Uranium in Soil Individual Dose Calculator - HELP
(last updated 8 Sep 2004)
Contents:
This calculator gives rough estimates of the radiation risk for an individual
living on soil contaminated from uranium and its decay products and/or living
in a home built from contaminated material. It is based on a residential
exposure scenario (view schematic 
)
considering the following pathways: ingestion of soil, inhalation of fugitive
dusts, external exposure, ingestion of produce grown in the soil, ingestion of
contaminated groundwater, and inhalation of radon.
The calculator mainly uses the models and default parameters presented in U.S.
EPA's Soil Screening Guidance for Radionuclides (SSGR).
Differences of the approach used in this calculator, compared to the SSGR:
-
While the SSGR determines radionuclide concentrations in soil for a given
target risk (10-6), this calculator performs the inverse
operation: it determines the health risk for a given radionuclide concentration
in soil.
-
External radiation exposure indoors also includes the contribution from
building materials.
-
For each pathway, the risk contributions from all relevant radionuclides are
summed up.
-
A risk is also determined for ingestion of contaminated groundwater, while the
SSGR only compares radionuclide concentrations to maximum contaminant levels
(MCL) etc.
-
The pathway of radon inhalation is included in the analysis, while the SSGR
intentionally omitted it for the high uncertainties connected to it. The
calculations and parameters used for this pathway are based on UNSCEAR 1993.
The kind and degree of contamination of the soil and/or the building material
is defined in the Input Data
table.
The parameters used for the calculation can be set in the Exposure Parameters
and Site Parameters tables. These parameters show reasonable initial
values which can be modified as needed. Any assumptions made for the
calculations are described on this page.
Since the EPA's Soil Screening Guidance is intended to identify areas that can
be excluded from further study, most parameter values selected are
conservative. The risk calculated using these parameters therefore may
overestimate the risk at many real sites.
Since the Soil Screening Guidance is intended for use at an early stage of site
assessment, EPA used only simple models that are based on easily obtainable
parameters. This is the reason why these models were selected for this
calculator. If, however, more site specific data is available, the use of a
more sophisticated modeling software such as DOE's RESRAD, NRC's DandD, or
EPA's PRESTO (see Dose calculation software
) is recommended.
The Result field lists the excess lifetime cancer morbidity risk (in
percent) for each exposure pathway. Moreover, annual dose rates are presented
for each pathway, to facilitate comparison; these are obtained by applying
ICRP's radiation risk coefficient to the risk figures. However, the dose rates
obtained this way may differ considerably from dose rates calculated directly
using ICRP's models and dose coefficients.
The calculated uranium concentration in drinking water is shown, to allow for
an assessment of the chemical hazard of uranium, which is not covered by the
risk calculation. This value can be compared to standards such as WHO's
provisional guideline of 15 µg/L, or EPA's drinking water standard of 30 µg/L,
for example: both of them are based on the chemical toxicity of uranium (see
current standards).
For the ingestion pathways, the daily uranium ingestion rate is shown, to allow
for an assessment of the chemical hazard via comparison to standards, such as
WHO's tolerable daily intake (TDI) of 0.6 µg per kg body weight (i.e. 36 µg/d for
60-kg-adult).
Also, the radon concentrations in indoor and outdoor air are shown. These
reflect the contribution from radon exhalation from soil, and, for indoors,
also from radon exhalation from the building materials.
The contents of the Result field can be highlighted and copied for further use.
This calculator is suitable for offline use.
Cautionary Notice
Some of the parameters used for the calculations vary over several orders of
magnitude, in particular those covering soil properties and groundwater
migration. Meaningful results for the pathways of radon inhalation and
groundwater ingestion at real sites can therefore only be obtained, if site
specific values are entered for these parameters.
|
- Contaminant concentration in soil
-
Enter number, select unit and type
If no concentration is known or if the types from the pick list are not
applicable, leave this field empty and enter the activity concentrations
directly.
Average concentrations of natural uranium in soil are 3 mg/kg, with decay
products in equilibrium.
- Activity concentrations in soil
-
activity concentrations for the radionuclides in soil, in Bq/g or pCi/g, as
selected.
The suffix +D for a radionuclide means that its short-lived decay products are
assumed to be present in secular equilibrium
|
Nuclide | Short lived decay products |
| U-238 +D |
Th-234, [Pa-234m, Pa-234] |
| Ra-226 +D |
Rn-222, Po-218, Pb-214, Bi-214, Po-214 |
| Pb-210 +D |
Bi-210, Po-210 |
| U-235 +D |
Th-231 |
| Ac-227 +D |
[Th-227, Fr-223], Ra-223, Rn-219, Po-215, Pb-211, Bi-211, [Tl-207, Po-211] |
Note: [ ] indicates branching
In case a soil contaminant concentration is entered, the corresponding activity
concentrations are determined automatically. But, activities can also be
entered or modified independently.
- Activity concentration in building material
-
activity concentrations for the radionuclides in building material, in Bq/g or
pCi/g, as selected.
Leave this field empty, if the contribution from the building material is not
of interest. The suffix +D for a radionuclide means that its short-lived decay
products are assumed to be present in secular equilibrium
Typical values: [UNSCEAR 1993]
|
Material | Ra-226 [Bq/g] |
| Typical masonry |
0.05 |
| Granite blocks |
0.09 |
| Coal ash aggregate |
0.15 |
| Alum shale concrete |
1.3 |
| Phosphogypsum |
0.6 |
| Natural gypsum |
0.02 |
These parameters are depending on the behaviour of the residents living on the
site.
This section includes parameters which are used for more than one exposure
pathway.
- ED (exposure duration) yr
-
number of years residing on the contaminated site
The SSGR uses a figure of 30 years, since this is a high estimate for the time
spent on one site in the U.S. A more conservative approach would assume
lifetime here, or 70 years, for example.
- EF (exposure frequency) d/yr
-
number of days spent on-site per year
These are the days the person spends not completely off-site.
- ETo (outdoor exposure time fraction) unitless
-
fraction of time spent outdoors on-site on on-site-days
- ETi (indoor exposure time fraction) unitless
-
fraction of time spent indoors on-site on on-site-days
The value of 0.683 (that is 68.3%) used in SSGR is in no way conservative.
UNSCEAR uses 0.8, and for persons without outside employment, the fraction may
even reach 0.9.
- Age Adjusted
-
- IRa (adult soil ingestion rate) mg/d
-
- IRc (child soil ingestion rate) mg/d
-
- EDc (child exposure duration) yr
-
(the remainder, that is ED - EDc, is used as adult exposure
duration)
- IRs (soil ingestion rate) mg/d
-
time-weighted average soil ingestion rate for children and adults; calculated
from IRa, IRc, EDc, and ED (shown for display
only)
- Adult Only
-
- IR s (soil ingestion rate) mg/d
-
- IRi (air inhalation rate) m3/d
-
The inhalation rate varies with activity level, age, weight, sex, and general
physical condition. Typical values are: (note that the table values are per
hour!)
|
Inhalation Rates (m3/h) |
| |
Activity Level |
| Resting |
Light |
Moderate |
Heavy |
| Adult male |
0.7 |
0.8 |
2.5 |
4.8 |
| Adult female |
0.3 |
0.5 |
1.6 |
2.9 |
| Average adult |
0.5 |
0.6 |
2.1 |
3.9 |
| Child, age 6 |
0.4 |
0.8 |
2.0 |
2.4 |
| Child, age 10 |
0.4 |
1.0 |
3.2 |
4.2 |
From these hourly rates, a mix can be compiled to obtain the daily inhalation
rate.
- IRvf (vegetable and fruit ingestion rate) kg/year
-
total annual consumption of vegetable and fruit
- IRlv (leafy vegetables ingestion rate) kg/year
-
total annual consumption of leafy vegetables
It includes consumption of vegetables such as spinach and lettuce.
- CPF (contaminated plant fraction from the site) unitless
-
fraction of total vegetable/fruit consumption that is homegrown on the
contaminated site
This pathway addresses ingestion of ground water contaminated by the migration
of contaminants through soil to an underlying potable aquifer. Because the
equations developed for this pathway assume an infinite source, they can
violate mass-balance considerations, especially for small sources (Method 1).
To address this concern, mass-limit-based equations have been included for this
pathway when the size (i.e., area and depth) of the contaminated soil source is
known or can be estimated with confidence (Method 2).
- IRw (drinking water intake rate) L/d
-
These parameters describe properties of the site. They are mostly independent
of the behaviour of the residents (with the exception of those building
parameters depending on the ventilation behaviour).
Note: Many of the following descriptions are heavily relying on [Yu
1993].
- Surface area
-
Surface area of contaminated soil.
Pick nearest value.
- ACF (area correction factor for gamma radiation) unitless
-
correcting factor for gamma radiation exposure from small source areas - looked
up from Surface Area
- V (fraction of vegetative cover) unitless
-
fraction of the contaminated site that is covered by vegetation
It is assumed that no soil particles are resuspended into air from the
vegetated areas.
- ds (average source depth) m
-
thickness of the contaminated soil layer.
This parameter is only required, if the Migration to Groundwater is to be
determined with Method 2 (see below), or if, for the calculation of the radon
release, the default assumption of an infinite source depth is inadequate, in
particular for thin layers (< 4 m) of contaminated soil and/or high
diffusion coefficients.
Where the actual average depth of contamination is uncertain, a conservative
estimate should be used (e.g., the maximum possible depth in the unsaturated
zone). At many sites, the average water table depth may be used unless there is
reason to believe that contamination extends below the water table. In the
latter case the calculator cannot be applied.
The soil type can be initialized to representative values for Sand, Silt
(Default), and Clay. Note that for each of these types the parameters may vary
over wide ranges.
The initialization affects the parameters in the soil section, plus parameter
FAF (Building section). Other parameters are not affected by this
initialization, while, in reality, more parameters are depending on the soil
type.
- rhob (dry soil bulk density) kg/L
-
- epsilon (total soil porosity) Lpore/Lsoil
-
ratio of the pore volume (air- and water-filled) to the total volume of the
soil
| Sand |
0.25 - 0.50 |
| Silt |
0.35 - 0.50 |
| Clay |
0.40 - 0.70 |
- thetaw (water-filled soil porosity) Lwater/Lsoil
-
ratio of the water-filled pore volume to the total volume of the soil.
The possible values range from near zero for dry soils approaching zero
saturation, up to the value of the total porosity for fully saturated soils.
Because clayey soils swell upon wetting, the values for these soils can exceed
their total porosity.
- f (radon emanation fraction from soil) unitless
-
fraction of the total amount of radon produced by radium decay that escapes
from the soil particles and gets into the pores of the soil.
It depends on the soil material and the moisture content. It varies over a
range of 0.1 - 0.4 or more; typical values are in the range of 0.2 - 0.3.
- De (soil effective radon diffusion coeff.) m2/s
-
defined from Fick's equation as the ratio of the diffusive flux density of
radon activity across the pore area to the gradient of the radon activity
concentration in the pore or interstitial space.
This value is calculated from epsilon and thetaw (see above), but
can be modified as needed.
Caution: The effective (or interstitial) diffusion
coefficient De is not to be confused with the bulk radon diffusion
coefficient D. D is obtained by multiplying De by the total soil
porosity (epsilon). The use of the terminology for the diffusion coefficients
in literature is highly inconsistent - in some cases, the symbols of D and De
are used reversely!
The diffusion coefficient in porous media is a property of the
diffusing species, the pore structure, the type of fluids present in the pores,
the adsorption properties of the solid matrix, the fluid saturations, and
temperature.
The effective radon diffusivity values in porous media (soils and concrete
included) vary over a wide range of several orders of magnitude depending on
the porous material and particularly on its degree of water saturation.
Typically, the effective diffusion coefficient of radon in unconsolidated soil
material with a low moisture content is about 10-6 m2/s.
The upper limit is represented by the radon diffusion coefficient in open air,
Do, which is about 1.1 x 10-5 m2/s. At the
lower extreme, in a fully saturated soil material the radon diffusion
coefficient may be as low as 10-10 m2/s.
The building material can be initialized to representative values for ordinary
concrete (default), natural gypsum, and clay bricks.
- rhom (material density) kg/L
-
- epsilonm (total material porosity) Lpore/Lmatl
-
ratio of the pore volume to the total volume
The porosity of building materials varies over a range of 0.01 - 0.7.
- fm (radon emanation fraction from material) unitless
-
fraction of the total amount of radon produced by radium decay that escapes
from the material particles and gets into the pores of the material.
|
Material | typical | range |
| Brick (clay) |
0.04 |
0.02 - 0.1 |
| Concrete (ordinary) |
0.15 |
0.1 - 0.4 |
| Gypsum (natural) |
0.08 |
0.03 - 0.2 |
- De_m (material effective radon diffusion coeff.) m2/s
-
defined from Fick's equation as the ratio of the diffusive flux density of
radon activity across the pore area to the gradient of the radon activity
concentration in the pore or interstitial space.
Caution: The effective (or interstitial) diffusion
coefficient De is not to be confused with the bulk radon diffusion
coefficient D. D is obtained by multiplying De by the total porosity
(epsilon). The use of the terminology for the diffusion coefficients in
literature is highly inconsistent - in some cases, the symbols of D and De
are used reversely!
The diffusion coefficient in porous media is a property of the
diffusing species, the pore structure, the type of fluids present in the pores,
the adsorption properties of the solid matrix, the fluid saturations, and
temperature.
The effective radon diffusivity values in building materials vary over a wide
range of several orders of magnitude (10-11 - 10-6).
- DFi (indoor dust dilution factor) unitless
-
ratio of airborne dust concentration indoors on-site to the concentration
outdoors on-site.
It is based on the fact that a building provides shielding against entry of
wind-blown dust particles.
- GSF (indoor gamma shielding factor) unitless
-
Ratio of the indoor external gamma radiation level form soil on-site to the
outdoor gamma radiation level on-site.
It is based on the fact that a building provides shielding against penetration
of gamma radiation.
- FDF (fraction of radon diffusing through floor) unitless
-
This parameter depends on the properties of the building floor. For a bare
earth floor it is 1. Typical values are 0.07 for an intact concrete floor (20
cm thick), and 0.2 for a cracked concrete floor (20 cm thick, with an array of
1 cm wide cracks every 1 m) [UNSCEAR 1993].
- FAF (ratio of advection to diffusion through floor) unitless
-
This parameter depends on the underpressure in the building and the
permeability of the underlying soil. It is affected by the soil type
initialization.
Typical values for an underpressure of 5 Pa are: (derived from [UNSCEAR 1993])
| |
Permeability [m2] |
| 10-13 |
10-12 |
10-11 |
10-10 |
10-9 |
| Cracked floor |
1.4 |
1.5 |
2.7 |
15.0 |
8.3 |
| Bare earth |
1.1 |
1.2 |
1.6 |
7.3 |
3.3 |
Permeability of representative soil types [Nazaroff 1988]
|
Soil type | Permeability [m2] |
| Uniform, coarse sand |
5 x 10-10 |
| Uniform, medium sand |
1 x 10-10 |
| Clean, well-graded sand and gravel |
1 x 10-11 |
| Uniform, fine sand |
5 x 10-12 |
| Well-graded, silty sand and gravel |
5 x 10-13 |
| Silty sand |
1 x 10-13 |
| Uniform silt |
5 x 10-14 |
| Sandy clay |
5 x 10-15 |
| Silty clay |
1 x 10-15 |
| Clay |
1 x 10-16 |
- BRH (building room height) m
-
ratio of the volume of the total internal space of the building to the internal
area of its floor surface.
For one-story houses without a basement, the values typically lie within the
range of 2.2 - 3.0 m.
- WAF (ratio of contaminated room surface area to floor surface area) unitless
-
ratio of the internal room surface area consisting of contaminated building
material to the floor surface area.
Typical values are:
|
contaminated surface | WAF ratio |
| floor only |
1 |
| ceiling only |
1 |
| walls only *) |
2.5 |
| all surfaces *) |
4.5 |
*) for average 4m x 4m room and 2.5m room height
- dw (wall thickness) m
-
- lambdaV (building air exchange rate) per hour
-
This parameter expresses the rate at which the total air contained within the
building is replaced (or renewed) per hour. In the United States, the average
ventilation rate during the seasons when houses are kept closed lies within the
range of 0.1 - 1.0 per hour.
- Fi (indoor radon progeny equilibrium factor)
-
fraction of potential alpha decay energy of the short-lived radon decay
products in indoor air, compared to secular equilibrium.
The equilibrium factor is defined as:
F = (0.106 cPo-218 + 0.514 cPb-214 + 0.380 cBi-214)
/ cRn-222
where cx stands for the activity concentration of the nuclide x.
The factor depends on the air exchange rate of the building, among others. A
typical indoor value is 0.4.
- City, State (Climatic Zone)
-
Pick the city with the most similar climatic conditions
(map)
.
Sorry: US-Sites only :-(
- Q/C (inverse of the mean conc. at the center of square source) g/m2-s
per kg/m3
-
The Surface Area and City/Climate Zone are used to look up a Q/C.
- Um (mean annual windspeed) m/s
-
The City/Climate Zone is used to look up a value for Um.
- Ut (equivalent threshold value of windspeed at 7 m) m/s
-
minimum windspeed at a height of 7 meters that is needed to cause dust on-site.
The value of 11.32 m/s corresponds to a threshold friction velocity of 0.625
m/s at ground level. This value is corrected for the presence of nonerodible
elements in the surface soil.
- Fo (outdoor radon progeny equilibrium factor)
-
fraction of potential alpha decay energy of the short-lived radon decay
products in the on-site outdoor air, compared to secular equilibrium.
The equilibrium factor is defined as:
F = (0.106 cPo-218 + 0.514 cPb-214 + 0.380 cBi-214)
/ cRn-222
where cx stands for the activity concentration of the nuclide x.
The outdoor equilibrium factor depends on source area and climatic conditions.
A typical outdoor value for an infinite source area is 0.8. For small source
areas, it can decrease to 0.25, for example.
- METHOD 1: Partitioning Equation for Migration to Ground Water
-
- DF (dilution factor) unitless
-
ratio of leachate contaminant concentration in the contaminated soil (Cw)
to leachate contaminant concentration in the groundwater aquifer, from which
the potable water is taken.
The dilution factor of SSGR defaults to 20 for a 0.5-acre source.
If you have all of the parameters needed to calculate a dilution factor, you
may use Method 2.
- Kd (soil-water partition coefficient) L/kg
-
ratio of the mass of solute species adsorbed or precipitated on the solids per
unit of dry mass of the soil to the solute concentration in the liquids.
The coefficient represents the partition of the solute in the soil matrix and
soil water, assuming that equilibrium conditions exist between the soil and
solution phases. The transfer of radionuclides from the liquid to the solid
phase or vice versa may be controlled by mechanisms such as adsorption and
precipitation, depending on the radionuclides.
The Kd values for uranium, for example, vary over more than 6 decades
between 0.4 and 1,000,000, and, for a given pH, the range still covers 4
decades:
Kd values for uranium [L/kg]
(EPA 1999b Table 5.17 )
|
pH
|
Minimum | Maximum |
| 3 |
< 1 |
32 |
| 4 |
0.4 |
5,000 |
| 5 |
25 |
160,000 |
| 6 |
100 |
1,000,000 |
| 7 |
63 |
630,000 |
| 8 |
0.4 |
250,000 |
| 9 |
< 1 |
7,900 |
| 10 |
< 1 |
5 |
> See also Figure J.4 (EPA 1999b)
(note: vertical
axis shows decadic logarithm of Kd
)
For some elements, default Kd values are provided. These are
conservative default values taken from Table C.2a of the SSGR User's Guide. For
guidance on when it is appropriate to replace this default value and use a
site-specific Kd
value, refer to Part 5.2 of the SSGR Technical Background Document.
For the other elements, there are no default Kd values available.
These elements are only considered, if site-specific Kd values are
entered.
A Kd for these elements must be developed on a site-specific basis
to evaluate the potential for fate and transport of this contaminant from soil
to groundwater. See part C.2 of the SSGR User's Guide for guidance on
developing site-specific Kd
values.
For comparison purposes, the Kd
values can also be initialized to the less conservative default values used in
DOE's RESRAD and NRC's DandD models.
Due to the high variability of the Kd values, meaningful calculation
results for the actual health risk from ingestion of the contaminated
groundwater from an existing site can only be obtained, if site-specific values
are available. Otherwise, only estimates for certain assumptions can be made.
- METHOD 2: Mass-Limit Equation for Migration to Ground Water
-
This method only works if site-specific values are entered for all of these
parameters plus for ds in the Soil section.
For information about calculating site-specific values for the parameters
included in the Mass-limit equations please refer to sections 2.6 and 2.7 of
the SSGR Technical Background Document.
- I (Infiltration Rate) m/yr
-
rate of water infiltration from surface into contaminated soil (precipitation
plus irrigation minus evaporation minus runoff)
- K (aquifer hydraulic conductivity) m/yr
-
The hydraulic conductivity of a soil is a measure of the soil's ability to
transmit water when submitted to a hydraulic gradient. On the basis of Darcy's
law, the hydraulic conductivity is defined as the ratio of Darcy's velocity to
the applied hydraulic gradient.
The values of saturated hydraulic conductivity in soils vary within a wide range
of several orders of magnitude, depending on the soil material:
| Clean sand |
102 - 105 |
| Silty sand |
101 - 104 |
| Silt, loess |
10-2 - 102 |
| Glacial till |
10-5 - 101 |
| Unweathered marine clay |
10-5 - 10-2 |
- i (hydraulic gradient) m/m
-
The hydraulic gradient is the change in hydraulic head per unit of distance of
the groundwater flow in a given direction.
In an unconfined (water table) aquifer, the horizontal hydraulic gradient of
groundwater flow is approximately the slope of the water table. In general, the
hydraulic gradient of groundwater flow in a highly permeable geologic material,
such as sand or gravel, is far less than that in a geologic material with a low
permeability, such as silt and clay.
- L (source length parallel to ground water flow) m
-
maximum horizontal distance measured in the contaminated zone, from its
upgradient edge to the downgradient edge, along the direction of the
groundwater flow in the underlying aquifer.
- da (aquifer thickness) m
-
thickness of the potable water aquifer beneath the contaminated soil zone
General
This calculator takes no account of radioactive decay: this simplification
causes some error for Pb-210 and Ac-227 in case of disequilibrium with their
respective parent nuclides (this also concerns Migration to Groundwater Method
1 in case of different Kd values for these nuclides and their
respective parents).
EPA's SSGR also does not account for decay, while a decay term has been added
to the equations used in EPA's online SSGR calculator. The decay term chosen,
however, is not adequate for use in decay chains, as found with uranium.
Other than in the SSGR, where the fractions of time the individual spends
on-site are inconsistently applied to the various pathways, this calculator
applies the General Exposure Parameters to all pathways in the same way.
Risk coefficients used
The calculator determines the Lifetime Excess Cancer Risk from exposure to
radionuclides in soil via the pathways described. The risk coefficients per
unit exposure used are EPA's Radionuclide Cancer Morbidity Slope Factors (see
Table D.1 of the SSGR User's Guide). These slope factors are taken from the
Health Effects Assessment Summary Tables (HEAST)
(Note: figures of this link outdated). The slope factors are derived primarily
from: Health Risks from Low-Level Environmental Exposure to Radionuclides,
Federal Guidance Report No. 13, Part I - , U.S. EPA, 1999 (also known as
FGR13). (download
FGR13 as PDF 3MB
)
For inhalation of radon-222-progeny the risk coefficient of 0.000283 per WLM
(or 8.0 x 10-5 per mJ¡¤h/m3
) from ICRP 65 is used.
For conversion from risk to effective dose, ICRP's cancer morbidity coefficient
for the public of 0.06 per Sv is used (ICRP 60). This value, rather than the
fatal cancer coefficient of 0.05 per Sv is chosen, since EPA's slope factors
are for cancer morbidity rather than fatal cancer.
Pathway-specific Models
Ingestion of Soil
For the age-adjusted case, a time-weighted ingestion rate is determined.
Inhalation of Fugitive Dust
The model first determines a particulate emission factor based on wind speed
and climatic site conditions, and then determines exposure. For indoor
exposure, an attenuation factor is applied.
The model internally uses F(x), a function dependent on Ut/Um)
not explicitly described in the SSGR:
The F(x) function is derived using Cowherd et al. (1985):
x = 0.886 * Ut / Um
For x = 0 ... 2, see F(x) plot in Figure 4-3
on p. 36
For x > 2, F(x) may be approximated by: F(x) = 0.18 ( 8 x3
+ 12 x ) exp(-x2)
External Exposure
For source areas smaller than 2 acres (0.8 ha), a correction factor is applied
to account for the finite geometry. For external exposure from soil inside the
building, an attenuation factor is used. The dose factors used are for infinite
source depth.
For the indoor external radiation exposure from building materials, a dose
coefficient of 0.461 nGy/h per Bq/kg is used independent of the building
geometry, in connection with a coefficient of 0.7 Sv/Gy [UNSCEAR 1993].
Ingestion of Produce
The only pathway taken into consideration for the ingestion of produce grown on
the contaminated soil is the root uptake of radionuclides by the plants. The
soil-to-plant transfer factors are taken from Table C.3 in Appendix C of the
SSG User's Guide. Other possible pathways, such as irrigation, dust deposition
on leaves, etc. are not considered. It is assumed that the roots only extend
through contaminated soil.
Ingestion of Groundwater
Simplifying Assumptions for the Migration to Ground Water Pathway:
-
Contaminants are uniformly distributed throughout the zone of contamination
-
Soil contamination extends from the surface to the water table (i.e.,
adsorption sites are filled in the unsaturated zone beneath the area of
contamination
-
There is no chemical or biological degradation in the unsaturated zone
-
Equations do not account for decay
-
Equilibrium soil/water partitioning is instantaneous and linear in the
contaminated soil
-
The receptor well is at the edge of the source (i.e., there is no dilution from
recharge downgradient of the site) and is screened within the plume
-
The aquifer is unconsolidated and unconfined (surficial)
-
Aquifer properties are homogenous and isotropic
-
Chelating or complexing agents not present
-
No facilitated transport (e.g., colloidal transport of inorganic contaminants
in aquifer)
Method 1 (Partitioning Equation) assumes that the source is infinite (i.e.,
steady-state concentrations will be maintained in ground water over the
exposure period of interest).
This method uses a simple linear equilibrium soil/water partition equation to
estimate contaminant release (nuclide-specific) in soil leachate. Contaminant
concentration in the receiving aquifer is obtained using a dilution factor.
Method 2 (Mass-Limit Equation) assumes that the source is finite, and that the
entire volume of contamination leaches (nuclide-inspecific) over the exposure
duration.
It uses a simple water-balance equation to calculate a dilution factor to
account for reduction of soil leachate concentration from mixing in an aquifer.
Inhalation of Radon
This pathway is not included in the SSGR and was adapted from [UNSCEAR 1993].
First, the amount of radon-222 passing through the soil surface is calculated.
For outdoor concentrations in air, the atmospheric conditions and the source
area are considered, assuming that no radon is released from soil outside of
the contaminated area. For indoor air concentrations, passage from the soil
through a cracked floor, plus release from the building materials through the
wall surface is considered, and the building air exchange rate is taken into
account. Other factors, such as infiltration of outdoor air are neglected.
If no source depth ds is entered, an infinite source depth is
assumed.
There is no account for radon-220 (also known as thoron - a member of the
Thorium-232 decay series) in this calculator.
U.S. EPA: Soil
Screening Guidance for Radionuclides
Soil
Screening Guidance for Radionuclides: User's Guide
, EPA/540-R-00-007, U.S. Environmental Protection Agency, Washington, D.C.,
October 2000
Soil
Screening Guidance for Radionuclides: Technical Background Document
, EPA/540-R-00-006, U.S. Environmental Protection Agency, Washington, D.C.,
October 2000
Soil Screening Guidance for
Radionuclides: Online Calculator
Caution: This calculator produces erroneous output, if the activity unit Bq,
rather than pCi is selected.
[Cowherd 1985] Cowherd, C. et al.: Rapid Assessment of Exposure to Particulate
Emissions from Surface Contamination. Prepared for U.S. EPA, Office of
Health and Environmental Assessment, Washington, DC., EPA/600/8-85/002, 1985
> View/Download
[EPA 1999a] Understanding Variation in Partition Coefficient, Kd,
Values, Volume 1: The Kd Model of Measurement, and Application of
Chemical Reaction Codes, U.S. EPA, EPA-402-R-99-004A, Washington, D.C.,
1999, 220 p.
> View/Download
¡¤ Download PDF
[EPA 1999b] Understanding Variation in Partition Coefficient, Kd,
Values, Volume 2: Review of Geochemistry and Available Kd Values for
Cadmium, Cesium, Chromium, Lead, Plutonium, Radon, Strontium, Thorium, Tritium
(3H), and Uranium, U.S. EPA, EPA-402-R-99-004B, Washington,
D.C., 1999, 326 p.
> View/Download
¡¤ Download PDF
[Nazaroff 1988] W. Nazaroff, A. Nero (Eds.): Radon and its decay products in
indoor air
, New York 1988
[UNSCEAR 1993] Sources and Effects of Ionizing Radiation
, United Nations Scientific Committee on the Effects of Atomic Radiation,
UNSCEAR 1993 Report to the General Assembly, with Scientific Annexes, United
Nations, New York, 1993, 922 p.
[Yu 1993] C. Yu, J.J. Cheng, et al.:
Data Collection Handbook To Support Modeling Impacts Of Radioactive Material In
Soil
, Environmental Assessment and Information Sciences Division, Argonne National
Laboratory, Argonne, Illinois, ANL/EAIS-8, April 1993, 165 p.