In November 2018, EPA updated its “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 are also useful tools for identifying initial cleanup goals at a site. In this role, SLs provide long-term targets to use during the analysis of different remedial alternatives.
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. The web calculator allows users to select or define:
SLs are updated once or twice a year. The last update (prior to the November 2018 update) occurred in May 2018. Changes to the RSLs tables are summarized in the “What’s New” area of the site. Probably the most notable changes in the November 2018 update were the addition of lanthanum and lanthanum salt values, along with changes in how dioxin congeners are referenced in the user guide and the toxicity equivalence factor (TEF) for HpCDD. We do not anticipate that the majority of hazardous waste sites will be affected by these changes.
One of the more problematic issues associated the use of RSLs is what happens when RSLs change. It can be very frustrating, especially when working with a large suite of chemicals, when screening levels change in the middle of say, putting a large report or risk assessment together. 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, don’t 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.
Published in Cox-Colvin’s January 2019 Focus on the Environment newsletter.
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.