Theme: 09. Vapor Intrusion

Topic Area: 9a. Advances in Vapor Intrusion Investigations

Formatted Title:

Background Indoor Air Levels of Volatile Organic Compounds in California Residences

Background/Objectives:

Understanding typical ranges of background indoor air concentrations for volatile organic compounds (VOCs) is important in evaluating vapor intrusion (VI) because it can help differentiate between sources of indoor air pollutants and aid in the interpretation of sampling results and risk communications. Some regulatory agencies provide guidance for comparing indoor air data to background concentration data to assess the VI pathway at contaminated sites. However, the VI regulatory landscape has been inconsistent, including the approach for incorporating background indoor air as a line of evidence in VI assessments. Literature background values are available, but many of these studies are older and lacked adequate analytical sensitivity, or otherwise include sample populations that were largely collected in states other than California.

Approach/Activities:

California is a unique state with 16 different climate zones and a robust regulatory environment with a vested interest in indoor air background and its potential to confound the VI pathway. To assist with advancing the science for VI evaluations and understanding of indoor air background, we initiated a new indoor air background study in February 2023, which includes the collection of indoor air samples for the analysis of over 100 VOCs. The study is targeting 100 occupied homes located in communities throughout California. As of October 2023, 50 samples have been collected.

Results/Lessons Learned:

The data to date indicate several VOCs being routinely detected above residential indoor air screening levels. This presentation will describe the study methodology, sample group selection criteria, and sampling procedures. Chemical data results summaries and a comparison of the chemical data to other studies as well as a range of screening levels and observed correlations to building characteristics (foundation type, attached garage, HVAC) will be discussed.

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Kelly Chatterton