Background Organics Subtraction
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Soil and water samples containing fresh or decomposed leaves are known as biogenic organic compounds (BOCs,) and are a significant issue during autumn and winter when there are large quantities of fallen leaves. Everyday activity quickly crushes the leaves onto the road and increased rainfall carries leaves in the runoff.
When BOCs are analysed by the standard laboratory GC-FID analysis (gas chromatography /flame ionization detection) the method gives a significantly higher result for Total Petroleum Hydrocarbon than the true value, typically of between 2,000 - 4000 mg/kg of TPH, making it hazardous under WM3 guidance even when there are no petroleum compounds present. This incorrect classification of the soil waste category causes unnecessary and expensive remediation or disposal.
If a sample contains BOCs the sample extract should be cleaned before GC-FID analysis to prevent over-reporting of TPH. The usual method, an activated silica based compound cleanup cartridge, is time consuming, requiring 3 individual analyses which increases the cost of analysis significantly, plus the cost of the cleanup procedures. This method also does not remove the waxy coatings such as carnauba that leaves use as waterproofing. These coatings consist of predominantly C21 – C35 alkanes, which are also found in petroleum derived compounds. The silica cleanup cannot remove these compounds, so they are still included in the results for TPH.
The QED hydrocarbon analyser recognises, but ignores these BOCs, giving a true picture of TPH levels in the sample. If significant concentrations of BOCs are detected, the results are flagged by the QED as containing BOCs. This easy to use analyser will give accurate and reliable TPH results within five minutes of collecting the sample, either on site or in a simple laboratory, and at low cost. The results and hydrocarbon identification are now accepted by the EA, waste management companies and contractors as sufficiently robust to be used to classify waste soil for WM3.