Soil & Groundwater Analysis | Specialty Gases | Coregas NZ

Soil and groundwater analysis

Soil and ground water samples are analysed to assess the environmental impact of any chemical spillages and emissions. The samples are analysed using high purity specialty gases

A 'down to earth' example of how Coregas specialty gases are used for environmental protection is the monitoring of soil and ground water pollution at service stations in Australia. The Protection of the Environment Operations - Underground Petroleum Storage Systems (UPPS) - Regulation 2008 requires all petrol station sites with operational underground storage to utilise groundwater monitoring wells, which must be suitably positioned to detect leaks from underground petrol storage tanks and related piping systems. Groundwater from these wells must be monitored at six-monthly intervals and any measurement of contaminants above the notifiable levels must be reported to the EPA.

Some of the ground water contaminants and their notifiable levels are:

  • Total petroleum hydrocarbons
    in the range of C10 - C40      600µg/L
  • Benzene                                  950µg/L
  • Toluene                                   300µg/L
  • Ethyl Benzene                   140µg/L
  • o-Xylene                                  350µg/L
  • m and p-Xylene                        200g/L
  • Ethanol                                   1400µg/L

The main contaminants of potential concern, as shown above, include petroleum hydrocarbon fractions in the range of C10 to C40 which are analysed as total recoverable hydrocarbons (TRHs). The term TRH has replaced the term TPH (total petroleum hydrocarbons); it represents the combination of biogenic and petrogenic (petroleum) hydrocarbons extracted by selected solvents.

Analysis of TRHs in petrol station groundwater samples is bread-and-butter work for many environmental laboratories operating across Australia and the established method for this analysis is to use a GC-FID. The gas chromatograph uses high purity Helium 5.0 grade as a carrier gas and the flame ionisation detector requires high purity Hydrogen 5.0 grade as a fuel gas and high purity Zero Air as the oxidiser source. In addition to these instrumentation gases, it is also necessary to use high precision calibration gas mixtures. Coregas supplies laboratories across Australia with these products on a daily basis.

For highly sensitive measurements with dilute samples requiring low detection limits, it is necessary to upgrade the above 5.0 grade (99.999% purity) gases to Helium 6.0 grade which has a purity of 99.9999%. This will minimise any background interference in the analytical result.

In addition to the analysis of groundwater samples every six months, it is required to take soil samples at suitable intervals. To determine where best to take samples, a combination of human sensory observation and analytical techniques are used. Field observations would include sample colour, staining or the presence of odours. Analytical techniques would, for example, use an organic vapour analyser such as a photoionisation detector (PID) to detect VOCs which are characteristically emitted to the nearby air from contaminated soil. Periodic calibration of PID detectors with calibration gas mixtures containing hydrocarbons is required to ensure reliable and accurate operation.