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page title goes here Risk Assessment

PRG What's New

The What's New section keeps users informed of toxicity value changes, exposure parameter changes, isotope-specific parameter changes, and any equation format changes. Please check this site frequently to be advised of any recent changes.

February 2024

Section 2.5.5 was added to the user's guide providing caloric values of produce and animal products. This information, combined with the intake rates given in sections 2.5.1 and 2.5.2, will allow for the selection of a reasonable number of produce and animal products to include for the resident and farmer scenarios.

February 2023

As a result of an extensive independent external peer review of the DCC, several changes were made to the PRG tool.

  • The composite worker soil equation for external exposure has been modified to allow for the worker to spend time indoors and outdoors. The default parameters have not changed; however, in site-specific mode, the time spent indoors and outdoors can be changed.
  • The calculator will now allow selection of individual source depths when "Soil 2-D External Exposure" media is selected, rather than returning results for all five depths.
  • A new FAQ was added explaining the application of Peak PRGs with future maximum risk up to billions of years in the future.
  • Instead of containing the calculator flow in a single browser tab, a new tab is opened for the site-specific page and the results page. This feature eliminates the need to reselect the radionuclides on the calculator main page and allows for site-specific parameters to be changed without losing data when using the back button. More details are presented in this FAQ.
  • Section was added to the user's guide expanding on the derivation of the irrigation rate (Ir) and period (F).
  • Section 4.10.9 was added to the user's guide expanding on the derivation of modeling parameters for animals and animal products.
  • Two new sections were added to Table 1 providing resident and farmer age-adjusted intake fractions for produce and farm products.
  • Many sections of the home page, user's guide, and equations pages were updated with clarifying language.

January 2023

  • The presentation of the decay order of a limited number of metastable isotopes in the PRG calculator output tables and plots was corrected. Some tool output tables and/or decay plots were presenting the non-metastable isotope before the metastable. This decay order correction only impacted the calculation of a limited number of Peak PRGs.
  • The Peak PRG values for resident, soil to groundwater, recreator, and farmer land uses were updated to correct a temporary misapplication of the exposure duration. Other land uses and PRG output options were not impacted.

September 2022

  • Default PRG Generic Tables are now available. They were last available September 2014. They will be revised in the future as changes are made to the defaults in the PRG calculator.

July 2022

  • The Secular Equilibrium PRG output option now presents the results on a mass basis in addition to activity.

May 2022

  • The Peak PRG output option now offers the ability to select a time period of interest. Section of the User's Guide describes the usage of this option and gives guidance on when it is applicable.
  • The new Peak PRG output option and the consumption of local food portion of the PRG calculator was peer reviewed. The peer review comments and EPA resolution can be found here. The resolution of the comments resulted in many language updates and additions to the User’s Guide to improve understanding and readability.
  • The Radionuclide Decay Chain tool was added to the navigation box. This tool can predict the activity after a period of time (T) given a measurement of activity (A) for the chain parent.

June 2021

  • The Peak PRG output option is no longer a separate calculator and is merged with the main calculator. Section 2.2.1 of the User's Guide now includes a description of the Peak PRG and supporting documentation. Section 2.2.5 of the User's Guide has been added to give a comparison on the new peak PRG option to the other PRG output options for the common Superfund nuclides. This section discusses six categories of isotopes based on the relationship of the parent and progeny half-lives to explain how some Peak PRGs are more like SE PRGs and how some Peak PRGs are more like parent only with decay PRGs. Of particular interest are the transuranic Peak PRGs and how they relate to their long-lived progeny Peak PRGS. Tables and graphs are presented.
  • Section 2.5 of the User's Guide has been updated. Fish exposure parameters have been separated into finfish and shellfish for the farmer land use. This includes new intake rates and transfer factors. Peppers have been added to the list of produce in the farmer and resident land uses. New intake rates are provided for all produce and animal products based on updated chapters of the Exposure Factors Handbook. The updated intake rates, MLFs, and transfer factor sources were provided in the draft of the revised Biota Modeling Technical Memorandum, which was finalized in September without any revisions that would change PRG calculator runs.
  • In the past Ra-226 and Ra-228 were included in the tap water inhalation route as a protective measure against the likelihood that radon would also be present. New programming has been added that removed these metals from the inhalation route and replaced them with radon and radon's short-lived progeny. On the site-specific page of the calculator, the user can alter the air exchange rate in the house for the resident and the farmer land uses. By changing the air exchange rate the radon progeny will be in disequilibrium. The new programming activates the tap water inhalation for radon for every isotope that decays into radon (i.e., Ac-227, Pu-240, U-238, etc.). Section 4.10.9 has been added to the User's Guide describing how the air exchange rate can impact progeny equilibrium. Sections 4.1.4 and 4.8.3 have been updated appropriately.
  • Section 2.8 of the User's Guide has been added to describe some advanced uses of the calculator. Topics discussed are replicating old +D PRGs and postprocessing calculator results with a spreadsheet.

October 2020

  • A new PRG output option was added, called peak PRG, which calculates the activity of the parent radionuclide to be protective of the peak excess lifetime cancer risk (ELCR) for the entire decay chain over time. For waste profiles that contain a refined radionuclide product with a relatively long half-life, the progeny may present more ELCR in the distant future than the parent in the present. By modeling the decay of the parent, with the ingrowth of all progeny, a protective peak PRG can be calculated and used to compare against current monitoring or sample data for the protection of future receptors. Benefits of the peak PRG are that future dates of peak ELCR are known. This knowledge helps make remedial decisions that are protective of future populations while reducing remediation costs, by not remediating a site where decay will reduce the ELCR naturally in a reasonable amount of time. Peak PRGs can also help design waste criteria and landfill caps protective of future ELCRs. The peak PRG output option is currently in a separate calculator and is discussed in a separate User's Guide instead of Section 2.2 "PRG Output Options" of the User's Guide which discusses the other three PRG output options. In the User's Guide there is a link to a technical report describing the development of this new PRG output option.

    The new peak PRG output option is now the preferred default PRG option for use at Superfund sites. In the near future the peak PRG calculator and User's Guide will be merged into one tool.

November 2019

  • The recreator incidental ingestion of surface water intake rates were updated to reflect changes in Table 3.7 of EFH 2019.

January 2019

  • All risk values are now calculated based on chronic daily intakes (CDI). These CDIs are provided in the risk output tables. Please see section 2.7.1 of the user guide for more information on how risk is calculated using CDIs.

May 2018

  • Updates to soil gamma shielding factors (GSFo and GSFb) have been implemented in the calculator. All GSF values were recalculated using MCNP to achieve a lower error and correct the non-linear regression issue for some isotopes. Each common Superfund isotopes full spectrum of emission energies was rerun. The monoenergetic values for low energy emissions were rerun for all other isotopes. Secondary photons produced during positron emissions were also included. The technical memorandum is still being updated, but the new GSF values can be found here.
  • While running the user provided option in site-specific mode, the calculator was showing duplicate records for C, H, Hg, I, Ni, Ru, S, and Te elemental isotopes. These duplicate records have been removed.

January 2018

  • The soil gamma shielding factor (GSFo and GSFb) database has been updated:
    • GSFo and GSFb values, for cover thicknesses 10cm - 100cm, were swapped between isotopes and their respective metastable isotopes. This has been corrected.
    • Some GSFo and GSFb values for non-gamma emitters were defaulted to 1 for all cover thicknesses. The values for these isotopes were changed to 0 for all cover thicknesses, as the minimum cover depth of 10cm would block all alpha and beta radiation. A list of the isotopes affected can be found here.
    • The isotopes listed below are also non-gamma emitters that previously had shielding factor values other than 1. The GSFo and GSFb values for these isotopes have also been set to 0 for all cover thicknesses. It is possible that progeny are gamma emitters as in the case of Cs-137 with its progeny Ba-137m.
      • Bi-210, Bk-249, Cs-137, Pm-147, Po-210, Pr-143, Pu-241, Tc-99, Y-90, Zn-69

July 2017

  • 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.
  • The soil gamma shielding factor (GSFo and GSFb) database has been updated:
    • Zr-97 GSFo values have been added for the 2 - 10 m cover depths.
    • Ra-226 and Ra-228 GSFo values have been added for the 0 to 100 cm cover depths. These missing values impacted any secular equilibrium PRG and risk outputs that included Ra-226 or Ra-228 as parents or progeny.
    • For the soil volume source thickness, the GSFo values have been corrected to match the supporting documentation for the 0 to 100 cm cover depths. The values incorporated represent a source depth of 1 meter to simulate infinite soil volume; previous values were based on a 2 meter simulation depth.

April 2017

  • New soil to plant transfer factors are available for carbon isotopes. See section 2.5.4 in the User's Guide.
  • Corrections to the secular equilibrium output were made for the soil to groundwater PRGs and the user-provided risk results.

January 2017

  • New inhalation Risk and Dose Coefficients are avilable for Rn-222, Rn-220, Bi-212, Bi-214, Pb-212, Pb-214, and Po-218.
  • The ingestion rate while swimming was updated based on Table 3.5 in EFH 2011. The recommended values of 120 ml/hr for children and 71 ml/hr for adults are now used.

December 2016 (revised)

  • The secular equilibrium (SE) PRG calculation has been revised. An unexpected error occurred in the SE PRGs when the ability to select more than one isotope was provided. The results have been restored to their initial values prior to the ability to select more than one isotope for SE PRG calculation.

December 2016

  • The +D and +E isotopes have been removed from the selection list. Now, a user may select the 'Assume secular equilibrium' to see PRG output for the entire chain.
  • In the resident, farmer, and indoor worker soil external exposure equations, a new variable has been added (GSFb) to account for the gamma shielding provided by clean soil cover under a building. It is combined with GSFi, the shielding provided by the building, to reduce exposures to receptors inside a building which is on top of clean soil over contaminated soil.
  • Previously, produce intake rates were based on general fruit and vegetable consumption rates. Now, the produce intake rates are derived from 22 individual produce items, found in the 2011 Exposure Factors Handbook, that contribute to the overall produce ingestion PRG. Mass loading factors (MLFs) were also improved, from a single MLF that was applied to all produce, to 22 individual MLFs that correspond with the 22 individual produce items that make up the new produce intake rates. In site-specific mode, users will now able to select additional animal products including Goat Milk, Sheep Milk, Goat Meat, and Sheep Meat, which are not included in the default animal product PRGs. Users will also be able to select Rice and Grains, which are not included in the default produce PRG. Formerly, the transfer factors used in this risk assessment tool were specific to element only. Now, the transfer factors are element, climate zone, soil type, and produce specific. For more detailed information, Biota Modeling in EPA's Preliminary Remediation Goal and Dose Compliance Concentration Calculators explains where these new intake rates, MLFs, and transfer factors were sourced and how they will be applied to the PRG calculator. This file is engineered for 2 sided printing.
  • The MCL document was modified to remove +D and +E isotopes.

November 2015

  • Additional source depth-specific soil gamma shielding factors (GSF) are now given for cover depths of 2 to 10 meters. The values are presented in this appendix.

September 2015

  • The MCL concentrations used in the soil to groundwater land use scenario have been updated.
  • The spreadsheet deriving the child and adult intake rates for biota was revised and derivation of the indoor and outdoor exposure times was added.

November 2014

  • The OSWER Directive concerning use of exposure parameters from the 2011 Exposure Factors Handbook recommends an adult body weight of 80 kg. While body weight isn't directly used in the PRG equations, the biota intakes in the Exposure Factors Handbook are given in g/kg body weight - day. New child and adult intake rates from the 2011 Exposure Factors Handbook were added for produce, milk, beef, pork, fish, eggs and poultry for the farmer and resident. See the User Guide for details on biota intake derivations. This spreadsheet shows how the child and adult intakes were derived from the data presented in the 2011 Exposure Factors Handbook.
  • The decay function was added to the resident, recreator and farmer biota PRGs that are back-calculated to soil.

September 2014

  • This calculator follows the recommendations in the OSWER Directive concerning use of exposure parameters from the 2011 Exposure Factors Handbook.
  • New slope factors have been programmed that were derived following FGR 12 and 13 using the updated isotope list from ICRP 107. 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.
  • The resident (and farmer) tap water scenario now includes the contribution from consuming produce irrigated with contaminated tap water. This is analgous to the resident soil scenario including the contribution consuming produce grown in contaminated soil.
  • Immersion was added to the tap water and recreational scenarios to address external exposure from gamma and beta emitters.
  • The Agricultural uptake models were completely changed. Now users can back calculate protective concentrations in water and soil as well as the produce itself. The water concentrations also now include irrigation of crops.
  • Farmer output now provides an interactive graph that depicts PRGs for when both soil and water are contaminated.
  • New Biota transfer factors and soil to water partition coefficients from the IAEA Technical Report Series No. 472 have been programmed into a hierarchy of sources. Section 2.3 of the User Guide describes the sources of the parameters and gives the hierarchy for each.
  • A forward risk assessment option was added to the calculator page. By selecting this option the user is asked for media concentrations and the risk is returned using PRG equation inputs.
  • Recreator scenario added for soil/sediment, surface water and generic game (land and fowl). Because there are very few default values for exposure parameters, the user must provide most of the exposure inputs.
  • Source depth-specific soil area correction factors (ACF) are now provided. Unique ACFs are now given for the various slope factors (ground plane, 1 cm, 5 cm, 15 cm and infinite depth). For further information on the derivation of the isotope-specific/area-specific ACF values for 2-D areas see the Center for Radiation Protection Knowledge ACF report and appendix containing +D and +E values.
  • Source depth-specific soil gamma shielding factors (GSF) are now given for the various slope factors (ground plane, 1 cm, 5 cm, 15 cm and infinite depth) and various soil cover depths. The Center for Radiation Protection Knowledge has provided GSFo values here and appendix containing +D and +E values.
  • The radionuclide decay chains, provided in the calculator output, have been updated to reflect new decay information provided in ICRP 107. In addition to tabular results, a visual diagram is provided depicting the branching fractions.
  • Two construction worker scenarios were added for the assessment of particulates emitted into the air from standard vehicle traffic as well as activities such as dozing, grading, tilling and excavating.

March 2011

  • The calculator results, presented in Becquerels, were modified to correct a units conversion problem.

August 2010

  • New tables were generated to correct the use of the wrong gamma shielding factor for worker soils.

July 2010

  • New tables were generated to reflect the changes made in June.

June 2010

  • Many updates were performed to make this calculator current with the EPA Superfund guidance in the radiological BPRG and SPRG, and the chemical RSL calculators. They are:
    • An ambient air scenario was added that evaluates PRGs with and without radioacive decay, identical to the ambient air scenario in the radiological BPRG and SPRG calculators.
    • A composite worker was added to evaluate Industrial PRGs that is identical to the RSL website.
    • The indoor air dilution factor was removed from the indoor component pieces of the resident, worker and farmer inhalation PRG scenarios to be consistent with the RSL website.
    • The tap water equations were modified to have the ingestion rate age-adjusted between children and adults consistent with the RSL website.
    • The ACF parameter was made isotope-specific and specific for eight different areas (slab sizes) similar to the SPRG caclulator.
    • Soil PRG equations for external exposure were added for ground plane, 1cm, 5cm and 15cm slope factors similar to the SPRG caclulator.
    • Exposure times for the resident and workers in the PRG equations were made identical to the RSL website.

March 2009

  • Half-lifes were added for Ba-133m+D, Cf-248+D, Fm-254+D, Hf-182+D, Ir-192m+D, Np-237+D, Pd-103+D, Ra-227+D, Ra-228+D, Sm-145+D, U-232+D and U-235+D. Because of these additions, PRG are now being generated in the calculator. Download tables will be updated at the next revision.

December 2008

  • The half-life of Am-242m was changed from 152 to 141 years.

July 2004

  • The default values for ETow-o (Outdoor Worker Exposure Time Outdoor) and ETiw-i (Indoor Worker Time Indoor) have been changed back to 0.33 from 1.0. This change is because the external exposure route was inadvertently affected. To sustain the desired intention of a worker being exposed 8 hours of the 8 hour worker day, the inhalation rate for workers was changed to 60 m3/day (this reflects an hourly inhalation rate of 2.5m3/hour).
  • The default values for ETowo (Outdoor Worker Exposure Time Outdoor) and ETiwi (Indoor Worker Time Indoor) have been changed from 0.33 to 1.0. This change reflects the desired intention of a worker being exposed 8 hours of the 8 hour worker day.

September 2002

  • The format of the PRG website has been updated to reflect the new EPA standard template.

August 2002

  • The agricultural equations have been updated to include ingestion of swine, ingestion of eggs, and ingestion of poultry.

May 2002

  • Adult-only ingestion slope factors for workers have been updated for the following radionuclides:
    • Ra-226+D => 2.95E-10 (risk/pCi)
    • U-235+D => 5.03-11 (risk/pCi)
    • U-238+D => 5.62E-11 (risk/pCi)
  • Also, the soil equations for tritium (H-3) have been modified to reflect a soil-to-air volatilization factor of 17 (m3/kg) which replaces the Particulate Emission Factor.

August 2001

January 2001

  • Note to Users: There has been a new release of toxicity values for radionuclides as presented in HEAST. Essentially, every slope factor has changed. In addition, oral values are tabulated separately for ingestion of tap water, dietary intakes (food), and incidental soil ingestion. Please consult the User's Guide section on radionuclide carcinogenicity for the derivation of radionuclide slope factors and guidance on their use. Also please note that the output of the Preliminary Remediation Goal and Human Health Exposure Modeling sections will reflect these changes in toxicity values.