Illinois Administrative Code
Title 35 - ENVIRONMENTAL PROTECTION
Part 742 - TIERED APPROACH TO CORRECTIVE ACTION OBJECTIVES
Subpart D - DETERMINING AREA BACKGROUND
Section 742.405 - Determination of Area Background for Soil
Universal Citation: 35 IL Admin Code ยง 742.405
Current through Register Vol. 48, No. 38, September 20, 2024
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.
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