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Contamination: tread lightly when assessing sites

Defining ‘contamination’ within site-specific characteristics is easier said than done. Watch video.

The National Environmental Management Waste Act (Nemwa) prescribes some onerous conditions to landowners in respect of defining and reporting on the extent of contamination present on land under their responsibility.

Incorrect application of the science pertaining to the measurement and definition of contamination could over and under predict the liability due to contamination, says Carl Steyn, a soil remediation specialist who addressed a workshop on the subject hosted by Golder Associates in Midrand.

See an interview with Steyn below:

“Part of the ambiguity comes from the fact the legislation does not specify analytical methods to apply for comparison with the new screening values published in GN. R 331,” says Steyn. This means the technique to be applied remains at the discretion of the person performing the analysis, and if done without care, may lead to incorrect conclusions with possible legal ramifications.

“So statistically speaking, the first step assessors need to do is establish the ‘background’ concentration for the soil, and if this has been exceeded, establish where the excess comes from,” says Steyn. These baseline comparisons provide the values with which to determine which constituents and areas should be evaluated further. But it’s vital that site specific baseline measurements are evaluated due to the high variability of soils.

Steyn and his team sampled numerous natural soils, outside industrial areas, to inform their ideas about the levels of various materials that could be expected in South African soils. “Some constituents such as lead, copper, manganese have more than 20 percent of samples exceeding the set screening values.   So it is highly likely that one of these constituents will result in most sites screening as “contaminated” when in fact they are naturally occurring,” says Steyn. The experiment naturally forced a rethink of what exactly the term “normally present” really means.

To perform this type of analysis accurately, it’s vital to understand the soil’s properties and perform site specific screening. As an example, Steyn cited the difference inherent in industrial areas. “Natural baseline assumptions would suggest that the presence of an element like lead should not exceed 66mg/kg. But our work in Germiston suggests a regional industrial baseline of 340mg/kg, which is above the natural baseline but well in excess of the soil screening value of 20mg/kg,” says Steyn.

Organic constituents such as polyaromatic hydrocarbons are also present in high baseline concentrations in industrialised areas which need to be taken into account before applying a one-size-fits-all approach. “Mindless screening could potentially over and under predict your liability” says Steyn.

Another challenge for local practioners is that South Africa does not have screening values for all compounds. This means some baseline concentrations mostly fall back on those established by the Environmental Protection Agency (EPA) in the United States. The basis of the EPA screening values differs from that of South Africa and should be taken into account when screening for constituents of concern.

Steyn suggested following a protocol when assessing sites, which comprises:


  • First consider the site history when determining how constituents of concern are related to values determined during analysis.
  • Approach assessments in a phased manner. Screening is not a risk approach.
  • Determine soluble concentrations additional to total concentrations even as part of an initial phase 1 screening.
  • Soil cannot be assessed in isolation; you need to conceptually understand site conditions. This includes assessing source-pathway-receptor links, and any other unique factors that could cause results to vary from the screening values.
  • Pay attention to the soluble results – these are good indicators of risk and which constituents require further assessment. The solubility variation could also give you the tools to remedy contamination.


As with any investigation, the more data collected, the more certain your evaluation becomes.

With the onus on companies to report findings where soil concentrations exceed set screening levels, it’s absolutely critical to be sure you have done the work properly. “So we invert the question: what level of uncertainty do we require for notification? This talks to significance and risk, and may well require extending to Phase 2 and 3 studies,” says Steyn.

This article forms part of an education series sponsored by Golder Associates on the risks industry faces.

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