Note

The RAIS presents this updated PRG calculator in response to the following: incorporating RAGS Part E dermal guidance, incorporating chemical-specific parameters from the lastest EPI release, addition of air as a media, addition of ATSDR toxicity values, addition of California EPA toxicity values and conversion to a new database structure. The previous RAIS PRG calculator presented PRGs 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 PRGs for radionuclides, use the RAIS Preliminary Remediation Goals (PRGs) for Radionuclides calculator.

Currently, the agricultural equations for the RAIS chemical and radionuclide PRG 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 for radionuclides includes ingestion of produce and the RAIS radionuclide equation does not.

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 PRGs presented on this site are chemical-specific concentrations for individual contaminants in air, water, soil and biota that may warrant further investigation or site cleanup. It should be emphasized that PRGs are not cleanup goals or cleanup standards. PRGs should not be confused with or used as cleanup levels or cleanup standards required by the Applicable or Relevant and Appropriate Requirements (ARARs) under CERCLA. PRGs should not be used as cleanup levels for a site until the other remedy selection identified in the relevant portions of the National Contingency Plan (NCP), 40 CFR Part 300, have been evaluated and considered.

It should be noted that the PRGs 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://epa.gov/swerrims/riskassessment/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

Risk-based PRGs are derived from equations combining exposure assumptions with chemical-specific toxicity values.

2.2 Exposure Assumptions

PRGs 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 PRGs. 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 PRGs or site-specific screening levels are used, it is important to clearly demonstrate the equations and exposure parameters used in deriving PRGs at a site. A discussion of the assumptions used in the PRG calculations should be included in the decision document for a CERCLA site.

2.3 Toxicity Values

In a 2003 memo, EPA Superfund revised its hierarchy of human health toxicity values, providing three tiers of toxicity values. Three tier 3 sources were identified in that guidance, but it was acknowledged that additional tier 3 sources may exist. The 2003 guidance did not attempt to rank or put the identified tier 3 sources into a hierarchy of their own; however, when developing this calculator for the RAIS, a hierarchy was needed for all sources. The toxicity values used in this calculator are consistent with the 2003 guidance. Toxicity values from the following sources, in the order in which they are presented below, are used as the defaults in this calculator.

EPA's Integrated Risk Information System (IRIS)

Federal Register. Thursday December 7, 2000. Part II, Environmental Protection Agency. 40 CFR Parts 9, 141, and 142 - National Primary Drinking Water Regulations; Radionuclides; Final Rule. p 76713.

World Health Organization toxicity equivalence factors (TEFs).  Van den Berg et al. (2006) presents the WHO 2005 TEFs for carcinogenic dioxins and furans and polychlorinated biphenyls. Ahlborg et al. (1994) presents the WHO 1994 TEFs for carcinogenic polychlorinated biphenyls 170 and 180 in Toxic equivalency factors for dioxin-like PCBs: Report on a WHO-ECEH and IPCS consultation, December 1993. Chemosphere, Vol. 28, No. 6, 1049-1067. Polycyclic aromatic hydrocarbon TEFs are presented in Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons.

The Provisional values (PROV) derived by EPA's Superfund Health Risk Technical Support Center (STSC) for the EPA Superfund program.

The California Environmental Protection Agency/Office of Environmental Health Hazard Assessment's toxicity values- http://www.oehha.ca.gov/risk/ChemicalDB/index.asp

The Agency for Toxic Substances and Disease Registry (ATSDR) minimal risk levels (MRLs)- http://www.atsdr.cdc.gov/mrls/index.html

Other sources such as NCEA that were provided to the RAIS for use on the Oak Ridge Reservation.

The EPA Superfund program's Health Effects Assessment Summary. (Note that the HEAST website is not open to users outside of EPA, but access can be obtained for use on Superfund sites by contacting Dave Crawford at Crawford.Dave@epa.gov).

Values withdrawn from IRIS or HEAST.

When using toxicity values other than tier 1, users are encouraged to carefully review the basis for the value, and to document its use in decision documentation on a site.

2.3.1 Noncancer Toxicity Values

Noncancer toxicity values are reference doses and reference concentrations. The current, or recently completed, EPA toxicity assessments used in these screening tables (IRIS and PROV) define a reference dose, or RfD, as an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, or using categorical regression, with uncertainty factors generally applied to reflect limitations of the data used. RfDs are generally the toxicity value used most often in evaluating noncancer health effects at Superfund sites. Various types of RfDs are available depending on the exposure route (oral or inhalation), the critical effect (developmental or other), and the length of exposure being evaluated (chronic or subchronic). Some of the PRGs in this calculator also use Agency for Toxic Substances and Disease Registry (ATSDR) chronic oral minimal risk levels (MRLs) as oral chronic RfDs and intermediate oral MRLs as subchronic RfDs. The HEAST RfDs used in these PRGs were based upon then current EPA toxicity methodologies, but did not use the more recent benchmark dose or categorical regression methodologies.

2.3.1.1 Chronic Oral Reference Doses

A chronic oral RfD is defined as an estimate (with uncertainty spanning perhaps an order of magnitude or greater) of a daily oral exposure level for the human population, including sensitive subpopulations, that is likely to be without an appreciable risk of deleterious effects during a lifetime. Chronic oral RfDs are specifically developed to be protective for long-term exposure to a compound. As a guideline for Superfund program risk assessments, chronic oral RfDs generally should be used to evaluate the potential noncarcinogenic effects associated with exposure periods greater than 7 years (approximately 10 percent of a human lifetime). Chronic oral reference doses and ATSDR chronic oral MRLs are expressed in units of mg/kg-day.

2.3.1.2 Subchronic Oral Reference Doses

EPA has begun developing subchronic oral RfDs, which are useful for characterizing potential noncarcinogenic effects associated with shorter-term exposures by the oral route. As a guideline for Superfund program risk assessments, subchronic oral RfDs should generally be used to evaluate the potential noncarcinogenic effects of exposure periods between two weeks and seven years. Such short-term exposures can result when a particular activity is performed for a limited number of years or when a chemical with a short half-life degrades to negligible concentrations within several months. Subchronic oral reference doses and ATSDR intermediate oral MRLs are expressed in units of mg/kg-day.

2.3.2 Reference Concentrations

The current, or recently completed, EPA toxicity assessments used in these screening tables (IRIS and PPRTV assessments) define a reference concentration (RfC) as an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, or using categorical regression with uncertainty factors generally applied to reflect limitations of the data used. Various types of RfCs are available depending on the exposure route (oral or inhalation), the critical effect (developmental or other), and the length of exposure being evaluated (chronic or subchronic). These screening tables also use ATSDR chronic inhalation MRLs as chronic RfCs, intermediate inhalation MRLs as subchronic RfCs and California Environmental Protection Agency (chronic) Reference Exposure Levels (RELs) as chronic RfCs. These screening tables may also use some RfCs from EPA's HEAST tables.

2.3.2.1 Chronic Inhalation Reference Concentrations

The chronic inhalation reference concentration is generally used for continuous or near continuous inhalation exposures that occur for 7 years or more. EPA chronic inhalation reference concentrations are expressed in units of mg/m³. Cal EPA RELs are presented in µg/m³ and have been converted to mg/m³ for use in these screening tables. Some ATSDR inhalation MRLs are derived in parts per million (ppm) and some in mg/m³. For use in this table, all were converted into mg/m³.

2.3.2.2 Subchronic Inhalation Reference Concentrations

The subchronic inhalation reference concentration is generally used for inhalation exposures that are between 2 weeks and 7 years. Subchronic inhalation reference concentrations are expressed in units of mg/m3. As noted above, some ATSDR (intermediate) inhalation MRLs were derived in ppm and converted for use in this table into mg/m3.

2.3.3 Cancer Toxicity Values

Slope factors and unit risk values are used to assess cancer risk. A slope factor and the accompanying weight-of-evidence determination are the toxicity data most commonly used to evaluate potential human carcinogenic risks. Generally, the slope factor is a plausible upper-bound estimate of the probability of a response per unit intake of a chemical over a lifetime. The slope factor is used in risk assessments to estimate an upper-bound lifetime probability of an individual developing cancer as a result of exposure to a particular level of a potential carcinogen. Slope factors should always be accompanied by the weight-of-evidence classification to indicate the strength of the evidence that the agent is a human carcinogen. The ATSDR does not derive cancer toxicity values (e.g. slope factors or inhalation unit risks). Some slope factors used in these screening tables were derived by the California Environmental Protection Agency, whose methodologies are quite similar to those used by EPA's IRIS and PPRTV assessments.

2.3.3.1 Oral Slope Factors

The oral slope factor evaluates the probability of an individual developing cancer from oral exposure to contaminant levels over a lifetime. Oral slope factors are expressed in units of (mg/kg-day)^-1

2.3.3.2 Inhalation Unit Risk

The IUR is defined as the upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 µg/m³ in air. Inhalation unit risk toxicity values are expressed in units of (mg/m³)^-1.

2.3.4 Toxicity Equivalence Factors

Some chemicals are members of the same family and exhibit similar toxicological properties; however, they differ in the degree of toxicity. Therefore, a toxicity equivalence factor (TEF) must first be applied to adjust the measured concentrations to a toxicity equivalent concentration.

The following table contains the various dioxin-like toxicity equivalency factors for Dioxins, Furans and PCBs (Van den Berg et al. (2006)), which are the World Health Organization 2005 values.

* Di-ortho values come from Ahlborg, U.G., et al. (1994), which are the WHO 1994 values from Toxic equivalency factors for dioxin-like PCBs: Report on WHO-ECEH and IPCS consultation, December 1993 Chemosphere, Volume 28, Issue 6, March 1994, Pages 1049-1067.

Carcinogenic polycyclic aromatic hydrocarbons

Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons (EPA/600/R-93/089, July 1993), recommends that a toxicity equivalency factor (TEF) be used to convert concentrations of carcinogenic polycyclic aromatic hydrocarbons (cPAHs) to an equivalent concentration of benzo(a)pyrene when assessing the risks posed by these substances. These TEFs are based on the potency of each compound relative to that of benzo(a)pyrene. For the toxicity value database, these TEFs have been applied to the toxicity values. Although this is not in complete agreement with the direction in the aforementioned documents, this approach was used so that toxicity values could be generated for each cPAH. Additionally, it should be noted that computationally it makes little difference whether the TEFs are applied to the concentrations of cPAHs found in environmental samples or to the toxicity values as long as the TEFs are not applied to both. However, if the adjusted toxicity values are used, the user will need to sum the risks from all cPAHs as part of the risk assessment to derive a total risk from all cPAHs. A total risk from all cPAHs is what is derived when the TEFs are applied to the environmental concentrations of cPAHs and not to the toxicity values.

The following table presents the TEFs for cPAHs recommended in Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic Hydrocarbons.

Toxicity Equivalency Factors for Carcinogenic Polycyclic Aromatic Hydrocarbons

2.4 Chemical-specific Parameters

Several chemical specific parameters are needed for development of the SLs. Different hierarchies are used for organic and inorganic compounds.

2.4.1 Organic Compounds

1. Values were taken from http://www.epa.gov/opptintr/exposure/pubs/episuite.htm. These programs estimate various chemical-specific properties. The calculations for these SL tables use the experimental values for a property over the estimated values.

2. EPA Soil Screening Level (SSL) Exhibit C-1.

3. WATER8, which has been replaced with WATER9.

4. Syracuse Research Corporation (SRC). 2005. CHEMFATE Database. SRC. Syracuse, NY. Accessed July 2005.

5. Syracuse Research Corporation (SRC). 2005. PHYSPROP Database. SRC. Syracuse, NY. Accessed July 2005.

2.4.2 Inorganic Compounds

For unitless Henry's Law (ammonia, chlorine, cyanogen, cyanogen chloride, hydrogen cyanide only):

1. Syracuse Research Corporation (SRC). 2005. PHYSPROP Database. SRC. Syracuse, NY.
   (http://www.syrres.com/esc/physdemo.htm).

2. Yaws' Handbook of Thermodynamic and Physical Properties of Chemical Compounds. Knovel, 2003.
   (http://www.knovel.com).

For Kd (soil-water partition coefficient):

1. EPA Soil Screening Level (SSL) Table C.4 (http://www.epa.gov/superfund/health/conmedia/soil/index.htm).

2. Baes, C.F. 1984. Oak Ridge National Laboratory. A Review and Analysis of Parameters for Assessing Transport of Environmentally Released Radionuclides through Agriculture. http://homer.ornl.gov/baes/documents/ornl5786.html. Values are also found in Superfund Chemical Data Matrix (SCDM)
   (http://www.epa.gov/superfund/sites/npl/hrsres/tools/scdm.htm).

For molecular weights:

1. EPI (http://www.epa.gov/oppt/exposure/pubs/episuite.htm)

2. Syracuse Research Corporation (SRC). 2005. PHYSPROP Database. SRC. Syracuse, NY.
   ( http://www.syrres.com/esc/physdemo.htm).

For Vapor Pressure:

1. NIOSH Pocket Guide to Chemical Hazards (NPG), NIOSH Publication No. 97-140, February 2004.
   (http://www.cdc.gov/niosh/npg/npg.html).

2. 2) Syracuse Research Corporation (SRC). 2005. CHEMFATE Database. SRC. Syracuse, NY.
   ( http://www.syrres.com/esc/chemfate.htm).

3. Syracuse Research Corporation (SRC). 2005. PHYSPROP Database. SRC. Syracuse, NY.
   ( http://www.syrres.com/esc/physdemo.htm).

For diffusivity in air and water, if desired at all, for the gasses and mercuric compounds:

1. WATER 9, (EPA 2001). See section 4.9.2.

3. Using the PRG Calculator

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

• Prioritizing multiple sites or operable units or areas of concern within a facility or exposure units
• Setting risk-based detection limits for contaminants of potential concern (COPCs)
• Focusing future site investigation and risk assessment efforts
• Identifying contamination which may warrant cleanup
• Identifying sites, or portions of sites, which warrant no further action or investigation

PRGs are provided for multiple exposure pathways and for chemicals with both carcinogenic and noncarcinogenic effects. Default PRGs correspond to either a 10^-6 risk level for carcinogens or a Hazard Quotient (HQ) of 1 for non-carcinogens. Site specific PRGs corresponding to an HQ other than1 may be appropriate. Site specific PRGs based upon a cancer risk than 10^-6 can be calculated and may be appropriate based upon site specific considerations. However, caution is recommended to ensure that cumulative cancer risk for all actual and potential carcinogenic contaminants found at the site do not have a residual (after site cleanup, or when it has been determined that no site cleanup is required) cancer risk exceeding 10^-4.

3.1 Developing a Conceptual Site Model

When using PRGs, the exposure pathways of concern and site conditions should match those taken into account by the calculator. (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 PRGs 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 Superfund: Users Guide (EPA 1996) contains the steps for developing a CSM.

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

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

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

3.2 Background

Natural background concentrations should be considered prior to applying PRGs. Background levels 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).

3.3 Potential Problems

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

• Applying PRGs to a site without adequately developing a conceptual site model that identifies relevant exposure pathways and exposure scenarios.
• Not considering the effects from the presence of multiple contaminants, where appropriate.
• Use of the PRGs or cleanup levels without adequate consideration of the other NCP remedy selection criteria on CERCLA sites.
• Use of outdated PRGs (as more recent toxicity values may exist).

4. Technical Support Documentation

The PRGs consider human exposure to individual contaminants in air, water, soil and biota. The equations and technical discussion are aimed at developing risk-based PRGs. 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 PRGs on a site should be presented with supporting rationale in the decision document on CERCLA sites.

4.1 Residential Soil

4.1.1 Noncancer

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

incidental ingestion of soil

inhalation of particulates emitted from soil

dermal contact with soil

Total

4.1.2 Carcinogenic

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

incidental ingestion of soil

inhalation of particulates emitted from soil

dermal contact with soil

Total

4.1.3 Mutagenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil,

dermal contact with soil,

Total.

4.1.4 Vinyl Chloride - Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil,

dermal contact with soil,

Total.

4.2 Outdoor Worker Soil

4.2.1 Noncancer

The outdoor worker soil land use equation, presented here, contains the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal exposure.

Total.

4.2.2 Carcinogenic

The outdoor worker soil land use equation, presented here, contains the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal exposure.

Total.

4.3 Excavation/Construction Outdoor Worker Soil

4.3.1 Noncancer

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, and

dermal exposure.

Total.

4.3.2 Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal exposure.

Total.

4.4 Indoor Worker Soil

4.4.1 Noncancer

The indoor worker soil land use equation, presented here, contains the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

Total.

4.4.2 Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

Total.

4.5 Recreational Soil/Sediment

4.5.1 Noncancer

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

incidental ingestion of soil,

inhalation of particulates emitted from soil,

dermal contact with soil.

Total.

4.5.2 Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil,

dermal contact with soil.

Total.

4.5.3 Mutagenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil,

dermal contact with soil.

Total.

4.5.4 Vinyl Chloride - Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil,

dermal contact with soil.

Total.

4.6 Tapwater

4.6.1 Noncarcinogenic

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

ingestion of water,

dermal contact with water and

inhalation of volatiles

Total.

4.6.2 Carcinogenic

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

ingestion of water,

dermal contact with water and

inhalation of volatiles

Total.

4.6.3 Mutagenic

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

ingestion of water,

dermal contact with water and

inhalation of volatiles

Total.

4.6.4 Vinyl Chloride - Carcinogenic

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

ingestion of water,

dermal contact with water and

inhalation of volatiles

Total.

4.7 Recreation Surface Water

4.7.1 Noncarcinogenic

The surface water land use equations, presented here, contain the following exposure routes:

ingestion of water and

dermal contact with water

Total.

4.7.2 Carcinogenic

The surface water land use equations, presented here, contain the following exposure routes:

ingestion of water and

dermal contact with water

Total.

4.8 Ambient Air

4.8.1 Resident

4.8.1.1 Noncarcinogenic

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

inhalation of volatiles

4.8.1.2 Carcinogenic

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

inhalation of volatiles

4.8.1.3 Mutagenic

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

inhalation of volatiles

4.8.1.4 Vinyl Chloride - Carcinogenic

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

inhalation of volatiles

4.8.2 Outdoor Worker

4.8.2.1 Noncarcinogenic

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

inhalation of volatiles

4.8.2.2 Carcinogenic

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

inhalation of volatiles

4.8.3 Indoor Worker

4.8.3.1 Noncarcinogenic

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

inhalation of volatiles

4.8.3.2 Carcinogenic

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

inhalation of volatiles

4.8.4 Excavation/construction Worker

4.8.4.1 Noncarcinogenic

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

inhalation of volatiles

4.8.4.2 Carcinogenic

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

inhalation of volatiles

4.9 Ingestion of Fish

4.9.1 Concentration in Fish

4.9.1.1 Noncarcinogenic

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

consumption of fish.

4.9.1.2 Carcinogenic

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

consumption of fish.

4.9.2 Concentration in Surface Water

4.9.2.1 Noncarcinogenic

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

consumption of fish.

4.9.2.2 Carcinogenic

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

4.10.1.1 Noncarcinogenic

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

consumption of fruits and vegetables.

4.10.1.2 Carcinogenic

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

4.10.2.1 Noncarcinogenic

consumption of fruits and vegetables.

4.10.2.2 Carcinogenic

consumption of fruits and vegetables.

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

4.10.3.1 Noncarcinogenic

consumption of fruits and vegetables.

4.10.3.2 Carcinogenic

consumption of fruits and vegetables.

4.10.4 Back-calculated Concentration in Soil and Water for Fruits and Vegetables

4.10.4.1 Noncarcinogenic

consumption of fruits and vegetables.

4.10.4.2 Carcinogenic

consumption of fruits and vegetables.

4.10.5 Concentration in Milk

4.10.5.1 Noncarcinogenic

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

consumption of milk.

4.10.5.2 Carcinogenic

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

consumption of milk.

4.10.6 Back-calculated Concentration in Water Only for Milk

4.10.6.1 Noncarcinogenic

consumption of milk.

4.10.6.2 Carcinogenic

consumption of milk.

4.10.7 Back-calculated Concentration in Soil Only for Milk

4.10.7.1 Noncarcinogenic

consumption of milk.

4.10.7.2 Carcinogenic

consumption of milk.

4.10.8 Back-calculated Concentration in Soil and Water for Milk

4.10.8.1 Noncarcinogenic

consumption of milk.

4.10.8.2 Carcinogenic

consumption of milk.

4.10.9 Concentration in Beef

4.10.9.1 Noncarcinogenic

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

consumption of beef.

4.10.9.2 Carcinogenic

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

consumption of beef.

4.10.10 Back-calculated Concentration in Water Only for Beef

4.10.10.1 Noncarcinogenic

consumption of beef.

4.10.10.2 Carcinogenic

consumption of beef.

4.10.11 Back-calculated Concentration in Soil Only for Beef

4.10.11.1 Noncarcinogenic

consumption of beef.

4.10.11.2 Carcinogenic

consumption of beef.

4.10.12 Back-calculated Concentration in Soil and Water for Beef

4.10.12.1 Noncarcinogenic

consumption of beef.

4.10.12.2 Carcinogenic

consumption of beef.

4.11 Supporting Equations and Parameter Discussion

There are two inhalation variables in the above land use equations that require further explanation: the particulate emission factor (PEF) and the volatilization factor (VF).

4.11.1 Particulate Emission Factor (PEF)

Inhalation of contaminants 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.

4.11.2 Volatilization Factor (VF)

The soil-to-air VF is used to define the relationship between the concentration of the contaminant in soil and the flux of the volatilized contaminant to air. VF is calculated from the equation below using chemical-specific properties and either site-measured or default values for soil moisture, dry bulk density, and fraction of organic carbon in soil. The Soil Screening Guidance: User's Guide describes how to develop site measured values for these parameters.

VF is only calculated for volatile organic compounds (VOCs). VOCs, for the purpose of this guidance, are chemicals with a Henry's Law constant of 1 x 10^-5 atm-m³/mole or greater and with a molecular weight of less than 200 g/mole.

Diffusivity in Water (cm²/s)

Diffusivity in water can be calculated from the chemical's molecular weight and density, using the following correlation equation based on WATER9 (U.S. EPA, 2001):

If density is not available, diffusivity in water can be calculated using the correlation equation based on U.S. EPA (1987). The value for diffusivity in water must be greater than zero. No maximum limit is enforced.

Diffusivity in Air (cm²/s).

Diffusivity in air can be calculated from the chemical's molecular weight and density, using the following correlation equation based on WATER9 (U.S. EPA, 2001):

If density is not available, diffusivity in air can be calculated using the correlation equation based on U.S. EPA (1987). For dioxins, diffusivity in air can be calculated from the molecular weight using the correlation equation based on EPA's Dioxin Reassessment (U.S. EPA, 2000).

4.11.3 Target Risk and Hazard Quotient

Additional significant inputs which can be modified when using the calculator are the target levels of cancer and non-cancer risk. The target risk levels for calculating generic PRGs are an extension of the Superfund program's "Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions" (OSWER Directive 9355.0-30) guidance which states:

"Where the cumulative carcinogenic site risk to an individual based on reasonable maximum exposure for both current and future land use is less than 10^-4 and the non-carcinogenic hazard quotient is less than 1, action generally is not warranted unless there are adverse environmental impacts. However, if Maximum Contaminant Levels (MCLs) or non-zero Maximum Contaminant Level Goals (MCLGs) are exceeded, action generally is warranted."

Action is generally not warranted when the cumulative site risk level is less than 10^-4 for carcinogens or a hazard quotient of 1 for non-carcinogens. Since PRGs are meant to be protective levels, the default risk level for PRGs for individual chemicals correspond to a 10^-6 risk level for carcinogens and a Hazard Quotient (HQ) of 1 for non-carcinogens.

The site decision document for the site should explain the rationale for using cancer and non-cancer risk levels other than the default values in calculated PRGs.

5. Special Considerations

Most of the PRGs are readily derived by referring to the above equations. However, there are some cases for which the standard equations do no apply and/or external adjustments to the PRGs are not recommended. These special case chemicals are discussed below.

5.1 Cadmium

The PRGs for Cadmium are based on the oral RfD for water which is slightly more conservative (by a factor of 2) than the RfD for food. Because the PRGs are considered screening values, we elected to use the more conservative RfD for cadmium. However, reasonable arguments could be made for applying an RfD for food (instead of the oral RfD for water) for some media such as soils.

5.2 Lead

Residential PRGs for Lead (Region 9 EPA and California EPA) are derived based on pharmacokinetic models. Both EPA's Integrated Exposure Uptake Biokinetic (IEUBK) Model and California's LeadSpread model are designed to predict the probable blood lead concentrations for children between six months and seven years of age who have been exposed to lead through various sources (air, water, soil, dust, diet and in utero contributions from the mother). Run in the reverse, these models also allow the user to calculate lead PRGs that are considered "acceptable" by EPA or the State of California.

EPA uses a second Adult Lead Model to estimate PRGs for an industrial setting. This PRG is intended to protect a fetus that may be carried by a pregnant female worker. It is assumed that a cleanup goal that is protective of a fetus will also afford protection for male or female adult workers. The model equations were developed to calculate cleanup goals such that there would be no more than a 5% probability that fetuses exposed to lead would exceed a blood lead level (PbB) of 10 F g/dL. An updated screening level for soil lead at commercial/industrial (i.e., nonresidential) sites of 800 ppm is based on a recent analysis of the combined phases of NHANES III that chooses a cleanup goal protective of all subpopulations.

For more information on EPA's lead models and other lead-related topics, please go to:

http://www.epa.gov/oerrpage/superfund/health/contaminants/lead/index.htm.

For more information on California's LeadSpread Model and Cal-Modified PRGs for lead, please go to:

http://www.dtsc.ca.gov/AssessingRisk/leadspread.cfm.

5.3 Manganese

The IRIS RfD (0.14 mg/kg-day) for manganese is from all sources, including diet. The author of the IRIS assessment for manganese recommended that the dietary contribution from the normal U.S. diet (an upper limit of 5 mg/day) be subtracted when evaluating non-food (e.g. drinking water or soil) exposures to manganese, leading to a RfD of 0.071 mg/kg-day for non-food items. The explanatory text in IRIS further recommends using a modifying factor of 3 when calculating risks associated with non-food sources due to a number of uncertainties that are discussed in the IRIS file for manganese, leading to a RfD of 0.024 mg/kg-day. This modified RfD has been used in the derivation of some manganese screening levels, such as earlier Region 9 PRGs for soil and water. For more information regarding the Manganese RfD, users are advised to contact the author of the IRIS assessment on Manganese.

5.4 Vanadium and Thallium Compounds

The oral RfD for Thallium, used in this website, is derived from the IRIS oral RfD for Thallium Sulfate by factoring out the molecular weight (MW) of the sulfate ion. Thallium Sulfate (Tl₂S0₄) has a molecular weight of 504.82. The two atoms of Thallium contribute 81% of the MW. Thallium Sulfate's oral RfD of 8E-05 multiplied by 81% gives a Thallium oral RfD of 6.48E-05.

The oral RfD toxicity value for Vanadium, used in this website, is derived from the IRIS oral RfD for Vanadium Pentoxide by factoring out the molecular weight (MW) of the oxide ion. Vanadium Pentoxide (V₂0₅) has a molecular weight of 181.88. The two atoms of Vanadium contribute 56% of the MW. Vanadium Pentoxide's oral RfD of 9E-03 multiplied by 56% gives a Vanadium oral RfD of 5.04E-03.

5.5 Uranium

"Uranium Soluble Salts" uses the IRIS oral RfD of 3E-03. For the insoluble salts of Uranium, the oral RfD of 6E-04 may be used from the Federal Register, Thursday December 7, 2000. Part II, Environmental Protection Agency. 40 CFR Parts 9, 141, and 142 - National Primary Drinking Water Regulations; Radionuclides; Final Rule. p 76713.

5.6 Chromium (VI)

For Chromium (VI) (Cr6), IRIS shows an air unit risk of 1.2E-2 per (µg/m 3). However, the supporting documentation in the IRIS file states that this toxicity value is based on an assumed 1:6 ratio of Cr6:Cr3. Because of this assumption and in an effort to be transparent, RSLs based on this cancer toxicity value are presented as "Chromium, Total (1:6 ratio Cr VI:III)" numbers.

In the RSL Table, the Cr6 specific value (assuming 100% Cr6) is derived by multiplying the IRIS Cr6 value by 7. This is considered to be a conservative and protective and is consistent with the State of California's interpretation of the Mancuso study that forms the basis of Cr6's toxicity values.

It is recommended that valent-specific data for Chromium be collected when Chromium is likely to be an important contaminant at a site, and when Cr6 may exist. In the absence of valent-specific data, screening levels for total Chromium are provided. If you are working on a chromium site, you may want to contact the appropriate regulatory officials in your region to determine what their position is on this issue.

5.7 Aminodinitrotoluenes

The IRIS oral RfD of 2E-03 for 2,4-Dinitrotoluene is used as a surrogate for 2-Amino-4,6-Dinitrotoluene and 4-Amino-2,6-Dinitrotoluene.

5.8 PCBs

Aroclor 1016 is considered low risk and assigned appropriate toxicity values. All other Aroclors are assigned the high risk toxicity values.

5.9 Soil Saturation Limit

The soil saturation concentration, "sat", corresponds to the contaminant concentration in soil at which the absorptive limits of the soil particles, the solubility limits of the soil pore water, and saturation of soil pore air have been reached. Above this concentration, the soil contaminant may be present in free phase, i.e., nonaqueous phase liquids (NAPLs) for contaminants that are liquid at ambient soil temperatures and pure solid phases for compounds that are solid at ambient soil temperatures.

Equation 4-10 is used to calculate "sat" for each volatile contaminant. As an update to RAGS HHEM, Part B (USEPA 1991a), this equation takes into account the amount of contaminant that is in the vapor phase in soil in addition to the amount dissolved in the soil's pore water and sorbed to soil particles.

Chemical-specific "sat" concentrations must be compared with each VF-based PRG, because a basic principle of the PRG volatilization model is not applicable when free-phase contaminants are present. How these cases are handled depends on whether the contaminant is liquid or solid at ambient temperatures. Liquid contaminant that have a VF-based PRG that exceeds the "sat" concentration are set equal to "sat" whereas for solids (e.g., PAHs), soil screening decisions are based on the appropriate PRGs for other pathways of concern at the site (e.g., ingestion).

5.10 PRGs exceeding Unity

Risk-based PRGs for some chemicals in soil may exceed unity (>1,000,000 mg/kg), which cannot occur in the environment.

5.11 PRG Theoretical Ceiling Limit

The ceiling limit of 10⁺⁶ mg/kg is equivalent to a chemical representing 10% by weight of the soil sample. At this contaminant concentration (and higher), the assumptions for soil contact may be violated (for example, soil adherence and windborne dispersion assumptions) due to the presence of the foreign substance itself.

5.12 Mutagens

Some of the cancer causing analytes in this tool operate by a mutagenic mode of action for carcinogenesis. There is reason to surmise that some chemicals with a mutagenic mode of action, which would be expected to cause irreversible changes to DNA, would exhibit a greater effect in early-life versus later-life exposure. Cancer risk to children in the context of the U.S. Environmental Protection Agency's cancer guidelines (U.S. EPA, 2005) includes both early-life exposures that may result in the occurrence of cancer during childhood and early-life exposures that may contribute to cancers later in life. In keeping with this guidance, separate cancer risk equations are presented for mutagens. The mutagen vinyl chloride has a unique set of equations. Consult Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens, EPA/630/R-03/003F, March 2005 for further information. http://www.epa.gov/oswer/riskassessment/sghandbook/chemicals.htm provides more detailed information about what chemicals are considered mutagens.

Table 1. Standard Default Factors

Symbol	Definition (units)	Default	Reference
PRGs
PRGres-sol-nc-ing	Resident Soil Noncarcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-nc-der	Resident Soil Noncarcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-nc-inh	Resident Soil Noncarcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-nc-tot	Resident Soil Noncarcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-ca-ing	Resident Soil Carcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-ca-der	Resident Soil Carcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-ca-inh	Resident Soil Carcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-ca-tot	Resident Soil Carcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-sol-mu-ing	Resident Soil Mutagenic Ingestion (mg/kg)	Mutagen-specific	Determined in this calculator
PRGres-sol-mu-der	Resident Soil Mutagenic Dermal (mg/kg)	Mutagen-specific	Determined in this calculator
PRGres-sol-mu-inh	Resident Soil Mutagenic Inhalation (mg/kg)	Mutagen-specific	Determined in this calculator
PRGres-sol-mu-tot	Resident Soil Mutagenic Total (mg/kg)	Mutagen-specific	Determined in this calculator
PRGres-soil-ca-vc-ing	Resident Soil Carcinogenic Vinyl Chloride Ingestion (mg/kg)	Vinyl Chloride -specific	Determined in this calculator
PRGres-soil-ca-vc-der	Resident Soil Carcinogenic Vinyl Chloride Dermal (mg/kg)	Vinyl Chloride-specific	Determined in this calculator
PRGres-soil-ca-vc-inh	Resident Soil Carcinogenic Vinyl Chloride Inhalation (mg/kg)	Vinyl Chloride-specific	Determined in this calculator
PRGres-soil-ca-vc-tot	Resident Soil Carcinogenic Vinyl Chloride Total (mg/kg)	Vinyl Chloride-specific	Determined in this calculator
PRGow-sol-nc-ing	Outdoor Worker Soil Noncarcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGow-sol-nc-der	Outdoor Worker Soil Noncarcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGow-sol-nc-inh	Outdoor Worker Soil Noncarcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGow-sol-nc-tot	Outdoor Worker Soil Noncarcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGow-sol-ca-ing	Outdoor Worker Soil Carcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGow-sol-ca-der	Outdoor Worker Soil Carcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGow-sol-ca-inh	Outdoor Worker Soil Carcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGow-sol-ca-tot	Outdoor Worker Soil Carcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-nc-ing	Excavation/Construction Worker Soil Noncarcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-nc-der	Excavation/Construction Worker Soil Noncarcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-nc-inh	Excavation/Construction Worker Soil Noncarcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-nc-tot	Excavation/Construction Worker Soil Noncarcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-ca-ing	Excavation/Construction Worker Soil Carcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-ca-der	Excavation/Construction Worker Soil Carcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-ca-inh	Excavation/Construction Worker Soil Carcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGew-sol-ca-tot	Excavation/Construction Worker Soil Carcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGiw-nc-ing	Indoor Worker Soil Noncarcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGiw-nc-inh	Indoor Worker Soil Noncarcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGiw-nc-tot	Indoor Worker Soil Noncarcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGiw-ca-ing	Indoor Worker Soil Carcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGiw-ca-inh	Indoor Worker Soil Carcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGiw-ca-tot	Indoor Worker Soil Carcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-nc-ing	Recreation Soil Noncarcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-nc-der	Recreation Soil Noncarcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-nc-inh	Recreation Soil Noncarcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-nc-tot	Recreation Soil Noncarcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-ca-ing	Recreation Soil Carcinogenic Ingestion (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-ca-der	Recreation Soil Carcinogenic Dermal (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-ca-inh	Recreation Soil Carcinogenic Inhalation (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-ca-tot	Recreation Soil Carcinogenic Total (mg/kg)	Contaminant-specific	Determined in this calculator
PRGrec-sol-mu-ing	Recreation Soil Mutagenic Ingestion (mg/kg)	Mutagen-specific	Determined in this calculator
PRGrec-sol-mu-der	Recreation Soil Mutagenic Dermal (mg/kg)	Mutagen-specific	Determined in this calculator
PRGrec-sol-mu-inh	Recreation Soil Mutagenic Inhalation (mg/kg)	Mutagen-specific	Determined in this calculator
PRGrec-sol-mu-tot	Recreation Soil Mutagenic Total (mg/kg)	Mutagen-specific	Determined in this calculator
PRGrec-soil-ca-vc-ing	Recreation Soil Carcinogenic Vinyl Chloride Ingestion (mg/kg)	Vinyl Chloride -specific	Determined in this calculator
PRGrec-soil-ca-vc-der	Recreation Soil Carcinogenic Vinyl Chloride Dermal (mg/kg)	Vinyl Chloride-specific	Determined in this calculator
PRGrec-soil-ca-vc-inh	Recreation Soil Carcinogenic Vinyl Chloride Inhalation (mg/kg)	Vinyl Chloride-specific	Determined in this calculator
PRGrec-soil-ca-vc-tot	Recreation Soil Carcinogenic Vinyl Chloride Total (mg/kg)	Vinyl Chloride-specific	Determined in this calculator
PRGwater-nc-ing	Resident Tapwater (Groundwater) Noncarcinogenic Ingestion (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-nc-der	Resident Tapwater (Groundwater) Noncarcinogenic Dermal (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-nc-inh	Resident Tapwater (Groundwater) Noncarcinogenic Inhalation (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-nc-tot	Resident Tapwater (Groundwater) Noncarcinogenic Total (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-ca-ing	Recreation Tapwater (Groundwater) Carcinogenic Ingestion (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-ca-der	Resident Tapwater (Groundwater) Carcinogenic Dermal (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-ca-inh	Resident Tapwater (Groundwater) Carcinogenic Inhalation (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-ca-tot	Resident Tapwater (Groundwater) Carcinogenic Total (µg/L)	Contaminant-specific	Determined in this calculator
PRGres-water-ca-vc-ing	Resident Tapwater (Groundwater) Carcinogenic Vinyl Chloride Ingestion (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-ca-vc-der	Resident Tapwater (Groundwater) Carcinogenic Vinyl Chloride Dermal (µg/L)	Contaminant-specific	Determined in this calculator
PRGres-water-ca-vc-inh	Resident Tapwater (Groundwater) Carcinogenic Vinyl Chloride Inhalation (µg/L)	Contaminant-specific	Determined in this calculator
PRGres-water-ca-vc-tot	Resident Tapwater (Groundwater) Carcinogenic Vinyl Chloride Total (µg/L)	Contaminant-specific	Determined in this calculator
PRGwater-mu-ing	Resident Tapwater (Groundwater) Mutagenic Ingestion (µg/L)	Mutagen-specific	Determined in this calculator
PRGwater-mu-der	Resident Tapwater (Groundwater) Mutagenic Dermal (µg/L)	Mutagen-specific	Determined in this calculator
PRGwater-mu-inh	Resident Tapwater (Groundwater) Mutagenic Inhalation (µg/L)	Mutagen-specific	Determined in this calculator
PRGwater-mu-tot	Resident Tapwater (Groundwater) Mutagenic Total (µg/L)	Mutagen-specific	Determined in this calculator
PRGrec-water-nc-ing	Recreation Surface Water Noncarcinogenic Ingestion (µg/L)	Contaminant-specific	Determined in this calculator
PRGrec-water-nc-der	Recreation Surface Water Noncarcinogenic Dermal (µg/L)	Contaminant-specific	Determined in this calculator
PRGrec-water-nc-tot	Recreation Surface Water Noncarcinogenic Total (µg/L)	Contaminant-specific	Determined in this calculator
PRGrec-water-ca-ing	Recreation Surface Water Carcinogenic Ingestion (µg/L)	Contaminant-specific	Determined in this calculator
PRGrec-water-ca-der	Recreation Surface Water Carcinogenic Dermal (µg/L)	Contaminant-specific	Determined in this calculator
PRGrec-water-ca-tot	Recreation Surface Water Carcinogenic Total (µg/L)	Contaminant-specific	Determined in this calculator
PRGres-air-nc	Resident Air Noncarcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGres-air-ca	Resident Air Carcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGres-air-ca-vinyl chloride	Resident Air Carcinogenic Vinyl Chloride (µg/m3)	Vinyl Chloride-specific	Determined in this calculator
PRGres-air-mu	Resident Air Mutagenic (µg/m3)	Mutagen-specific	Determined in this calculator
PRGow-air-nc	Outdoor Worker Air Noncarcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGow-air-ca	Outdoor Workder Air Carcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGiw-air-nc	Indoor Worker Air Noncarcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGiw-air-ca	Indoor Workder Air Carcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGew-air-nc	Excavation/Construction Worker Air Noncarcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGew-air-ca	Excavation/Construction Workder Air Carcinogenic (µg/m3)	Contaminant-specific	Determined in this calculator
PRGres-fsh-nc-ing	Resident Fish Noncarcinogenic (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-fsh-ca-ing	Resident Fish Carcinogenic (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-fshw-nc-ing	Resident Surface Water Fish Noncarcinogenic (mg/kg)	Contaminant-specific	Determined in this calculator
PRGres-fshw-ca-ing	Resident Surface Water Fish Carcinogenic (mg/kg)	Contaminant-specific	Determined in this calculator
PRGag-prod-nc-ing	Agriculture Fruits and Vegetables Noncarcinogenic Ingestion	Contaminant-specific	Determined in this calculator
PRGag-prod-ca-ing	Agriculture Fruits and Vegetables Carcinogenic Ingestion	Contaminant-specific	Determined in this calculator
PRGw-ag-prod-nc-ing	Agriculture Fruits and Vegetables Noncarcinogenic Back-calculated Concentration in Water Ingestion	Contaminant-specific	Determined in this calculator
PRGw-ag-prod-ca-ing	Agriculture Fruits and Vegetables Carcinogenic Back-calculated Concentration in Water Ingestion	Contaminant-specific	Determined in this calculator
PRGs-ag-prod-nc-ing	Agriculture Fruits and Vegetables Noncarcinogenic Back-calculated Concentration in Soil Ingestion	Contaminant-specific	Determined in this calculator
PRGs-ag-prod-ca-ing	Agriculture Fruits and Vegetables Carcinogenic Back-calculated Concentration in Soil Ingestion	Contaminant-specific	Determined in this calculator
PRGsw-ag-prod-nc-ing	Agriculture Fruits and Vegetables Noncarcinogenic Back-calculated Concentration in Soil and Water Ingestion	Contaminant-specific	Determined in this calculator
PRGsw-ag-prod-ca-ing	Agriculture Fruits and Vegetables Carcinogenic Back-calculated Concentration in Soil and Water Ingestion	Contaminant-specific	Determined in this calculator
PRGag-milk-nc-ing	Agriculture Milk Noncarcinogenic Ingestion	Contaminant-specific	Determined in this calculator
PRGag-milk-ca-ing	Agriculture Milk Carcinogenic Ingestion	Contaminant-specific	Determined in this calculator
PRGw-ag-milk-nc-ing	Agriculture Milk Noncarcinogenic Back-calculated Concentration in Water Ingestion	Contaminant-specific	Determined in this calculator
PRGw-ag-milk-ca-ing	Agriculture Milk Carcinogenic Back-calculated Concentration in Water Ingestion	Contaminant-specific	Determined in this calculator
PRGs-ag-milk-nc-ing	Agriculture Milk Noncarcinogenic Back-calculated Concentration in Soil Ingestion	Contaminant-specific	Determined in this calculator
PRGs-ag-milk-ca-ing	Agriculture Milk Carcinogenic Back-calculated Concentration in Soil Ingestion	Contaminant-specific	Determined in this calculator
PRGsw-ag-milk-nc-ing	Agriculture Milk Noncarcinogenic Back-calculated Concentration in Soil and Water Ingestion	Contaminant-specific	Determined in this calculator
PRGsw-ag-milk-ca-ing	Agriculture Milk Carcinogenic Back-calculated Concentration in Soil and Water Ingestion	Contaminant-specific	Determined in this calculator
PRGag-beef-nc-ing	Agriculture Beef Noncarcinogenic Ingestion	Contaminant-specific	Determined in this calculator
PRGag-beef-ca-ing	Agriculture Beef Carcinogenic Ingestion	Contaminant-specific	Determined in this calculator
PRGw-ag-beef-nc-ing	Agriculture Beef Noncarcinogenic Back-calculated Concentration in Water Ingestion	Contaminant-specific	Determined in this calculator
PRGw-ag-beef-ca-ing	Agriculture Beef Carcinogenic Back-calculated Concentration in Water Ingestion	Contaminant-specific	Determined in this calculator
PRGs-ag-beef-nc-ing	Agriculture Beef Noncarcinogenic Back-calculated Concentration in Soil Ingestion	Contaminant-specific	Determined in this calculator
PRGs-ag-beef-ca-ing	Agriculture Beef Carcinogenic Back-calculated Concentration in Soil Ingestion	Contaminant-specific	Determined in this calculator
PRGsw-ag-beef-nc-ing	Agriculture Beef Noncarcinogenic Back-calculated Concentration in Soil and Water Ingestion	Contaminant-specific	Determined in this calculator
PRGsw-ag-beef-ca-ing	Agriculture Beef Carcinogenic Back-calculated Concentration in Soil and Water Ingestion	Contaminant-specific	Determined in this calculator
Toxicity Values
RfDo	Chronic Oral Reference Dose (mg/kg-day)	Contaminant-specific	EPA Superfund hierarchy
RfC	Chronic Inhalation Reference Concentration (mg/m3)	Contaminant-specific	EPA Superfund hierarchy
CSFo	Chronic oral Slope Factor (mg/kg-day)-1	Contaminant-specific	EPA Superfund hierarchy
IUR	Chronic Inhalation Unit Risk (µg/m3)-1	Contaminant-specific	EPA Superfund hierarchy
Miscellaneous Variables
TR	target risk (unitless)	1 × 10-6	Determined in this calculator
THQ	target hazard quotient (unitless)	1	Determined in this calculator
Ingestion, Inhalation and Dermal Contact Exposure Parameters
K	Andelman Volatilization Factor (L/m3)	0.5	U.S. EPA 1991b (pg. 20)
Kp	permeability constant (cm/hr)	Contaminant-specific
BWa	Body Weight - adult (kg)	70	U.S. EPA 1991a (pg. 15)
BWc	Body Weight - child (kg)	15	U.S. EPA 1991a (pg. 15)
BWow	Body Weight - outdoor worker (kg)	70	U.S. EPA 1991a (pg. 15)
BWiw	Body Weight - indoor worker (kg)	70	U.S. EPA 1991a (pg. 15)
BWew	Body Weight - excavation/construction worker (kg)	70	U.S. EPA 1991a (pg. 15)
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-year/kg-day)	114	Calculated using the age-adjusted intake factors equation
IFSMadj	Mutagenic Resident Soil Ingestion Rate - Age-adjusted (mg-year/kg-day)	489.5	Calculated using the age-adjusted intake factors equation
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-year/kg-day)	1.086	Calculated using the age-adjusted intake factors equation
IFWMadj	Mutagenic Drinking Water Ingestion Rate - Age-adjusted (L-year/kg-day)	3.39	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)	14.8×103	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPfr-a	Produce Ingestion Rate - Fruit - Adult (mg/day)	56.2×103	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPfr-adj	Produce Ingestion Rate - Fruit - Age-adjusted (mg-year/kg-day)	25.2×103	Calculated using the aged adjusted intake factors equation
IRPvg-c	Produce Ingestion Rate - Vegetables - Child (mg/day)	10.4×103	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPvg-a	Produce Ingestion Rate - Vegetables - Adult (mg/day)	28.5×103	U.S. EPA 1997a (Table 13-61). U.S. EPA 1998 (Table C-1-2)
IRPvg-adj	Produce Ingestion Rate - Vegetables - Age-adjusted (mg-year/kg-day)	13.9×103	Calculated using the aged adjusted intake factors equation
IRMc	Milk Ingestion Rate - Child (mg/day)	265×103	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRMa	Milk Ingestion Rate - Adult (mg/day)	615×103	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRMadj	Milk Ingestion Rate - Age-adjusted (mg-year/kg-day)	317×103	Calculated using the aged adjusted intake factors equation
IRBc	Beef Ingestion Rate - Child (mg/day)	12.9×103	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRBa	Beef Ingestion Rate - Adult (mg/day)	138×103	U.S. EPA 1997a (Table 13-28). U.S. EPA 1998 (Table C-1-3)
IRBadj	Beef Ingestion Rate - Age-adjusted (mg-year/kg-day)	52.5×103	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.
BCF	Fish Bioconcentration Factor (L/kg)	Contaminant-specific
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
CFb	Fraction of Beef Consumed that is Contaminated	1	U.S. EPA 1998
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)
SAc	Resident soil surface area - child (cm2)	2800	U.S. EPA 2002 (Exhibit 1-2)
SAa	Resident soil surface area - adult (cm2)	5700	U.S. EPA 2002 (Exhibit 1-2)
SArec	Recreation surface water surface area (cm2)	18000	U.S. EPA 2004
AFc	Resident soil adherence factor-child (mg/cm2)	0.2	U.S. EPA 2002 (Exhibit 1-2)
AFa	Resident soil adherence factor-adult (mg/cm2)	0.07	U.S. EPA 2002 (Exhibit 1-2)
DFSadj	Resident soil dermal contact factor- age-adjusted (mg-year/kg-day)	361	Calculated using the age-adjusted intake factors equation
DFSMadj	Mutagenic Resident soil dermal contact factor- age-adjusted (mg-year/kg-day)	1445	Calculated using the age-adjusted intake factors equation
SAow	Outdoor Worker soil surface area - adult (cm2)	3300	U.S. EPA 2002 (Exhibit 1-2)
SAow	Excavation/Construction Worker soil surface area - adult (cm2)	3300	U.S. EPA 2002 (Exhibit 1-2)
AFow	Worker soil adherence factor-child (mg/cm2)	0.2	U.S. EPA 2002 (Exhibit 1-2)
AFew	Excavation/Construction Worker soil adherence factor-child (mg/cm2)	0.3	U.S. EPA 2002 (Exhibit 1-2)
ABSd	Fraction of contaminant absorbed dermally from soil (unitless)	Contaminant-specific	U.S. EPA 2004 (Exhibit 3-4)
GIABS	Fraction of contaminant absorbed in gastrointestinal tract (unitless) Note: if the GIABS is >50% then it is set to 100% for the calculation of dermal toxicity values.	Contaminant-specific	U.S. EPA 2004 (Exhibit 4-1)
Exposure Frequency, Exposure Duration, Exposure Time and Averaging Time Variables
ATr	Averaging time - resident (days/year)	365	U.S. EPA 1989 (pg. 6-23)
ATrec	Averaging time - recreation (days/year)	365	U.S. EPA 1989 (pg. 6-23)
ATow	Averaging time - outdoor worker (days/year)	365	U.S. EPA 1989 (pg. 6-23)
ATiw	Averaging time - indoor worker (days/year)	365	U.S. EPA 1989 (pg. 6-23)
ATew	Averaging time - excavation/construction worker (days/year)	365	U.S. EPA 1989 (pg. 6-23)
ATag	Averaging time - Agriculture (days/year)	365	U.S. EPA 1989 (pg. 6-23)
LT	Lifetime (years)	70	U.S. EPA 1989 (pg. 6-22)
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)
EFow	Exposure Frequency - outdoor worker (days/yr)	225	U.S. EPA 1991a (pg. 15)
EFiw	Exposure Frequency - indoor worker (days/yr)	250	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
EFag	Exposure Frequency - agricultural (days/yr)	350	U.S. EPA 1991a (pg. 15)
EDr	Exposure Duration - resident (yr)	30	U.S. EPA 1991a (pg. 15)
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)
ETres	Exposure Time - resident (hr/day)	24
ETrec	Exposure Time - recreation (hr/day)	1
ETow	Exposure Time - outdoor worker (hr/day)	8
ETiw	Exposure Time - indoor worker (hr/day)	8
ETew	Exposure Time - excavation/construction worker (hr/day)	8
ETc	Exposure time - child (hr/event)	1	U.S. EPA 2004
ETa	Exposure time - adult (hr/event)	0.58	U.S. EPA 2004
EV	Events (events/day)	1	U.S. EPA 2004
EVc	Events per day - child	1	U.S. EPA 2004
EVa	Events per day - adult	1	U.S. EPA 2004
Particulate Emission Factor Variables
PEFw	Particulate Emission Factor - Minneapolis (m3/kg)	1.36 × 109(region-specific)	Determined in this calculator
Q/Cwp	Inverse of the Mean Concentration at the Center of a 0.5-Acre-Square Source (g/m2-s per kg/m3)	93.77 (region-specific)	Determined in this calculator
V	Fraction of Vegetative Cover (unitless)	0.5	U.S. EPA 1996a (pg. 23)
Um	Mean Annual Wind Speed (m/s)	4.69	U.S. EPA 1996a (pg. 23)
Ut	Equivalent Threshold Value of Wind Speed at 7m (m/s)	11.32	U.S. EPA 1996a (pg. 23)
F(x)	Function Dependent on Um /Ut (unitless)	0.194	U.S. EPA 1996a (pg. 23)
A	Dispersion constant unitless	PEF and region-specific	U.S. EPA 2002 (pg. D-6 to D-8)
As	Areal extent of the site or contamination (acres)	0.5 (range 0.5 to 500 )	U.S. EPA 2002 (pg. D-2)
B	Dispersion constant unitless	PEF and region-specific	U.S. EPA 2002 (pg. D-6 to D-8)
C	Dispersion constant unitless	PEF and region-specific	U.S. EPA 2002 (pg. D-6 to D-8)
Volatilization Factor Variables
VFs	Volatilization Factor - Minneapolis (m3/kg)	Contaminant-specific	U.S. EPA. 1996b (pg. 24)
Q/Cwv	Inverse of the Mean Concentration at the Center of a 0.5-Acre-Square Source (g/m2-s per kg/m3)	68.81	U.S. EPA. 1996b (pg. 24)
DA	Apparent Diffusivity (cm2/s)	Contaminant-specific	U.S. EPA. 1996b (pg. 24)
T	Exposure interval (s)	9.5×108	U.S. EPA. 1996b (pg. 24)
ρb	Dry soil bulk density (g/cm3)	1.5	U.S. EPA. 1996b (pg. 24)
θa	Air-filled soil porosity (Lair/Lsoil)	0.28	U.S. EPA. 1996b (pg. 24)
n	Total soil porosity ( Lpore/Lsoil)	0.43	U.S. EPA. 1996b (pg. 24)
θw	Water-filled soil porosity (Lwater/Lsoil)	0.15	U.S. EPA. 1996b (pg. 24)
ρs	Soil particle density (g/cm3)	2.65	U.S. EPA. 1996b (pg. 24)
Di	Diffusivity in air (cm2/s)	Contaminant-specific	U.S. EPA. 1996b (pg. 24)
H'	Dimensionless Henry's Law Constant	Contaminant-specific	U.S. EPA. 1996b (pg. 24)
Dw	Diffusivity in water (cm2/s)	Contaminant-specific	U.S. EPA. 1996b (pg. 24)
Kd	Soil-water partition coefficient (Koc×foc)	Contaminant-specific	U.S. EPA. 1996b (pg. 24)
Koc	Soil organic carbon-water partition coefficient	Contaminant-specific	U.S. EPA. 1996b (pg. 24)
foc	Organic carbon content of soil (g/g)	0.006	U.S. EPA. 1996b (pg. 24)