Vapor Intrusion’s New Hot Topic – Short-term TCE Toxicity

During the past few years, the U.S. EPA and state agencies have worked to formulate vapor intrusion guidance in response to changes in U.S. EPA guidance on the toxicity of trichloroethylene (TCE). TCE is a compound used as a degreaser and that is a degradation product of tetrachloroethylene (drycleaner solvent). In this blog we provide background information and technical points to better inform a TCE vapor intrusion investigation that may better serve parties in this regulatory environment of uncertainty, considering that the government agencies have not yet all finalized their TCE guidance.

In September 2011, U.S. EPA finalized its TCE toxicological review, which includes toxicity values for noncarcinogenic and carcinogenic effects for TCE (follow this link:  http://www.epa.gov/iris/subst/0199.htm). The toxicity values for carcinogenic effects lowered the risk-based concentrations for long-term exposures to TCE in air.  Another revision to TCE toxicity guidance was the additional consideration of short-term (i.e., 24-hour) exposures to TCE. This is a noteworthy change in guidance because prior to the 2011 guidance, TCE exposures were evaluated over the longer term (e.g., > 20 years) and now regulated parties need to be concerned with evaluation of TCE over a short-term period of 24-hours if there is the potential for a woman of child bearing age to be exposed. One of the noncarcinogenic effects associated with exposure to TCE is cardiac malformations in a developing fetus. While there is significant scientific debate around that endpoint, several agencies have developed guidance specifically addressing potential short-term exposures to TCE.

Here are some examples of TCE supplemental guidance:

These guidance documents recommend that TCE non-cancer screening levels be applied on a short-term exposure basis (not on an annual average) due to the potential developmental effects. This has major implications for site investigations, data evaluation and decision making, which agencies are still trying to resolve on a case-by-case basis. This is a critical matter to regulated parties because indoor air data collection can be subject to wide ranging temporal variations (e.g., up to two orders of magnitude in variability) in measured concentrations at most buildings.

Our risk assessment team serves clients on resolving the complexities of potential TCE short-term exposures including developing site-specific solutions that can be implemented at a reasonable cost.  Here are some considerations for a site-specific approach TCE vapor intrusion investigation that we employ:

  • Collect indoor air samples using passive diffusion samplers to quantify indoor air concentrations over longer periods of exposure (several days or weeks). An additional consideration is that guidance about passive indoor air sampling from various state and federal agencies is limited.
  • Collect indoor air samples using a continuous monitoring device.
  • Immediate response actions if indoor air TCE concentrations are measured above short-term action levels. Example ways to reduce exposure include increasing building pressurization and/or ventilation, sealing potential conduits where vapors may be entering the building, treating indoor air (carbon filtration, air purifiers), installing and operating engineered exposure controls (sub-slab/crawlspace, depressurization systems), and temporarily relocating occupants.
  • Installing mitigation systems to induce subslab depressurization.
  • Treat indoor air using new filtration systems.
  • Indoor air sampling under “worst case conditions”. This may include sampling during period of colder outdoor temperatures (winter months), and sampling when the building’s HVAC system is turned off.

Kennedy/Jenks has conducted numerous vapor intrusion investigations and has assisted our clients in developing solutions to address the potential for short-term exposures to TCE. Please contact us if you would like more information.

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