A purpose of this guidance is to provide a PRG calculation tool to assist risk assessors, remedial project managers, and others involved with risk assessment and decision-making at CERCLA sites in developing PRGs. This database is based on Risk Assessment Guidance for Superfund: Volume I, Human Health Evaluation Manual (Part B, Development of Risk-based Preliminary Remediation Goals) (RAGS Part B). RAGS Part B provides guidance on calculating risk-based PRGs. Initially used at the scoping phase of a project using readily available information, risk-based PRGs may be modified based on site-specific data gathered during the RI/FS study. PRG development and screening should assist staff in streamlining the consideration of remedial alternatives. Chemical-specific PRGs are from two general sources. These are: (1) concentrations based on potential Applicable or Relevant and Appropriate Requirements (ARARs) and (2) risk-based concentrations. ARARs include concentration limits set by other environmental regulations, such as Safe Drinking Water Act maximum contaminant levels (MCLs). The second source for PRGs, and the focus of this database tool, is risk-based calculations that set concentration limits using carcinogenic toxicity values under specific exposure conditions.

The recommended approach for developing remediation goals is to identify PRGs at scoping, modify them as needed at the end of the RI or during the FS based on site-specific information from the baseline risk assessment, and ultimately select remediation levels in the Record of Decision (ROD). In order to set radionuclide-specific PRGs in a site-specific context, however, assessors must answer fundamental questions about the site. Information on the radionuclides that are present onsite, the specific contaminated media, land-use assumptions, and the exposure assumptions behind pathways of individual exposure is necessary in order to develop radionuclide-specific PRGs. The PRG calculator provides the ability to modify the standard default PRG exposure parameters to calculate site-specific PRGs.

This database tool presents standardized risk-based PRGs and variable risk-based PRG calculation equations for radioactive contaminants. Ecological effects are not considered in the calculator for radionuclides PRGs.

PRGs are presented for resident soil, outdoor worker soil, indoor worker soil, composite worker soil, recreator soil, farmer soil, construction worker soil, tap water, air, farm products, and fish ingestion. The risk-based PRGs for radionuclides are based on the carcinogenicity of the contaminants. Cancer slope factors (SFs) used are provided by the Center for Radiation Protection Knowledge. The main report is Calculations of Slope Factors and Dose Coefficients, and the tables of slope factors are in a separate appendix.

Non-carcinogenic effects are not considered for radionuclide analytes except for uranium, for which both carcinogenic and non-carcinogenic effects are considered. To determine PRGs for the chemical toxicity of uranium, and for other chemicals, go to the Regional Screening Levels for Chemical Contaminants at Superfund Sites webpage.

The standardized PRGs are based on default exposure parameters and incorporate exposure factors that present reasonable maximum exposure (RME) conditions. This database tool presents PRGs in both activity and mass units. Once this database tool is used to retrieve standard PRGs or calculate site-specific PRGs, it is important to clearly demonstrate the equations and exposure parameters used in the calculations. Discussion of the assumptions that go into the calculated PRGs should be included in the document where the PRGs are presented, such as a Remedial Investigation (RI) Report or Feasibility Study.

This website combines current Center for Radiation Protection Knowledge SFs with standard exposure factors to estimate contaminant concentrations in environmental media (biota, air, soil, and water) that are protective of humans (including sensitive groups) over a lifetime. Sufficient knowledge about a given site may warrant the use of site-specific assumptions that may differ from the defaults. Exceeding a PRG usually suggests that further evaluation of the potential risks is appropriate. The PRGs presented on this website can be used to screen pollutants in environmental media, trigger further investigation, and provide initial cleanup goals, if applicable. PRGs should be applied in accordance with guidance from EPA Regions.

In addition to this guidance, for relevant training, see the internet-based course "Radiation Risk Assessment: Updates and Tools."

This website offers the ability to quickly look up or calculate PRGs. Within the PRGs are many complex models that require a greater understanding when using the calculator in site-specific mode. The sections that follow expand upon these models and should be consulted before generating site-specific PRGs.

2.1 General Considerations

PRGs are radionuclide concentrations that correspond to certain levels of risk from exposure to air, soil, water, and biota. Slope Factors (SFs), for a given radionuclide represent the risk equivalent per unit intake (i.e., ingestion or inhalation) or external exposure of that radionuclide. In risk assessments, these SFs are used in calculations with radionuclide concentrations and exposure assumptions to estimate risk from exposure to radioactive contamination. The calculations may be rearranged to generate PRGs for a specified level of risk. SFs may be specified for specific body organs or tissues of interest or as a weighted sum of individual organ risk, termed the effective risk equivalent. These SFs may be multiplied by the total activity of each radionuclide inhaled or ingested per year, or the external exposure concentration to which a receptor may be exposed, to estimate the risk to the receptor. Slope Factors used are provided by the Center for Radiation Protection Knowledge. The main report is Calculations of Slope Factors and Dose Coefficients, and the tables of DCFs are in a separate appendix.

Inhalation slope factors are tabulated separately for each of the three lung absorption types considered in the lung model currently recommended by the International Commission on Radiological Protection (ICRP) and, where appropriate, for inhalation of radionuclides in vapor or gaseous forms.

The designations "F", "M", and "S" presented in the Radionuclide Table under the heading "ICRP Lung Type" refer to the lung absorption type for inhaled particulate radionuclides, expressed as fast (F), medium (M), or slow (S), as used in the current ICRP model of the respiratory tract. The inhalation slope factor values tabulated in the Radionuclide Table for each radionuclide have been selected based on the following guidelines: (1) For those elements where Table 4.1 of Federal Guidance Report No. 13 (and Table 2 of ICRP Publication 72) specifies a recommended default lung absorption type for particulates, the inhalation slope factor for that type is tabulated in the Radionuclide Table for each radioisotope of that element; (2) For those elements where no specific lung absorption type is recommended and multiple types are indicated as plausible choices, the inhalation slope factor reported in the Radionuclide Table for each radioisotope of that element is the maximum of the values for each of the plausible lung absorption types; and (3) Where Federal Guidance Report No. 13 specifies risk coefficients for multiple chemical forms of certain elements (tritium, carbon, sulfur, iodine, and mercury), the inhalation slope factor value for the form estimated to pose the maximum risk is reported in the Radionuclide Table, in most cases.

Inhaled particulates are assumed to have an activity median aerodynamic diameter (AMAD) of 1 um, as recommended by the ICRP for consideration of environmental exposures in the absence of specific information on physical characteristics of the aerosol. Where appropriate, radionuclides that may be present in gas or vapor form are designated by "G" and "V", respectively; such radionuclides include tritium, carbon, sulfur, nickel, ruthenium, iodine, tellurium, and mercury.

The most common land uses and exposure assumptions are included in the equations on this website: Resident Soil, Composite Worker Soil, Outdoor Worker Soil, Indoor Worker Soil, Construction worker Soil, Farmer Soil, Recreator Soil, resident Air, Composite Worker Air, Outdoor Worker Air, Indoor Worker Air, Construction worker Air, Farmer Air, Recreator Air, Tap water, Soil to Groundwater, and Ingestion of Fish.

The PRGs are generated with standard exposure route equations using EPA SFs and exposure parameters. Exposures to other media can be addressed by other calculators. For exposure to contaminated materials inside and outside building, use the BPRG (Preliminary Remediation Goals for Radionuclides in Buildings at Superfund Sites) and the SPRG (Preliminary Remediation Goals for Radionuclides on Outdoor Surfaces at Superfund Sites), respectively. A PRG calculator receptor represents the reasonably maximum exposed (RME) individual, as does a BPRG receptor. Since the PRG RME is often outside and the BPRG RME is always indoors, an individual receiving both indoor and outdoor exposures at a site should be protected when both tools are used.

For the calculation of soil ingestion slope factors, area correction factors, and gamma shielding factors, a standard soil density of 1.6 g/cm³ has been used.

2.2 PRG Output Options

The calculator offers four options for calculating PRGs. Previous versions of this calculator employed slope factors that included progeny ingrowth for 100 years, designated "+D." The +D slope factors are no longer included in the pick list; see section 2.9.2 to learn more. The PRGs presented in sections 2.2.1 and 2.2.2 independently model progeny during migration to groundwater and biota uptake, while the +D PRGs did not. This section describes the potential applications of the four choices and recommends a default PRG calculation.

2.2.1 PRG Output Option #1: Assumes period of peak risk (with decay and progeny ingrowth)(Peak PRG)

This is the preferred PRG calculation option and is marked as the default selection in the calculator. The Peak PRG is calculated for the time period when the parent and progeny activities present the most risk. The underlying assumption of the Peak PRG option is that a pure isotope was released and progeny begin ingrowth and decay. This PRG is protective, as future progeny may contribute more risk than the parent. When a single isotope is selected, the calculator identifies all the progeny in the chain. The PRGs for each progeny are combined with the parent based on their fractional contribution (FC). The FC is determined by branching fractions, where a progeny may decay into more than one isotope. Section 2.2.2 presents details on calculating the FC. Unlike previous PRG output options that included progeny contribution (i.e., +D PRGs as discussed in section 2.9.2.), the Peak PRG models each progeny independently of the parent for half-life, migration to groundwater, and biota uptake. The PRG provided in the output is the inverse sum of the reciprocal PRGs of the parent and all the progeny present at the period of peak risk. All PRG equation images are presented without a radioactive decay term; however, decay and ingrowth is included in this PRG option.

When the Peak PRG output option is selected, the PRG Calculator shows the individual progeny contributions for the total PRG. At the top of the output page, the results are separated into tabs by media. In the Peak PRG output, the individual exposure routes are presented separately. This is done to help determine which exposure routes are risk drivers that may help to focus site-specific remedial efforts. The period of peak risk may differ for some exposure routes (e.g., external, soil ingestion, food ingestion, and inhalation) as well as the total Peak PRG. Forward risk calculations are also available for this output option.

The Peak PRG output option can be run for an infinite time period or a user-defined time period.

2.2.1.1 Infinite Time

The default setting for the Peak PRG option is to search for the period of peak risk out to infinity. To accomplish this, the Peak PRG uses a Bateman solver to determine the parent and progeny activities out to a trillion years. This isotopic activity curve is then converted to risk, and another routine selects the time period with the most risk from parent and progeny and determines the parent activity (PRG) that would represent the target risk. Users should note that for long-lived isotopes that have a peak risk that begins in the future, progeny are likely already ingrown, and the secular equilibrium (SE) PRGs may be appropriate. This ORNL Technical Memorandum offers explanation of the derivation of the Peak PRGs.

2.2.1.2 User-defined Time Period

The user may also select a defined time period to search for the period of peak risk. This option operates just like the infinite time option but stops searching for the period of peak risk at a user-defined time in the future. Predefined time points of 10,000, 1,000, and 100 years are offered as well as the option for the user to enter a specific time period between 70 and one trillion years. These options are only offered for use in certain situations where a regulatory agency is concerned about risk within a defined time period. If a risk peak hasn't been resolved in the defined time period, as is the case when progeny are still ingrowing, the risk interval will be calculated for the last exposure duration span. For instance, if the time period of 100 years is selected for default resident soil for U-238 (ED of 26 years), years 74 to 100 will be selected by default, because U-238 peak risk isn't until year 3,981,072. When the peak risk occurs within the user defined time period, the last exposure duration span is not used. For radionuclides with short half-lives relative to the land use ED, like Ac-227, the peak risk PRGs for the infinite, 10,000, 1,000, and 100 year time periods are equal.

User-defined time periods should only be considered when a purified radionuclide was recently disposed or released. These time periods should not be considered when a radionuclide has been present long enough for progeny to ingrow (e.g., uranium, thorium, and radium as ore material). The default selection of infinity is the preferred option for use on Superfund sites being remediated for unrestricted future land uses.

Click Here for a Tutorial on Understanding Peak PRG Graphs

The following images provide instructions for exploring and understanding the peak risk graphs.

2.2.2 PRG Output Option #2: Assumes Secular Equilibrium Throughout the Chain (no decay - parent and progeny in constant equilibrium)

This was the default PRG calculation option prior to the release of the Peak PRG. When a single isotope is selected, the calculator identifies all the progeny in the chain. The PRGs for each progeny are combined with the parent based on their FC. The FC is determined by branching fractions, where a progeny may decay into more than one isotope. The FC calculation process is described later in this section. The resulting PRG is now based on secular equilibrium of the full chain. For straight chain decay, all the progeny would be at the same activity of the parent, and the PRG provided in the output would be the inverse sum of the reciprocal PRGs of the parent and all the progeny. Unlike previous PRG output options that included progeny contribution (i.e., +D PRGs as discussed in section 2.9.2.), the secular equilibrium PRG models each progeny independently of the parent for half-life, migration to groundwater, and biota uptake. All the soil PRG equation images are presented without a radioactive decay term. Decay is not included in this PRG option, as the assumption of secular equilibrium is that the parent is continually being renewed.

When the secular equilibrium PRG output option is selected, the PRG Calculator now gives the option to show the individual progeny contributions for the PRG (and risk) output. When the option to display progeny contribution is selected, the PRG Calculator output gives the secular equilibrium PRG and the individual progeny PRGs in separate tables.

A total PRG is calculated using the following formula:

The EPA Decay Chain tool provides the branching fractions for each radionuclide's decay chain, based on the ICRP 107 data. The branching fractions presented, for non-converging chains, are used directly in the PRG equation above for the FC (fractional contribution) term. Convergence in a chain is when there are multiple decay pathways to a particular isotope or when multiple isotopes can decay to a particular isotope. When a chain converges, as is the case with the Ra-226 chain, the effect of multiple branches needs to be taken into account. Consider the branching fractions in the Ra-226 decay chain in the table below.

Nuclide	Half-life	Mode	Mass	Branching Fraction	Progeny	Branching Fraction	Progeny
Ra-226	1600 years	A	226.025409	1.00e+0	Rn-222
Rn-222	3.8235 days	A	222.017577	1.00e+0	Po-218
Po-218	3.10 minutes	B-,A	218.008973	1.00e+0	Pb-214	2.00e-4	At-218
Pb-214	26.8 minutes	B-	213.999805	1.00e+0	Bi-214
At-218	1.5 seconds	A,B-	218.008694	9.99e-1	Bi-214	1.00e-3	Rn-218
Bi-214	19.9 minutes	B-,A	213.998711	1.00e+0	Po-214	2.10e-4	Tl-210
Rn-218	3.50e-2 seconds	A	218.005601	1.00e+0	Po-214
Po-214	1.64e-4 seconds	A	213.995201	1.00e+0	Pb-210
Tl-210	1.3 minutes	B-	209.990073	1.00e+0	Pb-210
Pb-210	22.2 years	B-,A	209.984188	1.00e+0	Bi-210	1.90e-8	Hg-206
Bi-210	5.01 days	B-,A	209.984120	1.00e+0	Po-210	1.32e-6	Tl-206
Hg-206	8.15 minutes	B-	205.977514	1.00e+0	Tl-206
Po-210	138.38 days	A	209.982873	1.00e+0	Stable Pb-206
Tl-206	4.2 minutes	B-	205.976110	1.00e+0	Stable Pb-206

For example, the branching fraction presented in the above table for At-218 decaying to Rn-218 is 0.1% (0.001 or 1.0E-03); however, this isn't the complete picture, because At-218 appears in the chain as only 0.02% of Po-218 decay. To determine the true fractional contribution of Rn-218 to the whole chain, multiply the two branching fraction ratios together as follows: 2.0E-04 x 1.0E-03 = 2.0E-07. Technically, to calculate the fractional contribution of each isotope in a chain, each unique pathway to that isotope should have its branching fractions multiplied together and each result summed. The tables below present this process for At-218, Rn-218, Tl-210, Hg-206, and Tl-206, respectively. The FCs for the other progeny are all 1.0.

Determination of Fractional Contribution (FC) from Converging Branching Fractions in the Ra-226 Decay Chain.
At-218 FC
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218						Fraction
1	1	2.00E-04						2.00E-04
Total FC								2.00E-04
Rn-218 FC
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Rn-218					Fraction
1	1	2.00E-04	1.00E-03					2.00E-07
Total FC								2.00E-07
Tl-210 FC
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Bi-214	Bi-214 to Tl-210				Fraction
1	1	2.00E-04	1	2.10E-04				4.20E-08
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to Pb-214	Pb-214 to Bi-214	Bi-214 to Tl-210
1	1	1	1	2.10E-04				2.10E-04
Total FC								2.10E-04
Hg-206 FC
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Rn-218	Rn-218 to Po-214	Po-214 to Pb-210	Pb-210 to Hg-206		Fraction
1	1	2.00E-04	1.00E-03	1	1	1.90E-08		3.8E-15
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Bi-214	Bi-214 to Po-214	Po-214 to Pb-210	Pb-210 to Hg-206
1	1	2.00E-04	1	1	1	1.90E-08		3.8E-12
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Bi-214	Bi-214 to Tl-210	Tl-210 to Pb-210	Pb-210 to Hg-206
1	1	2.00E-04	1	1	1	1.90E-08		3.8E-12
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to Pb-214	Pb-214 to Bi-214	Bi-214 to Po-214	Po-214 to Pb-210	Pb-210 to Hg-206
1	1	1	1	1	1	1.90E-08		1.90E-08
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to Pb-214	Pb-214 to Bi-214	Bi-214 to Tl-210	Tl-210 to Pb-210	Pb-210 to Hg-206
1	1	1	1	2.10E-04	1	1.90E-08		3.99E-12
Total FC								1.90E-08
Tl-206 FC
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Rn-218	Rn-218 to Po-214	Po-214 to Pb-210	Pb-210 to Bi-210	Bi-210 to Tl-206	Fraction
1	1	2.00E-04	1.00E-03	1	1	1.00E+00	1.32E-06	2.64E-13
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Rn-218	Rn-218 to Po-214	Po-214 to Pb-210	Pb-210 to Hg-206	Hg-206 to Tl-206
1	1	2.00E-04	1.00E-03	1	1	1.90E-08	1.00E+00	3.80E-15
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Bi-214	Bi-214 to Po-214	Po-214 to Pb-210	Pb-210 to Bi-210	Bi-210 to Tl-206
1	1	2.00E-04	1	1	1	1.00E+00	1.32E-06	2.64E-10
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Bi-214	Bi-214 to Po-214	Po-214 to Pb-210	Pb-210 to Hg-206	Hg-206 to Tl-206
1	1	2.00E-04	1	1	1	1.90E-08	1.00E+00	3.80E-12
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Bi-214	Bi-214 to Tl-210	Tl-210 to Pb-210	Pb-210 to Bi-210	Bi-210 to Tl-206
1	1	2.00E-04	1	2.10E-04	1	1.00E+00	1.32E-06	5.54E-14
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to At-218	At-218 to Bi-214	Bi-214 to Tl-210	Tl-210 to Pb-210	Pb-210 to Hg-206	Hg-206 to Tl-206
1	1	2.00E-04	1	2.10E-04	1	1.90E-08	1.00E+00	7.98E-16
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to Pb-214	Pb-214 to Bi-214	Bi-214 to Po-214	Po-214 to Pb-210	Pb-210 to Bi-210	Bi-210 to Tl-206
1	1	1	1	1	1	1.00E+00	1.32E-06	1.32E-06
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to Pb-214	Pb-214 to Bi-214	Bi-214 to Po-214	Po-214 to Pb-210	Pb-210 to Hg-206	Hg-206 to Tl-206
1	1	1	1	1	1	1.90E-08	1.00E+00	1.90E-08
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to Pb-214	Pb-214 to Bi-214	Bi-214 to Tl-210	Tl-210 to Pb-210	Pb-210 to Bi-210	Bi-210 to Tl-206
1	1	1	1	2.10E-04	1	1.00E+00	1.32E-06	2.77E-10
Ra-226 to Rn-222	Rn-222 to Po-218	Po-218 to Pb-214	Pb-214 to Bi-214	Bi-214 to Tl-210	Tl-210 to Pb-210	Pb-210 to Hg-206	Hg-206 to Tl-206
1	1	1	1	2.10E-04	1	1.90E-08	1.00E+00	3.99E-12
Total FC								1.34E-06

2.2.3 PRG Output Option #3: Does Not Assume Secular Equilibrium, Provides Results for Progeny Throughout Chain (with decay where appropriate)

This option displays the PRGs calculated with half-life decay that accounts for half-lives shorter than the exposure duration. See section 4.10.7 to learn more about the half-life decay function. In addition to the selected isotope, all the individual progeny PRGs are displayed. Each PRG is determined with each isotope's respective half-life and not that of its parent isotope. This option does not assume secular equilibrium and presents all the individual progeny PRGs, so that the risk assessor can identify any isotopes that will be present and those that have no data. Users can alter progeny half-life to match the parent isotope or other progeny or to account for ingrowth and decay over a chain. The individual isotope PRGs then would be combined (using the inverse sum of reciprocals method described in section 2.9.2) to give a parent PRG protective of progeny ingrowth.

2.2.4 PRG Output Option #4: Does Not Assume Secular Equilibrium, Selected Isotopes Only (with decay where appropriate)

This option displays PRGs for only the selected isotopes with half-life decay that accounts for half-lives shorter than the exposure duration. See section 4.10.7 to learn more about the half-life decay function. In this output, secular equilibrium is not assumed, progeny PRGs are not displayed, and progeny contribution is not combined into the PRG for the selected isotope. This option is useful when contamination is from one radionuclide with a very long half-life, where secular equilibrium would be too conservative.

2.2.5 Comparison of Peak PRG to the other 3 PRG Output Options

The Peak PRG output option returns results that are similar to one of the three other output options, depending upon the selected isotopes. For example, some transuranic isotopes (TRUs), such as Pu-238, Pu-239, Pu-240, and Am-241, have relatively short half lives in comparison to subsequent progeny. In such cases, equilibrium is not achieved. The activity of the relatively long-lived progeny grows in slowly, in some cases taking thousands of years to reach a significant fraction of the total activity. Furthermore, the activity of the progeny only reaches a small fraction of the parent's initial activity. For example, U-234 reaches a maximum activity of about 0.04 percent of the initial Pu-238 activity at approximately 1000 years. As such, the PRG for the parent only option is very similar to that of the Peak PRG option.

Conversely, secular equilibrium (SE) only occurs when the half-life of the progeny is much shorter than the half-life of the parent. When the progeny has a longer half-life than the parent, equilibrium does not exist. The assumption of SE in these cases significantly overestimates the activity of the progeny, resulting in a much lower PRG.

The following table presents a comparison of the default composite worker soil PRG options for Pu-238, Pu-239, Pu-240, and Am-241 and their long-lived progeny U-234, U-235, U-236, and Np-237, respectively. This table shows that each parent has a half-life about four orders of magnitude shorter than its progeny. As expected, of the three PRG options presented, the SE PRG is always the most protective (smallest). For the TRU isotopes, the peak and the parent only PRGs are shown to be essentially identical, and for the long-lived progeny, the SE and Peak PRG are more closely related. Also of interest is that the SE PRGs for the TRU isotopes and their long-lived progeny are very similar but slightly more protective than the TRU isotope PRGs. This is expected, as the risk contribution to the parent PRG is only different by one isotope in a long chain.

Isotope	Half-life (years)	Parent only PRG (pCi/g)	SE PRG (pCi/g)	Peak PRG (pCi/g)
Transuranics With Relative Short Half-lives Compared to Progeny
Am-241	4.32E+02	4.67E+00	8.40E-02	4.67E+00
Pu-238	8.77E+01	1.41E+01	2.02E-02	1.41E+01
Pu-239	2.41E+04	1.22E+01	7.27E-02	1.22E+01
Pu-240	6.56E+03	1.23E+01	1.52E-02	1.23E+01
Long-lived Progeny of Transuranics Above, Respectively
Np-237	2.14E+06	3.06E+00	8.56E-02	1.05E-01
U-234	2.46E+05	2.78E+01	2.03E-02	3.42E-02
U-235	7.04E+08	3.15E-01	7.31E-02	7.31E-02
U-238	4.47E+09	3.12E+01	2.00E-02	2.00E-02

The above figure shows a decay curve for Am-241 over one million years with an initial activity of 10,000 pCi. The progeny levels are near zero because the first progeny is long-lived relative to the parent. The figure below is for Np-237, the first progeny of Am-241, which has a half-life approximately four orders of magnitude longer than its parent. In the figure below, the initial activity was also 10,000 pCi. At 1 million years, the progeny activity is approximately four orders of magnitude higher than the Am-241 decay curve. This analysis demonstrates the reason the Peak PRG is similar to the parent only PRG for these transuranics with short half-lives relative to their progeny.

To further evaluate the Peak PRG option, the table below presents the three PRG output options for the common Superfund nuclides, in an effort to categorize the decay characteristics. The table presents the default composite worker soil PRGs at a target risk of 1E-06. Several categories are identified.

Category 1: TC-99 and I-129 make up the first category, where the decay is straight to stable over a period of time much greater than the exposure duration (ED). In this case, all three PRG output options return the same value.

Category 2: H-3 and C0-60 make up the second category, where the decay is also straight to stable, but the half-life is a fraction of the ED. In this case, the Peak PRG matches the parent-only PRG and the SE PRG is overprotective.

Category 3: U-235, U-238, and Th-232 make up the third category, where the decay chain is long and the parent half-life is much longer than the progeny. In this case, the Peak PRG matches the SE PRG and the parent only PRGs are under protective.

Category 4: U-234, Ra-226, Ra-228, Sr-90, Cs-137, Th-228, and Th-230 comprise the fourth category, where the SE PRGs and the Peak PRGs are much closer than the Peak PRGs and parent-only PRGs. There are multiple reasons the parent only PRGs are under protective compared to the Peak PRGs.

Category 5: I-131 comprises the fifth category, where the Peak PRG only matches the parent-only PRG. In this instance, there is only one progeny and both chain members have a relatively short half-life compared to ED.

Category 6: The final category is the focus of this section and consists of the transuranic isotopes: Pu-239, Am-241, Pu-240, and Pu-238. In these instances, the parent has a short half-life relative to immediate progeny, and the Peak PRGs match the parent only PRGs.

Common Superfund Isotopes (half-life)	SE Total PRG	Parent Only Total PRG	Peak PRG Total PRG	Peak PRG = SE?	Peak PRG = Parent Only?	Percent Peak PRG larger than SE	Percent Parent-only PRG larger than Peak PRG
Category 1
Tc-99 (0.211M years)	7.67E+02	7.67E+02	7.67E+02	Yes	Yes	0%	0%
I-129 (15.7M years)	9.23E+00	9.23E+00	9.23E+00	Yes	Yes	0%	0%
Category 2
H-3 (12.3 years)	1.61E-01	2.99E-01	2.99E-01	No	Yes	86%	0%
Co-60 (5.27 years)	1.42E-02	4.83E-02	4.83E-02	No	Yes	240%	0%
Category 3
U-235 (704M year)	7.31E-02	3.15E-01	7.31E-02	Yes	No	0%	331%
U-238 (4.47B years)	2.00E-02	3.12E+01	2.00E-02	Yes	No	0%	155900%
Th-232 (14.1B years)	1.53E-02	1.70E+01	1.53E-02	Yes	No	0%	111011%
Category 4
U-234 (0.246M years)	2.03E-02	2.78E+01	3.42E-02	Nearly	No	68%	81187%
Ra-226 (1600 years)	2.03E-02	3.05E+00	2.08E-02	Nearly	No	2.5%	14563%
Ra-228 (5.75 years)	1.53E-02	7.50E+00	4.92E-02	Nearly	No	222%	15144%
Sr-90 (28.8 years)	6.76E+00	3.84E+01	9.00E+00	Nearly	No	33%	327%
Cs-137 (30.2 years)	6.90E-02	5.71E+01	9.07E-02	Nearly	No	31%	62855%
Th-228 (1.91 years)	2.38E-02	1.07E+02	2.16E-01	Nearly	No	808%	49437%
Th-230 (75400 years)	2.03E-02	1.78E+01	2.20E-02	Nearly	No	8%	80809%
Category 5
I-131 (0.022 years)	1.09E-01	8.62E+01	8.62E+01	No	Yes	78983%	0%
Category 6
Pu-239 (24100 years)	7.27E-02	1.22E+01	1.22E+01	No	Yes	16681%	0%
Am-241 (432 years)	8.40E-02	4.67E+00	4.67E+00	No	Yes	5460%	0%
Pu-240 (6560 years)	1.52E-02	1.23E+01	1.23E+01	No	Yes	80821%	0%
Pu-238 (87.7 years)	2.02E-02	1.41E+01	1.41E+01	No	Yes	69702%	0%

*PRGs presented in this table are for TR = 1.0E-06 (pCi/g).

2.2.6 PRG output options and media that use decay

As stated in section 2.2.1, a Bateman solver is used to calculate decay and ingrowth as part of the Peak PRG model. Also, as stated in section 2.2.2, decay is not included in the secular equilibrium output because it is assumed that the parent is continually being renewed. The other 2 output options, described in sections 2.2.3 and 2.2.4, apply the decay function according to the table below. See section 4.10.7 to learn more about the half-life decay function used for the last 2 output options.

Media	Is decay applied?
Soil (soil and 2D)	Yes
Air	With and without decay options are presented
Water (surface, tap, & soil to groundwater)	No
Biota-Direction Ingestion	No

2.3 Slope Factors/Risk Coefficients (SFs)

EPA classifies all radionuclides as Group A carcinogens ("carcinogenic to humans"). Group A classification is used only when there is sufficient evidence from epidemiologic studies to support a causal association between exposure to the agents and cancer. The appendix radionuclide table, from the Center for Radiation Protection Knowledge, lists ingestion, inhalation, and external exposure cancer slope factors (risk coefficients for total cancer morbidity) for radionuclides in conventional units of picocuries (pCi). Ingestion and inhalation slope factors are central estimates in a linear model of the age-averaged, lifetime attributable radiation cancer incidence (fatal and nonfatal cancer) risk per unit of activity inhaled or ingested, expressed as risk/pCi. External exposure slope factors are central estimates of lifetime attributable radiation cancer incidence risk for each year of exposure to external radiation from photon-emitting radionuclides distributed uniformly in a thick layer of soil, expressed as risk/yr per pCi/gram soil. External exposure slope factors can also be used that have units of risk/yr per pCi/cm² soil. When combined with site-specific media concentration data and appropriate exposure assumptions, slope factors can be used to estimate lifetime cancer risks to members of the general population due to radionuclide exposures. EPA currently provides guidance on inhalation risk assessment in RAGS Part F (Risk Assessment Guidance for Superfund Volume I: Human Health Evaluation Manual, Part F, Supplemental Guidance for Inhalation Risk Assessment). This guidance only addresses chemicals. The development of inhalation slope factors for radionuclides differs from the guidance presented in RAGS Part F for development of inhalation unit risk (IUR) values for chemicals.

The SFs from the Center for Radiation Protection Knowledge differ from the values presented in HEAST. The SFs were calculated using ORNL's DCAL software in the manner of Federal Guidance Report 12 and 13. For the calculation of soil ingestion slope factors, a standard soil density of 1.6 g/cm³ has been used. The radionuclides presented are those provided in the International Commission on Radiological Protection (ICRP) Publication 107. This document contains a revised database of nuclear decay data (energies and intensities of emitted radiations, physical half-lives, and decay modes) for 1,252 naturally occurring and man-made radionuclides. ICRP Publication 107 supersedes the previous database, ICRP Publication 38, published in 1983.

Inhalation risk and dose coefficients for Rn-222, Rn-220, Bi-212, Bi-214, Pb-212, Pb-214, and Po-218 were updated in January 2017 and can be found here. The updated values are for inhalation of individual radionuclides without accompanying progeny but include the contribution to risk from ingrowth of radioactive progeny in the body following intake of a parent radionuclide. This approach allows the user to derive cancer risk and effective dose estimates for any known or hypothetical combination of Rn-222 or Rn-220 and its short-lived progeny in air. Rn-219 is not included in the update due to the large uncertainty in the distribution of decays of Rn-219 and its progeny in the body.

2.3.1 Metastable Isotopes

Most dose and risk coefficients are presented for radionuclides in their ground state. In the decay process, the newly formed nucleus may be in an excited state and emit radiation (e.g., gamma rays) to lose the energy of the state. The excited nucleus is said to be in a metastable state, which is denoted by the chemical symbol and atomic number appended by "m" (e.g., Ba-137m). If additional higher energy metastable states are present, then "n", "p", ... is appended. Metastable states have different physical half-lives and emit different radiations and thus unique dose and risk coefficients. In decay data tabulations of ICRP 107), if the half-life of a metastable state was less than 1 minute, then the radiations emitted in de-excitation are included with those of the parent radionuclide. Click to see a graphical representation of the decay of Cs-137 to Ba-137.

Eu-152, in addition to its ground state, has two metastable states: Eu-152m and Eu-152n. The half-lives of Eu-152, Eu-152m, and Eu-152n are: 13.5 y, 9.31 m and 96 m, respectively, and the energy emitted per decay is 1.30 MeV, 0.080 MeV, and 0.14 MeV, respectively.

2.4 Radionuclide-Specific Parameters

Several radionuclide-specific parameters are needed for development of the PRGs. The parameters are selected from a hierarchy of sources.

2.4.1 Sources

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

1. IAEA TRS 472 (IAEA). Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Terrestrial and Freshwater Environments. Technical Reports Series No. 472. International Atomic Energy Agency, Vienna. 2010. [IAEA TRS 364. Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Temperate Environments (Technical Reports Series No. 364), 1994 was used to supplement egg, poultry and swine transfer factors.] Spreadsheet of values.
2. Environment Agency (EA). Initial radiological assessment methodology - part 2 methods and input data. Spreadsheet of values.
3. NCRP 123 (NCRP). NCRP Report No. 123, Screening Models for Releases of Radionuclides to the Atmosphere, Surface Water, and Ground. National Council on Radiation Protection and Measurements. January 22, 1996. Spreadsheet of values.
4. EPA Radionuclide Soil Screening Level (SSL). Soil Screening Guidance for Radionuclides: User's Guide. Office of Solid Waste and Emergency Response (OSWER) Directive 9355.4-16A. October 2000. Spreadsheet of values.
5. RESRAD. User's Manual for RESRAD Version 6. Environmental Assessment Division, Argonne National Laboratory. July 2001. Spreadsheet of values.
6. BAES. A Review and Analysis of Parameters for Assessing Transport of Environmentally Released Radionuclides through Agriculture. C. F. Baes III, R. D. Sharp, A. L. Sjoreen, R.W. Shor. Oak Ridge National Laboratory 1984. Spreadsheet of values.
7. ICRP 107. Nuclear Decay Data for Dosimetric Calculations. International Commission on Radiological Protection Publication 107. Ann. ICRP 38 (3), 2008.
8. EPAKD. Understanding Variation in Partition Coefficient, Kd, Values. Volume II: Review of Geochemistry and Available Kd Values for Cadmium, Cesium, Chromium, Lead, Plutonium, Radon, Strontium, Thorium, Tritium (3H), and Uranium. Office of Air and Radiation. EPA 402-R-99-004B. August 1999. Volume III: Review of Geochemistry and Available Kd Values for Americium, Arsenic, Curium, Iodine, Neptunium, Radium, and Technetium. Office of Air and Radiation. EPA 402-R-04-002C. July 2004. Spreadsheet of values.

2.4.2 Hierarchy by Parameter

Generally the hierarchies below are followed.

1. Half-life (yr), Decay mode, Atomic weight, Atomic number and Decay energy. ICRP 107.
2. Milk transfer factor (TF_dairy (day/L)). IAEA, EA, NCRP, RESRAD. TF_dairy is the volumetric activity density in milk (pCi/L) divided by the daily intake of radionuclide (pCi/day).
3. Beef transfer factor (TF_beef (day/kg)). IAEA, EA, NCRP, RESRAD. TF_beef is the mass activity density in beef (pCi/kg fresh weight) divided by the daily intake of radionuclide (in pCi/d).
4. Fin Fish bioconcentration factor (BCF (L/kg)). IAEA, EA, RESRAD. BCF is the ratio of the radionuclide concentration in the fin fish tissue (pCi/kg fresh weight) from all exposure pathways relative to that in water (pCi/L).
5. Shellish bioconcentration factor (BCF (L/kg)). IAEA. BCF is the ratio of the radionuclide concentration in the shellfish tissue (pCi/kg fresh weight) from all exposure pathways relative to that in water (pCi/L).
6. Poultry transfer factor (TF_poultry (day/kg)). IAEA. TF_poultry is the mass activity density in poultry (pCi/kg fresh weight) divided by the daily intake of radionuclide (in pCi/d).
7. Egg transfer factor (TF_egg (day/kg)). IAEA. TF_egg is the mass activity density in egg (pCi/kg fresh weight) divided by the daily intake of radionuclide (in pCi/d).
8. Swine transfer factor (TF_swine (day/kg)). IAEA. TF_swine is the mass activity density in swine (pCi/kg fresh weight) divided by the daily intake of radionuclide (in pCi/d).
9. Sheep Milk transfer factor (TF_sheep-milk (day/L)). IAEA. TF_sheep-milk is the volumetric activity density in sheep milk (pCi/L) divided by the daily intake of radionuclide (pCi/day).
10. Sheep transfer factor (TF_sheep (day/kg)). IAEA, EA. TF_sheep is the mass activity density in sheep (pCi/kg fresh weight) divided by the daily intake of radionuclide (in pCi/d).
11. Goat Milk transfer factor (TF_goat-milk (day/L)). IAEA. TF_goat-milk is the volumetric activity density in goat milk (pCi/L) divided by the daily intake of radionuclide (pCi/day).
12. Goat transfer factor (TF_goat (day/kg)). IAEA. TF_goat is the mass activity density in goat (pCi/kg fresh weight) divided by the daily intake of radionuclide (in pCi/d).
13. Soil-to-water partition coefficient (K_d (mg/kg-soil per mg/L water or simplified = L/kg)). EPAKD, IAEA, SSL, RESRAD, BAES. (K_d is the ratio of the mass activity density (pCi/kg) of the specified solid phase (usually on a dry mass basis) to the volumetric activity density (pCi/L) of the specified liquid phase.
14. Soil-to-plant transfer factor-wet (Bv_wet (pCi/g plant per pCi/g soil)). IAEA, EA, NCRP, SSL, RESRAD, BAES. The values for cereal grain are used from IAEA. Bv_wet is the ratio of the activity concentration of radionuclide in the plant (pCi/kg wet mass) to that in the soil (pCi/kg dry mass). Note: Some Bv_wet values were derived from Bv_dry sources, assuming the ratio of dry mass to fresh mass was presented in the source documents.
• For carbon, the only value in the hierarchy is found in RESRAD. This value is excluded, as it overestimates root uptake. See section 2.5.4 for a detailed discussion of the carbon transfer factor derivation.
15. Soil-to-plant transfer factor-dry (Bv_dry (pCi/g plant per pCi/g soil)). IAEA, EA, NCRP, SSL, RESRAD, BAES. The values for cereal grain are used. Bv_dry is the ratio of the activity concentration of radionuclide in the plant (pCi/kg dry mass) to that in the soil (pCi/kg dry mass). Note: Some Bv_dry values were derived from Bv_wet sources, assuming the ratio of dry mass to fresh mass was presented in the source documents.
• For carbon, the only value in the hierarchy is found in RESRAD. This value is excluded, as it overestimates root uptake. See section 2.5.4 for a detailed discussion of the carbon transfer factor derivation.

Bv_wet and Bv_dry can be determined using the following equations.

and:

2.5 Biota Modeling

2.5.1 Produce Modeling

There are 23 individually calculated PRGs that make up the default produce PRG. The 23 individual fruits and vegetables, as well as animal products selected for use in the PRG calculator, have ingestion rates for homegrown biota in the Exposure Factors Handbook (EFH). Each individual PRG is determined based on produce-specific data, such as intake rate, soil-to-plant transfer factors (Bv_wet), and soil mass loading factor (MLF). These 23 individual PRGs are then summed by inverse reciprocal to determine a total produce PRG. The MLFs and intake rates used in the determination of the default biota PRGs are based on fresh weight. Intake rates, MLFs, and transfer factors were updated in June 2021 in a revised Technical Memorandum. The final version of this document was published in September 2021 and may be found here.

2.5.1.1 Intake Rates (g/day)

Table 2.5.1-A provides all of the default produce intake rates that are used to determine the total produce PRG. The delineation of (FW) in the column header indicates that the intake rates are for fresh weight; these are the intake rates used when the tool is run in default mode. In site-specific mode, the user may choose between Fresh Weight (FW) or Cooked Weight (CPW), which takes cooking and prepartion loss into account. In addition, the user may also add rice and cereal grain to the produce output. These intake rates can be found in Table 2.5.1-B below and are only given in dry weight (DW). In user-provided mode, the user may change produce-specific and element-specific parameters to model produce that is not provided in this tool, such as soil-to-plant transfer factor, mass loading factor, contaminated fraction, and intake rates.

In addition, a local food survey can be conducted. Much of the methodology in the Guidance for Conducting Fish and Wildlife Consumption Surveys may be useful for surveying produce consumption to determine site-specific food intake rates. Another potential source for intake rates, particularly for food exposures not included in the Exposure Factors Handbook, is the Food Commodity Intake Database (FCID). If the FCID is used, the user must convert the data to g/day, as it is required for use in this tool.

To determine which produce are commonly cultivated in the area around the site, users should contact their county extension office. The National Pesticide Information Center has an interactive map that allows users to choose their state and county and then connects them to their county extension office.

Table 2.5.1-A	Intake Rate for Farmer Child (g/day) (FW)	Intake Rate for Farmer Adult (g/day) (FW)	Intake Rate for Resident Child (g/day) (FW)	Intake Rate for Resident Adult (g/day) (FW)	Intake Rate for Farmer Child (g/day) (CPW)	Intake Rate for Farmer Adult (g/day) (CPW)	Intake Rate for Resident Child (g/day) (CPW)	Intake Rate for Resident Adult (g/day) (CPW)
Fruit
Apples	82.7	84.8	72.0	73.9	42.9	44.0	37.3	38.3
Berries other than Strawberries	24.2	35.2	24.2	35.2	12.5	18.2	12.5	18.2
Citrus	206.0	306.5	206.0	306.5	106.8	158.9	106.8	158.9
Peaches	98.2	103.1	110.2	115.7	50.9	53.5	57.1	60.0
Pears	79.6	59.8	69.4	52.1	41.3	31.0	36.0	27.0
Strawberries	27.5	40.6	27.5	40.6	14.2	21.1	14.2	21.1
Vegetables
Asparagas	11.9	40.1	11.9	40.1	8.1	27.4	8.1	27.4
Beets	6.0	34.4	6.0	34.4	4.1	23.5	4.1	23.5
Broccoli	14.8	34.1	13.2	30.5	10.1	23.3	9.0	20.8
Cabbage	11.0	79.5	11.8	85.1	7.5	54.3	8.0	58.1
Carrots	13.1	24.4	14.5	27.1	8.9	16.6	9.9	18.5
Corn	31.6	82.1	23.2	60.2	21.6	56.1	15.8	41.1
Cucumbers	16.3	54.9	24.5	82.3	11.2	37.5	16.7	56.2
Lettuce	3.4	36.7	3.4	36.7	2.3	25.0	2.3	25.0
Lima Beans	22.0	33.9	22.0	33.9	15.0	23.2	15.0	23.2
Okra	9.4	30.4	9.4	30.4	6.4	20.8	6.4	20.8
Onions	7.5	27.3	5.9	21.5	5.1	18.6	4.0	14.7
Peas	20.4	31.6	22.6	35.0	13.9	21.6	15.5	23.9
Peppers	7.4	23.9	5.9	19.1	5.1	16.3	4.1	13.0
Pumpkins	21.2	63.5	21.2	63.5	14.5	43.4	14.5	43.4
Snap Beans	28.7	54.5	28.3	53.8	19.6	37.2	19.3	36.8
Tomatoes	42.2	94.0	36.0	80.1	28.9	64.2	24.6	54.7
White Potatoes	52.4	141.8	47.3	127.8	35.8	96.9	32.3	87.3
Total	837.5	1517.1	816.4	1485.5	486.7	932.6	473.5	911.9

Table 2.5.1-B	Intake Rate for Farmer Child (g/day) (DW)	Intake Rate for Farmer Adult (g/day) (DW)	Intake Rate for Resident Child (g/day) (DW)	Intake Rate for Resident Adult (g/day) (DW)
Rice	49.6	98.9	41.0	81.9
Cereal Grain	48.1	84.8	39.8	70.2
Total	97.7	183.7	80.8	152.1

2.5.1.2 Soil-to-Plant Transfer Factors (Bv_wet)

The new soil-to-plant transfer factors (Bv_wet) from IAEA (TRS-472) are unique to climate zone, soil type, and produce type. There are three climate zones (Temperate, Tropical, and Subtropical), seven soil types (Default, Sand, Loam, Clay, Organic, Coral Sand, and Other), and 25 produce types implemented in the PRG calculator. When the tool is run in default mode, the climate zone is temperate, the soil type is Default (which applies to all soil types), and 23 produce types are used. Corn and rice are not used in default mode because the parameters used for these are based on dry weight, whereas the other 23 produce are based on fresh weight. For rice, IAEA did not specify a particular climate zone; therefore, the rice transfer factors have been applied to all three climate zones.

Climate Zones

The following map of the Holdridge Life Zones shows how the climate zones are distributed across the United States. Additionally, the Köppen-Geiger climate classification maps are available. This resource could be consulted to apply site-specific climate zone inputs for calculating PRGs and risk for ingestion of produce items. The Köppen-Geiger climate zone classification for every county in the U.S.A. is available here.

*The Holdridge life zones of the conterminous United States in relation to ecosystem mapping. Journal of Biogeography, 26, 1032.

Soil Types

Table 2 below describes the soil classification used in TRS-472. The Coral Sand and Other soil types are not listed in Table 2. The 'Other' soil type classification, in a temperate climate, was created for soils without characterization data and for mineral soils with unknown sand and clay contents (TRS-472, pg. 9). For tropical climates, the 'Coral Sand' soil type classification was changed from 'Other', given in TRS-472, because it refers to soils that are outside the classification scheme used here, such as Marshall Island soils, classified by the authors as coral sand soil (TRS-472, pg. 73).

*Technical Report Series no. 472.

*Land Data Assimilation Systems (LDAS). NASA

Produce Types

The following table illustrates which soil-to-plant transfer factor categories from IAEA are used for each produce type in the PRG calculator. The individual produce output only lists the category name from IAEA; however, a value from a secondary source may be utilized.

Table 2.5.1-C	Primary Transfer Factor Category	Primary Transfer Factor Source	Secondary Transfer Factor Category	Secondary Transfer Factor Source	Tertiary Transfer Factor Category	Tertiary Transfer Factor Source
Fruit
Apples	Woody Tree	IAEA	Fruit	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Berries other than Strawberries	Shrub	IAEA	Fruit	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Citrus	Woody Tree	IAEA	Fruit	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Peaches	Woody Tree	IAEA	Fruit	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Pears	Woody Tree	IAEA	Fruit	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Strawberries	Herbaceous	IAEA	Fruit	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Vegetables
Asparagas	Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Beets	Root	IAEA	Root Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Broccoli	Non-Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Cabbage	Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Carrots	Root	IAEA	Root Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Corn	Maize Grain	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Cucumbers	Non-Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Lettuce	Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Lima Beans	Legume Seed	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Okra	Non-Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Onions	Root*	IAEA	Root Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Peas	Legume Seed	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Peppers	Non-Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Pumpkins	Non-Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Snap Beans	Legume Seed	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Tomatoes	Non-Leafy Vegetable	IAEA	Green Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
White Potatoes	Tuber	IAEA	Root Vegetable	EA	None	NCRP-123, RADSSL, RESRAD, and Baes
Grains
Rice	Rice	IAEA	None	NCRP-123	None	RADSSL, RESRAD, and Baes
Cereal Grain	Cereal Grain	IAEA	None	NCRP-123	None	RADSSL, RESRAD, and Baes

*The IAEA TRS-472 guidance lists onions as both root vegetables and non-leafy vegetables. The environment agency (EA), however, only lists onions as root vegetables. When the ORNL/TM-2016/328 was originally released, onion was listed as a non-leafy vegetable. For consistency with EA and due to root vegetable BVs being generally more protective, the onion BV designation was updated from non-leafy vegetable to root vegetable.

While included in the initial hierarchy analysis, RESRAD and BAES sources do not contribute to the current output. They are retained in the user guide for informational purposes.

Please open the flow chart in a new tab to view a larger image. Carbon is missing from this chart. Please see section 2.5.4 of this user guide for information about how a soil-to-plant transfer factor was derived for Carbon in the PRG calculator.

2.5.1.3 Irrigation Rate (I_r) and Period (F) Derivation

The default irrigation rate used in the produce models is based on the commonly reported requirement of 1 inch of water per square foot per week. To convert this value to units of L/m² - day used in the calculator, the following conversions are necessary.

If 1 square foot = 144 square inches, then 1 inch of water/sqft makes 144 cubic inches which is equal to 2.36 L/sqft per week. There are 10.76 square feet per square meter and 7 days per week. The following equation presents all the conversions to convert the units.

2.36 L/ft² - week × 10.76 ft²/m² × 1 week/7 days = 3.62 L/m² - day (truncated).

The calculator assumes all the water will be coming from irrigation and not rainfall. The average rainfall for the continental United States is 30 inches per year or 0.762 meters per year. The area of the United States is 8.08E+12 square meters. Using the above conversion process the average daily rainfall is 2.1 L/m² - day. Use the calculator in site-specific mode to adjust the irrigation rate to match the meteorological conditions at your site.

The default Irrigation period is 0.25. This equates to 3 months of the year or about 91 days. Using seed to harvest times for 65 fruits and vegetables a range of 70 to 95 days was calculated to be the growing season when irrigation would occur. An irrigation period of 91 days, or a 0.25 fraction of the year, represents a protective irrigation rate. The seed to harvest times and watering requirements for specific fruits and vegetables are presented in the following table.

Table 2.5.1-D*	days to harvest	days to harvest (min)	days to harvest (max)	watering requirement (inches)
Fruit
Banana	NA			great amount
Blackberry	NA			evenly moist
Cantaloupe (Melons)	70-100	70	100	1 or more/week
Kiwifruit	NA			evenly moist
Melons (Honeydew)	70-100	70	100	1 or more/week
Pineapple	NA			evenly moist
Raspberry	NA			evenly moist
Strawberry	NA			evenly moist
Watermelon	65-90	65	90	1-2/week
Vegetables
Artichoke	365			moist soil
Arugula	40	40	40	moist soil
Asparagus	730			1 inch
Beans	60	60	60	1-1.5/week
Beets	45-65	45	65	1/week
Belgium Endive	21-28	21	28	evenly moist
Broccoli	70-100	70	100	1-2/ week
Brussels Sprouts	85-110	85	110	1 or more/week
Cabbage	80-180	80	180	1-1.5/week
Cardon	28-42	28	42	evenly
Carrots	50-80	50	80	1/week
Cauliflower	55-100	55	100	moist always
Celeriac	90-120	90	120	moist always
Celery	112	112	112	well watered
Chard (Swiss)	55-60	55	60	moist always
Chayote	120-150	120	150	moist always
Chickpeas (garbanzo beans)	100	100	100	evenly moist
Chicory and Radicchio	85-100	85	100	evenly moist
Chinese cabbage	50-70	50	70	lightly moist
Collards	85-95	85	95	1-1.5/week
Corn (sweet)	60-100	60	100	1 or more/week
Cresses	quick			evenly moist
Cucumbers	55-65	55	65	1/week
Eggplant	100-150	100	150	1/week
Endive and Escarole	85-100	85	100	evenly moist
Fava Beans	85	85	85	do not over water
Florence Fennel	90-115	90	115	moist but not wet
Garlic	120-150	120	150	moist but not wet
Horseradish	140-160	140	160	evenly moist
Jerusalem Artichoke (Sunchoke)	120-150	120	150	even watering
Kale	70-80	70	80	well watered
Kohlrabi	48-60	48	60	evenly moist
Leeks	75-120	75	120	evenly moist
Lettuce (Head)	40-50	40	50	regular even water
Lettuce (Leaf)	65-90	65	90	regular even water
Lima Beans	60-80	60	80	1/week
Mizuna	40	40	40	moist but not wet
Mustard Greens	30-40	30	40	moist never dry
New Zealand Spinach	55-65	55	65	evenly moist
Okra	55-65	55	65	1/week
Onions	80-150	80	150	evenly moist
Parsnips	100-130	100	130	moist but not wet
Peanuts	120-130	120	130	1/week
Peas	55-80	55	80	evenly moist
Peas (Southern)	60-90	60	90	moist never dry
Peppers	60-95	60	95	evenly moist
Potato (Sweet)	100-150	100	150	1/week
Potatoes	75-135	75	135	moist but not wet
Pumpkins	90-120	90	120	1-1.5/week
Radicchio	60-100	60	100	evenly moist
Radish	20-60	20	60	moist but not wet
Rhubarb	730			moist but not wet
Rutabaga	60-90	60	90	moist never dry
Salsify	120-150	120	150	evenly moist
Scorzonera	120-150	120	150	evenly moist
Shallots	100-120	100	120	1/week
Sorrel	60	60	60	evenly moist
Soybeans	45-100	45	100	evenly moist
Spinach	37-53	37	53	evenly moist
Squash (Summer)	50-65	50	65	evenly moist
Squash (Winter)	60-110	60	110	evenly moist
Taro	200			well watered
Tomatillos	65-70	65	70	moist not totally dry
Tomatoes	40-80	40	80	moist but not wet
Turnips	30-60	30	60	1-2/week
Zucchini	40-60	40	60	evenly moist
Average		70	95

* Harvest to Table

2.5.2 Animal Product Modeling

2.5.2.1 Intake Rates (g/day)

In default mode, the (FW) intake rates from Table 2.5.2-A are used. Similar to produce, there is an option to select Cooked Weight in site-specific mode. The intake rates for poultry include chicken, turkey, and duck. In default mode, the parameters used for poultry and eggs are for chicken specifically (i.e., Q_p, etc.). If eggs and poultry are selected in site specific mode, the user will have the option to switch between chicken, turkey, duck, and goose, which will change the previously mentioned respective parameters; however, the transfer factor used will still be meant for chicken or duck per TRS-472. If the user has a specific transfer factor for turkey or goose, then user-provided mode should be used.

Table 2.5.2-A	Intake Rate for Farmer Child (g/day) (FW)	Intake Rate for Farmer Adult (g/day) (FW)	Intake Rate for Farmer Child (g/day) (CPW)	Intake Rate for Farmer Adult (g/day) (CPW)
Dairy - Cow	1116.4	1438.0	n/a	n/a
Beef	64.6	270.1	31.9	133.5
Swine	32.2	151.1	15.9	74.7
Poultry	48.8	175.5	24.1	86.7
Egg	25.1	97.3	n/a	n/a
Fish	36.1	155.9	22.1	95.6
Shellfish	21.3	208.9	13.0	128.1
Total	1344.5	2496.8	107	518.6

Site-Specific mode also offers the user the option to add animal products from Table 2.5.2-B to the output. The tool has transfer factors for these products; however, the user will need to enter their own intake rate data, as the tool does not provide any. Again, a local food survey can be conducted, which may utilize much of the methodology in the Guidance for Conducting Fish and Wildlife Consumption Surveys for surveying animal product consumption to determine site-specific food intake rates. In addition, the Food Commodity Intake Database (FCID) may be used to find intake rate data, but the user must convert the data to g/day, as it is required for use in this tool.

Table 2.5.2-B	Intake Rate for Farmer Child (g/day) (FW)	Intake Rate for Farmer Adult (g/day) (FW)	Intake Rate for Farmer Child (g/day) (CPW)	Intake Rate for Farmer Adult (g/day) (CPW)
Sheep	n/a	n/a	n/a	n/a
Sheep Milk	n/a	n/a	n/a	n/a
Goat	n/a	n/a	n/a	n/a
Goat Milk	n/a	n/a	n/a	n/a

2.5.2.2 Animal Transfer Factors (TF)

While included in the initial hierarchy analysis, RADSSL and BAES sources do not contribute to the current output. They are retained in the user guide for informational purposes. Please see section 2.4.1 for the transfer factor source hierarchy.

Please open the flow chart in a new tab to view a larger image.

2.5.3 Mass Loading Factor

A mass loading factor (MLF) is the amount, or mass, of soil that adheres to the plant surface. The following table lists the MLFs used in this tool according to plant type. For more information on how these were derived, please see the Technical Memorandum: Biota Modeling in EPA's Preliminary Remediation Goal and Dose Compliance Concentration Calculators for Use in EPA Superfund Risk Assessment: Explanation of Intake Rate Derivation, Transfer Factor Compilation, and Mass Loading Factor Sources: 2021 Revision.

Table 2.5.3-A	Mass Loading Factor (MLF)	Units	Reference
Fruit
Apples	1.60E-04	g dry soil / g fresh plant	EA (2009)
Berries other than Strawberries	1.66E-04	g dry soil / g fresh plant	EA (2009)
Citrus	1.57E-04	g dry soil / g fresh plant	EA (2009)
Peaches	1.50E-04	g dry soil / g fresh plant	EA (2009)
Pears	1.60E-04	g dry soil / g fresh plant	EA (2009)
Strawberries	8.00E-05	g dry soil / g fresh plant	EA (2009)
Vegetables
Asparagas	7.90E-05	g dry soil / g fresh plant	EA (2009)
Beets	1.38E-04	g dry soil / g fresh plant	EA (2009)
Broccoli	1.01E-03	g dry soil / g fresh plant	Hinton (1992), SSG-Appendix G
Cabbage	1.05E-04	g dry soil / g fresh plant	EA (2009)
Carrots	9.70E-05	g dry soil / g fresh plant	EA (2009)
Corn	1.45E-04	g dry soil / g fresh plant	Pinder & McLeod (1989), SSG-Appendix G
Cucumbers	4.00E-05	g dry soil / g fresh plant	EA (2009)
Lettuce	1.35E-02	g dry soil / g fresh plant	Hinton (1992), SSG-Appendix G
Lima Beans	3.83E-03	g dry soil / g fresh plant	Hinton (1992), SSG-Appendix G
Okra	8.00E-05	g dry soil / g fresh plant	EA (2009)
Onions	9.70E-05	g dry soil / g fresh plant	EA (2009)
Peas	1.78E-04	g dry soil / g fresh plant	EA (2009)
Peppers	2.22E-03	g dry soil / g fresh plant	EA (2009)
Pumpkins	5.80E-05	g dry soil / g fresh plant	EA (2009)
Snap Beans	5.00E-03	g dry soil / g fresh plant	Hinton (1992), SSG-Appendix G
Tomatoes	1.77E-03	g dry soil / g fresh plant	Hinton (1992), SSG-Appendix G
White Potatoes	2.10E-04	g dry soil / g fresh plant	EA (2009)
Grains
Cereal Grains	2.50E-01	g dry soil / g dry plant	Hinton (1992)
Rice	2.50E-01	g dry soil / g dry plant	Hinton (1992)
Pasture	2.50E-01	g dry soil / g dry plant	Hinton (1992)

2.5.4 Soil-to-Plant Transfer Factor Derivation for Carbon

The value of 5.5 given in Table D.3 of the RESRAD User's Manual for carbon root uptake was derived from data in Ng et al. 1968. Table 4 of Ng 1968 presents a carbon composition in typical agricultural soil of 2.00E+04 ppm and a carbon composition in terrestrial plants of 1.10E+05 ppm in Table 10A. 1.10E+05 divided by 2.00E+004 gives the value of 5.5 reported in RESRAD. This value assumes that all the carbon in the plant is taken up by the roots; however, this is not the case. Photosynthesis is the primary source of carbon in plants. Carbon may be present in gas form in soils and volatilize into the plant canopy, where it may be taken up by the plant in some fraction depending on atmospheric conditions. It is typically estimated that 2% of plant carbon comes from soil (either directly or by uptake from the sub-canopy atmosphere). The other 98% of plant carbon comes from the above-canopy atmosphere, which is assumed not to contain carbon from the contaminated site. Consider that a plant is about 90% water and of the 10% dry matter about 40% is carbon. Therefore, plants comprise about 4% carbon on a fresh weight basis. A mineral soil is typically about 2% to 5% organic matter, which corresponds to 0.8% to 2% carbon on a dry mass basis. Thus, taking the ratio of carbon contents results in a transfer factor of 4%/(0.8% to 2%) = 5.0 to 2.0 g fresh plant/g dry soil. The next step is to apply the 2% fraction of plant carbon derived from soil. The resulting range of transfer factors is 0.1 to 0.04 (2%*(5.0 to 2.0)). The value of 0.1 is chosen for the calculation of PRGs and is used for all the BVwet values. BVdry values are derived for each plant type based on individual moisture content. For comparison purposes, the 5.5 value from RESRAD gives a transfer factor of 0.11 if the 2% assumption is made.

The above derivation assumes that all the carbon taken up by the plant is radioactive. In situations where radioactive carbon is mixing with stable carbon, a site-specific transfer factor can be derived using a model called "specific activity". Essentially, specific activity is the concentration ratio of the radioactive form to the stable form of carbon. Specific activity assumes that within a compartment (i.e., soil), the radioactive contaminant mixes with the stable form both chemically and physically. Plants uptake the element in the same ratio as it exists in the soil compartment, resulting in the same ratio in the plant as in the soil compartment.

To determine a site-specific soil-to-plant transfer factor, actual site data must be available. Further, the flux rate of the element must be in a steady-state condition. The environmental compartments must be well defined and the fluxes between compartments well understood. For further information, refer to the following: AMEC/004041/007 section 5, ANL/EAD-4 Appendix L, and IAEA TECDOC 1616 page 550.

2.5.5 Caloric Values of Produce and Animal Products

This section presents the caloric values of the produce, and animal products discussed in Section 2.5.1&2. These caloric values (kcal/g) are then multiplied by the intake rates (g/day) from 2.5.1-A&B to give dailiy caloric intake values (kcal/day). With this information it will be possible to select the appropraite produce and animal products for site-specific analysis to ensure a sustainable caloric intake for the receptors chosen. Caloric values for additional produce and seafood not currently given in the calculator are also presented. The caloric values presented are based on fresh (raw) weight and the weight after cooking. All of the caloric data was taken from the USDA's FoodData Central search tool with preference to the "Foundation Foods" and the "Atwater General Factors" energy data for caloric information.

This spreadsheet contains all of the intake rates from Section 2.5.1&2 and the caloric values from the USDA used to calculate the caloric information presented in Tables 2.5.5-A - 2.5.5-J. This spreadsheet can be used to calculate unique caloric intakes on a site-specific basis.

Table 2.5.5-A presents the caloric intake of the adult and child farmer for the default produce types.

Table 2.5.5-A	Calories for Farmer Child (kcal/day) (FW)	Calories for Farmer Adult (kcal/day) (FW)	Calories for Farmer Child (kcal/day) (CPW)	Calories for Farmer Adult (kcal/day) (CPW)	USDA kcal/g FW	USDA Note FW	USDA kcal/g CPW	USDA Note CPW
Fruit
Apples	51.27	52.58	22.74	23.32	0.62	red delicious	0.53	boiled, skinless
Berries other than Strawberries	15.49	22.53	na	na	0.64	blueberries	na
Citrus	107.12	159.38	na	na	0.52	navel orange	na
Peaches	45.17	47.43	na	na	0.46		na
Pears	50.15	37.67	na	na	0.63		na
Strawberries	9.90	14.62	na	na	0.36		na
Vegetables
Asparagus	2.38	8.02	1.78	6.03	0.20		0.22
Beets	2.58	14.79	1.80	10.34	0.43		0.44
Broccoli	5.77	13.30	3.54	8.16	0.39		0.35
Cabbage	3.41	24.65	1.73	12.49	0.31	green	0.23
Carrots	6.29	11.71	3.12	5.81	0.48		0.35
Corn	27.18	70.61	20.74	53.86	0.86	yellow	0.96	yellow
Cucumbers	2.61	8.78	na	na	0.16		na
Lettuce	0.58	6.24	na	na	0.17	iceberg	na
Lima Beans	74.36	114.58	17.25	26.68	3.38	mature seeds	1.15	mature seeds
Okra	3.10	10.03	1.41	4.58	0.33		0.22
Onions	2.85	10.37	2.24	8.18	0.38	yellow	0.44
Peas	16.52	25.60	5.84	9.07	0.81	green	0.42
Peppers	1.70	5.50	1.43	4.56	0.23	bell, green	0.28	sweet, green
Pumpkins	5.51	16.51	2.90	8.68	0.26		0.20
Snap Beans	11.48	21.80	6.86	13.02	0.40	green	0.35	green
Tomatoes	7.60	16.92	5.20	11.56	0.18	red	0.18	red
White Potatoes	36.16	97.84	32.94	89.15	0.69		0.92	baked
Total	489.18	811.45	131.5	295.48

Table 2.5.5-B presents the caloric intake of the adult and child resident for the default produce types.

Table 2.5.5-B	Calories for Resident Child (kcal/day) (FW)	Calories for Resident Adult (kcal/day) (FW)	Calories for Resident Child (kcal/day) (CPW)	Calories for Resident Adult (kcal/day) (CPW)	USDA kcal/g FW	USDA Note FW	USDA kcal/g CPW	USDA Note CPW
Fruit
Apples	44.64	45.82	19.77	20.30	0.62	red delicious	0.53	boiled, skinless
Berries other than Strawberries	15.49	22.53	na	na	0.64	blueberries	na
Citrus	107.12	159.38	na	na	0.52	navel orange	na
Peaches	50.69	53.22	na	na	0.46		na
Pears	43.72	32.82	na	na	0.63		na
Strawberries	9.90	14.62	na	na	0.36		na
Vegetables
Asparagus	2.38	8.02	1.78	6.03	0.20		0.22
Beets	2.58	14.79	1.80	10.34	0.43		0.44
Broccoli	5.15	11.90	3.15	7.28	0.39		0.35
Cabbage	3.66	26.38	1.84	13.36	0.31	green	0.23
Carrots	6.96	13.01	3.47	6.48	0.48		0.35
Corn	19.95	51.77	15.17	39.46	0.86	yellow	0.96	yellow
Cucumbers	3.92	13.17	na	na	0.16		na
Lettuce	0.58	6.24	na	na	0.17	iceberg	na
Lima Beans	74.36	114.58	17.25	26.68	3.38	mature seeds	1.15	mature seeds
Okra	3.10	10.03	1.41	4.58	0.33		0.22
Onions	2.24	8.17	1.76	6.47	0.38	yellow	0.44
Peas	18.31	28.35	6.51	10.04	0.81	green	0.42
Peppers	1.36	4.39	1.15	3.64	0.23	bell, green	0.28	sweet, green
Pumpkins	5.51	16.51	2.90	8.68	0.26		0.20
Snap Beans	11.32	21.52	6.76	12.88	0.40	green	0.35	green
Tomatoes	6.48	14.42	4.43	9.85	0.18	red	0.18	red
White Potatoes	32.64	88.18	29.72	80.32	0.69		0.92	baked
Total	472.05	779.82	118.85	266.37

Table 2.5.5-C presents the caloric intake of the adult and child farmer and resident for the default grains.

Table 2.5.5-C	Calories for Farmer Child (kcal/day) (DW)	Calories for Farmer Adult (kcal/day) (DW)	Calories for Resident Child (kcal/day) (DW)	Calories for Resident Adult (kcal/day) (DW)	USDA kcal/g DW	USDA Note
Rice	178.06	355.05	147.19	294.02	3.59	white, raw
Cereal Grain	175.57	309.52	145.27	256.23	3.65	corn
Total	353.63	644.57	292.46	550.25

Table 2.5.5-D provides the caloric content of more produce.

Table 2.5.5-D	USDA kcal/g FW	USDA Note FW	USDA kcal/g CPW	USDA Note CPW
Fruit
Apricot	0.48		na
Avocado	1.6	raw	na
Banana	0.89		na
Blackberries	0.43		na
Cantaloupe	0.43		na
Cranberries (fresh)	0.46		na
Dates	2.77	medjool	na
Grapefruit	0.33	white	na
Grapes	0.80	green	na
Honeydew Melon	0.36		na
Kiwifruit	0.64		na
Lemon	0.29	peeled	na
Lime	0.3		na
Mandarin Oranges	0.53		na
Mango	0.6		na
Nectarine	0.43		na
Pineapple	0.60		na
Plums	0.46		na
Pomegranate	0.83		na
Raspberries	0.52		na
Sweet Cherries	0.71		na
Tangerine	0.53		na
Watermelon	0.3		na
Vegetables
Artichoke	0.73	Jerusalem	0.53
Brussels Sprouts	0.43		0.36
Cauliflower	0.25		0.23
Celery	0.17		0.18
Green Onion	0.27	tops	na
Leaf Lettuce	0.22		na
Mushrooms	0.44	shiitake	0.56	shiitake
Radishes	0.16		0.17
Spinach	0.28	mature	0.23
Sweet Potato	0.79	skinless	0.90
Turnips	0.28		0.22
Winter Squash	0.40	acorn	0.34	acorn
Zucchini	0.21		0.15

Table 2.5.5-E provides the caloric content of more grains.

Table 2.5.5-E	USDA kcal/g DW	USDA Note
Amaranth	3.71
Barley Grain	3.52	pearled
Buckwheat	3.56
Bulgur	3.42
Flax Grain	3.50	flakes
Khorasan	3.37
Millet	3.76
Oat Grain	2.46	bran
Quinoa	3.68
Rye	3.38
Sorghum	3.29
Spelt	3.38
Wheat	3.31	soft red winter

Table 2.5.5-F presents the caloric intake for the default animal products.

Table 2.5.5-F	Calories for Farmer Child (kcal/day) (FW)	Calories for Farmer Adult (kcal/day) (FW)	Calories for Farmer Child (kcal/day) (CPW)	Calories for Farmer Adult (kcal/day) (CPW)	USDA kcal/g FW	USDA note FW	USDA kcal/g CPW	USDA note CPW
Dairy - Cow	681.00	877.18	na	na	0.61	whole	na
Beef	156.98	656.34	78.47	328.41	2.43	80/20 raw	2.46	pan-broiled
Swine	73.42	344.51	47.22	221.86	2.28	ground raw	2.97	cooked
Poultry	64.90	233.42	45.55	163.86	1.33	ground, raw	1.89	ground, pan-browned
Egg	35.89	139.14	na	na	1.43	egg whole	1.55	hard-boiled
Fish	51.98	224.50	40.66	175.90	1.44	bluefin, raw	1.84	bluefin, cooked
Shellfish	18.11	177.57	11.57	114.01	0.85	crustaceans, shrimp, raw	0.99	crustaceans, shrimp, cooked
Total	1082.28	2652.65	224.78	1016.86

Table 2.5.5-G presents the caloric content of sheep and goat products.

Table 2.5.5-G	USDA kcal/g FW	USDA note FW	USDA kcal/g CPW	USDA note CPW
Sheep	2.82	lamb, ground, raw	2.83	lamb, ground, broiled
Sheep Milk	1.08	milk, fluid	na
Goat	1.09	game meat, goat, raw	1.43	game meat, goat, roasted
Goat Milk	0.69	milk, fluid	na

Table 2.5.5-H provides the caloric content of more seafood items.

Table 2.5.5-H	Calories for Farmer Child (kcal/day) (FW)	Calories for Farmer Adult (kcal/day) (FW)	Calories for Farmer Child (kcal/day) (CPW)	Calories for Farmer Adult (kcal/day) (CPW)	USDA kcal/g FW	USDA note FW	USDA kcal/g CPW	USDA note CPW
Finfish
Catfish	34.30	148.11	23.21	100.38	0.95	channel, wild	1.05	channel
Cod	29.60	127.84	23.21	100.38	0.82	Atlantic, raw	1.05	Atlantic
Flounder/Sole	25.27	109.13	19.01	82.22	0.70	flatfish, raw	0.86	flatfish
Haddock	26.71	115.37	19.89	86.04	0.74	raw	0.90
Halibut	32.85	141.87	24.53	106.12	0.91	raw	1.11
Ocean Perch	28.52	123.16	21.22	91.78	0.79	raw	0.96
Orange Roughy	27.44	118.48	23.21	100.38	0.76	raw	1.05
Pollock	33.21	143.43	26.08	112.81	0.92	Atlantic, raw	1.18	Atlantic
Rainbow Trout	42.96	185.52	33.15	143.40	1.19	wild, raw	1.50	wild
Rockfish	35.02	151.22	27.40	118.54	0.97	raw, striped bass	1.24	striped bass
Salmon, Red	55.23	238.53	76.25	329.82	1.53	sockeye, raw	3.45	sockeye, smoked
Salmon, Pink	45.85	197.99	33.81	146.27	1.27	raw	1.53
Swordfish	51.98	224.50	38.01	164.43	1.44	raw	1.72
Tilapia	34.66	149.66	28.29	122.37	0.96	raw	1.28
Tuna	51.98	224.50	40.66	175.90	1.44	bluefin, raw	1.84	bluefin
Shellfish
Blue Crab	18.53	181.74	10.79	106.32	0.87	raw	0.83	moist heat
Clams	18.32	179.65	19.24	189.59	0.86	raw	1.48	moist heat
Lobster	16.40	160.85	11.57	114.01	0.77	northern, raw	0.89	northern, moist heat
Oysters	10.86	106.54	13.26	130.66	0.51	eastern, raw	1.02	eastern, moist heat
Scallops	14.70	144.14	14.43	142.19	0.69	mixed species, raw	1.11	bay and sea, steamed
Shrimp	18.11	177.57	12.87	126.82	0.85	crustaceans, shrimp, raw	0.99	crustaceans, shrimp, cooked

Combining the default intake rates in Tables 2.5.1-A&B with the caloric data presented in Tables 2.5.5-A-F, the total amount of calories consumed with the produce, grains, and animal products are determined for the default adult and child farmer.

Table 2.5.5-I presents the total calories per day for the default farmer.

Table 2.5.5-I	Calories for Farmer Child (kcal/day) (FW)	Calories for Farmer Adult (kcal/day) (FW)	Calories for Farmer Child (kcal/day) (CPW)	Calories for Farmer Adult (kcal/day) (CPW)
Produce	489.18	811.45	131.5	295.48
Grains (DW)	353.63	664.57	353.63	664.57
Animal Products	1082.28	2652.65	224.78	1016.86
Total	1952.09	4128.67	709.91	1976.90

Combining the default intake rates in Tables 2.5.1-A&B with the caloric data presented in Tables 2.5.5-A-F, the total amount of calories consumed with the produce and grains are determined for the default adult and child resident.

Table 2.5.5-J presents the total grams and calories per day for the default resident.

Table 2.5.5-J	Calories for Resident Child (kcal/day) (FW)	Calories for Resident Adult (kcal/day) (FW)	Calories for Resident Child (kcal/day) (CPW)	Calories for Resident Adult (kcal/day) (CPW)
Produce	472.05	779.82	118.85	266.37
Grains (DW)	292.46	550.25	292.46	550.25
Total	764.51	1330.07	411.31	816.62

2.6 PRGs in Context of Superfund Modeling Framework

This PRG calculator focuses on the application of generic and simple site-specific approaches that are part of a larger framework for calculating concentration levels for complying with risk-based criteria. Generic PRGs for a 1 × 10^-6 cancer risk standard are provided by viewing either the tables in the PRG Download Area section of this calculator or by running the PRG Calculator section of this website with the "Defaults" option. Part 3 of the Soil Screening Guidance for Radionuclides: Technical Background Document provides more information about five more detailed soil-to-groundwater models that are part of the same framework.

Generic PRGs are calculated from the same equations presented in the site-specific portion of the calculator, but they are based on a number of default assumptions chosen to be protective of human health for most site conditions. Generic PRGs can be used in place of site-specific PRG levels; however, in general, they are expected to be more protective than site-specific levels. The site manager should weigh the cost of collecting the data necessary to develop site-specific PRGs with the potential for deriving a higher PRG that provides an appropriate level of protection.

The framework presented in Part 3 of the Soil Screening Guidance for Radionuclides: Technical Background Document includes more detailed modeling approaches that take into account more complex site conditions than the generic or simple site-specific methodology used for the soil-to-groundwater scenario in this calculator. More detailed approaches may be appropriate when site conditions (e.g., very deep water table, very thick uncontaminated unsaturated zone, soils underlain by karst or fractured rock aquifers) are substantially different than those assumed in the generic or simple-site methodology presented in this calculator. Further information on using more detailed approaches may be found in "Simulating Radionuclide Fate and Transport in the Unsaturated Zone: Evaluation and Sensitivity Analyses of Select Computer Models" (U.S. EPA 2002c). This report provides a detailed technical analysis of five unsaturated zone fate and transport models for radionuclides.

To avoid unnecessary inconsistency between radiological and chemical risk assessment and radiological dose assessment at the same site, users should generally use the same model for chemical and radionuclide risk assessment and radionuclide dose assessment. If there is a reason on a site-specific basis for using another model, justification for doing so should be developed. The justification should include specific supporting data and information in the administrative record. The justification normally would include the model runs using both the recommended EPA PRG model and the alternative model. Users are cautioned that they should have a thorough understanding of both the PRG recommended model and any alternative model when evaluating whether a different approach is appropriate. When alternative models are used, the user should adjust the default input parameters to be as close as possible to the PRG inputs, which may be difficult since models tend to use different definitions for parameters. Numerous computerized mathematical models have been developed by EPA and other organizations to predict the fate and transport of radionuclides in the environment; these models include single-media unsaturated zone models (for example, groundwater transport) as well as multi-media models. These models have been designed for a variety of goals, objectives, and applications; as such, no single model may be appropriate for all site-specific conditions. Generally, even when a different model is used to predict fate and transport of radionuclides through different media, EPA recommends using the PRG calculators for the remedial program to establish the risk-based concentrations to ensure consistency with CERCLA, the NCP, and EPA's Superfund guidance for remedial sites. Prior to using another model for risk assessment at a CERCLA remedial site, EPA regional staff should consult with the Superfund remedial program's National Radiation Expert (Stuart Walker, at (703) 603-8748 or walker.stuart@epa.gov). For more information on this issue, please see questions 10 and 16 on pages 12 and 17-18 of Radiation Risk Assessment At CERCLA Sites: Q & A (EPA 540-R-012-13, May 2014).

At CERCLA sites, carcinogenic risk to receptors should generally not exceed 1 × 10^-4. How that is achieved is a risk management decision that varies at different sites, which is why it is not detailed in the PRG calculator documentation. At CERCLA remedial sites, excess cancer risk from both radionuclides and chemical carcinogens should be summed to provide an estimate of the combined risk presented by all carcinogenic contaminants. For more information, see question 29 in Radiation Risk Assessment At CERCLA Sites: Q & A. This document contains even more information on the CERCLA risk assessment process for radioactively contaminated sites in general, including the role of the PRG calculator. The PRG calculator is recommended by EPA to develop risk-based PRGs for Superfund remedial radiation risk assessments.

2.7 Understanding Risk Output on the PRG Website

The PRG calculator provides an option to "Select risk output". This requires the calculator to be run in "Site Specific" mode. Note: The "Soil-to-Groundwater" medium does not have risk output, and the risk option will become disabled when selected. The risk values presented on this site are radionuclide-specific values for individual contaminants in air, water, soil, and biota that may warrant further investigation or site cleanup.

2.7.1 General Considerations for the Risk Output

The first step in the risk assessment process is hazard identification, where site data is screened against PRGs to identify radionuclides of potential concern (ROPCs). The "Risk Characterization" step, in the risk assessment process, incorporates the outcome of the exposure and toxicity assessment steps to calculate the Excess Lifetime Cancer Risk (ELCR) identified in the data screening part of the hazard identification step. ELCR is calculated for each land use determined appropriate for the site. The ELCR sum is presented for each exposure route for all ROPCs and for each ROPC across all exposure routes. The process used to calculate ELCR in this calculator follows the traditional method of first calculating a CDI (Chronic Daily Intake).

The basic equation for calculating ELCR is:

The secular equilibrium equation for calculating ELCR is:

The risk results are color coded to identify risk ranges and radionuclides of concern (ROCs). The colors and the associated risk ranges are presented in the table below.

Excess Lifetime Cancer Risk
Risk Range	Risk < 0.000001	Risk > 0.000001	Risk > 0.0001
Color Code	No shading	Yellow	Red

2.7.2 General Considerations for Entering Site Data

There are four calculator output options available to the user.

• PRG Output Option #1: Assumes period of peak risk (with decay and progeny ingrowth) (Peak PRG)
• PRG Output Option #2: Assumes Secular Equilibrium Throughout the Chain (no decay - parent and progeny in constant equilibrium)
• PRG Output Option #3: Does Not Assume Secular Equilibrium, Provides Results for Progeny Throughout Chain (with decay where appropriate)
• PRG Output Option #4: Does Not Assume Secular Equilibrium, Selected Isotopes Only (with decay where appropriate)

The first two options include progeny contributions in the risk calculations of the parent. The third and fourth options do not. However, if the third option is selected, the media concentrations for the progeny are automatically populated with the concentration entered for the parent. The progeny will have their risk calculated independent of each other. This autofill feature is not available when isotope chains overlap. The autofill feature is solely for convenience and does not assume secular equilibrium.

If the data is collected from a site where secular equilibrium is assumed to be present, the user need only enter the activity of the parent in the calculator, and a representative risk of the parent and all progeny will be presented in the calculator output. In the case of non-secular equilibrium, the current "state of the chain" may not be known or easily calculated. In the case of relatively fast decaying isotopes, significant decay or ingrowth of progeny may have occurred since the sample date. Further, determining future activity of the contaminants may be useful in planning for future release of a property.

A Decay Chain Activity Projection Tool has been developed, where the user can select an isotope, enter a length of time to allow decay and ingrowth, and enter the beginning activity of the parent. The results of this tool, pictured below, are the activities of the parent and progeny at the end of the decay and ingrowth of progeny time. These activities can be entered into the PRG calculator to calculate risk using the third and fourth PRG Output options.

2.7.3 One-Hit Rule

The linear risk equations, listed above, are valid only at low risk levels (below estimated risks of 0.01). For sites where radiological exposure might be high (estimated risks above 0.01), an alternate calculation should be used. The one-hit equation, which is consistent with the linear low-dose model, should be used instead (RAGS, part A, ch. 8). The one-hit rule is applied as follows:

ELCR = 1 - exp^{(-CDI × SF)}

or, when necessary for tap water inhalation:

ELCR = 1 - exp^{(-CDI × SF × A_eq)}

The definitions for these equation parameters are provided in section 2.7.1. See section 4.10.8 for information about A_eq. The results presented in the PRG use this rule. In the following instances, the one-hit rule is used independently in the risk output tables:

• Risk from a single exposure route for a single radionuclide.
• Summation of single radionuclide risk (without one-hit rule applied to single radionuclide results) for multiple exposure routes (right of each row).
• Summation of risk (without one-hit rule applied to single radionuclide results) from a single exposure route for multiple radionuclides (bottom of each column).
• Summation of total risk (without one-hit rule applied to single radionuclide results or summations listed above) from multiple radionuclides across multiple exposure routes (bottom right hand cell).

2.8 Sensitivity /Uncertainties Analysis

Uncertainties exist in any default PRG equation and they can often be resolved by changing an exposure parameter value.

A sensitivity/uncertainty analysis is the quantitative assessment of how changing a single value impacts the PRG calculation. Sensitivity analyses are generally conducted to determine what variables in a PRG equation have the greatest impact when changed. Evaluating the uncertainty associated with a PRG calculation can identify a need for site-specific parameters. If the level of uncertainty is acceptable, then the PRGs can be used accordingly. However, if the resulting uncertainty is not acceptable, the sensitivity analysis will help to identify those parameters that, if measured on a site-specific basis, would decrease uncertainty to the greatest extent.

Examples of site-specific variables that can greatly impact a PRG are:

• soil-to-water partition coefficients,
• biota transfer factors,
• water to air volatilization,
• gamma shielding factors, and
• area correction factors

Examples of site-specific exposure parameters that can greatly impact a PRG are:

• exposure duration,
• intake rates, and
• fraction ingested of contaminated biota

The quantitative assessment of uncertainties in the transport and exposure parameters provides considerable information about the variability and sensitivity of the calculated default PRGs. These results are important because point estimates of these parameters are used to determine the extent of remediation necessary through the Superfund process. The point estimates provided as guidance by the U.S. Environmental Protection Agency (EPA) are often conservative and can result in an overestimate of the potential risk. The intent of this section is to raise awareness of the potential cost savings of developing site-specific values for key parameters. The results can be used to quantify the degree to which the standard default values overestimate the predicted percentiles of exposure (typically 90-95th percentile values) that they are intended to estimate and to determine which parameters are responsible for the majority of the variation. Please see Guidance for Conducting Risk Assessments and Related Risk Activities for the DOE-ORO Environmental Management Program for additional information.

There are several methods for identifying the most important contributors to uncertainty. Monte Carlo simulation with either Simple Random Sampling (SRS) or Latin Hypercube Sampling (LHS) is often the most robust method for propagating uncertainty through either simple or complex models. Please see An Introductory Guide to Uncertainty Analysis in Environmental and Health Risk Assessment for additional information.

Many of the PRG equations are linear, and changing a parameter has a directly proportional impact on the PRG. For example, doubling the intake rate in a fish ingestion PRG will reduce the PRG by half.

2.9 Advanced Calculator Uses (Postprocessing and Replicating Discontinued PRG Options)

The PRG calculator results, when exported in a spreadsheet, can be used to create site-specific PRGs that cannot be developed solely within the calculator. This postprocessing of results can be useful when the calculator doesn't offer the precision necessary for remedial decision. Additionally, the calculator can be used to replicate the old +D PRGs.

2.9.1 Postprocessing Calculator Results to Incorporate Site-Specific MCNP Factors

Nearly all of the exposure parameters in the PRG equations can be changed by using the site-specific option in the calculator. Further, many of the isotope-specific values (i.e., slope factors, dose coefficients, partition coefficients, and transfer factors for plants and animals) can be changed by using the user-provided option in the calculator. While many options are given for users to select site size and clean soil cover, it may be necessary to derive a "factor" specific to a particular site using tools like Monte Carlo Nuclear Particle (MCNP). For example, a user may want to use MCNP or another tool to develop a site-specific ACF for an unusual situation (e.g., a site that consists of flat land that is next to a cliff face and both are contaminated). The following is a brief description of how to postprocess calculator results when including the results for a factor that was developed in another tool such as MCNP. All variables in the ingestion and inhalation equations can be changed in the calculator itself; the external exposure route is the most likely to require postprocessing.

The calculator offers the option to export results in a spreadsheet format. Using the spreadsheet, the "factor" supplied by the calculator can be substituted with a site-specific factor supplied by the user. The procedure is relatively straight forward, as all the factors are in the denominator of the screening level equations. Simply multiply the screening level by the ratio of the default factor to the site-specific factor.

This general process does work; but please consider the following, as further steps may be necessary:

• If adjusting a factor in the external exposure route, the total PRG needs to be recalculated using the inverse sum of reciprocals.
• If adjusting a factor in parentheses, such as a resident outdoor Gamma Shielding Factor (GSF_o), then more postprocessing is required.
• When adjusting a PRG calculated by the secular equilibrium option, factors for all the progeny need to be calculated and totaled using the inverse sum of reciprocals.
• The Peak PRG results are impossible to post process because the state of the chain (decay and ingrowth of all members) can't be replicated in a spreadsheet. Section 2.2.5 discusses what PRG output options are closest to the Peak PRG. In many cases, the parent only with decay or the SE PRGs may be identical to the Peak PRG. Post processing one of these substitute PRG options can replicate the Peak PRG results.

Here is an example of the PRG calculator default results for external (2-D soil volume) exposure for an indoor worker exposed to soil. The default GSF_i is 0.4 and represents the shielding provided by general subfloor materials from contaminated soil. In the case of a commercial building being constructed on a concrete slab, a site-specific shielding factor can be generated with MCNP and the site-specific PRG recalculated following the procedure discussed previously. Suppose a GSF_i was determined to be 0.2 with MCNP for Ra-226 without consideration of progeny. Users should note that post processing for Ra-226 would require these steps for each of the progeny with an external slope factor.

The original results are below and show a GSF_i of 0.4 (cell F5) and a PRG of 17.6 pCi/g (cell G5).

The postprocessed results are below with a GSF_i of 0.2 (cell H5) showing the resulting site-specific PRG (cell J5) is twice as large as the default value above, as expected. The green shaded cells need to be added and programmed by the user. Below the green cells, the formula for the postprocessing procedure is given.

Please contact your EPA regional risk assessor before post processing PRG calculator results for Superfund sites.

2.9.2 Replicating the Old +D PRGs

Prior to 2017, "+D" designated slope factors and subsequently +D PRGs were available as the preferred PRG output option. This designation indicated that the slope factor included the contribution from ingrowth of progeny out to 100 years. Similarly, +E indicated ingrowth out to 1000 years. HEAST provided the original table of the +D radionuclide slope factors, and ORNL 2014c with appendix provides the +D slope factors previously used in this calculator. The intention of this designation was to make PRGs protective by including the contributions from their short-lived decay products that were, at times, difficult to measure. The +D designation indicated that the parent radionuclide PRG included the risk contribution from its short-lived progeny. The PRGs presented in sections 2.2.1 and 2.2.2 independently model progeny during migration to groundwater and biota uptake, while the +D PRGs did not. The use of the +D PRGs was discontinued because of the following reasons that led to imprecision in the +D PRGs:

• The half-life of the parent isotope was used for all the short-lived progeny included in the +D to calculate decay.
• The K_d of the parent was used for all the short-lived progeny in the soil-to-water partitioning PRGs to calculate downgradient water concentrations.
• The biota transfer factors for the parent was used for all the short-lived progeny included in the +D to calculate nuclide uptake into plants and animals.

The steps to replicate the old +D PRGs are as follows.

• Select the PRG output option described in section 2.2.3 (Does Not Assume Secular Equilibrium, Provides Results for Progeny Throughout Chain).
• Select Site-Specific, then User-provided on the calculator main page.
• At this point, there are three ways to proceed to calculate +D PRGs.
• The easiest way is to just change the slope factors to the +D slope factors found in HEAST and adjust any exposure parameters. On the results page, the parent isotope PRG will be a +D PRG because +D slope factors were used.
• Alternatively, on the Site-Specific page, every isotope-specific parameter and every exposure parameter can be changed to match the old +D PRG inputs including: half-life, K_d, biota transfer factors, gamma shielding factors, and area correction factors. Make appropriate changes to all isotopes; specifically, do not change the slope factors to +D slope factors. The results of this endeavor will be a very close approximation to the old +D PRGs.
• Finally, if the desire is to determine what a modern version of a +D PRG would be, change nothing for any of the isotopes.
• For the second and third options above, on the results page, the individual isotope PRGs will be presented. The last step is to combine the appropriate parent and progeny PRGs to make a +D PRG. This is done by taking the inverse sum of the reciprocals of the individual PRGs. Replication of the +D PRGs for the biota route will be impossible, as the models have changed. Consult the table below to determine what progeny should be included in the summation method.

For the time-being, the RAIS Radionuclide PRG Calculator still offers +D PRGs. Below is a table of progeny and the terminal radionuclide used in +D and +E slope factors and dose coefficient development.

Progeny used for Derivation of +D and +E Slope Factors and Dose Coefficients

Principal Radionuclide (half-life in years)	Associated decay chain	Terminal Radionuclide	Half-life (years)
Cs-137+D (30.2)	Ba-137m	Ba-137	stable
Cs-137+E (30.2)	Ba-137m	Ba-137	stable
Pu-239+D (2.41E+04)	U-235m	U-235	7.04E+08
Pu-239+E (2.41E+04)	U-235m	U-235	7.04E+08
Ra-226+D (1.60E+03)	Rn-222, Po-218, Pb-214, At-218, Bi-214, Rn-218, Po-214, Tl-210	Pb-210	22
Ra-226+E (1.60E+03)	Rn-222, Po-218, Pb-214, At-218, Bi-214, Rn-218, Po-214, Tl-210	Pb-210	22
Ra-228+D (5.75E+00)	Ac-228	Th-228	2
Ra-228+E (5.75E+00)	Ac-228	Th-228	2
Rn-222+D (1.05E-02)	Po-218	Pb-214	5.10E-05
Rn-222+E (1.05E-02)	Po-218	Pb-214	5.10E-05
Sr-90+D (28.8)	Y-90	Zr-90	stable
Sr-90+E (28.8)	Y-90	Zr-90	stable
Th-232+D (1.41E+10)	Ra-228, Ac-228	Th-228	1.91E+00
Th-232+E (1.41E+10)	Ra-228, Ac-228, Th-228, Ra-224, Rn-220, Po-216, Pb-212, Bi-212, Po-212, Tl-208	Pb-208	stable
U-235+D (7.04E+08)	Th-231	Pa-231	3.3E+04
U-235+E (7.04E+08)	Th-231	Pa-231	3.3E+04
U-238+D (4.47E+09)	Th-234, Pa-234m, Pa-234	U-234	2.4E+05
U-238+E (4.47E+09)	Th-234, Pa-234m, Pa-234	U-234	2.4E+05

The sections that follow describe how to use the generic download tables. The generic download tables are to be used in the absence of site-specific exposure data. When site-specific exposure data is available, these sections also provide information developing a conceptual site model, addressing background radiation, and potential limitations of the PRG models presented in this guidance.

3.1 Using the PRG Tables

The tables in the PRG Download Area provide generic concentrations in the absence of site-specific risk assessments. Screening concentrations can be used for:

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

3.2 Developing a Conceptual Site Model

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

The CSM below presents the land uses, media, and exposure routes quantified in this calculator along with hypothetical source and release mechanisms.

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

• Are there potential ecological concerns?
• Is there potential for land use other than those listed in the PRG calculator (i.e. , resident and worker)?
• 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)?
• Are all current and potential future land uses presented?
• What media may become contaminated in the future?
• Is the selected PRG output option appropriate for the equilibrium of the site contaminants?

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

3.3 Background Radiation

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

3.4 Potential Problems and Limitations

As with any risk-based 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 PRG levels to a site without adequately developing a conceptual site model that identifies relevant exposure pathways and exposure scenarios;
• Use of PRG levels as cleanup levels without the consideration of other relevant criteria such as ARARs;
• Use of PRG levels as cleanup levels without verifying numbers with a health physicist/risk assessor;
• Use of outdated PRG levels tables that have been superseded by more recent publications;
• Not considering the effects from the presence of multiple isotopes; and
• Not considering the individual model limitations as described in section 4 (e.g., inhalation of tap water only considers C-14 and H-3 as well as Rn-222, Rn-220, and Rn-219, including their short-lived progeny.

Table 1 presents the definitions of the variables and their default values. The PRG default values and exposure models are consistent with the Dose Compliance Concentrations for Radionuclides (DCC) calculator. Both the PRG and DCC calculator default values are consistent with the Regional Screening Levels for Chemical Contaminants at Superfund Sites (RSL) calculator, when the same pathways are addressed (e.g., ingestion and inhalation), and are analogous when pathways are similar (e.g., dermal and external exposure). This calculator, the DCC, and the RSL all follow the recommendations in the OSWER Directive concerning use of exposure parameters from the 2011 Exposure Factors Handbook. Any alternative values or assumptions used in remedy evaluation or selection on a CERCLA site should be presented with supporting rationale in Administrative Records.

Table 1. Recommended Default Exposure Parameters