EPA-600/R-96-045
April 1996
SITE-SPECIFIC PROTOCOL
FOR MEASURING SOIL RM)ON POTENTIALS
FOR FLORIDA HOUSES
Final Report
by
Kirk K. Nielson, Vera. C. Rogers, and Rodger B. Holt
Rogers & Associates Engineering Corporation
P.O. Box 330
Salt Lake City, UT 84110-0330
EPA Interagency Agreement RWFL 933783
Florida DCA Contract 94RD-30-13-00-22-002
DCA Project Officer: Mohammad Madani
Florida Department of Community Affairs
2740 Centerview Drive
Tallahassee, FL 32399
EPA Project Officer: David C. Sanchez
National Risk Management Research Laboratory
Research Triangle Park, NC 27711
University of Florida Project Director: David E. Hintenlang
Department of Nuclear Engineering Sciences
202 Nuclear Sciences Center, University of Florida
Gainesville, FL 32611
Prepared for:
Florida Department of Community Affairs
2740 Centerview Drive
Tallahassee, FL 32399
and
U. S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
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FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
ana strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
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ABSTRACT
This report derives and presents a protocol for site-specific characterization of radon
potentials that is consistent with existing residential radon protection maps. Although the
radon protection maps provide quick and inexpensive regional estimates of radon potential
category, it is also desirable to be able to measure the radon potential category of a particular
site. Therefore, the site-specific protocol and basis presented in this report are designed to
guide the measurement and interpretation of radon-related features at a site to give further
guidance on the possible need for radon-protective construction features.
The site-specific protocols identified in this report can provide valuable information
to builders or developers that may know of or suspect anomalous site conditions that could
increase the radon potential above the mapped category. Such conditions could include
effects from previous land uses, observations of unusual soil or mineral occurrences, or deep
water tables in areas of highly permeable soil (gravelly or fractured). Alternatively, land
developers may suspect their land has lower radon potential than its mapped category,
leading them to consider reduction or elimination of special radon controls unless they are
specifically shown to be needed. In either of these cases, site-specific tests assist in making
a more informed decision. Any decisions involving site-specific testing should also consider
the relative costs of using conservative radon controls versus the costs of site-specific testing,
and should also consider the EPA guidance on reducing radon risks even from levels in the
range below 4 pCi L"1.
The method for defining the site-specific protocol utilizes sensitivity analyses of radon
entry into a reference house as determined by the RAETRAD model. By using the same
model, reference house, and parameters used for the residential radon protection maps, the
protocol derived here has a basis that corresponds to that of the maps. The sensitivity
analyses identified radium concentration, soil layer depth, soil density, soil texture, and water
table depth as being the independent parameters affecting indoor radon levels. Radium
concentration and water table depth were dominant. Soils up to 2.4 m deep contributed to
indoor radon in uniform-radium scenarios, and soil layers of approximately 0.6 m thickness
significantly affected levels in cases of non-uniform radium distributions.
A conservative upper limit for indoor radon concentrations, defined as the 95%
confidence limit for radon in the reference house, was defined mathematically to correspond
to the radon protection map. A RAETRAD estimate of this parameter using geometric mean,
values and geometric standard deviations of the parameter values is numerically equivalent.
The number of samples needed to represent a site was determined from the equivalent
regional precision attained by the radon protection map. Based on the sensitivity of the
contributing soil depth and layer thickness, the site-specific measurements were shown to
require 20 samples per 4,000 m2 (1 acre). These samples are distributed throughout four
depth increments that extend to a depth of 2.4 meters. A special formula is derived to obtain
equivalent precision for a smaller parcel of land using less samples. The mathematical
calculations are performed by a special-purpose computer code called RAETRAD-F.
The site-specific protocol involves drilling five boreholes for every 4,000 m2 of land to
be characterized, and analyzing each 4,000 m2 parcel (or fraction thereof) as a separate
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parcel. Twenty soil samples obtained from the borings are used for radium measurements.
The soil borings are also used for density and textural estimates unless default values are
chosen for these parameters. A soil radon measurement is used to detect the potential
presence of anomalous elevated-radium materials at depths below 2.4 m. The site water
table depth distribution is defined from either soil survey data or site observations for use
in soil moisture calculations. The site measurements are submitted as requested by the
RABTRAD-F code, and are processed to determine the upper limit for indoor radon
concentrations in the reference house at the site. Using the same category definitions as for
the residential radon protection map, the RAETRAD-F code determines whether the site is
in the low, intermediate, or elevated map category for radon protection purposes.
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CONTENTS
Page
Abstract i u
Figures v iii;
Tables i x
1. INTRODUCTION 1-1
1.1 Background 1-1
1.2 Objectives and Technical Approach 1-2
1.3 Scope 1-3
2. MODEL SIMULATIONS AND PARAMETER SENSITIVITY 2-1
2.1 Radon Simulation Methods and Parameters 2-1
2.1.1 The RAETRAD Model 2-2
2.1.2 The Reference House 2-4
2.1.3 Reference Soil Parameters 2-4
2.2 Radon Sensitivity Analyses 2-6
2.3 Results and Interpretation of Sensitivity Analyses 2-9
3. MATHEMATICAL DEFINITION OF SITE-SPECIFIC RADON POTENTIAL 3-1
3.1 Equation for the Site-Specific Radon Potential 3-1
3.2 Parameter Specification 3-3
3.3 Determination of the Minimum Number of Soil Samples 3-4
3.4 Soil Radium GSD for Fewer than 20 Samples 3-8
3.5 Maximum Site Area 3-8
3.6 Automated Calculations 3-9
4. PROTOCOL FOR SITE-SPECIFIC RADON POTENTIAL MEASUREMENT 4-1
4.1 Use of the Site-Specific Radon Potential Protocol 4-1
4.2 Site-Specific Measurement Protocol 4-2
4.2.1 Site Sampling and Measurements 4-2
4.2.2 Soil 226Ra Concentration 4-3
4.2.3 Soil Density 4-3
4.2.4 Soil Textural Classification 4-4
4.2.5 Soil 222Rn Concentration 4-4
4.2.6 Water Table Depth 4-5
4.3 Analysis of Site-Specific Measurements 4-6
5. SUMMARY AND CONCLUSIONS 5-1
6. LITERATURE REFERENCES 6-1
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FIGURES
Number Page
2-1 Two-dimensional grid and boundaries defining the house and soil 2-3
regions analyzed by RAETRAD.
2-2 Sensitivity of indoor radon to soil textural class. 2-9
2-3 Sensitivity of indoor radon to surface soil emanating 226Ra 2-10
concentrations.
2-4 Sensitivity of indoor radon to geologic soil emanating 226Ra 2-11
concentrations.
2-5 Sensitivity of indoor radon to soil density. 2-12
2-6 Sensitivity of indoor radon to water table depths. 2-13
2-7 Comparison of parameter sensitivities. 2-14
2-8 Sensitivity of indoor radon to thickness of elevated-radium layers. 2-16
2-9 Sensitivity of indoor radon to soil air permeability. 2-17
2-10 Sensitivity of indoor radon to soil radon diffusion. 2-17
3-1 Variation of fn with n. 3-7
3-2 RAETRAD-F calculation of the site radon protection category. 3-10
viii
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TABLES
Number Page
2-1 Reference house parameters used in radon entry simulations. 2-4
2-2 Reference soil properties used in radon entry simulations. 2-5
4-1 SCS soil texture classes. 4-4
ix
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Chapter 1
INTRODUCTION
1.1 BACKGROUND
Radon (222Rn) gas from the decay of naturally occurring radium (226Ra) in soils can
enter buildings through their foundations. If the radon entry rate is elevated and the
building is not well ventilated, radon can accumulate to levels that can significantly increase
the occupants' risks of lung cancer with chronic exposure. The degree of health risk is
proportional to the long-term average level of radon exposure. The U.S. Environmental
Protection Agency (EPA) attributes 7,000 to 30,000 lung cancer fatalities annually to radon,
and recommends remedial action if indoor radon levels average 4 picoeuries per liter (pCi L"1)
or higher (EPA92a; EPA92b).
The Florida Department of Community Affairs (DCA), under the Florida Radon
Research Program (FRRP), has developed radon-protective building standards to reduce
radon-related health risks (SanBO; DCA94). The standards require passive radon barriers
and active sub-slab ventilation to reduce radon entry in regions that are prone to elevated
radon levels. Because of the incremental costs of the radon control features, the standards
seek to balance the control feature costs with the benefits of reduced radon risk. This cost-
benefit balance has led to the development of radon protection maps to show the regions of
Florida where no special radon controls are justified, where only passive radon controls are
justified, and where both passive and active controls are justified (Nie95b; Nie95e). The
radon protection maps give the most cost-effective guidance on regional needs for special
radon controls. They also include a margin of safety to ensure that the majority of buildings
in a given map area will not exceed the desired radon level on an annual-average basis.
While the radon protection maps give quick and inexpensive regional guidance on the
need for special radon controls in new buildings, it is also desirable to be able to measure the
radon potential category of particular sites. Although site-specific analyses are not generally
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required, they can give valuable guidance in some cases. For example, a prospective builder
may know or suspect anomalous conditions at a site (from previous land use, soil or mineral
observations, or deep water table) that could increase the radon potential above its mapped
category. Alternatively, the builder may have reason to suspect that the land has lower
radon potential than its mapped category, leading him to want to reduce or eliminate radon
controls unless they are specifically shown to be needed. In either case, site-specific tests
could help lead to a more informed decision. The decision should also consider the relative
costs of using conservative radon controls versus testing, as well as the EPA guidance on
further reducing radon levels even in the range below 4 pCi L"1 (EPA92b).
A previous assessment of site-specific radon potential measurement methods
conducted under the FRRP was aimed at identifying simple site measurements that could
give inexpensive but useful surrogates for soil radon potentials (Nie9oa). It reviewed
previous attempts to quantify site-specific radon potentials with empirical indices (Eat84;
DSM85; Kun89; Tan89; PeaSO) and compared site radon flux and gamma-ray measurements
with indoor radon levels at 26 residential sites. The simple site measurements were
correlated with indoor radon levels and mapped radon potentials. However, these site
measurements alone could not determine radon potentials with sufficient precision to justify
widespread use of site-specific measurements.
1.2 OBJECTIVES AND TECHNICAL APPROACH
This report reassesses site-specific radon potential measurements by examining more
closely the range of fundamental parameters that control radon potentials. The present study
is aimed at defining and characterizing more directly the site parameters that contribute to
calculated radon potentials. Its broader objective is to provide a reliable alternative to the
radon protection maps for estimating the soil radon potential of a specific building site. This
study derives from fundamental parameters and model analyses the minimum set of site
parameters that can determine the radon potential of a site. The analyses are based on
radon entry into and accumulation in a reference house, thereby giving them the same basis
as the residential radon protection map. The model analyses utilize the RAdon Emanation
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and TRAnsport into Dwellings (RAETRAD) model (Nie94) to determine the critical
parameters. The approach and model analyses are consistent with previous modeling
approaches and definitions of soil radon potential (Naz89; Yok92).
In the present analyses, the minimum set of site parameters that defines radon
potential is used to define a set of minimum sample requirements to characterize the site
properties that control radon potential. From the sample requirements, a field sampling and
measurement protocol is developed to measure the critical parameters at a site using the
appropriate level of sampling and replication. The proposed field measurements require
analysis by the RAETRAD model to determine a reference-house radon potential that is
consistent with existing residential radon protection maps.
1.3 SCOPE
This report presents the model simulations of radon generation and entry into a
reference house under different conditions that define the sensitivity of radon levels to
different site parameters. The critical site parameters that must be characterized are
determined from the sensitivity analyses. The minimum sample and measurement
requirements then are determined for each critical parameter, and the sample and
measurement requirements finally are used to define a protocol for estimating site-specific
radon potentials.
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Chapter 2
MODEL SIMULATIONS AND PARAMETER SENSITIVITY
Model simulations of radon generation and movement from soils into houses were used
to estimate the dependence of indoor radon levels on different site parameters and to identify
critical parameters that control radon potential. The simulations focused on long-term
average values to avoid the temporal radon fluctuations from varying soil and house
conditions. This chapter describes the methods and parameters used for the radon
simulations, the sensitivity analyses that were conducted, and the results of the analyses.
The analyses are used to demonstrate which site parameters are critical in determining
radon potential and which have secondary or smaller influences on radon potential.
2.1 RADON SIMULATION METHODS AND PARAMETERS
Indoor radon concentrations depend on a site-specific combination of soil and building
characteristics. To estimate radon potentials for open land, the same reference-house
approach was used as in earlier analyses to develop soil radon potential maps (Nie95b). The
approach entails placement of a hypothetical reference house on the individual soil profiles
that occur in different regions, and simulation of radon generation and movement from these
soils into the reference house. This approach determines the expected geographic variations
ill indoor radon due to varying soil conditions without regard to the peculiarities of individual
houses. The approach is appropriate here because the intended site-specific radon potential
classifications are to be used as potential alternatives to corresponding estimates from the
radon protection maps. For consistency, the reference house defined in the present study is
the same reference house used in the earlier radon map analyses.
The simulations of radon entry into the reference house also utilized soil and geology
definitions that were consistent with the prior analyses for radon maps (Nie9ob). For
example, soil radium distributions were defined to be uniform throughout the strata in an
upper layer of approximate 2.5 m thickness, and they were also defined to be uniform
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throughout a lower, geology-dominated zone that was also approximately 2.5 m thick.
Realistic distributions of soil water contents throughout both zones were determined from soil
water drainage properties and estimated water table depths. The drainage properties were
listed for individual soils in the State Soil Geographic Data Base (STATSGO) (SCS91) for the
radon maps and were calculated from soil texture and density data (Nie92) for the present
analyses.
2.1.1 The RAETRAD Model
The RAETRAD model (Nie94) was used for simulating radon generation and transport
from the various soil profiles into the reference house. RAETRAD provides a conceptual and
mathematical basis to evaluate how close and how strong a radon source must be for
particular soil and ground water conditions to exert a given effect on indoor radon levels.
RAETRAD is implemented as a steady-state, numerical-analytical computer code that
simulates (a) radon generation and decay in soil regions around a house and in the house
understructure (e.g., floor slab, footings); (b) diffusive and pressure-driven advective
movement of radon through the soils and the house understructure; and (c) radon
accumulation in a mixed, single-chamber house with a defined ventilation rate. Multiphase
radon source and transport equations explicitly represent the solid soil particles, pore water,
and air-filled pore space (Rog91a; Rog93). Numerical equations represent varied spatial
distributions of radon sources, soil properties, water contents, and boundaries.
In the RAETRAD analyses, parameters characterizing the reference house were held
constant for all cases. The house was placed on different configurations of soils, radon
sources, water distributions, and other parameters for each simulation. In the numerical
analysis, RAETRAD first computed complete arrays of properties for all soil and house
locations. These included the material thickness, radium concentration, radon emanation
fraction, porosity, water content, mean particle diameter, radon diffusion coefficients
(horizontal and vertical), air permeabilities (horizontal and vertical), and textural
classification. RAETRAD next used the air permeabilities and indoor-outdoor air pressure
difference- to compute steady-state pressures and air flow velocities at each numerical node.
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RAETRAD then used the air flow velocities with radon source parameters, diffusion
coefficients, and water distributions to solve the radon differential equation for radon
concentrations and fluxes at each numerical node. Finally, RAETRAD integrated the radon
fluxes entering the floor and crack areas of the house over the house footprint area, and
determined the steady-state indoor radon concentration from, the competing radon entry rate
and the house ventilation rate. Figure 2-1 illustrates the reference house and soil
configuration analyzed and the dominant air flow and radon diffusion pathways.
Center of
Symmetry
Pressure-driven
air flow;
Advective radon
transport
Outdoor Boundary:
House:
Ventilatory
Floor
Crack
Floor Slab
Radial
Dimension
Fill Soil
o w
Gas
Diffusion
Son Regions
Figure 2-1. Two-dimensional grid and boundaries defining the house and soil
regions analyzed by RAETRAD.
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2.1.2 The Reference House
The site-specific radon potential estimates utilize a reference house that corresponds
to the one used previously for radon potential maps (Nie95b) to give the site-specific analyses
a com mon basis for estimating equivalent radon potentials. The reference house, represented
in Figure 2-1, consists of a 143-m2 (1.540-ft2) rectangular, slab-on-grade structure that is
defined to have the approximate characteristics of Florida single-family dwellings. The
dominant house characteristics affecting indoor radon include the indoor air pressure, the
indoor-outdoor air exchange rate, and the type and quality of foundation design and
construction. Other properties of the house are listed in Table 2-1. The house is defined to
have a floating-slab floor design, causing a shrinkage crack of approximately 0.5 cm width
at the slab perimeter.
Table 2-1. Reference house parameters used in radon entry simulations
Parameter
Value
Parameter
Value
Footprint dimensions
8.6 m x 16.5 m
Slab water/cement ratio
0.55
Interior volume
350 m3
Floor slab thickness
10 cm
External ventilation
0.25 h'1
Floor slab porosity
0.22
Floor crack width
0.5 cm
Slab 226Ra-emanation
0.07 pCi g1
Floor crack location
Slab perimeter
Exterior footing depth
61 cm
Fill soil thickness
30 cm
Slab air permeability
IxlO"11 cm2
Indoor air pressure
-2.4 Pa
Slab Rn diffusion
8xl0'4 cm2 s"1
2.1.3 Reference Soil Parameters
Soils were broadly categorized into a surface category and a deeper, geologic category
for consistency with previous analyses for radon potential maps (Nie95b). A set of reference
soil properties was defined as a basis for comparison, even though individual soil properties
were varied as part of the sensitivity analyses. The reference soil properties are listed in
Table 2-2. Other soil properties requiring definition by RABTRAD include layer thickness.
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air permeability, radon diffusion coefficient, moisture, radon emanation fraction, and porosity.
The thickness of each layer was defined as 30 cm, as used previously to define RAETRAD
mesh node spacing. Soil air permeability and radon diffusion coefficients were defined
automatically by KAETRAD from soil porosity, water content, and mean particle diameter
using empirical correlations (Rog91b). The air permeability and diffusion coefficients were
defined identically for both horizontal and vertical directions, assuming that all soils were
isotropic. Soil water contents were defined from the distance of the soil layer above the water
table and from its density and textural classification (Nie92).
Table 2-2. Reference soil properties used in radon entry simulations.
Parameter
Value
Parameter
Value
Soil density
1.6 g cm"3
Soil 226Ra
1.8 pCi g"1
Soil porosity
0.407
Water table
5.2 m
Textural class
Sand
Surface/geologic zones
2.4 m each
Soil radon emanation fractions were defined from the empirical trend with radium
concentrations for consistency with previous radon map calculations (Nie95b). This trend
function had the form:
E = min(0.55, 0.15 Ra + 0.20), Ra < 8 pCi g"1 (1)
E = 0.50 Ra > 8 pCi g"\
where E = radon emanation fraction (pCi of 222Rn emanated per pCi 222Rn generated)
Ra = soil 226Ra concentration (pCi g"1).
For the reference radium concentration of 1.8 pCi g"1, the reference radon emanation fraction
was determined from equation (1) to be 0.47. Soil porosity was calculated from soil density
and specific gravity as:
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p = 1 - p/pg
(2)
where p = soil porosity (cm3 pore space per cm3 bulk space)
p = soil bulk density (g cm'3, dry basis)
pg = soil specific gravity (g cm"3).
A default value of 2.7 g cmJ was used for soil specific gravity.
2.2 RADON SENSITIVITY ANALYSES
Numerous sensitivity analyses were conducted with the RAETRAD model to determine
which site parameters strongly affect site radon potentials and which have secondary or
smaller influences. Because of the interdependence of many site parameters, only the
independent parameters were varied in the main group of sensitivity analyses. For example,
water table depth was used along with soil density and textural classification to compute
moisture distributions. Therefore, soil moistures were not varied independently, but their
values were allowed to vary as water table, density, and texture were varied.
Based on independence considerations, the 12 soil-defining parameters required by
RAETRAD (texture, thickness, depth, radium, density, emanation fraction, porosity, moisture,
mean particle diameter, radon diffusion coefficient, air permeability, and water table depth)
were reduced to five that were varied in the main group of sensitivity analyses. The five
included texture, depth, radium, density, and water table depth. Layer thickness was kept
constant (30-em layers) for consistency with previous calculations, and because it is a model
parameter rather than a site parameter. The depth parameter was considered to apply only
to radium distributions since water contents and their dependent parameters already varied
with depth from the water table. For consistency with the previous surface and geologic soil
assignments for the upper and lower soil zones (Nie95b), these were the primary depth
parameters used in the radon simulations. Soil gas radon was also analyzed as a possible
surrogate for deep-soil radium concentration to detect potential high-radium anomalies
beneath the sampling depth range.
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RAETRAD analyses were performed to determine the net radon concentration in the
reference house, when placed on the reference soils, while individually varying each of the
five independent parameters. Analyses first were performed in which the entire soil column
(to simulation depths of 6 m.) consisted of alternative soil textures. For example, RAETRAD
permits automatic selection of each of the 12 Soil Conservation Service (SCS) textural
classifications (sand, loamy sand, sandy loam, sandy clay loam, sandy clay, loam, clay loam,
silty loam, clay, silty clay loam, silty clay, and silt) (SCS75). In each simulation, the entire
soil column was defined as a different, uniform soil class, and the resulting changes in
calculated moistures, diffusion coefficients, and permeabilities were reflected in the calculated
indoor radon concentration.
In the next sets of analyses, the effects of varying radium concentrations in the surface
soil zone (0 - 2.4 m) were evaluated by analyses that varied the radium concentrations in this
zone. Corresponding analyses held the surface-soil radium concentration constant while
varying the geologic-soil radium concentrations. These estimated the effects of the upper-
zone layer thickness in shielding the influence from the lower zone. These analyses were
conducted using a surfacc-soil radium concentration of 4 pCi g"1 in addition to the reference
value of 1.8 pCi g'1. The purpose of using the additional surface radium concentration was
to examine potential interactions between the surface and geologic radium levels on the
indoor radon concentration trends.
In the next set of analyses, the density of all soils throughout the 6-m profile was
varied systematically throughout the range of 1.1 g cm*3 to 2.0 g cm"3. This range included
the intermediate 1.6-g cm"3 reference density, and was designed to examine soil compaction
effects on radon entry from variations in soil porosity and capillary suction, which in turn
affect moisture, radon diffusion, and air permeability.
In the final set of analyses, the depth of the water table was decreased from its
reference position at 5 m by successive 0.3 m increments until it approached the surface. In
these analyses, as with the density variations, the effects on indoor radon were sought from
the indirect effects of the parameter variation. In this case, shallower water tables permitted
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greater capillary elevation of soil moistures, thereby reducing the radon diffusion and air
permeability of the soil.
A semi-quantitative approach was used to help interpret the sensitivity analyses. The
relative sensitivity of each parameter was estimated using a log-log plot of the indoor radon
concentrations calculated in each simulation versus the parameter of interest. Although the
textural classifications had no direct numeric scale for such a plot, they were assigned integer
values for comparison purposes, starting at 1 for sand and increasing to 12 for silt. The
slopes of the lines on the plot, near the parameter value of interest, correspond to the power-
curve (y = axb) dependence of each parameter. This approach helped to rank the relative
importance of" each parameter to help estimate its relative value in site-specific
meas urements.
In a separate set of simulations, alternating layers of elevated-radium and low-radium
soils were varied in thickness to estimate a suitable layer thickness for compositing and
measurement of field samples. These simulations used the same reference house and soil
parameters as the other simulations, but varied the thickness of each soil zone from 30 cm
to 300 cm. The thickness where the layer-order effects became acceptably small "was used
to estimate an appropriate vertical range for collecting and compositing field samples.
Two other supplementary sets of sensitivity analyses were also performed for the
surface soil air permeability and radon diffusion coefficient. Although the effects of these
parameters were already included indirectly as they were affected by varying water table, soil
texture, and soil density, their explicit sensitivity was also required for calculating the
uncertainty in site radon potential in Section 3. For the permeability analyses, the air
permeability of soils was made uniform throughout the soil profile and was varied above and
below its typical range in near-surface soils while all other parameters were held constant.
For the diffusion analyses, the radon diffusion coefficient of soils was made uniform
throughout the soil profile and was varied above and below its typical range in near-surface
soils while all other parameters were held constant.
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2.3 RESULTS AND INTERPRETATION OF SENSITIVITY ANALYSES
The results of the sensitivity analyses for soil textural classifications are presented
in Figure 2-2. The decreasing pore sizes associated with each textural class cause increased
capillary retention of water in soil pores, thereby lowering air permeability and radon
diffusion coefficients and reducing the movement of radon from soils into the reference house.
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Figure 2-2. Sensitivity of indoor radon to soil textural class.
2-9
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The results of the analyses of sensitivity to surface soil emanating radium
concentrations are presented in Figure 2-3. The expected linear dependence is demonstrated
by analyses covering an emanating radium concentration range of 0 to 5 pCi g"1. Emanating
radium is the product of the total soil radium concentration and the radon emanation
coefficient (as defined by equation (1). As illustrated, the total soil radium concentrations in
the deeper, geologic zone were held constant at 1.8 pCi g"1 for these analyses.
Water Table Depth: 5.2 m
Soil Density: t.6g/cc
Total Geologic Radium
(depth > 2.4 m): 1.8 pCi/g (E = 0.47)
- S
¦ C
0 1 2 3 4 5
Emanating Radium Concentration in 0 - 2.4 m Depth Soils (pCi/g)
Figure 2-3. Sensitivity of indoor radon to surface soil
emanating 22GRa concentrations.
2-10
-------
The results of the analyses of sensitivity to geologic (deep) soil emanating radium
concentrations are presented in Figure 2-4. A linear dependence is again observed, but with
a smaller slope. The five emanating radium concentrations used for these analyses
correspond to the low, intermediate, elevated, Bone Valley, and disturbed Bone Valley
categories for geologic radium concentrations that were used previously in generating the
radon maps (Nie95b). As illustrated, the total soil radium concentrations in the surface zone
were held constant at 1.8 or 4.0 pCi g"1 for these analyses, giving parallel lines that suggest
an approximate independence of the surface and geologic radium effects. Since the deep
(geologic) zone radium profile has less effect than that for the surface zone and it is difficult
to measure, it can be extrapolated from the deepest measurements or defined from soil gas
radon measurements.
20
15
10
0
» 1— 1 1
Total Surface Soil Radium:
1 i ' *
4.0 pCi/a (E = 0.55)
.JL—
—©""""'"'Total Surface Soil Radium:
1.8 pCi/g (E = 0.47)
:
Water Table Depth: 5.2 m
-
Soil Density: 1.6 g/cc
*
¦
Soil Type: Sand
i , i . i
0
8
10
Emanating Radium Concentration in Soils Deeper than 2.4 m (pCi/g)
Figure 2-4. Sensitivity of indoor radon to geologic soil
emanating 22GRa concentrations.
2-11
-------
The results of the analyses of sensitivity to soil density are presented in Figure 2-5.
A strong dependence is suggested by the low-density end of the curve, but increases above
soil densities of 1.7 to 1.8 g cm"3 have little effect. The strong dependence at low densities
is dominated by the compression of a given radium concentration into a progressively smaller
soil volume and the emanation of radon into progressively smaller pore volumes, both of
which give higher radon concentrations in soil pore spaces. At higher soil densities, however,
the competing effects of reduced permeability and diffusion, caused by increased capillary
water retention, reduce the rate at which radon enters the reference house.
Soi! Type: Sand
Soil Radium: 1.8 pCi/g (E = 0.47}
Water Table Depth: 5.2 m
Geologic Density (>2.4 m): 1.6 g'cc
Soi! Density (top 2.4 m, g/cc)
Figure 2-5. Sensitivity of indoor radon to soil density.
2-12
-------
The results of the analyses of sensitivity to the depth of the water table are presented
m Figure 2-6. A strong sensitivity is demonstrated at shallow water table depths, but the
radon increases decrease until they become unimportant at water table depths beyond
approximately 2.4 m. Based on the sensitivity analyses for soil texture, the depth for
constant radon would be shallower for smaller-diameter soils because of their increased
capillary water retention at greater distances above the water table.
' = 1 ! 1 1 1 1 1 i r
1 — ~ m 1
'¦= 4
1 -
0
-» * 1 *
0
"O ' C ¦ —Q p. o-
Soil Type: Sand
Soil Radium: 1.8 pCi/g (E = 0.47)
Soil Density: 1.6 g/cc
* « »
100 200 300 400
Water Table Depth (cm)
500
600
Figure 2-6. Sensitivity of indoor radon to water table depths.
2-13
-------
The radon concentrations from. Figures 2-2 through 2-6 were plotted together on a
single log-log plot to compare the overall sensitivities of each parameter. In this plot,
illustrated in Figure 2-7, the slope of the curve at the point of interest gives the parameter
sensitivity at that value of the parameter, expressed as the exponent b for the power curve
(y = axb). The most sensitive parameter is the surface soil radium concentration, which has
a sensitivity exponent of b = 0.81 at Ra-E = 1 pCi g'1 of emanating radium. As illustrated,
this sensitivity increases at higher radium concentrations, approaching b = 1.0 and
potentially raising indoor radon levels above 20 pCi L"1 as the emanating radium
concentration, approaches 5 pCi g"1. The sensitivity of the deeper, geologic soil radium level
is smaller, with an exponent of b - 0.13 at Ra-E = 1 pCi g'1 of emanating radium. Its
sensitivity also.increases at higher radium concentrations, and can raise indoor radon levels
above 10 pCi L"1 as the emanating radium concentration approaches 10 pCi g"1.
100 r
i i i / .¦ r i i
i : ' • 1 i
-t j r .¦ ij
o 10
Surface Soil
Radium:
b=0.81
at RaE=1pCi/g
Geologic Soil
Radium:
b-0.13
at RaE~1pCi/g
Density:
b=0.35
at
1.6 a/cm3
Texture:
b--0.27
for sand to
sandy loam
Water Table
Depth:
b=0.77
at 100 cm
.1
'
'
.1
10
Parameter
100
1000
Figure 2-7. Comparison of parameter sensitivities.
2-14
-------
The second most sensitive parameter shown in Figure 2-7 is the water table depth,
with, an exponent of b = 0.77 at 1 m depth. This sensitivity increases even more for shallower
water tables, but the shallow water tables protect against elevated indoor radon by blocking
radon movement. For deeper water tables, which allow increased indoor radon, the
sensitivity to the water table depth becomes smaller, approaching negligible values at water
tables deeper than 2-3 m.
Soil density has a relatively low sensitivity exponent of b = 0.35 at a typical density
value of 1.6 g cm"3. The total range of possible densities is limited, as shown in Figure 2-7,
giving this parameter relatively little chance to significantly affect indoor radon levels.
Soil textural classification, like water table depth, allows most radon entry in its least
sensitive region, as plotted in Figure 2-7. Its average sensitivity corresponds to an exponent
of only b = -0.27 in the sand to sandy loam region, which is typical of Florida fill soils. In
soils with smaller pore sizes, the greater capillary suction maintains higher moisture levels,
which reduce radon movement toward the house.
The analyses of soil layer thickness effects are summarized in Figure 2-8, which shows
the radon concentrations computed for a house over inter-leaved layers of low-radium and
high-radium soils. When the thicknesses of the inter-leaved layers is small, the soil profile
approaches homogeneity, and the bias caused by layer ordering becomes small. The biases
shown in Figure 2-8 are conservatively high for most situations, since alternating adjacent
soil layers do not ordinarily differ by more than a factor of eight in emanating radium
concentration. Based on these analyses, an approximate 61-cm (2-ft) thick soil layer is
estimated to contain adequate resolution for field sampling and measurement of soil radium
concentrations for computing radon entry into the reference house.
2-15
-------
10
8
High Radium
Layer at Top
17% Average Error
from 61 cm Layers
Average = 6.2 pCi/L
Alternating Soil Layers
with 2.2 and 0.26 pCi/g
of Emanating Radium
Low Radium
Layer at Top
0
30 60 90 120 150 180 210 240 270 300
Layer Thickness (cm)
Figure 2-8. Sensitivity of indoor radon to thickness of elevated-radium layers.
The results of the two supplementary sensitivity analyses are shown in Figures 2-9
and 2-10 for the soil air permeability and radon diffusion coefficient, respectively. Since both
of these parameters were found to have a square-root dependence (b = 0.5) when analyzed
individually, both comparisons are plotted against the square root of the coefficient to
illustrate this mathematical relationship.
2-16
-------
o
Q.
c
o
ca
c
CD
a
c
o
O
c
o
TJ
CIS
cc
o
o
X3
c
y= 1.2678 +6159.8x RA2 = 0.995
0.U000 0.0002 0.0004 0.0006
Square Root of Air Permeability (cm2)
0.0008
Figure 2-9. Sensitivity of indoor radon to soil air permeability.
O
Q.
O
"S3
05
a
c
o
O
c
o
"O
CO
DC
o
o
T3
y = 1.6637 + 14.802x R*2 = 0.987
0.1 0.2
Square Root of Radon Diffusion Coefficient (cm2/s)
Figure 2-10. Sensitivity of indoor radon to soil radon diffusion.
2-17
-------
Chapter 3
MATHEMATICAL DEFINITION OF SITE-SPECIFIC RADON POTENTIAL
This chapter develops the methodology for determining site-specific radon potentials.
The methodology and the resultant equations and specifications are consistent with the radon
potentials given in the radon protection map for residential construction (Nie95c). The
development of the equation for specifying radon potential is presented first, followed by a
discussion of the parameters needed for the equation. The rationale for the minimum
number of soil samples is then given, followed by a section detailing the estimate of the
maximum area to be included in one determination.
3.1 EQUATION FOR THE SITE-SPECIFIC RADON POTENTIAL
The radon potential for a residential building site is defined to correspond to the
definition used for the residential radon protection map. The radon protection map displays
the calculated radon concentration in a reference house that would not be exceeded if the
reference house were placed on at least 95% of the land areas in a geographic region (map
polygon). Stated more simply, the radon protection map shows the 95% confidence limit of
radon concentrations calculated for the reference house. The mapped concentrations were
computed from geographic distributions of the soil physical and radiological properties to
estimate the upper limit of indoor radon expected in an area for buildings corresponding to
the reference house.
For site-specific estimates, the regional geographic distributions of soil radiological and
physical properties are replaced by measurements made at the site. Although the site
measurements lead to a more representative calculation of radon entry into the reference
house, variations at the site and uncertainties in estimating certain parameters still lead to
a distribution of different possible radon concentrations. This distribution is defined to be
log-normal, consistent with the mapped distributions, and is used to estimate a 95%
confidence limit for indoor radon that is mathematically consistent with the mapped values.
3-1
-------
The equation for the site-specific radon potential is defined from the log-normal
distribution parameters for indoor radon concentrations calculated for the reference house
using site-specific soil parameters. An annual-average radon concentration is first calculated
for the reference house from seasonal values using the RAKTRAD algorithm with the
geometric means of the measured site parameters. A geometric standard deviation (GSD)
is then calculated to represent the indoor radon variability associated with the distributions
of the site-specific parameters. The radon concentration in the reference house at the 95%
confidence limit is finally calculated from the estimated geometric mean and GSD to estimate
the site-specific radon potential as:
C95 = Cem G'-"5 (3)
= site-specific radon potential, at 95% confidence limit, for residences (pCi L"1)
= net radon concentration calculated for the reference house from
geometric means of the site parameters (pCi L"1)
= GSD of the indoor radon distribution (dimensionless)
= inverse of the normal distribution integral at 95% (standard deviations).
where C95
Cgm
G
1.645
The GSD of the indoor radon distribution is estimated from a sensitivity-weighted sum
of the variances of the individual parameters that contribute to the total uncertainty in the
indoor radon calculation. Since the distributions are log-normal, the component uncertainties
are GSDs, which require log-transformation for the usual quadratic addition of uncertainties,
giving the expression:
G = expW X; [lnCg^Of } (4)
where g~, = GSD of parameter i
bj - power-curve dependence of indoor radon on parameter i.
3-2
-------
The bj weighting factors give the correct weighting to the GSD of each parameter in
proportion to the influence of the parameter on indoor radon, concentrations.
3-2 PARAMETER SPECIFICATION
The main parameters affecting indoor radon and contributing to the uncertainties in
equations (3) and (4) are described in Chapter 2. They include the radium concentrations in
the soil, the water table depths, and the soil physical characteristics, which include density
and textural classification. Other soil parameters that depend on these properties include
air permeability (K) and radon diffusion coefficient (D). Extensive measurements of K and
D for Florida soils reveal that they are log-normally distributed with GSDs of g; = 2.3 and g;
= 2.0, respectively (Rog91b). As illustrated by Figures 2-9 and 2-10, radon concentrations
calculated for the reference house vary as the square root of K and also as the square root
of D, so b( = 0.5 for both of these g( values in equation. (4).
The geometric mean density for the Florida soils comprising the radon protection map
is calculated as 1.5 g cm"3, with a GSD of = 1.1 (Nie95b). Furthermore, the sensitivity
analyses in Figure 2-7 show that indoor radon levels only depend on soil density by the factor
bj = 0.35. The small GSD and small bs sensitivity mean that uncertainties in soil density
have a negligible contribution to C95, so the state-average default value of soil density, p =
1.5 g cm"3, can be used. The density term in the summation in equation (4) is 0.001,
compared to 0.173 and 0.120 for the K and D terms, respectively.
Since the dependence of reference-house radon concentrations on soil radium is
approximately linear in Figure 2-7 (bj = 0.8, but approaches unity at higher radium levels),
it is given a linear dependence (b. = I) for use in equation (4). Similarly, GSD for the water
table parameter is assigned a b; = 1 sensitivity, which corresponds to water table depths
slightly shallower than 1 m. This GSD is calculated from the variation in indoor radon
concentrations that is caused by water table variations. Equations (3) and (4) can be written
in a combined form with the above numerical values as:
3-3
-------
C95 = Cgm exp{ 1.645 V 0.294 + lln(gRa))z + [ln(gwt)]2 }
(5)
where 0.294 - combined variance from permeability, diffusion, and density (dimensionless)
gRt = GSD of site radium concentrations (dimensionless)
gwt = GSD of indoor radon from varying site water table depths (dimensionless).
The geometric mean and GSDs of the soil radium concentrations and water table
depths at a site are computed for use in determining Cgm and G as:
- exp{ [£, ln(Xj)] / n } (6)
and
gx = exp{ ViJj [InfX,) - ln(Xgm)lz/(n-l) } (7)
geometric mean of the parameter X (X = either radium or
radon concentration from water table depth)
measured value of the parameter X
GSD of the parameter X
number of field measurements of the parameter.
3.3 DETERMINATION OF THE MINIMUM NUMBER OF SOIL SAMPLES
Soil samples are used to characterize different soil layers to determine the soil radium
concentrations, the residual moisture contents, and indirectly, the default D and K values.
A sufficient number of soil samples must be collected to characterize both the geometric mean
soil radium concentration and the GSD of the radium distribution. The number of samples
collected also must be adequate to limit the uncertainty in the GSD to a value consistent with
the radium variability associated with the radon protection map. The following analysis
assumes a unit analysis area of 4,000 m2 (1 acre). A larger unit area would not be
represented adequately by the stated number of samples.
where -
Xi =
3-4
-------
Because soil radium concentrations in Florida are generally distributed log-normally
(Nie95b), their logarithms are normally distributed, and the standard deviations of their
logarithms therefore follow a chi-squared distribution (Fre87). The minimum number of soil
samples required to determine the geometric mean radium concentration within a given
degree of precision depends on the upper limit of the GSD of the radium concentrations. The
number of soil samples required therefore can be expressed in terms of a fractional
uncertainty that represents the interval between the upper limit and the best estimate
(geometric mean) as:
V (n-1) / Xp.n-! - 1 = " (8)
where n = number of samples
Xpn-i - chi-squared value for n-1 degrees of freedom and for (1-p) confidence
p = probability of exceeding a given chi-squared value
u = fractional uncertainty required (consistent with radon protection map).
Solving equation (8) for n gives:
n = 1 + (1 + uf Xpirt.i • (9)
Tliis equation must be solved iteratively because the Xp,n-i values also depend on n. The soil
radium concentrations for the radon protection map were obtained from National Uranium
Resource Evaluation (NURE) data (EGGS1), and had typical uncertainties in the 25% to 35%
range. Using an uncertainty limit of 25% {u - 0.25) for the site-specific soil radium data, a
90% confidence limit for the radium GSD (p = 0.1), and solving for the 95% confidence limit
on the transformed radium data gives a minimum value of n = 19. For practical purposes,
the minimum n is rounded to 20. Thus, at least 20 soil radium samples must be collected
and analyzed for the 4,000-m2 (1-acre) site to have the same degree of confidence in the site-
specific radon potential as in the radon protection map.
3-5
-------
Other criteria from the sensitivity analyses in Chapter 2 give further information on
how the minimum of 20 soil samples should be distributed. Figure 2-6 shows that a depth
of approximately 2.4 m (8 ft) is the maximum depth from which soil can influence indoor
radon, providing the soil is uniform and has the limiting sandy texture. Furthermore, Figure
2-S shows that soil samples should be collected at intervals not exceeding approximately 0.6
m (2 ft). Therefore, if 2.4-m (8-ft) boreholes are sampled with compositing over 0.6-m (2-ft)
intervals, four samples will be obtained from each borehole and a minimum of five boreholes
¦will be required to represent the 4,000 m2 unit area.
For areas smaller than 4,000 m2, a smaller number of soil samples can be considered.
However, fewer samples increases the uncertainty in the upper limit for the GSD, which also
increases the calculated radon potential compared to the value that would be calculated if 20
samples were used. The following section presents the alternative calculation approach to
accommodate fewer than 20 samples for a site smaller than 4,000 m2.
3,4 SOIL RADIUM GSD FOR FEWER THAN 20 SAMPLES
The recommended minimum number of soil samples for radium analyses is 20.
However, a mathematical accommodation can be made to utilize a smaller number of soil
samples for areas smaller than 4,000 m2 (1 acre). The smaller number of samples increases
the upper interval for the 907o confidence limit of the GSD (and for the 95% confidence limit
of soil radium concentration). This increase is equivalent to an increase in the GSD for a 20-
sample set. The mathematical approach determines a factor, fn, which transforms the GSD
among the actual number of samples to an equivalent 20-sample GSD. The transformed GSD
is larger to maintain an equivalent upper confidence limit for radium with the smaller
number of samples to that which would be obtained with 20 samples. The expression for fn
is derived from equation (8) to be:
f„ - ^^(n-TVxIg^ <10>
3-6
-------
The X0.9 n-i is f°r n-1 degrees of freedom, and the tn is the t statistic for n-1 degrees of
freedom. Substituting the values for t20 and Xo 919 and rearranging gives:
f„ = 0.463 tn V (n-1) / Xo.g,n-i dD
The variation in fn is shown as a function of n in Figure 3-1. The curve, a regression
equation for fn, is given by:
fn = 1 / [0.279 + 0.071 n - 0.0018 n2], (12)
which has a correlation coefficient of r2 = 0.994.
Equation (11)
1 / [0.279+0.071 n-0.0018n 2 ]
1
~5 10 15 2 0
n
Figtire 3-1- Variation of fn with n.
3-7
-------
When fewer than 20 samples are used for the radium determinations, the GSD for
radium in equation (5) is transformed as:
&Ra = sfe3.11-
This transformation requires that the site have a slightly lower Cpm than if 20 samples were
analyzed to compensate for the increased uncertainty in satisfying the prescribed C95 cut
point limits.
3-5 MAXIMUM SITE AREA
The maximum site area that can be considered in an individual analysis is restricted
so that an area exceeding 4 pCi L'1 cannot be justified by merely averaging it with a greater
area of low-radon land. The maximum site area is determined from a criterion based on the
sensitivity of any one borehole in indicating intermediate or elevated radon levels while the
others indicate low radon levels. The criterion is defined numerically such that if one
borehole in the area indicates an intermediate ("yellow") radon potential designation of C95
> 4.1 pCi L"1 while the other boreholes indicate lower radon potentials of C95 = 0.3 pCi If1,
the site is designated with an intermediate radon potential. Mathematically, this defines the
ineaualitv:
4.0 g£645 < [4.1 + 0.3 (nb-l)I / nb
(14)
where 4.0
SRn
4.1
0.3
nw
radon boundary between low and intermediate categories (pCi L"1)
GSD of the statewide radon concentration distribution (= 2.07)
lowest detectable radon level exceeding the radon boundary (pCi L"!)
background radon level typical of the low radon category (pCi L"1)
number of boreholes.
3-8
-------
The left-hand side of equation (14) uses equation (3) to restrict the radon potential to
4.0 pCi L"1. If the inequality is used in equation (14), then nfa becomes the maximum number
of boreholes. Solving the equality for nb gives 4.2 boreholes, which is rounded to a maximum
of 5 boreholes. Therefore, the maximum area that can be included in a site-specific
determination of radon potential is the area represented by 5 boreholes, which was shown
in Section 3.3 to correspond to 4,000 m2 (1 acre).
3.6 AUTOMATED CALCULATIONS
A specialized version of the RAETRAD computer code has been developed to
implement the equations in this chapter using site-specific measurements to define radon
generation and entry into the reference house. The computer code is called RAETRAD-F
(RogSo), and is designed to complete the calculation sequence illustrated in Figure 3-2. The
code first calculates the geometric means and GSDs of the measured soil radium
concentrations, and determines the seasonal water table distribution as it was defined for the
radon protection maps (Nie95b). It then compares the measured soil radon concentration
with concentrations calculated from the radium m easurements and uses the larger of the two
to extrapolate the deep-soil radium concentrations throughout the 2.4 - 5.0 m range.
The RAETRAD-F code next computes best estimates of indoor radon concentrations
for the different seasonal water table conditions using the geometric means of the radium
measurements. After determining the geometric mean annual radon concentration in the
reference house, Cgm, from the seasonal values, the variations among seasonal conditions arid
among the radium concentrations are used in equation (5) to estimate Cg5. If less than five
boreholes were used to characterize the site, the code also corrects g^ as in equation (13)
before using it in equation (5). The resulting radon protection category is determined by
comparing Cg3 to the 4.0-pCi L"1 and 8.3-pCi L"1 cut points used in the radon protection map
to determine whether the site is in the low, intermediate, or elevated radon protection
category.
3-9
-------
Loop for 2-3 Water
y Table Depths
Calculate Cg,
[Equation (5)]
Load Reference House
Parameters
Calculate 2-3 Water Table
Depths & Durations
Get Radium, Density, Water
Table, Radon, & Texture Data
Print Input Data, C95, and
Radon Protection Category
Calculate Radium, & Density
Averages for Soil Layers
RAETRAD Calculation of
Radon in the Reference House
Extrapolate Deep-Zone Radium
from Deepest Radium Measuremen
or Soil Radon Equivalent
Calculate Layer-Average Moistures
from Texture & Density for Each
Water Table Depth
Figure 3-2. RAETRAD-F calculation of the site radon protection category
3-10
-------
Chapter 4
PROTOCOL FOR SITE-SPECIFIC RADON POTENTIAL MEASUREMENT
A protocol has been developed for measuring the radon protection category of a building site.
The protocol is proposed for use as an alternative to the radon protection map for determining whether
a site falls into the low, intermediate, or elevated radon potential category. Depending on the category
that is determined, passive and possibly active radon controls may be required in residential construction
to satisfy the indoor radon criteria of the Florida Standard for Radon-Resistant Residential Building
Construction (DCA94).
This chapter describes the intended use of the site-specific radon potential measurement protocol,
the individual parameters that may be measured at a site to determine its radon potential category, and
the method for analysis of the site-speciilc measurements.
4.1 USE OF THE SITE-SPECIFIC RADON POTENTIAL PROTOCOL
The protocol described in this chapter for measuring the radon potential category of a building
site is intended to provide an alternative to the use of the residential radon protec tion map for estimating
the radon protection category of a site. Once the radon protection category is determined from site-
specific measurements, however, the site-specific determination supersedes any generic estimates of
radon protection category that are based on the residential radon protection map.
The measurements required by this protocol shall be made after completion of any site
contouring or other activities that may affect the water table or the distribution of soils that will be
present beneath the building, excluding above-grade fill soil that may be placed within the perimeters
of the building footprint. The performance of this protocol, including collection and analysis of
samples, data, and the interpretation thereof, shall be performed by a Florida Health and
Rehabilitative Sendees certified radon specialist. The protocols used for sampling and measurement
shall conform to the protocols given in "Standard Measurement Protocols, Florida Radon Research
4-1
-------
Program," Environmental Protection Agency report EPA-600/8-91-212 (Wil91) or subsequent
versions of this protocol document, or to applicable protocols defined by the American Society
of Testing and Materials (ASTM).
This protocol shall be applied to individual areas of land (including contiguous
building lots) that have a total area of 4,000 m2 (1 acre) or smaller to determine their radon
protection category for residential building construction. Larger land areas shall be divided
into 4,000 m2 parcels for the purposes of site-specific radon potential characterization.
Special provisions for characterizing smaller sites are contained in the protocol.
4.2 SITE-SPECIFIC MEASUREMENT PROTOCOL
The site-specific sampling and measurements shall utilize locations representative of
the planned or potential building locations. Five parameters shall be measured or otherwise
characterized specifically for the site, as described in this section. The parameters are: (a)
soil 226Ra Concentration, (b) soil density, (c) soil textural classification, (d) 222Rn concentration
in soil gas (a check on deep-soil radon sources), and (e) water table minimum depth and
duration.
4.2.1 Site Sampling and Measurements
Sampling of soils at the site shall utilize five boreholes spread over the entire site at
locations corresponding to planned or potential building sites. For sites smaller than 4,000
m2, sampling shall utilize at least one borehole for every planned or potential residential
building location. If the site consists of an individual lot for a single building, sampling
boreholes may be reduced to as few as one, provided that if only one borehole is used, it is
supplemented with two additional soil samples. The two supplementary samples shall
originate from locations at least 10 m away from the borehole location and from each other,
and from soils representing the 0-61-cm depth interval to represent both horizontal and
vertical variations. Soils shall be collected from each borehole to represent four different
4-2
-------
depth intervals. The depth intervals are 0-61 cm, 61-122 cm, 122-183 cm, and 183-244 cm. The borehole
samples and any supplementary samples shall be used for measurement of density and for textural
classification. The remaining material from each depth interval shall be composited for individual
measurements of radium concentration. The concentration of radon in the soil gas shall be measured at
or near each borehole site. Observations of water table depth may utilize any location(s) on the site or on
vicinity property.
4.2.2 Soil 226Ra Concentration
The concentrations of 226Ra shall be measured from gas-tight sealed, equilibrated aliquots of
individual samples using a calibrated gamma-ray spectrometer. The spectrometer shall be calibrated by
analyses of standard reference materials and blanks in the same gas-tight sealed and equilibrated container
configuration as used for the samples. Suitable standard reference materials include soils, ores, or spiked
earthen materials obtained from or prepared from liquid sources from the U.S. Department of Commerce
(National Institute of Standards and Technology), EPA, or other sources approved by the DCA. The
concentrations of 226Ra shall be reported individually in pCi g"1 on a dry mass basis.
4.2.3 Soli Density
The in-situ density of soils shall be measured from the masses of samples of known volume using
Standard Test Method for Density of Soil in Place by the Drive-Cylinder Method (ASTM83) or by other
methods approved by the DCA. Equipment used for the density measurements shall be suitably calibrated.
The soil density measurements shall be reported in g cm"3 on a dry mass basis and may be reported
individually (all 20 samples), as averaged by layer (four layer means), or as averaged for the entire site (one
overall mean). Because of the relatively low sensitivity of indoor radon levels to soil density, the soil
density need not be measured for the site-specific evaluation. If in-situ soil density is not measured at the
site, a default value of 1.5 g cm'3 shall be used in the analyses for computing the site radon protection
category.
4-3
-------
4.2.4 Soil Textural Classification
The textural classification of the site soils shall utilize laboratory or field methods
(SCS75) to group the soils into one of the twelve textural classes defined by the U.S Soil
Conservation Service, listed in Table 4-1. The soil textural classes may be reported
individually (all 20 samples), as aggregated by layer (four layer classes, determined from
layer-composite samples), or as aggregated for the entire site (determined from one site-
composite sample). If visually distinct classes are discernable among different samples, the
site composite determination may not be used. Because of the conservative results obtained
with the sand classification and the prevalence of sandy soils throughout Florida, the soil
textural classification need not be performed for the site-specific evaluation. If the textural
classification is not performed on the site soils, a default classification of "sand" shall be used
in the analyses for computing the site radon protection category.
Tabic 4-1 SCS soil texture classes
1. Sand 5. Sandy clay 9. Clay
2. Loamy sand 6. Loam 10. Silty clay loam
3. Sandy loam 7. Clay loam 11. Silty clay
4. Sandy clay loam 8. Silty loam 12. Silt
4.2.5 Soil 222Rn Concentration
The concentration of 222Rn in soil gas shall be sampled by drawing soil gas from a
driven tube or equivalent sampling system and measuring the 222Rn concentration with a
suitably calibrated radon measurement system. The soil radon measurements shall be
conducted at each borehole location at a depth of 1.2 m or greater. To avoid soil disturbance,
the soil gas samples shall be collected before drilling the boreholes, or afterward providing
they are collected approximately 2-3 m away from the borehole locations. The soil radon
measurement is designed to help detect and characterize the possible presence of an
underlying soil layer with elevated radium concentration.
4-4
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If the water table is found to be shallower than 1.2 m at the time of field sampling,
the requirement for a soil radon measurement is waived, provided that (a) the minimum
water table depth is less than 0.6 m and (b) there is no evidence to suggest that sampling
during an alternative season would provide a sufficiently deeper water table (below 1.2 m)
for successful sampling. If either of these conditions is not satisfied, another soil radon
measurement shall be attempted during a different season (3 to 9 months later). If the water
table is again shallower than 1.2 m, the requirement for a soil radon measurement at the site
shall be waived.
4.2.6 Water Table Depth
The depth of the water table at the site shall be specified in a manner that is
consistent with the water table specifications used in developing the residential radon
protection map (Nie95b). For the radon protection map, the minimum water table depth (in
cm) and duration (in months) were specified from data in the STATSGO data base (SCS91).
These data were in turn derived from county soil survey information, as is typically contained
in local county soil survey reports (e.g., Tho85). If county soil survey reports are used as the
data source, the water table data should be defined from the soil or combinations of soils that
comprise the site. Average values shall be computed to represent the data in cases where
ranges are reported (i.e., 70 cm would be computed to represent a reported water table depth
range of 60 to 80 cm).
Iflocal area information is unavailable, or if site-specific measurements are otherwise
to be utilized, the measurements shall be derived from at least four seasonal measurements
of water table depth at 3-month intervals. The most shallow of these shall be defined as the
minimum water table depth, and a minimum duration of 3 months shall be defined unless
a longer time is indicated by the measurements.
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4.3 ANALYSIS OF SITE-SPECIFIC MEASUREMENTS
The site-specific measurement data shall be assembled and analyzed using the
RAETRAD-F computer code (Rog95). The RAETRAD-F code is designed to automatically
implement the equations in Chapters 2 and 3 of this report with the reference house
specifications in a way that corresponds to the calculations performed for the residential
radon protection map. The user is first prompted to enter the site identification information
and individual site measurement data. The code then computes the appropriate statistical
parameters for the radium measurements, the annual water table distribution from the water
table data, the soil moistures from the texture and density data, and all other required
parameters for computing an annual average indoor radon distribution for the reference
house. Upon computing this distribution, a C95 value is computed and compared to the 4.0-
pCi I/1 and 8.3-pCi I/1 cut points, and the site is designated to have either low, intermediate,
or elevated radon potential. The printed output of the RAETRAD-F code includes the user-
specified input parameters, the calculated C95 value, and the site radon potential designation.
4-6
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Chapter 5
SUMMARY AND CONCLUSIONS
The residential radon protection map gives the best available estimate of radon
potential category if no site-specific data are available. However, the resolution of the map
is too low to make reliable site-specific determinations. Therefore, the site-specific protocol
and basis presented in this report are designed to guide the measurement and interpretation
of features at a site to give further guidance on the possible need for radon-protective
construction features.
The site-specific protocols identified in this report can provide valuable information
in cases where a builder or developer knows of or suspects anomalous conditions at a site
that could increase its radon potential above the mapped category. Examples of these
anomalous conditions could include effects from previous land uses, observations of unusual
soil or mineral occurrences, or deep water tables in areas of highly permeable soil (gravelly
or fractured). Alternatively, the land developer may suspect the land has lower radon
potential than its mapped category, leading him to consider reducing or eliminating special
radon controls unless they are specifically shown to be needed. In any of these cases, site-
specific tests can help in making a more informed decision. Any decisions involving site-
specific testing should also consider the relative costs of using conservative radon controls
versus the costs of site-specific testing, as well as the EPA guidance on further reducing
radon levels even in the range below 4 pCi L"1 (EPA92b).
The method for defining the site-specific protocol utilizes sensitivity analyses of radon
entry into a reference, house as determined by the RAETRAD model. By using the same
model, reference house, and other parameters used for the residential radon protection maps,
the protocol derived here has a basis that corresponds to that of the maps. The sensitivity
analyses identified radium concentration, soil layer depth, soil density, soil texture, and water
table depth as being the independent parameters affecting indoor radon levels. Of these,
radium concentration and water table depth were dominant. Soils up to 2.4 m deep
5-1
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contributed to indoor radon in uniform-radium scenarios, and soil layers of approximately 0.6
m thickness significantly affected radon levels in cases of non-uniform radium distributions.
A conservative upper limit for indoor radon concentrations, defined as the 95%
confidence limit for radon in the reference house, was defined mathematically to correspond
to the radon protection map. A RAETRAD estimate of this parameter using geometric mean
values and geometric standard deviations of the parameter values is numerically equivalent.
The number of samples needed to represent a site was determined from the equivalent
regional precision attained by the radon protection map. Based on the sensitivity of the
contributing soil depth and layer thickness, the site-specific measurements were shown to
require 20 samples for every 4,000 m2 (1 acre). These samples are distributed throughout
four depth increments that extend to a depth of 2.4 meters. A special formula is derived to
obtain equivalent precision for a smaller parcel of land using less samples. The mathematical
calculations are performed by a special-purpose computer code called RAETRAD-F.
The site-specific protocol involves drilling five boreholes per 4,000 m2 of land to be
characterized and analyzing each 4,000 m2 parcel (or fraction thereof) as a separate parcel.
Twenty soil samples obtained from the borings are used for radium measurements. The soil
borings are also used for density and textural estimates unless default values are chosen for
these parameters. A soil radon measurement is used to detect the potential presence of
anomalous elevated-radium materials at depth. The site water table depth distribution is
defined from either soil survey data or site observations for use in soil moisture calculations.
The site measurements are submitted as requested by the RAETRAD-F code and are
processed to determine the upper 1 imit for indoor radon concentrations in the reference house
at the site. Using the same category definitions as for the residential radon protection map,
the RAETRAD-F code determines whether the site is in the low, intermediate, or elevated
map category for radon protection purposes.
5-2
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Chapter 6
LITERATURE REFERENCES
ASTM83 Standard Test Method for Density of Soil in Place by the Drive-Cylinder Method. Philadelphia.
PA: American Society for Testing and Materials, report D2937-83, 1983.
DCA94 Florida Department of Community Affairs, Florida Standard for Radon-Resistant Residential
Building Construction, Tallahassee FL: Florida Department of Community Affairs, draft final
report, RAE-9226/4-4, July 1994.
DSM85 DSMA Atcon, Ltd., A Computer Study of Soil Gas Movement into Buildings, Ottawa: Department
of Health & Welfare, report 1389/1333, 1985.
Eat84 Eaton, R.S., and Scott A.G., Understanding Radon Transport into Houses, Radiation Protection
and Dosimetry 7, 251, 1984.
EGG81 E G & G Geometries. Aerial Gamma Ray and Magnetic Survey, Gainesville and Daytona Beach
Quadrangles, Florida, Grand Junction, CO: U.S. Department of Energy report GJBX-101, March
1981.
EPA92a U.S. Environmental Protection Agency, A Citizen's Guide to Radon, second edition, The Guide
to Protecting Yourself and Your Family from Radon, Washington, DC: U.S. Environmental
Protection Agency report 402-K92-001, May 1992.
EPA92b U.S. Environmental Protection Agency, Technical Support Document for the 1992 Citizen's Guide
to Radon, Washington D.C.: U.S. Environmental Protection Agency report EPA-400-R-92-011
(NTIS PB92-218395), May 1992.
Fre87 Freund, J .E., and Walpole, R.E., Mathematical Statistics, Englewood Cliffs, NJ: Prentice-Hall,
Inc., fourth edition, 1987.
6-1
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Kim89 Kunz, C., Laymon, C.A., and Parker, C., Gravelly Soils and Indoor Radon, in Proceedings: The
1988 Symposium on Radon and Radon Reduction Technology, Vol. \,EPA-600/9-89/006a (NTIS
PB89-167480), p. 5-75, March 1989.
Naz89 Nazaroff. W.W., and Sextro, R.G., Technique for Measuring the Indoor 222Rn Source Potential of
Soil, Environmental Science and Technology 23,451-458, 1989.
Nie92 Nielson, K.K., and Rogers. V.C., Radon Transport Properties of Soil Classes for Estimating Indoor
Radon Entry, in Indoor Radon and Lung Cancer: Reality or Myth?, F.T. Cross, ed., Richland,
WA: Battelle Press, p. 357-372, 1992.
Nie94 Nielson, K.K., Rogers, V.C., Rogers, V., and Holt, R.B., The RAETRAD Model of Radon
Generation and Transport from Soils into Slab-on-Grade Houses, Health Physics 67, 363-377,
1994.
Nie95a Nielson, K.K.. Ilolt, R.B., and Rogers, V.C., Site-Specific Characterization of Soil Radon
Potentials, Research Triangle Park, NC: U. S. Environmental Protection Agency report EPA-
600/R-95-161, November 1995.
N ie95b Nielson, K.K., Holt, R.B., and Rogers, V.C., Statewide Mapping of Florida Soil Radon Potentials,
Research Triangle Park, NC: U.S. Environmental Protection Agency report EPA-600/R-95-I42a, b
(NTIS PB96-104351, - 104369), September 1995.
Nie95c Nielson, K.K., Holt, R.B., and Rogers, V.C., Residential Radon Resistant Construction Feature
Selection System, Research Triangle Park, NC: U. S. Environmental Protection Agency report
EPA-600/R-96-005, February 1996.
Pea90 Peake, R.T., and Schumann, R.R., Regional Radon Characterizations, in Field Studies of Radon
in Natural Rocks, Soils, Land, and Water, U.S. Geological Survey Bulletin, L.C.S. Gundersen and
R.B. Wanty, eds., 1990.
6-2
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Rog9 la Rogers, V.C., andNielson, K.K., Multiphase Radon Generation and Transport in Porous Materials,
Health Physics 60:807-815, 1991.
Rog91 b Rogers, V.C., and Nielson, K.K.. Correlations for Predicting Air Permeabilities and ~Rn Diffusion
Coefficients of Soils, Health Physics 61:225-230, 1991.
Rog93 Rogers, V.C., and Nielson, K.K., Generalized Source Terra for the Multiphase Radon Transport
Equation, Health Physics 64, 324-326, 1993.
Rog95 Rogers, V., Nielson, K.K., Rogers, V.C., and Holt, R.R., RAETRAD-F: Users' Guide for
Analyzing Site-Specific Measurements of Soil Radon Potential Category- for Florida Houses, Salt
Lake City, UT: Rogers & Associates Engineering Corp. report RAE-9226/7-2. 1996.
San90 Sanchez, D.C., Dixon, R., and Williamson, A.D., The Florida Radon Research Program:
Systematic Development of a Basis for Statewide Standards, in Proceedings: The 1990
International Symposium on Radon and Radon Reduction Technology, Vol. 3, EPA-600/9-9 l-026c
(NTIS PB91-234468), July 1991.
SCS75 Soil Conservation Service, Soil Taxonomy, A Basic System of Soil Classification for Making and
Interpreting Soil Surveys, Washington D.C.: U.S. Department of Agriculture, Soil Conservation
Service, Agriculture Handbook No. 436, 1975.
SCS91 Soil Conservation Service, State Soil Geographic Data Base (STATSGO) Data Users Guide,
Lincoln, Nebraska: National Soil Survey Center, Soil Conservation Service, U. S. Department of
Agriculture, draft report, 84pp, 1991.
Tan89 Tanner, A.B., A Tentative Protocol for Measurement of Radon Availability from the Ground, in
Proceedings: The 1988 Symposium on Radon and Radon Reduction Technology, Vol. 2, EPA-
600/9-89-006b (NTIS PB89-167498), p. 3-15, March 1989.
Tho85 Thomas, B.P., Cummings, E., and Wittstruck, W.H., Soil Survey of Alachua County Florida.
Gainesville, FL: U.S. Department of Agriculture, Soil Conservation Service, 1985.
6-3
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Wil91 Williamson, A.D., and Finkel, J.M., Standard Measurement Protocols, Florida Radon Research
Program, Research Triangle Park, NC: U.S. Environmental Protection Agency report EPA-600/8-
91-212 (NTIS PB92-115294), November 1991.
Yok92 Yokel, F.Y., and Tanner, A.B., Site Exploration for Radon Source Potential, Gaithersburg, MD:
U.S. Department of Commerce, National Institute of Standards and Technology report NIST1R-
5135,1992.
6-4
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TECHNICAL REPORT DATA
(Please read Inztmclicm on the reverse before comp
t. REPORTNO.
EPA-600/R-96-045
2.
4. TITLE AN ~ SUBTITLE
e.
Site-specific Protocol for Measuring Soil Radon
"Potentials for Florida Houses
5. REPORT DATE
April 1998
6. PERFORMING ORGANIZATION CODE
7.Au.HORCs)Kirk Km Nxelson, Vera C. Rogers, and
Rodger B. Holt
8. PERFORMING ORGANIZATION REPORTNO.
RAE-9228/3-3R1
S. PEHFORM1NG ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Rogers and Associates Engineering Corporation
P.O. Box 330 '
Salt Lake City, Utah 84110-0330
"WKmW^a933783; and
DCA 94RD-30-13-00-22-002
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final: 4/94-6/95
14.SPONSORING AGENCY CODE
EPA/60.0/13
5.supplementary notes ^ppcD project officer is David C. Sanchez, Mail Drop 54, 916/
541-2979. DCA project officer is Mohammad Madani, Florida Dept. of Community
Affairs, 2740 Centerview Dr. , Tallahassee, FL 32399.
is.AssiRACTrj-j^g rep0r{. describes a protocol for site-specific measurement of radon
potentials for Florida houses that is consistent with existing residential radon protec-
tion maps. The protocol gives further guidance on the possible need for radon-pro-
tective house construction features. In applying the test results, the user should also
consider the relative costs of using conservative radon controls and the EPA guid-
ance on further reducing radon levels even in the range < 4 pCi/L. The measure-
ments included in the protocol were selected from sensitivity analyses of radon entry
intoThe^same reference^Eouse as was used to develop the radon protection maps. The
sensitivity analyses also utilized the same RAdon Emanation and TRAnsport into
Dwellings (RAETRAD) model, proving a common basis to that of the maps. The sen-
sitivity analyses identified radium concentration, soil layer depth, soil density, soil
texture, and water table depth as the independent parameters dominating indoor ra-
don. Radium concentration and water table depth were most impprtant. Soils up to
2.4 m deep contributed to indoor radon in uniform-radium scenarios, and soil layers
about 0. 6 m thick significantly affected radon in cases of non-uniform radium distri-
butions. A conservative upper limit for radon potentials was defined as the 95% con-
fidence limit for radon in the reference house.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.lDENTlFlERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Radon
Soils
Measurement
Residential Buildings
Construction
Pollution Control
Stationary Sources
Indoor Air
Florida
13 B
07B
08G, 08M
14C-
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
50
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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