Where to Obtain Background Concentration Information

Where to Obtain Background Concentration Information
Background concentration information is derived on a site-specific basis using
samples from nearby “background” locations. The basic principle in identifying
background sampling locations is to find areas that resemble as closely as possible soil conditions at the site had a discharge or release not occurred. The selection of background sampling locations is a matter of professional judgment, but the following points should be considered:
• The background sampling area must be clearly unaffected by releases from the
subject site, or any other site. When characterizing natural background conditions,
samples are best taken from areas with minimal anthropogenic impact (e.g., natural areas and parks). In e stablishing anthropogenic background, sampling in areas where contaminants may accumulate should be avoided unless data are needed specifically for comparison with similar features found on a site. These data should be evaluated separately from other anthropogenic background samples. Because selection of background sampling locations is a matter of professional judgment, it is best to obtain concurrence from FDEP staff before obtaining background samples. The following areas are inappropriate to sample when determining soil background:
1. Fill areas;
2. Areas where known or suspected hazardous substances, petroleum, solid or
hazardous wastes or waste waters are managed, treated, handled, stored or
disposed;
3. Areas affected by runoff from a roadway;
4. Parking lots and areas affected by runoff from parking lots or other paved areas;
5. Railroad tracts or railway areas or other areas affected by their runoff;
6. Areas of concentrated air pollutant depositions or areas affected by their runoff;
7. Storm drains or ditches presently or historically receiving industrial or urban
runoff
• Natural concentrations of inorganics can vary with soil type. When determining
natural background, the soil type for the site and background locations should be
the same, if possible.
• Both natural and anthropogenic chemical concentrations can vary with soil depth. Consequently, background samples should be taken from the same soil horizon(s) as the site soil samples.
• Concentrations from background studies published in the literature cannot be used as the basis of comparison with site concentrations. Published background studies may be of value in determining whether a site-specific background data set lies within the range of observations by others. If not, the validity of the site-specific background data set may need to be evaluated.
• In measuring chemical concentrations in background samples, the same analytical methods used for site samples should be employed.
• The background data set should be examined carefully for the presence of
outliers, i.e., data that may not in fact represent background conditions. Formal
outlier tests as well as professional judgment can be used in evaluating the
background data set.