Hydrocarbon-Contaminated Soil: Testing and Remediation Options.

Petroleum products such as diesel, petrol and oils contain mixtures of hydrocarbons. Their behaviour varies: some components may give rise to vapour concerns, while others may persist in soil or affect water. The assessment needs to consider the likely product, site conditions and potential routes of exposure, rather than treating every oil stain as the same problem.

A review of previous site use, fuel tanks, drainage and earlier reports helps define the investigation. Sampling should test the suspected source area and address the possible spread of contamination. Groundwater or vapour investigation may be needed where the conceptual site model identifies a relevant pathway.

For chemical assessment, laboratories may analyse total petroleum hydrocarbons (TPH), individual compounds or appropriate hydrocarbon fractions. The test suite should reflect the suspected source and the purpose of the assessment; a single TPH number is not a complete remediation specification.

Results should be interpreted against the proposed use of the land and the people, water or other receptors that could be affected. A value used to assess residential exposure is not automatically a waste-disposal threshold. Similarly, an acceptable result for one sampled location does not establish the condition of the entire site.

The investigation informs an options appraisal. Depending on the contamination and site conditions, suitable approaches may include removing affected soil or using an appropriate treatment process. The selected method must address the identified risks, practical constraints and regulatory requirements. Not every fuel-contaminated site needs wholesale excavation, and no treatment should be promised before the assessment supports it.

Where historic industrial fill is also present, read about heavy metals in soil and made ground. Buried tar requires its own assessment: see our coal tar and bitumen guide.

If soil will leave site as waste, its classification and the receiving facility's requirements must be established before transport. Waste acceptance criteria (WAC) testing is not a substitute for waste classification. The completed works should be documented against the remediation objectives, including verification and any further monitoring required.