Theme: 09. Vapor Intrusion

Topic Area: 9b. Vapor Intrusion Mitigation and Effectiveness

Formatted Title:

Vapor Intrusion Mitigation Systems: Is a Parking Garage Enough?

Background/Objectives:

Background/Objectives. Properly designed parking garages can be an ideal solution to mitigate potential vapor intrusion (VI) while simultaneously meeting site redevelopment objectives. Some state VI guidance documents make general statements that the use of a parking garage that complies with applicable building codes will not need further environmental regulatory actions. However, there is little readily available information as to the effectiveness of “mitigation via parking garage” or the effects of more recent, efficient, and sustainable ventilation practices incorporated into current parking garage designs.

Approach/Activities:

Approach/Activities. This presentation will provide a review of available information that addresses this topic, including ITRC’s Building Design for Passive VI Mitigation and Minnesota Pollution Control Agency’s Parking Facilities and VI Mitigation: Design and Operation Considerations. To illustrate using a parking garage as part of a site mitigation plan, an example modeling exercise will step through indoor air concentrations that may be predicted for a site with an underground ventilated parking garage overlain by ground floor residential/commercial spaces. Following the example, data from several existing sites with parking garages will be presented to compare empirical data to the example exercise. Discussion of the empirical data will include information to consider when incorporating VI mitigation objectives into parking garage design and the potential need for enhancement features like gas-tight vapor barriers or further assessment of interior preferential pathways such as elevator shafts and stairwells.

Results/Lessons Learned:

Results/Lessons Learned. This presentation will document recommended due diligence for planned parking garages as it relates to VI. Results of the literature and data review indicate that ‘VI mitigation via parking garage’ typically will be effective for a site but that it is key for practitioners to understand why and to make modifications if additional measures are appropriate. Factors that may require additional action are parking garages with ‘on-demand’ ventilation systems, garages with frequently occupied spaces such as a parking office, garages that need to manage groundwater and garages with elevator shafts directly over high subsurface impacts.

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Catherine Regan