United States National Risk Management

Environmental Protection Research Laboratory

Agency Cincinnati, OH 45268

EPA Project Summary

Research and Development EPA/600/SR-95/145 February 1996

The report gives results of radiological analyses of soil and fill samples

and data interpretations by the University of Florida in support of the Florida

Radon Research Program (FRRP). Moisture, radium-226, and radon emanation

coefficient determinations were performed on samples collected and submitted during 1992 by the FRRP New

House Evaluation Program (NHEP) and

the FRRP Research House Program.

During this period, 164 samples representing 31 sites were received and analyzed; this provided a 1991-92 cumulative of 288 samples from 75 sites. Since

much of the 1992 sampling represented

a continuation of work performed in

1991, the cumulative 1991-92 data were

analyzed.

The North Florida NHEP sites

(Gainesville vicinity) were characterized

by fill with almost exclusively low radium-226 content (<1 pCi/g). Of the 41

sites sampled in 1991-92, the radium

content of the first 0.9 m of the substrate was <1 pCi/g at 76% of the sites,

1-10 pCi/g at 22%, and in excess of 10

pCi/g (12 pCi/g) at one site. In 1992, the

sampling depth was increased to include a profile to 1.8 m. The range of

results was comparable for the first

and second 0.9 m depths, but the distribution shifted toward higher values

(more sites exceeding 2 pCi/g) for the

deeper increment.

For the Central Florida NHEP sites of

both years, most of the fill samples

and a high percentage of the native

soil sites (70-75%) had radium conSoil and Fill Laboratory

Support–1992, Radiological

Analyses, Florida Radon

Research Program

centrations exceeding 1 pCi/g. These

sites are characterized by elevated radioactivity (1 to >10 pCi/g) fill over a

wide range of substrate concentrations

(<1 to >10 pCi/g).

This work supports conclusions from

previous years. A large portion of the

fill used in Florida construction is of a

low radium content. However, elevated

radium concentrations do occur in soil

at some Florida construction sites, and

fill with elevated radioactivity may be

an issue in selected circumstances. The

extent and source of elevated radioactivity fills should be investigated further and building code development

should continue to consider a soil/fill

radioactivity standard. At some locations (for example, North Florida) nearsurface soil gas radon may originate

from deeper than 1 m, and thus shallow soil samples may not be adequate

for identifying radon potential.

With respect to the research houses

and test modules, these laboratory

analyses verified that the sites and test

fills are generally representative of the

conditions observed at the NHEP construction sites in the respective regions.

This Project Summary was developed

by the National Risk Management Research Laboratory’s Air Pollution Prevention and Control Division, Research

Triangle Park, NC, to announce key

findings of the research project that is

fully documented in a separate report

of the same title (see Project Report

ordering information at back).

C.E. Roessler, H. Mohammed, R. Richards, and H. Nyugen
2

Introduction

The report gives results of soil and fill

analyses performed by the University of

Florida in support of the Florida Radon

Research Program (FRRP). Radiological

characteristics were determined on

samples collected during 1992 by the Research House Program and the New

House Evaluation Program (NHEP) of the

FRRP.

This work is a continuation of efforts to

characterize the radon1 source potential

of Florida soil and fill materials. In 1989, a

survey of 35 sites distributed statewide

examined fill materials at construction sites

(66.6%) and native surficial soil at construction or existing house sites (33.3%).

In addition, insitu permeability and soil

gas radon measurements were performed

at a subset of these sites. Work in 1990

emphasized insitu permeability and soil

gas radon measurement and soil sampling at 23 statewide sites as prepared for

construction. In 1991, the research contractors for the NHEP program submitted

samples collected at 42 construction sites

in areas of suspected elevated radon potential in North Florida (Alachua County)

and Central Florida (primarily Polk County).

Samples were also received from the

Alachua County and Polk County FRRP

Research House sites.

The work in 1992 involved continued

support of the FRRP NHEP and Research

House projects and analysis of the 1991-

92 cumulative data.

Methodology

Samples were collected to represent

both the sub-slab fill material and the upper (1-2 m) portion of the underlying substrate. In the laboratory, soil samples were

dried and portions were sealed in a container, counted with high resolution

gamma-ray spectrometry shortly after sealing, held for ingrowth of radon and its

short-lived decay products, and counted

at least one more time. Radium concentrations and radon emanation coefficients

were calculated from the activity associated with 295.2-, 351.9-, and 609.3-keV

peaks of the short-lived radon daughters.

The radium concentration was based on

the projected equilibrium radon-222 activity; radon emanation coefficient was determined from the pair of values corresponding to pre-ingrowth and equilibrium

radon concentrations.

Sample collection methods for the Research House Project are specified in a

separate Florida research houses guidance document.

Results and Discussion

During 1992, 164 samples representing

31 sites were received and processed;

this provided a 1991-92 cumulative of 288

samples from 75 sites.

Radiological Characteristics at

NHEP Sites

The North Florida NHEP sites

(Gainesville vicinity) were characterized by

fill with almost exclusively low radium-226

content (<1 pCi/g) over predominantly low

activity near-surface substrate. Fill samples

had concentrations of <1 pCi/g at 30 of 31

sites. At one site, moderately elevated

radioactivity fill (3 pCi/g) was found over

low activity (<1 pCi/g) surficial substrate.

Compared to the 1991 sites, the 1992

sites had a greater percentage of slightly

to moderately elevated radium concentrations (1-10 pCi/g) in the first 0.9 m. For

the upper 0.9 m of the 41 sites sampled in

1991-92, 76% had <1 pCi/g, 22% had 1 -

10 pCi/g, and only one site exceeded 10

pCi/g (12 pCi/g). Because it appeared that

the radon gas was originating from deeper

than the 0.9 m sampled in 1991, profiles

to 1.8 m were collected in 1992. The range

of results was comparable for the first and

second 0.9 m depths, but the distribution

shifted toward higher values (more sites

exceeding 2 pCi/g) for the deeper increment.

For the Central Florida NHEP sites of

both years, most of the fill samples and a

high percentage of the native soil sites

(70-75%) had radium concentrations exceeding 1 pCi/g. These sites are characterized by elevated radioactivity (1 to >10

pCi/g) fill over a wide range of substrate

concentrations (<1 to >10 pCi/g).

Radiological Characteristics at

Research House Sites

At the North Florida Research House,

radium concentrations in the first 1.8 m

for two different cores near the house

were in the range of 4-7 pCi/g. These

values are moderately elevated and indicate that the radon source is near the

surface with a relatively uniform distribution at this site. This compares to the

several North Florida NHEP house sites

that had elevated radium in the near-surface substrate. The sub-slab material from

the suction pit was much lower in radioactivity and presumably represents fill. The

general material excavated from the pit

had concentrations on the order of only

0.3-0.4 pCi/g, while pieces of clay found

in this material had slightly elevated radium concentrations in the range of 1-2

pCi/g.

The fill and the substrate at the Central

Florida Test Modules Florida Institute of

Phosphate Research (FIPR) site had radium concentrations on the order of 5-8

pCi/g; these values are comparable to the

median values observed for soil and fill at

the Central Florida NHEP sites.

In 1992 a module was constructed in

Central Florida to permit testing of the

contribution of fill material to indoor radon.

This site has a low near-surface radon

source — radium concentrations in the

first 1.5 m were on the order of 0.1 to 0.2

pCi/g. The test materials selected to represent “medium” radioactivity fill (waste

sand tailings from phosphate rock

benefication) had concentrations on the

order of 4 pCi/g. The test materials selected to represent “hot” fill (phosphate

rock concentrate, the benefication product), had concentrations on the order of

33 pCi/g. These concentrations are comparable to values typically reported for

these materials and verify the selection of

these materials to represent or simulate

two levels of fill radioactivity.

Fill from a Central Florida source and in

use in a test chamber had radium concentrations in the range of 4-6 pCi/g. These

concentrations are comparable to those in

the moderately elevated substrate and fill

samples from the Central Florida NHEP

sites.

Conclusions and

Recommendations

The 1991 and 1992 work under this

project leads to the following conclusions

and recommendations.

 1. The observations for North

Florida support earlier conclusions (1989 and 1990) that a

large portion of the fill actually

used in Florida construction is of

a low radium content. Availability

of low radioactivity fill should not

be a deterrent to adopting radioactivity standards for construction

fill.

 2. Elevated radium concentrations

do occur in some Florida soil and

fill samples in actual house construction. Building code development should continue to consider

a soil/fill radioactivity standard.

 3. Fill with elevated radioactivity can

be an issue in selected circumstances (this was observed at the

Central Florida NHEP sites). The

1

In the report, the term “radon” designates the radon

isotope, radon-222. The term “radium” denotes the

radium isotope, radium-226.
3

extent and source of these fills

should be investigated further.

 4. Mining-related land (such as reclaimed overburden and/or sand

tailings areas) may present a radon source. These soils may

have characteristics different from

those of undisturbed soils and

directly excavated fills. The program should be reviewed to assess whether this land category

is receiving adequate attention in

sampling and radon potential

modeling.

 5. These and other studies indicate

that, at some locations in North

Central Florida, the near-surface

soil gas radon may originate from

deeper than 1 m. Therefore, sampling in this region should continue to be for a 2-m or greater

depth profile, especially if elevated soil gas radon has been

detected at the site.

6. The observation that the radon

source may be deeper than 1 m

indicates that shallow soil

samples, in the absence of additional information about the depth

profile, may not be adequate for

identifying radon potential.

 7. With respect to the research

houses and test modules, these

laboratory analyses verified that

the sites and test fills are generally representative of the conditions observed among the NHEP

construction sites in the respective regions.
4

C. Roessler, H. Mohammed, R. Richards, and H. Nyugen are with The University

of Florida, Gainesville, FL 32611.

David C. Sanchez is the EPA Project Officer (see below).

The complete report, entitled “Soil and Fill Laboratory Support—1992, Radiological

Analyses, Florida Radon Research Program,” (Order No. PB96-140579; Cost:

$17.50, subject to change) will be available only from:

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

Telephone: 703-487-4650

The EPA Project Officer can be contacted at:

Air Pollution Prevention and Control Division

National Risk Management Research Laboratory

U.S. Environmental Protection Agency

Cincinnati, OH 45268

• •

United States

Environmental Protection Agency

National Risk Management Research Laboratory (G-72)

Cincinnati, OH 45268

EPA/600/SR-95/145

Official Business

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