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January 24, 2022

EPA Requests Comment on Draft TSCA Screening Methodology to Evaluate Chemical Exposures and Risks to Fenceline Communities

The ACTA Group

On January 21, 2022, the U.S. Environmental Protection Agency (EPA) announced the availability of and solicited public comments on the “Draft TSCA Screening Level Approach for Assessing Ambient Air and Water Exposures to Fenceline Communities Version 1.0” (screening level methodology). 87 Fed. Reg. 3294. EPA will use the screening level methodology to evaluate potential chemical exposures and associated potential risks to fenceline communities in its Toxic Substances Control Act (TSCA) risk evaluations. EPA will hold a virtual peer review meeting of the Science Advisory Committee on Chemicals (SACC) March 15-17, 2022, to consider and review the methodology and to present results of applying it to 1-bromopropane (1-BP) (air pathway), N-methylpyrrolidone (NMP) (water pathway), and methylene chloride (MC) (air and water pathway). Comments are due February 22, 2022.


The Biden EPA announced on June 30, 2021, several policy changes surrounding TSCA risk evaluations issued by the previous Administration and the path forward for the “first 10” chemicals to undergo risk evaluation. According to the press release, under the previous Administration, the “first 10” risk evaluations did not assess air, water, or disposal exposures to the general population because these exposure pathways were already regulated, or could be regulated, under other EPA-administered statutes, such as the Clean Air Act (CAA), Safe Drinking Water Act (SDWA), or Clean Water Act (CWA). EPA states that the approach to exclude certain exposure pathways also resulted in a failure to address consistently and comprehensively potential exposures to potentially exposed or susceptible subpopulations (PESS), including fenceline communities (i.e., communities near industrial facilities). The Biden Administration reversed this policy, and EPA developed the screening level methodology to examine further whether the policy decision to exclude air and water exposure pathways from the risk evaluations will lead to a failure to identify and protect fenceline communities.

Screening Level Methodology

EPA developed the screening level methodology to evaluate potential exposures and associated potential risks to human receptors in proximity to facilities releasing chemicals undergoing risk evaluation under TSCA Section 6 to the ambient air and to waterbodies receiving facility releases (direct or indirect) of chemicals undergoing risk evaluation under TSCA Section 6. EPA states that it considers these receptors a subset of the general population and categorizes them as “fenceline communities.” Additionally, one or more receptors comprising fenceline communities can be of any age, including reproductive age, health status, or other factors, such as chemical sensitivity, and therefore may also be considered PESS.

For purposes of the proposed screening level methodology, EPA limits the proximity of receptors evaluated to those less than or equal to 10,000 meters from a facility releasing chemicals undergoing risk evaluation under TSCA Section 6 to the ambient air. For evaluated aquatic exposure routes, EPA limits proximity to the extent of the identified waterbody receiving a facility discharge and therefore does not have a specific distance associated with the human receptor. Therefore, for purposes of the screening level methodology, EPA is defining “fenceline communities” as follows:

Members of the general population that are in proximity to air emitting facilities or a receiving waterbody, and who therefore may be disproportionately exposed to a chemical undergoing risk evaluation under TSCA section (6). For the air pathway, proximity goes out to 10,000 meters from an air emitting source. For the water pathway, proximity does not refer to a specific distance measured form [sic] a receiving waterbody, but rather to those members of the general population that may interact with the receiving waterbody and thus may be exposed.

The proposed screening level methodology states that it “uses reasonably available data, information, and models to quantify environmental releases, evaluate exposures to fenceline communities and characterize risks associated with such releases and exposures for certain air and water pathways previously not evaluated in published risk evaluations.” The overall approach for the screening level methodology is summarized below:

Assessment Step
Air Pathway
Water Pathway
Release Assessment
• Use 2019 Toxics Release Inventory (TRI) Data.

• Where no 2019 TRI data are available, estimate releases based on past TRI data, estimation methods used in final risk evaluations, and TRI surrogate data (TRI data from other occupational exposure scenarios (OES)).
• Use release scenarios from final risk evaluations, which incorporate direct and indirect release data from both TRI and Discharge Monitoring Report (DMR) information depending on chemical.
Exposure Assessment
• Use the American Meteorology Society/Environmental Protection Agency Regulatory Model (AERMOD) to estimate ambient air exposure concentrations for receptors at eight finite distances and one area distance out to 10,000 meters from a facility releasing the chemical evaluated to the ambient air.

• When applicable, use the Indoor Environmental Concentrations in Buildings with Conditioned and Unconditioned Zones (IECCU) to estimate indoor air exposure concentrations for residents who live above or adjacent to a releasing facility.
• Use modeled surface water concentrations from final risk evaluations to evaluate drinking water and incidental oral/dermal exposure; surface water concentrations were estimated using the Exposure and Fate Assessment Tool (E-FAST) 2014.
Risk Characterization
• Use human health hazard endpoints from the final risk evaluations applied to the above scenarios for a continuous-exposure basis.

EPA intends to apply the screening level methodology to seven of the “first 10” chemicals undergoing risk evaluation under TSCA Section 6, as summarized in the table below, as well as future chemicals undergoing risk evaluation under TSCA Section 6, across the conditions of use (COU) considered in the associated risk evaluations.

 Air Pathway
Water Pathway
Case study chemicals
• 1-BP

• MC

• MC
Additional chemicals subject to screening level analyses

• Trichloroethylene (TCE)

• Perchloroethylene (PCE)

• Carbon tetrachloride

• 1,4-Dioxane


• Carbon tetrachloride

• (1,4-Dioxane water pathways will be examined via a separate Supplement to the published Risk Evaluation)

When assessing exposures for industrial/commercial COU, the screening level methodology states that EPA generally defines an OES to capture the basic, underlying source of exposure for a given COU. Although the proposed screening level methodology does not involve evaluation of occupational exposures, EPA “carries the OES label through this work to allow categorization of multiple facilities which may be involved with a single COU.”

EPA provides three case study chemicals (1-BP, MC, and NMP) to illustrate the application of the proposed screening level methodology. EPA carries the case studies through the processes of the environmental release assessment, exposure assessment, risk calculations, and associated risk characterizations based on the proposed screening level methodology. The screening level methodology notes that while all three case study chemicals are chemicals for which EPA published risk evaluations between 2020 and 2021, the results “are not final agency actions and will not be used as presented to support risk management actions or associated rulemaking activities resulting from the published risk evaluations at this time.”

The 1-BP case study includes evaluation of 15 air pathway OES. EPA identified additional risks for 14 of the 15 OES. An analysis of the water pathway for 1-BP was conducted in the published problem formulation and discussed in the published risk evaluation. The analysis found that exposure to 1-BP via the water pathway is not expected for 1-BP due to physical-chemical and fate properties of 1-BP, along with low reported releases to water (five pounds total in a year for all facilities). Since exposure via the water pathway is not expected for 1-BP, EPA states that it “does not intend to conduct screening level analysis of the water pathway for fenceline communities.”

The MC case study includes evaluation of 17 air pathway OES. EPA identified additional risks for eight of the 17 OES. EPA also evaluated 13 water pathway OES for MC. EPA states that it identified additional risk for one of the 13 OES evaluated for the drinking water pathway, but none for the incidental oral/dermal pathways.

The NMP case study includes evaluation of six water pathway OES. EPA identified no additional risks for any of these OES. EPA notes that although this work currently does not include evaluation of the air pathway for NMP, NMP is included among the seven of the “first 10” chemicals undergoing risk evaluation for which EPA will conduct a screening level analysis using the final screening level analysis framework for the air pathway.

SACC Peer Review and Next Steps

EPA’s background documents, related supporting materials, and draft charge questions to the SACC are available in Docket ID EPA-HQ-OPPT-2021-0415 and on the SACC website. EPA will provide additional background documents (e.g., SACC members and consultants participating in this meeting and the meeting agenda) as the materials become available. Registration is required to receive the webcast meeting link and audio teleconference information. EPA states that it intends to announce registration instructions on the SACC website by early February 2022.

EPA will use public comments and the SACC peer review to modify the screening level methodology, as appropriate. EPA states that it plans to use the screening level methodology to determine the risks to fenceline communities from the air and water pathways that were not assessed previously for seven of the “first 10” chemicals for which EPA published risk evaluations. For the “next 20” chemicals undergoing risk evaluation and beyond, EPA plans to expand this first version of the framework to include a method to address broader potential environmental justice concerns and cumulative or aggregate exposures to chemicals.


EPA’s 2021 decision to include fenceline communities in TSCA risk evaluations is in line with the logic behind the 9th Circuit’s ruling in Safer Chemicals Healthy Families v. U.S. Envtl. Prot. Agency. The court decided EPA was incorrect in excluding legacy and associated disposal activities from the risk evaluation process because that approach contradicted TSCA’s plain language. OCSPP’s new approach evaluates multiple pathways of exposure and represents a more comprehensive assessment of the potential risks posed to populations, rather than arbitrarily placing individuals into categories of presumed occupational exposure only or consumer exposure only.

It is not practical to conduct an individual exposure assessment for each American. EPA must rely, therefore, on information it can reasonably apply to the general population. “General population” is a category of human receptor commonly evaluated under TSCA, but it is considered separately from occupational receptors (i.e., workers and occupational non-users). Since the 2016 TSCA amendments require EPA to consider PESS, EPA’s screening level approaches will reasonably account for a subset of receptors in the general population that it identified as “fenceline communities.”

There are four possible outcomes from including the screening level analyses for fenceline communities in the “first 10” TSCA risk evaluations. EPA may identify additional unreasonable risks for ambient air only, for ambient water only, for both ambient air and water; or that neither pathway presents additional unreasonable risks. The ultimate outcome of including these screening level analyses is largely dependent upon the risk determination previously published. First, if EPA identified no unreasonable risks inthe published risk evaluation under the COU and EPA does not identify unreasonable risks from the screening level analyses, then EPA will not propose restrictions on the chemical substance. Second, if EPA identified unreasonable risks for a given COU in the published risk evaluation and unreasonable risk is identified in the screening level analysis for that same COU, then EPA has evidence in this scenario to proceed with risk management on the chemical substance for this COU (see Bergeson & Campbell, P.C.’s (B&C®) December 29, 2021, memorandum on EPA’s whole chemical approach). The third outcome EPA envisions is that both the initial and additional unreasonable risks are due to uncontrolled fugitive emissions, resulting in risk management actions, including the establishment of an existing chemical exposure limit (ECEL). Related to outcome three, EPA may conclude, pursuant to TSCA Section 9, that the unreasonable risks are better managed under another EPA-administered federal law (e.g., under the CAA or SDWA). Finally, EPA may determine that a COU initially found to have no unacceptable risk is now determined to pose an unacceptable risk due to the inclusion of the fenceline exposures. In this case, EPA expects to conduct additional analyses to substantiate the screening level analyses and, based upon the outcome of the additional analyses, either retain the original no unacceptable risk determination or revise the risk determination to unreasonable and move to risk management rulemaking.

Ambient Air Pathway

EPA’s proposed “pre-screening analysis” appears to utilize a new methodology, but the heart of the Integrated Indoor/Outdoor Air Calculator (IIOAC) is the decades old AERMOD. If the IIOAC results support a full screening level analysis, TRI data will be fed into AERMOD to determine the expected exposures at multiple distances from the emission source. In the case of receptors living above or adjacent to a releasing facility, the so-called “co-resident screening methodology” will utilize EPA’s IECCU model.

EPA claims that TRI data are appropriate for screening level analyses because TRI data are not as limited as and are more current than National Emissions Inventory (NEI) data. EPA also acknowledges the uncertainties in using the TRI data set, presenting a list of data sources not captured by TRI. These sources include facilities that do not meet the manufacturing, processing, use, or employment thresholds, and those that are within a sector not covered by TRI. Further, there is not a “one-to-one” comparison between data submitted to TRI and each OES, nor is the annualized average (as reported under TRI) used by EPA necessarily reflective of short-term, high-level “bolus” types of exposures that may occur on any given workday. EPA reports a “medium” level of confidence, according to its 2018 systematic review protocol, in using TRI data for this purpose.

Ambient Water Pathway

EPA’s draft methodology evaluates releases to water from point sources only, and proposes that the applicable TRI and DMR data be fed into the E-FAST model commonly used in the TSCA program. Similar to the ambient air pathway, some “one-to-one” comparisons cannot be made due to differences in reporting. B&C encourages entities that may be impacted by this proposed screening to verify the NAICS and/or SIC codes used by EPA to ensure proper identification of their interests. While it is unclear how measured (finished) drinking water concentrations relate to ambient water exposure, those data are proposed as a source for exposure via drinking water. EPA does not state whether it will cap modeled exposures if there is an enforcement limit (e.g., a Maximum Contaminant Limit) for a particular contaminant. Modeled surface water concentrations are proposed as the sources for incidental oral exposure while swimming and incidental dermal exposure while swimming, both of which are determined by EPA’s Swimmer Exposure Assessment Model (SWIMODEL).

EPA’s release of the draft screening level approaches illustrates the increasing complexity stakeholders can expect to see in EPA’s TSCA risk evaluations. By considering potential exposures of fenceline communities, EPA is taking an important step in ensuring it is comprehensively protecting public health. As with any evaluation, however, care must be taken to ensure that the available data are utilized properly. B&C and The Acta Group are prepared to assist interested parties with their interactions with EPA and other stakeholders regarding the “first 10,” the “next 20,” and subsequent TSCA risk evaluations.