Risk Screening Levels

What are Risk Screening Levels and how are they used?

The Risk Screening Levels (RSLs) are created using the most current information about health effects of the VOCs (provided by EPA), along with project-specific exposure scenarios (a set of assumptions about how people could be exposed). The assumptions are very conservative (protective) and are designed to result in RSLs that protect human health with a sufficient margin of safety.

Air sampling results are compared with RSLs to evaluate what we are doing to control emissions and to provide information about potential human health risks. Due to samples being collected offsite and for 24 hours (versus the previous 10-hour samples), the project-specific exposure scenario has been updated to a more conservative approach and more consistent with residential receptors (i.e., 24-hour exposure times over 350 days per year).

What have been the results from the air monitoring program?

Air samples, which have been collected from the perimeter since remediation started in May 2017, were tested for site contaminants. Running averages for all chemicals tested previously have tracked below project screening levels, except naphthalene (a component of coal tar, commonly familiar as the chemical in mothballs.)

Sources of naphthalene in air include cigarette smoke, automobile exhaust, and residential wood combustion. Typical urban background naphthalene levels are approximately 1 μg/m3 (micrograms per cubic meter).

What about naphthalene concentrations offsite?

Naphthalene samples collected at the fence line are not an accurate representation of concentrations in residential areas. EPA is conducting 24-hour air sampling at offsite locations to better characterize naphthalene concentrations in the areas where people live, work, and shop.

Because EPA’s risk-based screening level for naphthalene is an average over the life of the project, EPA is calculating a running average at each residential building and commercial area. EPA has set a risk-based screening level of 3.13 μg/m3 based on residential exposure (24 hours per day, 350 days per year.)

What if a chemical is detected above the RSL?

Risk screening levels are not “not to exceed” values. Short-term exceedances are not unexpected and do not pose an immediate risk to people's health but allow for necessary adjustments for onsite work.

The RSLs are used principally to make risk management decisions for controlling emissions during remediation work at the site. Levels in air below the RSLs do not require any special measures to control emissions - site work and monitoring continue as normal.

Detecting chemicals in air at levels above the RSLs triggers additional protective measures, such as applying larger quantities of vapor-suppressing foams and performing additional air monitoring. The purpose of these additional measures is to reduce the levels in air when feasible.