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The U.S. Environmental Protection Agency (EPA) identified an area of contaminated groundwater near First Street and Jefferson Street in Grants, Cibola County, New Mexico. EPA identified several businesses that may have released chlorinated solvents that migrated into the groundwater. These facilities include Holiday Cleaners, R&L Laundry, a former dry cleaner at 605 First Street, a former Mountain States Telephone and Telegraph Company station, and a work shed at 700 First Street.

Previous investigations have documented that groundwater at the site is contaminated with high concentrations of chlorinated organic solvents. The solvents detected at the highest concentrations in water samples from area monitoring wells were tetrachloroethylene (PCE) at a maximum concentration of 26,000 g/L and trichloroethylene (TCE) at a maximum concentration of 6,500 g/L. This health consultation will focus on these two chemicals.

The contaminated groundwater has migrated into residential neighborhoods. Because the groundwater is only 4 to 6 feet below ground surface, it is possible that volatile organic chemicals (VOC) in the water could volatilize and migrate upward through the soil into houses located over the contaminated groundwater plume. People living in these houses could then be exposed to VOCs by inhaling indoor air. To assess this potential, EPA collected indoor air samples from residences in the area.

EPA asked ATSDR to assess whether exposure to indoor air contamination with VOCs poses a health hazard to occupants of the homes.


In October 2003, EPA collected 24-hour indoor air samples from six private homes using stainless steel Summa canisters with a flow restriction valve. EPA collected air samples from living areas in each home. In some of the homes, air samples were also collected in the crawl space or basement of the home.

EPA also collected soil gas samples from the same properties and analyzed them for VOCs. All indoor air and soil gas samples were analyzed using EPA Method TO-15.

The soil gas samples contained high concentrations of VOCs. The highest concentration of TCE detected in a soil gas sample was approximately 857,000 g/m3, and the highest concentration of PCE detected in a soil gas sample was just over 949,000 g/m3. Both high soil gas concentrations were detected in samples from the same location, the sixth house (#6) located on First Street.

Table 1.

Indoor air readings for the three residences with the highest concentrations of TCE and PCE.
House number Room Location TCE (g/m3) PCE (g/m3)
#3 crawl space 28 46
  Hallway 5 8
#5 Outdoor 0.3 1
  Basement 103 128
  Basement 3 1
  living room 87 179
#6 crawl space 62 21
  living room 9 5


The movement of VOCs from the soil into an enclosed structure can vary by season. Factors that can influence such VOC migration include temperature, barometric pressure, and precipitation. Because of these and other variables, VOC concentrations in samples collected on a single day–as the samples in this case were–may not accurately represent year-round conditions.

ATSDR also noted that the final pressure in the Summa canisters after the samples had been collected varied from 0–24 negative psi. This variability indicates that air samples collected were not comparable between homes, or even within the same home. In some instances, only low volume air samples were collected; in others, the canister completely equilibrated with the atmosphere, which could alter the results.


ATSDR derives Minimum Risk Levels (MRL) that can be used to evaluate the risks posed by exposure to hazardous chemicals. A MRL is an estimate of daily human exposure to a dose of a chemical that is likely to be without an appreciable risk of adverse noncancerous effects over a specified duration of exposure. The MRL for intermediate term exposures (15-364 days) to TCE is 100 ppb (546 g/m3). None of the measured indoor air concentrations of TCE exceeded this value. The MRL for chronic term exposures (>365 days) to PCE is 40 ppb (271 g/m3). None of the measured indoor air concentrations of TCE or PCE exceeded this value. Therefore, no non-cancer adverse health effects would be expected to result from exposure to the concentrations of TCE and PCE detected in indoor air during the sampling event.

Experimental studies have shown that exposure to high doses of TCE or PCE can cause cancer in laboratory animals. Epidemiological studies of human exposure to TCE and PCE have given mixed results: some studies concluded that human exposure to these chemicals is associated with an increased risk of cancer, whereas other studies have seen no such effect. On the basis of the available evidence, the Department of Health and Human Services categorized both TCE and PCE as reasonably anticipated to be a human carcinogen.

EPA has withdrawn its cancer slope factors for TCE and PCE pending further evaluation. Therefore, the increased cancer risks, if any, from inhalation exposures to TCE and PCE cannot be quantitated. Furthermore, a one-time measurement of indoor air VOC concentrations may not be representative of long-term exposures.


ATSDR considers children in its evaluations of exposures to environmental contamination. Children may have higher exposure to indoor air VOCs than adults because a) they spend more time at home, b) they are more active (resulting in higher respiratory rates), and c) they have a higher resting respiratory minute ventilation rate than adults. Therefore, ATSDR uses health guidelines that are protective of children.


  1. The high concentrations of TCE and PCE in groundwater and soil vapor indicate the potential for the migration of high concentrations of TCE and PCE into indoor air.

  2. The concentrations of TCE and PCE detected during one round of indoor air sampling were not at concentrations that would be expected to pose a public health hazard for non-cancer health effects.

  3. In order to better assess the hazard for the potential toxicity of long-term exposure to VOCs, additional indoor sampling is needed to better characterize long-term indoor air VOC concentrations in living areas.

  4. ATSDR concludes that this site poses an indeterminate public health hazard. Additional data are needed to better characterize long-term exposure to indoor air VOCs. In addition, the lack of cancer slope factors for TCE and PCE precludes a quantitative risk estimate for exposures to these contaminants.


  1. The concentrations of indoor air VOCs in the first round of sampling exceeded EPA Action Levels in several homes. Furthermore, the high concentrations of TCE and PCE in groundwater and soil gas indicate the potential for migration of TCE and PCE into indoor air. Therefore, ATSDR concludes that it would be prudent public health policy to consider implementing remedial actions in those homes where indoor air VOC concentrations exceed EPA Action Levels.

  2. Consider conducting additional air monitoring to better assess long-term exposure to VOCs in indoor air. To ensure that samples are representative, such sampling should be conducted during different seasons and during different meteorological conditions.


Kenneth Orloff, PhD, DABT
Senior Toxicologist
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation
Agency for Toxic substances and Disease Registry

Reviewed by:

Gregory M. Zarus
Strike Team Leader
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry

Donald Joe, PE
Exposure Investigations and Consultation Branch
Division of Health Assessment and Consultation
Agency for Toxic Substances and Disease Registry

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