Update on M&C Exposure 

Pathway Modeling 

Rose Gogliotti, MS, SC&A, Inc.

Bob Barton, CHP, SC&A, Inc.

Advisory Board on Radiation and Worker Health, Metals & 

Controls Corp. Work Group

May 12, 2023
2

SC&A action items

 Reconsider NIOSH Building 10 subsurface one-toone model (thorium issue)

 Reevaluate how burial ground data are used in 

modeling

 Explore if current ingestion model accounts for 

glove use
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Subsurface indoor: Approach to internal dose

 Model:

– Soil contains 6,888 pCi/g uranium (U) (95th percentile of pipe scale 

sampling)

– Dust loading equal to 95th percentile Mound air sampling

– 2 months per year

 Data: 

– 1995 Weston study to characterize drain lines

– 20 sediment samples analyzed for isotopic uranium

– Additional 1995 samples taken from priority 2 and 3 lines omitted
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Subsurface indoor: Thorium

 No thorium (Th) or gross alpha measurements subsurface in 

Building 10

 NIOSH model assumes equivalent amounts by weight of 

natural U and Th-232

– Documentation shows U operations far exceeded Th

– No evidence suggests that equal weights of Th should be expected 

when U is present

– Insufficient information to establish that it could not be that high

– Cannot rule out a 1:1 mass ratio of U to Th; the approach is claimant 

favorable
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Subsurface indoor: Concerns

 Representativeness of samples

– Impossible to quantify potential pipe dilution over time

– Coagulants may have concentrated some of the contamination into 

specific areas

– Based on the available data: 

• May be possible to potentially bound the exposures such that workers are unlikely 

to receive a higher dose in the aggregate over the course of a year

• Small fraction of pipes deemed contaminated

• All materials below slab, both inside and outside pipes, assumed to be 

contaminated at 95th percentile activity 

– Examples of other residual period comparisons include Linde and 

Chapman Valve
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Finding 1:

Building 10 

subsurface 

external 

exposures not 

bounded

SC&A finds that NIOSH’s proposed external 

dose rate assumptions are inconsistent with 

the contamination levels assumed for the 

subsurface of Building 10. SC&A’s 

independent calculations suggest dose 

rates from the modeled pathway are 

expected to be substantially greater. 

NIOSH’s 2017 SEC ER proposed using the 

95th percentile dosimetry values (with 

adjustments for missed dose) of 

200 mrem/year (16.7 mrem/month). SC&A 

believes it is more appropriate to assign 

elevated subsurface exposures inside 

Building 10 using the 95th percentile of the 

dosimetry with occupancy adjustments.
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Subsurface indoor: Dust loading concerns

 October 15, 2020: NIOSH interviewed a subject matter expert 

(SME) about a Mound air sampling study for use as a 

surrogate modeling parameter

 May 20, 2021: Representatives of work group, NIOSH, and 

SC&A participated in reinterview of SME
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Dust loadings: Surrogate data criteria

1. Hierarchy of data: No covered bioassays 

or air monitoring data exist to take 

precedence over Mound data.

2. Exclusivity requirements: The WG has 

deemed remediation air sampling data 

not applicable.

3. Temporal considerations: The Mound 

excavations occurred in 1996, while M&C 

excavations occurred from 1968 through 

1996. The passage of time has not 

significantly altered backhoe operations, 

hand digging, or their ability to generate 

airborne dust.

4. Plausibility: The dust loading data have 

a range consistent with values expected 

from general excavation activities.

5. Site and process similarities: Outdoor 

and indoor dust loading during 

excavation activities apply to these same 

activities as those at M&C and might 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. Very little can be done to 

accommodate these types of site-specific 

characteristics, except to use a degree of 

professional judgement on the 

applicability of data to place an upper 

bound on the dust loading factor.
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Subsurface outdoor: Approach to internal dose

 Model:

– Soil contains 117.86 pCi/g U (95th percentile soil samples)

– Soil contains 87.5 pCi/g Th (95th percentile soil samples)

– Dust loading equal to 95th percentile Mound air sampling

– 2 months per year

 Data: 

– 2,391 soil samples collected prior to remediation in 1980s and 1990s

• 1,629 samples were analyzed for gross alpha

• 762 samples were collected for U and Th and analyzed using isotopic 

identification
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Subsurface outdoor: Work group concerns

 “Debris buried in the burial site was not representative of 

radioactive materials (U and Th) handled throughout the AWE 

operational period (1952-67), but was a selective sample of 

those materials, largely from 1958-1961” (NIOSH, 2021a, p. 2).

– Data do not represent entirety of operations

– Do represent material present during residual period in the burial site

– Ratios of U to Th not being used to establish Th concentrations indoor
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Subsurface outdoor concerns: 1968 soil disturbance

Soil grading in 1968 following the construction of Building 12

 Dates of soil grading unknown but early in the residual period (began 

January 1, 1968)

 Any materials dispersed in 1968 throughout the site would be the same 

materials that workers were exposed to during the remainder of the 

residual period

 Disturbance happened early in the residual period; soil sampling from the 

burial area in the 1980s and 1990s could be considered representative of 

potential exposures encountered by maintenance workers
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Subsurface outdoor concerns: 1980 soil disturbance

Installation of the compressed airline in August 1980

 According to a 1981 NRC inspection report (NRC, 1981, PDF p. 128), the area that was 

dug up was “slightly contaminated” and “a trained health physicist, surveyed the material 

dug up and placed any contaminated materials into 55 gallon drums. Eleven 55 gallon 

drums were sent to . . . Barnwell, South Carolina.” 

 Remaining soils reburied (area later resurveyed and found to be below NRC release 

criteria).

 Burial area large compared to the small volume displaced by trench.

 Unlikely disturbance altered the distribution of materials in the burial grounds significantly 

enough to make later surveys not representative of the earlier exposure potential.
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Subsurface outdoor 

concerns: 

Occupancy

“NIOSH will assume an 

occupancy rate of two 

months per year for 

subsurface work 

(2000 hours per year x 2/12 

{fraction of year} = 333.33 

hours per year). If the 

subsurface work area (e.g., 

inside or outside) cannot be 

determined, the most 

claimant-favorable work 

location will be assigned” 

(NIOSH, 2021b, p. 14).

Observation 1: SC&A reviewed the 

claimant interviews and does not 

believe that there is sufficient 

evidence to limit any individual’s 

subsurface exposures to a single 

subsurface scenario. The interviews 

indicate that, irrespective of an 

individual’s job title, they may have 

been asked to complete any task on 

site. SC&A believes that means an 

individual could have participated in 

both indoor and outdoor subsurface 

scenarios within a year.
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Roof and overhead: Approach to internal dose

 Model:

– 95th percentile removable contamination level of 8.99 dpm/100 cm2

– resuspension factor (RF) of 10-5 per meter

– a breathing rate of 1.2 m3/hr

– 1 month per year

 Data:

– 285 grid average alpha surveys 

– Surveys were completed by Texas Instruments (TI) in 1982 in support of 

license termination 

– Completed before the positive temperature coefficient powder explosion 

(believed to have occurred in the late 1980s or early 1990s)

– Subsequent cleanup activities would not likely impact results
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Roof and overhead: Roof weathering concerns

 Only 40 of 285 measurements used were from the roof

– Measurements were taken radially around exhaust pipes (no prior cleaning)

– TI noted that exhaust from fuel monitoring area showed essentially background 

radioactivity in the air being discharged

– Assuming 10 percent removable contamination: direct survey of 2.6 dpm/100 cm2 and a 

95th percentile of 29.0 dpm/100 cm2 (roughly double the amount modeled by NIOSH for 

the aggregate roof and overhead model)

– Weather effect: Reasonable to assume source term depletion occurred over ~14 years of 

the residual period

– Suggests roof not bounded by combined model but doses still <1 mrem in 1982

 1982 NRC: “Fixed and removable contamination levels measured during the 

inspection are comparable to those in the licensee’s close-out survey” (NRC, 

1982, PDF p. 25) 
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Welding: Approach to internal dose

 Model:

– Source term: 89.94 dpm/100 cm2 (95th percentile measured 

contamination)

– Resuspension factor: 10-3/m

– Exposure time: 48 hours/year

 Data:

– identical to the 1982 data used in the roof and overhead but assumes 

100% removable contamination
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Welding: Work group and SC&A concerns

 SC&A raised a concern (finding 2) in its 2019 and 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 

 Echoed by the WG during September 2, 2020, WG meeting 

 To date, this issue has not been resolved 

 Likely a “TBD issue” rather than an SEC issue
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HVAC maintenance

 Model:

– Source term: 1.23 x 10-4 dpm/μg

– 10-5 resuspension factor

– Specific airborne contamination: 100,000 μg/m3 dust loading in vent

– 1 hr/year (standard breathing rate of 1.2 m3/hr)

 Data:

– 7,765 gross-alpha swipe data collected near the end of Atomic Weapons 

Employer (AWE) operations in 1966 and 1968

– Represents removable contamination found at the site at the end of 

operations

– End of the AWE operations period: 

• Non-HFIR areas were cleaned and released for use

• Cleaning would be expected to reduce the contamination during the residual period 
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Remaining (non-maintenance)

 Represents remaining work in generally accessible parts of the 

site

 Model:

– Source term: 12.3 dpm/100 cm2

– Source term depletion per ORAUT-OTIB-0070

– Balance of year (1,451 hours)

 Data:

– 7,765 gross-alpha swipe data collected at the end of AWE operations in 

1966 and 1968 (identical to HVAC model data)
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Summary of modeled internal dose pathways

Model

Year of 

measurements used 

in model

Uranium internal 

dose (mrem) *

Thorium internal 

dose (mrem) *

Subsurface inside 1995 17 29

Subsurface outside 1980s and 1990s <1 2

Roof and overhead 1982 <1 <1

Welding 1982 6 17

HVAC 1966 and 1968 <1 <1

Remaining 1966 and 1968 <1 1

* Modeled internal doses shown are committed effective doses provided for comparison. Under the 

EEOICPA, annual organ doses are assigned.
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OCAS-TIB-009 ingestion modes

 Mode 1: Inhaled materials caught in mouth, throat, 

and lungs are removed by normal lung function to 

gastrointestinal tract

 Mode 2: Material in air settles onto food and drink 

and is later ingested

 Mode 3: Material is transferred from contaminated 

surfaces to hands and is subsequently ingested 
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Does TIB-009 model account for ungloved hands?

 Yes, Mode 3 includes inadvertent hand-to-mouth 

ingestion

–Applies to the transfer of material from contaminated 

surfaces to the hands

–Covers ingestion from using contaminated hands to

• eat, 

• drink, and 

• smoke
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References

National Institute for Occupational Safety and Health (NIOSH). (2017). SEC petition 

evaluation report Petition SEC-00236, Metals and Controls Corp.

https://www.cdc.gov/niosh/ocas/pdfs/sec/metcont/metconter-236.pdf

NIOSH. (2021a, Feb. 8). Response to comments related to soil disturbances at the 

burial ground [Memorandum]. https://ftp.cdc.gov/pub/FOIAREQ/184829-508.pdf

NIOSH. (2021b). Response to comments from the Metals and Controls Corp. Work 

Group meeting held on September 2, 2020 [Response paper]. 

https://ftp.cdc.gov/pub/FOIAREQ/184642_red-508.pdf

U.S. Nuclear Regulatory Commission (NRC). (1981). Inspection on June 8-12, 

1981 (Report No. 70-33/81-07). https://semspub.epa.gov/work/01/209715.pdf

NRC. (1982). Region I Report 70-33/82-03. SRDB Ref. ID 161187