Section 742.405  Determination of Area Background for Soil

a)         Soil sampling results shall be obtained for purposes of determining area background levels in accordance with the following procedures:

1)         For volatile chemicals, sample results shall be based on discrete samples;

2)         Unless an alternative method is approved by the Agency, for contaminants other than volatile chemicals, sample results shall be based on discrete samples or composite samples. If a person elects to use composite samples, each 0.5 acre of the area to be sampled shall be divided into quadrants and 5 aliquots of equal volume per quadrant shall be composited into 1 sample;

3)         Samples shall be collected from similar depths and soil types, which shall be consistent with the depths and soil types in which maximum levels of contaminants are found in the areas of known or suspected releases; and

4)         Samples shall be collected from areas of the site or adjacent to the site that are unaffected by known or suspected releases at or from the site.  If the sample results show an impact from releases at or from the site, then the sample results shall not be included in determining area background levels under this Part.

b)         Area background shall be determined according to one of the following approaches:

1)         Statewide Area Background Approach:

A)        The concentrations of inorganic chemicals in background soils listed in Appendix A, Table G may be used as the upper limit of the area background concentration for the site.  The first column to the right of the chemical name presents inorganic chemicals in background soils for counties within Metropolitan Statistical Areas.  Counties within Metropolitan Statistical Areas are identified in Appendix A, Table G, Footnote a.  Sites located in counties outside Metropolitan Statistical Areas shall use the concentrations of inorganic chemicals in background soils shown in the second column to the right of the chemical name.

B)        Soil area background concentrations determined according to this statewide area background approach shall be used as provided in Section 742.415(b) of this Part.  For each parameter whose sampling results demonstrate concentrations above those in Appendix A, Table G, the person shall develop appropriate soil remediation objectives in accordance with this Part, or may determine area background in accordance with subsection (b)(2).

2)         A statistically valid approach for determining area background concentrations appropriate for the characteristics of the data set, and approved by the Agency.

(Source:  Amended at 37 Ill. Reg. 7506, effective May 15, 2013)