AEL believes in using the right tools when approaching an environmental site investigation. For sites with volatile organic compounds (VOCs) in the soil or groundwater, this can involve the use of a photoionization detector (PID) for on-site environmental testing.

VOCs are unstable compounds, usually originating from solvents. When present in soil and exposed to oxygen, they readily off-gas into air which can be a significant risk to human health.

A PID uses an ultraviolet light source to break down VOCs into positive and negative ions. The charge of the ions is measured by the PID, and this is represented as a measure of the concentration of VOCs in air. PIDs are non-selective, meaning that all VOCs are detected, and cannot be separated out in the testing results. Laboratory analysis is required to determine concentrations of individual VOC compounds, but on-site testing can provide a solid indication of samples that require further testing.

The process of detecting VOCs within soil, through on-site testing, requires the collection of VOCs in an enclosed space (before they can escape). This is generally accomplished by placing a small amount of soil in a container (jar or new plastic storage bag), about half full. The container is then sealed for a period of time to allow the VOCs to off-gas (headspace development). The PID is then inserted into the container to measure the concentration of VOCs.