Statistical Applications for Environmental Analysis and Risk Assessment

Chapter 20Determination of Background and Applications in Risk Assessment

20.1 Introduction and Overview

In the environmental contaminant context, background usually refers to substances or locations that are naturally occurring in an area and not influenced or affected by site-related activities. For example, many metals or metalloids such as aluminum, arsenic, iron, and manganese occur naturally in soils and groundwater. Therefore, if a naturally occurring constituent is found in the soil, groundwater or other environmental medium at a site, and the site concentrations of the constituent are comparable to background concentrations of the constituent in the area, the site owner may not be responsible for any cleanup actions, even if the constituent concentrations exceed the regulatory screening levels or allowable limits.

Conversely, if the substance exists in the background but the concentrations found at the site are higher than the background concentrations, then the site owner may be required to implement remediation actions to reduce the site concentrations down to the background levels. However, if a baseline risk assessment is being performed to evaluate the overall exposure health risks attributable to contaminants at a site, the regulatory guidance recommends against excluding any site chemicals that exceed the regulatory screening levels simply on the grounds that they are present at concentrations equal to or lower than background concentrations. As a result, the ...