page title goes here Risk Assessment
This figure depicts the migration of radon (Rn) in soil gas from radioactively contaminated soil and groundwater into buildings at a Superfund site. Radon in soil gas is shown to enter buildings through cracks in the foundation and openings for utility lines similar to other forms of contamination. Atmospheric conditions and building ventilation are shown to influence radon soil gas intrusion.
Welcome to the "Radon Vapor Intrusion Screening Level (RVISL) Calculator Home Page for Radionuclide Contaminants at Superfund Sites". This website was developed with the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) under an Interagency Agreement with the U.S. Environmental Protection Agency (EPA). The main purpose of this guidance is to provide a RVISL calculation tool to assist risk assessors, remedial project managers, and others involved with risk assessment and decision-making at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) sites in developing RVISLs or preliminary remediation goals (PRGs) for indoor Rn-222, Rn-220, and Rn-219 that are risk or dose based and for showing compliance with the UMTRCA indoor radon standards for Rn-222 and Rn-220.
The RVISL website is now the generally recommended source of indoor radon screening levels (SLs) from radioactive contaminants at Superfund sites for all EPA regions. The RVISL calculator output provides screening values and risk and dose estimates for residential and commercial/industrial exposures to radon in soil gas, air, and groundwater. The unified use of the RVISLs to screen radon at Superfund sites promotes national consistency. The RVISL uses the same database of toxicity values, chemical parameters, and inhalation exposure equations as the PRGs for Radionuclide Contaminants at Superfund Sites calculator. RVISLs are a type of PRG and both are a specific variety of the broad screening level (SL) category.
Note that for CERCLA remedial actions, dose assessment is generally done only to show compliance with a dose-based Applicable or Relevant and Appropriate Requirement (ARAR). EPA would recommend, where possible, Regions use measurements of radon indoors rather than rely on the transport portions of the RVISL. In particular, testing of groundwater or soil gas is not required to demonstrate compliance with RVISL Working Levels (WL), risk, or dose targets.
The RVISL calculator provides default parameters that can be modified to reflect site-specific conditions. In addition, the calculator presents the option to compare the indoor air concentration, entered by the user or derived from groundwater or soil gas activities, to state standards or Uranium Mill Tailings Radiation Control Act (UMTRCA) standards, which also may be potential ARARs. Below is a general description of SLs for radon. If the calculator is used with non-default inputs in a decision on a Superfund site, it is recommended that the inputs be clearly identified and justified by the user.
To ensure proper use of the calculator, please review the What's New, User's Guide, and Frequently Asked Questions links. In these pages, limitations of the RVISL models are discussed such as the inapplicability to landfills and disposal sites.
The EPA has prepared a fact sheet for the general public that describes RVISL uses, RVISL calculator operation, and land uses available for assessment. Additionally, this fact sheet describes the RVISL content in greater detail for EPA staff.
The RVISL calculator provides updated guidance for developing SLs or PRGs for indoor Rn-222, Rn-220, and Rn-219 that are risk- or dose-based and for showing compliance with the UMTRCA indoor radon standards for Rn-222 and Rn-220. The RVISL, therefore, supersedes the risk assessment approach in Preliminary Remediation Goals for Radionuclides in Buildings (BPRG) electronic calculator, the dose assessment approach in ARAR Dose Compliance Concentrations Goals for Radionuclides in Buildings (BDCC) electronic calculator, and Q17 of the guidance document "Radiation Risk Assessment At CERCLA Sites: Q & A" issued on May 2014. Computer codes such as the RVISL, which were developed to predict hazards from potential human exposure to radon concentrations in indoor air, are based on simplified equations and protective assumptions. While RVISLs may be imprecise for an individual house or structure they are protective in nature for screening a wide variety of buildings. EPA recommends that, where possible, Regions use measurements of radon indoors rather than rely on the transport portions of the RVISL. In particular, testing of groundwater or soil gas is not required to demonstrate compliance with RVISL WL, picocurie per liter (pCi/L), risk, or dose targets.
Users should note that since background radon levels are typically outside the risk range (i.e., greater the 1× 10-4), the RVISL calculator is likely to be used primarily for ARAR compliance. For example, the UMTRCA indoor radon standards 40 CFR 192.12(b)(1) and 192.41(b) were identified as likely Federal ARARs for Rn-222 and Rn-220 in Attachment A of the EPA guidance document Establishment of Cleanup Levels for CERCLA Sites with Radioactive Contamination. There are some state standards expressed in concentrations (pCi/L) or dose (mrem/yr) that, if more stringent than the UMTRCA standards, may be selected as ARARs.
Superfund sites are addressed under the authority of the CERCLA of 1980, which was amended by the 1986 Superfund Amendments and Reauthorization Act. EPA developed RVISLs for human health protection that are generally recommended, medium-specific, risk-based screening-level concentrations intended for use in identifying areas or buildings that may warrant further investigation of the radon intrusion pathway.
Rn-222 is commonly called radon because its parent is radium-226. Rn-220 is commonly called thoron because its parent isTh-232. Rn-219 is commonly called actinon because its parent is Ac-227. Click the decay chain link to see the decay series for Rn-222, Rn-220, and Rn-219. The metal groups in these images are based on Los Alamos National Laboratory literature. See section 2.2 of the User's Guide to learn what progeny are evaluated in this web calculator. More details about the decay chains can be found in the EPA's Decay Chain Tool.
This tool is based on the Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air (June 2015). Vapor intrusion occurs when there is a migration of vapor-forming chemicals or radon from any subsurface source into an overlying building. Recognition of soil vapor intrusion to buildings and other enclosed spaces began in the 1980s with concerns over radon intrusion. Subsequently, there was an increasing awareness that anthropogenic chemicals (e.g., petroleum hydrocarbons and chlorinated solvents) in soil, groundwater, and sewers and drainlines could also pose threats to indoor air quality via the vapor intrusion pathway.
The RVISL calculator results were previously verified. The documentation from these may be seen on the Internal Verification and External Verification pages. The RVISL calculator was also previously peer reviewed, and the documentation of the review may be seen here.
The website was initially made available for use in a transmittal memo entitled "Distribution of the Superfund Radon Vapor Intrusion Screening Level (RVISL) Electronic Calculator", May 26, 2021.
Related CERCLA Calculators and Guidance
It should also be noted that calculating a RVISL addresses neither noncancer toxicity, nor potential ecological risk. Of the radionuclides generally found, at CERCLA sites, only uranium has potentially significant noncancer toxicity. EPA's VISL Calculator should be used to assess chemical exposures resulting from air, groundwater, and sub-slab or exterior soil gas. When assessing sites with uranium as a contaminant, it may also be necessary to consider the noncancer toxicity of uranium, using other tools, such as EPA's Regional Screening Levels (RSLs) for Chemical Contaminants at Superfund Sites electronic calculator for uranium in soil, water, and air, and the WTC for uranium inside buildings. EPA's PRG Calculator should be used to assess radionuclide cancer risk for soil, water, and air. EPA's SPRG Calculator should be used to assess radionuclide cancer risk for hard outside surfaces, and the BPRG Calculator for radionuclide cancer risk inside buildings. EPA's DCC Calculator should be used to assess radionuclide dose for soil, water, and air, BDCC Calculator for radionuclide dose inside buildings, and the SDCC Calculator for radionuclide dose for hard outside surfaces. Similarly, some sites with radiological contaminants in sensitive ecological settings may also need to be evaluated for potential ecological risk. EPA's guidance "Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessment" contains an eight step process for using benchmarks for ecological effects in the remedy selection process.