Vapor Intrusion Survey

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Risk

Forty-eight (48%) of respondents have set numerical risk-based values for indoor air. A similar number of respondents (48%) did not know what their state's position was regarding the use of Occupational Health and Safety Administration (OSHA) standards at commercial vapor intrusion sites versus risk-based screening values. Respondents were more likely to evaluate for vapor intrusion when chemicals found in commercial buildings were not being used in the workplace. Most of the respondents consider background when doing a vapor intrusion evaluation.

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47-50. Has your agency set numerical criteria for the following media to evaluate the potential for vapor intrusion?

47. Soil
48. Soil gas vapor
49. Groundwater
50. Indoor air



51. If numerical criteria are set for indoor air concentrations, are they:
a. Default agency-wide numerical criteria?
b. Site-specific numerical criteria modified by exposure scenarios and site conditions?
c. Generic empirical attenuation factors, similar to U.S. EPA draft generic screening values, are
used.
d. Based on human health risk levels?
e. Based on regional or published background concentrations?



52-54. Does your agency require evaluation of the vapor intrusion pathway if:

52. Workplace concentrations are higher than OSHA levels (or state equivalent)?
53. Workplace concentrations are higher than agency numerical criteria but less than OSHA levels
(or state equivalent) if the chemicals detected are the same as the chemicals used in the
workplace?
54. Workplace concentrations are higher than agency numerical criteria but less than OSHA levels
(or state equivalent) if the chemicals detected are different than the chemicals used in the
workplace?



55. When evaluating indoor air results, how does your agency treat background contamination (from ambient air, household products, construction materials, etc.)?
a. Background not considered. (Procedures do not differentiate between background VOC
concentrations and subsurface VOC contributions to indoor air.)
b. Modeling is preferred over sampling to avoid background interferences.
c. VOC concentrations detected in indoor air below background are not considered in the
evaluation/risk assessment.
d. Weight-of-evidence approach that considers indoor and outdoor observations, other
subsurface data, VOC concentration patterns, etc.
e. Literature indoor air background values are used as the lower limit in developing numerical
criteria when risk-based target concentrations are lower.
f. Unknown.




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