Ill. Admin. Code tit. 35, § 620.410 – Groundwater Quality Standards for Class I: Potable Resource Groundwater

a) Inorganic Chemical Constituents

Except due to natural causes or as provided in Section 620.450, concentrations of the following chemical constituents must not be exceeded in Class I groundwater:

CASRN	Constituent	Standard (mg/L)^a,b
7429-90-5	Aluminum	l.9^c
7440-36-0	Antimony	0.006^d
7440-38-2	Arsenic^e	0.01^d
7440-39-3	Barium	2.0^d
7440-41-7	Beryllium	0.004^d
7440-42-8	Boron	2.0^f
7440-43-9	Cadmium	0.005^d
16887-00-6	Chloride	200^g
7440-47-3	Chromium (total)	0.l^d
7440-48-4	Cobalt	0.0012^c
7440-50-8	Copper	0.5^h
143-33-9	Cyanide	0.2^d
7681-49-4	Fluoride	4^d
7439-89-6	Iron	5^g
7439-92-1	Lead	0.0075ⁱ
7439-93-2	Lithium	0.04^j
7439-96-5	Manganese	0.l5^k
7487-94-7	Mercury (mercuric chloride)	0.002^d
7439-98-7	Molybdenum	0.308^c
7440-02-0	Nickel	0.077^c
14797-55-8	Nitrate as N	10^d
14797-73-0	Perchlorate	0.0081^c
7440-14-4	Radium (combined 226+228)	5^d
7782-49-2	Selenium	0.02^f
7440-22-4	Silver	0.058^c
14808-79-8	Sulfate	400^g
	TDS (total dissolved solids)	1,200^g
7440-28-0	Thallium	0.002^d
7440-62-2	Vanadium	0.00027^c
7440-66-6	Zinc	l.2^c

Constituent Name and Groundwater Quality Standard Notations

^aThe standard unit for radium (combined 226+228) is picocuries per liter (pCi/L).

^bThe inorganic groundwater quality standards are based on total metal analyses for the evaluation of human health effects.

^cThe standard is calculated using the Human Threshold Toxicant Advisory Concentration (HTTAC) procedures at Appendix A.

^dThe standard is based on the Maximum Contaminant Level (MCL), promulgated by USEPA, Office of Water, and Illinois Primary Drinking Water Standards specified in 35 Ill. Adm. Code 611.

^eThe constituent meets the definition of a "carcinogen" in Section 620.110.

^fThe standard is based on beneficial use for irrigation of crops, per "Water Quality Criteria", by National Academy of Sciences, incorporated by reference in Section 620.125.

^gThe standard is the 95% confidence concentration stated in the Agency's "Integrated Water Quality Report and Section 303(d) List", incorporated by reference in Section 620.125.

^hThe standard is based on beneficial use for watering livestock, per "Water Quality Criteria", by National Academy of Sciences, incorporated by reference in Section 620.125.

ⁱ The standard is 50% of the USEPA "action level" of 0.015 mg/L for lead. The USEPA action level applies at the service connection. The standard is reduced by 50% as a safety margin, based on the assumption that 50% of water would be treated.

^jThe standard is the "LLOQ" or "LCMRL" as defined in Section 620.110.

^kThe standard is promulgated at 35 Ill. Adm. Code 611.300.

b) Organic Chemical Constituents

Except due to natural causes or as provided in Section 620.450 or subsection (c) of this Section, concentrations of the following organic chemical constituents must not be exceeded in Class I groundwater:

CASRN	Constituent	Standard (mg/L)
83-32-9	Acenaphthene	0.23^a
67-64-1	Acetone	3.5^a
15972-60-8	Alachlor^b	0.002^c
116-06-3	Aldicarb	0.003^c
120-12-7	Anthracene	1.2^a
319-84-6	alpha-BHC (alpha-benzene hexachloride)^b	0.000012^d
71-43-2	Benzene^b	0.005^c
56-55-3	Benzo(a)anthracene^e	0.00025^d
205-99-2	Benzo(b)fluoranthene^e	0.00025^d
207-08-9	Benzo(k)fluoranthene^e	0.0025^d
50-32-8	Benzo(a)pyrene^e	0.0002^c
65-85-0	Benzoic acid	15^a
78-93-3	2-Butanone (methyl ethyl ketone)	2.3^a
1563-66-2	Carbofuran	0.04^c
75-15-0	Carbon disulfide	0.38^a
56-23-5	Carbon tetrachloride^b	0.005^c
12789-03-6	Chlordane^b	0.002^c
108-90-7	Chlorobenzene	0.l^c
67-66-3	Chloroform^b	0.07^f
218-01-9	Chrysene^e	0.025^d
94-75-7	2,4-D (2,4-dichlorophenoxy acetic acid)	0.07^c
75-99-0	Dalapon	0.2^c
53-70-3	Dibenzo(a,h)anthracene^e	0.0001^g
96-12-8	1,2-Dibromo-3-chloropropane (dibromochloropropane)^e	0.0002^c
1918-00-9	Dicamba	0.12^a
95-50-1	o-Dichlorobenzene (1,2-dichlorobenzene)	0.6^c
106-46-7	p-Dichlorobenzene (1,4-dichlorobenzene)^b	0.075^c
75-71-8	Dichlorodifluoromethane	0.77^a
75-34-3	1,1-Dichloroethane	0.77^a
107-06-2	1,2-Dichloroethane^b	0.005^c
75-35-4	1,1-Dichloroethylene	0.007^c
156-59-2	cis-1,2-Dichloroethylene	0.07^c
156-60-5	trans-1,2-Dichloroethylene	0.l^c
75-09-2	Dichloromethane (methylene chloride)^e	0.005^c
78-87-5	1,2-Dichloropropane^b	0.005^c
117-81-7	Di(2-ethylhexyl)phthalate^b	0.006^c
84-66-2	Diethyl phthalate	3.1^a
84-74-2	Di-n-butyl phthalate	0.38^a
99-65-0	1,3-Dinitrobenzene	0.001^g
121-14-2	2,4-Dinitrotoluene^b	0.001^g
606-20-2	2,6-Dinitrotoluene^b	0.0001^g
88-85-7	Dinoseb	0.007^c
123-91-1	1,4-Dioxane (p-dioxane)^b	0.00078^d
145-73-3	Endothall	0.l^c
72-20-8	Endrin	0.002^c
100-41-4	Ethylbenzene^b	0.7^c
106-93-4	Ethylene dibromide (1,2-dibromoethane)^b	0.00005^c
206-44-0	Fluoranthene	0.15^a
86-73-7	Fluorene	0.15^a
58-89-9	gamma-HCH (gamma-Hexachlorocyclohexane, lindane)^b	0.0002^c
13252-13-6	HFPO-DA (hexafluoropropylene oxide dimer acid GenX)	0.000010^c
2691-41-0	HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)	0.77^a
76-44-8	Heptachlor^b	0.0004^c
1024-57-3	Heptachlor epoxide^b	0.0002^c
77-47-4	Hexachlorocyclopentadiene	0.05^c
193-39-5	Indeno(l,2,3-c,d)pyrene^e	0.00025^d
98-82-8	Isopropylbenzene (cumene)^b	0.38^a
93-65-2	MCPP (mecoprop)	0.1^g
1634-04-4	MTBE (methyl tertiary-butyl ether)	0.038^a
72-43-5	Methoxychlor	0.04^c
90-12-0	1-Methylnaphthalene	0.27^a
91-57-6	2-Methylnaphthalene	0.015^c
95-48-7	2-Methylphenol (o-cresol)	0.19^a
91-20-3	Naphthalene	0.077^a
98-95-3	Nitrobenzene	0.0077^a
1336-36-3	PCBs (polychlorinated biphenyls as decachloro-biphenyl)^b	0.0005^c
375-73-5	PFBS (perfluorobutanesulfonic acid)	0.002^c
355-46-4	PFHxS (perfluorohexanesulfonic acid)	0.000010^c
375-95-1	PFNA (perfluorononanoic acid)	0.000010^c
335-67-1	PFOA (perfluorooctanoic acid)^b	0.000004^bc
1763-23-1	PFOS (perfluorooctanesulfonic acid)	0.000004^bc
87-86-5	Pentachlorophenol	0.001^c
108-95-2	Phenol	0.1^h
1918-02-1	Picloram	0.5^c
129-00-0	Pyrene	0.12^a
121-82-4	RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)	0.062^a
122-34-9	Simazine	0.004^c
100-42-5	Styrene	0.l^c
118-96-7	TNT (2,4,6-trinitrotoluene)	0.0077^a
93-72-1	2,4,5-TP (silvex)	0.05^c
127-18-4	Tetrachloroethylene^b	0.005^c
108-88-3	Toluene	1^c
8001-35-2	Toxaphene^b	0.003^c
120-82-1	1,2,4-Trichlorobenzene	0.07^c
71-55-6	1,1,1-Trichloroethane	0.2^c
79-00-5	1,1,2-Trichloroethane	0.005^c
79-01-6	Trichloroethylene^e	0.005^c
75-69-4	Trichlorofluoromethane	1.2^a
99-35-4	1,3,5-Trinitrobenzene	0.46^a
75-01-4	Vinyl chloride^e	0.002^c
1330-20-7	Xylenes	10^c

Constituent Name and Groundwater Quality Standard Notations

^aThe standard is the Human Threshold Toxicant Advisory Concentration (HTTAC), calculated using procedures specified in Appendix A.

^bThe constituent meets the definition of a "carcinogen" in Section 620.110.

^cThe standard is based on the Maximum Contaminant Level (MCL), promulgated by USEPA, Office of Water, and Illinois Primary Drinking Water Standards in 35 Ill. Adm. Code 611.

^dThe standard is the Human Nonthreshold Toxicant Advisory Concentration ("HNTAC"), calculated using procedures specified in Appendix A.

^eThe constituent meets the definition of a "mutagen" in Section 620.110.

^fThe standard is based on the Maximum Contaminant Level Goal ("MCLG"), promulgated by USEPA, Office of Water.

^gThe standard is the "LLOQ" or "LCMRL" as defined in Section 620.110.

^hThe standard is based on 35 Ill. Adm. Code 302.208.

c) Complex Organic Chemical Mixtures
1. 1) Concentrations of the following chemical constituents must not be exceeded in Class I groundwater:
  CASRN Constituent Standard (mg/L)
  71-43-2 Benzene^a 0.005^b
  Total BETX 11.705^c
  Constituent Name and Groundwater Quality Standard Notations
  ^aThe constituent meets the definition of a "carcinogen" in Section 620.110.
  ^bThe standard is based on the Maximum Contaminant Level (MCL), promulgated by USEPA, Office of Water, and Illinois Primary Drinking Water Standards at 35 Ill. Adm. Code 611.
  ^cThe standard is the total combined standard of benzene, ethylbenzene, toluene, and xylenes.
2. 2) Atrazine and Metabolites
  Concentrations of the following chemical constituents must not be exceeded in Class I groundwater.
  CASRN Constituent Standard (mg/L)
  1912-24-9 Atrazine 0.003^a
  Total Atrazine and Metabolites 0.003
  6190-65-4 DEA (desethyl-atrazine)
  1007-28-9 DIA (desisopropyl-atrazine)
  3397-62-4 DACT (diaminochlorotriazine)
  Groundwater Quality Standard Notation
  ^aThe standard is based on the Maximum Contaminant Level (MCL), promulgated by USEPA, Office of Water, and Illinois Primary Drinking Water Standards at 35 Ill. Adm. Code 611.
d) pH
Except due to natural causes, a pH range of 6.5 - 9.0 units must not be exceeded in Class I groundwater.
e) Beta Particle and Photon Radioactivity
1. 1) Except due to natural causes, the average annual concentration of beta particle and photon radioactivity from man-made radionuclides must not exceed a dose equivalent to the total body or any internal organ greater than 4 mrem/year in Class I groundwater. If two or more radionuclides are present, the sum of their dose equivalent to the total body or any internal organ must not exceed 4 mrem/year in Class I groundwater except due to natural causes.
2. 2) Except for the radionuclides specified in subsection (e)(3), the concentration of man-made radionuclides causing 4 mrem total body or organ dose equivalent must be calculated on the basis of a 2 liter per day drinking water intake using the 168-hour data in compliance with the procedure specified in NCRP Report Number 22, incorporated by reference in Section 620.125(a).
3. 3) Except due to natural causes, the average annual concentration assumed to produce a total body or organ dose of 4 mrem/year of the following chemical constituents must not be exceeded in Class I groundwater:
  CASRN Constituent Critical Organ Standard (pCi/L)
  10028-17-8 Tritium Total Body 20,000
  10098-97-2 Strontium-90 Bone Marrow 8.0

f) No facility that is subject to 35 Ill. Adm. Code 811 or 814 must comply with any requirement or standard of those rules to the extent it incorporates or is otherwise based on any of the following constituents or their standards under this Section:

CASRN	Constituent
13252-13-6	HFPO-DA (hexafluoropropylene oxide dimer acid GenX)
375-73-5	PFBS (perfluorobutanesulfonic acid)
355-46-4	PFHxS (perfluorohexanesulfonic acid)
375-95-1	PFNA (perfluorononanoic acid)
335-67-1	PFOA (perfluorooctanoic acid)
1763-23-1	PFOS (perfluorooctanesulfonic acid)

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

CASRN	Constituent	Critical Organ	Standard (pCi/L)
10028-17-8	Tritium	Total Body	20,000
10098-97-2	Strontium-90	Bone Marrow	8.0

CASRN	Constituent	Standard (mg/L)
1912-24-9	Atrazine	0.003^a
	Total Atrazine and Metabolites	0.003
6190-65-4	DEA (desethyl-atrazine)
1007-28-9	DIA (desisopropyl-atrazine)
3397-62-4	DACT (diaminochlorotriazine)