A method to evaluate soil gas VOC influx into houses

The entry of soil gas volatile organic compounds (VOCs) into buildings is recognized as an exposure pathway which can contribute to human health impacts by the degradation of indoor air quality. Typically, buildings which are affected by soil gas VOCs are situated on or in close proximity to contaminated lands, i.e. landfill sites, lands affected by contaminated soil or groundwater plumes, etc. Although experience has shown that generally soil gases have limited impacts when diffusion is the primary mechanism, there are situations where advective processes dominant. In such cases the impact to indoor air can be significant. This study was designed to develop a practical protocol to evaluate the impact of soil gas VOCs on indoor air caused by advective processes. The method was based on the monitoring of temporal concentration variability of the pollutants and the driving force which influenced this variability. Barometric fluctuations produced a bidirectional airflow across the subsurface envelope. By sampling VOCs indoors during high flux periods and during times when the airflow was directed towards the soil, the contribution of soil gas VOCs can be subtracted from other sources. Results were compared to standard mathematical screening predictions and implications to risk assessment procedures are discussed.