Section 611.311  MCLs for Organic Chemical Contaminants

a)         Maximum Contaminant Levels for Volatile Organic Chemical Contaminants. The MCLs for VOCs apply to CWS suppliers and NTNCWS suppliers: 

b)         USEPA, under section 1412 of SDWA identifies in this subsection (b) granular activated carbon (GAC), packed tower aeration (PTA), or oxidation (OX) as BAT, treatment technique, or other means available for achieving compliance with the MCLs for VOCs, and SOCs in subsections (a) and (c) except for per-and polyfluoroalkyl substances (PFAS), as indicated:

*See the Board note at the end of this Section.

c)         The following maximum contaminant levels (MCLs) in Tables 1 and 2 to subsection (c) for synthetic organic contaminants apply to CWS and NTNCWS suppliers; Table 2 also contains health-based water concentrations (HBWCs) for selected per-and poly-fluoroalkyl substances (PFAS) used in calculating the Hazard Index.

1)         MCLs for SOCs (except for PFAS) apply to CWS and NTNCWS suppliers:

* See the Board note at the end of this Section.

2)         MCLs and HBWCs for PFAS apply to CWS and NTNCWS suppliers:

¹ The PFAS Mixture Hazard Index (HI) is the sum of component hazard quotients (HQs), which are calculated by dividing the measured component PFAS concentration in water by the relevant health-based water concentration when expressed in the same units (shown in ng/l for simplification). The HBWC for PFHxS is 10 ng/l; the HBWC for HFPO-DA is 10 ng/l; the HBWC for PFNA is 10 ng/l; and the HBWC for PFBS is 2000 ng/l.  A PFAS Mixture Hazard Index greater than 1 (unitless) indicates an exceedance of the health protective level and indicates potential human health risk from the PFAS mixture in drinking water.

Hazard Index = ([HFPO-DA_water ng/l]/[10 ng/l]) + ([PFBS_water ng/l]/[2000 ng/l]) + ([PFNA_water ng/l]/[10 ng/l]) + ([PFHxS_water ng/l]/[10 ng/l])

HBWC = health-based water concentration

HQ = hazard quotient

ng/l = nanograms per liter

PFAS_water = the concentration of a specific PFAS in water

d)         USEPA, under section 1412 of SDWA identifies in Table 1 to subsection (d) the BAT, treatment technique, or other means available for achieving compliance with the maximum contaminant levels for all regulated PFAS identified in subsection (c).

Table 1 to Subsection (d) BAT for PFAS Listed in Subsection (c)(2)

Abbreviations (BAT)

e)         USEPA, under section 1412 of SDWA, identifies in Table 1 to subsection (e) the affordable technology, treatment technique, or other means available to suppliers serving 10,000 persons or fewer for achieving compliance with the MCLs for all regulated PFAS identified in subsection (c)(2)

Section 611.311(e) List of SSCTs for PFAS.

¹ Section 1412(b)(4)(E)(ii) of SDWA specifies that small system compliance technologies (SSCTs) must be affordable and technically feasible for small systems. 

²SDWA specifies three categories of small systems: (i) those serving 25 or more, but fewer than 501, (ii) those serving more than 500, but fewer than 3,301, and (iii) those serving more than 3,300, but fewer than 10,001.

³Technology rejects a large volume of water and may not be appropriate for areas where water quantity may be an issue.

BOARD NOTE:  This Section derives from 40 CFR 141.61.  More stringent state MCLs for 2,4-D, heptachlor, and heptachlor epoxide appear at Section 611.310.  In 40 CFR 141.6(g), USEPA postponed the effectiveness of the MCLs for aldicarb, aldicarb sulfone, and aldicarb sulfoxide until it took further action on those MCLs. See 40 CFR 141.6(g) and 57 Fed. Reg. 22178 (May 27, 1992).  USEPA later stated that it anticipated taking no action until 2005 on a federal national primary drinking water regulation (NPDWR) applicable to the aldicarbs. 68 Fed. Reg. 31108 (May 27, 2003).  In 2005, USEPA indicated no projected date for final action on the aldicarbs. See 70 Fed. Reg. 27501, 671 (May 16, 2005). An entry for the aldicarbs last appeared in USEPA's Spring 2007 semiannual regulatory agenda, indicating no projected dates for further action.  See 72 Fed. Reg. 23156, 97 (Apr. 30, 2007); see also 72 Fed. Reg. 70118, 23 (Dec. 10, 2007) (the first USEPA regulatory agenda that included no entry for the aldicarbs).  As of early 2022, USEPA did not include the aldicarbs among the NPDWRs on its webpage.  USEPA, Ground Water and Drinking Water, National Primary Drinking Water Regulations (www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations; accessed February 16, 2022).  While the Board must maintain entries for aldicarb, aldicarb sulfoxide, and aldicarb sulfone to maintain consistency with the literal text of the federal rules (see Sections 7.2 and 17.5 of the Act; 42 U.S.C. 300g-2; 40 CFR 142.10), the Board intends that no aldicarb requirements apply in Illinois until after USEPA adopts such requirements, and the Board removes this statement.

(Source:  Amended at 50 Ill. Reg. 2531, effective February 17, 2026)