Widely Used EPA Regional Screening Levels Updated in November 2021

By: Nate Wanner, CP, CPG

On November 17, 2021, EPA released its Fall 2021 update to their “Regional Screening Levels for Chemical Contaminants at Superfund Sites.”   The updated RSLs (dated November 2021) replace the May 2021 version. The November 2021 update includes RSL changes for approximately 80 compounds, including new RSLs for three PFAS compounds. This is the first time that PFAS compounds have been assigned RSLs.

Screening levels (SL) are risk-based concentrations derived from standardized equations combining exposure information assumptions with EPA toxicity data.  The EPA website is the source of screening levels for all the EPA regions, thus the term Regional SLs or RSLs.

SLs are used for site “screening” and as initial cleanup goals, if applicable. SLs are not de facto cleanup standards and should not be applied as such. The SL’s role in site “screening” is to help identify areas, contaminants, and conditions that require further attention at a particular site. Generally, at sites where contaminant concentrations fall below SLs, no further action or study is warranted under the Superfund and RCRA Corrective Action programs, so long as the exposure assumptions at a site match those considered by the SL calculations. Chemical concentrations above SLs would not automatically designate a site as “dirty” or trigger a response action; however, exceeding a SL suggests that further evaluation of the potential risks by site contaminants is appropriate.

SLs can be obtained on the RSL website from either the generic summary tables or using the RSL calculator.  The generic summary tables are presented at a target cancer risk (TR) of 1E-06, and at either target hazard quotients (THQ) of 1.0 or 0.1.  The generic summary tables provide a list of contaminants, CAS number, toxicity values and chemical-specific information, MCLs, and the lesser (more protective) of the cancer and noncancer SLs for resident soil, industrial soil, resident air, industrial air, tap water, and leaching to groundwater exposure scenarios.  The summary tables are available as PDF or Excel files. The web calculator provides users considerably more flexibility to develop site-specific SLs using a combination of user-defined and default input variables.

SLs are usually updated twice a year, typically in November and May. The prior update occurred in May 2021. Changes to the RSLs tables are summarized in the “What’s New” page, including spreadsheet files comparing the newly updated RSLs and toxicity information to the previous version. Only the chemicals for which changes occurred are included in the comparison files.  This is a good way to see if an RSL for a contaminant of interest changed and if it went up or down.  Some of the more common contaminants in environmental medial for which RSLs have changed at a THQ of 0.1 include acetone, 1-bromo-2-chloroethane, cadmium, p-cresol, chloroethane, ethylene glycol, hexachlorobenzene, Lindane, nickel (acetate, carbonate, carbonyl, hydroxide, oxide, refinery dust), 1,2,4,5-textrachlorobenzene, and o-xylene.

One of the more problematic issues associated the use of RSLs is what happens when RSLs change.  This always seems to happen in the middle of putting together a large report or risk assessment. What do you do?  Many practitioners feel that you are obliged to use the most recent screening levels in every case; others feel that screening levels identified in an approved plan or agreement become set in stone.  To best manage the change, the workplan or agreement should clearly state how this will be addressed.  Also, do not count on EPA or states informing you of new updates, especially if a critical screening level has gone up. I recommend signing up to automatically receive notification when new releases are available.

We will continue to keep a close eye on RSL changes when they come out and consider how they could affect the projects we manage.  If you have a project that you think may be affected by these changes, please contact us so that we can discuss whether any actions are required.

Published in the Focus on the Environment, December 2021

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Nate Wanner is a Cox-Colvin Senior Scientist with over 15 years of experience leading and completing environmental projects, in addition to six years as an educator and IT director. He holds a BS in Geology: Water Resources from Ohio University and a Masters in Geographic Information Systems from Penn State University. His areas of expertise include brownfields, underground storage tanks, due diligence and database services. Nate is an Ohio EPA VAP Certified Professional (CP), a Certified Professional Geologist (CPG) with the American Institute of Professional Geologists (AIPG) and is a registered Professional Geologist (PG) in Kentucky, and a Licensed Professional Geologist (LPG) in Indiana.