

and February 1983, NRC inspectors (NRC & TI, 1982–1983, PDF pp. 9–14) made 938 direct 

alpha, beta-gamma, and gamma measurements in 67 grid blocks in Building 10 outside of HFIR, 

9 grid blocks in Building 4, and 2 grid blocks in Building 3. The NRC inspectors reported that 

“Direct alpha measurements did not exceed 175 dpm/100cm 2 (92.6% ≤ 50 dpm)” (PDF p. 11) 

inside Building 10 (measurements taken in non-HFIR areas). Assuming 10 percent of the direct

measured activity was removable, the maximum seen in 1983 is comparable to the GM of the 

operation period swipe samples, 12.3 dpm/100 cm 2. The NRC inspectors also took 81 swipe 

samples. The only two samples inside Building 10 in excess of 10 dpm/100 cm 2 were 

20.3 dpm/100 cm 2 and 11.2 dpm/100 cm 2, both of which are also comparable to the GM used by 

NIOSH. SC&A believes the consistency of these values supports NIOSH’s use of the late 

operations period swipe sample data to bound residual period exposures. 

6.2 External exposures from HVAC maintenance

NIOSH proposes assigning a quarterly GM gamma dose rate of 12 mrem/quarter 

(4 mrem/month) and a quarterly GM skin dose rate of 36 mrem/quarter (12 mrem/month). For 

the HVAC maintenance pathway, which NIOSH intends to assume 1 hour of occupancy per 

year, an annual penetrating dose and skin dose of less than 1 mrem is assigned. 

SC&A modeled external doses to a worker changing HVAC filters to compare the doses to the 

NOSH doses. Such a worker could potentially receive a skin dose from airborne contaminated 

dust settling on their skin during this operation. Using conservative assumptions about the dust 

loading and specific activity, the settling velocity recommended by Battelle-TBD-6000 (NIOSH,
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2011), and the skin dose rates discussed in Appendix C to SC&A’s (2018a) initial ER review, 

SC&A finds that the annual skin dose from this pathway is much less than 1 mrem. Therefore, 

the NIOSH-proposed values are comparable to the SC&A-modeled doses. 

7 Remaining Exposures

NIOSH assumes the balance of a worker’s employment (remaining period) was spent on site on 

tasks in the generally accessible parts of the site. These exposures are referred to as “nonmaintenance,” which is somewhat of a misnomer in terms of work function. They are intended to 

refer to all other work activities that are not covered by the other defined pathways. These 

exposures include work and maintenance activities that occurred in the parts of M&C that were 

generally accessible to all workers on most days. NIOSH (2021a, p. 14) indicates that dose will 

be assigned as follows:

For exposures incurred by workers for the balance of the year, NIOSH will use 

the GM (12.3 dpm/100cm2) . . . . Using this GM surface contamination value and 

a 10-5 resuspension factor, the gross alpha airborne concentration in Building 10 

was calculated to be 0.0123 dpm/m3

. Source-term depletion adjustments (per the 

guidance in ORAUT-OTIB-0070) will be considered to determine the nonmaintenance exposure rates throughout the residual period. 

Table 4 of NIOSH (2021a) provides an example of the doses calculated in the remaining 

pathway. SC&A was able to approximately replicate the calculated annual committed effective 

doses in table 4 (<1 mrem), as shown in example 7-1. SC&A is providing this example to 

establish SC&A understood the assumptions NIOSH was using to calculate doses from this 

exposure pathway. Organ doses rather than committed effective doses are assigned in DRs 

performed under EEOICPA. 

Example 7-1: Maximum annual uranium intakes and committed effective doses from nonmaintenance activities (remaining period)

∗

10,000 PPmm2

mm2 ∗ μCCii

2,220,000 ddoomm ∗

10−5

mm ∗

1.2 mm3

hllddPP ∗

1,451 hllddPPdd

ooiiaaPP

= 9.65 ∗ 10−6 μCCii/ooiiaaPP

UU iiiihaaaaaaiiiillii ddllddii = 9.65 ∗ 10−6 μCCii/ooiiaaPP ∗

2.52 ∗ 104 mmPPiimm

μCCii = 0.24 mmPPiimm/ooiiaaPP

ddPPaaiiiiddmm iiiilliiddiiiillii iiiiiiaaiiii = iiiilliiddiiiillii PPaaiiii ∗ UU ddddPPffaaPPii ∗ llPPPPddooaaiiPPoo ffaaPPiillPP

10−4 mm2

hllddPP ∗ 12.3 ddoomm100 PPmm2 ∗ μCCii2,220,000 ddoomm ∗

10,000 PPmm2

mm2 ∗

1,451 hllddPPdd

ooiiaaPP

= 8.03 ∗ 10−5 μCCii/ooiiaaPP
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UU iiiilliiddiiiillii ddllddii = 8.03 ∗ 10−5 μCCii/ooiiaaPP ∗

1.81 ∗ 102 mmPPiimm

μCCii = 1.46 ∗ 10−2 mmPPiimm/ooiiaaPP

iiiihaaaaaaiiiillii ddllddii + iiiilliiddiiiillii ddllddii = 0.243

mmPPiimm

ooiiaaPP

+ 0.015

mmPPiimm

ooiiaaPP

= 0.26 mmPPiimm/ooiiaaPP

Thorium doses are calculated by replacing the uranium DCFs with thorium DCFs, resulting in a 

committed dose calculation of approximately 1 mrem per year maximum. NIOSH indicates that, 

since the results are gross-alpha, NIOSH will assign the most claimant-favorable mixture of 

thorium or uranium. 

7.1 Data source

NIOSH (2021a, p. 13) indicates that NIOSH will use “7,765 gross-alpha swipe data collected at 

the end of AWE operations in 1966 and 1968.” This is the same data source evaluated in 

section 6.1 of this report. 

7.2 External dose from remaining period

NIOSH proposes assigning a quarterly GM gamma dose rate of 12 mrem/quarter 

(4 mrem/month) and a quarterly GM skin dose rate of 36 mrem/quarter (12 mrem/month), both 

with a GSD equal to the Battelle-TBD-6000 default value of 5 (NIOSH, 2011). For the 

remaining period of time not modeled by other pathways (non-maintenance exposures), this 

equates to a total annual penetrating dose of 35 mrem/year and a skin dose of 105 mrem/year, 

when prorating to 1,451 hours per year. NIOSH proposes assuming a claimant-favorable gamma 

energy of 100 percent 30–250 keV and electron energy of 100 percent >15 keV. NIOSH (2021a, 

p. 15) states: 

For all non-maintenance work exposures, source-term depletion adjustments will 

be considered (per the guidance in ORAUT-OTIB-0070) to determine the nonmaintenance exposure rates throughout the residual period. 

SC&A believes it is appropriate to apply the penetrating dose rate of 4 mrem/month and beta 

dose rate of 12 mrem/month to the remaining period (non-maintenance exposures).

SC&A is aware of additional direct survey measurements from the 1982 survey performed by TI 

and verified by NRC inspectors (NRC & TI, 1982–1983). As a check, SC&A assessed the results 

of 40 sets of alpha direct measurements performed on the floors areas inside Building 10 by TI 

(1982, appendix A, section 4.2.2, PDF p. 28). According to TI (1982, PDF p. 7), “TI selected the 

floors of areas identified as processing unclad materials for these measurements because floors 

represent the worst condition for holding residual radioactivity.” For each area, TI listed the 

maximum activity and the average of all measurements in the given area. SC&A calculated the 

95th percentile of these average grid readings to be 234.44 dpm/100 cm2 (23,444 dpm/m2).

Assuming the contamination to be due to natural uranium in equilibrium with its short-lived 

progeny, SC&A applied the DCF of 3.94×10-10 mR/h per dpm(α)/m2 from Battelle-TBD-6000 

(NIOSH, 2011, table 3.10) to obtain an exposure rate of 9.24×10-6 mR/h, which is undetectable 

in the presence of natural background. Assuming an exposure duration of 1,451 hours/year, 

SC&A derived an annual exposure of 0.0134 mR, which is far below the minimum exposure that 
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needs to be considered in a DR. The corresponding beta skin dose rate, based on the DCF of 

3.82×10-8 mrad/h per dpm(α)/m2

 listed by NIOSH (2011, table 3.10), is 1.30 mrad/year, which is 

just above the 1 mrem/year threshold for radiation doses that need to be addressed by a DR. This 

suggests that the proposed NIOSH assumptions for external dose bound the likely exposures 

during the remaining period. 

8 Conclusions and Recommendations

SC&A reviewed each of the six exposure pathways described by NIOSH (2021a). This review 

identified one finding and one observation, both of which relate to subsurface exposure 

modeling. With the modifications suggested in the finding and observation, SC&A believes 

internal and external doses from each maintenance exposure pathway can be bounded. 

SC&A recommends NIOSH develop guidance for dose reconstructors that allows modification 

to the established occupancy factors if statements in the computer-assisted telephone interview or 

evidence in the energy employee’s employment records suggest a different breakdown of work 

may be more appropriate. SC&A also recommends that NIOSH include guidance to help dose 

reconstructors prorate doses for partial years of employment. SC&A is unaware of any other 

AWE sites with many exposure pathways where precedent has been set for the treatment of 

partial years of employment. Developing guidance would help ensure partial years of 

employment are treated consistently in all M&C cases. SC&A recommends prorating all 

occupancy factors based on partial years of employment.
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9 References

ASTRA, Inc. (1962). Analysis of possible nuclear material losses and possible liabilities 

associated with present fuel manufacturing at Metals & Controls, Inc., Attleboro, Massachusetts

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Creative Pollution Solutions, Inc. (CPS). (1992). Radiological characterization of Texas 

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Metals and Controls Corporation Work Group. (2020). Wednesday, September 2, 2020 

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National Institute for Occupational Safety and Health. (2004). Estimation of ingestion intakes

(OCAS-TIB-009, rev. 0). https://www.cdc.gov/niosh/ocas/pdfs/tibs/oc-t9-ro.pdf 

National Institute for Occupational Safety and Health. (2006). Site profile for Atomic Weapons 

Employers that worked uranium and thorium metals (Battelle-TBD-6000, rev. F0; PNWD-3738, 

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National Institute for Occupational Safety and Health. (2011). Site profiles for Atomic Weapons 

Employers that worked uranium metals (Battelle-TBD-6000, rev. 1). 

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rev. 01). https://www.cdc.gov/niosh/ocas/pdfs/tibs/or-t70-r1.pdf 

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Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

National Institute for Occupational Safety and Health. (2018b, September 12). Metals and 

Controls Special Exposure Cohort (SEC 236) issues matrix. 

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the SC&A review of the NIOSH white paper dated April 23, 2018 [Memorandum]. 

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Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

Sowell, L. L. (1985). Radiological survey of the Texas Instruments site Attleboro, Massachusetts

(RSAP/SMPB-8). SRDB Ref. ID 94371 

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ID 161141, PDF pp. 989–1166

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Attleboro, Massachusetts. SRDB Ref. ID 163071 

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water, and soil (Federal Guidance Report No. 12, EPA-402-R-93-081). 

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Attachment A: Building 10 Pipes Remediation

Figure A-1. Building 10 removed drain lines

Source: Adapted from Weston (1996b), figure 5.3 (PDF p. 175). 
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Figure A-2. Remediated drain lines

Source: Adapted from Weston (1996b), figure 5.4 (PDF p. 176). 
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Figure A-3. Drain lines left in place in affected areas

Source: Adapted from Weston (1996b), figure 5.5 (PDF p. 178).