U.S. Environmental Protection Agency (EPA) Regional Screening Levels (RSLs) change often. The most recent update in June 2017 was only 13 months from the prior update (May 2016). Because EPA consistently updates RSLs, individuals assessing risk on sites that rely on these EPA RSLs may have exceedances one year, but not the next, or vice versa. Knowing when these updates occur is key for conducting accurate risk assessments and making important remedial decisions for sites.

EPA RSLs background

EPA RSLs are comparison values for residential and commercial/industrial exposures to soil, air, and tap water that are used to promote national consistency for screening chemicals at many different types of sites. The EPA has a website that is now the source of screening levels for all EPA regions in the U.S. The website provides tables of risk-based screening levels (calculated using the latest toxicity values) and default exposure assumptions and physical/chemical properties. The RSLs are used in many stages of site investigations including, but not limited, to project scoping, risk investigations, and risk assessment.

As mentioned above, new research means the EPA RSLs are almost constantly changing. Not only are the RSL toxicity values changing for specific constituents, but new toxicity values are being used for constituents that did not have values before, and many changes have been made to the RSL User’s Guide.

2017 RSLs update

Specific to the most recent update from May 2016 to June 2017 RSLs,  RSL values for the following notable constituents of concern were updated:
 

• 1,1,2-Trichloro-1,2,2-trifluoroethane (all RSLs decreased)
• 1,2,3-Trimethylbenzene and 1,2,4-Trimethylbenzene (all RSLs increased)
• 1,2-Dichloropropane (all RSLs decreased, with the exception of MCL-based SSL, which remained the same). It is also worth noting that the Inhalation Unit Risk value for this constituent was updated on September 6, 2017 because of a conversion error and has been updated in the RSL tables.
• 1,3,5-Trimethylbenzene (all RSLs decreased; Residential/Industrial air RSLs were also added that were not available in May 2016 list)
• 2,4,6-Tribromophenol (Residential/Industrial soil and Tapwater RSL, and Risk-based SSL were added that were not available in May 2016 list)
• Benzo(a)pyrene (all RSLs increased, with the exception of Residential/Industrial air RSLs, which decreased; MCL-based SSL remained the same)

RSL increases or decreases can be determined by reviewing the EPA RSL Generic Tables webpage. Several other constituent changes were made and can be reviewed on the EPA RSL What’s New webpage.

What keeping up with the latest RSLs can mean for your site

Maintaining a working knowledge of current and proposed RSLs can save you valuable time and resources. Trihydro maintains the most recent RSL values and provides them for each site we work on. If an update is needed for your project, our staff incorporate the most recent RSL table into analytical tables for your reporting and decision-making.