Note

The RAIS presents this updated Risk calculator in response to the following: incorporating chemical-specific parameters from the lastest EPI release, addition of air as a media, and conversion to a new database structure. The previous RAIS Risk calculator presented Risks for radionuclides and chemcials together. Recent development of chemical and radionuclide exposure equations has necessitated that the RAIS separate the chemicals and the radionuclides. To calculate risks for chemicals, use the RAIS Risk Exposure Models for Chemicals calculator.

Currently the agricultural equations for the RAIS chemical and radionuclide risk calculators are identical. The EPA's Preliminary Remediation Goals for Radionuclide Calculator offers more biota choices but with a different plant/soil/water uptake method. The EPA's resident soil equation includes ingestion of produce and the RAIS radionuclide equation does not to be consistent with the chemcial risk equation.

1. Introduction

The purpose of this calculator is to assist Remedial Project Managers (RPMs), On Scene Coordinators (OSC’s), risk assessors and others involved in decision-making at hazardous waste sites and to determine whether levels of contamination found at the site may warrant further investigation or site cleanup, or whether no further investigation or action may be required.

The risk values presented on this site are chemical-specific values for individual contaminants in air, water, soil and biota that may warrant further investigation or site cleanup.

It should be noted that the risks in this calculator are based upon human health risk and do not address potential ecological risk. Some sites in sensitive ecological settings may also need to be evaluated for potential ecological risk. EPA's guidance "Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessment" http://www.epa.gov/superfund/programs/risk/ecorisk/ecorisk.htm contains an eight step process for using benchmarks for ecological effects in the remedy selection process. For ecological effects use the Ecological Benchmark tool on this site.

2. Understanding the Calculator Results

2.1 General Considerations

This portion of the risk assessment process is generally referred to as "Risk Characterization". This step incorporates the outcome of the previous activities and calculates the risk or hazard resulting from potential exposure to chemicals via the pathways and routes of exposure determined appropriate for the source area.

The basic equation for calculating excess lifetime cancer risk is:

Risk = CDI × SF

where:

Risk = a unitless probability of an individual developing cancer over a lifetime;
CDI = chronic daily intake or dose [pCi or pCi-year/g]
SF = slope factor, expressed in [risk/pCi or risk-g/pCi-year]

2.2 Exposure Assumptions

Risks are based on default exposure parameters and factors that represent Reasonable Maximum Exposure (RME) conditions for long-term/chronic exposures and are based on the methods outlined in EPA’s Risk Assessment Guidance for Superfund, Part B Manual (1991) and Soil Screening Guidance documents (1996 and 2002).

Site-specific information may warrant modifying the default parameters in the equations and calculating site-specific risks. In completing such calculations, the user should answer some fundamental questions about the site. For example, information is needed on the contaminants detected at the site, the land use, impacted media and the likely pathways for human exposure.

Whether these generic risks or site-specific risks are used, it is important to clearly demonstrate the equations and exposure parameters used in deriving risks at a site. A discussion of the assumptions used in the risk calculations should be included in the decision document for a CERCLA site.

2.3 Toxicity Values

EPA classifies all radionuclides as Group A carcinogens. The radionuclide table from HEAST lists ingestion, inhalation and external exposure cancer slope factors (risk coefficients for total cancer morbidity) for radionuclides in conventional units of picocuries (pCi). Ingestion and inhalation slope factors are central estimates in a linear model of the age-averaged, lifetime attributable radiation cancer incidence (fatal and nonfatal cancer) risk per unit of activity inhaled or ingested, expressed as risk/pCi. External exposure slope factors are central estimates of lifetime attributable radiation cancer incidence risk for each year of exposure to external radiation from photon-emitting radionuclides distributed uniformly in a thick layer of soil, and are expressed as risk/yr per pCi/gram soil. When combined with site-specific media concentration data and appropriate exposure assumptions, slope factors can be used to estimate lifetime cancer risks to members of the general population due to radionuclide exposures.

3. Using the Radionuclide Risk Calculator

The risk calculator provides generic concentrations in the absence of site-specific exposure assessments. These concentrations can be used for:

• Prioritizing multiple sites within a facility or exposure units
• Setting risk-based detection limits for contaminants of potential concern (COPCs)
• Focusing future risk assessment efforts
• When appropriate for the site, consideration as risk-based cleanup levels

3.1 Developing a Conceptual Site Model

When using risks, the exposure pathways of concern and site conditions should match those taken into account by the screening levels. (Note, however, that future uses may not match current uses. Future uses of a site should be logical as conditions which might occur at the site in the future.) Thus, it is necessary to develop a conceptual site model (CSM) to identify likely contaminant source areas, exposure pathways, and potential receptors. This information can be used to determine the applicability of screening levels at the site and the need for additional information. The final CSM diagram represents linkages among contaminant sources, release mechanisms, exposure pathways, and routes and receptors based on historical information. It summarizes the understanding of the contamination problem. A separate CSM for ecological receptors can be useful. Part 2 and Attachment A of the Soil Screening Guidance for Radionuclides: Users Guide (EPA 2000a) contains the steps for developing a CSM.

As a final check, the CSM should answer the following questions:

• Are there potential ecological concerns?
• Is there potential for land use other than those listed in the risk calculator (i.e. , residential and industrial)?
• Are there other likely human exposure pathways that were not considered in development of the risks?
• Are there unusual site conditions (e.g. large areas of contamination, high fugitive dust levels, potential for indoor air contamination)?

The risks may need to be adjusted to reflect the answers to these questions.

3.2 Radionuclide Background

Natural background radiation should be considered prior to applying risks as cleanup levels. Background and site-related levels of radiation will be addressed as they are for other contaminants at CERCLA sites. For further information, see EPA's guidance "Role of Background in the CERCLA Cleanup Program", April 2002, (OSWER 9285.6-07P). It should be noted that certain ARARs specifically address how to factor background into cleanup levels. For example, some radiation ARAR levels are established as increments above background concentrations. In these circumstances, background should be addressed in the manner prescribed by the ARAR.

3.3 Potential Problems

As with any risk based tool, the potential exists for misapplication. In most cases, this results from not understanding the intended use of the risks. In order to prevent misuse of the risks, the following should be avoided:

• Applying risk levels to a site without adequately developing a conceptual site model that identifies relevant exposure pathways and exposure scenarios.
• Use of risk levels as cleanup levels without the consideration of other relevant criteria such as ARARs.
• Use of risk levels as cleanup levels without verifying numbers with a health physicist/risk assessor.
• Use of outdated risk levels tables that have been superseded by more recent publications.
• Not considering the effects from the presence of multiple isotopes.

4. Technical Support Documentation

The chronic daily intake (CDI) equations consider human exposure to individual contaminants in air, water, soil, sediment and biota. The technical discussion is aimed at producing risk results. The following text presents the land use equations and their exposure routes. Table 1 presents the definitions of the variables and their default values. Any alternative values or assumptions used in developing risks on a site should be presented with supporting rationale in the decision documents.

4.1 Residential Soil

The residential soil land use equations, presented here, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil,

external exposure to ionizing radiation and

4.2 Outdoor Worker Soil

The outdoor worker soil land use equations, presented here, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil,

external exposure to ionizing radiation and

4.3 Indoor Worker Soil

The indoor worker soil land use equations, presented here, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil,

external exposure to ionizing radiation and

4.4 Excavation/Construction Outdoor Worker Soil

The excavation worker/construction outdoor worker soil land use equations, presented here, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil,

external exposure to ionizing radiation and

4.5 Recreational Soil

The recreational soil land use equations, presented here, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil,

external exposure to ionizing radiation and

4.6 Tapwater

The tapwater land use equation, presented here, contains the following exposure routes:

ingestion of water,

inhalation of volatiles and

4.7 Recreational Surface Water

The surface water land use equation, presented here, contains the following exposure route:

ingestion of water

4.8 Ambient Air

4.8.1 Resident

The ambient air land use equation, presented here, contains the following exposure route:

inhalation

4.8.2 Outdoor Worker

The ambient air land use equation, presented here, contains the following exposure route:

inhalation

4.8.3 Indoor Worker

The ambient air land use equation, presented here, contains the following exposure route:

inhalation

4.8.4 Excavation/Construction Worker

The ambient air land use equation, presented here, contains the following exposure route:

inhalation

4.9 Ingestion of Fish

4.9.1 Concentration in Fish

The ingestion of fish equation, presented here, contains the following exposure route:

consumption of fish.

4.9.2 Concentration in Surface Water

The ingestion of fish equation, presented here, contains the following exposure route:

consumption of fish.

Note: the consumption rate for fish is not age adjusted for this land use.

4.10 Agriculture

4.10.1 Concentration in Fruit and Vegetables

The ingestion of fruits and vegetables equation, presented here, contains the following exposure route:

consumption of fruits and vegetables.

4.10.2 Back-calculated Concentration in Water Only for Fruits and Vegetables

consumption of fruits and vegetables.

4.10.3 Back-calculated Concentration in Soil Only for Fruits and Vegetables

consumption of fruits and vegetables.

4.10.4 Concentration in Milk

consumption of milk.

4.10.5 Back-calculated Concentration in Water Only for Milk

consumption of milk.

4.10.6 Back-calculated Concentration in Soil Only for Milk

consumption of milk.

4.10.7 Concentration in Beef

The ingestion of beef equation, presented here, contains the following exposure route:

consumption of beef.

4.10.8 Back-calculated Concentration in Water Only for Beef

consumption of beef.

4.10.9 Back-calculated Concentration in Soil Only for Beef

consumption of beef.

4.11 Supporting Equations and Parameter Discussion

There are three parts of the above land use equations that require further explanation. The first is explanation of two inhalation variables: the particulate emission factor (PEF) and the volatilization factor (VF). The second is the use of the radionuclide decay constant (λ). The third is the explanation of the area correction factor (ACF).

4.11.1 Particulate Emission Factor (PEF) and Volatilization Factor (VF)

Inhalation of isotopes adsorbed to respirable particles (PM10) was assessed using a default PEF equal to 1.36 x 109 m³/kg. This equation relates the contaminant concentration in soil with the concentration of respirable particles in the air due to fugitive dust emissions from contaminated soils. The generic PEF was derived using default values that correspond to a receptor point concentration of approximately 0.76 µg/m³. The relationship is derived by Cowherd (1985) for a rapid assessment procedure applicable to a typical hazardous waste site, where the surface contamination provides a relatively continuous and constant potential for emission over an extended period of time (e.g. years). This represents an annual average emission rate based on wind erosion that should be compared with chronic health criteria; it is not appropriate for evaluating the potential for more acute exposures. Definitions of the input variables are in Table 1.

With the exception of specific heavy metals, the PEF does not appear to significantly affect most soil screening levels. The equation forms the basis for deriving a generic PEF for the inhalation pathway. For more details regarding specific parameters used in the PEF model, refer to Soil Screening Guidance: Technical Background Document. The use of alternate values on a specific site should be justified and presented in an Administrative Record if considered in CERCLA remedy selection.

Note: the generic PEF evaluates wind-borne emissions and does not consider dust emissions from traffic or other forms of mechanical disturbance that could lead to greater emissions than assumed here.

EPA derived a default volatilization factor (VF) value of 17 m³/kg for tritium. The VF replaces the PEF in the risk equations when tritium is being addressed. This VF value is based on a steady-state model that assumes, on average, tritium in soil pore water and tritium in air (as tritiated water vapor) will be distributed in the environment in proportion to the average water content in soil and air. EPA assumes a mean atmospheric humidity of 6 grams of water per cubic meter of air (g/m³) nationwide (Etnier 1980) and an average soil moisture content of 10% (i.e., 100 grams of water per kilogram of soil). Given these assumptions, EPA calculates the VF term for tritium as

VFH-3 = 100 g H2O/kg soil ÷ 6 g H2O/m³ air

= 17 m³ air/kg soil

= 17 m³/kg

EPA believes that this value is appropriate for the average case, both outdoors and indoors. However, site managers can derive a site-specific VF term for tritium that may be more appropriate for a specific site, considering local atmospheric humidity and soil moisture content.

4.11.2 Radionuclide Decay Constant

The residential soil, outdoor worker, indoor worker, and agricultural soil land uses (all the soil related land uses) have a decay constant term which is based on the halflife of the isotope (λ). λ= Decay constant (0.693/halflife) yr-1. The intention of this term is to make realistic risks by including the contributions from their short-lived decay products, assuming equal activity concentrations (i.e. , secular equilibrium) with the principal or parent nuclide in the environment. (Note that there is one exception to the assumption of secular equilibrium. For the inhalation slope factor for Rn-222+D reported in the table, EPA assumes a 50% equilibrium value for radon decay products (Po-218, Pb-214, Bi-214and Po-214) in air. ) In most cases, site-specific analytical data should be used to establish the actual degree of equilibrium between each parent radionuclide and its decay products in each media sampled. However, in the absence of empirical data, the "+D" values for radionuclides should be used unless there are compelling reasons not to do so. The term (1 - eλt) takes into account the number of halflives that will occur within the ED to calculate an appropriate value. Definitions of the input variables are in Table 1.

4.11.3 Area Correction Factor

The RAGS/HHEM Part B model assumes that an individual is exposed to a source geometry that is effectively an infinite slab. The concept of an infinite slab means that the thickness of the contaminated zone and its aerial extent are so large that it behaves as if it were infinite in its physical dimensions. In practice, soil contaminated to a depth greater than about 15 cm and with an aerial extent greater than about 1,000 m² will create a radiation field comparable to that of an infinite slab. (U.S. EPA. 2000a)

To accommodate the fact that in most residential settings the assumption of an infinite slab source will result in overly conservative SSLs, an adjustment for source area is considered to be an important modification to the RAGS/HHEM Part B model. Thus, an area correction factor, ACF, has been added to the calculation of SSLs. (U.S. EPA. 2000a)

For further description of the ACF, follow the link here.

Table 1. Standard Default Factors

Symbol	Definition (units)	Default	Reference
CDIs
CDIres-sol-rad-ing	Resident Soil Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIres-sol-rad-inh	Resident Soil Radionuclide Inhalation (pCi)	Contaminant-specific	Determined in this calculator
CDIres-sol-rad-ext	Resident Soil Radionuclide External (pCi-year/g)	Contaminant-specific	Determined in this calculator
CDIow-sol-rad-ing	Outdoor Worker Soil Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIow-sol-rad-inh	Outdoor Worker Soil Radionuclide Inhalation (pCi)	Contaminant-specific	Determined in this calculator
CDIow-sol-rad-ext	Outdoor Worker Soil Radionuclide External (pCi-year/g)	Contaminant-specific	Determined in this calculator
CDIew-sol-rad-ing	Excavation/Construction Worker Soil Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIew-sol-rad-inh	Excavation/Construction Worker Soil Radionuclide Inhalation (pCi)	Contaminant-specific	Determined in this calculator
CDIew-sol-rad-ext	Excavation/Construction Worker Soil Radionuclide External (pCi-year/g)	Contaminant-specific	Determined in this calculator
CDIiw-rad-ing	Indoor Worker Soil Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIiw-rad-inh	Indoor Worker Soil Radionuclide Inhalation (pCi)	Contaminant-specific	Determined in this calculator
CDIiw-sol-rad-ext	Indoor Worker Soil Radionuclide External (pCi-year/g)	Contaminant-specific	Determined in this calculator
CDIrec-sol-rad-ing	Recreation Soil Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIrec-sol-rad-inh	Recreation Soil Radionuclide Inhalation (pCi)	Contaminant-specific	Determined in this calculator
CDIrec-sol-rad-ext	Recreation Soil Radionuclide External (pCi-year/g)	Contaminant-specific	Determined in this calculator
CDIwater-rad-ing	Resident Tapwater (Groundwater) Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIwater-rad-inh	Resident Tapwater (Groundwater) Radionuclide Inhalation (pCi)	Contaminant-specific	Determined in this calculator
CDIrec-water-rad-ing	Recreation Surface Water Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIres-air-rad	Resident Air Radionuclide (pCi)	Contaminant-specific	Determined in this calculator
CDIow-air-rad	Outdoor Worker Air Radionuclide (pCi)	Contaminant-specific	Determined in this calculator
CDIiw-air-rad	Indoor Worker Air Radionuclide (pCi)	Contaminant-specific	Determined in this calculator
CDIew-air-rad	Excavation/Construction Worker Air Radionuclide (pCi)	Contaminant-specific	Determined in this calculator
CDIres-fsh-rad-ing	Resident Fish Radionuclide (pCi)	Contaminant-specific	Determined in this calculator
CDIres-fshw-rad-ing	Resident Surface Water Fish Radionuclide (pCi)	Contaminant-specific	Determined in this calculator
CDIag-prod-rad-ing	Agriculture Fruits and Vegetables Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIw-ag-prod-rad-ing	Agriculture Fruits and Vegetables Radionuclide Back-calculated Concentration in Water Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIs-ag-prod-rad-ing	Agriculture Fruits and Vegetables Radionuclide Back-calculated Concentration in Soil Ingestion	Contaminant-specific	Determined in this calculator
CDIag-milk-rad-ing	Agriculture Milk Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIw-ag-milk-rad-ing	Agriculture Milk Radionuclide Back-calculated Concentration in Water Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIs-ag-milk-rad-ing	Agriculture Milk Radionuclide Back-calculated Concentration in Soil Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIag-beef-rad-ing	Agriculture Beef Radionuclide Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIw-ag-beef-rad-ing	Agriculture Beef Radionuclide Back-calculated Concentration in Water Ingestion (pCi)	Contaminant-specific	Determined in this calculator
CDIs-ag-beef-rad-ing	Agriculture Beef Radionuclide Back-calculated Concentration in Soil Ingestion (pCi)	Contaminant-specific	Determined in this calculator
Slope Factors
SFs	Ingestion Slope Factor - soil (risk/pCi)	contaminant-specific	HEAST
SFf	Ingestion Slope Factor - food (risk/pCi)	contaminant-specific	HEAST
SFw	Ingestion Slope Factor - water (risk/pCi)	contaminant-specific	HEAST
SFi	Slope Factor - inhalation (risk/pCi)	contaminant-specific	HEAST
SFX	Slope Factor - external exposure (risk/yr per pCi/g)	contaminant-specific	HEAST
Dose and Decay Constant Variables
TR	Target Risk	1 × 10-06
tres	Time - resident (years)	30	U.S. EPA 1991a (pg. 15)
trec	Time - recreation (years)	30	U.S. EPA 1991a (pg. 15)
tow	Time - outdoor worker (years)	25	U.S. EPA 1991a (pg. 15)
tiw	Time - indoor worker (years)	25	U.S. EPA 1991a (pg. 15)
tew	Time - excavation/construction worker (years)	25	U.S. EPA 1991a (pg. 15)
tag	Time - Agriculture (years)	30	U.S. EPA 1991a (pg. 15)
λ	Decay Constant	= 0.693/halflife	Developed for Radionuclide Soil Screening calculator
Miscellaneous Variables
Csoil	concentration of contaminant in soil (pCi/g)	User-input
Cg-water	concentration of contaminant in groundwater (pCi/L)	User-input
Cs-water	concentration of contaminant in surface water (pCi/L)	User-input
Cair	concentration of contaminant in air (pCi/m3)	User-input
Cfish	concentration of contaminant in fish (pCi/g)	User-input
Cproduce	concentration of contaminant in produce (pCi/g)	User-input
Cmilk	concentration of contaminant in milk (pCi/g)	User-input
Cbeef	concentration of contaminant in beef (pCi/g)	User-input
DFi	Dilution Factor - indoor (unitless)	0.4	U.S. EPA 2000a. (pg. 2-20). U.S. EPA 2000b. (pg. 2-13)
ACF	Area Correction Factor (unitless)	0.9	U.S. EPA 2000a. (pg. 2-22). U.S. EPA 2000b. (pg. 5-1)
GSF	Gamma Shielding Factor (unitless)	0.4	U.S. EPA 2000a. (pg. 2-22). U.S. EPA 2000b. (pg. 2-18)
BCF	Fish Bioconcentration Factor (L/kg)	Contaminant-specific
K	Andelman Volatilization Factor (L/m3)	0.5	U.S. EPA 1991b (pg. 20)
CFp	Fraction of Produce Consumed that is Contaminated	1	U.S. EPA 1998
CFm	Fraction of Milk Consumed that is Contaminated	1	U.S. EPA 1998
CFp	Fraction of Beef Consumed that is Contaminated	1	U.S. EPA 1998
Inhalation, Ingestion, and Consumption Rates
IRSc	Resident Soil Ingestion Rate - Child (mg/day)	200	U.S. EPA 1991a (pg. 15)
IRSa	Resident Soil Ingestion Rate - Adult (mg/day)	100	U.S. EPA 1991a (pg. 15)
IFSadj	Resident Soil Ingestion Rate - Age-adjusted (mg/day)	120	Calculated using the age-adjusted intake factors equation
IFAadj	Inhalation Rate -resident -age-adjusted (m3/day)	18	Calculated using the age adjusted intake factors equation
IRAa	Inhalation Rate - adult (m3/day)	20	U.S. EPA 1991a (pg. 15)
IRAc	Inhalation Rate - child (m3/day)	10	U.S. EPA 1997a (pg. 5-11)
IRAiw	Inhalation Rate - indoor worker (m3/day; based on a rate of 2.5m3/hr for 24hr)	60	U.S. EPA 1997a (pg. 5-11)
IRAow	Inhalation Rate - outdoor worker (m3/day; based on a rate of 2.5m3/hr for 24hr)	60	U.S. EPA 1997a (pg. 5-11)
IRAew	Inhalation Rate - excavation/construction worker (m3/day; based on a rate of 2.5m3/hr for 24hr)	60	U.S. EPA 1997a (pg. 5-11)
IRWc	Drinking Water Ingestion Rate - Child (L/day)	1	U.S. EPA 1989 (Exhibit 6-11)
IRWa	Drinking Water Ingestion Rate - Adult (L/day)	2	U.S. EPA 1989 (Exhibit 6-11)
IFWadj	Drinking Water Ingestion Rate - Age-adjusted (L/day)	1.8	Calculated using the age-adjusted intake factors equation
IFWrec	Recreation Water Ingestion Rate (L/hr)	0.05	U.S. EPA Region 4
IRFa	Fish Ingestion Rate (g/day)	54	U.S. EPA 1991a (pg. 15)
IRow	Soil Ingestion Rate - outdoor worker (mg/day)	100	U.S. EPA 2001 (pg. 4-3)
IRiw	Soil Ingestion Rate - indoor worker (mg/day)	50	U.S. EPA 1991a (pg. 15)
IRew	Soil Ingestion Rate - excavation/construction worker (mg/day)	330	U.S. EPA 2002
IRPfr-c	Produce Ingestion Rate - Fruit - Child (mg/day)	14.8	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPfr-a	Produce Ingestion Rate - Fruit - Adult (mg/day)	56.2	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPfr-adj	Produce Ingestion Rate - Fruit - Age-adjusted (mg/day)	47.92	Calculated using the aged adjusted intake factors equation
IRPvg-c	Produce Ingestion Rate - Vegetables - Child (mg/day)	10.4	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPvg-a	Produce Ingestion Rate - Vegetables - Adult (mg/day)	28.5	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPvg-adj	Produce Ingestion Rate - Vegetables - Age-adjusted (mg/day)	24.88	Calculated using the aged adjusted intake factors equation
IRMc	Milk Ingestion Rate - Child (mg/day)	265	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRMa	Milk Ingestion Rate - Adult (mg/day)	615	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRMadj	Milk Ingestion Rate - Age-adjusted (mg/day)	545	Calculated using the aged adjusted intake factors equation
IRBc	Beef Ingestion Rate - Child (mg/day)	12.9	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRBa	Beef Ingestion Rate - Adult (mg/day)	138	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRBadj	Beef Ingestion Rate - Age-adjusted (mg/day)	112.98	Calculated using the aged adjusted intake factors equation
Irrrup	root uptake from irrigation multiplier (L/kg)	contaminant-specific	Calculated
Irrres	resuspension from irrigation multiplier (L/kg)	contaminant-specific	Calculated
Irrdep	aerial deposition from irrigation multiplier (L/kg)	contaminant-specific	Calculated
Rupp	dry root uptake for pasture multiplier (unitless)	=BVdry
Rupv	wet root uptake for vegetables multiplier (unitless)	=BVwet
Qp-b	Beef Fodder Intake Rate (kg/day)	11.77	U.S. EPA 1999a (pg 10-23). U.S. EPA 1997b.
Qp-m	Dairy Fodder Intake Rate (kg/day)	16.9	U.S. EPA 1999a (pg 10-23). U.S. EPA 1997b.
Qw-dairy	Dairy Water Intake Rate (kg/day)	92	U.S. EPA 1999a (pg 10-23).
Qw-beef	Beef Water Intake Rate (kg/day)	53	U.S. EPA 1999a (pg 10-23).
Qs-m	Dairy Soil Intake Rate (kg/day)	0.41	U.S. EPA 1999a (pg 10-23). U.S. EPA 1997b.
Qs-b	Beef Soil Intake Rate (kg/day)	0.39	U.S. EPA 1999a (pg 10-23). U.S. EPA 1997b.
fp-b	fraction of year animal is on site (unitless)	1
fp-m	fraction of year animal is on site (unitless)	1
fs-b	fraction of animal's food is from site (unitless)	1
fs-m	fraction of animal's food is from site (unitless)	1
Fm	Milk Transfer Factor (day/kg)	Contaminant-specific	ANL. 1993. NCRP 1996.
Fb	Beef Transfer Factor (day/kg)	Contaminant-specific	ANL. 1993. NCRP 1996.
Ir	Irrigation rate (L/m2-day)	3.62	Personnal communication
F	irrigation period (unitless)	0.25 (based on 3 months per year)	Personnal communication
λB	effective rate for removal (1/day)	λi + λHL	NCRP 1989
λE	decay for removal on produce (1/day)	λi + (0.693/tw)	NCRP 1989
λHL	soil leaching rate (1/day)	0.000027	NCRP 1989
λi	decay (1/day)	0.693/TR - radionuclides, 0 - non-radionuclides	NCRP 1989
tW	weathering half -life (day)	14	NCRP 1989
TR	half-life (days)	Contaminant-specific
MLFpasture	Pasture plant mass loading factor (unitless)	0.25	Hinton, T. G. 1992
MLFprodude	Produce plant mass loading factor (unitless)	0.26	Pinder, J. E., and K. W. McLeod. 1989
tb	long term deposition and buildup (day)	10950	NCRP 1985
tv	above ground exposure time (day)	60	NCRP 1985
If	interception fraction (unitless)	0.42	Miller, C. W. 1980
Yv	plant yield (wet) (kg/m2)	2	NCRP 1985
P	area density for root zone (kg/m2)	240	Hoffman, F. O., R. H. Gardner, and K. F. Eckerman. 1982; Peterson, H. T., Jr. 1983; McKone, T. E. 1994
T	translocation factor (unitless)	1	NCRP 1984
Res	= MLF (produce or pasture)
Exposure Frequency, Exposure Duration, and Exposure Time Variables
EFr	Exposure Frequency - residential (days/yr)	350	U.S. EPA 1991a (pg. 15)
EFrec	Exposure Frequency - recreation (days/yr)	75
EFrec-w	Water Exposure Frequency - recreation (days/yr)	45	U.S. EPA 1991a (pg. 15)
EFag	Exposure Frequency - agricultural (days/yr)	350	U.S. EPA 1991a (pg. 15)
EFiw	Exposure Frequency - indoor worker (days/yr)	250	U.S. EPA 1991a (pg. 15)
EFow	Exposure Frequency - outdoor worker (days/yr)	225	U.S. EPA 1991a (pg. 15)
EFew	Exposure Frequency - excavation/construction worker (days/yr)	20	one month of the worker year, or approximately 20 days per year
EDr	Exposure Duration - resident (yr)	30	U.S. EPA 1991a (pg. 15)
EDag	Exposure Duration - agricultural (yr)	40	U.S. EPA 1994a U.S. EPA 1998 (Table C-1-7)
EDc	Exposure Duration - child resident (yr)	6	U.S. EPA 1991a (pg. 15)
EDrec	Exposure Duration - recreation (yr)	30	U.S. EPA 1991a (pg. 15)
EDow	Exposure Duration - outdoor worker (yr)	25	U.S. EPA 1991a (pg. 15)
EDiw	Exposure Duration - indoor worker(yr)	25	U.S. EPA 1991a (pg. 15)
EDew	Exposure Duration - excavation/construction worker (yr)	1	U.S. EPA 1991a (pg. 15)
ETiwi	Exposure Time - indoor worker (indoor) (hr/hr)	0.33	Eight Hours per 24 hr Day
ETiwo	Exposure Time - indoor worker (outdoor) (hr/hr)	0
ETowi	Exposure Time - outdoor worker (indoor) (hr/hr)	0
ETowo	Exposure Time - outdoor worker (outdoor) (hr/hr)	0.33	Eight Hours per 24 hr Day
ETewi	Exposure Time - excavation/construction worker (indoor) (hr/hr)	0
ETewo	Exposure Time - excavation/construction worker (outdoor) (hr/hr)	0.33	Eight Hours per 24 hr Day
ETres	Exposure Time - resident (hr/day)	24
ETri	Exposure Time - resident (indoor) (hr/hr)	0.683	U.S. EPA 2000a. (pg. 2-22). U.S. EPA 2000b. (pg. 2-17). U.S. EPA 1997a (Table 15-131)
ETro	Exposure Time - resident (outdoor) (hr/hr)	0.073	U.S. EPA 2000a. (pg. 2-22). U.S. EPA 2000b. (pg. 2-17). U.S. EPA 1997a (Table 15-132)
ETrec	Exposure Time - recreation (hr/day)	1
Particulate Emission Factor Variables
PEF	Particulate Emission Factor - Minneapolis (m3/kg)	1.36 x 109	U.S. EPA 1996a (pg. 23), U.S. EPA 1996b (pg. 31)
Q/C	Inverse of the Mean Concentration at the Center of a 0.5-Acre-Square Source (g/m2-s per kg/m3)	93.77	U.S. EPA 1996a (pg. 23), U.S. EPA 1996b (pg. 31)
V	(fraction of vegetative cover) unitless	0.5	U.S. EPA 1999b, U.S. EPA 1996a (pg. 23), U.S. EPA 1996b (pg. 31)
Um	mean annual wind speed) m/s	4.69	U.S. EPA 1999b, U.S. EPA 1996a (pg. 23), U.S. EPA 1996b (pg. 31)
Ut	equivalent threshold value of wind speed at 7m) m/s	11.32	U.S. EPA 1991b, U.S. EPA 1996a (pg. 23), U.S. EPA 1996b (pg. 32)
F(×)	function dependent on Um/Ut) unitless	0.194	U.S. EPA 1991b, U.S. EPA 1996a (pg. 23), U.S. EPA 1996b (pg. 31)

---

ANL 1993. Manual for Implementing Residual Radioactive Materials Guidelines Using RESRAD, Version 5.0. Argonne National Laboratory, Argonne, IL. ANL/EAD/LD-2

Etnier 1980. Till, J. E., H. R. Meyer, E. L. Etnier, E. S. Bomar, R. D. Gentry, G. G. Killough, P. S. Rohwer, V. J. Tennery, and C. C. Travis "Tritium-An Analysis of Key Environmental and Dosimetric Questions", ORNL/TM-6990. pg 15.

IAEA 1994. Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Temperate Environments. International Atomic Energy Agency

NEC. Swine Nutrition Guide. Cooperative Extension Service / South Dakota State University and University of Nebraska / U.S. Department of Agriculture. Nebraska Cooperative Extension EC 95-273-C. The pig water ingestion numbers are derived from the USDA "Swine Nutrition Guide. " USDA assumes a pig consumes 1/4 to 1/3 gallon of water for every pound of dry feed. The midpoint of this range (7/24 gallons of water) was used with the default dry feed (4.7 kg) to come up with 11.4 gallons per day default water intake.

NCRP 1996. Screening Models for Releases of Radionuclides to Atmosphere, Surface Water, and Ground, Vols. 1 and 2, NCRP Report No. 123. National Council on Radiation Protection and Measurements. http://www.ncrp.com/rpt123.html

U.S. EPA. 1988. Limiting Values of Radionuclide Intake and Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion. Federal Guidance Report No. 11. Office of Radiation Programs, Washington, DC. EPA-520/1-88-020. http://homer.hsr.ornl.gov/vlab/FedGR11.html

U.S. EPA 1989. U.S. Environmental Protection Agency (U.S. EPA). Risk assessment guidance for Superfund. Volume I: Human health evaluation manual (Part A). Interim Final. Office of Emergency and Remedial Response. EPA/540/1-89/002.

U.S. EPA 1990. Interim Final Methodology for Assessing Health Risks Associated with Indirect Exposure to Combustor Emissions. Environmental Criteria and Assessment Office. ORD. EPA-600-90-003. January.

U.S. EPA 1991a. U.S. Environmental Protection Agency (U.S. EPA). Human health evaluation manual, supplemental guidance: "Standard default exposure factors". OSWER Directive 9285.6-03.

U.S. EPA 1991b. Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation Manual (Part B, Development of Risk-Based Preliminary Remediation Goals). Office of Emergency and Remedial Response. EPA/540/R-92/003. December 1991

U.S. EPA. 1993. External Exposure to Radionuclides in Air, Water, and Soil. Federal Guidance Report No. 12. Office of Radiation and Indoor Air, Washington, DC. EPA 402-R-93-081. http://homer.hsr.ornl.gov/VLAB/FedGR12.html

U.S. EPA. 1994a. Estimating Exposure to Dioxin-like Components - Volume III: Site-Specific Assessment Procedure. Review Draft. Office of Research and Development. Washington D.C. EPA/600/6-88/005Cc. June.

U.S. EPA 1994b. Radiation Site Cleanup Regulations: Technical Support Documents for the Development of Radiation Cleanup Levels for Soil – Review Draft. Office of Radiation and Indoor Air, Washington, DC. EPA 402-R-96-011A. http://www.epa.gov/radiation/docs/cleanup/402-r-96-011a.htm View Appendix C here

U.S. EPA. 1994c. Revised Draft Guidance for Performing Screening Level Risk Analyses at Combustion Facilities Burning Hazardous Wastes. Attachment C, Draft Exposure Assessment Guidance for RCRA Hazardous Waste Combustion Facilities. Office of Emergency and Remedial Response. Office of Solid Waste. December 14.

U.S. EPA. 1996a. Soil Screening Guidance: User's Guide. Office of Emergency and Remedial Response. Washington, DC. OSWER No. 9355.4-23

U.S. EPA. 1996b. Soil Screening Guidance: Technical Background Document. Office of Emergency and Remedial Response. Washington, DC. OSWER No. 9355.4-17A

U.S. EPA. 1997a. Exposure Factors Handbook. Office of Research and Development, Washington, DC. EPA/600/P-95/002Fa.

U.S. EPA. 1997b. Parameter Guidance Document. National Center for Environmental Assessment, NCEA-0238.

U.S. EPA. 1998. Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities. Office of Solid Waste, Washington, DC. EPA530-D-98-001A http://www.epa.gov/epaoswer/hazwaste/combust/risk.htm

U.S. EPA. 1999a. Data Collection for the Hazardous Waste Identification Rule. Office of Solid Waste, Washington, DC. http://www.epa.gov/epaoswer/hazwaste/id/hwirwste/risk.htm

U.S. EPA 1999b. Volume II, "Review of Geochemistry and Available Kd Values for Cadmium, Cesium, Chromium, Lead, Plutonium, Radon, Strontium, Thorium, Tritium (3H), and Uranium. Office of Radiation and Indoor Air. Washington, DC. EPA 402-R-99-004B, August 1999.

U.S. EPA 1999c. Cancer Risk Coefficients for Environmental Exposure to Radionuclides. Federal Guidance Report No. 13. Office of Radiation and Indoor Air. EPA 402-R-99-001. September 1999. http://www.epa.gov/radiation/federal/

U.S. EPA. 2000a. Soil Screening Guidance for Radionuclides: User's Guide. Office of Emergency and Remedial Response and Office of Radiation and Indoor Air. Washington, DC. OSWER No. 9355.4-16A

U.S. EPA. 2000b. Soil Screening Guidance for Radionuclides: Technical Background Document. Office of Emergency and Remedial Response and Office of Radiation and Indoor Air. Washington, DC. OSWER No. 9355.4-16

U.S. EPA 2002. Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites. OSWER 9355.4-24. December 2002.