Contaminated Land?

Pollution tracking?

Monitoring underground leakage?

 

The VOC-Mole™ from Markes International offers low-cost soil screening of large commercial, waste and brownfield sites for all common volatile and semi-volatile organics.

Moles are arranged in a grid pattern over key areas of a site. Organic pollutants migrate into the hollow stainless steel probes and are collected diffusively or using pumps onto sorbent tubes. Subsequent analysis is via thermal desorption-gas chromatography and all measurements are relative.

Leaks, spills and contamination hotspots may be quickly pinpointed and the plume or flow of contamination tracked.

VOC-Mole™

The VOC-Mole Soil Probe is available in three probe lengths; 11¾-inch; 18-inch and 36-inch. Its unique aluminium sampling cap is an Mi™ copyrighted design which renders the probe suitable for both diffusive and pumped sampling. An industry standard diffusive sampler can be connected inside the probe, while tubing for pumped samplers may be attached to the external connector. This allows a variety of different sampling regimes to be undertaken, for example:

  • standard diffusive monitoring over a long time period (i.e. 24 hours
  • pumped monitoring with the sample tube placed within or outside the probe
  • the connection of two tubes in series, one inside, one outside the probe body, to monitor potential breakthrough of highly volatile components.

The sampling cap contains double Viton® O-Ring seals to prevent the ingress of water, wildlife and general soil debris.

Tube and sampling cap assemblies may be prepared in the laboratory, and sealed ready for transportation to the field, where the probes may already be in situ.

Application Examples

Land fill / public waste sites

 

Soil probes have been used to monitor hydrocarbons in and around landfill sites containing domestic and light industrial waste. Pumped sorbent tubes were used and analysis was by thermal desorption GC-MS. Data obtained show that benzene concentrations are higher on older parts of a site and this is thought to be related to microbial activity. The underground migration of volatile organic contaminants from the waste sites was also demonstrated with the identification of a plume of pollution following the direction of the ground water as it moved away from the site.

 

Gasoline retail outlets and car service stations

 

Samples were collected around a gas station / car wash facility. Pumped sampling was used, as in the above example. In addition to volatile hydrocarbons, chlorinated solvents were detected in significant concentrations. They are commonly used as degreasing agents and were thought to derive from the car wash.

 

Productive industrial sites

 

Productive or derelict, industrial sites, particularly those in the chemical / petrochemical sector, present one of the more serious risks of organic contamination of the soil and ground water. Soil probes provide the ideal technology for cost effectively surveying the large areas involved.

 

In practice, most surveys of petrochemical plants have been carried out using large numbers of probes pushed into the surface of the ground. Natural migration of the volatile organics upwards through the soil means that the probes are able to accurately define the surface coordinates of a contamination source. This done, excavation at that location will usually identify the actual cause of the contamination and the depth of soil that must be removed or treated. Brief repeat monitoring exercises with soil probes can be used throughout an excavation to provide supplementary information if required and also to confirm that remediation is complete.

 

Large scale monitoring surveys like this are typically carried out using probes containing diffusive tubes which are typically exposed inside the soil probes for 24 hours. Before attaching the tube to the probe cap to begin the diffusive sampling process, the seal at the top of the probe sampling cap can be temporarily removed and air drawn through to a hand held total hydrocarbon (flame ionisation detector) or total aromatic (photo ionisation detector) measuring instrument.

 

At the end of the sampling period, the tubes are uncoupled from the probe sampling cap, resealed and transported to the laboratory for analysis by thermal desorption–GC(-MS) which provides information on the mass retained and identity of each individual compound retained. Given the wide range of toxicity of different organic compounds, speciated information of this type is always useful for soil surveys and is invaluable whenever the history of a site is unclear or when there is risk of cross contamination from a neighbouring source. While conventional thermal desorption–GC–FID systems are more olerant of wide variations in analyte concentration, the complementary information provided by total hydrocarbon/aromatic instruments forewarns the laboratory and helps prevent overload and contamination of more sensitive mass spectrometer detectors.

 

Detailed contour maps of underground pollution can be built up using the soil probe data.

 

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