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PFAS Statewide Investigation Network: Community Water Supply Sampling

In 2021, the Illinois Environmental Protection Agency (Illinois EPA) completed a statewide investigation into the prevalence and occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in finished water at 1,428 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 were 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 contacted the CWS Responsible Operator in Charge to schedule a time to collect the samples for PFAS analysis. There was no cost to CWS for this sampling.

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

PFAS Analyte Namea
Acronym Chemical Abstract Services Registry Number (CASRN)
​Perfluorotetradecanoic acid ​PFTA ​376-06-7 ​C13F27COOH
​Perfluorotridecanoic acid ​PFTrDA 72629-94-8​ ​C12F25COOH12F2
​Perfluoroundecanoic acid ​PFUnA 2058-94-8​ C10F21COOH10F2​
​Perfluorodecanoic acid ​PFDA 335-76-2​ ​C9F19COOH
​Perfluorododecanoic acid ​PFDoA ​307-55-1 ​C11F23COOH
​Perfluorononanoic acid ​PFNA ​375-95-1 C8F17COOH​
​Perfluorooctanoic acid ​PFOA ​335-67-1 C7F15COOH​
​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 ​PFBS 375-73-5​ C4F9SO3H​
​N-ethyl perfluorooctanesulfonamidoacetic acid ​NEtFOSAA ​2991-50-6 C10H6F17NO2S​
​N-methyl perfluorooctanesulfonamidoacetic acid ​NMeFOSAA ​2355-31-9 C11H6F17NO4S​
​2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid ​HFPO-DA (GenX acid)
​13252-13-6b ​C6HF11O3
​4,8-dioxa-3h-perfluorononanoic acid ​DONA (ADONA acid)
​919005-14-4c C10H11N4NaO5S​
​ ​ ​ ​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 collected samples from the entry point of the CWS distribution system for analysis. Illinois EPA followed a strict chain-of-custody protocol and used the same laboratory for all sample analysis to ensure adherence to U.S. EPA Method 537.1. Following sample validation and review by Illinois EPA, Illinois EPA provided analytical results to the CWS. The analytical results are also available on the Illinois EPA’s Drinking Water Watch system.  In addition to making results available on Drinking Water Watch, Illinois EPA posted the data and tracked the investigation effort through the PFAS Investigation Network Interactive Dashboard and Map.

Overall, preliminary results show that 1,275 entry points sampled did not have detections of any of the 18 PFAS chemicals analyzed. Illinois EPA identified 70 entry points to CWS distribution systems where one or more PFAS chemicals was detected in concentrations above health-based guidance levels, and 82 entry points to CWS distribution systems where one or more PFAS chemicals was detected in concentrations above the minimum reporting limit but below the health-based guidance levels.* Some communities in Illinois purchase water from other CWS sources and are reflected under the providing community on the PFAS Sampling Network Interactive Dashboard and Map. The minimum reporting limit is the lowest concentration of a substance that the laboratory can reliably quantify using a given analytical method. Using U.S. EPA Method 537.1, the minimum reporting limit for each of 18 PFAS chemicals analyzed in the statewide sampling investigation is 2 nanograms per liter (ng/L) or parts per trillion (ppt). All data collected during the Statewide Sampling Investigation has been submitted to the United States Geological Survey for further review.

*One entry point sampled during the investigation had an initial detection above the minimum reporting limit but below the health-based guidance level. This entry point was taken offline by the community before a confirmation sample was collected and is only reflected in the Overall Network count.

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
Acronym Health-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

*The Health-Based Guidance Level for HFPO-DA is updated to 21 ng/L based on U.S. EPA Office of Water's issuance of a final oral reference dose in October 2021. The Illinois EPA calculated the prior Health-Based Guidance Level using U.S. EPA Office of Water's draft oral reference dose. 

Illinois EPA notified the CWS of any elevated results, and Illinois EPA collected confirmation samples. The CWS then informed 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 provided 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 were identified in finished water, the Illinois EPA is requiring 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

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