Background levels: Identifying naturally occurring chemical substances (Publication 2033) is for environmental professionals to use when assessing contaminated land. It contains steps to confirm if a substance is at a naturally occurring background level in land and groundwater. It is an important step in understanding if land is contaminated.

The guidance is part of the state of knowledge for background level assessments under Section 36(b) of the Environment Protection Act 2017. The steps in the guidance draw on standard site assessment practices. The guidance includes case studies.

Section 35 of the Act defines contaminated land. It is land where a substance is present on or under the surface of the land, and: 

• is present in a concentration above the background level
• creates a risk of harm to human health or the environment.

In some cases, it may be simpler to first identify whether the substance creates a risk of harm to human health or the environment. If it does not present a risk of harm then the land is not contaminated land under the Environment Protection Act 2017. 

The background level is the naturally occurring concentration. EPA can also make a determination of a background level. A background level can also be set in the environment reference standard (ERS).

A background level assessment includes a preliminary site investigation. This helps to understand the characteristics of the site and historical land use. A background reference site or sites is identified for comparison. Sampling of reference sites may be needed.

Use multiple lines of evidence for the assessment. Diffuse anthropogenic sources of contamination are not considered to be naturally occurring.