Revised Draft 

EVALUATION OF RADON LEVELS IN BUILDING 40 AT 

BLOCKSON CHEMICAL 

Prepared by 

S. Cohen & Associates 

1608 Spring Hill Road, Suite 400 

Vienna, Virginia 22182 

August 12, 2008 

Disclaimer 

This document is made available in accordance with the unanimous desire of the Advisory Board on 

Radiation and Worker Health (ABRWH) to maintain all possible openness in its deliberations. However, 

the ABRWH and its contractor, SC&A, caution the reader that at the time of its release, this report is predecisional and has not been reviewed by the Board for factual accuracy or applicability within the 

requirements of 42 CFR 82. This implies that once reviewed by the ABRWH, the Board’s position may 

differ from the report’s conclusions. Thus, the reader should be cautioned that this report is for 

information only and that premature interpretations regarding its conclusions are unwarranted.
TABLE OF CONTENTS 

Summary......................................................................................................................................... 3 

1.0 Background......................................................................................................................... 5 

2.0 Applicability of ORAUT-OTIB-0043 ................................................................................ 5 

3.0 Radon Measurements in Building 40.................................................................................. 9 

4.0 Building 40 Radon Modeling............................................................................................ 11 

4.1 Phase 1 – Scoping Analysis.................................................................................. 12 

4.2 Phase 2 – Follow-up Investigations...................................................................... 13 

4.3 Phase 3 – Monte Carlo Analysis........................................................................... 14 

5.0 References......................................................................................................................... 16 

Appendix A: Review of Radon Exposure Estimates Derived from Summary Data in 

ORAUT-OTIB-0043......................................................................................................... 18 

Appendix B: Comprehensive Analyses of 222Rn Concentrations in Building 40........................ 22 

Revised Draft – Blockson Radon Analysis 2 SC&A – August 12, 2008 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker Health for 

factual accuracy or applicability within the requirements of 42 CFR 82.
SUMMARY 

At the request of the Advisory Board, SC&A presents this report to assist the Board in its 

deliberations on the SEC petition for Blockson Chemical Company. Described are multiple 

approaches for defining the bounding average annual radon concentration for Building 40 at 

Blockson during the qualification period. 

SC&A first evaluated the application of the use of Florida phosphate industry data, as adapted 

from ORAUT-OTIB-0043, as a surragate for Blockson radon exposures. In this evalaution, 

SC&A found these data to be applicable in certain aspects and deficient in others. One 

deficiency that we identified in our earlier investigations had to do with the statistical analysis of 

surrogate data. SC&A re-analyzed the data used in OTIB-0043, extracting the individual 

analyses, where possible, from datasets used for the OTIB-0043 analysis. The bounding (95th

percentile) value assigned from OTIB-0043 was 2.33 pCi/L (0.112 WLM/y). After expanding 

the data, SC&A derived a 95th percentile (bounding) radon concentration of 7.78 pCi/L. 

However, subsequent discussion of this matter with NIOSH revealed that NIOSH deliberately 

used the 95th th percentile value of the means of the datasets, as opposed to the 95 percentile of the 

individual measurements, because the latter approach would be unrealistically conservative. 

SC&A agreed with this rationale, but suggested that this rationale be provided in OTIB-0043. 

SC&A found on the “O” drive the results of a 1983 industrial hygiene survey performed at the 

former Blockson Chemical site by the (then) current owner, Olin Corporation (Marseglia 1983). 

At the time of the survey, the plant was continuing to operate as a phosphate products producer. 

The products made by Olin were fertilizers, rather than monosodium phosphate that was 

produced by Blockson Chemical. However, the phosphoric acid production, an intermediate 

step, was most likely not affected by this transition to different end products. In the 1983 survey, 

radon daughter measurements were made in three locations, which appear by their description to 

be in Building 40. For two of the locations, the radon results were nil; but at the third location, 

“40 filtration,” by applying information from the report and other sources, SC&A found the WL 

and WLM from this survey to be 0.002WL and 0.0235 WLM/y, respectively, or less than 

1 pCi/L. 

SC&A went to great lengths, including additional worker interviews, with the participation of 

NIOSH and the chair of the work group, to evalaute the degree to which the measurements made 

in 1983 are indicative of those radon levels that might have been present during the qualification 

period. Our investigations revealed that there were most likely significant modifications made to 

the building ventilation systems between the qualification period and 1983. There is also 

evidence from worker interviews that the phosphoric acid production increased during this time 

frame, creating the potential for even greater radon concentrations in Building 40 in 1983, as 

compared to the qualification period. Nevertheless, we found it difficult to conclude that the 

radon measurements made in 1983 can be considered representative or bounding of the radon 

concentrations present during the qualification period. 

Lastly, as a means to independently assess the reasonableness of NIOSH’s default radon 

concentration of 2.33 pCi/L, SC&A performed a series of deterministic and probabilistic 

analyses to evaluate the possible radon concentrations that might have been present in Building 

Revised Draft – Blockson Radon Analysis 3 SC&A – August 12, 2008 

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40 during the qualification period. In order to scope the range of potential radon concentrations, 

SC&A varied the radon release fraction from the ore dissolved in the acid tanks and the building 

ventilation rate to evaluate the possible range of concentrations. The following table summarizes 

the results of these deterministic calculations. 

Table S-1. Radon Concentrations (pCi/L) based on Deterministic Analysis 

Release fraction from acid (f) ACHa

0.0 0.2 0.4 0.6 0.8 1.0 

0.5 0.44 18.52 36.61 54.70 72.79 90.88 

1.5 0.15 6.24 12.33 18.42 24.51 30.60 

2.5 0.09 3.75 7.41 11.07 14.73 18.39 

3.5 0.06 2.68 5.30 7.92 10.53 13.15 

4.5 0.05 2.09 4.12 6.16 8.20 10.23 

5.5 0.04 1.71 3.37 5.04 6.71 8.37 

Note: A description of the models used to derive these values is 

provided in Appendix B. 

a

 Air changes per hour 

The term “deterministic” is used here, because the calculations are performed using a set of fixed 

or deterministic values for the key calculational parameters. As may be noted, depending on the 

values selected for the radon release fraction and air exchange rate, radon concentrations from 

below 1 pCi/L to as high as 90 pCi/L are derived. 

In light of these uncertainties, SC&A performed a Monte Carlo simulation of the model, which 

we believe can help the Board in judging which of these values best represents the radon 

concentration in Building 40 during the qualification period. The results of the Monte Carlo 

simulation are as follows. 

 Table S-2. Percentile Values of 222Rn Concentrations (pCi/L) 

Percentile Value 

0% 0.02

5% 0.78

10% 1.50

15% 2.24

20% 2.97

25% 3.70

30% 4.44

35% 5.20

40% 5.99

45% 6.84

50% 7.72

55% 8.73

60% 9.87

65% 11.28

70% 13.06

75% 15.54

80% 19.08

85% 24.77

90% 35.37

95% 61.95

100% 651.00

Revised Draft – Blockson Radon Analysis 4 SC&A – August 12, 2008 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker Health for 

factual accuracy or applicability within the requirements of 42 CFR 82.
The results indicate that the default value of 2.33 pCi/L selected by NIOSH in OTIB-0043 falls 

within the range of values and may, in fact, be an appropriate value, especially if only a small 

fraction of the radon in the ore entering Building 40 escapes from the ore during the grinding and 

digestion process and enters the Building 40 atmosphere. However, given the large uncertainties 

in radon release fractions from the ore during crushing and digestion and the uncertainty in the 

air exchange rate for Building 40, a higher default value may be needed. For example, the 

results of this analysis indicate that one can be 95% confident that the average airborne radon 

concentration in Building 40 during the qualification period was less than about 62 pCi/L. 

1.0 BACKGROUND 

On January 10, 2007, SC&A issued its review of the Blockson Chemical Company Special 

Exposure Cohort Petition (SEC), the Technical Basis Document (TBD) (Tomes and Glover 

2007), the Evaluation Report, and selected supporting documentation. One of the findings 

(Finding No. 5) in SC&A’s draft report dealt with the data, models, and assumptions used by 

NIOSH for reconstructing radon exposures to workers at Blockson. Subsequent to the issuance 

of that report, there were numerous work group meetings and an exchange of white papers 

related to this matter, which were effective in addressing many aspects of this issue. This matter 

was further discussed at the Advisory Board meeting held in St. Louis on June 24–26, 2008. 

During that meeting, the Board requested that SC&A specifically address the results of a series 

of worker interviews and calculations that were performed by SC&A and NIOSH in the 2-week 

period prior to the meeting to gain further insight into the radon issue. This report has been 

prepared in response to that request, and to capture in one place the work group discussions that 

led up to the matters discussed at the St. Louis meeting. 

The root cause of the radon issue at Blockson is that there are no identified measurements of 

radon at Blockson Chemical during the SEC qualification period of January 1, 1951, to 

December 31, 1962. The only available measurements were made during an industrial hygiene 

survey conducted in 1983 by the Olin Corporation, the then owner of the Blockson site 

(Marseglia 1983). These measurements were made well after the cessation of uranium extraction 

activities conducted in Building 55 and consisted of 10 radon working level (WL) measurements 

in various indoor and outdoor locations at the site. Although these data are of interest, there is 

some question as to whether they can be used to reconstruct radon exposures of workers decades 

earlier. To remedy this limitation, Tomes and Glover (2007) used radon measurements collected 

at other phosphate facilities (i.e., surrogate data) as the basis for reconstructing radon exposures 

of Blockson workers during the qualification period. Hence, there is some question whether the 

surrogate data can reasonably be used to bound the exposures at Blockson during this period. 

The following sections explore this issue. 

2.0 APPLICABILITY OF ORAUT-OTIB-0043 

Tomes and Glover (2007) and the SEC-00058 evaluation used the radon analysis from ORAUT 

2006 to assign a bounding radon exposure for workers at Blockson. The surrogate data in 

ORAUT 2006 upon which the Blockson bounding radon exposure is based are from a report by 

Birky et al. (1998) and consist of measurements made in a number of phosphate plants in 

Florida. The plants employ the wet production process for phosphoric acid, similar to the 

Revised Draft – Blockson Radon Analysis 5 SC&A – August 12, 2008 

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process at Blockson, and the radon measurements presented were made at various locations 

throughout the plant. Those measurements made in locations obviously not representative of 

phosphoric acid production, e.g., mining rock tunnels, wet rock loading, and mining operations, 

were appropriately excluded from the dataset. 

The radon data listed by ORAUT 2006 were obtained using a number of measurement methods, 

including e-perm, track-etch, and continuous working level monitors. While all are recognized 

and trusted methods, each method has its unique quality factors, and no quality control data are 

presented upon which to determine the overall quality of the dataset. However, all these devices 

were included in the device performance testing portion of the former EPA Radon Proficiency 

Program. The suppliers of these devices were required to maintain quality assurance programs 

and meet rigid quality performance requirements as part of the testing program. As a result, 

SC&A concluded that the measurements met the data quality requirements required by the EPA. 

In the analysis of the Birky data, ORAUT states that 130 data values are contained in the dataset; 

however, Attachment B of ORAUT 2006 lists only 128 values, including 7 values that are below 

the limit of detection (LOD). These values represent individual measurements as well as mean 

values of measurements that span periods of up to 14 years. According to ORAUT, “The 

datasets that gave summary radon concentrations for a span of years were given equal weight 

with those that gave concentrations over shorter periods.” The variance of a set of values that 

include the mean values of a large number of individual measurements would be smaller than the 

variance of the individual values. Consequently, as discussed further in Appendix A to the 

present report, the 95th percentile, which ORAUT derives from this set of mean values, would be 

more indicative of the 95th th percentile of the mean values than of the 95 percentile of the 

individual measurements. 

Table B-3 of ORAUT 2006 lists summary statistics on measured radon concentrations at eight 

locations in the area of a chemical plant over a period of 5 years, including the mean, the sample 

variance, and the total number of samples at each location. These are unlike the data on the other 

120 measurements, which comprise only the mean concentrations, even for measurements that 

span periods of up to 14 years, as well as individual measurements. SC&A calculated a 

weighted mean that represents 713 values, combining the mean values at these eight locations, 

which comprise 593 individual measurements, with the 120 other measurements, which, for lack 

of better information, were each assigned a weight of 1. This weighted mean was 2.08 pCi/L, 

compared to an unweighted mean of 128 values of 1.01 pCi/L. We also calculated an expanded 

variance of the 713 values. Based on this variance, we derived a 95th percentile value of 

7.78 pCi/L, which is considerably higher than the 95th percentile value of 2.33 pCi/L 

(0.112 WLM/y) cited by ORAUT and adopted by Tomes and Glover (2007) for use in the 

assessment of Blockson workers. 

SC&A suggested that a default radon concentration of 7.78 pCi/L might be a more appropriate 

value for Blockson Chemical for all locations covered in the SEC, except in the rock 

crushing/calciner area. In addition, we suggested an indoor equilibrium factor of 0.4, as 

recommended by UNSCEAR (2000). For the rock crushing/calciner area, SC&A suggested an 

outdoor equilibrium factor of 0.6, as recommended by UNSCEAR. Thus, SC&A suggested a 

revised (bounding) value for the rock crushing/calciner area of 0.56 WLM/y, and for all other 

Revised Draft – Blockson Radon Analysis 6 SC&A – August 12, 2008 

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covered areas, we suggested a value of 0.37 WLM/y. A detailed discussion of the SC&A 

assessment of the radon data from ORAUT (2006) is presented in Appendix A. 

These suggestions were provided to the work group in an SC&A white paper and discussed 

during a work group meeting held on June 5, 2008. During that meeting, NIOSH acknowledged 

that the recommended default value of 2.33 pCi/L of radon is more representative of the 95th

percentile of a set of means of individual measurements than the 95th percentile of a set of 

individual measurements. However, NIOSH provided convincing arguments that, since no one 

individual would be expected to be continually exposed to the upper 95th percentile value, it is 

more appropriate to use the 95th percentile of the means as opposed to the 95th percentile of the 

individual values. SC&A concurred with this philosophy, but stated that ORAUT 2006 would 

benefit from a thorough discussion of this matter. 

In addition to issues related to how the Birky et al. data were used, SC&A expressed concern 

regarding how well the data taken at wet process phosphate plants represent conditions at 

Blockson during the time period of uranium extraction. Given that we have only general 

descriptions of the Blockson monosodium phosphate production plant that we can compare to 

the Florida phosphate plants, we can only speculate that they were not vastly different in terms of 

the radon exposures that plant personnel experienced. SC&A’s investigations into this matter in 

support of earlier work group meetings revealed that measurements in the Birky et al. dataset 

appear to represent activities at Blockson through phosphoric acid production, except that no 

radon measurements were made at calciner locations. Since most of the radium was removed in 

the production of phosphoric acid, it is not likely that significantly elevated radon levels would 

result from production of monosodium phosphate or the extraction of uranium. 

 

EPA (1978) reported measurements of radon in the calciner area at wet process phosphate plants. 

The EPA study was performed at an Idaho wet process plant, where the radon level in the 

calciner was reported as 0.18 pCi/L of radon. This is equivalent to 0.0011 WL and 

0.013 WLM/y. SC&A concluded that these low levels will have no affect on the analysis 

presented in OTIB-0043. It is noteworthy that it has been established through worker interviews 

that the calciner at Blockson was located outdoors. While it is not known if the calciner at the 

Idaho plant was indoors or outdoors, in either case it would not underestimate the associated 

values at Blockson. 

One measure of the appropriateness of using Florida wet process plant data as a surrogate for 

Blockson is to compare the amount of ore processed at each of the facilities. The following 

comparison, which is based on an earlier SC&A white paper, assumes that the amount of 

phosphoric acid produced per ton of ore is equivalent at the two facilities, and the concentrations 

of radioisotopes in the phosphate ore, particularly 226Ra, are equivalent. Since Blockson 

processed phosphate ore from Florida and the wet process for phosphoric acid production is used 

in both cases, these assumptions are reasonable. 

Guimond (1977) states, “Since approximately 4 metric tons of gypsum are produced per ton of 

phosphoric acid, a large phosphoric acid plant would produce about 2.5 million metric tons of 

gypsum per year.” Guimond credits Slack 1968 for the numbers. From this we can calculate 

that 6.25 × 105 tons of phosphoric acid is produced per year in a large phosphoric acid plant: 

Revised Draft – Blockson Radon Analysis 7 SC&A – August 12, 2008 

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Revised Draft – Blockson Radon Analysis 8 SC&A – August 12, 2008 

 6.25 × 105 (tons/y of phosphoric acid) = 2.5 × 106 (metric tons gypsum/y)

 4 (metric tons gypsum/ton acid) 

In an OCAS response to a review by SC&A (OCAS 2007), Tom Tomes indicated that 100 lbs of 

U3O8 were produced per day by Blockson, and that each liter of phosphoric acid contained 

63 mg of U3O . Using these values, 7.2 × 105

8 liters of phosphoric acid would have been 

produced each day at Blockson: 

 7.2 × 105 (L/day) = [100 (lb/day U3O )][4.536 × 105

8 (mg/lb)] ÷ [63(mg U3O8 per L of acid)] 

3 5 This is equivalent to 1.33 × 10 tons of phosphoric acid per day or 4.65 × 10 tons of phosphoric 

acid per year produced at Blockson. 

 1.33 × 105 5 (tons/day) = [7.2 × 10 (L/day)][1675 (g/L)] ÷ [9.072 × 105 (gm/ton)] 

 4.65 × 105

 (tons/y) = [1.33 × 105 (tons/day)][350 (days/y)] 

Thus the amount of phosphoric acid produced at a large wet-process phosphoric acid plant is 

1.34 times greater than that produced per year at Blockson. 

 1.34 = 6.25 × 105 tons/y of phosphoric acid at a large plant

 4.65 × 105 tons/y of phosphoric acid at Blockson 

The phosphate production at Blockson was similar in most respects to the wet process plants that 

were the basis of the ORAUT (2006) radon data. Given that the amount of ore, and presumably 

the annual inventory of 226Ra available for producing radon, was less than that at larger plants, 

we were inclined to believe that the bounding radon values (perhaps as revised to accommodate 

the 95th percentile issue discussed above) presented by Tomes and Glover (2007) are acceptably 

representative of Blockson. 

Since there are no measurements available before the mid- to late-1970s from phosphate plants, 

it is not possible to compare radon levels from the two time periods. As reported in one of 

SC&A’s earlier white papers, based on available information (Birky 2005), SC&A then believed 

that the plant processes did not change significantly over the time frames involved, and that there 

were few, if any, process modifications instituted in the plants to reduce radon levels. There 

were personnel protective measures (e.g., the wearing of dust masks) and personnel monitoring 

(e.g., TLD monitoring) instituted at some phosphate plants. SC&A concluded at that time that 

the use of the later data, as described in OTIB-0043, especially the 95th percentile data (perhaps 

as revised), represents the earlier exposure conditions at Blockson in a sufficiently claimantfavorable fashion. However, the work group requested that SC&A and NIOSH explore this 

matter further. 

SC&A further examined the appropriateness of the use of surrogate data obtained from the 

Florida phosphate industry for the Blockson process, specifically to determine if the phosphoric 

acid production plants in Florida were better ventilated than Building 40 at Blockson. From a 

review of the available literature, it appears that in most of the phosphate plants in Florida, the 

size reduction (ball milling) and the reactor (attack) tanks, where the pulverized phosphate rock 

was reacted with sulfuric acid, were in essentially open buildings with no external walls. 

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factual accuracy or applicability within the requirements of 42 CFR 82.
SC&A interviewed, via telephone, J. Wesley Nall, a member of the Polk County (Florida) Public 

Health Unit, who was one of the authors of the Birky et al. (1998) study of radiation exposures in 

the phosphate industry. He was quite familiar with phosphoric acid production plants and 

confirmed that they were housed in multi-story, mostly open-sided buildings with enclosed, airconditioned control rooms. The flooring was steel grating, and no forced ventilation was used. 

SC&A also spoke with a retired EPA employee who was involved in the studies of the phosphate 

industry in the 1970s. His description of the phosphoric acid plants was virtually identical to that 

described in the preceding paragraph. 

These statements are based on generalizations of the Florida phosphate plants and, because the 

plants whose data were included in the Birky et al. (1998) dataset are not specifically identified, 

it is not possible to determine the exact nature of the enclosures for those phosphoric acid 

operations. However, based on all the information available on Blockson, including recent 

worker interviews, Building 40 contained the milling equipment and reactor tanks in an enclosed 

building with an unknown (if any) amount of forced ventilation, and it cannot be ruled out that 

the Florida plants were in open, better ventilated structures. Hence, at this point in our 

investigations, we were concerned that the surrogate data might have substantial limitations as 

applied to Blockson. This concern became the focal point of subsequent investigations by both 

NIOSH and SC&A, which are described below. 

3.0 RADON MEASUREMENTS IN BUILDING 40 

In 1983, the Olin Corporation, then the owner of the Blockson site, performed an industrial 

hygiene survey (Marseglia 1983). At the time of the survey, the plant was continuing to produce 

phosphate products. The products produced by Olin were fertilizers, rather than monosodium 

phosphate that was produced by Blockson Chemical. However, the phosphoric acid production 

was most likely not affected by this transition to different end products. The production rate of 

phosphoric acid at the time this survey was performed, relative to that at Blockson during the 

uranium extraction period, is not known, except in a general sense. Recent interviews (see “O” 

drive) of Blockson workers indicate that a significant increase in acid production occurred after 

the qualification period and before 1983. These same workers also indicated that some 

building/process modifications were instituted to exhaust dust and acid fumes. 

During the 1983 survey, radon daughter measurements were made in three locations, which 

appear by their description to be in Building 40, the phosphoric acid production building. These 

are identified as, “40 grinder platform,” “40 screening platform,” and “40 filtration” (Marseglia 

1983). The information contained in the report indicates the radon daughter measurements were 

made using the Kusnetz method. This method employs a high-volume air sampler to collect 

radon daughters and, following a measured time period, determines the gross alpha count rate. 

The radon concentration is then determined by applying the following formula (Birky et al. 

1998): 

Revised Draft – Blockson Radon Analysis 9 SC&A – August 12, 2008 

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where: 

WL = radon concentration in units of working level (WL) 

C = net alpha count rate (gross alpha cpm - bkgd cpm) 

V = volume of air sampled in liters (avg cfm × time sampled [min] × 28.32 L/cf) 

E = counting efficiency (cpm/dpm) 

K = correction factor as supplied on the “Kusnetz Method Working Level 

Sampling” form 

The Kusnetz correction factor (K) is a predetermined factor whose value depends on the time 

lapse from sample collection to counting. 

The following table, taken from the Olin survey report (Marseglia 1983), gives the locations and 

raw data for the radon daughter measurements. 

Table 1. Radon Daughter Sample Results 

Sample 

Volume, Liters 

Elapsed Counts/ 

Sample ID Location time, min 5 min 

RAD-4-28-83-1 hygrade area 16.4 51 0 

" 2 #32 belt area 16.4 49 4 

" 3 40 grinder 

platform 

16.4 86 0 

" 4 40 screening 

platform 

16.4 84 0 

" 5 Gyp pile 30.1 52 5 

" 6 SF 30.1 40 1 

" 7 STPP 30.1 44 18 

" 8 40 filtration 27.4 50 7 

" 9 SSF 24.7 40 2 

" 10 TRP-2 

Northeast corner 

(downwind) 

27.4 48 0 

As can be seen in the above table, two of the measurements in Building 40 resulted in zero 

counts and one, “40 filtration,” 7 counts per 5 minutes. Since we do not know the counter 

efficiency, we cannot use the above formula to directly calculate the WL value associated with 

7 counts per 5 minutes. However, since the report gives a WL of 0.0042 for the STPP location 

(18 c/5min), the WL at “40 filtration” can be determined by: 

 where the subscript “40” refers to the “40 filtration” location, while “STPP” refers to the 

“STPP” location. 

Revised Draft – Blockson Radon Analysis 10 SC&A – August 12, 2008 

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WL40 = 0.00196 WL 

C40 = 7 

KSTPP = 142 (corresponding to elapsed time of 44 min) (Birky et al. 1998, Table B-7) 

VSTPP = 30.1 L 

WLSTPP = 0.0042 WL 

CSTPP = 18 

K40 = 150 (corresponding to elapsed time of 50 min) (Birky et al. 1998, Table B-7) 

V40 = 27.4 L 

This WL value measured in Building 40 in 1983 is well below the bounding WL value(s) 

recommended for Blockson. As such, these data would seem to confirm that the use of the 

Florida data as a surrogate for Blockson appear to be claimant favorable. However, the use of 

these measurements to discern the possible radon concentrations in Building 40 during the 

qualification period of January 1, 1951, to December 31, 1962, obviously depends on the degree 

to which the operations and conditions affecting radon concentrations were similar for the two 

time periods (i.e., 1951–1962 versus 1983). Based on worker interviews, there were changes to 

Building 40 to improve the ventilation and/or exhaust systems. One of the workers recently 

interviewed believed these changes took place in 1979 or 1980. Another recently interviewed 

worker believed that the ventilation was upgraded around 1961. In the late 1960s or early 1970s, 

plastic cones were placed over the digester tanks to improve ventilation. Both workers reported 

the production was increased during the terms of their employment, which started in 1947 and 

1951, respectively. Hence, at this point in our investigations, we had concerns regarding the 

usefulness of both the Florida data and the 1983 Blockson data as surrogates for evaluating 

worker exposures to radon and radon progeny at Blockson during the qualification period. 

4.0 BUILDING 40 RADON MODELING 

Given the uncertainties discussed above regarding the assignment of bounding radon 

concentrations during the qualification period for Blockson Building 40, SC&A, together with 

NIOSH, initiated a series of telephone interviews with workers to gain additional insight into the 

Blockson operations and building layout, including ventilation, both during the qualification 

period and in 1983, the time at which the radon progeny measurements were made. This was 

done to determine if substantial changes in the ventilation system and operations might have 

occurred between these two time periods, changes that could help to confirm or possibly 

invalidate the use of the 1983 data as a surrogate for the qualification time period. During these 

inquiries, both SC&A and NIOSH realized that we were compiling information that would allow 

us to model the radon concentrations that may have existed in Building 40 during the 

qualification period. Hence, SC&A initiated a modeling effort approximately 1 week before the 

St. Louis meeting. As will be discussed, the modeling effort proceeded in three phases. The first 

phase consisted of a simple scoping analysis that was performed to support the work group 

meeting. This was followed by a more in-depth analysis that was initiated after the St. Louis 

meeting (Phase 2). Finally, in light of the substantial uncertainties in the range of possible input 

parameters for the model (e.g., building volume, radon release fraction, and air exchange rate), 

we also performed a Monte Carlo simulation (Phase 3). Phases 2 and 3 are being reported herein 

to the work group for the first time. 

Revised Draft – Blockson Radon Analysis 11 SC&A – August 12, 2008 

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4.1 Phase 1 – Scoping Analysis 

Using the “Single Chamber Model” (Environmental Instruments Canada Inc. n/d), a scoping 

calculation was performed to estimate the range of potential radon levels in Blockson Building 

40. This model calculates the radon concentration at equilibrium in a single enclosure using 

input values for the radon source term, the enclosure volume, and the ventilation rate. This 

model calculates the equilibrium radon concentration that results in an enclosed structure (box) 

for a given constant radon input rate (pCi/s) and a constant ventilation rate, expressed as building 

volume turnovers per hour (h-1). For the purpose of this scoping analysis, we assumed that the 

radon in the phosphate rock was in full equilibrium with the 226Ra at the time that the rock was 

transported into Building 40 for processing. The input rate of radon into the building atmosphere 

was assumed to be the product of the 226Ra (Rn) activity concentration (pCi/ton), the radon 

release fraction (the fraction of radon atoms in the ore that escapes from the ore and enters the 

building volume), and the feed rate of the ore (tons/s). At equilibrium, the radon input rate is 

equal to the radon exit rate through ventilation and the radon concentration remains constant. 

The radon source term was calculated using the “Radon Generated by a Process Model” 

(Environmental Instruments Canada Inc. n/d). This model calculates the radon source term using 

inputs of percent uranium in the ore, feed rate of the ore, and the release fraction for radon from 

the ore in the process. The values used were: 

 % U3O8: 0.014% 

 Ore Feed Rate: 35.7 tons/h (6,000 tons/week) 

1 Release Fraction: 0.3

5 This results in a calculated release rate of 4,370 Bq/s (1.18 × 10 pCi/s) of radon into 

Building 40. The volume of Building 40 was estimated, based on a drawing of the plant recently 

provided to SC&A by a former worker and a scale drawing by Wynveen et al. (1983), to be 

24,000 m3 (89 m × 28 m × 9.75 m). The “Single Chamber Model” was run for ventilation rates 

of 1, 2.5, and 5 h-1. These ventilation rates were selected from the range of values for 

commercial buildings reported in several publications, primarily Fradella 2005, Parker 1985, and 

Turk 1989. In addition, a conversation with Dr. Mort Lippmann, Professor of Industrial Hygiene 

at New York University Medical Center, Institute of Environmental Medicine, revealed that in 

his opinion, the air turnover rate in a building such as Building 40 at Blockson would not be less 

than 1 per hour. Hence, we set 1 air turnover per hour as our lower bound in this scoping 

analysis. 

Table 2 presents the results of scoping calculation that were performed by SC&A to assess the 

degree to which the radon concentrations measured at Florida facilities and the values measured 

Revised Draft – Blockson Radon Analysis 12 SC&A – August 12, 2008 

 1 In the analysis that was discussed at the St. Louis meeting, SC&A employed a default radon release fraction 

of 0.3, because it was believed to be the default radon emanation coefficient adopted in RESRAD. In preparing this 

report, we revisited this parameter and found that the current version of RESRAD uses a default radon emanation 

coefficient of 0.25. 

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2 in 1983 at Blockson are compatible and consistent with model results. Values similar to these

were presented and discussed at the work group meeting held in St. Louis on June 24, 2008. 

Table 2. Phase 1 Parametric Analysis of Radon Concentrations in Building 40 

Ventilation Rate Parameter 1/hr 2.5/hr 5/hr 

Radon (pCi/L) 17.5 7.1 3.5 

WL1 0.07 0.028 0.014 

WLM/y .82 0.33 0.16 1

Radon daughter equilibrium factor = 0.4 (See below) 

For reference, the bounding radon assigned from OTIB-0043 was 2.33 pCi/L (0.112 WLM/y). 

SC&A’s revised bounding radon value was 7.73 pCi/L (0.37 WLM/y). Hence, this scoping 

analysis revealed that the default radon concentration adopted by NIOSH in OTIB-0043 did not 

appear to be incompatible with the modeled results.3

 

The work group discussed this matter during the full Board meeting held on June 24–26, 2008. 

During that meeting, it became apparent that these scoping analyses were considered important 

by the work group and the Board. In addition, since the radon concentrations derived by SC&A 

and discussed at the meeting were not formally delivered to the work group and had not yet 

undergone SC&A’s QA process, nor had the work group or NIOSH had a chance to review the 

reported values, the work group and the Board requested that SC&A complete its modeling 

evaluations, perform the required QA checks, and formally deliver its report on this matter to the 

work group as soon as possible. In response to this request, SC&A commenced additional 

follow-up investigations. 

4.2 Phase 2 – Follow-up Investigations 

Following the St. Louis meeting, SC&A initiated a more thorough review of the literature to gain 

further insight into the reliability of the model and the possible range of values for the model 

input parameters. Of particular importance is the radon source term in Building 40 and the air 

turnover rate. Table 3 shows the radon concentrations modeled for Building 40 using a full 

range of alternative assumptions for each of these parameters. A detailed description of that 

analysis is provided in Appendix B. 

 2

 The values presented and discussed during the work group meeting were lower than these, primarily due to 

revisions in our understanding of the volume of Building 40; i.e., subsequent to the St. Louis meeting, we 

determined that the footprint of Building 40 was smaller than that initially assumed and discussed during the St. 

Louis meeting. 

3 Also of interest is the relationship of radon concentration (at equilibrium) to ventilation rate. For a constant 

input rate of radon, the relationship of radon concentration to ventilation rate is inversely proportional; thus, a 5-fold 

increase in ventilation rate (1/hr to 5/hr) results in a 5-fold decrease in the equilibrium radon concentration. The 

working level will not be exactly proportional to the radon concentration, as the radon daughter equilibrium fraction 

decreases as the ventilation rate increases. However, if we adopt the typical indoor equilibrium fraction of 0.4 cited 

by UNSCEAR (2000), the inverse proportional relationship also applies to WL (and WLM/yr) and ventilation rate. 

Revised Draft – Blockson Radon Analysis 13 SC&A – August 12, 2008 

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b Table 3. Radon Concentrations (pCi/L)

Release fraction from acid (f) 

ACHa 0.0 0.2 0.4 0.6 0.8 1.0 

0.5 0.44 18.52 36.61 54.70 72.79 90.88 

1.5 0.15 6.24 12.33 18.42 24.51 30.60 

2.5 0.09 3.75 7.41 11.07 14.73 18.39 

3.5 0.06 2.68 5.30 7.92 10.53 13.15 

4.5 0.05 2.09 4.12 6.16 8.20 10.23 

5.5 0.04 1.71 3.37 5.04 6.71 8.37 a Air changes per hour 

b A description of the models used to derive these values is 

provided in Appendix B. 

As may be noted, depending on the modeling assumptions used, the average annual radon 

concentration in Building 40 during the qualification period could be as low as 0.04 pCi/L 

(which is well below typical outdoor natural background levels) to as high as 91 pCi/L. When 

confronted with the enormous uncertainty associated with the above “what if” analyses, SC&A 

perfomed a Monte Carlo analysis. Monte Carlo analyses are especially useful when 

deterministic analyses (i.e., those presented in Table 3) yield such variable results that they are of 

little use in making informed decisions. 

4.3 Phase 3 – Monte Carlo Analysis 

As described above, our follow-up investigations revealed that the input parameters used to 

derive the average annual radon concentration in Building 40 during the qualification period are 

highly uncertain, resulting in very different results, depending on the selected input parameters. 

In order to address these uncertainties in a more formal manner, we performed a Monte Carlo 

analysis. A detailed description of that analysis is provided in Appendix B. In summary, we 

assigned the following distributions to the key input parameters used in this calculation. 

Table 4. Distributions of Input Parameters Used in Monte Carlo Analysis 

Revised Draft – Blockson Radon Analysis 14 SC&A – August 12, 2008 

Symbol Description Units Distribution Parm 1a Parm 2b Parm 3c Fixedd

S Specific activity of 226Ra Bq/kg normal 1,460 287 1,460 

tr residence time of ore in Building 40 s triangular 7,200 14,400 21,600 14,400

εd dry emanation coefficient — lognormal 0.113 1.545 0.113 

εw wet emanation coefficient — lognormal 0.299 1.498 0.299 

f evolution fraction of Rn from sulfuric acid — uniform 0.000 1.00 ─

r air exchange rate s

-1 uniform 2.78e-05 1.53e-03 ─

V Volume of building m3 uniform 17,321 23,983 20,652

a

 Mean of normal distribution, geometric mean of lognormal, or lower limit of uniform or triangular distributions

b

 Standard deviation of normal distribution, geometric standard deviation of lognormal, upper limit of uniform 

distribution, or mode of triangular distribution 

c

 Upper limit of triangular distribution

d

 Used in sensitivity analysis reported in Table 3

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Note that the key parameters that contribute to the uncertainty are the following: 

(1) Fraction of radon trapped in the crystalline structure of the pulverized phosphate rock that 

emanated from the reaction vessels and entered the Building 40 atmosphere 

(2) Building air exchange rate 

(3) Volume of building 

Using these assigned distributions for the input parameters, we obtained the following results. 

Table 5. Percentile Values of 222Rn Concentrations (pCi/L) 

Percentile Value 

0% 0.02 

5% 0.78 

10% 1.50 

15% 2.24 

20% 2.97 

25% 3.70 

30% 4.44 

35% 5.20 

40% 5.99 

45% 6.84 

50% 7.72 

55% 8.73 

60% 9.87 

65% 11.28 

70% 13.06 

75% 15.54 

80% 19.08 

85% 24.77 

90% 35.37 

95% 61.95 

100% 651.00 

These results indicate that we can be 95% certain that the true but unknown average annual 

radon concentration in Building 40 during the qualification period was less than 62 pCi/L. 

Revised Draft – Blockson Radon Analysis 15 SC&A – August 12, 2008 

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5.0 REFERENCES 

Birky, B.K. et al. 1998. “Evaluation of Exposure to Technologically Enhanced Naturally 

Occurring Radioactive Materials (TENORM) in the Phosphate Industry: Final Report,” FIPR 05-

046-155 (Florida Institute of Phosphate Research). 

http://fipr1.state.fl.us/fipr/fipr1.nsf/9bb2fe8f45c4945e85256b58005abaec/deb248481f98842e852

56b2f005d7524!OpenDocument

Birky, B.K. 2005. “Phosphate Plant Radon Levels,” electronic mail to R. Gard (Oak Ridge 

Associated Universities Team), September 1, Florida Institute of Phosphate Research, Bartow, 

Florida. 

Environmental Instruments Canada Inc. n/d. Uranium Safety Toolkit v2.0, , 

http://members.shaw.ca/eic/Tools/index.htm

EPA (U.S. Environmental Protection Agency) 1978. “Radiological Surveys Of Idaho Phosphate 

Ore Processing – The Wet Process Plant,” Technical Note: ORP/LV–78–1, April 1978. 

Fradella, J., and J. Siegel 2005. “An Evaluation of Shelter-In-Place Strategies in Four Industrial 

Building.” Proceedings: Indoor Air 2005, pp. 3360–3362. 

Guimond, R.J., W.A. Mills, S.T. Windham 1977. “Radiation Exposures in the Florida 

Phosphate Industry,” International Radiation Protection Association Meeting #4, Paris, France,

Volume 3, pp. 1049–1052. 

Marseglia, L.M. 1983. “Joliet Radiation Survey.” In Olin Corporation, Surveys and 

Radiological Data of the Former Blockson Chemical Company Site, provided to ORAUT, 2007 

[SRDB Ref ID 30623]. 

OCAS (Office of Compensation Analysis and Support) 2007. Response to Remaining Issues for 

the Blockson SEC Evaluation Review by SC&A. Tom Tomes, National Institute for 

Occupational Safety and Health, OCAS. November 13, 2007. 

ORAUT (Oak Ridge Associated Universities Team) 2006. Characterization of Occupational 

Exposure to Radium and Radon Progeny During Recovery of Uranium from Phosphate 

Materials, ORAUT-OTIB-0043, Rev. 00. January 6, 2006. 

Parker, G. 1985. “Measurement of Air Exchange Rates in Residential and Commercial 

Buildings in the Northwest: Techniques and Results,” PNL-SA-15607; CONF-8505167-1, 1985. 

Slack, A.V. 1968. Disposal or Use of Gypsum, Phosphoric Acid, Vol. 1. 

Tomes, T., and S. Glover 2007. Technical Basis Document for Atomic Energy Operations at 

Blockson Chemical Company, Joliet, Illinois,” OCAS-TKBS-0002, Rev. 2. National Institute for 

Occupational Safety and Health, Office of Compensation Analysis and Support: 

http://www.cdc.gov/niosh/ocas/pdfs/tbd/ocblockson-r2.pdf

Revised Draft – Blockson Radon Analysis 16 SC&A – August 12, 2008 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker Health for 

factual accuracy or applicability within the requirements of 42 CFR 82.
Turk, B., et.al, 1989. Commercial Building Ventilation Rates and Particle Concentrations, 

ASHREA Transactions, Vol.95, Part 1. 

UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) 2000. 

“UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes,” Vol. I: “Sources,” 

Annex B, “Exposures from Natural Radiation.” 

http://www.unscear.org/unscear/en/publications/2000_1.html

Wynveen, R. A., et al. 1983. “Formerly Utilized MED/AEC Sites Remedial Action Program: 

Radiological Survey of Chemicals Group, Olin Corporation (Formerly Blockson Chemical 

Company), Joliet, Illinois, March 27-November 28, 1978,” DOE/EV-0005/35, ANL-OHS/HP83-103. Argonne, Illinois: Argonne National Laboratory. 

Revised Draft – Blockson Radon Analysis 17 SC&A – August 12, 2008 

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APPENDIX A: REVIEW OF RADON EXPOSURE ESTIMATES DERIVED FROM 

SUMMARY DATA IN ORAUT-OTIB-0043 

A.1 Verification of OTIB-0043 Radon Exposure Estimates based on the Equal Weight 

Assumption 

The summary data on radon exposures presented in Attachment B of ORAUT-OTIB-0043 

(ORAUT 2006) were used by NIOSH to estimate the geometric mean (GM), geometric standard 

deviation (GSD), and 95th percentile of worker radon exposures. The OTIB calculations were 

performed with an assumption of equal weighting for all reported data points in the Attachment 

B tables that are not grayed out. The applicable data points include many values that are the 

means of sets of measurements, as well as many individual measurements. Some of the means 

represent large datasets, while other mean values represent smaller datasets. 

The assumption of equal weighting is not applicable when the means represent very different 

sample sizes. However, the equal-weight assumption was used to develop the estimated radon 

exposures reported in Table 4-4 of OTIB-0043. In this section of the current report, the equal 

weight assumption is applied to confirm the NIOSH estimates. In the following section, the 

mean values in Table B-3 of OTIB-0043 are weighted proportionally to the sample size 

represented by each mean value to develop more appropriate weighted estimates of worker radon 

exposure. 

Although OTIB-0043 states that 130 data values are contained in the non-shaded rows of the 

Attachment B tables, only 128 values are listed there, including seven values in Table B-1 that 

are below the limit of detection (LOD) reported as “<0.5 pCi/L.” Two methods are used here to 

estimate a lognormal distribution using the equal-weight assumption: the maximum likelihood 

method (MLM) and a graphical method based on normal scores. The MLM requires that 

surrogate values be imputed for the seven LOD values. The midpoint of the uncertainty range 

(LOD/2 = 0.25 pCi/L) was used for these seven values. In the graphical method, these seven 

points are not included on the graph, but their ranks are used when computing the normal scores. 

The results of these two analyses are compared with the OTIB-0043 estimates in Table A-1. As 

shown in the table, the lognormal distributions estimated using the MLM and graphical methods 

have a GM and GSD that are very similar to the GM and GSD reported in OTIB-0043 for the 

Attachment B data. The estimated (arithmetic) mean, standard deviation, and 95th percentile also 

closely match. 

The normal score plot used in the graphical method is shown in Figure A-1. Note that the fitted 

regression line underestimates the high readings in the upper tail of the distribution. As shown in 

Table A-1, the 95th percentile of the empirical distribution (i.e., the data points in Figure A-1) is 

significantly higher than the 95th percentile estimated from the fitted lognormal distribution, 

2.9 pCi/L versus the 2.3 pCi/L estimate reported in OTIB-0043. 

Revised Draft – Blockson Radon Analysis 18 SC&A – August 12, 2008 

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A.2 Radon Exposure Estimates based on the Expanded Table B-3 Datasets 

Many of the mean values reported in the Attachment B tables do not include detailed information 

on the underlying dataset. However, the mean values reported in Table B-3 of OTIB-0043 are 

accompanied by other statistics that describe the underlying dataset, such as the number of 

samples and the variance of the sample values. The sample sizes for these eight datasets range 

from 24 to 118, indicating that a wide range of weights should be considered. The smallest 

dataset in Table B-3 (labeled “gypsum stack flux test”) has a mean value that is the second 

highest value contained in the entire dataset (6.52 pCi/L). Other, larger datasets summarized in 

Table B-3 also have relatively high mean values when compared to the mean value of 

approximately 1 pCi/L for the equally weighted data shown in Table A-1. Although other tables 

in Attachment B include mean values, only Table B-3 contains additional information on the 

variance of the underlying datasets from which the means were derived. The sample variance 

provides a measure of the spread of the values in each dataset about the mean. When the means 

are treated as single values, this information is lost. As a result, any estimate of the 95th

percentile that does not include this information will be biased to the low side. 

The mean values in Table B-3 were assigned weights in proportion to the size of sample each 

mean represents. All other valid data values in the Attachment B tables were assigned a weight 

of 1, as in the equally weighted approach. A weighted mean was calculated using these weights. 

The variance reported for each dataset in Table B-3 and the sample size were used to estimate 

the sum of squared deviations of the data values when determining the weighted standard 

deviation. The estimated weighted means and standard deviations were then used to calculate 

the parameters of a weighted lognormal distribution that represents the population of exposures 

in Attachment B. The required calculations are shown in Table A-2. The weighted mean is 

estimated as 1,482.49 ÷ 713 = 2.079 pCi/L, approximately twice as high as the unweighted mean 

value. The weighted standard deviation is estimated as (17,834/713)1/2 = 5.01 pCi/L.

The weighted lognormal estimates are compared with the unweighted estimates from 

Section A-1 in Table A-3. Although both methods yield similar estimates for the GM, the 

weighted estimates have a GSD that is twice as large as the unweighted estimate. This results in 

a much higher estimate of the 95th percentile when the weighted approach is used (7.78 versus 

2.33 pCi/L). A graphical comparison of the GM, GSD, and 95th percentiles is shown in 

Figure A-2. 

Table A-1. Characteristics of Lognormal Distributions for Radon Measurements in 

OTIB-0043 Attachment B 

Revised Draft – Blockson Radon Analysis 19 SC&A – August 12, 2008 

Lognormal 

Parameters 

95th

Percentile

Standard 

deviation GM Mean Source of Estimates GSD 

mu Sigma 

N (pCi/L) (pCi/L) (pCi/L) (pCi/L) 

Maximum likelihood -0.323 0.738 128 0.724 2.092 2.438 0.951 0.757

Graphical method -0.351 0.784 128 0.704 2.191 2.558 0.958 0.790

OTIB-0043 estimates -0.286 0.688 130 0.751 1.989 2.330 0.951 0.731

Median 

Empirical Distribution -- -- 128 0.700 -- 2.900 1.006 1.169

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y = 0.7844x - 0.351

R2

 = 0.9728

-2.5

-1.5

-0.5

0.5

1.5

2.5

-3 -2 -1 0 1 2 3

Normal Score

Ln (Rn concentration [pCi/L])

Figure A-1. Normal Score Plot of Attachment B Radon Measurements 

Table A-2. Derivation of Weighted Lognormal Distribution Using Expanded Data for 

Table B-3 Means 

Count Mean Sample Values for analysis: C · μ C · V Σ (x - μ) (C) (μ) variance (V)

NE gypsum stack well 90 2.43 18.45 218.7 1660.5 1671.57

Auto shop SE fence 56 2.89 23.73 161.84 1328.88 1365.69

SW of plant 31 0.35 0.22 10.85 6.82 99.52

Burn area fence 118 1.89 27.39 223.02 3232.02 3236.25

Liming station ladder 105 1.9 25.36 199.5 2662.8 2666.17

Environmental monitoring well 101 2.6 55.26 262.6 5581.26 5608.65

Gypsum stack flux test 24 6.52 24.52 156.48 588.48 1061.77

Cooling pond hand rail 68 2.08 26.85 141.44 1825.8 1825.80

All other Attachment B tables 120 0.9005 108.06 131.946 298.67

2.079a Total 713 1482.49 17834.10

Note: Columns 1–4 from ORAUT (2006, Table B-3) 

a

 μw = weighted mean 

Revised Draft – Blockson Radon Analysis 20 SC&A – August 12, 2008 

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Table A-3. Comparison of Unweighted and Weighted Distributions for Attachment B Data 

95th GM percentile 

Revised Draft – Blockson Radon Analysis 21 SC&A – August 12, 2008 

Lognormal models μy

a σyb GSD (pCi/L) (pCi/L) 

OTIB-0043 -0.286 0.688 0.75 1.99 2.33

Weighted Distribution -0.226 1.384 0.80 3.99 7.78 a

 Mean of logs = ln(GM) 

b

 Standard deviation of logs = ln(GSD) 

0.75

1.99

2.33

0.80

3.99

7.78

0

2

4

6

8

GM GSD 95th Percentile

OTIB-0043 Weighted Distribution

Figure A-2. Comparison of OTIB-0043 Estimates with Lognormal Parameter Estimates 

Using Expanded Data in Table B-3 

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APPENDIX B: COMPREHENSIVE ANALYSES OF 222RN CONCENTRATIONS IN 

BUILDING 40 

In order to gain greater insight into the possible range of radon concentrations in Building 40 

during the qualification period, SC&A (1) performed a comprehensive review of available 

documentation and literature pertinent to modeling radon buildup inside structures in which 

phosphate rock was processed, (2) carefully reviewed Blockson documentation, and 

(3) interviewed several former Blockson workers. Using this information, we first performed 

two sets of analyses to estimate the average annual radon concentration in Building 40 during the 

qualification period. The first was a parametric analysis, in which we used the most likely values 

of several uncertain parameters, while varying stepwise the values of the two parameters most 

likely to affect the radon concentrations. In the second, we applied Monte Carlo techniques to 

construct a probability distribution of these concentrations. 

We begin this discussion with an overview of the processes employed in Building 40 and of the 

characteristics of the building. We then present a detailed discussion of the analysis, including 

the sources of the data, and the results and conclusion. 

B.1 Processes in Building 40 

B.1.1 Processing of Phosphate Ore 

According to “Emission Factor Documentation . . .” 1993: 

Phosphate rock from the mines is first sent to beneficiation units to separate sand 

and clay and to remove impurities. Steps used in beneficiation depend on the type 

of rock. A typical beneficiation unit for separating phosphate rock mined in 

Florida begins with wet screening to separate pebble rock, which is larger than 

1.43 millimeters (mm) (0.056 inch), or 14 mesh, and smaller than 6.35 mm 

(0.25 in.) from the balance of the rock. The pebble rock is shipped as pebble 

product. The material that is larger than 0.85 mm (0.033 in.), or 20 mesh, and 

smaller than 14 mesh is separated using hydrocyclones and finer mesh screens 

and is added to the pebble product. The fraction smaller than 20 mesh is treated 

by two-stage flotation. The flotation process uses hydrophilic or hydrophobic 

chemical reagents with aeration to separate suspended particles. Phosphate rock 

mined in North Carolina does not contain pebble rock. . . . Like Florida rock, the 

fraction that is less than 10 mesh is treated by two-stage flotation, and the 

fraction larger than 10 mesh is used for secondary road building. 

The ore received at the Blockson plant would have been beneficiated prior to shipment from 

Florida. The ore “is maintained at about 10 percent moisture” (“Emission Factor Documentation 

. . .” 1993). Twenty-mesh ore consists of particles < 0.841 mm in diameter (Perry and Green 

1984). Very fine particles would have been removed by the floatation process. Once received at 

Blockson, the ore was stored in 100-ft-high silos until it was ready to be used for producing 

phosphoric acid. The first step in phosphate production was the calcining of the ore in an 

outdoor oven at temperatures of 1,400–1,600oF (1,033–1,144 K). The calcined ore was then 

Revised Draft – Blockson Radon Analysis 22 SC&A – August 12, 2008 

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transferred to Building 40 by means of a continuous-screw conveyer. “Dried or calcined rock is 

ground in roll or ball mills to a fine powder, typically specified as 60 percent by weight passing a 

200-mesh sieve” (“Emission Factor Documentation . . .” 1993). (Two-hundred mesh 

corresponds to a particle diameter of 74 μm, Perry and Green 1984). The ground ore was then 

transferred to a tank of sulfuric acid. According to a former Blockson worker, 66% sulfuric acid 

was sent to Building 40, where it was further diluted with water. Since the dilution of sulfuric 

acid is an exothermic process, the temperature of the resulting liquid would be above ambient. 

According to another former worker, the tanks contained steam coils to heat the sulfuric acid 

further. 

B.1.2 Emission of Radon 

Radon-222 (referred to as “radon” in the remainder of this appendix) could have been released 

from the phosphate ore at various stages of the process. About 30% of the radon generated by 

the radioactive decay of 226Ra in the wet ore would emanate into the pore space; the remaining 

70% would remain in the crystalline matrix. During the calcining, virtually all volatile 

components, including water and radon, would be driven out of the rock. Some additional radon 

would grow in during the period of approximately 4 h during which the rock is transported 

through Building 40 and ground to the desired fineness. The radon emanation coefficient from 

the dry phosphate ore is approximately 11%.4

 Once the ore is transferred to the acid, the 

crystalline matrix would have been dissolved. Most of the 226Ra would precipitate, but the radon 

would remain in solution. Since the warm acid was agitated during the digestion process, some 

of the dissolved radon could potentially have escaped into the air. 

B.2 Characteristics of Building 40 

B.2.1 Size of Building 

The size of the interior of Building 40 plays an essential role in calculating the radon 

concentration in the ambient air: the larger the space, the lower the concentration. A former 

Blockson worker furnished SC&A and OCAS a plan of the Joliet plant and marked the location 

of Building 40 on this drawing (see Figure B-1). We used that drawing to identify Building 40 

on a drawing of the plant showing soil sampling locations (Wynveen et al. 1983, Figure 10), 

which is reproduced in Figure B-2, with the location of Building 40 shown in red. We used the 

map scale displayed in the drawing to estimate the dimensions of Building 40. The interior is 

assumed to be 32 ft (9.75 m) high, the same as Building 55 (Lopker and Block 1951, 

Appendix B). According to a former worker, the building also housed a silica production 

operation, separated by a brick wall from the rest of the plant. This wall may be represented by a 

line shown in Figure B-1 that divides the north and south portions of the building, and the 

phosphoric acid operation may have taken place in the north part of the building. 

Revised Draft – Blockson Radon Analysis 23 SC&A – August 12, 2008 

 4

 A more detailed discussion of these data is presented later in the present report. 

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Revised Draft – Blockson Radon Analysis 24 SC&A – August 12, 2008 

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factual accuracy or applicability within the requirements of 42 CFR 82.
Figure B-2. Environmental Soil Sampling Locations at Former Blockson Chemical 

Company Plant (Wynveen et al. 1983, Figure 10) 

 

B.2.2 Building Ventilation 

The ventilation rate, also referred to as the air turnover rate, of Building 40 also plays a crucial 

role in calculating the radon concentrations. Three former workers were interviewed via 

teleconference by Wanda Munn, Chair of the Advisory Board Work Group on Blockson 

Chemical SEC; Tom Tomes of NIOSH/OCAS; and SC&A personnel. All three workers were 

asked about the building ventilation—their recollections varied. Only two of the workers had 

worked inside Building 40, so they would most likely have more accurate recollections about the 

conditions inside the building. 

Revised Draft – Blockson Radon Analysis 25 SC&A – August 12, 2008 

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According to Worker #1 (the numbering is arbitrary): 

The plant was generally a closed plant with just a few doors. There were small 

windows at the very top of the plant,5 but he never saw them opened or could not 

say for sure if they could be opened. The few doors would be propped open 

during the hot summer months. There were a lot of fumes in the plant. . . . There 

was a stack that vented the tanks, but without forced air. (Tomes 2008a)6

According to Worker #2: 

The building had roof vents and roof fans. He said there were windows or 

openings on the first floor that allowed air to enter the building that could be 

pushed out, but were generally closed. He said they were on the long sides [of the 

rectangular building] and were about 3 feet by 5 feet. They supplied ventilation 

air for the digestors on the second floor. (Tomes 2008b)3

 

Both workers stated that new ventilation was installed or existing ventilation upgraded some 

time between about 1960 and 1980. 

B.3 Methodology 

Radon could have been released into Building 40 through two mechanisms: 

(1) Emanation from ore within the building, before, during, and after the grinding of the ore 

(2) Evolution from the hot sulfuric acid after the crushed ore is dissolved 

Radon emanates from the solid matrix of the phosphate ore by recoil of the radon atom following 

the emission of an alpha particle by its parent nuclide, 226Ra. According to UNSCEAR (2000), 

“The range of recoil distance for 222Rn is 20–70 nm in common minerals.” This distance is less 

than 0.1% of the diameter of the crushed ore particles, which is less than 74 μm. Consequently, 

the crushing of the ore would have little effect on the radon emanation. 

In mechanism 2, radon that has remained embedded in the solid matrix of the rock would enter 

into the acid solution after the rock has dissolved. There are no readily available data on the rate 

of evolution of radon from aqueous solutions. However, since the ~30% sulfuric acid is heated 

and agitated to promote the dissolution of the ore, such evolution cannot be ruled out. (See 

further discussion in Section B.5.) 

The rate of release of radon into the building atmosphere, as well as its removal by air exchange 

and radioactive decay, is given by the following differential equation: 

Revised Draft – Blockson Radon Analysis 26 SC&A – August 12, 2008 

 5

 This observation is consistent with a photograph of Building 55 and an adjacent structure shown in Barr et al. 

1953. Both buildings appear only to have windows just below the level of the roofs. 

6

 Excerpted from interview notes prepared by Mr. Tomes—not a verbatim quote. 

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factual accuracy or applicability within the requirements of 42 CFR 82.
 B = atoms of daughter product (222Rn) 

 R = processing rate of ore 

= 9.45 kg/s 

 Rw = weekly processing rate 

= 6,000 tons/week (Lopker and Block 1951) = 5.443 × 106 kg/week 

 tw = weekly operating time 

 = 160 h/week = 576,000 s (assume three shifts/d, 7 d/week, 8 h downtime for 

maintenance) 

S = specific activity of 226Ra in phosphate rock (Bq/kg) 

tr = residence time of phosphate rock in Building 40 (s) 

εd = emanation coefficient of radon from dry phosphate rock 

f = fraction of radon evolving from sulfuric acid 

εw = emanation coefficient of radon from wet phosphate rock 

λ = decay rate of 222Rn 

= 2.0979 × 10-06 s

-1

r = outside air exchange rate inside Building 40 (s-1) 

The first term inside the large parentheses in the first line of Equation 1 represents the rate at 

which radon emanates from the phosphate ore during its passage through Building 40. The 

second term (the algebraic fraction with λ in the denominator) represents the evolution of radon 

after the rock is dissolved in sulfuric acid. The first term in the numerator represents the 

evolution of radon that results from the decay of 226Ra in the dry rock following calcining, while 

the second term represents the evolution of radon that was in secular equilibrium with 226Ra in 

the wet rock prior to calcining. The final term of Equation 1 represents the removal of radon due 

to ventilation and radioactive decay. Radioactive decay of radon during the calcining step is not 

accounted for, nor is the reduction in the specific activity of 226Ra due to radioactive decay 

during this process. 

The second line in Equation 1 denotes the steady-state solution to the first line: the rate of 

change equals zero. This condition allows a direct solution of the first line in Equation 1: 

Revised Draft – Blockson Radon Analysis 27 SC&A – August 12, 2008 

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The activity concentration of radon in the ambient air is given by: 

C = activity concentration of radon in Building 40 (Bq/m3) 

V = volume of Building 40 

B.3.1 Method of Calculation 

Many of the parameters used to calculate the radon concentration, including the radon emanation 

coefficients, the specific activity of 226Ra in phosphate ore, fraction of radon evolving from 

sulfuric acid, the air exchange rate, and the residence time of the ore, are variable and/or 

uncertain. In order to study the dependence of the radon concentrations on the values of the 

variable parameters, we performed two sets of analyses: 

(1) Deterministic analysis, in which the parameters were assigned one or more fixed values 

(also referred to as “parametric analysis”) 

(2) Probabilistic analysis, using Monte Carlo methods 

The variability and uncertainty in the values of these parameters can be expressed by probability 

distributions. For parameters that are uncertain or variable, Monte Carlo sampling methods are 

used to pick the particular set of values in a given calculation, called a realization. In the present 

analysis, the estimation of each concentration involved 100,000 realizations. Each individual 

calculation is deterministic—it employs a set of fixed values of the relevant parameters and 

produces a fixed result. These 100,000 results themselves form a probability distribution. Thus, 

the radon concentration can be expressed in terms of a mean, a standard deviation, the median, 

or, say, the 95th percentile. The analysis was performed using the Microsoft Excel add-in, 

Crystal Ball Version 2000.2 (Decisioneering 2001). 

B.3.2 Input Parameters 

In the following sections, we discuss the values of the uncertain parameters. The distributions 

used in the uncertainty analysis are discussed first, followed by the fixed value or range of values 

selected 

Revised Draft – Blockson Radon Analysis 28 SC&A – August 12, 2008 

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B.3.2.1 Specific Activity of 226Ra in Phosphate Rock 

Hull and Burnett (1996) reported the specific activities of 226Ra in 13 samples of phosphate rock 

from central Florida.7 Only the mean and standard deviation of the individual assays are listed in 

their report. In the present analysis, the specific activity of 226Ra is represented by a normal 

distribution, with the same mean and standard deviation as reported by Hull and Burnett. The 

parameters characterizing this distribution are listed in Table B-1. The mean (listed in the last 

column) is used as a fixed value in the parametric analysis. 

Table B-1. Distributions of Input Parameters Used in Monte Carlo Analysis 

Parm 1a Parm 2b Parm 3c Fixedd Symbol Description Units Distribution

specific activity of 226 S Ra Bq/kg normal 1,460 287 1,460

tr residence time of ore in Building 40 s triangular 7,200 14,400 21,600 14,400

εd dry emanation coefficient — lognormal 0.113 1.545 0.113

εw wet emanation coefficient — lognormal 0.299 1.498 0.299

f evolution fraction of Rn from sulfuric acid — uniform 0.000 1.00 ─

s

-1 r air exchange rate uniform 2.78e-05 1.53e-03 ─

m3 V Volume of building uniform 17,321 23,983 20,652

a

 Mean of normal distribution, geometric mean of lognormal, or lower limit of uniform or triangular distributions.

b

 Standard deviation of normal distribution, geometric standard deviation of lognormal, upper limit of uniform 

distribution, or mode of triangular distribution. 

c

 Upper limit of triangular distribution. 

d

 Fixed values used in parametric analysis 

B.3.2.2 Residence Time of Phosphate Ore in Building 40 

We estimate that the time required to grind the ore, together with the transfer time to the grinder 

and then to the acid tank, to be 4 h, with a range of 2 to 6 h. The residence time is therefore 

represented by a triangular distribution with the aforementioned parameters. The parameters 

used in the calculation are listed in Table B-1. The mode is used as a fixed value in the 

parametric analysis. 

B.3.2.3 Emanation Coefficients of Radon 

Burnett et al. (1988) reported the loss of radon from samples of bulk phosphate rock under both 

wet and dry conditions. Ten of the samples were from Florida phosphate deposits. Because the 

data resemble a lognormal more than a normal distribution, we calculated the geometric mean 

and the geometric standard deviation for each set of measurements. Because one measurement 

of the dry emanation coefficient appeared to be an outlier, we utilized only nine of the measured 

values. We represented both the wet and the dry emanation coefficients by lognormal 

distributions. The geometric mean and the geometric deviation of each set of measurements are 

listed in Table B-1, which were adopted for the distributions in the present analysis. The 

geometric mean is used as a fixed value in the parametric analysis. 

 7

Revised Draft – Blockson Radon Analysis 29 SC&A – August 12, 2008 

 The phosphate from this region has higher concentrations of radionuclides than the rock from northern 

Florida (the other region studied by these authors) and is therefore adopted to produce a claimant-favorable analysis. 

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B.3.2.4 Fraction of Radon Evolving from Sulfuric Acid 

In the absence of available data on the evolution of radon from dilute, hot sulfuric acid, the 

fraction of evolved radon was assigned a uniform distribution ranging from 0 to 1. This 

parameter is varied stepwise over the same range in the parametric analysis. 

B.3.2.5 Air Exchange Rate in Building 40 

Sparse data exist on the exchange rates of outside air for industrial buildings, such as 

Building 40. The recollection of two former workers who worked inside the building differ as to 

the placement of the windows and the existence of forced air exhaust systems during the covered 

period. 

 

The most applicable data was presented by Parker (1985), who measured the air exchange rates 

in two industrial buildings, using SF6 as a tracer. One building was a machine/wood shop, with a 

floor area of 20,000 ft2 (~1,860 m2). This is comparable to the area of Building 40, which is 

estimated to be 1,776 m2. General ventilation of the shop is through 12-ft × 25-ft bay doors, 

which were opened periodically during the 2-h period of measurement. The shop does not have 

a central HVAC system—local ventilation is provided for welding or metal stripping. The 

measured rate was 5.5 air changes per hour. Three measurements made when the shop was 

unoccupied and all outside doors were closed showed an average rate of 0.1 air changes per hour. 

A second building studied by Parker was a single-story warehouse of approximately 100,000 ft2

(~9,300 m2), over five times the area of Building 40. According to Parker: 

The warehouse is heated by overhead forced air electric heaters, but has no 

central HVAC system. Cooling is via several roof-mounted mechanically opened 

vents. The warehouse contains several 12-ft × 25-ft bay doors at either end of the 

building. During a working day, these doors are normally open and one or two 

receiving doors on the west side of the building are opened periodically. 

Measured rates during a working day were 0.05 air changes per hour in the morning and 0.2 in 

the afternoon. The rates averaged about 0.06 during non-working hours. 

Other data primarily apply to residential structures. Yu et al. (1993) list a default rate of 0.5 air 

changes per hour for use with the RESRAD computer code. EPA (1997, Table 17-31) 

recommends a median of 0.45 air changes per hour for risk assessment studies. Godish (2001, 

Figure 11.5) indicates that ~44% of North American houses had rates of 0.25–0.5 air changes per 

hour in the early 1980's. 

We assigned a uniform distribution of 0.1–5.5 air changes per hour to the ventilation rate of 

Building 40. The low end of the distribution is based on the geometric mean of two 

measurements during working hours in the warehouse reported by Parker (1985). The high end 

is based on the single measurement during working hours in the machine/wood shop reported by 

the same author. The values used in the analysis are listed in Table B-1. This parameter was 

varied stepwise over a range of 0.5–5.5 air changes per hour in the parametric analysis. 

Revised Draft – Blockson Radon Analysis 30 SC&A – August 12, 2008 

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B.4 Results 

The results of the parametric analysis of radon concentrations were presented in Table 3 of the 

main body of the present report. A statistical summary of the probabilistic analysis is presented 

in Table B-2. The percentile values are listed in Table B-3, while Figure B-3 is a graphical 

representation of the probability distribution. This distribution has a mean of 16.6 ± 0.1 pCi/L, a 

median of 7.72 pCi/L, and a 95th percentile of 61.95 pCi/L. Judging from Figure B-3 and from 

the percentile values, the distribution is approximately lognormal, with a geometric standard 

deviation of 3.55, as calculated from the median and the 95th percentile values. 

Table B-2. Statistical Summary of Monte Carlo Analysis: 222Rn Concentrations (pCi/L) 

Statistic Value 

Trials 99,861

Mean 16.63

Median 7.72

Standard Deviation 31.76

Variance 1,008.41

Skewness 5.88

Kurtosis 52.35

Coeff. of Variability 1.91

Range Minimum 0.02

Range Maximum 651.00

Range Width 650.98

Mean Std. Error 0.10

Table B-3. Percentile Values of 222Rn Concentrations (pCi/L) 

Percentile Value 

0% 0.02 

5% 0.78 

10% 1.50 

15% 2.24 

20% 2.97 

25% 3.70 

30% 4.44 

35% 5.20 

40% 5.99 

45% 6.84 

50% 7.72 

55% 8.73 

60% 9.87 

65% 11.28 

70% 13.06 

75% 15.54 

80% 19.08 

85% 24.77 

90% 35.37 

95% 61.95 

100% 651.00 

Revised Draft – Blockson Radon Analysis 31 SC&A – August 12, 2008 

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B.5 Discussion of Probabilistic Analysis 

The distribution of radon concentrations spans a wide range, with a 70-fold difference between 

the 5th and 95th percentile values, indicating a large uncertainty in the analysis. As was discussed 

in Section B.3, the analysis incorporates a number of uncertain input parameters. The greatest 

uncertainty involves the fraction of the radon in the matrix of the phosphate rock that evolves 

from the aqueous sulfuric acid before the acid is pumped out of Building 40. Radon is quite 

soluble in cold water. In equilibrium, the volumetric concentration of radon in water at 0oC is 

51% of its concentration in the gas phase. However, that ratio is reduced to 11.4% at 50oC and 

to 8.6% at 10oC (Jenkins and Cook 1961, Table II). Thus, even for water at 0oC, the equilibrium 

concentration in the air would be about twice that in the water. Given the much larger volume of 

building air, which is constantly being exchanged with the outside air, virtually all the radon 

would evolve into the atmosphere under static equilibrium conditions (i.e., no influx or removal 

of the aqueous sulfuric acid). An even greater fraction of the radon would evolve since, as stated 

earlier, the acid was kept at an elevated temperature. However, these observations do not cast 

any light on the rate at which the radon evolves from the acid. Since, according to our model, 

much more radon is dissolved in the acid than evolves from the ore in the building before it is 

dissolved in the acid, this uncertainty can have a profound effect on the results. 

A lesser but still significant source of uncertainty is the building air exchange rate. The upper 

end of the range of this parameter is over 50 times greater than the lower end. According to 

Equation 3, the radon concentration is inversely proportional to r + λ, the air exchange rate plus 

the radioactive decay constant of 222Rn. However, since the ventilation rate (0.1–5.5 air changes 

per hour), is far greater than the decay constant (~0.00755 h-1), the concentration essentially 

varies as the reciprocal of the ventilation rate. The ventilation rate can thus cause an 

approximately 50-fold difference in the radon concentration. A still lesser source of uncertainty, 

not explicitly addressed by our model, is the possibility of incomplete mixing of the building 

atmosphere with the outside air. Such incomplete mixing would most likely have a lesser effect 

on the local radon concentration than the uncertainty in the ventilation rate—this effect is most 

likely subsumed by the wide range of ventilation rates employed in the analysis. 

Revised Draft – Blockson Radon Analysis 32 SC&A – August 12, 2008 

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-

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

3.27 133.47 263.67 393.86 524.06

Concentration (pCi/L)

No. trials

Figure B-3. Probability Distribution of 222Rn Concentrations (pCi/L) 

B.6 Conclusion 

We conclude that the results of this analysis can be used to place a plausible upper bound on the 

average radon concentrations in Building 40. For instance, it is quite unlikely that the average 

concentration would have exceeded 62 pCi/L, the 95th percentile value of our probabilistic 

analysis. 

Revised Draft – Blockson Radon Analysis 33 SC&A – August 12, 2008 

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Appendix B References 

Barr, J.A., Jr., J.W. Ruch, and R.F. Borlik. 1955. “Recovering Uranium As By-Product in 

Phosphate Processing,” Rock Products, (October), 96–102. 

Burnett, W.C., et al. 1988. “Release of Radium and Other Decay-Series Isotopes From Florida 

Phosphate Rock,” FIPR 05-016-059 (Florida Institute of Phosphate Research). 

http://www1.fipr.state.fl.us/FIPR/FIPR1.nsf/659556957d393fd685256afc000a4af1/31573005bc5

36bd885256b2f005ad314!OpenDocument. 

Decisioneering, Inc., 2001. Crystal Ball 2000 (Version 2000.2) [Computer software and 

manual]. Denver, Colorado: Author. 

“Emission Factor Documentation for AP-42 section 8.18 (now 11.21), Phosphate Rock 

Processing.” 1993. Washington, DC: U.S. Environmental Protection Agency. 

http://www.epa.gov/ttn/chief/ap42/ch11/bgdocs/b11s21.pdf.

EPA (U.S. Environmental Protection Agency) 1997. “Exposure Factors Handbook.” 

EPA/600/P-95/002Fa. Washington, DC: Author. 

Godish, T. 2001. Indoor Environmental Quality. Boca Raton, Florida: Lewis Publishers. 

Hull, C.D., and W.C. Burnett, 1996. "Radiochemistry of Florida Phosphogypsum." Journal of 

Environmental Radioactivity, 32(3), 213-238. 

Jenkins, A.C., and G.H. Cook, 1961. “Chapter VII: Gas Phase Properties.” In G. H. Cook (Ed.), 

Argon, Helium and the Rare Gases: Vol. 1. History, Occurrence, and Properties. New York: 

Interscience Publishers. 

Lopker, E.B., and L. Block, 1951. Letter from E.B. Lopker and L. Block (Blockson Chemical 

Company) to Sheldon Wimpfen, U. S. Atomic Energy Commission. July 31, 1951. 

Parker, G.B. 1985. “Measurement of Air Exchange Rates in Residential and Commercial 

Buildings in the Northwest: Techniques and Results,” PNL-SA-13057, DE85012444. 

Perry, R.H., and D.W. Green, 1984. Perry's Chemical Engineers' Handbook (6th ed.) New 

York: McGraw-Hill Book Company. 

Tomes, T., 2008a. “Summary of Interview with [name redacted] Conducted by Phone on June 

16, 2008, from approximately 12:00 PM until 12:40 PM.” 

Tomes, T., 2008b. “Summary of Interview with [name redacted] Conducted by Phone on June 

17, 2008, from approximately 2:15 PM until 3:00 PM.” 

Revised Draft – Blockson Radon Analysis 34 SC&A – August 12, 2008 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker Health for 

factual accuracy or applicability within the requirements of 42 CFR 82.
UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) 2000. 

“UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes,” Vol. I: “Sources,” 

Annex B, “Exposures from Natural Radiation.” 

http://www.unscear.org/unscear/en/publications/2000_1.html

Wynveen, R.A., et al. 1983. “Formerly Utilized MED/AEC Sites Remedial Action Program: 

Radiological Survey of Chemicals Group, Olin Corporation (Formerly Blockson Chemical 

Company), Joliet, Illinois, March 27–November 28, 1978,” DOE/EV-0005/35, ANL-OHS/HP83-103. Argonne, Illinois: Argonne National Laboratory. 

Yu, C. et al., 1993. “Data Collection Handbook to Support Modeling the Impacts of Radioactive 

Materials in Soil,” ANL/EAIS-8. Argonne, Illinois: Argonne National Laboratory. 

 

Revised Draft – Blockson Radon Analysis 35 SC&A – August 12, 2008 

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However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker Health for 

factual accuracy or applicability within the requirements of 42 CFR 82.