Further description:-  Receptor: Buildings 

Glossary Entry
Entity that may be adversely affected by contact with or by exposure to a contaminant of concern, here 
buildings
Risk Assessment: Receptor Buildings

Risk Assessment: Receptor Buildings

 

1.     Summary

 

At sites where soils or groundwater contain volatile and/or semi-volatile contaminants (semi-volatile: 0.04 < H < 4 · 10-6, where H = dimensionless Henry coefficient), there is the potential that contaminant vapors may migrate from the subsurface into overlaying buildings. Beside near-term safety hazards (e.g. explosions, acute health effects, aesthetic problems), which can be observed in the indoor air under worst-case conditions, most frequently contaminant concentrations are relatively low. However, an assessment is required to determine whether there is an unacceptable of health effects.

 

2.     Definitions

 

The subsurface to indoor air pathway represents a specific pathway of exposure in the human health risk assessment. The same definitions are valid as established in "Risk Assessment: Receptor Human Health".

 

3.     Receptor Identification and Characterization

 

The subsurface to indoor air pathway represents a specific pathway of exposure in the human health risk assessment. Receptor identification and characterization takes place according to the principles described in "Risk Assessment: Receptor Human Health".

 

4.     Description of Contaminant Release Processes

 

An assessment of the subsurface to indoor air pathway considers a contaminant source located in some distance below floor of an enclosed building constructed with a basement or constructed slab-on-grade. The source is ether a soil-incorporated volatile/semi-volatile contaminant or a volatile/semi-volatile contaminant in groundwater. Driven by molecular diffusion the volatilized contaminant migrates from the top boundary of the source towards the soil surface, where it reaches the zone of influence of an overlaying building. There the contaminant vapor enters into the indoor air through cracks between the foundation and the basement slab floor or within the slab floor structure. This sweep effect is induced by convective air movement due to a pressure differential between the soil surface and the building. The negative pressure with respect to the soil surface within the structure is generated by stack effects because of heating of the interior air, and unbalanced mechanical ventilation.

 

5.     Data Sources

 

Data required for the calculation of vapor intrusion into buildings can be obtained from the following sources:

 

  • Soil property databases,
  • Contaminant property databases,
  • Construction guideline for buildings,
  • Hygienic standards for indoor air quality;
  • Climatic/meteorological databases.

 

6.     Literature

 

American Petroleum Institute (1998):

Assessing the Significance of Subsurface Contaminant Vapor Migration to Enclosed Spaces, Site-Specific Alternatives to Generic Estimates. API Publication No. 4674. American Petroleum Institute. Washington D.C.

 

American Petroleum Institute. (2002):

Practical Guidance for Assessing the “Groundwater to Indoor Air” Vapor Migration Pathway at Petroleum Hydrocarbon Sites.

 

Ettinger, R. (2002):

Vapor Intrusion Modeling: Theory and Implications. Indoor Air Session, Technical Support Project Meeting. Denver, CO.

 

Fischer, M. L., A. J. Bentley, K. A. Dunkin, A. T. Hodgson, W. W. Nazaroff, R. G. Sexto, and J. M. Daisey (1996):

Factors affecting indoor air concentrations of volatile organic compounds at a site of subsurface gasoline contamination. Environ. Sci. Technol., 30(10):2948-2957.

 

Johnson, P. C., R. A. Ettinger, J. Kurtz, R. Bryan , and J. E. Kester. (2002):

Migration of Soil Gas Vapors to Indoor Air: Determining Vapor Attenuation Factors Using a Screening-Level Model and Field Data from the CDOT-MTL Denver, Colorado. Technical Task Force Bulletin No. 16, American Petroleum Institute.

 

U.S. Environmental Protection Agency (2002):

Draft of the Guidance for Evaluating The Vapor Intrusion to Indoor Air Pathway from Groundwater Soils (Subsurface Vapor Intrusion Guidance). Office of Solid Waste and Emergency Response (OSWER). Washington D.C.

 

U.S. Environmental Protection Agency (2003):

User's Guide for Evaluating Subsurface Vapor Intrusion into Buildings. Office of Emergency and Remedial Response. Washington D.C.

 

 

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