What is contaminated land risk assessment? Risk means the combination of: • the likelihood that harm, or pollution of water, will occur as a result of contaminants in, on or under the land, and • the scale and seriousness of such harm or pollution if it did occur Therefore, assessing risk involves estimating what might happen, how bad it might be, and using this knowledge to help make decisions. It may be difficult to get exact measurements of contamination, know how widespread it is and predict what harm it may cause due to: • a lack of scientific information about how substances in the soil behave • variations in contaminant levels, eg they often vary with depth and from one spot to the next • variations in the possible effects of contamination in different circumstances, eg different land use, other contaminants in the soil, and • the difficulty of predicting when and how substances might cause harm to people, animals or water, or how they might react with other substances in the soil Risk assessments should