2008 CPEO Brownfields List Archive

From: Lenny Siegel <lennysiegel@gmail.com>
Date: Fri, 18 Jul 2008 11:15:44 -0700 (PDT)
Reply: cpeo-brownfields
Subject: [CPEO-BIF] Perc screening level
Tetrachloroethylene - also known as perchloroethylene, perc, or PCE - is the dry-cleaning chemical and solvent found at thousands, perhaps hundreds of thousands of sites across the country, often in conjunction with TCE, which is a PCE breakdown product. People are exposed to PCE through drinking water and household water vapors, emissions from dry cleaners and other users of the chemicals, vapor intrusion from PCE groundwater plumes, and from off-gases from dry-cleaned clothes. PCE is one of the most common contaminants at small brownfields sites.

In May 2008 three EPA Regions published a harmonized set of Regional Risk Screening Levels (RSLs), formerly known as Preliminary Remediation Goals. See http://epa-prgs.ornl.gov/chemicals/index.shtml. They listed a inhalation screening level for PCE (in a residential scenario) of .41 micrograms per cubic meter, corresponding to a excess lifetime cancer risk of 10^-6 (one in a million).

On June 26, 2008 U.S. EPA announced the availability of a draft toxicological review for PCE. To download the draft, go to
and scroll down to Downloads. This document has a long way to go before it's finalized, but if the final risk factor remains the same, it will drive down the residential inhalation risk screening level to .1 micrograms per cubic meter. This is below outdoor background concentrations in much of the country.

Recognition of PCE's true risks should lead to an accelerated phase-out of the compound in dry-cleaning, but even if its use were to stop tomorrow there would be a vast number of sites, in strip malls and under residences, schools, day-care centers, and other workplaces with shallow groundwater plumes of PCE. Even if adjusted for occupational exposures - because people spend less time at work than at home - the new risk findings suggest that any structure with proven, or even likely vapor intrusion from PCE should be mitigated - with subslab depressurization systems, other forms of ventilation, and/or vapor barriers - to bring levels down to concentrations in the outdoor air.

And even that is not enough. At the Information Technology High School in Queens, New York, sampling found that concentrations of PCE in the school were 1.2 micrograms per cubic meter, but that the chemical was not coming from below. Instead, it was entering the school from the outdoor air. As dry cleaners are required to switch to other cleaning chemicals, outdoor concentrations should drop. (Since PCE breaks down in air, there must be continuing releases to maintain such concentrations.) Any building mitigated to today's outdoor levels will need to be revisited to match the safer outdoor levels that I anticipate.

Perhaps I'm being too optimistic. California is slowly phasing out PCE in dry-cleaning, but the rest of the country is only requiring that it be phased out in buildings where cleaners are collocated with residences. It seems that political/socio-economic factors - the difficulty in applying stringent environmental regulation to financially fragile mom-and-pop businesses - have held back risk-based regulation.

However, the solution to that socio-economic quandary is not to ignore the toxicological evidence, but to supplement regulation with technical and financial assistance. Years ago, a coalition of environmental groups here in Silicon Valley did something similar. Instead of forcing the sewage plants to pay fines for releasing heavy metals into the San Francisco Bay, we asked them to use the money to help small printed-circuit board manufacturers to switch over to environmentally responsible production processes. Something similar should be done to clear the air of PCE.

As I stated above, people are exposed to PCE through multiple pathways. The toxicological evidence demands that we address all those pathways at once, and soon.


Lenny Siegel
Executive Director, Center for Public Environmental Oversight
a project of the Pacific Studies Center
278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918

Brownfields mailing list

  Prev by Date: [CPEO-BIF] BoRit Asbestos site, Ambler, Pennsylvania
Next by Date: [CPEO-BIF] Building Environmental Policy Bridges
  Prev by Thread: [CPEO-BIF] BoRit Asbestos site, Ambler, Pennsylvania
Next by Thread: [CPEO-BIF] Building Environmental Policy Bridges

CPEO Lists
Author Index
Date Index
Thread Index