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 [mg/kg-day; risk/pCi]
SF = slope factor, expressed in [(mg/kg-day)^-1; pCi/risk]

The basic equation for calculating systemic toxicity (i.e., noncarcinogenic hazard) is:

Noncancer Hazard Quotient = CDI/RfD

where:

CDI = chronic daily intake for the toxicant, expressed in mg/kg-day
RfD = chronic reference dose for the toxicant, expressed in mg/kg-day

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.

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 Peer Reviewed Toxicity Values (PPRTVs) 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 Rich Kapuscinski at Kapuscinski.Rich@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 - Reference Doses

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 risks in this calculator also use Agency for Toxic Substances and Disease Registry (ATSDR) chronic oral minimal risk levels (MRLs) as oral chronic RfDs. The HEAST RfDs used in these risks 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 - 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 RfCa, intermediate inhalation MRLs as subchronic RfCa 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/m³and have been converted to mg/m³for 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/m³in air. Inhalation unit risk toxicity values are expressed in units of (µg/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

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

2.4.1 Sources

Many sources are used to populate the database of chemical-specific parameters. They are briefly described below.

1. The Estimation Programs Interface (EPI) SuiteTM was developed by the US Environmental Protection Agency's Office of Pollution Prevention and Toxics and Syracuse Research Corporation (SRC). 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.

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

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

8. 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).

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

10. CRC Handbook of Chemistry and Physics . (Various Editions)

11. Perry'sChemical Engineers' Handbook (Various Editions).McGraw-Hill. Online version available at:http://www.knovel.com/web/portal/browse/display?_EXT_KNOVEL_DISPLAY_bookid=2203&VerticalID=0. Green, Don W.; Perry, Robert H. (2008).

12. Lange's Handbook of Chemistry (Various Editions). Online version available at:http://www.knovel.com/web/portal/browse/display?_EXT_KNOVEL_DISPLAY_bookid=1347&VerticalID=0. Speight, James G. (2005). McGraw-Hill.

13. U.S. EPA 2004. Risk Assessment Guidance for Superfund Volume I: Human Health Evaluation Manual (Part E, Supplemental Guidance for Dermal Risk Assessment) Final. OSWER 9285.7-02EP.July 2004. Document and website http://www.epa.gov/oswer/riskassessment/ragse/index.htm">http://www.epa.gov/oswer/riskassessment/ragse/index.htm">http://www.epa.gov/oswer/riskassessment/ragse/index.htm.

2.4.2 Hierarchy by Parameter

Generally the hierarchies below will work for organic and inorganic compounds.

1. Organic Carbon Partition Coefficient (K_oc) (L/kg). Not applicable for inorganics. EPI estimated values; SSL, Yaw estimated values; EPI experimental values; Yaw Experimental values

2. Dermal Permeability Constant (K_p) (cm/hr). EPI estimated values; RAGS Part E.

3. Molecular Weight (MW) (g/mole). EPI; CRC89; PERRY; LANGE; YAWS

4. Water Solubility (S) (mg/L). EPI experimatal values; SSL; CRC; PERRY; LANGE; YAWS experimental values; Yaws estimated values; EPI estimated values; PHYSPROP

5. Unitless Henry's Law Constant (H'). EPI experimental values; SSL; YAWS experimental values; EPI estimated values; PHYSPROP

6. Henry's Law Constant (atm-m3/mole). EPI experimental values; SSL; YAWS experimental values; EPI estimated values; PHYSPROP

7. Diffusivity in Air (D_ia) (cm2/s). WATER9 equations; SSL

8. Diffusivity in Water (D_ia) (cm2/s). WATER9 equations; SSL

9. Fish Bioconcentration Factor (BCF) (L/kg). EPI experimental values; EPI estimated values

10. Soil-Water Partition Coefficient (K_d) (cm3/g). SSL; BAES

11. Density (g/cm3). CRC; PERRY; LANGE; IRIS

When using risks, 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 risks 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.

• Are there potential ecological concerns?
• Is there potential for land use other than those used in the CDI calculations (i.e., residential and commercial/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 risk equations may need to be adjusted to reflect the answers to these questions.

Natural background concentrations should be considered prior to calculating risks. 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).

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

• Applying risks 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 risks without adequate consideration of the other NCP remedy selection criteria on CERCLA sites.
• Use of outdated equations or toxicity values.

4.1.1 Noncancer Child

The residential soil CDI equations, presented here for child exposures, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal contact with soil.

4.1.2 Noncancer Adult

The residential soil CDI equations, presented here for adult exposures, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal contact with soil.

4.1.3 Noncancer Age-adjusted

The residential soil CDI equations, presented here for age-adjusted exposures, contain the following exposure routes:

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal contact with soil.

4.1.4 Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal contact with soil.

4.1.5 Mutagenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal contact with soil.

4.1.6 Vinyl Chloride - Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal contact with soil.

4.1.7 Supporting Equations for Residential Soil

Child Supporting Equations.

Adult Supporting Equations.

Age-adjusted Supporting Equations.

4.2.1 Noncancer

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal exposure.

4.2.2 Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal exposure.

4.3.1 Noncancer

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

incidental ingestion of soil and

inhalation of particulates emitted from soil.

4.3.2 Carcinogenic

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

incidental ingestion of soil and

inhalation of particulates emitted from soil.

4.4.1 Noncancer

The composite worker soil CDI equations, presented here, combine the most protecive exposure parameters from the outdoor and indoor worker. The composite worker contains the following exposure routes:

incidental ingestion of soil and

inhalation of particulates emitted from soil.

4.4.2 Carcinogenic

The composite worker soil CDI equations, presented here, contain the following exposure routes:

incidental ingestion of soil and

inhalation of particulates emitted from soil.

4.5.1 Noncancer

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal exposure.

4.5.2 Carcinogenic

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

incidental ingestion of soil,

inhalation of particulates emitted from soil, and

dermal exposure.

The recreational soil/sediment CDI equations, presented here for child exposures, contain the following exposure routes:

incidental ingestion of soil/sediment,

inhalation of particulates emitted from soil/sediment, and

dermal contact with soil/sediment.

4.6.2 Noncancer for Adult

The recreational soil/sediment CDI equations, presented here for adult exposures, contain the following exposure routes:

incidental ingestion of soil/sediment,

inhalation of particulates emitted from soil/sediment, and

dermal contact with soil/sediment.

4.6.3 Noncancer for Age-adjusted

The recreational soil/sediment CDI equations, presented here for age-adjusted exposures, contain the following exposure routes:

incidental ingestion of soil/sediment,

inhalation of particulates emitted from soil/sediment, and

dermal contact with soil/sediment.

4.6.4 Carcinogenic

The recreational soil/sediment CDI equations, presented here, contain the following exposure routes:

incidental ingestion of soil/sediment,

inhalation of particulates emitted from soil/sediment, and

dermal contact with soil/sediment.

4.6.5 Mutagenic

The recreational soil/sediment CDI equations, presented here, contain the following exposure routes:

incidental ingestion of soil/sediment,

inhalation of particulates emitted from soil/sediment, and

dermal contact with soil/sediment.

4.6.6 Vinyl Chloride - Carcinogenic

The recreational soil/sediment CDI equations, presented here, contain the following exposure routes:

incidental ingestion of soil/sediment,

inhalation of particulates emitted from soil/sediment, and

dermal contact with soil/sediment.

4.6.7 Supporting Equations for Recreational Soi/Sediment

Child Supporting Equations.

Adult Supporting Equations.

Age-adjusted Supporting Equations.

4.7.1 Noncarcinogenic for Child

The tapwater CDI equations, presented here for child exposures, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.7.2 Noncarcinogenic for Adult

The tapwater CDI equations, presented here for adult exposures, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.7.3 Noncarcinogenic for Age-adjusted

The tapwater CDI equations, presented here for age-adjusted exposures, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.7.4 Carcinogenic

The tapwater CDI equations, presented here, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.7.5 Mutagenic

The tapwater CDI equations, presented here, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.7.6 Vinyl Chloride - Carcinogenic

The tapwater CDI equations, presented here, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.7.7 Supporting Equations for Tapwater

Child Supporting Equations.

Adult Supporting Equations.

Age-adjusted Supporting Equations.

4.8.1 Noncarcinogenic

The tapwater CDI equations, presented here, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.8.2 Carcinogenic

The tapwater CDI equations, presented here, contain the following exposure routes:

ingestion of water,

dermal contact with water, and

inhalation of volatiles.

4.9.1 Noncarcinogenic Child

The surface water CDI equations, presented here for child exposures, contain the following exposure routes:

ingestion of water and

dermal contact with water.

4.9.2 Noncarcinogenic Adult

The surface water CDI equations, presented here for adult exposures, contain the following exposure routes:

ingestion of water and

dermal contact with water.

4.9.3 Noncarcinogenic Age-adjusted

The surface water CDI equations, presented here for age-adjusted exposures, contain the following exposure routes:

ingestion of water and

dermal contact with water.

4.9.4 Carcinogenic

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

ingestion of water and

dermal contact with water.

4.9.5 Mutagenic

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

ingestion of water and

dermal contact with water.

4.9.6 Vinyl Chloride

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

ingestion of water and

dermal contact with water.

4.9.7 Supporting Equations for Recreation Surface Water

Child Supporting Equations.

Adult Supporting Equations.

Age-adjusted Supporting Equations.

4.10.1 Resiedent

4.10.1.1 Noncarcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.10.1.2 Carcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.10.1.3 Mutagenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles

4.10.1.4 Vinyl Chloride - Carcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.10.2 Outdoor Worker

4.10.2.1 Noncarcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.10.2.2 Carcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.10.3 Indoor Worker

4.10.3.1 Noncarcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.10.3.2 Carcinogenic

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

inhalation of volatiles.

4.10.4 Composite Worker

4.10.4.1 Noncarcinogenic

The composite worker ambient air CDI equation, presented here, combines the most protective parameters from the outdoor and indoor workers. The composite worker contains the following exposure route:

inhalation of volatiles.

4.10.4.2 Carcinogenic

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

inhalation of volatiles.

4.10.5 Excavation/Construction Worker

4.10.5.1 Noncarcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.10.5.2 Carcinogenic

The Ambient air CDI equation, presented here, contains the following exposure route:

inhalation of volatiles.

4.11.1 Concentration in Fish

4.11.1.1 Noncarcinogenic

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

consumption of fish.

4.11.1.2 Carcinogenic

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

consumption of fish.

4.11.2 Concentration in Surface Water

4.11.2.1 Noncarcinogenic

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

consumption of fish.

4.11.2.2 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.

4.12.1 Concentration in Fruit and Vegetables

4.12.1.1 Noncarcinogenic

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

consumption of fruits and vegetables.

4.12.1.2 Carcinogenic

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

consumption of fruits and vegetables.

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

4.12.2.1 Noncarcinogenic

consumption of fruits and vegetables.

4.12.2.2 Carcinogenic

consumption of fruits and vegetables.

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

4.12.3.1 Noncarcinogenic

consumption of fruits and vegetables.

4.12.3.2 Carcinogenic

consumption of fruits and vegetables.

4.12.4 Concentration in Milk

4.12.4.1 Noncarcinogenic

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

consumption of milk.

4.12.4.2 Carcinogenic

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

consumption of milk.

4.12.5 Back-calculated Concentration in Water Only for Milk

4.12.5.1 Noncarcinogenic

consumption of milk.

4.12.5.2 Carcinogenic

consumption of milk.

4.12.6 Back-calculated Concentration in Soil Only for Milk

4.12.6.1 Noncarcinogenic

consumption of milk.

4.12.6.2 Carcinogenic

consumption of milk.

4.12.7 Concentration in Beef

4.12.7.1 Noncarcinogenic

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

consumption of beef.

4.12.7.2 Carcinogenic

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

consumption of beef.

4.12.8 Back-calculated Concentration in Water Only for Beef

4.12.8.1 Noncarcinogenic

consumption of beef.

4.12.8.2 Carcinogenic

consumption of beef.

4.12.9 Back-calculated Concentration in Soil Only for Beef

4.12.9.1 Noncarcinogenic

consumption of beef.

4.12.9.2 Carcinogenic

consumption of beef.

There are two inhalation variables in the above CDI equations that require further explanation: the particulate emission factor (PEF) and the volatilization factor (VF). Also there are supporting equations and practices presented for the dermal exposure to water route.

4.13.1 Particulate Emission Factor (PEF)

Inhalation of contaminants adsorbed to respirable particles (PM10) was assessed using a default PEF equal to 1.36 x 10⁹m³/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 ug/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.

4.13.2 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 Guidedescribes 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.

4.13.3 Dermal Contact with W ater Supporting Equations

Calculating PRGs for the dermal exposure to water route, following RAGS Part E Supplemental Guidance for Dermal Risk Assessment), requires calculation of B, t^* and τ. Note that the RAIS has replaced RAGS Part E's use of t_event with ET (exposure time) to maintain consistency with our other exposure routes.

• B is the dimensionless ratio of the permeability coefficient of a compound through the stratum corneum relative to its permeability coefficient across the viable epidermis.
  
  
• t* is the time to reach steady state.
  
  
• τ is the lag time per event.
  
  

RAGS Part E stresses the determination of whether a chemical is within the effective predictive domain (EPD) for the determination of dermal permeability constant (K_p) applicability. The RAIS PRG output provides determination of whether or not a chemical is within the EPD. The RAIS PRG output also displays our determination of the fraction of the chemical that is ultimately absorbed (FA). FA depends strongly on the chemical's lipophilic characteristic and molecular weight as expressed in the B parameter and the lag time. RAGS Part E has determined that dermal exposures contributing less than 10% of oral exposures are insignificant. However, the RAIS presents dermal PRGs regardless of contribution percent.