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States → EPA Region 9 — Tribal Water Systems

Community Water System · PWS 090605047

Colusa Southern System

Colusa, EPA Region 9 — Tribal Water Systems 95932-4018 - drinking water served from groundwater sources to 3,474 people, tracked in EPA SDWIS and UCMR5.

3,474
People served
395
EPA violations
0
Health-based
No PFAS
UCMR5 result

The verdict

EPA records 395 drinking-water violations at Colusa Southern System.

395
Total EPA violations on record
0%
Health-based (MCL / treatment failure)
3,474
People served by this system
0
PFAS compounds detected (UCMR5)

Water Quality Snapshot: Colusa Southern System

Colusa Southern System is a native american-owned community water system that delivers drinking water to 3,474 residents in Colusa, EPA Region 9 — Tribal Water Systems through 31 service connections. Its water is drawn from groundwater sources. EPA's Safe Drinking Water Information System records 395 total violations for this system , of which 0 (0%) are health-based, meaning a contaminant exceeded an EPA Maximum Contaminant Level or a required treatment technique failed. A further 142 monitoring and reporting violations are on file. The most recent violation on record dates to 2005.

The most frequently cited contaminant at this system is Nitrate, recorded in 6 violations (MR). This system was sampled under EPA's UCMR5 PFAS monitoring program and no PFAS compounds were detected above the minimum reporting level.

EPA Region 9 — Tribal Water Systems has thousands of regulated public water systems tracked by EPA under the Safe Drinking Water Act.

All figures above are sourced directly from EPA SDWIS and UCMR5 public data releases and are updated as EPA publishes new reporting cycles.

Population Served
3,474
Total Violations
395
Health-Based Violations
0
Water Source
Groundwater

System Details

System Type
Community
Owner Type
Native American
Connections
31
School/Daycare
No
MCL Violations
0
Monitoring Violations
142
Treatment Tech Violations
0

Violation History

Contaminant violations recorded by EPA.

Contaminant Category Count Latest
Nitrate MR 6 2004
Consumer Confidence Rule Other 5 2005
Toxaphene MR 3 2004
Methoxychlor MR 3 2004
Carbofuran MR 3 2004
LASSO MR 3 2004
Heptachlor MR 3 2004
Heptachlor epoxide MR 3 2004
2,4-D MR 3 2004
2,4,5-TP MR 3 2004
Pentachlorophenol MR 3 2004
1,2-DIBROMO-3-CHLOROPROPANE MR 3 2004
Total Polychlorinated Biphenyls (PCB) MR 3 2004
ETHYLENE DIBROMIDE MR 3 2004
Chlordane MR 3 2004
BHC-GAMMA MR 3 2004
Atrazine MR 3 2004
Dalapon MR 2 2004
Diquat MR 2 2004
Endothall MR 2 2004
Glyphosate MR 2 2004
Di(2-ethylhexyl) adipate MR 2 2004
OXAMYL MR 2 2004
Simazine MR 2 2004
Dinoseb MR 2 2004
Hexachlorocyclopentadiene MR 2 2004
2,3,7,8-TCDD MR 2 2004
HEXACHLOROBENZENE MR 2 2004
Benzo(a)pyrene MR 2 2004
1,2,4-Trichlorobenzene MR 2 2004

PFAS Testing Results (UCMR5)

Results from EPA's Fifth Unregulated Contaminant Monitoring Rule. 0 of 116 samples detected PFAS.

Contaminant Date Result MRL Status
11Cl-PF3OUdS 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
PFHxA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFMBA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFTA 6/5/2023 <8.00 ppt 8.00 ppt Not Detected
PFTrDA 6/5/2023 <7.00 ppt 7.00 ppt Not Detected
NEtFOSAA 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
NMeFOSAA 6/5/2023 <6.00 ppt 6.00 ppt Not Detected
PFBS 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFHpA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFHxS 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFNA 6/5/2023 <4.00 ppt 4.00 ppt Not Detected
PFOS 6/5/2023 <4.00 ppt 4.00 ppt Not Detected
PFOA 6/5/2023 <4.00 ppt 4.00 ppt Not Detected
ADONA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFDoA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFUnA 6/5/2023 <2.00 ppt 2.00 ppt Not Detected
9Cl-PF3ONS 6/5/2023 <2.00 ppt 2.00 ppt Not Detected
HFPO-DA 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
PFBA 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
6:2 FTS 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
4:2 FTS 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
8:2 FTS 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
PFPeA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFEESA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
NFDHA 6/5/2023 <20.00 ppt 20.00 ppt Not Detected
PFPeS 6/5/2023 <4.00 ppt 4.00 ppt Not Detected
PFHpS 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFDA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFMPA 6/5/2023 <4.00 ppt 4.00 ppt Not Detected
NMeFOSAA 6/5/2023 <6.00 ppt 6.00 ppt Not Detected
NEtFOSAA 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
PFTrDA 6/5/2023 <7.00 ppt 7.00 ppt Not Detected
PFTA 6/5/2023 <8.00 ppt 8.00 ppt Not Detected
PFHpS 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFPeS 6/5/2023 <4.00 ppt 4.00 ppt Not Detected
NFDHA 6/5/2023 <20.00 ppt 20.00 ppt Not Detected
PFEESA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFMBA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFPeA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
PFMPA 6/5/2023 <4.00 ppt 4.00 ppt Not Detected
8:2 FTS 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
PFHxS 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
6:2 FTS 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
PFBA 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
HFPO-DA 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
ADONA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected
9Cl-PF3ONS 6/5/2023 <2.00 ppt 2.00 ppt Not Detected
11Cl-PF3OUdS 6/5/2023 <5.00 ppt 5.00 ppt Not Detected
PFUnA 6/5/2023 <2.00 ppt 2.00 ppt Not Detected
PFHxA 6/5/2023 <3.00 ppt 3.00 ppt Not Detected

Verify This Water System

The figures above are aggregated from EPA's public databases. To verify the underlying records, or to file a complaint, request a Consumer Confidence Report, or check current monitoring status, go directly to the federal and state regulators that enforce the Safe Drinking Water Act for Colusa Southern System.

Federal Source of Truth

EPA SDWIS, Federal Reports

EPA's Safe Drinking Water Information System (SDWIS) holds the federal compliance record for every regulated public water system. Open the system-level report by PWS ID:

View PWS ID 090605047 on SDWIS

Source: EPA SDWIS Federal Reports Search

State Regulator

EPA Region 9 — Tribal Water Systems Drinking Water Authority

EPA Region 9 — Tribal Water Systems's primacy agency administers the Safe Drinking Water Act locally. Search EPA SDWIS for the current state contact, or use the state's public health or environment department portal.

Find 09 regulator via EPA SDWIS

Violation Timeline

Each row links to the EPA SDWIS public record for verification. Cross-reference the contaminant code on EPA's federal report to see violation dates, return-to-compliance status, and enforcement actions.

Year (latest) Contaminant Category Count EPA Record
2005 Consumer Confidence Rule Other 5 SDWIS / 090605047 / 7000
2004 Nitrate MR 6 SDWIS / 090605047 / 1040
2004 Toxaphene MR 3 SDWIS / 090605047 / 2020
2004 Methoxychlor MR 3 SDWIS / 090605047 / 2015
2004 Carbofuran MR 3 SDWIS / 090605047 / 2046
2004 LASSO MR 3 SDWIS / 090605047 / 2051
2004 Heptachlor MR 3 SDWIS / 090605047 / 2065
2004 Heptachlor epoxide MR 3 SDWIS / 090605047 / 2067
2004 2,4-D MR 3 SDWIS / 090605047 / 2105
2004 2,4,5-TP MR 3 SDWIS / 090605047 / 2110
2004 Pentachlorophenol MR 3 SDWIS / 090605047 / 2326
2004 1,2-DIBROMO-3-CHLOROPROPANE MR 3 SDWIS / 090605047 / 2931
2004 Total Polychlorinated Biphenyls (PCB) MR 3 SDWIS / 090605047 / 2383
2004 ETHYLENE DIBROMIDE MR 3 SDWIS / 090605047 / 2946
2004 Chlordane MR 3 SDWIS / 090605047 / 2959

How Colusa Southern System Compares

Cross-reference this system's record against state averages and the federal MCL framework for context.

Metric Colusa Southern System EPA Region 9 — Tribal Water Systems avg Federal benchmark
Total violations 395 - SDWA compliance, any non-zero count is a recorded breach
Health-based violations 0 - Indicates a contaminant exceeded a federal MCL
PFAS detection None - EPA final rule (2024): PFOA/PFOS MCL = 4.0 ppt
Population served 3,474 - Sizing context for compliance burden

Sources: EPA SDWIS and EPA National Primary Drinking Water Regulations (40 CFR Part 141). State averages computed across all regulated public water systems in EPA Region 9 — Tribal Water Systems.

Federal MCL reference, Safe Drinking Water Act thresholds ▼
Contaminant Federal MCL / Action Level Note
Lead 0 mg/L (Action Level: 0.015 mg/L) Lead and Copper Rule treatment technique
Arsenic 0.010 mg/L (10 ppb) Health-based MCL since 2006
Total Coliform Treatment technique (RTCR) Indicator organism, monitoring trigger
PFOA / PFOS (PFAS) 4.0 ppt each (final 2024 rule) Compliance deadline 2029 (EPA proposed extending to 2031, not yet final as of May 2026)
Nitrate (as N) 10 mg/L Acute health risk for infants

Frequently Asked Questions

Is Colusa Southern System water safe to drink? ▼
Colusa Southern System (PWS ID: 090605047) has 395 recorded violations in the EPA SDWIS database. No PFAS contamination was detected in UCMR5 testing. This system serves 3,474 people using Groundwater sources.
How many people does Colusa Southern System serve? ▼
Colusa Southern System serves 3,474 people in Colusa, EPA Region 9 — Tribal Water Systems. It is a Native American-owned system using Groundwater water sources with 31 service connections.
What type of violations does Colusa Southern System have? ▼
Colusa Southern System has 395 total violations: 0 health-based violations (MCL exceedances or treatment failures), 142 monitoring/reporting violations, and 0 treatment technique violations. Health-based violations indicate contaminant levels exceeded EPA safe limits.
Has PFAS been detected in Colusa Southern System water? ▼
No. Colusa Southern System was tested for PFAS under the EPA's UCMR5 monitoring program and no PFAS contamination was detected.
What water source does Colusa Southern System use? ▼
Colusa Southern System uses Groundwater as its primary water source. It is classified as a Community Water System (CWS), serving residential populations year-round.
Where does this data come from? ▼
All data comes from the EPA Safe Drinking Water Information System (SDWIS) and the UCMR5 PFAS monitoring program. SDWIS tracks compliance for all public water systems regulated under the Safe Drinking Water Act.
Data Sources: EPA Safe Drinking Water Information System (SDWIS), Q4 2025. PFAS data from EPA UCMR5 monitoring program (2023-2025). This data is provided for informational purposes only.

Read our methodology - how this data is sourced, computed, and verified.

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater Editorial

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This system's figures are rendered directly from EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.