Every Colorado public water system that reported a PFAS detection during EPA UCMR 5 monitoring, how many sit above the 2024 federal limits, and the standard Colorado applies. Concentrations are in nanograms per litre, the same unit as parts per trillion.
This is the United States view of the North American PFAS dataset. The complete dataset, including all 3,452 US systems and 97 Canadian sites, lives on the main PFAS contamination map.
State enforceable standard
These are Colorado groundwater and surface water quality standards, not drinking water MCLs. Colorado has no state drinking water PFAS MCL and defers to the federal rule for public water systems. HB22-1345 phases PFAS out of consumer products, and the Fountain Valley aquifer remains under active remediation.
Compound
Limit (ng/L)
Note
PFOA
70
Groundwater standard
PFOS
70
Groundwater standard
PFHxS
700
Groundwater standard
PFBS
400,000
Groundwater standard
US EPA PFAS National Primary Drinking Water Regulation (2024)
Last reviewed 2026-08-13. Verify against the agency source before making a compliance or remediation decision.
Full Colorado regulatory brief
Ranked by how far the worst single compound sits above its 2024 federal limit. Values are the maximum each system reported during its UCMR 5 monitoring period.
Water system
PWSID
Worst compound
Max ng/L
Times the limit
Snake River Wd
CO0159105
PFOS
22
5.5x
Widefield Wsd
CO0121900
PFOS
15.8
4.0x
Brighton City Of
CO0101025
PFOS
10.6
2.6x
Mountain Village Town Of
CO0157400
PFOS
7.5
1.9x
Thornton City Of
CO0101150
PFOA
7.1
1.8x
Todd Creek Village Md
CO0101157
PFOS
6.8
1.7x
Cherokee Md
CO0121125
PFOA
6.1
1.5x
Stonegate Md
CO0118076
PFOA
5.6
1.4x
Parker Wsd
CO0118040
PFOA
4.8
1.2x
Little Thompson Wd
CO0135477
PFOA
4.8
1.2x
Arapahoe Cnty Wwwa
CO0203002
PFOA
4.6
1.1x
Gunnison City Of
CO0126325
PFOS
4.2
1.1x
Rocky Ford City Of
CO0145600
PFOS
4.1
1.0x
Englewood City Of
CO0103045
PFOA
4
1.0x
Cottonwood Wsd
CO0118020
PFOA
4
1.0x
Silverthorne Town Of
CO0159095
PFHxS
3.7
0.4x
Lamar City Of
CO0150700
PFHxS
3.3
0.3x
Lochbuie Town Of
CO0162486
PFHxS
3
0.3x
South Adams County Wsd
CO0101140
PFPeA
11.4
Below limit
Aurora City Of
CO0103005
PFBA
7.8
Below limit
Open the full map and filter Colorado pins
Every count above is read straight from a published government file. Nothing is modelled, averaged, or estimated. The rules below are the exact rules used to produce the figures for Colorado.
Who is in UCMR 5. All public water systems serving more than 3,300 people, plus a national sample of 800 smaller systems. Private wells and most small systems are not monitored, so they cannot appear here.
Which systems are listed. Only systems whose state field is CO and that reported at least one measured PFAS detection. Systems that monitored and found nothing are not shown, and their absence is not evidence of contamination. That gives 37 systems in Colorado.
Systems that cannot be placed. 87 systems nationally reported a detection but have no serviced ZIP code published by EPA, so they carry no location and are excluded from these counts. National totals on the map page include them.
Which value is used. The highest result a system reported for each compound across its sampling events. Results flagged by EPA as non-detects are excluded, as are the lithium results carried in the same file.
The above a limit count. A system is counted when its maximum result for a compound exceeds the 2024 federal Maximum Contaminant Level: 4 ng/L for PFOA and PFOS, 10 ng/L for PFHxS, PFNA, and HFPO-DA. That is 13 systems in Colorado.
The Hazard Index count. Calculated with EPA's own mixture method for PFHxS, PFNA, HFPO-DA, and PFBS. A system is counted when the index is above 1. That is 2 systems in Colorado.
What monitoring data is not. Exceeding a 2024 limit in this dataset is not a compliance violation. The federal limits carry a 2029 compliance date, which EPA proposed on 18 May 2026 to move to 2031 for PFOA and PFOS in a rule that is not final, and treatment may have been installed since the sample was taken.
If any figure on this page does not match its source file, tell Nelson and it will be corrected or removed.
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