DCAS-PER-092, Subtask 4:

Review of Two Reworked Cases for the 

Evaluation of DCAS-PER-092

Ron Buchanan, PhD, CHP

Advisory Board on Radiation and Worker Health, 

Subcommittee for Procedure Reviews

February 16, 2023
2

Weldon Spring facilities

 Weldon Spring Plant (WSP), Weldon Spring Quarry (WSQ), 

and the Weldon Spring Raffinate Pits (WSRP)

 Referred to as the Weldon Spring Plant in general 

 Operated by the U.S. Atomic Energy Commission as a feed 

materials plant to process uranium and thorium ore by the 

Uranium Division of Mallinckrodt Chemical Works
3

Four periods of operation

1. Site acquisition and development, 1954–1957

2. Operational, 1957–1966

3. Post-operational, 1967–1985 – U.S. Department of Defense 

(DoD), not the U.S. Department of Energy (DOE), controlled:

– WSP during the post-operational period 1967–1985

– WSRP and WSQ during 1967–1974

4. Remediation, 1985–2002
4

EEOICPA coverage

 WSP employment is covered:

– Operational period (1957–1966)

– Remediation period (1985–2002)

 WSQ and WSRP employment is covered:

– Operational period (1957–1966)

– Post-operational period (1975–1984)

– Remediation period (1985–2002)
5

Radionuclides of dose significance

 Natural uranium processed 1957–1962

 After 1962, all uranium is assumed to be enriched to 1%

 Natural thorium

 Recycled uranium processed beginning in 1961

 Rn-222 and Ra-228 considered to be potentially significant for 

dose reconstruction (DR)
6

Weldon Spring environmental dose site profile

 ORAUT-TKBS-0028-4, rev. 00, issued June 28, 2005

 ORAUT-TKBS-0028-4, rev. 01, issued May 17, 2013

 ORAUT-TKBS-0028-4, rev. 02, issued March 29, 2017

 ORAUT-TKBS-0028-4, rev. 03, issued September 8, 2017

 ORAUT-TKBS-0028-4, rev. 04, issued March 27, 2020
7

Weldon Spring environmental dose program 

evaluation reports (PERs)

 DCAS-PER-051, issued March 4, 2015, to address changes in 

DR procedures using ORAUT-TKBS-0028-4, rev. 01 

 DCAS-PER-083, issued January 7, 2019, to address changes 

in DR procedures using ORAUT-TKBS-0028-4, rev. 03

 DCAS-PER-092, issued March 29, 2021, to address changes 

in DR procedures using ORAUT-TKBS-0028-4, rev. 04
8

TKBS-0028-4, rev. 04 changes that could 

increase assigned doses

 Environmental intakes of Rn-222 and Ra-228 were added for 

1963 through 1966

 U-234 intakes were added for the Weldon Spring Quarry for 

the years 1990, 1991, 1993–1996, and 1998–2001

 Onsite ambient gamma doses from 1957 to 1966 were 

previously applied as a constant value, but rev. 04 included 

geometric standard deviation (GSD) values that are to be 

applied to the lognormal distribution
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SC&A’s review of PER-092, tasks 1–3

 February 15, 2022 − Advisory Board on Radiation and Worker 

Health Subcommittee for Procedure Reviews (SPR) tasked 

SC&A to review DCAS-PER-092, “Weldon Spring Plant”

 June 9, 2022 − SC&A issued “A Review of NIOSH’s Program 

Evaluation Report DCAS-PER-092, ‘Weldon Spring Plant’” to 

fulfill tasks 1 through 3
10

Subtask 4: Conduct audits of a sample set of 

reevaluated DRs impacted by PER-092

 SPR tasked SC&A with a review of representative cases

 November 2, 2022 − NIOSH provided SC&A with two cases

 December 28, 2022 − SC&A provided a written report of the 

results of DR audit under subtask 4 to the SPR
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Subtask 4: Selection of cases

 Criterion for selection of cases:

– Criterion 1: environmental intakes of Rn-222 and Ra-228 during all or 

part of 1963–1966

– Criterion 2: environmental intake of U-234 at the WSQ during all or part 

of 1990, 1991, 1993–1996, and/or 1998–2001

– Criterion 3: onsite external ambient gamma dose during all or part of 

1957–1966
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Subtask 4 – Two cases from NIOSH

 Case A met criterion 1 and criterion 3 

 Case B did not meet: 

– Criterion 1 or criterion 3 because the energy employee (EE) was not 

employed at WSP during 1957–1966, and

– Criterion 2 was not applicable because the maximum U-234 intake for 

the EE’s employment period was greater for WSP compared to WSQ

 NIOSH stated that there were no claims with environmental 

U-234 intakes assigned from the WSQ 
13

Case A dose reconstruction

 EE worked throughout the site during one covered year

 Initial DR performed in 2006 for several cancers

 DR revised in 2018 because the EE was diagnosed with 

additional cancers

 DR was again revised in November 2020 as a result of the 

issuance of ORAUT-TKBS-0028, rev 04.
14

Case A: Assessment of external ambient dose

2018 DR:

 Calculated external ambient dose 

using the median gamma dose 

value 0.123 rem per year from 

table 4-4 of ORAUT-TKBS-0028-

4, rev. 03, for the year of covered 

employment 

 Dose assigned using a constant 

distribution with no uncertainty in 

the IREP input tables 

2020 reworked DR:

 Calculated external ambient dose 

using the median gamma dose 

value 0.123 rem per year from 

table 4-5 of ORAUT-TKBS-0028-

4, rev. 04, for the year of covered 

employment

 dose assigned using a lognormal 

distribution with a GSD of 3.160 in 

the IREP input tables
15

SC&A’s evaluation of case A external ambient 

dose assignment

 SC&A concurs with NIOSH dose assignments for most of the 

cancers

 However, SC&A had an observation
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SC&A’s evaluation of case A external ambient 

dose assignment – observation 1

 Observation 1: NIOSH did not use environmental dose 

conversion factor (DCF) for the non-skin cancer

– 2020 DR assigned the external ambient dose using a DCF of 1.0 for 

the non-skin cancer

– According to TKBS-0028-4, rev. 04, section 4.3.3, the isotropic 

exposure geometry is to be used for external ambient dose and the 

exposure (R)-to-organ DCF is to be used for the operational period 

(1957–1966)

– An overestimate of 0.057 rem was assigned
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Case A: Assessment of internal environmental 

dose

2018 DR:

 Calculated internal doses using 

environmental intake values given in 

table 4-3 of ORAUT-TKBS-0028-4, 

rev. 03, for U-234, Th-228, Th-230, 

Th-232, Pu-239, Pu-241, Am-241, 

Np-237, Tc-99, Ru-106, Zr-95, Nb95, Sr-90, and Ra-222 

 Assigned total internal doses using a 

lognormal distribution with a GSD of 

3.0 in the IREP input tables

2020 reworked DR:

 Calculated internal doses using 

environmental intake values given in 

table 4-4 of ORAUT-TKBS-0028-4, 

rev. 04, for the same radionuclides 

as used in 2018 DR 

 Assigned larger total internal doses 

using a lognormal distribution with a 

GSD of 3.0 in the IREP input tables
18

SC&A’s evaluation of case A internal 

environment dose assignment

 Compared the data and parameters used in NIOSH’s Chronic 

Annual Dose tools (CADs) to the values recommended in 

table 4-4 of TKBS-0028-4, rev. 04, and found them to be 

correct 

 Found the annual dose values correctly entered in the IREP 

input tables, using a lognormal distribution with a GSD of 3.0

 SC&A did have an observation about several of the cancers’ 

dose assignments.
19

SC&A’s evaluation of case A internal 

environment dose assignment – observation 2

 Observation 2: NIOSH did not always incorporate the date 

of cancer diagnosis

– For earlier cancers, the DR calculated doses using the CAD dose 

information from the last cancer 

– The DR included the entire year of internal dose for the year the cancer 

was diagnosed, rather than prorating the annual dose to the 

appropriate date of the earlier cancer diagnoses 

– This resulted in assigning approximately an extra 0.001 rem to each of 

the cancer sites other than the last cancer
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Case B dose reconstruction

 EE worked throughout the site for several years

 Initial DR performed in October 2010 

 DR revised in December 2010 because the EE was diagnosed 

with additional cancers

 DR was again revised in November 2020 as a result of the 

issuance of ORAUT-TKBS-0028, rev 04
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Case B: Assessment of external ambient dose

2010 December DR:

 Calculated overestimate of external 

ambient doses using the median gamma 

dose values of 0.123 rem per year from 

table 4-12 of ORAUT-TKBS-0028-4, rev. 

00, adjusted for an exposure time of 80 

hours per week, prorated for the 

employment years

 Dose assigned using a constant 

distribution with no uncertainty in the 

IREP input tables

2020 reworked DR:

 Calculated external ambient doses using 

the maximum average gamma dose 

values from table 4-7 of ORAUT-TKBS0028-4, rev. 04, assuming a more 

reasonable 2,500 hours of exposure per 

year (per CATI information), prorated for 

the employment years

 Dose was assigned using a constant 

distribution with no uncertainty in the 

IREP input tables
22

SC&A’s evaluation of case B external ambient 

dose assignment

 SC&A concurs with the numerical dose values NIOSH 

assigned

 However, SC&A had one observation and one finding about the 

dose assignments
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SC&A’s evaluation of case B external ambient 

dose assignment – observation 3

 Observation 3: NIOSH did not incorporate the diagnosis 

date for one of the cancers for external ambient dose

– It appears that NIOSH assigned the external ambient dose for the 

entire year to one of the cancers

– However, one of the cancers was diagnosed in the middle of the year

– This resulted in an additional 0.018 rem being assigned
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SC&A’s evaluation of case B external ambient 

dose assignment – finding 1

 Finding 1: NIOSH assigned ambient external dose with a 

constant distribution

– NIOSH assigned the ambient external doses for all cancers with a constant 

distribution and no uncertainty in the IREP input tables

– Section 4.4 of TKBS-0028-4, rev. 04, recommends for the post-operational external 

doses, the onsite ambient dose be represented as a normal distribution with a GSD of 

30%

– Annual dose values in table 4-7 of TKBS-0028-4, rev. 04, are the maximum of the 

average dose values for the different facilities at the site (not the 95th percentile)

– SC&A believes that the environmental external doses should have been assigned 

with a normal distribution

– SC&A reworked the DR assigning external ambient dose using a normal distribution 

with a GSD of 30% and derived a slightly greater combined POC value
25

Case B: Assessment of internal environmental 

dose

2010 December DR:

 Calculated internal doses using 

environmental intake values in table 4-7 

of ORAUT-TKBS-0028-4, rev. 00, for 

uranium, assigned as U-234, and 

recycled uranium components

 Assigned total internal doses using a 

lognormal distribution with a GSD of 3.0 

in the IREP input tables

2020 reworked DR:

 Calculated internal doses using 

environmental intake values in table 4-4 

of ORAUT-TKBS-0028-4, rev. 04, for U234, Th-228, Th-230, Th-232, Pu-239, 

Pu-241, Am-241, Np-237, Tc-99, Ru-106, 

Zr-95, Nb-95, Sr-90, and Ra-222 

 Assigned greater total internal doses to 

each of the cancer sites using a 

lognormal distribution with a GSD of 3.0 

in the IREP input tables
26

SC&A’s evaluation of case B internal 

environmental dose assignment

 Compared the data and parameters used in NIOSH’s CADs to 

the values recommended in table 4-4 of TKBS-0028-4, rev. 04, 

and found them to be correct

 Found annual dose values were correctly entered in the IREP 

input tables, using a lognormal distribution with a GSD of 3.0

 SC&A did have one observation about one of the cancers
27

SC&A’s evaluation of case B internal environmental 

dose assignment – observation 4

 Observation 4: NIOSH did not incorporate the date of 

diagnosis for one of the cancers for environmental internal 

dose

– For one of the cancers, the date of diagnosis was incorrectly entered in 

the CAD as 12/31/2001 instead of the correct diagnosis date 

– This resulted in an over-assignment of dose of ~0.001 rem
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Summary of SC&A’s evaluation of rework of 

two cases

 SC&A concludes that the doses for case A and case B were 

reevaluated in accordance with the requirements of DCAS-PER092, which addresses changes in ORAUT-TKBS-0028-4, rev. 04

 SC&A identified one finding in which the DR appeared to derive a 

slight underestimate of POC values

 SC&A identified four observations that indicated slight 

overestimates of dose

 Since the combined POC value was very low for each case, none of 

these observations would impact the outcomes of the cases
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Questions?
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References

National Institute for Occupational Safety and Health. (2005). Weldon Spring Plant – occupational 

environmental dose (ORAUT-TKBS-0028-4, rev. 00). 

https://www.cdc.gov/niosh/ocas/pdfs/arch/weldon4.pdf

National Institute for Occupational Safety and Health. (2015). Weldon Spring Plant (DCAS-PER-051, 

rev. 0). https://www.cdc.gov/niosh/ocas/pdfs/pers/dc-per51-r0.pdf

National Institute for Occupational Safety and Health. (2017a). Weldon Spring Plant – occupational 

environmental dose (ORAUT-TKBS-0028-4, rev. 02). 

https://www.cdc.gov/niosh/ocas/pdfs/arch/weldon4-r2.pdf

National Institute for Occupational Safety and Health. (2017b). Weldon Spring Plant – occupational 

environmental dose (ORAUT-TKBS-0028-4, rev. 03). 

https://www.cdc.gov/niosh/ocas/pdfs/arch/weldon4-r3.pdf

National Institute for Occupational Safety and Health. (2019). Weldon Spring Plant TBD revision

(DCAS-PER-083). https://www.cdc.gov/niosh/ocas/pdfs/pers/dc-per83-508.pdf
31

References 2

National Institute for Occupational Safety and Health. (2020). Weldon Spring Plant – occupational 

environmental dose (ORAUT-TKBS-0028-4, rev. 04). 

https://www.cdc.gov/niosh/ocas/pdfs/tbd/weldon4-r4-508.pdf

National Institute for Occupational Safety and Health. (2021). Weldon Spring Plant (DCAS-PER-092). 

https://www.cdc.gov/niosh/ocas/pdfs/pers/dc-per92-r0-508.pdf

SC&A, Inc. (2022). A review of NIOSH’s program evaluation report DCAS-PER-092, “Weldon Spring 

Plant” (SCA-TR-2022-PER092, rev. 0). https://www.cdc.gov/niosh/ocas/pdfs/abrwh/scarpts/sca-per92-

r0-508.pdf