Formatted Title:

Development of Representative Sediment Background Concentrations: Overview of Applicable ASTM Guidance

Background/Objectives:

A representative background concentration is a chemical concentration that is inclusive of naturally occurring sources and anthropogenic sources, similar to those present at a sediment site, but not originating from current or historical site-related releases or activities. Determination of representative background is a particular challenge at many urban sediment sites, which tend to be driven by the cleanup of bioaccumulative chemicals, such as polychlorinated biphenyls. Representative background concentrations frequently become the cleanup level at these sites in lieu of risk-based cleanup levels. If the representative background concentration is not determined correctly, this can result in unachievable cleanup levels and can impede the assessment of remedy performance.

Approach/Activities:

To address the shortcomings in available guidance, multiple ASTM guidance documents are now available that provide additional—and detailed—recommendations relevant to the determination of representative sediment background concentrations.

These ASTM guides include: E3242 Standard Guide for Developing Representative Background Concentrations at Sediment Sites—Data Evaluation and Development Methodologies; E3344 Standard Guide for Developing Representative Sediment Background Concentrations at Sediment Sites—Selection of Background Reference Areas; and E3382 Standard Guide for Developing Representative Background Concentrations at Sediment Sites—Framework Overview, Including Conceptual Site Model Considerations.

Collectively, these guides address the importance of establishing representative sediment background concentrations for sediment remedies and how to develop technically defensible representative sediment background concentrations following sound scientific practices. These guides provide an overview of necessary elements for determining representative background concentrations, including developing a robust conceptual site model and a framework for determining appropriate candidate background reference areas for a contaminated sediment site. ASTM E3242 provides a framework for the determination of representative background concentrations, including collection and/or data extraction of candidate background data sets, then using data visualization, high nondetect value assessments, evaluation of outliers, and chemical and geochemical evaluations to identify a representative background data set which is then used in the development of representative background concentration values. Appendices provide case studies involving different site scenarios, as well as an overview of outlier testing including assumptions, advantages, and disadvantages.

Results/Lessons Learned:

These ASTM guidance documents provide important and relevant guidance for the community—both regulated and regulator—applicable to state and federal cleanup sites, with the goal of generating scientifically defensible representative background concentrations for sediment cleanup sites.

Tripp Fisher

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Development of Representative Sediment Background Concentrations: Overview of Applicable ASTM Guidance