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. The project-specific exposure scenario is based on the assumption that an individual is located at the perimeter of the Quanta site during the entire time work is occurring. This equates to 10 hours per day, 5 days per week for 1.5 years.

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 the 17 VOCs present in the soil. All of the chemicals detected in air samples have been below the conservative RSLs with the exception of naphthalene. Naphthalene is most commonly known as the chemical in mothballs; it was also a component of coal tar. Sources of naphthalene in air include cigarette smoke, automobile exhaust and residential wood combustion.

Coal tar has a low odor threshold, which means you may be able to smell it even at very low concentrations. The odors can be noxious to some people. However, presence of the odor does not necessarily indicate a potential threat to public health. The human nose can detect coal/roofing tar odors at concentrations below air quality levels that indicate a health risk.

View the 17 VOCs Results Table (March 2017 - July 9, 2018)

What about naphthalene concentrations offsite?

Naphthalene samples collected at the fence line are not an accurate representation of concentrations in residential areas. Therefore, EPA has added 10- and 24-hour air sampling at off-site locations to better characterize naphthalene concentrations in the areas where people live, work and shop. More information about the offsite air monitoring can be found here.

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 offsite residential building and commercial area. EPA set a risk-based screening level for naphthalene of 4.62 μg/m3 (micrograms per cubic meter) for a 10-hour workday and, as announced on May 22, has added a screening level of 3.13 μg/m3 for the longer exposure time of 24 hours. These 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 on-site work.

What does it mean for naphthalene to be detected above the RSLs?

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.

Sixteen of the chemicals analyzed in the air samples have been recorded at levels below the conservative RSLs and, as mentioned previously, have therefore required no additional measures to control emissions.

What are effects of naphthalene on human health?

Health effects in humans are known to occur from exposure to high levels of naphthalene. Humans can become exposed to high levels by accidentally eating mothballs, or by breathing in naphthalene when using mothballs without sufficient air ventilation, or smoking tobacco, dispensing fuel in vehicles, or inhaling wood burning fireplace or firepit smoke. Some workers may also be exposed to high levels of naphthalene in air at industrial facilities.

Health effects that have been observed in humans with high levels of exposure (higher than what is observed the Quanta site) include respiratory tract irritation, effects to red blood cells and cataracts.

Though the human cancer risk to naphthalene is still a matter of scientific debate, the RSL has been conservatively set at a level intended to control cancer risks.

Based on current scientific understanding, the levels of naphthalene that have been detected in air at the perimeter of the site are well below the lowest levels known to produce adverse health effects in humans or laboratory animals. See below for references.*

What is being done to address odor?

Odor control measures at the Quanta site include using odor-suppressing foam and/or weather-proof hard-shell covering for exposed soil, limiting soil exposure to the air, and using perimeter misters that are designed to neutralize odors coming from the remediation work. More information is detailed here.


* The references consulted in preparing this section are listed below:

  • Agency for Toxic Substances and Disease Registry (ATSDR). 2005. Toxicological Profile for Naphthalene, 1-Methylnaphthalene, and 2-Methylnaphthalene.
  • American Conference of Governmental Industrial Hygienists (ACGIH). 2014. Documentation of the Threshold Limit Values (TLV), 7th Edition.
  • International Agency of Research on Cancer (IARC). 2002. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Some Traditional Herbal Medicines, Some Mycotoxins, Naphthalene and Styrene. Volume 82.
  • Scientific Committee on Occupational Exposure Limits (SCOEL). 2010. Recommendations from the Scientific Committee on Occupational Exposure Limits for Naphthalene. SCOEL/SUM/90. March.
  • U.S. Environmental Protection Agency (EPA). 2014. Integrated Risk Information System (IRIS) profile for Naphthalene, CASRN 91-20-3. (Link).
  • U.S. Environmental Protection Agency (EPA). 2008. Reregistration Eligibility Decision for Naphthalene. EPA 738-R-07-010. Office of Prevention, Pesticides and Toxic Substances. September.
  • U.S. National Toxicology Program (NTP). 2014. Report on Carcinogens, 14th Edition.