Santa Susana Field 

Laboratory (Area IV) 

SEC Petition-00235 

Preliminary Review

Presented by: 

Bob Barton, SC&A, Inc.

Draft version presented to SSFL Work Group March 25, 2019
Introduction and Background SEC Petition-00235 

 Periods prior to 1989 at SSFL are covered by three previous 

SEC’s:

 SEC-00093 (January 1, 1955 through December 31, 1958): 

inability to reconstruct both internal and external exposures* 

to individual members of the class.

*Although the official Advisory Board recommendation states that both internal 

and external dose reconstruction are infeasible, the NIOSH Evaluation Report 

for SEC-00093 concluded that external dose reconstruction was feasible.

 SEC-00156 (January 1, 1959 through December 31, 1964): 

inability to reconstruct internal exposures for individual 

members of the class (lack of sufficient bioassay for 

coworker analysis).

 SEC-00234 (January 1, 1964 through December 31, 1988): 

inability to reconstruct internal exposures to americium and 

thorium for individual members of the class.

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Introduction and Background SEC Petition-00235 (cont.)

 Original Petitioner Requested Definition:

“All employees of North American Aviation, to include corporate 

successors and subcontractors who worked at Area IV of the 

Santa Susana Field Laboratory (SSFL) from December 31, 1964 

through the present.”

 Class Evaluated by NIOSH:

“All employees of the Department of Energy, its predecessor 

agencies, and their contractors and subcontractors who worked at 

Area IV of the Santa Susana Field Laboratory in Ventura, County, 

California, from August 1, 1991 through June 30, 1993.”

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Introduction and Background SEC Petition-00235 (cont.)

 Note from SEC-00234 Conclusions (class added up to 1989):

“NIOSH has not identified any data that suggest the possibility for significant 

operational thorium or americium exposures after 1988 that cannot be bounded. 

Therefore, NIOSH has established an end date of December 31, 1988, for this SEC 

class.”

 NIOSH evaluated period for SEC-00235 (August 1, 1991 – June 30, 1993) 

based on the use of the bioassay contractor Controls for Environmental 

Pollution (CEP) during this timeframe. 

 CEP had been implicated in data falsification related to the bioassay program 

at Sandia National Laboratory and any results are considered invalid 

 Available in vitro results from CEP cannot be used either individually or in 

coworker models at SSFL (note: NIOSH does not utilize bioassay results 

evaluated by CEP for SSFL or any other covered site under EEOICPA).

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Introduction and Background SEC Petition-00235 (cont.)

 NIOSH released its Petition-00235 Evaluation Report on May 

11, 2017

 Summary of NIOSH Feasibility Determination/Conclusions

 No issues had been identified with the reconstruction of external 

exposures or medically related exposures. External dose to unmonitored 

workers can be reconstructed using derived coworker external doses 

(ORAUT OTIB-0077).

 In Vitro monitoring results were disqualified however an adequate Whole 

Body Count (in Vivo) program was still in use during this time.

 Confirmatory bioassay performed after CEP was removed as bioassay 

contractor showed no measurable internal exposures.

 Internal coworker intakes have been developed from bioassay results 

during the operational period (up to 1988) for uranium, plutonium and 

fission products that can be used to reconstruct internal exposures during 

the residual period (including the CEP period).

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Introduction and Background SEC Petition-00235 (cont.)

 SEC ER Discussed with SSFL/De Soto WG on December 4, 2017 

with two follow up action items for NIOSH:

 Item 1: Evaluate available air sampling data during the CEP period to help confirm that 

radiological conditions during this period are sufficiently similar and/or bounded by the 

conditions during the operational period.

 Item 2: The SEC-00235 SEC ER did not specifically discuss the potential for exposure to 

americium and thorium internal sources terms. NIOSH to specifically investigate and discuss 

the internal exposure potential to these sources.

 NIOSH delivered two whitepapers to the Work Group in November 

2018 to address these two issues.

 NIOSH presented the two whitepapers to the Work Group on 

December 4, 2019 at which time SC&A was tasked with review of the 

new information.

 SC&A delivered its review of the two whitepapers via the single 

document: “Review of Remaining Internal Dose Topics Related to the 

Evaluation of SEC-00235 at the Santa Susana Field Laboratory”

(February 20, 2019).

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SC&A Review Approach

 Site Research Database (SRDB): Review of currently available 

documentation on the SRDB (2,726 total documents for Area 

IV however only a subset are directly related to SSFL 

operations after 1988).

 Boeing Incident Database: Review of relevant incidents files 

contained in the Boeing Incident Database supplied by the 

petitioner (Core Advocacy for Nuclear and Aerospace Workers)

 Evaluation of General Area Gross Beta and Gross Alpha Air 

sampling data to compare the relative internal exposure 

potential during the SEC/CEP period

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Review of SRDB Documentation

 Purpose:

 Identify documentation of radiological projects involving 

americium and/or thorium during the post-1988 period at SSFL

 Identify documentation related directly to the SEC/CEP period 

that might invalidate the use of operational coworker intakes to 

reconstruct internal exposures

 Document types contained on the SRDB and reviewed 

include (but are not necessarily limited to):

 General Area Air (GA) and Breathing Zone (BZ) results

 Contamination Surveys

 Environmental Monitoring Evaluations

 Accident/Incident Reports

 Decontamination and Decommissioning Evaluations

 Other Planning/Occurrence Reports

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Review of SRDB Documentation (cont.)

 SRDB Documentation Includes interviews with 

during the period of 

interest:

 “As the various ETEC activities were terminated, the potential exposures to alphaemitters reduced significantly. As mentioned above, the primary isotopes of 

concern became Cs-137 and Co-60. While alpha-emitters were also part of the 

source-terms in Building 20 and the RMHF, these were at very low levels and were 

not routinely found in the contamination surveys of these locations.”

 “It is my opinion that Am-241 and thorium would have been minor contributors, if 

any, to internal dose. It is likely that this rationale is why there were relatively few 

bioassay requests made historically for these radionuclides. If Am-241 and thorium 

had been a significant internal dose contributor in the workplace of SSFL or De 

Soto, then it would logically have also been a potential environmental contaminant. 

This is not the case as demonstrated by the USEPA. The USEPA Area IV 

Radiological Study (2009–2012)... So, neither americium nor thorium are or were 

an environmental issue. One could arguably extrapolate back and imply that it was 

also not a workplace issue at SSFL or at De Soto, or at least, less so than 

uranium, plutonium, and mixed fission products, for which we had more than 

adequate bioassay data.” 

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Review of SRDB Documentation (cont.)

SC&A Conclusions based SRDB Documentation:

 SC&A did not identify any evidence of significant thorium 

or americium operations or unique exposure potential 

which would represent an unmonitored exposure that 

could not be feasibly bounded.

 SC&A did not identify evidence that suggests the internal 

exposure potential during the CEP period was 

significantly different than the operational period which 

would preclude the use of occupationally derived 

coworker intakes for plutonium, uranium and mixed 

fission products.

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Review of Boeing Incident Database

 Purpose:

 Identify incidents involving americium and/or thorium during the 

post-1988 period at SSFL

 Identify radiological incidents during the CEP period that might 

preclude the ability to perform dose reconstruction with sufficient 

accuracy

 Overview:

 Approximately 71 incident files related to SSFL post-1988 (19 of 

which involved the detectable spread of contamination)

 10 incident files related to SSFL during SEC-00235 evaluated 

period/CEP period (1 of which involved the detectable spread of 

contamination)

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Review of Boeing Incident Database (cont.)

SC&A Conclusions: 

 No incidents involving thorium were identified.

 Single incident involving Am-241*:

*This incident has only been recently discovered as part of a separate review of SEC-00246 for the De 

Soto facility and was not identified in the recent 2019 SC&A report for SEC-00235.

 Low level contamination of the hands involving the cleaning of a 

smoke detector in the control room

 Contamination on hands was “easily removed”

 No contamination was detected in the immediate vicinity of the work

 Nasal smears were negative for those involved

 Incidents reviewed did not indicate a significantly different internal 

exposure potential during the CEP period than during other D&D 

activities or the operational period for which coworker data is 

available.

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Evaluation of Air Sampling Data

Purpose: 

 Evaluate available general area (GA) air samples for 

gross beta and gross alpha taken during the 

operational period and SEC/CEP period

 Compare the general airborne contamination levels to 

help corroborate whether operationally-derived 

coworker intakes are sufficiently representative and/or 

bound conditions during the SEC/CEP period

 Allows for the use of available coworker intake values 

(ORAUT OTIB-0080) to reconstruct doses during the 

period when in vitro sampling has been invalidated.

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Evaluation of Air Sampling Data (cont.) – Maximum Gross Beta

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Evaluation of Air Sampling Data (cont.) – Average Gross Beta

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Evaluation of Air Sampling Data (cont.) – Maximum Gross Alpha

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Evaluation of Air Sampling Data (cont.) – Average Gross Alpha

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Evaluation of Air Sampling Data Conclusion

 General Area air samples at both the maximum and average 

quarterly levels helps corroborate that the measured values for 

controlled areas during the CEP period were bounded by the 

operational period for both gross beta and gross alpha 

measurements. 

 Quarterly GA air samples during the CEP period were all 

several orders of magnitude below the maximum permissible 

concentration (MPC) for both alpha and beta airborne 

contamination. 

 SC&A did not identify any evidence in the available air 

sampling data to suggest that internal exposure potential to the 

radionuclides of concern at SSFL would not be bounded by the 

operational bioassay data.

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Summary of SC&A Review

 Thorium and Americium Post-1988

 Current Exposure Assessment in an SEC Context: Available 

documentation does not indicate a source of exposure to thorium or 

americium that cannot be feasibly reconstructed with sufficiently 

bounding methods and assumptions.

 What about Dose Reconstructions?

 Current NIOSH methods assign “ambient” or “environmental” intakes of 

thorium and americium during the SEC and surrounding residual period

 Such intakes are based primarily upon stack emissions and are generally 

intended for non-radiological/unexposed worker dose reconstructions

 SC&A Suggestion: an alternate occupational model may be appropriate 

based on available breathing zone data, general area monitoring results, 

or administrative airborne contamination limits to account for the irregular 

exposure scenarios associated with D&D work.

 SEC/CEP Period (August 1991- June 1993): SC&A did not find evidence in 

the evaluation of air sampling data, SRDB documentation, or the Boeing 

Database to suggest that internal dose reconstruction was infeasible using 

operational coworker analysis.

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Additional Developments

 Core Advocacy for Nuclear and Aerospace Workers 

(petitioner for SEC-00235 and SEC-00246) notified 

NIOSH on January 28, 2019, that approximately 

1,463 boxes of DOE records relevant to SSFL have 

been identified

 The exact contents and relevancy of the boxes are 

not currently known

 Per information supplied by Core Advocacy, these 

boxes are scheduled to be made available no later 

than fall 2019. 

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Work Group Recommendations and/or Path Forward

 TBD

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Questions?

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