Full contaminant data, sample history, and sourcing for Glenn County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
677 well testing events on record, covering
27 analytes.
Data spans 1955 to 2021.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. CA Avg
Manganese
130
1960–2021
67%
14% of limit
↓ 95% below
Nitrate
421
1957–2021
95%
16% of limit
↓ 31% below
Iron
135
1958–2021
39%
7% of limit
↓ 95% below
Arsenic
125
1960–2021
97%
20% of limit
↓ 49% below
Sulfate
391
1957–2021
100%
7% of limit
↓ 64% below
Chloride
482
1957–2021
100%
6% of limit
↓ 79% below
Lead
81
1960–2021
28%
0% of limit
↓ 100% below
PFNA
municipal
19
2021–2025
0%
—
—
Uranium
66
1997–2021
95%
4% of limit
↓ 28% below
Radon
1
2006
100%
7% of limit
↓ 92% below
PFOS
municipal
19
2021–2025
0%
—
—
Boron
2
2006–2021
100%
9% of limit
↓ 45% below
Chromium (total)
2
2006–2021
0%
—
—
1,2,3-Trichloropropane
3
2006–2021
0%
—
—
HFPO-DA (GenX)
municipal
19
2021–2025
0%
—
—
Fluoride
223
1957–2021
97%
5% of limit
↓ 30% below
Nitrite
73
1997–2021
15%
1% of limit
↓ 51% below
Perchlorate
3
2006–2021
0%
—
—
PFHxS
municipal
19
2021–2025
0%
—
—
PFOA
municipal
19
2021–2025
0%
—
—
Tds
2
2006–2021
100%
—
↓ 45% below
Total Coliform
1
2006–2021
0%
—
—
Hardness
491
1957–2021
100%
—
~ typical
PFBS
municipal
19
2021–2025
0%
—
—
pH
648
1957–2021
100%
—
~ typical
E. coli
1
2006–2021
0%
—
—
Sodium
424
1957–2021
100%
—
↓ 71% below
Distribution shows the share of samples in each concentration band relative to the EPA Maximum Contaminant Level (MCL): Low = below half the MCL, Moderate = between half and the MCL, High = above the MCL. Analytes without an MCL (e.g. sodium, pH) show — in the limit columns. State average is based on county median values across CA.
Compare your result with Glenn County
Of the 125 arsenic tests on record for Glenn County (1960–2021),
3% found none, and half were below 2 µg/L.
Of the 482 chloride tests on record for Glenn County (1957–2021),
0% found none, and half were below 16 mg/L.
Of the 223 fluoride tests on record for Glenn County (1957–2021),
3% found none, and half were below 180 µg/L.
Of the 135 iron tests on record for Glenn County (1958–2021),
61% found none.
Of the 81 lead tests on record for Glenn County (1960–2021),
72% found none.
Of the 130 manganese tests on record for Glenn County (1960–2021),
33% found none, and half were below 0.67 µg/L.
Of the 421 nitrate tests on record for Glenn County (1957–2021),
5% found none, and half were below 1.51 mg/L.
Of the 391 sulfate tests on record for Glenn County (1957–2021),
0% found none, and half were below 18 mg/L.
Of the 66 uranium tests on record for Glenn County (1997–2021),
5% found none, and half were below 1.09 µg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Manganese 130 samples
Nitrate 421 samples
Iron 135 samples
Arsenic 125 samples
Sulfate 391 samples
Chloride 482 samples
Lead 81 samples
PFNA 19 samples
Uranium 66 samples
PFOS 19 samples
HFPO-DA (GenX) 19 samples
Fluoride 223 samples
Nitrite 73 samples
PFHxS 19 samples
PFOA 19 samples
Hardness 491 samples
PFBS 19 samples
pH 648 samples
Sodium 424 samples
Limited data (<15 samples) — interpret with caution
Radon 1 sample
Boron 2 samples
Chromium (total) 2 samples
1,2,3-Trichloropropane 3 samples
Perchlorate 3 samples
Tds 2 samples
Total Coliform 1 sample
E. coli 1 sample
Public vs. Private Water in Glenn County
35Active public water systems
37,146Residents on public water
34%Households on private wells
Public water systems in Glenn County are regulated by the EPA and must test and report contaminant levels. Private well owners are responsible for their own testing — there is no routine monitoring of private wells by any government agency.
CDC Health Outcome Correlations
Where contaminants detected in Glenn County have established associations with specific health outcomes, we cross-reference CDC PLACES county-level prevalence data. This is a contextual signal, not a causal claim.
This report aggregates data from the following public databases:
Water Quality Portal (WQP) — groundwater sample results for Glenn County from EPA, USGS, and state agencies. Browse WQP data →
EPA Safe Drinking Water Information System (SDWIS) — public water system inventory used to estimate the share of residents on private wells. Browse SDWIS →
Census ACS 5-Year Estimates — well and cistern household counts (variable DP04_0074E) used to calculate the private-well percentage for Glenn County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Glenn County, which informs which contaminants are geologically likely. USGS Aquifer Atlas →
EPA UCMR 5 (2023–2025) — PFAS occurrence data from public water systems, used as a proxy indicator for aquifer PFAS exposure. Rows marked "municipal" in the table above come from this source. About UCMR 5 →
EPA Toxics Release Inventory (TRI) — industrial facility chemical releases near Glenn County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Glenn County, used in contamination risk scoring. Superfund site search →
CDC PLACES — county-level health outcome prevalence (kidney disease, cancer, heart disease) correlated with detected contaminants. About CDC PLACES →
Methodology
Raw records are downloaded from the Water Quality Portal and normalized to µg/L (ppb). Records are deduplicated by sample ID and date, and certified outliers are excluded. Analyte names are mapped to EPA canonical forms. Detection rates, distribution bands, and MCL comparisons are computed from the normalized dataset.
Distribution bands use the EPA Maximum Contaminant Level as the threshold: concentrations below 50% of the MCL are classed as Low, between 50% and 100% as Moderate, and above 100% as High. For analytes without an MCL (sodium, hardness, pH), distribution is not computed.
State comparison uses the median of county median values across all counties in CA with at least one sample for that analyte.