Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Surrogate Data Usage

Blockson Chemical Company 

Special Exposure Cohort Petition SEC00225

James W. Neton, PhD, CHP

Associate Director for Science

Division of Compensation Analysis and Support

Advisory Board on Radiation and Worker Health 112th meeting

Idaho Falls, Idaho

August 9-10, 2016
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Radon Exposure During the Residual 

Contamination Period (1960-1991)

 Radium bearing waste deposited on large 

phosphogypsum stacks 

 Radon exposure in residual period from waste generated 

during the covered period (March 1951- June 1960) is 

reconstructed under Energy Employees Occupational 

Illness Compensation Program Act (EEOICPA)

 Exposure from phosphate plant production after Atomic 

Energy Commission (AEC) operations is not covered 

under EEOICPA
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Available Radon Exposure Data

 Several radon measurements in Building 55 in 1978 

were all low—maximum 0.61 pCi/liter

 Measurements made in 1983 at several locations on 

site were all low with maximum result of 0.0042 WL 

reported for the STPP (sodium tripolyphosphate) 

area

 Single measurement in 1983 taken at 

phosphogypsum pile was 0.0012 WL (0.29 pCi/L) 
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Radon Flux Data at Blockson

 In 1993, 300 radon flux measurements taken at the 

inactive stacks

 The weighted mean flux measurements was 4.1 

pCi/m2-s 

 The highest mean was 10.1 pCi/m2-s around the 

sides

 Radon concentration not reported with flux
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Estimates of Radon Exposures

 Radon flux values at Blockson similar to results reported for 

Texas City Chemicals (TCC) phosphogypsum stack

• Average value at TCC was 10.5 pCi/m2-s

 Both sites had the flux measurements taken around the inactive 

stacks after plants permanently closed

 Flux data for Texas City Chemicals includes radon 

concentration at top of the stack

 Factor applied to inactive stack radon concentration to allow for 

presumed higher concentration during active stack period 

during plant operations
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

2.1

0.42

0.29

0

0.5

1

1.5

2

2.5

1955 1960 1965 1970 1975 1980 1985 1990 1995

Rn (pCi/L)

Year

Radon Concentrations at the Phosphogypsum Piles

Texas City

Blockson

Expon. (Texas City)

(Adjusted)
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Review Against the Board’s Surrogate 

Data Criteria

 Hierarchy of Data

 Exclusivity Constraints

 Site or Process Similarities

 Temporal Considerations

 Plausibility

•
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Surrogate Data Evaluation 

 Hierarchy of Data

• No personnel monitoring data and only one radon 

concentration value available from 1983

• Process and source term data known but not useful in 

characterizing radon levels at the stacks

• Surrogate data from Texas City has distinct advantage over 

the above, but does require some adjustment
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Surrogate Data Evaluation – contd. 

 Exclusivity Constraints (stringent justification required)

• The available data on flux measurements at both sites were 

taken using Environmental Protection Agency (EPA)-approved 

methodology

• They both represent complete data sets that are 

representative of the flux rates at each site

• Simultaneous radon and flux measurements at Texas City 

allow for interpretation of flux data at Blockson
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Surrogate Data Evaluation – contd. 

 Site or Process Similarities

• Both sites created phosphogypsum waste by producing phosphoric acid 

from phosphate rock using the wet process

• Both sites used phosphate rock from Florida. The phosphate rock ores 

contained about 0.01% natural uranium

• The phosphogypsum stack at Blockson comprised 227 acres and was 90 

feet tall, while the stack at Texas City Chemicals was 35 acres and 30 feet 

tall

- Measurements were taken close to the stacks which would mitigate any 

issues related to stack size differences
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Surrogate Data Evaluation – contd. 

 Temporal Considerations

• Both Blockson and Texas City started AEC production 

activities in the 1950s

• Flux measurements at Texas City and Blockson taken on 

inactive stacks 

• Adjustments have been made to account for the relative 

emissions from active versus inactive piles

• EPA value used to increase emission rate by a factor of 5 

for active piles
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Surrogate Data Evaluation – contd. 

 Plausibility

• The radon concentrations of 2.1 pCiL at the start of the residual period and 

0.4 pCi/L in 1993 are consistent with known low concentrations associated 

with phosphogypsum stacks

• The value of 0.29 pCI/L measured at the phosphogypsum stacks in 1983 

is bounded by the predicted concentration of 0.69 pCi/L that is based on 

the Texas City Chemical data

• While the values are likely overestimates for the portion of the exposure 

due to AEC operations, it provides an upper bound estimate of a worker’s 

exposure
Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Conclusion

 Based on a review of the available information at Blockson 

Chemical and Texas City Chemicals, the application of 

outdoor radon concentration data at Texas City Chemicals to 

the phosphogypsum stacks at Blockson Chemical meets the 

Board’s criteria for surrogate data usage

 Using these data, along with an appropriate adjustment, the 

radon concentration data at Texas City Chemicals plausibly 

bounds the exposures to workers at the Blockson Chemical 

Company during the residual contamination period