Full contaminant data, sample history, and sourcing for Nassau County. For readers who want to go beyond the summary.
Contaminant Data — All Analytes
250 well testing events on record, covering
23 analytes.
Data spans 1940 to 2025.
Contaminant
Samples
Years
Detection Rate
Distribution LowModHigh
vs. Limit
vs. FL Avg
Iron
127
1959–2024
98%
5% of limit
↓ 98% below
Manganese
122
2005–2024
99%
2% of limit
↓ 93% below
Chloride
241
1940–2024
100%
10% of limit
↓ 80% below
Sulfate
182
1940–2024
100%
48% of limit
↑ 82% above
Arsenic
122
2005–2024
97%
5% of limit
↓ 62% below
Lead
122
2005–2024
97%
0% of limit
↓ 89% below
PFNA
municipal
16
2024–2025
0%
—
—
PFOA
municipal
16
2024–2025
0%
—
—
Fluoride
61
1959–2024
100%
16% of limit
↑ 122% above
HFPO-DA (GenX)
municipal
16
2024–2025
0%
—
—
Nitrite
4
2005–2015
0%
—
—
PFOS
municipal
16
2024–2025
0%
—
—
Nitrate
6
1965–2015
33%
1% of limit
↓ 79% below
PFHxS
municipal
16
2024–2025
0%
—
—
Radon
2
2015
100%
5% of limit
↓ 82% below
Uranium
4
2005–2015
0%
—
—
PFBS
municipal
16
2024–2025
0%
—
—
Hardness
70
1940–2015
100%
—
~ typical
Total Coliform
11
2005–2024
80%
—
~ typical
Sodium
167
1965–2024
100%
—
↓ 72% below
pH
168
1965–2024
100%
—
~ typical
E. coli
6
2005–2024
70%
—
~ typical
Fecal Coliform
5
2017–2020
100%
—
~ typical
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 FL.
Compare your result with Nassau County
Of the 122 arsenic tests on record for Nassau County (2005–2024),
3% found none, and half were below 0.5 µg/L.
Of the 241 chloride tests on record for Nassau County (1940–2024),
0% found none, and half were below 25 mg/L.
Of the 61 fluoride tests on record for Nassau County (1959–2024),
0% found none, and half were below 630 µg/L.
Of the 127 iron tests on record for Nassau County (1959–2024),
2% found none, and half were below 13.1 µg/L.
Of the 122 lead tests on record for Nassau County (2005–2024),
3% found none, and half were below 50 ng/L.
Of the 122 manganese tests on record for Nassau County (2005–2024),
1% found none, and half were below 0.878 µg/L.
Of the 182 sulfate tests on record for Nassau County (1940–2024),
0% found none, and half were below 120 mg/L.
Data Coverage & Gaps
Well-sampled analytes (15+ samples)
Iron 127 samples
Manganese 122 samples
Chloride 241 samples
Sulfate 182 samples
Arsenic 122 samples
Lead 122 samples
Fluoride 61 samples
Hardness 70 samples
Sodium 167 samples
pH 168 samples
Limited data (<15 samples) — interpret with caution
Nitrite 4 samples
Nitrate 6 samples
Radon 2 samples
Uranium 4 samples
Total Coliform 11 samples
E. coli 6 samples
Fecal Coliform 5 samples
No private-well PFAS data for Nassau County
We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Nassau County.
PFAS testing for private wells requires a dedicated lab panel (~$300–$500). If you are near a military base, airport, or industrial site, consider testing proactively. Learn more about PFAS →
Public vs. Private Water in Nassau County
53Active public water systems
65,831Residents on public water
40%Households on private wells
Public water systems in Nassau 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 Nassau 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 Nassau 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 Nassau County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Nassau 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 Nassau County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Nassau 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 FL with at least one sample for that analyte.