EPA system IL1970450 · Illinois

Joliet: Lithium at or above EPA's 10 ppb health reference level

System ID IL1970450; community water system; Illinois; source: groundwater; serves 160,000 people via 49,000 connections; status: active

In focus160,000people served, EPA registry

Public records. Clearer context.

Joliet is a local-government-owned community water system in Illinois serving about 160,000 people, matched to 11 ZIP codes.

PFAS treatment declared to EPA: None declared (22 of 22 sampling events) · PFAS found before UCMR 5: Yes, at 22 of 22 sampling events

PFAS and lithium: what EPA's national survey found

EPA tested this water for 30 substances and found 1. Lithium reached 54.7 ppb; EPA's health reference level, which is guidance and not a limit, is 10 ppb.

Between February 2025 and August 2025, EPA's UCMR 5 program tested 660 samples from 11 sampling locations for 30 contaminants (29 PFAS plus lithium). 1 were detected above the reporting level in at least one sample. Lithium reached 54.7 ppb in a single sample, at or above the health reference level of 10 ppb, which is non-regulatory.

Sampling-point average: mean of a location's two (ground water) or four (surface water) UCMR 5 results with non-detects counted as zero, EPA's method for comparing UCMR 5 data to the PFAS MCLs. EPA rounds to the reference value's significant digits before deciding whether an average is "greater than" an MCL (PFOA/PFOS averages count as above 4.0 ng/L only from 4.05 ng/L; lithium results count as above the 10 ppb reference only from 15 ppb). This site does not apply that rounding: "at or above" here means the measured value is numerically at or above the reference.

Utility-reported context (UCMR 5 questionnaire, aggregated across sampling events): PFAS previously found at this system: yes at 22 of 22 sampling events; potential PFAS sources nearby: no at 22 of 22 sampling events; PFAS treatment in place: no PFAS treatment at 22 of 22 sampling events.

Lead at customer taps

In the latest completed monitoring period, ending Jun 30, 2026, 9 in 10 sampled homes had lead at or below 6.5 ppb, below the 15 ppb action level that triggers utility action. The action level has been reached in 3 of the 24 periods on record.

In the most recent completed lead monitoring period, ending Jun 30, 2026, the 90th-percentile lead result at customer taps was 6.5 ppb, below the action level of 15 ppb; 3 of the 24 monitoring periods on record reached the action level. The 90th percentile is the value that 9 in 10 sampled homes were at or below. Values are in parts per billion (ppb).

Drinking water violations since Sep 3, 2016

EPA lists 11 violations since Sep 3, 2016. 1 is health-based, meaning a contaminant or treatment rule was not met. The other 10 concern missed monitoring, reporting or public notices.

EPA's SDWIS database lists 11 violations recorded since Sep 3, 2016: 1 health-based (a contaminant above its maximum contaminant level, a disinfectant above its maximum residual level, or a required treatment technique not met), 10 for monitoring or reporting.

Sanitary surveys and site visits

Most recent state inspection: Oct 24, 2025 (reason not recorded); 4 visits since Sep 3, 2021.

What you can do about these results

ZIP codes served

Sources

Data vintage: EPA UCMR 5 occurrence data, samples collected 2023-01-03 – 2026-06-17, final release, August 2026 (file dated Aug 28, 2026); EPA SDWIS via ECHO, 2026Q2 extract (file dated Jul 9, 2026); EPA service-area boundaries v3.0; Census 2020 ZCTAs. Page generated 2026-09-03.

• EPA ECHO detailed facility report
• EPA UCMR 5 Data Finder
• EPA service-area boundary: modeled, 37.4 sq mi