Section 620.450  Alternative Groundwater Quality Standards

a)         Groundwater Quality Restoration Standards

1)         Subsections (a)(3) and (a)(4)(B) apply to all released chemical constituents in groundwater within a groundwater management zone (GMZ) that are the subject of the GMZ approved under Section 620.250(c)(2).

2)         Subsection (a)(4)(A) applies to all released chemical constituents in groundwater within a three-dimensional region formerly encompassed by a GMZ that were the subject of the GMZ approved under Section 620.250(c)(2).

3)         Before the Agency issues a written determination approving the demonstration of the site owner or operator under Section 620.250(d)(1) or (d)(2), none of the standards specified in Section 620.410, 620.420, 620.430, or 620.440 apply to any released chemical constituent if the owner or operator performs and complies with the schedule for all parts of the GMZ.

4)         After the Agency issues a written determination approving the demonstration of the site owner or operator under Section 620.250(d)(1) or (d)(2), the standard for each released chemical constituent is:

A)        The standard specified in Section 620.410, 620.420, 620.430, or 620.440 if the concentration of the constituent, as determined by groundwater monitoring, is less than or equal to the standard for the applicable class of groundwater specified in one of those Sections; or

B)        The concentration of the constituent, as determined by groundwater monitoring, if the concentration exceeds the standard for the otherwise applicable class of groundwater specified in Section 620.410, 620.420, 620.430, or 620.440 and:

i)          To the extent practicable, the exceedance has been minimized and beneficial use, as appropriate for the otherwise applicable class of groundwater, has been returned; and

ii)         Any threat to public health or the environment has been minimized.

5)         The Agency must develop and maintain a list of all concentrations derived under subsection (a)(4)(B).  For each concentration, the list must identify the location of the corresponding GMZ.  On its website (https://epa.illinois.gov), the Agency must post the list and, at least semi-annually, update it.  In addition, at least annually, the Agency must submit the list to the Board for publication in the Environmental Register.

b)         Coal Reclamation Groundwater Quality Standards

1)         Any inorganic chemical constituent or pH in groundwater, within an underground coal mine, or within the cumulative impact area of groundwater for which the hydrologic balance has been disturbed from a permitted coal mine area under the Surface Coal Mining Land Conservation and Reclamation Act [225 ILCS 720] and 62 Ill. Adm. Code 1700 through 1850, is subject to this subsection (b).

2)         Before completion of reclamation at a coal mine, the standards specified in Sections 620.410(a) and (e), 620.420(a) and (e), 620.430, and 620.440 do not apply to inorganic constituents and pH.

3)         After completion of reclamation at a coal mine, the standards specified in Sections 620.410(a) and (e), 620.420(a), 620.430, and 620.440 apply to inorganic constituents and pH, except:

A)        The concentration of total dissolved solids (TDS) must not exceed:

i)          The post-reclamation concentration of TDS or 3000 mg/L, whichever is less, for groundwater within the permitted area; or

ii)         The post-reclamation concentration of TDS or 5000 mg/L, whichever is less, for groundwater in underground coal mines and in permitted areas reclaimed after surface coal mining if the Illinois Office of Mines and Minerals, Department of Natural Resources and the Agency have determined that no significant resource groundwater existed before mining (62 Ill. Adm. Code 1780.21(f) and (g)).

B)        The concentration of chloride, iron, manganese, and sulfate, must not exceed the post-reclamation concentration within the permitted area.

C)        pH must not exceed the post-reclamation concentration within the permitted area in Class I:  Potable Resource Groundwater described in Section 620.210(a)(4).

D)        The concentration of 1,3-dinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), nitrobenzene, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), 1,3,5-trinitrobenzene, and TNT (2,4,6-trinitrotoluene ) must not exceed the post-reclamation concentration within the permitted area.

4)         A refuse disposal area (not contained within the area from which overburden has been removed) is subject to the inorganic chemical constituent and pH requirements of:

A)        35 Ill. Adm. Code 302.Subparts B and C, except due to natural causes, for an area that began operating after February 1, 1983, and before November 25, 1991, if the groundwater is a present or potential source of water for public or food processing;

B)        Section 620.440(c) for an area that began operating before February 1, 1983, and has remained in continuous operation since that date; or

C)        Subpart D for an area that begins operating on or after November 25, 1991.

5)         For a refuse disposal area (not contained within the area from which overburden has been removed) that began operating before February 1, 1983, and is modified after that date to include additional area, this subsection (b) applies to the area that complies with subsection (b)(4)(C) and the following applies to the additional area:

A)        35 Ill. Adm. Code 302.Subparts B and C, except due to natural causes, for an additional refuse disposal area that began operating after February 1, 1983, and before November 25, 1991, if the groundwater is a present or potential source of water for public or food processing; and

B)        Subpart D for an additional area that began operating on or after November 25, 1991.

6)         A coal preparation plant (not in an area from which overburden has been removed) that contains slurry material, sludge, or other precipitated process material is subject to the inorganic chemical constituent and pH requirements of:

A)        35 Ill. Adm. Code 302.Subparts B and C, except due to natural causes, for a plant that began operating after February 1, 1983, and before November 25, 1991, if the groundwater is a present or potential source of water for public or food processing;

B)        Section 620.440(c) for a plant that began operating before February 1, 1983, and has remained in continuous operation since that date; or

C)        Subpart D for a plant that begins operating on or after November 25, 1991.

7)         For a coal preparation plant (not in an area from which overburden has been removed) that contains slurry material, sludge, or other precipitated process material, began operating before February 1, 1983, and is modified after that date to include additional area, this subsection (b) applies to the area that complies with subsection (b)(6)(C) and the following applies to the additional area:

A)        35 Ill. Adm. Code 302.Subparts B and C, except due to natural causes, for an additional area that began operating after February 1, 1983, and before November 25, 1991, if the groundwater is a present or potential source of water for public or food processing; and

B)        Subpart D for an additional area began operating on or after November 25, 1991.

c)         Groundwater Quality Standards for Specified Groundwater Subject to a No Further Remediation Letter under the Site Remediation Program (35 Ill. Adm. Code 740).  While a No Further Remediation Letter is in effect for a region formerly encompassed by a GMZ established under 35 Ill. Adm. Code 740.530, the applicable groundwater quality standards for the specified "contaminants of concern", as defined in 35 Ill. Adm. Code 740.120, within that area are the groundwater objectives achieved as documented in the approved Remedial Action Completion Report.

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