Soil gas containing VOCs entering homes near hazardous lands.

The entry of soil gas volatile organic compounds (VOCs) into houses has been recognized as a contributing factor in the degradation of indoor air quality. Typically, houses which are affected by soil gas VOCs are situated in close proximity to hazardous lands, i.e. landfill sites, lands affected by contaminated groundwater plumes, hydrocarbon spills, etc. Although there are hundreds of evaluations carried out yearly to assess the impact of soil-gas VOCs indoors, very few studies typically address the VOC concentration variability over time or the factors which influence this variability. Coupled to this problem is the presence of ubiquitous indoor or outdoor sources of VOCs. As a result of these difficulties, many investigations are far from accurate. This study was designed to develop a practical protocol to evaluate the impact of soil gas VOCs on indoor air. The method used, monitored the temporal concentration variability of methane and oxygen in the ambient air and the subsurface as well as the driving forces which influenced the variability. Using this data, it was concluded that barometric fluctuations produced a bidirectional airflow across the subsurface envelope. By sampling VOCs indoors during high flux periods and during time periods when the airflow was directed towards the soil, the contribution of soil gas VOCs can be subtracted from other sources. This allows investigators the possibility of identifying the origin of VOCs found indoors, as well as allowing the completion of more accurate risk assessments.