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 USC §552a and has been cleared for distribution. 

Memorandum

To: Savannah River Site Work Group and SEC Issues Work Group

From: SC&A, Inc.

Date: November 12, 2019

Subject: Review of NIOSH’s Refined Construction Trade Worker Stratification Comparisons for 

Plutonium

Background

An important facet of the use of Savannah River Site (SRS) coworker models developed in 

ORAUT-OTIB-0081, revision 04 (NIOSH, 2019a, “OTIB-0081”) is the assumption that 

subcontractor construction trade workers (CTWs) had the same work duties, and by extension, 

the same exposure potential, as the prime CTWs. In order to aid in evaluating this assumption, 

the National Institute for Occupational Safety and Health (NIOSH) performed an analysis, which 

was presented to the SRS work group in October 2017, that compared available plutonium 

urinalysis results in the NIOSH/Division of Compensation Analysis and Support Claims 

Tracking System (NOCTS) for three different worker strata: DuPont operational workers, 

DuPont CTWs, and subcontractor CTWs (NIOSH, 2017). That analysis stated the following 

regarding plutonium exposures and provided a supporting figure (figure 3 of NIOSH (2017), 

shown below as figure 1): 

for most years there is little difference in the 95 percentile urinary excretion 

between DuPont CTWs and Subcontractor CTWs. The exception appears to be in 

the later 1970s and 1980s. This observation is somewhat supported by 

contemporary interviews with subcontractor CTWs. Subcontractor CTW 

indicated that they were called in for more contaminated work to save the 

exposure of the onsite CTWs. For some years (1977-1979 and 1984-1986) this 

appears to be the case in that the 95th percentile of the subcontractor CTWs is a 

factor of 2-5 higher. [NIOSH, 2017] 

Subsequent discussion of this report with the SRS work group in November and December 2017 

(SRS WG, 2017, and ABRWH, 2017, respectively) noted that the subcontractor estimates appear 

to closely mirror or bound DuPont CTW estimates from 1976 through 1987. Significant 

differences were noted in 1977, 1979, 1985, and 1986. These discussions prompted NIOSH to 

pursue a more rigorous analysis comparing DuPont CTWs to subcontractor CTWs during this 

time period. NIOSH provided its updated analysis in the white paper, “Savannah River Site 

Plutonium Construction Trade Worker Stratification Refinement” (NIOSH, 2019b). This 

memorandum represents SC&A’s review of that white paper.
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Figure 1. NIOSH evaluation of plutonium urinalysis for DuPont construction trade workers, 

DuPont nonconstruction trade workers, and subcontractor construction trade workers from 1956

through 1988 (reproduced from NIOSH (2017))

Summary of NIOSH Results

The NIOSH white paper compiled additional data from available bioassay laboratory logbooks, 

where necessary,

1 and evaluated the years 1974, 1977, 1980, 1983, and 1986 for relative 

plutonium exposure. These data were then analyzed via current coworker analysis methods to 

derive annual excretion rates in order to model plutonium intakes in accordance with the current 

coworker modeling guidelines in the following NIOSH technical guidance: 

1 Per NIOSH (2019b), additional coding of laboratory logbook bioassay results was only necessary for 

subcontractor workers during the years 1974, 1983, and 1986.

• ORAUT-OTIB-0019, revision 01, “Analysis of Coworker Bioassay Data for Internal 

Dose Assignment” (NIOSH, 2005) 

• (ORAUT-RPRT-0053, revision 02, “Analysis of Stratified Coworker Datasets” (NIOSH, 

2014) 

• ORAUT-OTIB-0060, revision 02, “Internal Dose Reconstruction” (NIOSH, 2018) 

The resulting excretion rate comparison and derived intake rates from NIOSH (2019b) are shown 

in tables 1 and 2, respectively.

 
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Table 1. Geometric mean and 95th percentile urinary excretion rates reported in NIOSH (2019b) 

Year

Geometric 

mean DuPont 

CTW excretion 

rate 

(dpm/1.5 L)

Geometric mean 

subcontract 

CTW excretion 

rate (dpm/1.5 L)

Geometric 

mean ratio 

(DuPont/ 

Sub)* 

95th percentile 

DuPont CTW 

excretion rate 

(dpm/1.5 L)* 

95th percentile 

subcontract 

CTW excretion 

rate 

(dpm/1.5 L)* 

95th 

percentile 

ratio 

(DuPont/ 

Sub)* 

1974 0.004689 0.001439 3.26 0.122 0.039 3.12

1977 0.003447 0.001745 1.98 0.047 0.041 1.13

1980 0.005597 0.009319 0.60 0.110 0.165 0.67

1983 0.007492 0.005914 1.27 0.118 0.094 1.26

1986 0.01141 0.00917 1.24 0.091 0.121 0.75

*Value is not specifically reported in NIOSH (2019b) and is calculated by SC&A based on the reported geometric 

standard deviation.

Table 2. Geometric mean and 95th percentile derived intake rates reported in NIOSH (2019b) 

Years, 

solubility 

type

Geometric 

mean 

DuPont 

CTW intake 

rate (dpm/d)

Geometric 

mean 

subcontract 

CTW intake 

rate (dpm/d)

Geometric 

mean ratio 

(DuPont/ 

Sub)* 

95th 

percentile 

DuPont CTW 

intake rate 

(dpm/d)

95th 

percentile 

subcontract 

CTW intake 

rate (dpm/d)

95th 

percentile 

ratio 

(DuPont/ 

Sub)* 

1973–1978, 

M 0.7732 0.325 2.38 14.349 8.00 1.79

1973–1978, 

S 15.71 6.97 2.25 268.7 169.4 1.59

1979–1987, 

M 1.426 1.293 1.10 16.215 19.17 0.85

1979–1987, 

S 26.38 22.65 1.17 279.2 326.1 0.86

*Value is not specifically reported in NIOSH (2019b) 

NIOSH (2019b) concludes:

As can be seen by examination of the tables above, the geometric mean (GM) of 

the results for the DuPont CTWs are higher than that for the subcontractor CTWs 

for all years evaluated. For the 1973 through 1978 period, the 95th percentile 

intake results for the DuPont CTWs are higher as well. For the 1979 through 1987 

period, the subcontractor CTWs do have a higher 95th percentile due to the higher 

geometric standard deviation (GSD) of the data. . . . 

NIOSH believes it is reasonable to combine all CTWs into a single stratum for 

assignment of intakes in the SRS internal dose coworker study. [NIOSH, 2019b, 

pp. 6–7] 
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SC&A General Comments

As noted in the previous section and in NIOSH (2019b), at the 95th percentile, the subcontractor 

CTWs had higher excretion rates and derived intakes than DuPont CTWs for the period 1979 

through 1987. This is consistent with figure 1, which was originally produced by NIOSH and 

previously demonstrated that urinalysis results for subcontractor CTWs were either comparable 

to, or higher than, those of the DuPont construction workers. This is significant because the 

coworker model assignments for unmonitored construction workers have been proposed by 

NIOSH to be assigned at the 95th percentile (SRS WG, 2017, p. 27). 

Furthermore, a tabulation of the relative number of monitored claimant subcontract construction 

trade workers by year versus claimant DuPont CTWs found in NIOSH (2017) shows a 

significant increase in the number of monitored subcontractors beginning in approximately 1980 

(see figure 2, below). In addition, figure 5-1 (page 13) of ORAUT-RPRT-0094, revision 00, 

“Bioassay for Subcontractor Construction Trade Workers at the Savannah River Site from 1972 

to 1997” (NIOSH, 2019c), also indicates a general increase in the number of claimant 

subcontract workers beginning in the late 1970s and into the 1980s (see figure 3). Therefore, 

SC&A believes the fact that subcontract workers exhibit higher urinary excretion rates at the 

95th percentile of the distribution during this period is significant from the viewpoint of 

appropriate stratification.

Finding 1: In SC&A’s opinion, the conclusion that subcontractor construction trade 

workers had higher excretion rates and derived intakes at the 95th percentile is 

significant from the standpoint of stratification because the 95th percentile is what is 

proposed for assignment to unmonitored subcontract construction workers. 

Figure 2. NIOSH evaluation of the relative number of DuPont construction trade worker and 

subcontractor construction trade worker claimants monitored for plutonium from 1956

through1988 (NIOSH, 2017)
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Figure 3. Number of subcontractor construction trade worker claimants compared to all other 

SRS workers with claims as of August 2018 (NIOSH, 2019c, p. 13) 

It is important to note that the evaluation provided in NIOSH (2019b) only consisted of 5 of the 

18 years during the DuPont period (pre-1990). Additional data were only coded from the SRS 

logbooks for subcontractors and then for only 3 of the 18 DuPont years (1974, 1983, and 1986). 

In light of subcontractor construction workers showing elevated urinalysis values and derived 

intakes at the 95th percentile during the 1979–1987 period, a more rigorous analysis may be 

warranted to determine the extent to which such differences exist (or do not exist) in other years 

during the Special Exposure Cohort (SEC) period (post-September 1972). 

Observation 1: The evaluation in NIOSH (2019b) was limited to 5 years during the DuPont 

Era (1972–1989), and additional data (beyond previously captured NOCTS data) were

coded for only subcontractors during 3 of these 5 years. Given that subcontract 

construction workers showed higher derived intakes at the 95th percentile from 1979

through 1987, a more rigorous analysis during the SEC period may be appropriate to 

determine the extent to which such differences exist in other years, which may further 

prompt the need for stratification. 

SC&A Review of Subcontractor Designations

NIOSH (2019b) identifies subcontract workers based on their payroll identification number 

(PRID) and states the following concerning the interpretation of PRIDs:
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This original CTW dataset was stratified into prime versus subcontractor workers 

using SRS payroll identification (PRID) numbers. The PRID format protocol for 

subcontract CTWs is as follows:

• n-xxxxx where the prefix “n” is either 4, 5, 6, or a two digit number such 

as . The number to the right of the dash must be 5 digits. Examples are 

• xxxxx where xxxxx is a 5-digit number with no dashes. An example is 

. An example of a PRID to skip is 

Each result with a PRID meeting the above criteria was considered a 

subcontractor CTW. All other results were considered prime CTW related results. 

[NIOSH, 2019b, p. 3] 

SC&A examined the U.S. Department of Labor case files for 35 randomly selected claimants 

designated as subcontractors in the NIOSH (2019b) analysis. SC&A found that 13 of 35 

(~37 percent) reviewed claims indicate employment with the prime contractor despite their PRID 

numbers fitting the above criteria for subcontractors. A summary of these 13 claims is shown in 

table 3. 

Table 3. Summary review of 13 claimants with potentially incorrect designation as a 

subcontractor

Case* Claim PRID(s) Job Title(s) DOL Initial Case Notes

A [Redacted] [Redacted] Sheetmetal 

Worker

Only lists DuPont, Bechtel, and Westinghouse 

Savannah River Company (WSRC) as the 

covered employers (pp. 2–4, 8, 9). The 

Occupational Work History lists DuPont as the 

employer during the period of interest (p. 58). A 

copy of the energy employee’s (EE’s) resume also 

lists DuPont as the employer during the period of 

interest (p. 77).

B [Redacted] [Redacted] [Redacted] Page 19 indicates employment with E. I. DuPont 

Savannah River, then Bechtel in 1989, followed by 

Westinghouse for 1997–present. The general 

description of work duties also lists employment 

with the prime contractor (p. 147). A medical 

report from 1979 lists the employer as E. I. 

DuPont (p. 1094). Finally,

, as well as 

a from 1991, lists 

E. I. DuPont as the employer during the period of 

interest (pp. 768, 1123). 

C [Redacted] [Redacted] Carpenter The only employers mentioned are DuPont and 

Bechtel on standard EE-3 form; there is no 

mention of any subcontractor employment (pp. 4–

5). Termination of employment form from 1992 

checks “Bechtel Savannah River” rather than 

“Other” (p. 15).
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Case* Claim PRID(s) Job Title(s) DOL Initial Case Notes

D [Redacted] [Redacted] Sheetmetal 

Worker

Page 3, which displays the NIOSH Referral 

Summary Document, lists E. I. DuPont as the 

employer. Form EE-3 lists three subcontractors in 

addition to E. I. DuPont. EE-3 indicates 

employment with DuPont was from 1952 through 

1988; however, the actual covered employment is 

intermittent during this period. Two of the identified 

subcontractors indicate employment for just a few 

months, one of which was in 1973 (outside the 

covered employment periods). The other two 

subcontractor entries do not provide a timeframe 

(p. 7).

E [Redacted] [Redacted] [Redacted] On page 2, the Statement of Accepted Facts 

states: “The claimant reported on the EE-3 that 

[the EE] worked for Dupont Bechtel at Savannah 

River Site at Aiken SC from [redacted]. . . DOE 

verified and confirmed employment dates to be 

[redacted]. No other employment history is 

reported.” Medical admission form contains an 

entry for “employer,” but the entry is illegible (p.

35).

F [Redacted] [Redacted] Sheetmetal 

Worker

Page 3 indicates DuPont and WSRC as the 

employers. The Verification of Employment form 

checks “verified” and “contractor” (does not check 

“subcontractor”). The file labelled as “DOL ANRSD 

Return” contains the “Statement of Case” on page 

59, which states, “you specifically alleged that you 

had worked for E.I. Dupont and Westinghouse at 

the Savannah River Site. . . . The Department of 

Energy verified your employment history for the 

Savannah River Site.”

Additional note: Computer-assisted telephone 

interview conducted with EE indicates their 

supervisors from DuPont and Bechtel. 

G [Redacted] [Redacted] Construction 

Worker

Page 7 lists DuPont and Westinghouse as the 

employer. Pages 10–11 contain the Employment 

Verification Sheet, which lists DuPont and WSRC 

with “contractor” checked (“subcontractor” is not 

checked).
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Case* Claim PRID(s) Job Title(s) DOL Initial Case Notes

H [Redacted] [Redacted] [Redacted] The NIOSH Referral Summary Document 

indicates employment with the Nooter Corporation 

at SRS until April 1972 before changing 

employment to DuPont and then Bechtel (p. 3). 

The Employment Verification Sheet checks the 

box “contractor” and lists DuPont (p. 19). Page 60 

contains the Occupational History Interview, which 

affirms employment with DuPont and Bechtel 

during the SEC period. 

Additional note: The bioassay records provided by 

DOE appear to have a sticky note on the record 

that indicates: (see DOE Response 

page 21). Whole body count records from 1988 

and 1990 also reflect this PRID. 

I [Redacted] [Redacted] [Redacted] The NIOSH Referral Document and EE-3 form 

both indicate DuPont and Westinghouse as the 

employer (pp. 3, 7). A Request for Review by 

Medical Panels form affirms employment with the 

prime contractors (p. 115). A 

form from 1988 indicates the employer was 

DuPont (p. 123). Page 141 contains a detailed 

work history, which indicates DuPont at the start of 

covered employment.

J [Redacted] [Redacted] Sheetmetal 

Worker

Form EE-3 lists the employer as DuPont 

Construction (p. 5), which is also listed on pages 

125, 130, and 137. The EE-5 Employment 

Verification form indicates employment by the 

“contractor,” not a “subcontractor” (p. 105). 

EEOICPA-related correspondence also indicates 

employment with DuPont (p. 125). The 

Occupational History Interview further affirms 

employment with the prime contractor (DuPont) 

(pp. 130, 137).

K [Redacted] [Redacted] Transportation For EE-3 only lists E.I. DuPont as the employer. 

Page 19 contains a medical form from 1988 that 

lists E.I. DuPont under “usual occupation.” Three 

additional medical admission forms from 1987 and 

1988 indicate E. I. DuPont as the employer (pp. 

41, 42, and 46).

L [Redacted] [Redacted] Sheetmetal 

Worker

The NIOSH Referral Summary document lists the 

employers only as Bechtel and DuPont (pp. 3–4). 

The Employment Verification Sheet indicates 

“DUPONT” and checks “contractor” (does not 

check the “subcontractor” option) (p. 8).

M [Redacted] [Redacted] Laborer On page 2, the Statement of Accepted Facts 

states: “was employed with Westinghouse, a DOE 

contractor at Savannah River as a laborer from 

June 1978 to October 2000.” Page 24 

contains a medical record that lists the employer 

as Westinghouse/Bechtel.

*Arbitrarily assigned case designation for this report only.
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Finding 2: A review of 35 randomly selected subcontractor claimants used in the NIOSH 

analysis indicated that 13 of 35 (~37 percent) may have been incorrectly categorized as 

subcontractors using the PRID number as the sole indicator. 

The remaining 22 of the 35 reviewed claims all contained evidence of employment with 

subcontractors. SC&A also reviewed 25 randomly selected claimants designated as prime 

contract workers in the NIOSH (2019b) analysis, with all 25 appearing to be correctly assigned 

to the prime contract worker category. 

SC&A Comments on Additional Data Coding

As noted above, NIOSH (2019b) coded additional bioassay data for subcontractors during the 

years 1974, 1983, and 1986 in order to increase the number of results to a sufficient level for 

analysis. In short, the subcontractor evaluation for these years contains a combination of 

claimant monitoring and nonclaimant monitoring, while all other evaluations use only claimant 

monitoring. SC&A presumes the guiding assumption to justify this expansion is that the claimant 

population represents the same exposure potential as the nonclaimant population, as concluded in 

ORAUT-OTIB-0075, revision 01, “Use of Claimant Datasets for Coworker Modeling” (NIOSH, 

2016a).2 

2 SC&A reviewed revision 00 of ORAUT-OTIB-0075 (NIOSH, 2009) in 2010 and currently has 13 active 

findings associated with that review. 

To gain additional information as to the effect of adding nonclaimant data in the narrow context 

of this review, SC&A evaluated the subcontractor claimant data and additional logbook data 

separately for the years 1974, 1983, and 1986 as shown in table 4. The first thing to note is that 

the amount of additional logbook data for these 3 years is roughly nine times greater than the 

amount of claimant data. Therefore, any evaluation of the combined subcontractor strata would 

be dominated by the additional logbook data. By most of the evaluation criteria presented in 

table 4 (e.g., arithmetic average, rank order 95th percentile, and lognormal geometric mean), the 

claimant population has higher urinary excretion rates than the additional logbook subcontractor 

population. This trend was also apparent for 1974 when examining the lognormally fit 95th

percentile values. 

Observation 2: The urinary excretion rates for claimant subcontractors at the average 

and lognormal geometric mean suggest a higher exposure potential than nonclaimant 

subcontractors for the years in which nonclaimant data were used to supplement the 

evaluation (1974, 1983, and 1986). Because nonclaimant data dominate the evaluated 

subcontractor population in these years, this could have a significant effect on the 

combined subcontractor analysis and subsequent comparison to prime contract 

workers.

 
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Table 4. Comparison of claimant subcontractors and additional logbook subcontractors for the 

years 1974, 1983, and 1986

Category 1974 1983 1986 SC&A comments

Total number of 

subcontractors 

evaluated

216 641 1,130 The total evaluated subcontractor workers for the 

remaining 2 years was just 69 (1977) and 83 

(1980). By comparison, the number of claims for 

1985 (in which additional data were deemed 

necessary) was 97 (see row below).

Number of claimants 

(% of total)

26 

(12%)

63 

(10%)

97 

(9%)

Claimant population represents just 10% of the 

evaluated strata.

Number of additional 

logbook workers (% of 

total)

190 

(88%)

578 

(90%)

1,033 

(91%)

Additional logbook workers constitute 

approximately 90% of the evaluated strata.

Claimant arithmetic 

average

0.024 0.028 0.047 Claimant population bounds the additional 

logbook workers for all 3 years.

Logbook arithmetic 

average

0.011 0.023 0.043 No additional comments.

Claimant rank order 

95th percentile

0.1000 0.1000 0.1183 Claimant population bounds the additional 

logbook workers for 1974 and is equal for 1983 

and 1986.

Logbook rank order 

95th percentile

0.0797 0.1000 0.1183 No additional comments.

Claimant lognormally 

fit geometric mean

0.0105 0.0139 0.0266 Claimant population significantly bounds the 

additional logbook workers for all 3 years.

Logbook lognormally 

fit geometric mean

0.0009 0.0037 0.0098 No additional comments.

Claimant lognormal 

95th percentile

0.0568 0.0855 0.1533 Claimant population bounds the additional 

logbook workers for 1974 though is lower for 

1983 and 1986.

Logbook lognormal 

95th percentile

0.0352 0.0991 0.2011 No additional comments.

SC&A Comments on Regression Analysis

NIOSH (2019b) noted that oftentimes the available hardcopy data did not provide a normalized 

volumetric urinalysis result (i.e., disintegrations per minute (dpm)/day or dpm/1.5 liters (L)) but 

rather provided only an activity per sample disc (i.e., dpm/disc). NIOSH notes that without 

specific knowledge of the laboratory practices and standard calculation steps, it is not possible to 

convert the results given in dpm/disc to a standard volumetric result (dpm/1.5 L) in a typical 

manner. Therefore, NIOSH adopted an approximate approach in which a regression line was fit 

to pairs of data containing a numerical result for both dpm/disc and dpm/1.5 L. The underlying 

assumption is that there is a linear relationship between the two bioassay quantities. NIOSH 

developed the following linear regression parameters for each of the five years under analysis: 
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• 1974: slope = 8.9815, intercept = −0.1165 

• 1977: slope = 8.9292, intercept = −0.0886 

• 1980: slope = 8.8899, intercept = −0.0877 

• 1983: slope = 8.9682, intercept = −0.0897 

• 1986: slope = 6.5474, intercept = −0.0385 

Typically, when results are provided in the form of disintegrations per minute, as opposed to a 

raw quantity such as counts per minute, factors such as detection efficiency, chemical yield, and 

the branching ratios for the individual nuclide have already been taken into account. Therefore, 

the remaining unknown quantity would simply be the amount of aliquot that had been evaporated 

onto the disc prior to measurement. If the quantity of aliquot evaporated on each disc is 

reasonably constant, then a simple ratio should be sufficient to scale the result from dpm/disc to 

dpm/1.5 L. 

However, SC&A’s examination of the available database supplied by NIOSH identified sample 

results in which the dpm/disc result was zero or negative, yet a positive volumetric result 

(dpm/1.5 L) was recorded (see table 5). SC&A checked each of these pairs against the hardcopy 

logbook results to assure the accuracy of the transcription as found in column 5 of table 5. As 

seen in the table, several of the observed pairs used in the NIOSH (2019b) analysis appear to be 

in error. No quality assurance criteria were provided in NIOSH (2019b) to indicate the veracity 

of the transcription of hardcopy data underpinning the resulting analysis. Such an analysis should 

be conducted to assure that data transcribed from SRS laboratory logbooks are sufficiently 

accurate and within the acceptable bounds established in ORAUT-RPRT-0078, revision 00, 

“Technical Basis for Sampling Plan” (NIOSH, 2016b). That document establishes acceptable 

levels of transcription errors when data must be manually transcribed from hardcopy records. 

Finding 3: NIOSH (2019b) does not provide a discussion of or evidence that a quality 

assurance evaluation of the transcribed plutonium logbook data was performed to 

assure that derived excretion rates are sufficiently accurate for an effective comparison 

of the two strata of interest (subcontractors and prime contractors). 

In analyzing the plutonium disc data, SC&A identified several data pairs that contain a zero or 

negative result for dpm/disc but were associated with a volumetric bioassay result that was 

positive (see the first four rows of table 5). The verified data pairs call into question the use of a 

linear regression analysis to convert dpm/disc to dpm/1.5 L; however, such data pairs also raise 

questions about the veracity of the method in which a negative/zero measurement of an aliquot 

disc could result in a positively reported bioassay quantity. 

SC&A raised similar questions regarding the americium (Am)/curium/californium bioassay 

results discussed in SC&A’s review of the SRS coworker model (SC&A, 2019) in OTIB-0081. 

The SRS coworker model in OTIB-0081 uses claimant data in NOCTS for the formulation of 

coworker intakes; therefore, the variation of such data pairs in the hardcopy logbook results is 

not relevant to that document. 
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Table 5. SC&A-identified data pairs showing a negative/zero measurement with a positively 

reported volumetric bioassay quantity

SRDB Ref ID, 

PDF pages

Dpm/ 

disc 

result

Dpm/ 

1.5 L 

result

SC&A verification comment

51970, 

24–25

0 0.002 Verified.

53263, 

215–216

-0.003 0.113 Verified.

172166, 

286–287

0 0.09 Verified.

172171, 

42–43

0 0.038 Verified.

51970, 

108–109

-0.013 0.008 In error: Transcription appears to equate raw Pu 

measurements (dpm/disc) with raw Am measurements 

(dpm/disc).

172169, 

164–165

-0.005 0.0135 In error: Correct entry for dpm/1.5 L should be -0.135.

172169, 

156–157

-0.001 0.098 In error: Correct entry for dpm/1.5 L should be -0.098.

172166, 

250–251

0 0.091 Likely in error: Entries appear to read “-.000” and “-0.091.”

172169, 

174–175

0 0.092 Likely in error: Entries appear to read “-.000” and “-.092.”

52022, 

28–29

-0.038 0.7 Potentially in error: Interpretation of this record is difficult,

as the dpm/disc results are listed in linear order and the 

dpm/1.5 L results are in block form. The actual data pairs 

may have been mixed up as a result.

172171, 

103–104

-0.003 0.121 Potentially in error: Record is difficult to interpret; there is 

either a negative sign or a decimal on the record. If it is a 

negative sign, then there is no decimal and vice versa.

52022, 

16–17

-0.001 0.448 Potentially in error: Dpm/1.5 L value is crossed out;

therefore, it is difficult to tell if the result should have been 

“-.448.”

Observation 3: SC&A identified data pairs in which a zero or negative measurement of 

the activity on a given aliquot disc (dpm/disc) was reported as a positive volumetric 

bioassay result (dpm/1.5 L). SC&A believes this calls into question whether a reasonable 

numerical relationship between the individual aliquot measurements and normalized 

volumetric bioassay results can be effectively derived. 

To further evaluate the accuracy of the regression formulas presented in NIOSH (2019b), SC&A 

compared the available measurement pairs (dpm/disc and dpm/1.5 L) in cases where both 

quantities were positive against the predicted result based only on the dpm/disc result and the 

associated regression formula. While some data pairs were predicted by the regression formulas 

with reasonable accuracy (especially at higher relative values), SC&A found that the regression 

analysis had a particularly poor fit for the years 1980 and 1986, as shown in figures 4 and 5. 

Finding 4: The use of a regression analysis to convert raw bioassay results (dpm/disc) to 

a volumetric result (dpm/1.5 L) has not been technically justified and does not appear 

scientifically defensible. 
SC&A, Inc.

CTW Pu Stratification, page 13 November 12, 2019

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Figure 4. Comparison of the actual dpm/disc and dpm/day data pairs against predicted dpm/day 

values for 1980

Figure 5. Comparison of the actual dpm/disc and dpm/day data pairs against predicted dpm/day 

values for 1986
SC&A, Inc.

CTW Pu Stratification, page 14 November 12, 2019

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Privacy Act 5 USC §552a and has been cleared for distribution. 

Summary Conclusions 

The analysis presented in NIOSH (2019b) is limited to only a handful of years for evaluation 

(1974, 1977, 1980, 1983, and 1986) and restricted to claimant data, with the exception of 

subcontractors in 1974, 1983, and 1986 for which additional data were coded (see observations 1 

and 2). Evaluation of the additional data suggests that the exposure potential for claimant 

subcontractors during these years may be higher at the average and geometric mean levels than 

the nonclaimant subcontractors. This is also true for 1974 when the lognormal 95th percentile is 

higher for claimant subcontractors than for nonsubcontractors (see observation 2). 

In addition, SC&A notes that no quality assurance tests were discussed in NIOSH (2019b), 

though SC&A identified erroneous transcription errors associated with the dataset (see finding 3 

and observation 3). Furthermore, SC&A does not agree that the use of a linear regression method 

to further expand the dataset when normalized volumetric bioassay measurements are 

unavailable is scientifically accurate or defensible (see finding 4). SC&A has concerns about the 

quality assurance protocol used in transcribing the additional logbook data (see finding 3), and 

evidence also suggests that the methodology relying solely on PRID numbers to identify 

subcontractors may erroneously include prime contractors in the subcontractor strata (see 

finding 2).

Nonetheless, at face value, the NIOSH (2019b) evaluation demonstrates that subcontract CTWs

had higher estimated intakes at the 95th percentile than nonsubcontract CTWs for 1979–1987. 

Thus, SC&A does not agree that it has been demonstrably shown that subcontracted and 

nonsubcontracted CTWs are part of the same worker stratification for the purposes of coworker 

modeling and thus can be appropriately combined (see finding 1). SC&A suggests that further 

analysis be provided before such a conclusion can be reached. Further analysis might include 

(1) expansion to the remaining years of SEC-103, (2) expansion to include logbook results in all

strata evaluations, (3) quality assurance checks on the transcribed data, (4) confirmation of

subcontractor designations, and (5) removal of the regression methods employed in NIOSH

(2019b).

References

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

Privacy Act 5 USC §552a and has been cleared for distribution. 

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SC&A, Inc.

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Privacy Act 5 USC §552a and has been cleared for distribution. 

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