Land Contamination Identified

If land is contaminated or may be contaminated it is important to identify the presence of contamination. Contamination simply means an unacceptable risk to human health, to buildings and the environment. Remediation or site clean up is required.

But Identifying contamination requires assessment and measurement. The most common contaminants are VOC’s or volatile organic compounds.

The London, Stratford Olympic site is typical of a problem site requiring clean-up. A simple to use and relatively low cost screening Device was needed. Soil needed to be assessed and samples across an enormous area were taken and measured on site. The Phocheck Tiger PID was used by environmental consultants across the site to identify contamination.

Soil samples were collected into a clean sample container or bag. The containers were half filled to leave head space above the sample To allow for sampling. The sample container is shaken to thoroughly mix the soil sample with the air in the head space. The sample Is allowed to settle to room temperature, typically 20 deg C. The container is covered with aluminium foil and held in place by a rubber band around the rim of the container. Measurement of VOC levels can easily be identified by piercing the foil to draw sample into the PID. Levels of VOCs are either noted or logged to the instruments memory for later investigation. Unacceptably high levels indicate that further investigation is needed.

Because the Phocheck Tiger’s measurement is a broad band volatile organic compound concentration, it is important to investigate further To identify what the specific contaminant is. Many VOCs are mildly toxic. But others are highly toxic and the risk may be significant even when VOC levels appear relatively low.

The Phocheck Tiger and most PIDs are typically calibrated with a surrogate gas, usually isobutylene. But they are used for the detection of a wide range of gases that exhibit different responses.

In simple terms a PID has a lamp that generates an Ionisation voltage. All compounds have an Ionisation voltage. If the compound’s ionization potential Is lower than the lamp voltage, then that compound will be detected and a measurement provided.

When checking soil samples or performing a walk about survey of a suspected contaminated site, the PID is usually calibrated and configured to accurately Measure isobutylene. All measurements made can then be accurately quoted as ‘isobutylene equivalent’.

Sometimes, if you are aware of the history of the site under investigation, you may know what the specific contaminant is. It could be petrol or toluene or trichloroethylene for example. The PID has built in correction factors for these and 300 other compounds to allow correction of the reading.

Unfortunately on the Olympic site, in common with most others, there was a cocktail of compounds. The correction factors for the different compounds make it difficult And usually impossible to give a precise break down of different compounds.

To provide more precise details, it was necessary to send samples off site for further laboratory analysis. This is expensive and time consuming compared with using the Phocheck Tiger PID with an immediate VOC measurement and dynamic updates every second. The lab measurement is accurate and compound specific. But whilst the Phocheck Tiger measurement is not compound specific the volume of data will often mean better quality data with dynamic second by second measurement.

However, because the PID is non destructive, gas entering the instrument for measurement, also leaves the instrument in exactly the same condition.The exhaust gases from the Phocheck Tiger were easily collected into a ‘tedlar bag’ for subsequent laboratory analysis. This meant that detailed, compound specific analysis was only undertaken when necessary, as indicated by a high reading on the PID.

Whenever contaminated land is required to be put back into use, expensive and technically challenging measurement is needed. The Phocheck Tiger ensures costs are kept to a minimum whilst meeting the requirement to provide a comprehensive picture regards volatile organic compound contamination.