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620 Groundwater Quality

On December 8, 2021, the Illinois EPA proposed language to the Illinois Pollution Control Board (IPCB) to update 35 Ill. Adm. Code 620. On March 29, 2024, the Illinois Pollution Control Board published a first notice of the proposed rule in the Illinois Register. The proposed updates include ten new chemicals, including six PFAS (perfluorooctanoic acid [PFOA], perfluorooctanesulfonic acid [PFOS], perfluorononanoic acid [PFNA], perfluorohexanesulfonic acid [PFHxS], perfluorobutanesulfonic acid [PFBS], and hexafluoropropylene oxide dimer acid [HFPO-DA or GenX]), and adds three new atrazine metabolites whose concentrations are combined with atrazine when determining compliance with atrazine groundwater quality standards. Definitions are updated and references are consistent with those criteria and practices as incorporated. Site specific groundwater standards for designated Class III Special Resource Groundwater are also added. Exposure factors are updated, and the Human Non-Threshold Toxicant Advisory Concentration model for carcinogens is updated. Tables for similar-acting constituents are added. 

The Illinois EPA's rulemaking proposal for amendments to Ill. Adm. Code 620 can be found on the IPCB website at, https://pcb.illinois.gov/.  You may sign up to receive notifications for case updates by selecting "Search by Case", then in "Search Criteria" entering the following information:  Case #: R2022-018; Case Type: Rulemaking 

Key Provisions

  1. Updates the methodology located in Appendix A for developing oral reference doses (RfDs) when a verified RfD is not available. The updated methodology is the method used by U.S. EPA Integrated Risk Information Systems (IRIS), the Tier 1 source for selecting toxicity criteria.

  2. Updates Exposure Factors listed in the models as follows:

    Non-Carcinogen Model (Human Threshold Toxicant Advisory Concentration – HTTAC)
    Updated exposure factors from an average adult to a child 0-6 years of age to account for more sensitive populations.

    Symbol

    Parameter

    Existing Value

    Updated Value

    BW (kg)

    Body Weight

    70

    15

    W (L/day)

    Per Capita Daily Water Ingestion Rate

    2

    0.78

    Updated Value Sources
    BW: Exposure Factors Handbook, 2011 (U.S. EPA), Table 8-1; weighted average of mean body weights (birth to less than 6 years of age). Utilized in the U.S. EPA Regional Screening Level (RSL) calculator for a child 0 – 6 years of age.
    W:  Exposure Factors Handbook, 2011 (U.S. EPA), Tables 3-15 and 3-33; weighted average of 90th percentile consumer-only ingestion of drinking water (birth to less than 6 years of age). Utilized in the U.S. EPA Regional Screening Level (RSL) calculator for a child 0 – 6 years of age.

    Carcinogen Model (Human Non-Threshold Toxicant Advisory Concentration – HNTAC)
    Due to updates to the source of the HNTAC model, the model is updated as follows:

    Current Model

    Current Model Exposure Factors

    Symbol

    Parameter

    Existing Value

    BW (kg)

    Body Weight

    70

    IR (L/day)

    Daily Water Ingestion Rate

    2

    EF (days/year)

    Exposure Frequency

    350

    ED (year)

    Exposure Duration

    30

    Updated Model

    The age-adjusted drinking water ingestion rate (IFWadj) is an exposure value calculated using an age-adjusted intake factors equation to account for possible exposures during early childhood and as an adult, and equals 327.95 L/kg.

    Updated Exposure Factors for the IFWadj Equation

    Symbol

    Parameter

    Updated Value

    EF all (days/year)

    Exposure Frequency

    350

    EDchild (years)

    Exposure Duration – child

    6

    IRWchild (L/day)

    Daily Water Ingestion Rate – child

    0.78

    BWchild (kg)

    Body Weight – child

    15

    EDadult (year)

    Exposure Duration – adult

    20

    IRWadult (L/day)

    Daily Water Ingestion Rate – adult

    2.5

    BWadult (kg)

    Body Weight – adult

    80

    Updated Value Sources
    ED: Exposure Factors Handbook, 2011 (U.S. EPA), Table 16-108; 90th percentile for current residence time (26 years). Utilized in the U.S. EPA Regional Screening Level (RSL).
    IRWchild: Exposure Factors Handbook, 2011 (U.S. EPA), Tables 3-15 and 3-33; weighted average of 90th percentile consumer-only ingestion of drinking water (birth to less than 6 years of age). Utilized in the U.S. EPA Regional Screening Level (RSL) calculator for a child 0 – 6 years of age.
    IRWadult: Exposure Factors Handbook, 2011 (U.S. EPA), Table 3-33; weighted average of 90th percentile consumer-only ingestion of drinking water (greater than or equal to 21 years of age). Utilized in the U.S. EPA Regional Screening Level (RSL) calculator for an average adult.
    BWchild: Exposure Factors Handbook, 2011 (U.S. EPA), Table 8-1; weighted average of mean body weights (birth to less than 6 years of age). Utilized in the U.S. EPA Regional Screening Level (RSL) calculator for a child 0 – 6 years of age.
    BWadult: Exposure Factors Handbook, 2011 (U.S. EPA), Table 8-3; weighted average of mean body weights (adults 21 – 78). Utilized in the U.S. EPA Regional Screening Level (RSL) calculator for an average adult.

    An updated model is also added for carcinogens that operate by a mutagenic mode of action in order to account for increased cancer risks from childhood exposure.

    Updated HNTAC Model for Mutagens

    The age-adjusted drinking water ingestion factor for mutagens (IFWMadj) is an exposure value calculated using an age-adjusted intake factors equation, applying factors of 10, 3, and 1 to account for additional sensitivity for specific age groups for age-related exposure concerns. The IFWMadj equals 1,019.9 L/kg.

    Updated Exposure Factors for the IFWMadj Equation

    Symbol

    Parameter

    Updated Value

    EF - all (days/year)

    Exposure Frequency

    350

    ED0-2 (years)

    Exposure Duration 0-2 years of age

    2

    IRW0-2 (L/day)

    Daily Water Ingestion Rate – 0-2 years of age

    0.78

    BW0-2 (kg)

    Body Weight – 0-2 years of age

    15

    ED2-6 (years)

    Exposure Duration – ages 2-6

    4

    IRW2-6 (L/day)

    Daily Water Ingestion Rate – ages 2-6

    0.78

    BW2-6 (kg)

    Body Weight – ages 2-6

    15

    ED6-16 (years)

    Exposure Duration -  ages 6-16

    10

    IRW6-16 (L/day)

    Daily Water Ingestion Rate – ages 6-16

    2.5

    BW6-16 (kg)

    Body Weight – ages 6-16

    80

    ED16-26 (year)

    Exposure Duration – ages 16-26

    10

    IRW16-26 (L/day)

    Daily Water Ingestion Rate – ages 16-26

    2.5

    BW16-26 (kg)

    Body Weight – ages 16-26

    80

  3. Updates Class I groundwater quality standards in tables at Part 620.410 based on updates to toxicity values, exposure factors, and other methodologies.

  4. Updates Class II groundwater quality standards in tables at Part 620.420 based on updates to Class I groundwater quality standards and the application of chemical-specific factors to determine if treatment factors may be applied. The treatment factors are based on a constituent’s Dimensionless Henry’s Law Constant at 200C and Organic Carbon Partition Coefficient.

  5. (a.) Establishes groundwater quality standards for the following chemicals:

    CASRN

    Constituent

    Placement in Tables

    7429-90-5

    Aluminum

    Part 620.310(a)(3)(A)(ii)

    Part 620.410(a)

    Part 620.420(a)(2)

    7439-93-2

    Lithium

    Part 620.410(a)

    Part 620.420(a)(1)

    13252-13-6


    HFPO-DA (hexafluoropropylene oxide dimer acid, GenX)

     


    Part 620.310(a)(3)(A)(ii)

    Part 620.410(a)

    Part 620.420(a)(2)

    90-12-0

    1-Methylnaphthalene

    Part 620.310(a)(3)(A)(ii)

    Part 620.410(b)

    Part 620.420(b)

    7439-98-7

    Molybdenum

    Part 620.310(a)(3)(A)(ii)

    Part 620.410(a)

    Part 620.420(a)(1)

    375-73-5

    PFBS (perfluorobutanesulfonic acid)

    Part 620.310(a)(3)(A)(ii)

    Part 620.410(b)

    Part 620.420(b)

    355-46-4

    PFHxS (perfluorohexanesulfonic acid)

    Part 620.310(a)(3)(A)(ii)

    Part 620.410(b)

    Part 620.420(b)

    375-95-1

    PFNA (perfluorononanoic acid)

    Part 620.310(a)(3)(A)(ii)

    Part 620.410(b)

    Part 620.420(b)

    335-67-1

    PFOA (perfluorooctanoic acid)

    Part 620.410(b)

    Part 620.420(b)

    1763-23-1

    PFOS (perfluorooctanesulfonic acid)

    Part 620.310(a)(3)(A)(ii)

    Part 620.410(b)

    Part 620.420(b)


    (b.) Adds the following metabolites as a mixture to atrazine: DEA (desethyl-atrazine), DIA (desisopropyl-atrazine) and DACT (diaminochlorotriazine); and moves atrazine and its metabolites tables at Part 620.410(c)(2) and Part 620.420(c)(2) for complex chemical mixtures.

    (c.) Combines radium 226 and 228, forming CASRN 7440-14-4: radium (combined 226+228), and updates the groundwater quality standard from based on the former MCLs of 20 pCi/L each, to being based on the U.S. EPA drinking water MCL for radium (combined 226+228) of 5 pCi/L. The updates also establish a Class II groundwater quality standard (equal to the Class I standard) for radium (combined 226+228) and adds it to the table at Part 620.420(a)(2).

    (d.) Establishes a Class II groundwater quality standard for silver and adds it to the table at Part 620.420(a)(2).

  6. Updates constituent tables to include Chemical Abstract Services Registry Numbers (CASRNs) as additional identifiers for the constituents.

  7. Adds footnotes to tables identifying the sources or methods for determining the groundwater quality standards.

  8. Removes the explosive constituents at Parts 620.410(c) and 620.420(c); and integrates the constituents into Parts 620.410(b) and 620.420(b).

  9. Adds Appendix E, providing tables for similar-acting non-carcinogenic constituents by health effect (Table A) and similar-acting carcinogen constituents by cancer effect (Table B).

  10. Updates the names of the following constituents:

    CASRN

    Current Constituent Name

    Updated Constituent Name

    143-33-9

    Cyanide

    Cyanide (sodium cyanide)

    7681-49-4

    Fluoride

    Fluoride (sodium fluoride)

    7487-94-7

    Mercury

    Mercury (mercuric chloride)

    78-93-3

    2-Butanone (MEK)

    2-Butanone (methyl ethyl ketone)

    94-75-7

    2,4-D

    2,4-D (2,4-dichlorophenoxy acetic acid)

    96-12-8

    1,2-Dibromo-3-Chloropropane

    1,2-Dibromo-3-chloropropane (dibromochloropropane)

    95-50-1

    ortho-Dichlorobenzene

    o-Dichlorobenzene (1,2-dichlorobenzene)

    106-46-7

    para-Dichlorobenzene

    p-Dichlorobenzene (1,4-dichlorobenzene)

    75-09-2

    Dichloromethane

    Dichloromethane (methylene chloride)

    123-91-1

    P-Dioxane

    1,4-Dioxane (p-dioxane)

    106-93-4

    Ethylene Dibromide

    Ethylene Dibromide (1,2-dibromoethane)

    58-89-9

    Lindane (gamma-Hexachlorocyclohexane)

    gamma-HCH (gamma-Hexachlorocyclohexane, lindane)

    2691-41-0

    HMX (High Melting Explosive, Octogen)

    HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)

    1634-04-4

    Methyl Tertiary-Butyl Ether (MTBE)

    MTBE (methyl tertiary-butyl ether)

    95-48-7

    2-Methylphenol

    2-Methylphenol (o-cresol)

    1336-36-3

    polychlorinated biphenyls (PCBs) (as decachloro-biphenyl)

    PCBs (polychlorinated biphenyls as decachloro-biphenyl)

    121-82-4

    RDX (Royal Demolition Explosive, Cyclonite)

    RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)

    118-96-7

    2,4,6-Trinitrotoluene (TNT)

    TNT (2,4,6-trinitrotoluene)

  11. Adds carcinogen designations for the following chemicals:

    CASRN

    Constituent

    Carcinogen Classification

    Classification Source (year)

    106-46-7

    p-Dichlorobenzene (1,4-dichlorobenzene)

    2B

    IARC (1999)

    100-41-4

    Ethylbenzene

    2B

    IARC (2000)

    58-89-9

    gamma-HCH (gamma-Hexachlorocyclohexane, lindane)

    1

    IARC (2018)

    98-82-8

    Isopropylbenzene (cumene)

    2B

    IARC (2013)

    335-67-1

    PFOA (perfluorooctanoic acid)

    2B

    IARC (2017)
    IARC: International Agency for Research on Cancer

  12. Adds mutagen designations for the following chemicals:

    CASRN

    Constituent

    56-55-3

    Benzo(a)anthracene

    205-99-2

    Benzo(b)fluoranthene

    207-08-9

    Benzo(k)fluoranthene

    50-32-8

    Benzo(a)pyrene

    218-01-9

    Chrysene

    53-70-3

    Dibenzo(a,h)anthracene

    96-12-8

    1,2-Dibromo-3-chloropropane (dibromochloropropane)

    75-09-2

    Dichloromethane (methylene chloride)

    193-39-5

    Indeno(1,2,3-c,d)pyrene

    79-01-6

    Trichloroethylene

    75-01-4

    Vinyl Chloride

     

  13. Updates oral reference dose toxicity values for the following constituents whose groundwater quality standards are based on the HTTAC equation.

    CASRN

    Constituent

    Updated Oral Reference Dose (RfD)
    mg/kg-day

    Updated RfD Source

    7440-48-4

    Cobalt

    3E-04

    PPRTV

    14797-73-0

    Perchlorate

    7E-04

    IRIS

    7440-22-4

    Silver

    5E-03

    IRIS

    7440-66-6

    Zinc

    3E-01

    IRIS

    99-65-0

    1,3-Dinitrobenzene

    1E-04

    IRIS

    108-95-2

    Phenol

    3E-01

    IRIS

    121-82-4

    RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)

    4E-03

    IRIS


    Updates oral slope factor toxicity values for the following constituents whose groundwater quality standards are based on the HNTAC equations:

    CASRN

    Constituent

    Updated Oral Slope Factor (SFo)

    ( mg/kg-day)-1

    Updated SFo Source

    319-84-6

    alpha-BHC (alpha-benzene hexachloride)

    6.3E+00

    IRIS

    56-55-3

    Benzo(a)anthracene

    1.0E-01

    IRIS

    205-99-2

    Benzo(b)fluoranthene

    1.0E-01

    IRIS

    207-08-9

    Benzo(k)fluoranthene

    1.0E-02

    IRIS

    218-01-9

    Chrysene

    1.0E-03

    IRIS

    53-70-3

    Dibenzo(a,h)anthracene

    1.0E+00

    IRIS

    121-14-2

    2,4-Dinitrotoluene

    3.1E-01

    CalEPA

    606-20-0

    2,6-Dinitrotoluene

    1.5E+00

    PPRTV

    123-91-1

    1,4-Dioxane (p-dioxane)

    1.0E-01

    IRIS

    193-39-5

    Indeno(1,2,3-c,d)pyrene

    1.0E-01

    IRIS

    IRIS = Integrated Risk Information System (National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency
    PPRTV = Provisional Peer-Reviewed Toxicity Value (Superfund Health Risk Technical Support Center, National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency)
    CalEPA = Office of Environmental Health Hazard Assessment, California Environmental Protection Agency

Proposed Changes to 620 Sub Part A-F

Sub Part Section Proposed Changes
Part A 620.110 Adds definition of "Chemical Abstract Service Registry Numbers (CASRN)", "Lowest Concentration Minimum Reporting Level", and "Mutagen". Updates definition of "Carcinogen" to be consistent with updates to terminology used by U.S. EPA Integrated Risk Information System, and definition of "Detection" to language currently used in test methods. Removes the definition of "Practical Quantitation Level".
​ 620.125 Updates CFR references to most recent iteration of the code. Adds Illinois EPA "Integrated Water Quality Report and Section 303(d) List" (2016) and National Academy of Science "Water Quality Criteria" (1973) to incorporated references and updates several test methods. Adds references from the U.S. EPA Office of Research and Development, National Center for Environmental Assessment, U.S. EPA Risk Assessment Forum, and reference from U.S. EPA Office of Resource Conservation and Recovery. Updated for groundwater guidance from U.S. EPA 2017. 
Part B 620.210 Removes permeameter as an acceptable means to determine hydraulic conductivity. Adds the wellhead protection area of a community water supply well or well field as a specific area to which Class I groundwater quality standards are applicable.
​ 620.250 Lists a standard set of documentation that must be included with all groundwater management zone applications.
Part C 620.302 Adds to the list of examples of persons who do groundwater monitoring.
​ 620.310 Updates table at Part 620.310(a)(3)(A)(i) to include CASRN for each constituent; removes para-dichlorobenzene and ethylbenzene from the table due to their updated carcinogen classification which requires the carcinogen LCMRL or LLOQ to be a basis for determining if the degradation provisions are violated; adds a table at Part 620.310(a)(3)(A)(ii) depicting the constituents in the subsection, including the addition of carcinogens which standards are no longer based on PQLs or minimum reporting limits per the Board Note; removes MCPP (Mecoprop) due to its standard being based on the LCMRL; removes the Board Note as it excludes carcinogens with health-based standards and carcinogens whose standards are no longer the PQLs due to advances in laboratory techniques.
Part D 620.410 Adds Class I groundwater quality standards for ten new chemicals. Updates constituent tables to add CASRN for each constituent. Adds footnotes detailing the sources of the standards. Updates Class I groundwater quality standards as applicable. Removes explosive constituents table at 620.410(c) and integrates the constituents into table at 620.410(b). Moves atrazine from 620.410(b) to the complex chemical mixtures tables at 620.410(c) with the addition of atrazine metabolites.
​ 620.420 Adds Class II groundwater quality standards for ten new chemicals and two chemicals listed in 620.410 without prior Class II groundwater quality standards. Updates constituent tables to add a CASRN for each constituent, and update Class II groundwater quality standards as applicable. Adds footnotes detailing the sources of the standards. Removes explosive constituents table at 620.420(c) and integrates the constituents into table at 620.420(b). Moves atrazine from 620.420(b) to the complex chemical mixtures tables at 620.420(c) with the addition of atrazine metabolites.
​ 620.430 Establishes site specific Class III groundwater quality standards for chloride and pH at four dedicated nature preserves, which are caves, pursuant to 620.230(b). Establishes site specific Class III groundwater quality standards for chloride at two dedicated nature preserves, which are wetlands, pursuant to 620.230(b).
​ 620.440 Updates names of explosive constituents.
​ 620.450 Updates names of explosive constituents.
Part E 620.510 Requires that the 2009 Unified Guidance be used to determine background groundwater quality unless other methods are specified by regulation. Replaces the use of the PQL with the LLOQ, LCMRL or MDL, as appropriate to the nature of the chemical.
Part F 620.601 (b)-Updates code reference to 604.200.
​ 620.605 (b)(1) Designates the more stringent toxicity value of the (Human Threshold Toxicant Advisory Concentration (HTTAC) or Human Non-threshold Toxicant Advisory Concentration (HNTAC) as the guidance value in the absence of a Maximum Contaminant Level (MCL) or Maximum Contaminant Level Goal (MCLG).
    (b)(2) Removes the Human Non-threshold Toxicant Advisory Concentration (HNTAC) language and equation and relocates it to Appendix A.


Proposed Changes to 620 Appendices

Appendix Section Proposed Changes
A (a) Updates the per capita daily water consumption rate representative of a child for the HTTAC model, which is consistent with Illinois Administrative Code Part 742 and U.S. EPA Regional Screening Levels to account for more sensitive populations for noncancer effects (child per capita daily water consumption = 0.78 liters per day.
  (b)(1) Updates the ADE to represent exposure to a child age 0 - 6 years.
  (b)(2) Updates the ADE to utilize the body weight of 15 kg, representative of a child age 0-6 years, which is consistent with Illinois Administrative Code Part 742 and U.S. EPA Regional Screening Levels. 
  (b)(3) Revises methodology used to calculate guidance values when a verified oral reference dose is not available to make language consistent with U.S. EPA Reference Dose Guidance.
  (b)(4) Clarifies usage of uncertainty factors.
  (b)(5) and (6) Removes language based on updates to language in Appendix A(b)(3)
  (d)(1) Adds equation for calculating HNTAC guidance level for chemicals designated as mutagens.
  (d)(2) Updates equation for calculating HNTAC guidance levels for chemicals designated as carcinogens that are not designated as mutagens.
B (c) Removes language specific to mixtures of ortho-dichlorobenzene and para-dichlorobenzene, and 1,1-dichloroethane and 1,1,1-trichloroethane, and adds reference to Appendix E.
E ​ Provides tables of similar acting non-carcinogenic and carcinogenic constituents.