3209 Introductory guidance on petroleum hydrocarbon soil vapour assessment

Overview:

This publication was produced with the aim of introducing principles of vapour migration and measurement. It also provides the motivation, logic and rationale for the development of a guideline for soil vapour sampling and analyses in vapour intrusion assessments. A detailed guidance setting out the considerations and practical recommendations for the measurement of soil vapour will follow in due course.

UK policy promotes the development of brownfield sites over greenfield sites. Many of the hazardous substances at contaminated sites are volatile organic compounds (VOCs). These can pose a health risk via subsurface vapour intrusion to indoor air (vapour intrusion) and is often considered the primary exposure pathway for building occupants over VOC contaminated sites. Concerns over the potential for vapour intrusion commonly poses as a barrier to brownfield redevelopment.

Vapour intrusion is substantially different for petroleum hydrocarbons (PHCs) compared to chlorinated VOCs (CI-VOCs) because natural soil microbes can rapidly degrade PHCs in the presence of oxygen. Understanding the conditions and locations under which degradation occurs and is sustainable is a key component of understanding the potential risks for petroleum hydrocarbons.

Mathematical models of vapour intrusion exposures are conventionally used with conservative input values and/or assumptions and with a tendency to overestimate the risks. Indoor air quality measurements will be confounded by VOC contributions from interior sources and constituents in outdoor air. Therefore reliable measurement of soil vapour VOC concentrations can provide valuable information that is much less affected by background sources than indoor air sampling and can elucidate the role of biodegradation with more accuracy than using mathematical models alone.