Published in the May 2020 Focus on the Environment Newsletter
On May 19, 2020 EPA released its May 2020 update to their “Regional Screening Levels for Chemical Contaminants at Superfund Sites.” 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, tapwater, 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 November 2019. 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 constituents we run into at our sites for which a change in RSL occurred during the May 2020 update include dibenzofuran, naphthalene, and tetrahydrofuran. RSL changes with this update for these three compounds in industrial soil and tap water at TR 1E-06 and THQ 0.1 are as follows:
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.
George H. Colvin is a hydrogeologist with over 30 years of consulting experience. Much of his experience has focused on RCRA Corrective Action, RCRA closure, and groundwater investigation, monitoring, and cleanup. He holds a BS in Geology from Ohio University and MS in geology and hydrology from Vanderbilt University. He is a Certified Professional Geologist with the American Institute of Professional Geologists, a registered geologist in Kentucky, Pennsylvania, and Tennessee, and a Certified Hazardous Materials Manager.