1. a) Chemical constituents for which the Board has adopted standards under Section 620.260; or

2. b) Class III Special Resource Groundwater established under Section 620.230(b) and depicted in the Environmental Register, but only at the dedicated nature preserves identified in this subsection (b), and only for the conditions at those preserves for which standards are specified in this subsection (b).

   1. 1) The following standards apply for Pautler Cave Nature Preserve and Stemler Cave Nature Preserve (Environmental Register, May 2005, No. 611), Fogelpole Cave Nature Preserve (Environmental Register, May 2003, No. 587), and Armin Krueger Speleological Nature Preserve (Environmental Register, December 2009, No. 666):

      Chloride	20 mg/L
      pH	range of 7.0-9.0 Standard Units

   2. 2) The following standard applies for Cotton Creek Marsh Nature Preserve and Spring Grove Fen Nature Preserve (Environmental Register, July 2012, No. 697):

      Chloride

      45 mg/L

Except due to natural causes, concentrations of inorganic and organic chemical constituents and ranges of pH must not exceed the standards specified in Section 620.410. This prohibition does not apply to:

(Source: Amended at 49 Ill. Reg. 4488, effective March 28, 2025)