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

March 2020

• New daily vehicle kilometers traveled and length of roadway classes have been added.
• The 1/FD term has been removed from all mechanical PEF equations as it is a dispersion correction factor related to duration of construction and is not needed for these models.

May 2018

• 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.

September 2017

• 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. When the secular equilibrium SDCC output option is selected, the SDCC Calculator now gives the option to show the individual progeny contributions for the SDCC (and dose) output.

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.

September 2015

• The mechanical PEF equations were updated to represent new particle size multipliers (k-pp) for public paved roads from the 2011 AP 42 for Paved Roads.
• The silt loading factors (SLFs), by roadway class, have been updated with values from 2011 National Emissions Inventory, version 1 Technical Support Document June 2014 - DRAFT , Table 63, Page 104, concerning paved roads. Also new daily vehicle kilometers traveled and length of roadway classes have been updated. The source websites are annual vehicle kilometers traveled and length. The SLFs for urban collector roadway class are used for both major and minor collector roadway classes. Also, the rural interstate roadway class SLFs were used for the "other freeways and expressways" roadway class.
• The EPA has updated the emission factor equations for paved roads found in AP-42. The documentation of changes is presented in Emission Factor Documentation for AP-42, Section 13.2.1 Paved Roads. The changes are centered around the denominator in the SDCC PEF equations involving the functions of silt loading and vehicle weight. In addition, the emission factor for exhaust, brake, and tire wear was removed to eliminate the possibility of double counting emissions. These changes will result in new default mechanical PEFs.
• Evaluation of the AP-42 updates led to the investigation of the Q/C_m usage in calculating the five mechanical PEFs used in the SDCC equations. It was decided that the Q/C defaults for A, B and C dispersion constants from EPA 2002 would be used for all mechanical PEFs. This results in the Q/C_m being based on the Inverse of the ratio of the 1-h. geometric mean air concentration and the emission flux along a straight road segment bisecting a square site.
• New dose coefficients (DCFs) have been programmed that were derived following FGR 12 and 13 using the updated isotope list from ICRP 107. DCFs 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.
• A forward dose assessment option was added to the calculator page. By selecting this option, the user is asked for media concentrations and the dose is returned using SDCC equation inputs.
• Source depth-specific area correction factors (ACFs) are now provided. Unique ACFS are now given for the various DCFs (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 gamma shielding factors (GSFs) are now given for the various DCFs (ground plane, 1 cm, 5 cm, 15 cm, and infinite depth) and various soil cover depths. The Center for Radiation Protection Knowledge has provided GSF_o 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.

September 2014

• This calculator follows the recommendations in the OSWER Directive concerning use of exposure parameters from the 2011 Exposure Factors Handbook.

March 2011

• New generic tables are now available that address the issues listed in the previous entry.
• The calculator results, presented in Becquerels, were modified to correct a units conversion problem.

August 2010

• Many updates were performed to establish consistency with other calculators. These updates are mainly in appearance and in functionality.