The Illinois Environmental Protection Agency (Illinois EPA) will be conducting a statewide investigation into the prevalence and occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in finished water at 1,456 entry points to the distribution system representing 1,749 community water supplies (CWSs) across Illinois. The purpose of this investigation is to support the potential development and promulgation of maximum contaminant level (MCL) standards in Illinois for certain PFAS, and to respond to scientific data throughout the nation regarding the effects of PFAS on public health. Samples will be analyzed using United States Environmental Protection Agency (U.S. EPA) Method 537.1. Illinois EPA, in conjunction with the U.S. EPA, has developed a Quality Assurance Project Plan (QAPP) for this investigation network. The QAPP also contains a Standard Operating Procedure (SOP) for sample collection. For further detail see the Process to Establish Maximum Contaminant Levels for PFAS in Illinois.

Before conducting sampling at a CWS, Illinois EPA staff will contact the CWS Responsible Operator in Charge to schedule a time to collect the samples for PFAS analysis. There is no cost to CWS for this sampling.

The Illinois EPA will provide CWS owners and operators with the results of this sampling. If PFAS are present in concentrations above minimum reporting levels (MRLs), the Illinois EPA will return to collect a confirmation sample at the distribution system entry point(s). Based on the results of the confirmation sampling, additional evaluation or actions may be necessary to protect human health and the environment. The Illinois EPA’s sample analysis will include a total of 18 PFAS, listed on the chart below.

PFAS Analyte Namea
AcronymChemical Abstract Services Registry Number (CASRN)
​Perfluorotetradecanoic acid ​PFTA​376-06-7​C13F27COOH
​Perfluorotridecanoic acid​PFTrDA72629-94-8​​C12F25COOH12F2
​Perfluoroundecanoic acid​PFUnA2058-94-8​C10F21COOH10F2​
​Perfluorodecanoic acid​PFDA335-76-2​​C9F19COOH
​Perfluorododecanoic acid ​PFDoA​307-55-1​C11F23COOH
​Perfluorononanoic acid​PFNA​375-95-1C8F17COOH​
​Perfluorooctanoic acid ​PFOA​335-67-1C7F15COOH​
​Perfluoroheptanoic acid PFHpA
​Perfluorohexanoic acid​PFHxA​307-24-4​C5F11COOH
​Perfluorooctanesulfonic acid​PFOS​1763-23-1​C8F17SO3H
​Perfluorohexanesulfonic acid​PFHxS​355-46-4​C6F13SO3H
​Perfluorobutanesulfonic acid​PFBS375-73-5​C4F9SO3H​
​N-ethyl perfluorooctanesulfonamidoacetic acid ​NEtFOSAA​2991-50-6C10H6F17NO2S​
​N-methyl perfluorooctanesulfonamidoacetic acid ​NMeFOSAA​2355-31-9C11H6F17NO4S​
​2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid​HFPO-DA (GenX acid)
​4,8-dioxa-3h-perfluorononanoic acid​DONA (ADONA acid)
​ ​ ​ ​F-53B
​11-chloroeicosafluoro-3-oxaundecane-1-sulfonic acid​11Cl-PF3OUdS​763051-92-9d​C10HF20ClSO4
​9-chlorohexadecafluoro-3-oxanone-1-sulfonic acid ​9Cl-PF3ONS​756426-58-1e​C8HF16ClSO4

a = Some PFAS are commercially available as ammonium, sodium and potassium salts. This method measures all forms of the analytes as anions while the counterion is inconsequential. Analytes may be purchased as acids or as any of the corresponding salts.
b = HFPO-DA is one component of the GenX processing aid technology
c = ADONA is available as the sodium salt (no CASRN) and the ammonium salt (CASRN is 958445-448)
d = 11Cl-PF3OUdS is available in salt form (e.g. CASRN of potassium salt is 83329-89-9)
e = 9Cl-PF3ONS analyte is available in salt form (e.g. CASRN of potassium salt is 73606-19-6)

Illinois EPA Sample Collection Dissemination of Results

Illinois EPA representatives will collect samples from the entry point of the CWS distribution system for analysis. Illinois EPA will be following a strict chain-of-custody protocol and will be using the same laboratory for all sample analysis to ensure adherence to U.S. EPA Method 537.1. The laboratory will provide analytical results to the Illinois EPA within 30 days of sample receipt unless the Illinois EPA has requested an expedited turnaround time of either 14 days, 7 days, or an emergency response time of 3 days. Following sample validation and review by Illinois EPA, Illinois EPA will provide analytical results to the CWS. The analytical results will also be made available on the Illinois EPA’s Drinking Water Watch system.  In addition to making results available on Drinking Water Watch, Illinois EPA will post the data and track the investigation effort through the PFAS Investigation Network Interactive Dashboard and Map.

CWS Owner and Operator Sampling/PFAS Analysis

The owner/operators (o/o) conducting their own sampling for PFAS should use the Sample Collection SOP in Appendix F of the QAPP. In addition, CWS o/o should use a lab accredited by the National Environmental Laboratory Accreditation Conference (NELAC) to analyze for PFAS using U.S. EPA Method 537.1. NELAC has an online database that can be used to search for labs to analyze PFAS in drinking water.

Source Water Assessment

Now is a good time for CWS o/o to review and ensure their contingency plans are up to date and to review the Source Water Assessment and Protection (SWAP) Fact Sheet. The SWAP Fact Sheet that Illinois EPA developed includes an inventory of potential contamination sources and a determination of the susceptibility of the source water to contamination, but the CWS may need to update its SWAP Fact Sheet with current information. 

Response to PFAS present in CWS entry points

The Illinois EPA PFAS health-based guidance levels are provided in the table below. The levels are presented in nanograms per liter (ng/L), equal to parts per trillion (ppt). For reference: 1 milligram per liter (mg/L) or part per million (ppm) = 1,000 micrograms per liter (µg/L) or parts per billion (ppb) = 1,000,000 nanograms per liter (ng/L) or parts per trillion (ppt).

PFAS Analyte
AcronymHealth-Based Guidance Level 
Minimum Reporting Level (ng/L)
​Perfluorobutanesulfonic acid​PFBS​2,100
​Perfluorohexanesulfonic acid​PFHxS​140
​Perfluorononanoic acid​PFNA​21
Perfluorooctanesulfonic acid
​​Perfluorooctanoic acid
​Perfluorohexanoic acid
​Hexafluoropropylene oxide dimer acid

Illinois EPA will notify the CWS that an elevated result is likely, and Illinois EPA will collect confirmation samples. The CWS should prepare to inform consumers of these sample results through direct mailing, distribution of notices directly to customers, posting on the CWS website or other means. During confirmation sampling, the Illinois EPA will provide information to the CWS on treatment and source water options to assist the CWS as they address the presence of PFAS in finished water.  If PFAS are identified in finished water, the Illinois EPA will require more frequent monitoring for PFAS analytes and may also include other system specific efforts to eliminate or reduce the presence of PFAS in finished drinking water.

CWS Treatment

The owners/operators of CWS can obtain technical information on the removal of PFOA, PFOS, and other PFAS on the U.S. EPA website.

CWS Permits

A change in source or treatment will require the CWS to obtain construction and operating permits from the Illinois EPA. Pilot studies may be required to determine design parameters for treatment units for PFAS removal. Parameters such as loading rates, contact times, media selection, media life, maintenance, monitoring constituents and frequencies, and disposal considerations have to be justified to obtain a construction permit. Corrosion control studies may be required. Information on treatment considerations can be found on the U.S. EPA PFAS website.

PFAS Investigation Network Interactive Dashboard and Map