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On March 29, 2000, the Agency for Toxic Substances and Disease Registry (ATSDR) received a request from the U.S. Environmental Protection Agency (EPA) Region VIII to determine if the levels of indoor air contaminants in two homes pose a health threat. These homes are located on Lomond Lane in Lockwood, Montana above a groundwater plume contaminated primarily with tetrachloroethylene (PCE) and TCE (TCE). Several residents in the area are concerned about possible exposures from vapors migrating into their homes and have requested that health screenings be conducted.

In December 1999, ATSDR issued a health consultation for this site evaluating several potential health impacts from the groundwater contamination. One of the exposure pathways evaluated was the migration of VOCs into homes via soil gas. Based on the results of a screening model, ATSDR concluded that there was a possibility that vapors from the contaminated groundwater could enter the foundations of homes, causing an indoor air health hazard. ATSDR recommended that soil gas samples be collected from those homes under which groundwater contained vinyl chloride at levels greater 0.005 milligrams per liter (mg/L).


On January 18, 2000, EPA collected indoor air samples from the crawl spaces and living spaces of the two homes having the highest PCE levels in the private wells. Four-hour samples were collected onto carbon molecular sieve cartridges using a Gillian pump. EPA subsequently took steps to improve the indoor air quality in both homes by installing vents in the crawl spaces, placing air intakes in the attics, and replacing the duct work.

Based on ATSDR's previous evaluation of potential health impacts from indoor air contamination, the VOCs of concern for this site are tetrachloroethylene (PCE), TCE (TCE), vinyl chloride, and cis-1,2-dichloroethylene. In the first residence, PCE was found at 1500 ppb in the private groundwater well. Here, two indoor air samples were collected from the crawl space and one was collected from the dining room. The highest reported indoor air levels of PCE and TCE were 136.3 µg/m3 (or 20.1 parts per billion [ppb]) and 76.2 µg/m3 (or 14.2 ppb) respectively. Vinyl chloride was not detected. Cis-1,2-dichloroethylene was not included in the analysis. However, the highest level of trans-1,2-dichloroethylene was estimated at 1.5 µg/m3 (0.38 ppb) which is well below any level of health concern.

Other VOCs of concern were benzene, freon, methylene chloride, bromodichloroethane, and carbon tetrachloride. In addition, the laboratory reported the presence of carbon dioxide and other matrix interferences in the samples. Since sorbent tube matrix samples cannot be reanalyzed, many of the contaminant levels had to be estimated.

In the second residence, where PCE was found at 990 ppb in the private well, one indoor air sample was collected in the crawl space and one was collected in the family room. The laboratory prepared the samples collected from this residence differently in order to prevent the matrix interference problems encountered with the samples from the first residence. The highest PCE and TCE levels found in the second residence were 34.9 µg/m3 (5.1 ppb) and 6.8 ug/m3 (1.3 ppb) respectively. Neither vinyl chloride nor trans-1,2-dichloroethylene were detected. Other VOCs of concern detected in the indoor air samples were chloroform, carbon tetrachloride, and benzene.


The highest reported PCE level (20.1 ppb) from these two homes was found in the living space and is lower than that which would be expected to cause any non-carcinogenic health effects. ATSDR's current comparison value of 40 ppb is based on increased reaction time in dry cleaning workers exposed to an average of 15,000 ppb PCE for about 10 years and contains a safety factor of 100 [1]. A safety factor of 100 means that the comparison value is 100 times smaller than the lowest level shown to have any health effect. Therefore, even under the worst-case exposure found in these air samples, no public health threat is likely.

Epidemiological studies of workers exposed to PCE have not provided clear evidence that PCE causes cancer in exposed humans. The level of PCE detected in indoor air in these homes is well below occupational exposure levels and would not be expected to pose a significant cancer risk.

The highest reported level of TCE (14.2 ppb) was also found in the living space. This level is more than 1000 times lower than a level that has produced any adverse effect in animals, either cancerous or non-cancerous [2]. Therefore, the levels of TCE found are not expected to pose any public health hazard to exposed adults and children.

Although methylene chloride was found at levels as high as 41.6 ppb, it is commonly encountered as a laboratory contaminant and may not reflect the levels actually present in the indoor air. The remaining VOCs are not expected to cause adverse health effects.

It is important to note that many of the reported values were estimated because the levels exceeded the laboratory's analytical instrument calibration range. Therefore, the actual levels may be somewhat higher than those reported. In March 2000, EPA conducted an additional round of indoor air samples in the homes. The results of these analyses will be used to more accurately define the levels of indoor air contaminants in these homes.


  1. The reported levels of indoor air VOCs in the two homes on Lomond Lane are not likely to cause adverse health effects.

  2. The remediation undertaken by EPA to reroute air intakes in these homes is expected to reduce the VOC levels in the indoor air.

  3. Based on the available indoor air data, health screenings for adults and children are not warranted.


  1. Evaluate the results of additional air sampling when they become available to verify the validity of the above conclusions.


  1. ATSDR. Agency for Toxic Substances and Disease Registry. Toxicological profile for Tetrachloroethylene. Atlanta: U.S. Department of Health and Human Services; September 1997.

  2. ATSDR. Agency for Toxic Substances and Disease Registry. Toxicological profile for Trichloroethylene. Atlanta: U.S. Department of Health and Human Services; September 1997.


Gail E. Scogin
Environmental Health Scientist
Petitions Response Section
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation

Reviewed by

Ken Orloff, Ph.D.
Exposure Investigation Section
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation

Maurice West, P.E.
Deputy Branch Chief
Exposure Investigations and Consultations Branch
Division of Health Assessment and Consultation

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