On October 1, the Washington State Department of Ecology (Ecology) released new guidance with regards to Trichloroethylene (TCE) vapor intrusion. In addition to their new guidance document, Ecology finalized a fact sheet on TCE in residential indoor air in cooperation with the Washington State Department of Health.

Ecology recommends prompt action if there is any potential for short-term exposure, including expedited sampling and notice to affected building owners.

What is TCE?

As defined in Ecology’s fact sheet, TCE is a “colorless liquid solvent used to remove grease from metal parts. It is also an ingredient in some consumer products such as glues, paint removers, and gun cleaners.” In addition, Tetrachloroethylene (PCE), used in dry cleaning and metal-cleaning operations, can degrade into TCE over time.

Once released, TCE can move quickly through soil and into groundwater. Vapor intrusion occurs where TCE, in a gaseous form, migrates through the soil into the fissures and gaps in building foundations.

According to Ecology, long-term exposure to TCE can increase the risk of certain cancers and lead to other health problems. In addition, short-term exposure can cause severe negative fetal health effects.

Although the EPA recommends taking measurements over a 21-day period, Ecology now acknowledges that harm to fetal health may occur from exposure over a period of less than three weeks. Therefore, Ecology recommends prompt action to reduce TCE concentrations and/or to reduce exposure to women of childbearing age.

Any Exposure May Be Harmful To a Fetus – Immediacy Is Key

In its new guidance, Ecology strongly recommends prompt action for short-term inhalation exposure. Where there is the potential for TCE concentrations to exceed short-term action levels, Ecology recommends that investigators take quick action by notifying building owners and tenants of the possibility of an exceedance and determining whether women of childbearing age are current occupants.

If women of childbearing age are occupants, even if temporarily, Ecology recommends a site visit be scheduled as soon as possible. Ecology also recommends an air Sampling and Analysis Plan (SAP) be prepared and finalized so that sampling can be “immediately scheduled.”

Where the first sampling event does not exceed the short-term action level, multiple sampling events may be required. In addition, for any off-site lab work, Ecology recommends requesting expedited turn-around times, with a goal of three business days.

Where women of childbearing age are occupants of a building, data should be timely disclosed, even without first conducting any quality assessment or validation.

If TCE concentrations exceed the short-term action levels and a woman of childbearing age works or lives in the building, Ecology recommends that in addition to vapor intrusion mitigation methods, which should be implemented “as quickly as possible,” “other actions should be considered that would effectively reduce exposures during the interim.”

Prompt Action and MTCA Cleanup Standards

With regards to Model Toxics Control Act (MTCA) cleanup sites, Ecology clarified EPA guidance on early measures to mitigate TCE inhalation exposure. First, Ecology cautioned that increasing building pressurization or ventilation may not be practicable or effective. In addition, sealing potential vapor intrusion conduits should be undertaken as the initial response only if it can be completed quickly and sampling can be conducted to verify its effectiveness.

Where an exceedance is recorded, a “stop gap” response may be required right away while a long-term mitigation proceeds through planning. Regardless of the mitigation mechanism, Ecology recommends determining where and when women of childbearing age are on the premises and for how long they are present in the building.


As Ecology notes in their guidance, “[p]rotecting people inside affected buildings is a high priority and any needed action should not be delayed.” Short-term inhalation exposure may cause negative health effects much sooner than previously expected, with those effects amplified in women of childbearing age.

Building owners, investigators, and consultants need to be aware: prolonged mitigation planning will now need to proceed on a parallel track to the prompt action recommended by Ecology.