The International Information Center for Geotechnical Engineers

Sediment Quality Guidelines (SQGs): A Review and Their Use in Practice

 

 

USING SQGs IN PRACTICE

 

The use of SQGs in assessing the problems and risk associated with contaminated sediments at a site is an iterative process.  SQGs require minimal inputs in the way of site investigation data, however uncertainty is high when the guidelines are used without calibration.  Early stage predictions can be made on the spatial distributions of contamination with concentration level testing at multiple locations at a site.  They can also predict the concentration trend in time through contaminant decay.  This allows the SQG user to predict locations that are especially troublesome or one that do not require additional attention.  A breakdown of recommended uses for SQGs by SETAC is shown in Table 7.

 

Table 7. Recommended roles for SQGs by SETAC.

 

After the preliminary investigation and data collection, SQGs can also be indicative of areas that will require additional gathering of information such as measured concentrations that fall between the TEC and PEC.  As more data is analyzed, and the results of SQGs calculated, it will become evident if additional lines of evidence or sources should be explored.  An example flow chart of this process is shown in Figure 1.

 

If SQGs are deemed an appropriate method and indicator of conditions at a site, they can be calibrated using site-specific data to make the best predictions possible.  Examples of this would be laboratory tests for toxic response concentrations for particular contaminants or mixtures and benthos at the site or a more complex EqP model for the ecosystem at the site (NYSDEC).

 

Figure 1. The iterative process for SQGs recommended by NYSDEC.

 

SQGS AND BIOACCUMULATION

 

A phenomenon called bioaccumulation is known to be possible in a sediment contamination scenario.  Bioaccumulation is the increase in the concentration of a contaminant as it moves up the food chain.  Starting with small benthic organisms, as larger animals consume these organisms, the concentration present in larger organisms’ systems scales with the number of contaminated benthos consumed. Although still debated, contaminants currently known to biomagnify include PCBs, mercury, and DDT.  For humans, who are essentially at the top of the food chain, the description and prediction of biomagnification is especially interesting pertaining to public health and food source concerns.

 

Most SQGs, up to this point, do not account for bioaccumulation.  However, EqP SQGs are best-positioned to describe this process.  The New York State Department of Environmental Conservation’s (NYSDEC) standardized practice for the use of SQGs includes a procedure for estimating the effect of biomagnification in the ecosystem for contaminated sediments.

 

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