Draft 

Advisory Board on Radiation and Worker Health

National Institute for Occupational Safety and Health

Supplemental Review of M&C Work Group Issues 

Contract No. 75D30119C04183

Document No. SCA-TR-2022-SEC002, Revision 0

Prepared by

Joe Fitzgerald, MS, MPH

SC&A, Inc.

2200 Wilson Blvd., Suite 300

Arlington, VA 22201-3324

August 22, 2022 

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.

NOTICE: This document has been reviewed to identify and redact any information that is

protected by the Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 
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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 Supplemental Review of M&C Work Group Issues

Document number SCA-TR-2022-SEC002

Revision number 0 (Draft)

Supersedes NA

Effective date August 22, 2022 

Task manager Joe Fitzgerald, MS, MPH [signature on file]

Project manager Bob Barton, CHP [signature on file]

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

Record of revisions

Revision number Effective date Description of revision

0 (Draft) 8/22/2022 Initial issue
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Table of Contents

Abbreviations and Acronyms........................................................................................... 4

1 Introduction and Background.................................................................................... 6

2 Summary of NIOSH Evaluation Report Conclusions for Internal Dose 

Reconstruction ................................................................................................................ 8

3 Response to Lines of Inquiry .................................................................................. 10

3.1 Line of inquiry 1................................................................................................ 10

3.2 Line of inquiry 2................................................................................................ 16

3.3 Line of inquiry 3................................................................................................ 28

4 Conclusions ............................................................................................................ 36

5 References ............................................................................................................. 38

Attachment 1 ................................................................................................................. 44
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Abbreviations and Acronyms

ABRWH, Board Advisory Board on Radiation and Worker Health

AWE Atomic Weapons Employer

CFR Code of Federal Regulations

cm2 square centimeters

cpm counts per minute

D&D decontamination and decommissioning

DCAS Division of Compensation Analysis and Support

DOE U.S. Department of Energy

dpm disintegrations per minute

DU depleted uranium

EEOICPA Energy Employees Occupational Illness Compensation Program Act

ER evaluation report

F.R. Federal Register

GM geometric mean

GSD geometric standard deviation

HFIR High Flux Isotope Reactor

HVAC heating, ventilation, and air conditioning

IAEA International Atomic Energy Agency

M meter

m3 cubic meter

M&C Metals and Controls Corporation

μCi/mL microcurie per milliliter

μg/m3 micrograms per cubic meter

NIOSH National Institute for Occupational Safety and Health

NRC U.S. Nuclear Regulatory Commission

ORAU Oak Ridge Associated Universities

ORAUT Oak Ridge Associated Universities Team

OSHA Occupational Safety and Health Administration

pCi/g picocuries per gram

Pu plutonium

Rn radon

SDMP Site Decommissioning Management Plan

SEC Special Exposure Cohort
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SRDB Site Research Database

TI Texas Instruments, Incorporated

Th thorium

U uranium
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1 Introduction and Background

The Metals and Control Corporation (M&C) Work Group has conducted an extensive review of 

the National Institute for Occupational Safety and Health (NIOSH) petition evaluation report 

(ER) for Special Exposure Cohort (SEC) Petition SEC-00236. This included a series of work 

group meetings beginning in 2018, supported by technical assessments and information reviews 

by both NIOSH and SC&A, as well as feedback from former worker interviews and petitioner 

comments. With NIOSH and SC&A achieving general agreement about the more prominent 

issues surrounding dose reconstruction for the M&C residual period (1968–1997), the work 

group requested one additional review by SC&A. This supplemental review1 is intended to focus 

on any remaining lines of inquiry or outstanding issues relevant to the work group’s final review 

of the SEC-00236 ER that would benefit from additional assessment. 

1 This review was conducted by Joseph Fitzgerald, who did not participate in SC&A’s earlier review of the M&C

petition evaluation report.

This review is based on the available record of work group discussions, former worker input, and 

supporting documents, including NIOSH and SC&A reports, responses, white papers, and 

presentations. However, it does not represent a consensus among SC&A staff and is intended to 

be responsive to the work group’s request for a timely and supplemental means to inform final 

work group deliberations on M&C. It should be emphasized that in matters of interpreting 

plausibility and sufficient accuracy in the context of exposure modelling and bounding 

assumptions, there is obviously a high degree of professional judgment involved. The purpose of 

this review is to consider all such interpretations so that the Advisory Board on Radiation and 

Worker Health (Board) is in the best possible position to complete its review of the M&C 

evaluation report. 

It is acknowledged that reviews of Atomic Weapons Employer (AWE) sites with uranium and 

thorium operations are premised on a lack of source term and monitoring data during the residual 

period from which traditional dose estimation based on the Energy Employees Occupational 

Illness Compensation Program Act (EEOICPA) can be performed. Reliance is necessarily placed 

on dose-bounding approaches in Battelle-TBD-6000 (NIOSH, 2011d; “TBD-6000”) and 

ORAUT-OTIB-0070 (NIOSH, 2012a; “OTIB-0070”) that are based on available operational 

source term data, supplemented by any remedial-related or similar data that may be available 

during the residual time period. 

Two relevant questions can be revisited and probed for the SEC-00236 ER at this time:

1. Is there a valid basis for the application of the operational source term and survey data for 

M&C in this manner? 

2. Are there any sufficiently intrusive or disruptive activities or conditions during the M&C 

residual period, or uncertainties therein, that would raise doubts about the validity of that 

assumed source term and the plausibility of bounding exposure pathway analyses that 

complement it? 
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The following lines of inquiry serve to answer those two questions and are posited based on 

existing work group concerns: 

1. Line of Inquiry 1: Are the conditions and work activities associated with the M&C 

residual period unusual or different such that (a) standard modeling procedures do not 

apply and (b) exposure potentials higher than those addressed by OTIB-0070 and 

TBD-6000 and supporting exposure pathway bounding analyses may have resulted? 

2. Line of Inquiry 2: Are the exposure pathway bounding methods prescribed by the ER

and subsequent NIOSH reviews appropriate and consistent with how other AWE sites 

have been addressed?

3. Line of Inquiry 3: Are the available source term, survey data, and other information

applied by NIOSH to support its dose bounding methods sufficiently accurate and 

plausibly applied? 

While there remain open findings from past assessments for work group resolution,2 these issues 

appear to have been tentatively resolved between NIOSH and SC&A and await work group 

review (NIOSH, 2022a, pp. 3–5). This review does not critique past SC&A reviews or issue 

resolution; rather, it strives to offer a fresh assessment of NIOSH’s analyses and conclusions, 

past precedent with other AWE sites, and the available information itself.

2 For example, SC&A (2021a), finding 1, “Building 10 subsurface external exposures not bounded,” and SC&A 

(2019, 2020), finding 2, “NIOSH understated the resuspension factor related to activities accompanying welding,” 

and SC&A’s (2021b) dust loading review. 

Likewise, this review does not revisit other issues raised during the course of work group 

discussion (e.g., sediment reduction in drain pipes, consideration of explosions and fires, 

exposures to radium-226 glass beads, and exposure to thorium), because they have apparently 

been already addressed in discussions between the work group, SC&A, and NIOSH. While there 

remain some issues involving external dose assessment for the M&C residual period, this review 

confines itself to internal dose assessment concerns, because that has been the primary focus of 

the work group’s concern. 
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2 Summary of NIOSH Evaluation Report Conclusions for Internal 

Dose Reconstruction

As noted in the NIOSH ER for SEC-00236: 

During the residual radiation period from January 1, 1968 through March 21, 

1997, the primary source of covered exposure that M&C employees may have 

been exposed to was from the previous AWE Facility weapons-related work that 

generated residual uranium residues. Smaller amounts of residual thorium 

residues were also present. [NIOSH, 2017j, p. 20] 

For the operational period (1952–1967), monitoring data consist of area surface contamination 

surveys, analyzed for gross alpha content, with removable alpha contamination “generally below 

100 dpm/100 cm2” (NIOSH, 2017j, p. 24). From these survey data at the end of the operational 

period, “a resuspension factor of 10-6 m-1 was applied to the 95th percentile contamination levels 

(54.8 dpm/100 cm2) to estimate an air concentration (2.47 x 10-15 μCi/mL or 0.00548 dpm/m3) 

that would have been present at the start of the residual period (per guidance in ORAUT-OTIB0070)” (NIOSH, 2017j, p. 27). 

During the residual period itself, the first documented surface survey of these areas is dated 

November 1, 1982 (TI, 1982, PDF p. 12). As noted in the ER, the U.S. Nuclear Regulatory 

Commission (NRC) performed an “over check survey” of these same areas from January 31 to 

February 2, 1983 (NIOSH, 2017j, p. 24), with direct alpha measurements found to be below 175 

disintegrations per minute per 100 square centimeters (dpm/100 cm2) (with one exception) and 

an overall 92 percent below 50 dpm/100 cm2 (NRC, 1983, PDF p. 11). Based on these 

measurements, “A resuspension factor of 10-6 m-1 was applied to the 95th percentile 

contamination levels (14.5 dpm/100 cm2

) to estimate an air concentration (6.53 x 10-6 μCi/mL or 

0.00145 dpm/m3) that would have been present on November 1, 1982” (NIOSH, 2017j, p. 28). 

A source term depletion rate of 2.45×10-4 day-1 was calculated and applied to the air 

concentration available at the start of the residual period (0.00548 dpm/cubic meter (m3)) to 

arrive at year-by-year intake rates for M&C production workers during 1968–1997. 

More extensive contamination survey data are available both for non-EEOICPA covered 

activities and areas and for employees performing commercial work at M&C. The former cannot 

be assessed in the ER. While the latter would only be representative of conditions during 

commercial operations (or during decontamination and decommissioning (D&D)) and not those 

during the EEOICPA-covered residual period, the ER notes that NIOSH will not rely on them to 

bound doses, but “can consider these data [consisting of surface contamination surveys, air 

monitoring, urinalysis, and lung scans] as supporting evidence to validate the bounding method 

used in Section 7 of this report. (NIOSH, 2017j, p. 24). 

For dose reconstruction methods, the ER noted: 

All of the surface contamination surveys used to create these bounding methods 

were initially analyzed for gross alpha content; therefore, NIOSH will choose the 

most claimant-favorable isotope of thorium or uranium when estimating worker 
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doses. For thorium, both natural and triple-separated mixtures will be considered. 

[NIOSH, 2017j, p. 27] 

For the residual period itself, contamination measurements were taken on site involving an 

uncovered operation in Building 10 (the High Flux Isotope Reactor (HFIR)-related support 

work), and commercial-based D&D activities in the 1980s and 1990s. These are used by NIOSH, 

respectively, to make the case for the conservatism of its modeled soil contamination level 

(NIOSH, 2021a, pp. 7–8) and to validate its dose bounding methods. (NIOSH, 2017j, p. 24). 

For internal dose reconstruction for the M&C residual period, NIOSH “concludes that there are 

methods available in Battelle-TBD-6000, NUREG/CR-5512, and ORAUT-OTIB-0070, as well 

as available surface-contamination data, air-monitoring data, and operational descriptions, so that 

internal radiation doses can be reconstructed with sufficient accuracy for all employees during 

the period under evaluation” (NIOSH, 2017j, p. 30). 

Following the issuance of the ER, NIOSH developed six exposure pathway models for 

maintenance work activities that were described by M&C interviewees. NIOSH described this 

work as “although . . . sporadic and sometimes emergent in nature, it exposed workers in a 

manner that did not agree with the method described in the SEC-00236 ER (i.e., surface 

contamination resuspension)” (NIOSH, 2018, p. 2). These exposure pathways, for which 

bounding exposure models are provided, are heating, ventilation, and air conditioning (HVAC) 

maintenance, subsurface inside, subsurface areas outside, roof and overhead area, welding 

operations, and remaining exposures. 

NIOSH acknowledged that the default dust-loading value of 100 micrograms per cubic meter

(μg/m3

) suggested in OTIB-0070 and NUREG/CR-5512 (NRC, 1992), which was intended for a 

screening analysis for a long-term average, would not be appropriate for the intrusive subsurface 

work that former M&C workers described. Instead, a dust-loading factor of 212 μg/m3 was 

determined based on air sampling performed during excavation at the Mound Plant and was 

applied as “data from another facility to completely develop [the] exposure model” (NIOSH, 

2020d, p. 9).
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3 Response to Lines of Inquiry

The following subsections respond to the work group’s overarching concerns about conclusions 

in the ER for internal dose reconstruction for the residual period at M&C, as well as the work 

group’s subsequent deliberations. 

3.1 Line of inquiry 1 

Are the conditions and work activities associated with the M&C residual period unusual or 

different such that (a) standard modeling procedures do not apply and (b) exposure 

potentials higher than those addressed by OTIB-0070 and TBD-6000 and supporting 

exposure pathway bounding analyses may have resulted? 

A key concern raised by the work group was whether “maintenance work performed at M&C is 

unique, and therefore, standard modeling procedures do not apply” (NIOSH, 2020a, slide 3). 

NIOSH’s response is, in part, that “M&C operations were similar to operations at [other AWE 

sites]” and the “methods proposed for M&C by NIOSH and SC&A are similar and consistent 

with those previously approved by the Board” (NIOSH, 2020a, slide 12).

3.1.1 Uniqueness of AWE sites with defined SEC classes

On the question of uniqueness, NIOSH concludes that “it is clear these three residual periods [for 

Norton Company, Linde Ceramics, and Vitro Manufacturing] added to the SEC were for sites 

with unusual work activities with high dose potential for which NIOSH was unable to evaluate 

the source term; this is not the case at M&C” (NIOSH, 2020a, slide 9). 

The question of AWE uniqueness in the context of the applicability of the OTIB-0070 standard 

model and the feasibility of dose reconstruction is clearly a subjective one: There are no defined 

criteria, other than demonstrating that worker activities and conditions during the residual period 

may not be consistent with, or cannot be satisfied by, such modeling approaches.3 Such 

inconsistency could come from disruptive or intrusive worker activities or conditions leading to 

elevated exposure to contamination “with high dose potential” that (a) cannot be bound with 

sufficient accuracy due to unknown or uncertain source terms or exposure potential or (b) cannot 

be plausibly bound using data from other worker populations due to lack of job-specific 

information (these issues are further addressed in sections 3.2.2 and 3.3). From past AWE 

experience, these SEC-relevant activities have been typically associated with facility renovation, 

dismantlement, and remediation. 

3 Regarding the applicability of OTIB-0070, NIOSH notes that “although the procedures used by NIOSH [2012a] 

appear to be designed for routine exposures, NIOSH and the Board have adapted and relied upon them to bound 

non-routine exposures, such as those that occurred during M&C maintenance, or at other AWEs with foundries and 

steel mills” (NIOSH, 2020b, p. 13). While standard modeling procedures encompass these additional bounding 

analyses for source terms not addressed by OTIB-0070 resuspension assumptions for routine exposures, this 

question of uniqueness goes to whether M&C maintenance worker activities were sufficiently different or disruptive 

to obviate the applicability of this approach for such non-routine exposures.

For example, for the Norton Company AWE, facility dismantlement activities (1958–1962) 

during the residual period proved disruptive enough to have “altered the materials present and 
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placed employees close to the disturbed materials” (NIOSH, 2020a, slide 7). This brought into 

question the assumed source term based on the original gross alpha air monitoring results from 

the end of the operations period that were used for OTIB-0070 resuspension modeling. NIOSH 

concluded that “those data [from the operations period] cannot be assumed to bound all 

radioactive contamination and radiological contamination levels that could have arisen from the 

dismantling, clean-up, packaging and burial processes which were documented to have generated 

dust” (NIOSH, 2011a, p. 27). Fundamental to this SEC conclusion was the lack of source term, 

air monitoring, or worker monitoring data for these residual period activities, and evidence that 

“teardown and clean-up significantly altered the materials present and placed employees close to 

the disturbed materials” (NIOSH, 2020a, slide 7). 

For the Linde Ceramics Plant, the Board recommended, and an SEC class was designated, for all 

workers during the “renovation” phase of activities (1954–1969), within the residual period for 

that site (1954–2006). This renovation phase followed initial site cleanup and “could have caused 

the resuspension of fixed contamination,” and NIOSH found it is “reasonable to assume that this 

renovation work could have resulted in elevated airborne radioactivity” (NIOSH, 2011b, p. 22). 

The ER noted that “specific work details, including documentation of the actual start and end 

dates of renovation, dust control measures, location of work, and occupancy of areas are not 

available” (NIOSH, 2011b, p. 22). Fundamental to the Board’s conclusion and recommendation 

was the lack of a plausible bounding exposure estimate that could be applied site wide for all 

non-D&D workers during the renovation period, given the lack of information on what work 

those workers performed and under what exposure conditions (ABRWH, 2011, pp. 122–124; 

NIOSH, 2020a, slide 6). 

For Vitro Manufacturing, extensive remediation activities took place during the residual period 

(1960–1965) involving the remediation, transfer, and burial of residue uranium-processing 

waste. NIOSH found that “employees at the facility had potential for exposure to radiological 

source materials stored in open residue piles susceptible to contamination spread, and to 

radiological materials during decontamination and decommissioning activities including the 

eventual burial of the residue piles” (NIOSH, 2011c, p. 4). NIOSH’s SEC conclusion was 

founded on not having “access to personnel monitoring, workplace monitoring, or source term 

data to estimate unmonitored internal and external exposures” (NIOSH, 2011c, p. 5). 

From its review and comparison of the M&C residual period to that of other AWEs (NIOSH, 

2020b) on the question of M&C’s uniqueness, NIOSH concluded: 

M&C operations were similar to operations at these other sites. Uranium was 

machined at most of these sites; thorium is documented to have been at over half 

of them. Residual-period tasks performed by workers at these other sites, 

including contaminated soil excavation and welding and torch-cutting in 

contaminated areas, have been evaluated. The pathways leading to internal 

exposures from alpha-emitting radionuclides such as uranium and thorium are 

identical for workers at all of these sites: the inhalation and ingestion of 

resuspended, contaminated dust. [NIOSH, 2020b, p. 13] 

However, NIOSH also acknowledged that, based on the 2017 former worker interviews, “the 

information [received] indicated that the workers at M&C conducted more intrusive work into 
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subsurface areas than previously considered in the ER” (Division of Compensation Analysis and 

Support (DCAS), 2017, p. 1). As already noted, this led NIOSH to develop exposure pathway 

bounding analyses to address specific M&C maintenance worker exposures that could not be 

addressed by the resuspension model in OTIB-0070. 

3.1.2 Uniqueness of M&C work activities

The key issue before the work group, then, is why and how M&C is different from these AWE 

sites (or conversely, similar to those in the SEC) in terms of “unusual work activities with high 

dose potential for which NIOSH was unable to evaluate the source term” (NIOSH, 2020a, 

slide 9).

As pointed out by petitioners in affidavits, interviews, and oral and written statements, M&C 

workers conducted frequent routine and nonroutine maintenance work during the residual period 

that involved often intrusive and disruptive activities for which there was a potential for 

radiological intakes. These activities included drilling, sawing,4

 and jackhammering concrete 

slab flooring; subsurface drain cleaning and repair work involving radioactive sediments; 

subsurface and rooftop installation of site utility services; working on, in, and around 

contaminated mechanical equipment; working in utility manhole and trench networks; and 

excavating contaminated soils, including those adjacent to and potentially within an existing 

radioactive waste burial site and encompassing locations where “radioactive waste byproducts” 

were historically managed (Elliott, 2017, p. 1). 

4 While concrete floor sawing, itself, was often outsourced to third-party, outside contractors, M&C maintenance 

workers also performed this function for excavations (Elliott, 2022). 

Much of the utility services in Building 10 “had to be in the floor because of the overhead 

cranes” (NIOSH, 2017i, p. 16), necessitating frequent subsurface excavation to service and 

install utilities such as air and electrical conduits and drain lines. The work involved considerable 

time, usually days, but sometimes a week at a time (DCAS, 2017, p. 2) and up to 6 months for 

one project (NIOSH, 2017i, p. 11), working underground in manholes, trenches, sewers, and 

other confined spaces, with varying levels of contamination. As noted by a former worker, “you 

could be in a manhole for a week if there was a problem” (NIOSH, 2017a, p. 15), and “we were 

in trenches and manholes our whole working lives” (NIOSH, 2017a, p. 3). A supervisor noted: 

“We worked in the trenches. We cut trenches. We made trenches” (NIOSH, 2017i, p. 5). 

Notably, there was no air monitoring performed prior to worker entry into these manholes and 

other spaces5

 (NIOSH, 2017a, p. 14). Replacement and servicing of utility lines, such as air 

lines, took place in contaminated subsurface locations, reportedly including near and through a 

radioactive waste burial ground (NIOSH, 2017b, pp. 9–11). Work within the trenches included 

digging, sawing, drilling, grinding, and welding (Elliott, 2022, pp. 1–2), and for drain line 

unclogging, use of hand-cranked and power snakes (NIOSH, 2017i, p. 7). 

5 As an exception, confined space air sampling was performed for entry into deep concrete pits in Building 10, 

e.g., where “slitting equipment” was located (“it was the only time we used to call Health and Safety”), but only for 

deprived oxygen purposes (NIOSH, 2017i, pp. 5–6).
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When doing roof and truss penetrations for utility lines, preparation for welding activities would 

include blowing off accumulated dust with a compressed air tank, followed by prepping the truss 

beams with a wire brush, and then grinding it (NIOSH, 2017c, p. 8). 

Interviewed former maintenance workers spoke of cleaning out blocked drain lines from 

Building 10 on a regular basis: 

I would say that there were dozens of times that I worked over there. A lot of 

times when we worked over there, it would take days to finish a job. You had to 

find where the blockage was, saw cut the floor, break up all of the concrete with a 

sledge hammer, excavate it, get down in there and cut the line with a snap cutter, 

replace the line, fill it all in again with soil, and then pour the cement. [NIOSH,

2017c, p. 6] 

In terms of exposure potential, a health physicist who worked onsite during D&D made this 

distinction between how maintenance workers at M&C handled drain lines versus later 

commercial remediation workers:

I think that one of the differences that I would suggest is that these remediation 

workers are not handling the material inside the piping because usually it is dealt 

with in some way that it is a sealed entity. In many cases when there was piping 

or ductwork, the idea was not to take material out of it and clean it. The idea was 

to get rid of it. On the other hand, the maintenance worker’s job is to clean the 

pipe. So, I think the difference is the proximity to the source term, the handling of 

the source term, and their physical presence near the source term was probably a 

little different. [NIOSH, 2017d, p. 6] 

While this particular health physicist had overseen D&D activities at M&C in the 1990s, there is 

no record or account of actual health physics coverage or radiological monitoring during the 

residual period for maintenance workers in terms of overseeing their activities for purposes of 

identifying, monitoring, and controlling radioactive contaminant intakes and exposures6

(NIOSH, 2017a, pp. 4–5, 15; NIOSH, 2017c, pp. 3, 6, 11; NIOSH, 2017d, pp. 15–16). 

6 Two individuals, at separate times, were identified as having responsibilities for M&C health physics, but former 

workers who were interviewed do not recall those individuals actually performing monitoring or overseeing 

maintenance activities for radiation protection purposes (NIOSH, 2017c, pp. 3, 6, 11).

In terms of contrasting controlled D&D activities with the typical maintenance work performed 

at M&C, a former health physicist observed that D&D is a “controlled environment where the 

workers were very aware of what [they] were doing,” whereas the latter was “uncontrolled, 

unconfined, aggressive as hell, using mechanical processes that cause aggravation and clouds of 

dust” (NIOSH, 2017d, pp. 4–5). Moreover, maintenance worker “environments were rarely 

cleaned because they are not part of the normal process areas. Nooks, crannies, ductwork, 

ventilation, submerged piping, confined spaces, sumps; this is where they live. It’s not on the 

workforce shop floor” (NIOSH, 2017d, p. 5). 
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With M&C workers regularly performing such intrusive activities, as described, they could have 

been potentially exposed to elevated sources of radiological contamination. For example, 

maintenance workers dismantling, servicing, moving, or cleaning internally contaminated 

equipment may have been exposed to uranium or thorium at elevated activity levels, but these 

contamination levels were not surveyed.7

7 Routine maintenance on equipment is cited by former workers (NIOSH, 2017a, p. 5; NIOSH, 2017c, p. 3; 

NIOSH, 2017h, p. 4), and was performed by the M&C Repair and Maintenance group. It was also identified by 

NIOSH as not being addressed by the ER resuspension models (OTIB-0070) and involved “repurposing M&C 

equipment (e.g., removing and replacing mill units)” (DCAS, 2017, p. 1). A former worker noted that relocating 

equipment in Building 10 was a regular activity that typically took place on weekends (NIOSH, 2017a, p. 12). The 

status of equipment carried over from the pre-1968 AWE operational period is not addressed explicitly in the ER. It 

should be assumed that any equipment used in the operational period, prior to D&D, may have had internal 

contamination, as well as contamination under it, to which maintenance workers would have been later exposed 

when servicing that equipment or moving it. This issue was raised during Board discussions about the Linde SEC by 

a Board member with firsthand experience, who found that when workers “were actually moving, removing 

production processes . . . we always found the most contamination was in the footprint of these processes” 

(ABRWH, 2011, pp. 267–268). For M&C, it is reported that compressed air was typically used to clean mechanical 

equipment (Elliott & Lorenzen, 2017), which could have resuspended internal contaminants. The concentration of 

this contamination may be higher than that of surface contamination surveys conducted in 1967–1968 and could 

have included uranium and thorium particulates.

 Workers excavating, cutting, clearing, and removing 

radioactive sediment from drain lines may have been likewise exposed to uranium and thorium at 

elevated levels, sometimes exceeding 50,000 picocuries per gram (pCi/g) (NIOSH, 2017e, p. 8), 

but the historic scope, frequency, and maximum level of that exposure prior to 1995 is not 

documented. Workers excavating pits and trenches in elevated subsurface contaminated soils, 

including former waste burial sites (as established by later D&D surveys), may have been 

exposed to resuspended aerosols and particulates not only from the elevated uranium and 

thorium soil levels but also from higher airborne concentrations due to the confined spaces 

within which they were working.8

 

8 The Occupational Safety and Health Administration (OSHA) defines confined spaces and gives examples 

including pits, tanks, silos, sewers, underground utility vaults, and manholes (U.S. Department of Labor, 2015,

p. 25519). OSHA notes that pits, although typically open on top, can be completely underground or below grade and 

can still be a confined space (OSHA, 2015). The uncertainties posed by particulate and aerosol resuspension within 

confined spaces are discussed further in section 3.3.1 of this report.

While NIOSH has injected conservatism in its OTIB-0070 and related bounding analyses, using 

a 95th percentile distribution and other conservative assumptions to accommodate such 

uncertainties, the presence of residual radionuclide concentrations substantially in excess of 

those found in routine operational era surveys and later D&D characterization studies cannot be 

ruled out. 

The active and intrusive nature of the described maintenance work at M&C during the residual 

period clearly exceeded the residual period conditions and activities at other AWEs, as described 

in their corresponding evaluation reports and site profiles, and what would be assumed under 

OTIB-0070 for application of its resuspension and volumetric soil values. It falls within the 

continuum of post-operational intrusive activities ranging from Norton and Vitro (very active, 

D&D-like activities) to that of Linde (renovation activities), with M&C being closer to the latter, 

but without the radiological protection controls, protective equipment, and personnel monitoring 

that were typical of formal D&D programs. Table 1 provides an intercomparison of 15 AWEs, 
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including M&C, for their respective sources of exposure potential during residual periods and 

whether intrusive work activities took place that would have brought workers in close proximity 

with elevated exposure sources.

Table 1. Comparison of AWE sites: Sources of exposure potential and intrusive work 

activity during residual period

AWE site Source of exposure 

potential 

Intrusive work 

activity? (covered)

SEC class 

designated? Reference

Carborundum Resuspended U and 

Pu

No No NIOSH (2015a), 

pp. 50, 52

Baker Brothers Resuspended U No No NIOSH (2012b), 

pp. 33, 35–36

Hooker 

Electrochemical

Resuspended U No No NIOSH (2010a), 

pp. 24–26

Chapman 

Valve

Resuspended U No No NIOSH (2008b), 

pp. 17–18, 29–30

Bliss & 

Laughlin

Resuspended U No No NIOSH (2009), 

pp. 17, 21–22

Simonds Saw Resuspended U, Th No No NIOSH (2010b), 

pp. 54–55

Blockson Resuspended U, Th, 

Rn-222 exhalation

No No NIOSH (2015b), 

pp. 15–16, 24–29

Dow Chemical 

(Madison)

Resuspended U and 

Th, Th daughters

Yes (scrap handling) No NIOSH (2008c), 

pp. 8, 25–30

General Steel Resuspended U No No NIOSH (2008d), 

pp. 19, 24

Wah Chang Residual DU No No NIOSH (2010c), 

p. 20

United Nuclear Resuspended U No No NIOSH (2010d), 

pp. 41–42

Norton Dismantlement 

activities, 

resuspended U, Th

Yes

(tear-down, cleanup, 

disposal)

Yes NIOSH (2011a), 

p. 16

Linde Renovation activities, 

resuspended U

Yes 

(details lacking, D&D 

source terms 

applied)

Yes NIOSH (2011b), 

pp. 22–23

Vitro Remediation activities, 

resuspended U

Yes 

(removal/burial of 

contaminated 

material)

Yes NIOSH (2011c), 

pp. 12–13

M&C Intrusive maintenance 

activities, 

resuspended U and 

Th 

Yes 

(details lacking; D&D 

source terms 

applied). 6 exposure 

pathways modelled.

Petition 

pending

NIOSH 2018, 

NIOSH 2017j
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A judgment about the intrusiveness or disruptiveness of work activities during the residual 

period should be based on whether, as described by NIOSH, such activities would have “altered 

the materials present and placed employees close to the disturbed materials” (NIOSH, 2020a, 

slide 7). Based on worker interviews, affidavits, and presentations, backed up by available site 

documentation, M&C meets these subjective criteria. On that basis, the standard exposure model, 

as founded in OTIB-0070 and TBD-6000 and complemented by exposure pathway bounding, 

may not be sufficiently accurate for at least one or more of these pathways, as there could be a 

potential for higher potential exposure than would be bounded by that approach. At the very 

least, there is insufficient information available to rule out this possibility.

3.2 Line of inquiry 2 

Are the exposure bounding methods prescribed by the ER and subsequent NIOSH reviews 

appropriate and consistent with how other AWE sites have been addressed?

In its September 2, 2020, presentation before the work group, NIOSH concluded from its review 

of 16 petitions for 15 sites that handled uranium and thorium that the “types of radioactive 

material, the crafts personnel who worked with the material, and the tasks performed at M&C are 

found across all of the AWE sites” (NIOSH, 2020a, slide 12). NIOSH also found that the dose 

reconstruction methods proposed for M&C and these other sites are “similar and consistent with 

those previously approved by the Board” (NIOSH, 2020a, slide 12). 

This question originated with a concern expressed by work group members over “source data,” 

with the “missing piece [being] the work that was actually done.” It was also observed by a work 

group member that “this residual period is unusual compared to the other residual periods we’ve 

covered at other sites” (ABRWH, 2020a, p. 77). NIOSH’s subsequent review provided a 

“summary of bounding methods used for sites with residual radiation periods added to the SEC 

to compare to M&C” (NIOSH, 2020a, slide 3). 

The threshold questions are whether the bounding approach for nonroutine exposure pathways 

applied to M&C is consistent with past practice and precedent for AWE residual periods, and 

whether dose reconstruction methods prescribed for these pathways can be considered plausible 

and sufficiently accurate.

3.2.1 Similarity of M&C to other AWEs

Like other AWEs, M&C had residual contamination resulting from various earlier uranium (and, 

in some cases, thorium) operations, for which some degree of surface area surveying or air 

monitoring had been conducted during the prior operational period. The crafts personnel making 

up the M&C maintenance crew were similar to those at the other AWE sites, including laborers, 

pipefitters, mechanics, and carpenters. Many of the work activities were similar as well and 

included welding, excavating, and general facility maintenance. Up to this point, there is 

agreement with NIOSH’s conclusion that “M&C operations were similar to operations at these 

other sites” (NIOSH, 2020b, p. 13). 

However, the nature of much of the M&C maintenance work differed by the degree of its 

intrusiveness, which placed workers in close proximity to elevated contamination sources in 

normally inaccessible locations. As summarized in table 1, the 11 AWE sites listed by NIOSH in 
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its response paper (NIOSH, 2020b), with the addition of the three SEC sites, were compared with 

M&C in terms of worker activities and exposure pathways for their respective residual periods.9

9 For this review, the sections of these ERs and site profiles that addressed exposure sources and activities during 

the residual period were compared with M&C. With a few exceptions (e.g., the three SEC sites, radon at Blockson, 

thoron at Dow Chemical), exposures during the residual period for the other AWEs were attributed to routine 

resuspension of uranium and thorium from previous operations.

Unlike these other AWE sites, M&C workers were faced with frequent blockages in drain lines 

that required subsurface excavations through concrete and contaminated soils and the close-in 

cleaning out of contaminated sediments and residues. Unlike other sites, M&C workers 

conducted much of their maintenance activities, for extended periods of time, in confined spaces, 

which included pits, trenches, and manholes. Unlike other sites, M&C maintenance excavations 

included former burial ground areas containing elevated subsurface contamination. 

M&C’s residual phase included maintenance activities that conform more to the “building 

renovation” scenario in NUREG/CR-5512 (NRC, 1992) than it does the “building occupancy” 

scenario that more typifies OTIB-0070 resuspension assumptions for other AWEs. The building 

renovation scenario assumes that following initial D&D, “surface and volume sources will be 

disturbed, creating loose contamination,” and that “this loose contamination can produce higher 

concentrations of radionuclides in the air or on surfaces than the levels in an undisturbed 

building” (NRC, 1992, p. 3.1). Under this scenario, primary internal exposure pathways include 

inhalation of airborne radioactive dust and inadvertent ingestion of loose surface contamination 

(NRC, 1992, p. 3.1). Conversely, the building occupancy scenario assumes that workers “occupy 

a commercial facility in a passive manner without deliberately disturbing surface sources of 

residual contamination” (NRC, 1992, p. 3.9). Under this scenario, potential pathways of internal 

exposure include inhalation of resuspended surface contamination and inadvertent ingestion of 

surface contamination (NRC, 1992, p. 3.9). For convenience, attachment 1 reproduces figures 

3.3 and 3.1 from NUREG/CR-5512 that illustrate the contrast between these two scenarios. 

The precedent for addressing a building renovation scenario can be found in the Linde Ceramics 

Plant SEC ER. As noted previously, NIOSH found in the Linde Ceramics SEC-00107 ER that it 

is “reasonable to assume that [Linde’s] renovation work could have resulted in elevated airborne 

radioactivity” (NIOSH, 2011b, p. 22), and that the internal dose for workers at the facility could 

be bounded with the highest air-monitoring data captured during jackhammering from earlier 

renovations, which could be assumed to be the maximum intake potential (NIOSH, 2020a, 

slide 6). 

During its final review of the Linde SEC ER, the Board questioned this bounding approach. 

While jackhammering may have represented the highest measured contamination level (2.3 times 

the maximum allowable concentration air) for workers conducting that renovation activity 

(ABRWH, 2011, p. 263), members of the Board questioned whether it was appropriate to apply 

it as a bounding internal dose to non-D&D workers throughout the entire site for an extended 

time period, in the absence of information about these other work activities and related 

exposures. As noted by the Board Chair at that time, “we may have a bounding dose, but is it a 

plausible bounding dose, given how little information we have and the fact that most of these 
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people probably weren’t engaged in the activity [jackhammering] that we have done the dose 

reconstruction for?” (ABRWH, 2011, p. 124). 

As given further elaboration in Board deliberations, the issue raised is where to “draw the line” 

for how expansively a maximized10 exposure estimate is applied facility-wide or site-wide as a 

bounding dose (ABRWH, 2011, p. 129). Another consideration raised was that while such a 

conservatively constructed exposure estimate (or source term activity level) may be bounding, 

can it be considered “sufficiently accurate” if applied too broadly, for too long a time frame 

(ABRWH, 2011, p. 135)? The Board ultimately voted to recommend an SEC class for the Linde 

renovation period. 

10 The term maximized is used here to connote an exposure pathway bounding approach wherein NIOSH has 

estimated “the maximum radiation dose that could have been incurred under plausible circumstances” (NIOSH, 

2020a, slide 17) applying conservative assumptions. Conservative assumptions applied at M&C include 95th 

percentile (subsurface, HVAC, roof and ceiling), 10-3 resuspension, 200 milligrams per cubic meter dust load 

(HVAC), the same person doing the job, and the most claimant-favorable solubility type (NIOSH, 2020a, slide 17). 

Assuming an extended renovation-like period during M&C’s residual phase, during which 

disruptive maintenance activities were conducted, the question for the work group is whether the 

proposed dose-bounding approaches would be appropriate in the same context. For Linde, while 

exposure bounding was proposed based on a high airborne level taken for jackhammering, the 

extension of that assumed bounding air concentration value to the balance of the site for an 

extended time period was deemed not appropriate by the Board in the absence of information for 

non-D&D worker activities and their exposures (NIOSH, 2020b). 

3.2.2 Bounding approaches for M&C

As with Linde, NIOSH determined that the OTIB-0070 resuspension model did not adequately 

address and bound all of the M&C worker activities during the residual period. As acknowledged 

by NIOSH, “The ER models resuspension (OTIB-0070) and does not specifically address 

potential exposures from digging, snaking/replacing clogged drain lines, or repurposing M&C 

equipment (e.g., removing and replacing mill units)” (DCAS, 2017, p. 1). These activities—

which also included performing utility installations in contaminated roof areas and rafters, 

HVAC maintenance, and welding preparation—involved workers typically performing intrusive 

work with elevated dust loading. Following interviews with M&C former workers of that period, 

NIOSH developed exposure-bounding models for each of these nonroutine pathways to identify 

maximum soil or air concentrations values, amplified by a conservative 95th percentile 

distribution in determining the bounding value. Extensive reviews have already taken place 

regarding these models between NIOSH and SC&A and before the work group. 

Putting aside the apparent health physics technical validity of the modeling calculations and their 

obvious conservatism, the questions before the work group should be the same as those debated 

for the Linde residual period: (1) Are such bounding formulations sufficiently accurate (i.e., do 

they adequately represent the exposure potential involved)? and (2) Is it plausible to back-apply 
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them to a broad M&C maintenance worker population for a long period of time when actual 

information about their work activities or conditions may be limited?11

11 The only definitive information available for the actual maintenance work involved are the recollections of 

former workers that, while helpful to describe the general nature of their work, do not substitute for the lack of 

actual job and task records, exposure monitoring records, contamination surveys, and incident reports.

As noted in the Board’s deliberations on the Linde residual period, the question of where to draw 

the line is a subjective one, weighing the precision (or accuracy) of the bounding assumption and 

data, and the plausibility of their application to the target worker population. Precision should be 

considered in the context of the relative dose levels involved (this is addressed in response to 

question 3 in section 3.3). For plausibility, its appropriateness should be corroborated by 

information available about the workers, the actual work performed, and their exposure potential. 

On this basis, the bounding exposure pathway models for M&C can be reviewed, as described in 

sections 3.2.2.1–3.2.2.6. 

3.2.2.1 Subsurface inside

NIOSH selected the highest Building 10 subsurface drain line sediment concentration of total 

uranium (measured from 20 samples taken in 1995 as part of 1996 remediation 

characterization12

12 Performed by Roy F. Weston, Inc., as a part of a characterization of Building 10 drain lines for remediation. 

(Weston, 1996). 

) and calculated a 95th percentile concentration of 6,887.84 pCi/g for bounding 

uranium in subsurface maintenance activities (NIOSH, 2018, p. 7). The use of this 95th 

percentile concentration acknowledges that “maintenance could have potentially removed 

sediments with the highest uranium concentration” in prior residual years (NIOSH, 2018, p. 7). 

NIOSH concludes that “the Priority-1 drain lines, worked on by M&C employees and removed 

by Weston, contained the highest subsurface radioactive material concentrations to which 

workers were exposed” (NIOSH, 2018, p. 6). This exposure pathway model assumes dust 

loading equal to the 95th percentile of the Mound project air sampling and a worker occupancy 

of 2 months conducting this work. Subsurface activities included (SC&A, 2021a): 

• 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 

The appropriateness of this bounding assumption can be judged on whether it is sufficiently 

accurate and plausible to select a high sediment reading in 1995, amplified by a 95th percentile 

concentration value, to characterize all inside subsurface exposures to maintenance workers for 

the residual period timeframe (1968–1997). While the stated purpose of the remediation survey 

was to “assess the potential for inadvertent exposures to non-radiological workers performing 

routine drainage system maintenance” (Weston, 1996, p. 2), there are no additional data for 

M&C drain pipe sediment readings for residual years prior to 1995. 
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Former remediation workers involved with excavation and extraction at that time noted that 

extracted drain line residues included “metal chips and fines, and sludge” (NIOSH, 2017c, p. 10) 

and a “five-inch piece of an encapsulated fuel rod” (NIOSH, 2017c, p. 10), but they could not 

account for the “degree of blockage” over time13 (NIOSH, 2017e, p. 7) or actual history of 

sediment (or residue) activity levels. Elevated sediment concentrations were found in 

remediation surveys conducted on Priority-1 drain lines, with a “worst-case subsurface 

contamination” level of 53,000 pCi/g being measured in 1995 (NIOSH, 2018, p. 11). 

13 The 1995 remedial characterization surveys of the Priority-1 lines reported that 50–90 percent blockage from 

sediment and residue was found (Weston, 1996, p. 5).

Given the likelihood of such “hot spots” being present in historic pipeline sediments, NIOSH 

sought to corroborate the conservatism of its bounding source term by comparing M&C’s 

experience with six other AWE sites with documented drain line sediment sampling.14 That 

survey showed that “the maximum specific activity was at least an order of magnitude larger 

than the majority of other samples” which, in NIOSH’s belief, indicates that sporadic hot spots 

would not be unexpected at M&C and that there would not be a significant difference in the 

“mechanism of deposition and accumulation of sediment and pipe scale at M&C when compared 

to other sites” (NIOSH, 2021a, p. 6). NIOSH further believes this pattern shows that while there 

is a potential for such hot spots, “there is no indication of systemic conditions at these hot spot 

levels” (NIOSH, 2021b, slide 10). 

14 NIOSH reviewed Vitro, Bridgeport, Horizons, Peek Street, Mallinckrodt, and DeSoto (NIOSH, 2020a). 

The absence of actual records of historic drain pipe sediment activity levels at M&C before 

1995, coupled with accounts of frequent blockages involving contaminated sediments, rags, 

artifacts, and even a discarded fuel rod piece15 during the 27 years prior to D&D sampling, raises 

questions about the appropriateness of NIOSH’s bounding assumptions. While the presence of 

uranium and thorium in effluents are common attributes of the AWEs surveyed, these AWEs 

(and, notably, M&C) each had its own unique operations, equipment, and facility engineering; 

radiological, chemical, and mechanical processes; drain pipe composition, layout, and 

configurations; and effluent handling practices. Likewise, the comparative measurements taken 

at the six AWEs would have been influenced by the specific sampling method used at each site, 

location of the sampling, and the type of sample taken (e.g., dirt samples from floor drains, 

sediment samples from piping, average of aliquot samples taken from drains). All of these

variables would have influenced the systemic amount of, and contamination levels in, residues, 

sediments, and sludge. 

15 The accumulation of various artifacts in the M&C drain lines can be attributed to missing grates on the drains, 

which allowed production residues and items to go down them, contributing to blockages that were apparently 

aggravated by the presence of vegetable-based oils used in production that coagulated in the drain lines (NIOSH, 

2017i, pp. 6–8).

Would it be possible, if not likely, that the unique combination of covered and uncovered 

operations, conditions, configuration, and practices at M&C would have led to the generation 

and discharge of similarly unique radiologically contaminated effluents to its drain system? For 

example, the M&C Wire Department in Building 10 commonly used a vegetable-based mineral 

oil for drawing wire, which was known to coagulate upon discharge to the drainage system and 
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would frequently “plug up the drains” (NIOSH, 2017i, p. 6). Would it not be as likely that the 

regular release of a coagulant to the drain line system during active Building 10 operations 

(through 1981) would have led to more frequent and substantial blockages, perhaps involving 

higher concentrations of uranium and thorium as a function of the binding properties of the 

coagulant oil and other residues? While most of the drain line sediment samples taken at the 

surveyed AWEs were less than the 95th percentile (6,887 pCi/g) of the M&C sampling in 1995, 

would this necessarily be so with earlier M&C sediment hot spots?16

16 Regarding work group questions raised related to possible material dilution and extraction inside drain pipes

over time, 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” (SC&A, 2021a, p. 14). This 

conclusion, while reasonable, cannot be confirmed by available survey data and does not obviate the need to address 

the broader concern over the accuracy and plausibility of such bounding formulations in general, a concern that is 

addressed in section 3.3.

Another historical aspect of M&C drain lines is the accumulation of contaminant scale that has 

plated out inside the piping. This scaling was found in at least one instance at M&C to exceed 

1,000,000 dpm/100 cm2

 in a 4-inch mainline drain that was being cut and removed (NIOSH, 

2021a, p. 7). While such pipe scale has been identified at other AWE sites, M&C maintenance 

workers frequently cut, repaired, replaced, and cleaned out such piping during the residual years 

using power tools such as saws, drills, grinders, and powered snakes, as well as cutting torches. 

As noted by DOE in its hazard assessment of the Bridgeport Brass AWE, “the residual uranium 

could eventually be released . . . through intrusive work activities such as pipe cutting and 

removal” (DOE, 1996, PDF p. 11), and that “it is possible that under certain conditions (such as 

cutting through a steel pipe with a cutting torch) surface activity attached to the steel could be 

released with the steel particles” (DOE, 1996, PDF p. 48). Such work procedures would have 

generated fine airborne aerosols, including airborne contamination from the plated material, 

which would have been concentrated by the confined space (i.e., trenches, pits) atmosphere 

within which they were working. While the million-count reading represents a high activity 

level, contaminated scale elsewhere in M&C’s extensive drain line network could have had 

similar, if not higher, levels over the residual years. There is no available information to address 

this question at M&C. This exposure pathway is not addressed by the current models. 

Beyond these unique considerations, M&C maintenance workers regularly performed 

construction-like excavations, involving sawing, drilling, and jackhammering concrete floor 

slabs and subsurface digging, in order to install or modify equipment, and to access power 

conduits, airlines, and gas lines, as well as drain lines, all of which then required the 

aforementioned cutting, sawing, and drilling. While the 1995 drain line sediment reading is a 

high concentration level, can it be applied as a bounding exposure for unrelated inside subsurface 

work (i.e., non-drain line cleaning) for which little, if any, information is available and for which 

confined space atmospheres were involved? Does the Linde SEC precedent apply here? 

NIOSH acknowledges that M&C subsurface work has been described as “very intrusive and 

included accessing contaminated materials that had accumulated for decades without work 

controls to mitigate the hazard” (NIOSH, 2018, p. 8). Accordingly, NIOSH found that the default 

dust-loading value of 100 μg/m3 from OTIB-0070 and NUREG/CR-5512 was not appropriate for 

M&C subsurface work where “workers actively disturbed the contaminated material during 
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episodic responses throughout a given year” (NIOSH, 2018, p. 8). An increase in the dust 

loading factor for M&C subsurface activities was proposed based on dust-loading data from the 

Mound Plant Canal Clean-up Project (hereafter, the “Mound project”). The use of these

additional (called “surrogate” by NIOSH (2018), p. 9) data is reviewed in section 3.3.1, with the 

concern being that it apparently lacks treatment of confined space considerations, which directly 

impacts resuspension and dust loading, and its applicability to M&C. 

The former worker cited by NIOSH in its maintenance worker exposure model (NIOSH, 2018, 

p. 5), who stated that Exhibit 1 of the Weston 1996 characterization survey represented 

conditions prior to D&D activities, and therefore, offered “good insight into site conditions 

during the Residual Period and to which members of the class of employees subject to this SEC 

Petition were exposed” (Affidavit, 2016, p. 3), did not (and could not) account for whether 

higher activity sediments could have been handled at some earlier time by M&C maintenance 

workers performing cleanouts for the previous 27 years. 

The former 1990s worker quoted by NIOSH (2018, p. 6) as referring to the drains in Building 10 

as containing the “mother lode” of radioactive contamination (NIOSH, 2017e, p. 8) was likely 

correct about the significance of the contamination level involved in 1995. However, this worker 

would not have been able to distinguish which sediments and which jobs over time would have 

had the highest contamination and exposure potential for workers cleaning out or replacing 

earlier drain lines. Given the active radiological operations in Building 10 through 1981, it is just 

as likely that more frequent drain line blockages occurred in the earlier years involving higher 

activity sediment due to increased effluent volume related to operations, compounded by 

frequent discharge of the vegetable-based mineral oil that was implicated in the pipe clogging, as 

well as ongoing maintenance and cleanup of equipment. 

Adding to the inherent uncertainty of the back application of D&D era data is the disparity 

between the radiological control program that was administered for the remedial contractors 

compared with that of M&C maintenance workers. For D&D activities, a comprehensive 

radiation safety program was in place, defined by detailed procedures, facilitated by worker 

knowledge and training, overseen by experienced health physicists, and regulated by the NRC. 

For M&C maintenance activities, workers were unaware of the radiological contamination, with 

no radiological control program implemented, no apparent health physicist presence, and no 

radiological control oversight.17 Under such circumstances, M&C maintenance workers would 

have been more likely to have been exposed to elevated radioactive contamination during the 

course of their routine and nonroutine work, and no record of that exposure (e.g., source, 

contamination level, and exposure) would be available. 

17 The only relevant safety document was the M&C Health and Safety Manual, which former workers were not 

familiar with and apparently did not follow (refer to section 3.3.2). A fellow worker was identified by some 

interviewees as having radiological control responsibilities, but there is no evidence of radiological surveillance, 

worker monitoring, or oversight of work activities during the residual period (outside of D&D), other than one or 

two isolated instances (e.g., when a portable Geiger-Muller counter was borrowed to conduct a spot survey). 

Relevant to this question, NIOSH did point out that while the 53,000 pCi/g uranium sediment 

measurement in the Priority-1 drain line was the “worst-case subsurface contamination,” workers 

conducting the remedial work on these and other drain lines in 1995–1996 were not required to 
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wear respiratory protection (NIOSH, 2018, p.11). However, as emphasized by one former D&D 

worker, remedial work on drain pipes differed markedly from the corresponding work M&C 

maintenance workers performed; the former removed and disposed of the pipe, while the latter 

also repaired and cleaned out the pipe (NIOSH, 2017d, p. 6), with the degree of intrusiveness and 

potential exposure much greater for M&C maintenance workers. The D&D work was performed 

under strict monitoring and control procedures, overseen by a health physicist; the M&C 

maintenance work was conducted with none of that. 

While there are precedents for back-applying conservative D&D measurements for AWE 

residual periods (e.g., particulates in Linde utility tunnels and intakes at Chapman Valve), that 

modeling did not assume intrusive activities occurred or that those activities could involve higher 

exposures due to elevated exposure conditions, uncertain facility activities, or unknown 

contamination sources. The sediment readings taken in 1995 from a Priority-1 pipe obviously 

had a high uranium concentration, but is it the bounding case for all inside subsurface activities 

for the previous 27 years of the residual period? 

Finding 1. The back application of a high 1995 sediment survey result to bound inside 

subsurface activities is not adequately supported by information for M&C worker 

activities from the earlier residual time period. 

3.2.2.2 Subsurface areas outside

NIOSH used characterization data for outside subsurface areas “surrounding Building 10, in the 

former Burial Area, the Metals Recovery Area, the Building 11 Stockade Area, the Building 11 

Railroad Spur Area, and the Building 12 West and South Lawn Areas” (NIOSH, 2018, p. 7), 

with 2,391 soil samples collected in 1984 by Oak Ridge Associated Universities (ORAU) 

(Sowell, 1985) and in 1992 by Creative Pollution Solutions, Inc. (CPS, 1992) before remediation

(including 1994 remedial survey samples for areas outside of the Burial Area). Of these samples, 

1,629 were analyzed for gross alpha, and the remaining 762 were analyzed for isotopic uranium 

and thorium (NIOSH, 2018). To develop this model, NIOSH selected “594 lines of burial-site 

data” from the 1985 ORAU report (Sowell, 1985) and “blended them with data from other 

outside areas” to develop a 2,391-line spreadsheet that forms the basis of the exposure 

determination (NIOSH, 2021c, p. 2). 

NIOSH calculated the 95th percentile uranium soil concentrations for uranium and thorium and 

arrived at 118 pCi/g and 88 pCi/g, respectively, for the bounding subsurface soil concentrations. 

NIOSH acknowledges that outside maintenance work performed during the residual period 

(notably the air-line installation in 1980) could have removed radioactive sediments, thereby 

diminishing these later source term estimates. The calculated 95th percentile concentrations 

address this potential discrepancy (NIOSH, 2021a, p. 12). 

The appropriateness of this bounding assumption can be judged on whether (1) the outside 

maintenance excavations that took place at the M&C site prior to 1984 served to substantially 

spread, dilute, and otherwise alter the levels and contours of elevated subsurface contamination, 

and (2) whether, in the absence of actual measurements made of M&C site subsurface 

contamination prior to the 1984 ORAU and 1992 CPS surveys, whether these bounding values 

are sufficiently accurate, whether the 95th percentile value is sufficiently conservative, and 
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whether it is plausible to back-apply these values to the many and diverse maintenance worker 

excavation activities during the earlier years of the residual period for which records are lacking.

There are accounts of artifacts, residues, and soils with elevated contamination that were 

encountered at the radioactive burial ground during installation of an air-line in 1980 and, 

according to former worker interviews, by other maintenance activities.18

18 The M&C burial ground is located between Buildings 11 and 12, with burials taking place in 1958–1961 (and 

possibly earlier in the 1950s). As described in site documents, “uranium - and thorium - contaminated 

noncombustible scrap material and machinery were collected in 55-gallon steel drums and disposed of through 

authorized agencies, or were buried on-site in compliance with 10CFR20.304” (Sowell, 1985, p. 1; NIOSH, 2017j, 

pp. 16-17).

This installation 

required a trench to be dug through a portion of the burial ground. NIOSH believes the exposure 

of involved maintenance workers would not have been significant because, if they were, “the 

NRC would have directed M&C to use radiological controls, and reports of this work would be 

available similarly as they are for the other remediation tasks” (NIOSH, 2021c, p. 4). However, 

in 1980, information was limited to the types of contaminated waste material disposed of and the 

location, area, and depth of the burial site. It would seem that neither M&C nor NRC could have 

known about the configuration of subsurface uranium and thorium contaminants and their 

activity levels within the burial site and the attendant potential exposure, information that would 

not become available until the 1984 ORAU and 1992 CPS surveys.19

19 Following the 1984 survey, the NRC noted that “residual radioactive contamination remained in the burial area 

east of Building 11 and west of the recently constructed Building 12” (NRC, 1997a, p. 3). In 1990, the NRC listed 

the M&C site on the NRC’s nationwide Site Decommissioning Management Plan (SDMP) because “on-site 

disposals [of radioactive material] had been made but the location and extent of the disposals were not well-known,” 

and the extent and location of soil contamination on the site was also not well-known (NRC, 1997b, p. 2). The site 

was not removed from the SDMP until 1997, when a confirmatory survey showed no accessible contamination 

above the NRC criterion for unrestricted release (NRC, 1997a, pp. 4–5). 

NIOSH construes the lack 

of NRC regulatory direction to signify that the reported “elevated levels” were merely “above 

background, but less than release criteria (30 pCi/g),” and that “information related to this task 

supports NIOSH’s outside subsurface model, in that the 95th percentile contamination level 

NIOSH applied (118 pCi/g) is approximately four times higher than the contamination level 

these workers experienced” (i.e., 30 pCi/g) (NIOSH, 2021c, p. 4), but without giving any 

apparent substantiation beyond inferring how NRC staff would have perceived the risk and what 

action they would or would not have taken. 

In fact, these later D&D characterization surveys would show the following: 

• The ORAU (Sowell, 1985) survey results for several bore holes within the burial area 

found elevated concentrations of uranium (U)-235 ranging from 6.03 pCi/g to 20.6 pCi/g, 

and elevated concentrations of U-238 ranging from 5.48 pCi/g to 680 pCi/g (CPS, 1993, 

p. 5). 

• Survey results from the CPS (1992) pilot study, involving four trenches dug in the burial 

area, found that the concentration of total uranium in soil samples ranged from 8.22 to 

3,349 pCi/g total uranium (CPS, 1993, p. 6). 
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Upon initial remedial excavation by CPS at the burial site location where the most elevated 

subsurface sample had been previously identified:

a large pocket of debris [was identified] at a depth of approximately 4 - 6 feet. 

Some of the debris indicated surface readings with a pancake [Geiger-Muller] 

detector of greater than 20,000 counts per minute (cpm). The surrounding soil had 

concentrations from 100 pCi/g to > 5000 pCi/g total uranium based on gross alpha 

screening results.

The debris consisted of laboratory bottles, graphite crucibles, extruded uranium/ 

zirconium tubes, mounted uranium samples, 55 gallon drums, partial mock fuel 

elements, metal fines, uranium ingots, ductwork, uranium/aluminum plates, etc. 

[CPS, 1993, p. 12] 

Texas Instruments, Inc. (TI) concluded that, “since the levels of soil contamination and debris 

were higher than expected, an adjustment in the remediation approach was implemented” (CPS, 

1993, p. 13). 

The 1992 CPS radiological characterization survey found that “contaminants may have been 

disturbed and distributed over an unspecified area” (CPS 1992, p. 3). This survey concluded: 

This process or processes have left some areas with isolated elevated 

concentrations of Uranium and a distribution of other areas with less, if any, 

contamination. This phenomenon also helps explain the presence of contaminants, 

at nonuniform distributed concentrations, at varying depths. [CPS 1992, p. 3] 

Following completion of the 1992 remediation and survey of the burial area, TI identified soil 

contamination in three locations within the Metals Recovery Area (NRC, 1997a), adjacent to 

Building 5. This area was formerly involved with waste handling and included an open-air 

incinerator and liquid waste evaporator. The highest concentration of uranium identified in 

subsurface soil characterization and remediation sampling at that location was found to be 

17,000 pCi/g. Remediation activities in this area were conducted in April–November 1994. 

While NIOSH’s OTIB-0070 guidance provides a basis for mass-based assignments to calculate 

air concentrations, given the above sample data, when combined with appropriate dust loading 

factors, two issues present themselves: 

1. uncertainties surrounding the exposure potential of maintenance workers performing 

excavations in these contaminated soils

2. the inapplicability of the surrogate dust loading factor, a concern highlighted in 

section 3.3.1 of this review 

For the first issue, with the assumption of a geometric mean (GM) and geometric standard 

deviation (GSD) based on 2,391 sitewide soil samples, the question is whether these averaged 

values would adequately reflect the elevated subsurface soil concentrations to which a worker 

may be exposed if that worker had been excavating a hot spot, such as the waste burial site or 

Metals Recovery Area. Unlike the modeling approach taken for the subsurface inside, the outside 
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bounding soil concentration is not based on the 95th percentile of the highest potential 

concentration (i.e., sampling of Priority-1 drain lines), but that of the GM and GSD of a 

“blended” sampling of affected locations (NIOSH, 2021c, p. 2). NIOSH indicates that it has 

“reviewed the entire outside subsurface model data to determine if the burial ground samples are 

significantly different from the rest of the samples” and “found all of the outside areas’ data were 

consistent, making sense because the site grading . . . in 1980 was responsible for much of the 

contamination on the other parts of the site” (NIOSH, 2021c, p. 2). Of the two identified burial 

area disturbances (1968 and 1980), however, NIOSH indicates that the “site grading [in 1968] 

was the only major disturbance and was responsible for many contamination finds on other parts 

of the site”20 (NIOSH, 2021c, p. 4). 

20 These two statements appear contradictory; based on other NIOSH and SC&A findings, the second cited 

statement (for 1968) is the correct one.

However, for the burial site and Metals Recovery Area, uranium soil concentrations in excess of 

5,000 pCi/g and 17,000 pCi/g, respectively, were measured in later remedial subsurface surveys 

(1992–1994). From its subsurface characterization survey, CPS found the “presence of 

contaminants, at nonuniform distributed concentrations, at varying depths” (CPS, 1992, p. 3; 

emphasis added), meaning that the contaminants were not homogenously distributed by depth or 

area location. CPS concluded that this phenomenon was due to earlier landscaping processes 

(e.g., grading) that “left some areas with isolated elevated concentrations of Uranium and a 

distribution of other areas with less, if any, contamination” (CPS, 1992, p. 3). 

Trenching by a maintenance worker within one of these isolated hot spot locations could 

conceivably lead to exposure to uranium and thorium at levels higher than the 95th percentile 

concentration derived from the sitewide GM and GSD based on the blended 2,391 samples 

(notwithstanding that some samples from these locations were included). There are documented 

accounts by former maintenance workers of performing at least two excavations within the burial 

area, installing a compressed airline in one case (NIOSH, 2021c, p. 3) and an electrical conduit 

in another (ABRWH, 2018, pp. 124–126). There are accounts by workers that adjacent to 

Buildings 10, 11 and 12, they “worked well below grade on all manner of piping,” including the 

former outdoor incinerator area where they encountered “a lot of burnt black plastic and metals 

mixed with soil, and even the soil was blackened” (NIOSH, 2017c, p. 8). However, there is no 

further information available to account for where and how workers conducted what were likely 

other excavations in the burial area during the residual period to perform routine maintenance on 

the various gas lines, water main, communication cables, and other airlines and electrical 

conduits that crisscrossed near or within that area (CPS, 1993, p. 3). 

While the combined sampling data from the ORAU and CPS surveys can be said to be 

representative of the M&C site, can this “blended” model accommodate disparate concentrations 

of such elevated uranium concentrations at varying locations and depths? It is not apparent that 

the burial ground sample data would be “consistent” with other sampling locations at the M&C 

site (NIOSH 2021c, p. 2) in the face of the elevated subsurface concentrations identified by CPS. 

It is also not clear how the 95th percentile distribution of ORAU/CPS survey data can be applied 

as bounding for burial area excavations having such hot spot levels, when NIOSH acknowledges 
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that the “Sowell burial data contributes a small amount of data to one of our six exposure 

models” (NIOSH, 2021c, p. 2). 

For the second issue, the dust loading in an outside subsurface trench or pit would be likely 

magnified by the confined space atmosphere involved—an issue made more uncertain by the 

lack of site-specific data and the contribution of power tool-generated aerosols. The question of 

an appropriate and accurate dust loading factor remains an open issue. 

Observation 1. The use of blended D&D characterization survey data from 1984 and 1992 

to support a bounding dose for outside subsurface activities may not be necessarily 

bounding for work in nonuniform soil contamination, given the presence of hot spots 

that existed during the residual period at M&C.

3.2.2.3 Roof and overhead area

NIOSH used direct contamination survey measurements of the Building 10 roof and overhead 

environment based on 285 grid average alpha-contamination survey results taken in 1982. The 

95th percentile of these results is 89.9 dpm/100 cm2 with 10 percent of the results associated 

with removable activity per OTIB-0070, providing for a bounding removable contamination 

activity level of 8.99 dpm/100 cm2 (NIOSH, 2021b, slides 21–22). Given the direct 

measurements involved and their scope (which included undisturbed locations) and fit to the 

exposure potential (removable contamination), location (rafters), and timeframe, this exposure 

model and bounding calculation appear appropriate for their intended purpose. They were further 

validated by SC&A (2021a, pp. 20–22) in terms of accuracy and plausible application.

3.2.2.4 Welding operations

For welding operations, NIOSH assumed 100 percent of the gross alpha contamination activity 

involved (89.9 dpm/100 cm2

) is resuspended and assigned a conservatism factor of 10-3 to this 

95th percentile contamination level to account for the weld-preparation activity generating the 

highest airborne concentration during welding work. This results in a bounding air concentration 

activity level of 8.99 dpm/m3 for 48 hours per year (NIOSH, 2021a, p. 13). The conservative air 

concentration level provided in this model does not appear to be founded on actual results or 

experience at M&C and does not address resuspension in a confined space atmosphere. Welding 

did take place in some trench and pit venues, although it appears the referenced welding 

operations more often took place in open areas, such as the roof and in the rafters. However, the 

specificity of this maximizing air concentration level’s application to the welding operations 

employed at M&C supports its plausibility. 

SC&A’s review of the exposure pathway models noted that “SC&A raised a concern (finding 2) 

in its 2019 (SC&A, [2019]) and 2020 (SC&A, [2020]) reviews of welding and thorium activities 

that a resuspension factor of 10-3/m may not be adequate to represent the dust generated by 

grinding and wire brushing to prepare a surface for welding” (SC&A, 2021a, pp. 23–24). The 

M&C work group members repeated this concern during their meeting on September 2, 2020 

(ABRWH, 2020b). While this issue has not been resolved, SC&A agrees that this is a site profile

issue rather than an SEC issue, as does NIOSH (NIOSH, 2022a, p. 4). 
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3.2.2.5 HVAC maintenance

NIOSH adapted portions of a model developed by SC&A, with a geometric mean of 

12.3 dpm/100 cm2 calculated from 7,765 gross alpha swipe data collected at the end of AWE 

operations in 1966 and 1968. Using this surface contamination data and OTIB-0070, the gross 

alpha airborne concentration in Building 10 was estimated to be 0.0123 dpm/m3

. With an 

assumed dust loading providing a specific activity of airborne dust of 1.23E-4 dpm/μg, a 

bounding gross alpha air concentration of 12.3 dpm/m3 was calculated for the HVAC 

maintenance activity (NIOSH, 2021a, p. 13). In 1982–1983, the NRC made 938 direct alpha, 

beta-gamma, and gamma measurements in Building 10 outside of HFIR, which, when compared 

with the late operations (1966, 1968) swipe samples (assuming 10 percent of the direct measured 

activity was removable), showed comparability. This was found likewise with 81 swipe samples 

taken by the NRC at the time. Therefore, 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” (SC&A, 2021a, p. 25). 

3.2.2.6 Remaining exposures

As clarified in SC&A’s exposure pathway evaluation (SC&A, 2021a, p. 26):

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 “non-maintenance,” 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.

For remaining exposures, NIOSH applies a bounding gross alpha airborne concentration for 

Building 10 (0.0123 dpm/m3

) with OTIB-0070 source term depletion adjustments to determine 

non-maintenance worker exposure rates throughout the residual period (NIOSH, 2021b, 

slide 27). SC&A compared this bounding approach to the same 1982–1983 direct radiation 

surveys of floors inside of Building 10 taken by the NRC inspectors and determined that the 

resulting exposure to natural uranium was below background and would be considered de 

minimis for purposes of dose reconstruction (SC&A, 2021a, pp. 27–28). 

3.3 Line of inquiry 3 

Are the available source term, survey data, and other information applied by NIOSH to 

support its dose bounding methods sufficiently accurate and plausibly applied? 

A guiding principle NIOSH follows for addressing the “uncertainty around the work performed” 

or the “complete understanding of the work performed (e.g., one person doing all the 

maintenance work)” is that it is “NOT an issue when the bounding doses are very low, and 

specifically, during AWE residual periods such as at M&C” (NIOSH, 2020a, slide 14). To 

support the validity of its approach, NIOSH cites comments made by the former Board Chair:

“with the residual period, we are going to have lots of situations — we have 

already had them — where we don’t have very much information on the activities 
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and the ability, usually very little sampling data. We are going to be using 

OTIB-70 a lot in these situations without knowing much about what individuals 

did on the site. [ABRWH, 2011, p. 144] 

If you look back at all of our decisions for a period of time — and I think it also 

goes to our evaluation of dose reconstruction. If the absolute value of the 

exposure is relatively low, then we’re willing to accept more variability in the 

dose if it’s being calculated for an individual. And if the exposure’s absolute 

values are higher, then we’re looking for a more accurate dose reconstruction 

method. [ABRWH, 2013, p. 19] 

The first (2011) quote by the former Chair came from an extended discussion about the Linde 

Ceramics Plant residual period. It also included the discussion cited earlier in this report

expressing concerns about the plausibility of applying a conservatively high air concentration to 

all of a site’s workers based on a specific jackhammering activity. As the Chair stressed in that 

discussion, when information is lacking for affected worker populations, the application of 

generalized bounding doses, no matter how maximized, may not be appropriate (ABRWH, 2011, 

pp. 121–123). As the Chair explained:

To me, the lack of information — and we have no sampling data during this 

renovation time period. We have very little information on what was done at the 

site during this time period and who was involved, and how many people were 

involved, that it seems to me that [it] is just as appropriate to be designated a 

Special Exposure Cohort. 

I think putting it into our terms, we may have a bounding dose, but is it a 

plausible bounding dose, given how little information we have and the fact that 

most of these people probably weren’t engaged in the activity that we have done 

the dose reconstruction for? [ABRWH, 2011, pp. 123–124] 

NIOSH’s second cited (2013) quote was part of an extended discussion within the SEC work 

group about concepts and experience related to the issue of technical accuracy and the 

plausibility of applying upper bounds to the exposure of worker populations. As the former Chair 

noted in that discussion, “We all know we can upper-bound anything. So this always comes out 

with sort of what’s the plausibility of that” (ABRWH, 2013, p. 24). He elaborated later on this 

point: 

I think it's sort of a Linde example that I was giving and it really maybe 

convoluted different concepts. 

But we saw two issues. One is . . . as long we can do it in upper bound and that's a 

plausible upper bound for the highest exposed individuals, then that method was 

okay, and we didn't really look at how that upper bound was — the population it 

was being used for. And so it may be a plausible upper bound for a certain group, 

but it really may not be a sufficiently accurate plausible upper bound for the 

others in that same population. [ABRWH, 2013, pp. 37–38] 
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The preceding suggests that while less precision or accuracy could be tolerated if the exposure of 

a worker cohort is relatively low, the use of a high exposure or concentration value based on a 

set of specific workplace data to bound or represent that of other workers in a facility or on a site, 

particularly over a lengthy time period, would not be appropriate if their exposure potential could 

be higher, work conditions were different, or if there is lack of information upon which to make 

that judgment. 

Regarding conservatism, while any measurement can be made extremely conservative by the 

multiple layering of favorable assumptions and statistical 95th percentile values, the Board’s 

original question remains: Where do we draw the line with the application of bounding values? 

As pointed out during the Board’s Linde review, if “carried to an extreme, we could take any site

. . . and we could come up with what we think is the highest possible exposure at that site that 

would occur, and that would be bounding, and apply that to everybody that ever worked at the 

site” (ABRWH, 2011, p. 129). However, the essential questions, as the former Board Chair put 

it, are “is that a plausible bound? And, then, who are we trying to characterize?” (ABRWH, 

2011, p. 129). 

Various means of supporting or corroborating the accuracy, validity, and representativeness of 

bounding analyses were presented by NIOSH during work group discussions. Sections 3.3.1 and 

3.3.2 summarize and assess two of the key means. 

3.3.1 Surrogate data (Mound Plant dust loading)

NIOSH acknowledged that the default dust-loading value of 100 μg/m3 suggested in OTIB-0070 

and NUREG/CR-5512, which was intended for a screening analysis for a long-term average, 

would not be appropriate for the intrusive subsurface work that former M&C workers described.

Instead, a dust-loading factor determined during excavation at the Mound Plant was applied as a 

surrogate21 value to provide a corroborating basis for increasing the resuspension factor at M&C 

(NIOSH, 2018, p. 8). As described by NIOSH in its 2018 white paper on the M&C maintenance 

worker exposure model, 294 hi-volume air samples were taken at backhoe excavation activities 

at Mound in 1997, with air-sample collection media weighed before and after taking each sample 

to determine their dust loading in grams (NIOSH, 2018, p. 8). NIOSH compared the Mound 

project with the five criteria listed in section 3 of OCAS-IG-004, “The Use of Data from Other 

Facilities in the Completion of Dose Reconstructions Under the Energy Employees Occupational 

Illness Compensation Program Act” (NIOSH, 2008a), to describe how that project satisfies these 

criteria for the use of dust loading values from Mound as surrogate data for use at M&C 

(NIOSH, 2018, pp. 9–10). NIOSH found that each of these criteria were satisfied.

21 The term surrogate is used here for consistency, given its use by NIOSH in earlier work group discussions. It is 

understood that NIOSH has since “determined the data should be classified as hierarchy #4 data in accordance with 

OCAS-IG-004” (NIOSH, 2020d, p. 8). That guide indicates the use of this categorization is appropriate if “source 

term and process information (hierarchy #4) for a particular facility need to be supplemented to adequately 

characterize the workplace exposure conditions, it may be necessary to rely on data from another facility to 

completely develop an exposure model” (NIOSH, 2008a, p. 4). However, the issues raised in this section remain the 

same in terms of the appropriateness of applying the Mound data to M&C in this manner.
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SC&A reviewed NIOSH’s surrogate use of the Mound data in its October 2021 report, “SC&A 

Commentary on NIOSH’s Approach to Quantifying Outdoor and Indoor Airborne Dust 

Loadings” (SC&A, 2021b). That review found that “the Mound data and the data for indoor and 

outdoor excavation dust loadings described in section 3 can be considered a type of surrogate 

data, the use of which is governed by the Board’s surrogate data criteria (ABRWH, 2010)” 

(SC&A, 2021b, p. 11). The review of this approach included its application of dust loading data, 

how it satisfies the Board’s surrogate data policy, and supporting scientific literature. SC&A 

concluded that “NIOSH’s adoption of 212 μg/m3 for estimating respirable outdoor dust loading 

during excavation activities is reasonable but not necessarily bounding” (SC&A, 2021b, p. 20). 

For four of the five Advisory Board surrogate data criteria22

22 As noted by SC&A (2021b), the Board’s surrogate criteria are somewhat different than the surrogate criteria in 

OCAS-IG-004 (NIOSH, 2008), which NIOSH (2018) used to assess the applicability of the data to M&C.

—hierarchy of data, exclusivity 

requirements, temporal considerations, and scientific plausibility—as applied to use of the 

Mound project data, it is clear that the criteria are satisfied, as noted by SC&A in its 2021 review 

(SC&A, 2021b). However, for site and process similarities, this reviewer shares the reservations 

expressed by SC&A’s 2021 review.23

23 SC&A found that “the surrogate data criteria regarding outdoor and indoor dust loading during excavation 

activities certainly apply to these same activities as those at M&C and can also be considered generically applicable 

to outdoor and indoor excavation activities. However, for both indoor and outdoor excavation activities, there are 

likely many site-specific characteristics that can uniquely affect dust loadings, including the characteristics of the 

soil and the proximity of workers to the excavation activities. There is very little that can be done to accommodate 

these types of site-specific characteristics, except to use a degree of professional judgement that would tend to place 

an upper bound on the dust loading” (SC&A, 2021b, p. 11). 

 For example, in terms of specific site characteristics for 

M&C, it is not apparent how the Mound project addressed considerations related to resuspension 

or dust loading in a confined space, such as the various manholes, trenches, pits, and vault spaces 

at M&C in which maintenance workers actively worked. “Confined space” is defined as “a space 

which, by design, has limited openings for entry and exit, unfavorable natural ventilation which 

could contain or produce dangerous air contaminants, and which is not intended for continuous 

worker occupancy” (NIOSH, 2022b). Because air may not move in or out of confined spaces 

freely, gases and particulates can concentrate to higher levels than in an unconfined environment.

For example, in addition to the initial excavation operations using backhoes, concrete saws, and 

jackhammers, M&C maintenance workers would have entered such subsurface excavations and 

other confined spaces to perform hand digging and scraping; to remove soil, concrete, and other 

debris; to operate hand saws, grinders, and drills to perform penetrations and to cut lines; to pull, 

cut, clean out, and repair drain and air lines; and to clean up afterwards. Beyond the resuspension 

of dust experienced from backhoe, jackhammering, or comparable excavation, the elevated dust 

loading is associated with not only intrusive work in a confined space but also the actual 

generation of fine aerosols and particulates through the sawing, grinding, drilling, and welding 

that were a part of the work being conducted. In essence, the contrast is between airborne dust 

levels during backhoe operations (Mound project), and those experienced inside of a tight and 

enclosed pit, hole, or ditch with related sawing, grinding, drilling, hand digging, and pipe 

cleaning (M&C). A confounding factor is the uncertainty and lack of site-specific information 
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about the configuration, condition, activity, location, and timeframe of indoor and outside 

subsurface work that M&C workers performed during the residual period.

For M&C, it was not uncommon to be working in a trench doing routine utility repairs or pipe 

cleanouts for days and up to a week (DCAS, 2017, pp. 1–2), and for electrical, equipment, and 

tank installations, this could be longer. One installation project in Building 10 involved cutting 

out an existing drain line and installing new equipment, piping, and large tanks, necessitating a 

trench 100 feet long, with a depth of 8–10 feet in places, that was worked in for 6 months in 

1983-1984 (NIOSH, 2017i, p. 12). 

The lack of natural ventilation in a confined space is demonstrable and has a direct impact on 

resuspension and dust loading. To illustrate, while NIOSH applies a standard 10-6 m-1

resuspension factor in its OTIB-0070 evaluation, the International Atomic Energy Agency 

(IAEA) guidelines for “Radiological Aspects of Non-fixed Contamination of Packages and 

Conveyances” recommends a resuspension factor of 4×10-5 m-1 for dusty operations in confined 

spaces (IAEA, 2005, p. 11).24

24 IAEA-TECDOC-1449 references the Fairbairn model, which applies other parameters for modeling airborne 

contaminants. It is unclear how these parameters relate to similar OTIB-0070 considerations, although it does appear 

more conservative regarding confined spaces.

 The U.S. Department of Energy (DOE) “User’s Manual for 

RESRAD-BUILD Version 3” gives a resuspension factor of 4.3×10-5 m-1 for “active work in 

confined, unventilated space” (Argonne National Laboratory, 2003, p. J-33). Dust loading 

calculations for confined spaces would be expected to be similarly influenced, with knowledge 

of site conditions and mechanical processes important to gauging the level of airborne dust 

generated. 

For comparison, the 212 μg/m3

 dust loading factor, based on an empirical 95th percentile value 

from the highest monitored air concentration during the Mound excavation, is about double that 

of the 100 μg/m3 value suggested in OTIB-0070 (NIOSH, 2012a) and NUREG/CR-5512 (NRC, 

1992). However, the preceding scientific literature cites resuspension factors for confined spaces 

of about a factor of 40 times that of the recommended 10-6 m-1 resuspension factor in OTIB0070. And these factors do not account for the level of intrusive activity within the confined 

spaces by M&C maintenance workers, or for the use of power equipment generating fine 

aerosols and particulates (e.g., drain line scale).

As background on this issue, OSHA published a new construction standard for confined spaces 

(29 CFR 1926, Subpart AA), effective on August 3, 2015, that promulgated safety requirements 

for workers in construction confined spaces. OSHA defines confined spaces and cites examples 

including pits, tanks, silos, maintenance holes, sewers, enclosed drains, and manholes (NIOSH, 

2022b). OSHA notes that pits, although typically open on top, can be completely underground or 

below grade and can still be a confined space (OSHA, 2015). Supporting industry literature 

following promulgation of the Subpart AA standard noted that confined spaces “include tight 

work areas with reduced air flow” where work such as “welding, cutting, grinding, sanding or 

any high-energy activity can create . . . respirable particles and/or toxic aerosols” (Chase, 2019). 

The more deeply respirable particles are 4 microns or smaller and are typically generated from 

such high-energy work (Chase, 2021). The “potential of limited air movement and minimal 
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ambient air circulation in these spaces allows particulate concentrations to build quickly” (Chase,

2019). 

SC&A has already conducted literature surveys of indoor airborne dust loadings (SC&A, 2018, 

pp. 55–60; SC&A, 2021b, pp. 12–18) and found a range of concentrations that may have 

applicability. However, the surrogate criterion question remains: Were dust loading 

concentrations within the trenches of the Mound excavation adequately characterized via air 

sampling such that these data can be applied to corresponding confined work spaces at M&C? 

NIOSH noted in a September 2, 2020, presentation that “during the Mound study the highvolume air samplers were positioned close to the excavation, which reduces the impact of the 

larger outside air volume” (NIOSH, 2020a, slide 25). From notes from an interview conducted 

with someone knowledgeable about the project, the samplers were apparently about “15-20 ft” 

from excavation activities (NIOSH, 2020c, p. 6). From this description, it appears that the 

samplers were near the excavation activities but were not sampling air at or within the trenches 

during any worker activities that may have taken place within those confined spaces.

Given the likelihood that generation and resuspension of radioactive particulates and aerosols 

were higher in these confined spaces, leading to higher dust loading factors, the location of the 

Mound project air monitors and their proximity to any actual work being conducted within the 

excavated trenches would be a key consideration for satisfying the Board’s surrogate data policy. 

Given that the Mound project was conducted in an outdoor excavation site, another factor would 

be the presence of lateral air movement (wind), which would have diminished dust loading 

measurements taken there versus those applicable for confined space work areas, where it would 

not have been a factor.25

25 NIOSH notes that “windbreaks, tents, or ventilation were not used” during the Mound excavation nor during the 

M&C excavations (NIOSH, 2018, p. 9). 

 At the same time, as pointed out by SC&A (2021b, p. 21), “it can also 

be stated with a degree of certainty that it would be highly implausible that workers could be 

exposed for extended periods of time to dust loading of any size distribution of about 100 mg/m3

(100,000 μg/m3

) or greater because of the choking effect of such high levels.” 

For the application of the Mound project data to an indoor scenario at M&C, NIOSH assumes a 

conservative margin is provided by use of the 95th percentile case from that project, coupled 

with the “limited airborne-generating capacity of snakes and shovels . . . on wet soil inside” 

compared to operation of backhoes in an outside environment (NIOSH, 2020a, slide 25). 

However, the question of equivalency from the Board’s surrogate policy remains the same: Are 

the Mound project measurements reflective of the same work conditions and environment as 

those at M&C?

Finding 2. The application of surrogate data from the Mound project to provide a dustloading factor for M&C subsurface activities does not satisfy the Board’s surrogate data 

policy. 
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3.3.2 Building 10 routine alpha contamination surveys

NIOSH observed in a response to work group comments that, “although comprehensive sample 

data used to characterize earlier periods did not become available until 1983–1995, NIOSH is 

aware of the safety program that was in place during the residual period” (NIOSH, 2020b, p. 17). 

NIOSH proceeded in that response and others to

th

 “make the case that M&C’s area monitoring 

assures that the 95 percentile soil-contamination value is conservative based on routine surveys 

of Building 10 during the first 14 years of the residual period (1968-1981)” (NIOSH, 2021a, 

pp. 7–8). 

NIOSH’s case is founded on citing area contamination survey requirements and procedures from 

the M&C health and safety manual from 1968 and noting that NRC inspections during the 

residual period for the regulated HFIR facility “provide NIOSH with independent assurance that 

radiological controls were monitored or maintained” (NIOSH, 2021a, p. 8). Actual routine 

contamination survey results are available for the first 2 years (1968–1969) of the residual period 

for the HFIR operation in Building 10, with an assumption that such surveys continued until 

1981. NIOSH also references a summary of “typical” alpha contamination survey results for the 

HFIR facility work, provided from the environmental monitoring program, that it believes 

“clearly indicate[s] contamination was controlled within bldg.10 during the HFIR project” 

(NIOSH, 2021b, slide 17).

This reviewer respectfully disagrees with NIOSH’s position and related assumptions in this case.

Without corroborating testimony or evidence regarding the actual implementation of non-HFIR 

Building 10 workplace contamination surveillance procedures at M&C during the residual 

period, assurance cannot be placed solely on “typical” HFIR-specific survey results—although 

no actual routine contamination surveys were found26

26 Verified by NIOSH during the March 18, 2021, M&C work group meeting (ABRWH, 2021, p. 85). 

—or procedural requirements (e.g., a M&C 

safety manual or NRC inspection requirements). While “NIOSH believes [the M&C manual] 

adequately describes M&C’s established concern for contamination control” (NIOSH, 2021b, 

slide 14), this has no bearing on whether M&C management’s presumed concern translated into 

actual monitoring implementation and practice. NIOSH’s awareness that NRC must have 

“enforced these contamination surveys” for licensed HFIR operations because “whenever M&C 

wanted to change administrative requirements (e.g., frequency of surveys), they send a request to 

the NRC” (NIOSH, 2021b, slide 15), is presumptive and not corroborated. Likewise, NIOSH’s 

citing of NRC inspection results for HFIR operator knowledge, use of survey equipment, and 

licensee health physics training records does not corroborate that actual surveying took place and 

would have been carried over to non-HFIR spaces in Building 10 by virtue of the M&C health 

and safety manual. 

As demonstrated by past site reviews under EEOICPA, there are notable instances where actual 

implementation of radiological monitoring fell considerably short of matching what was 

documented in site manuals and procedures.27

27 Most notably, the DOE enforcement program invoked a 120-day DOE-wide moratorium in 1998–1999 for 

enforcement actions against DOE operating contractors to enable them to self-assess and, as necessary, make 

corrective actions for their internal dose evaluation programs in the face of widespread deficiencies in implementing 

and enforcing those programs in accordance with site policies and procedures and DOE regulations (DOE, 1999).

 Likewise, despite what undoubtedly was the 
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expertise of M&C engineers in pioneering low-level alpha counting and quantitative gamma 

spectrometry technologies, this is not relevant to, nor makes the case that, M&C routine 

contamination surveys continued unchanged in the early residual period, or that the presumed 

rigor of the HFIR contamination survey program carried over to routine monitoring and cleaning 

up of contamination in non-HFIR spaces of Building 10 for the residual period.

On the contrary, the only first-hand corroboration of the status of health physics monitoring and 

surveying practice in non-HFIR areas of Building 10 are the accounts of former M&C workers.

That testimony attests to (1) health physics personnel generally not being present during the 

residual period (not including those supporting remedial contractors), (2) worker unfamiliarity 

with the M&C health and safety manual, and (3) workers having little recollection of any routine 

alpha contamination surveys being conducted in Building 10 during the residual period (e.g., 

NIOSH, 2017c, pp. 3–4, 6; NIOSH, 2017d, pp. 9–10, 13, 15–16; NIOSH, 2017f, p. 3; NIOSH, 

2017b, p. 9; NIOSH, 2017e, p. 11; NIOSH, 2017g, p. 3; NIOSH, 2017i, p. 10; ABRWH, 2021, 

pp. 26–31; ABRWH, 2020b, p. 101). NIOSH’s conclusion that, “if widespread removable alpha 

contamination existed at levels higher than the 95th percentile in the areas where maintenance 

was performed, then the routine surveys would have eventually identified tracking throughout 

the plant during this 14-year period” (NIOSH, 2020b, p. 18), is not corroborated by actual 

evidence of any routine monitoring performed after 1969 in non-HFIR areas of Building 10. 

Observation 2. References to the M&C safety and health manual, NRC inspection results, 

operator training, and other programmatic considerations do not necessarily 

substantiate the conservatism of the 95th percentile soil contamination value being 

applied.
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4 Conclusions

Precedent suggests that while less precision or technical accuracy can be tolerated if the exposure 

of a worker cohort is relatively low, the use of a high exposure or concentration values based on 

these data to bound or represent that of other workers in a facility or on a site for long time 

periods would not be appropriate if their exposure potential could be higher, conditions were 

different, or if there is lack of information upon which to make those judgments. As noted in the 

Board’s deliberations on the Linde residual period, the question of where to draw the line for 

applying such bounding constructs is a subjective one, weighing the precision (or accuracy) of 

the bounding assumption and data, as well as the plausibility of their application to the target 

worker population.

The following findings and observations arise from this issue, as well as others addressed in this 

supplemental review.

1. Finding 1. The back application of a high 1995 sediment survey result to bound 

inside subsurface activities is not adequately supported by information for M&C 

worker activities from the earlier residual time period.

For the inside subsurface exposure model, the issue for the work group is whether it is 

plausible for an elevated sediment reading from a D&D drain pipe sediment survey in 

1995 to be assumed, in the absence of additional site-specific information, to be the 

bounding exposure for all M&C maintenance workers who may have conducted various 

(and diverse) subsurface activities inside Building 10 (and to a lesser extent, Building 4) 

for the earlier 27 years of the residual period. While the 1995 drain line reading is a high 

activity level, can it be applied as a bounding exposure for related and unrelated inside 

subsurface work for which little, if any, documented information is available and for 

which confined space atmospheres were involved? Given the active radiological 

operations in Building 10 through 1981, it is just as conceivable that more frequent drain 

line blockages occurred in the early years, involving higher activity sediment due to 

increased effluent volume related to operations, compounded by frequent discharge of 

vegetable-based mineral oil that was implicated in the pipe clogging, as well as routine 

maintenance of equipment. Unlike for D&D activities, for which the sediment sample 

was taken, M&C maintenance workers were unaware of the radiological contamination 

involved, and there was no radiological control program, no health physicists, and no 

oversight.

2. Observation 1. The use of blended D&D characterization survey data from 1984

and 1992to support a bounding dose for outside subsurface activities may not be 

necessarily bounding for work in nonuniform soil contamination, given the 

presence of hot spots that existed during the residual period at M&C.

For the burial site and Metals Recovery Area, uranium soil concentrations in excess of 

5,000 pCi/g and 17,000 pCi/g, respectively, were measured in later remedial subsurface 

surveys (1993–1994). Such hot spots were found at differing locations and depths, given 

the heterogeneity of contamination that originated with waste disposal (burial site) and 

waste incineration (Metals Recovery Area) and the non-uniform mixing that occurred in 

the 1968 site grading at M&C. The 95th percentile subsurface soil concentration derived 
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from the sitewide GM and GSD based on the selected and blended 2,391 samples taken 

during D&D characterization surveys, while including sampling data from these 

locations, may not necessarily bound exposures from excavation work performed by 

individual workers exclusively within these elevated hot spot locations. 

3. Finding 2. The application of surrogate data from the Mound project to provide a 

dust-loading factor for M&C subsurface activities does not satisfy the Board’s 

surrogate data policy.

The dust loading monitoring results for the Mound project excavation, being apparently 

derived from air samplers located near backhoe excavation, are not equivalent to and 

would not necessarily characterize dust loading within the confined spaces at M&C 

where subsurface maintenance activities were conducted.

4. Observation 2. References to the M&C safety and health manual, NRC inspection 

results, operator training, and other programmatic considerations do not 

necessarily substantiate the conservatism of the 95th percentile soil 

contamination value being applied.

The claim “that M&C’s area monitoring assures that the 95th percentile soilcontamination value is conservative based on routine surveys of Building 10 during the 

first 14 years of the residual period (1968-1981)” (NIOSH, 2021a, pp. 7–8) is not 

necessarily substantiated by the assumed strength of the M&C radiological surveillance 

program. Without corroborating accounts or evidence regarding the actual 

implementation of non-HFIR workplace contamination surveillance procedures at M&C, 

assurance cannot be placed solely on typical HFIR-specific survey results or the assumed 

implementation of procedural requirements such as the M&C safety manual or NRC 

inspection requirements. 
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Attachment 1 

This attachment reproduces images of building activity scenarios from NUREG/CR-5512, 

Vol. 1, “Residual Radioactive Contamination from Decommissioning: Technical Basis for 

Translating Contamination Levels to Annual Total Effective Dose Equivalent” (NRC, 1992). 

Figure A-1. Potential activities within the building occupancy scenario 

(NUREG/CR-5512, vol. 1, figure 3.1)

Source: NRC (1992).
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NOTICE: This document has been reviewed to identify and redact any information that is protected by the 

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

Figure A-2. Potential activities within the building renovation scenario 

(NUREG/CR-5512, vol. 1, figure 3.1)

Source: NRC (1992).