Data & Methodology — Grand Isle County

Full contaminant data, sample history, and sourcing for Grand Isle County. For readers who want to go beyond the summary.

Contaminant Data — All Analytes

1 well testing events on record, covering 12 analytes. Data spans 1990 to 2024.

Contaminant Samples Years Detection Rate Distribution LowModHigh vs. Limit vs. VT Avg
Iron 125 — 100%
17% of limit ↓ 92% below
Manganese 143 — 100%
10% of limit ↓ 98% below
Chloride 330 — 100%
15% of limit ↑ 71% above
Lead 457 — 100%
27% of limit ↓ 62% below
Nitrate 445 — 100%
2% of limit ↓ 24% below
Uranium 339 — 31%
3% of limit ↓ 59% below
Fluoride 377 — 100%
4% of limit ↑ 44% above
Arsenic 349 — 18%
10% of limit ↓ 81% below
Nitrite 443 — 100%
0% of limit ↓ 80% below
Sodium 133 — 100%
— ↑ 867% above
pH 145 — 100%
— ~ typical
Hardness 84 — 100%
— ↑ 255% above

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 VT.

Compare your result with Grand Isle County

Of the 349 arsenic tests on record for Grand Isle County, 82% found none.

Of the 330 chloride tests on record for Grand Isle County, 0% found none, and half were below 37 mg/L.

Of the 377 fluoride tests on record for Grand Isle County, 0% found none, and half were below 180 µg/L.

Of the 125 iron tests on record for Grand Isle County, 0% found none, and half were below 50 µg/L.

Of the 457 lead tests on record for Grand Isle County, 0% found none, and half were below 4 µg/L.

Of the 143 manganese tests on record for Grand Isle County, 0% found none, and half were below 5 µg/L.

Of the 445 nitrate tests on record for Grand Isle County, 0% found none, and half were below 250 µg/L.

Of the 339 uranium tests on record for Grand Isle County, 69% found none.

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Data Coverage & Gaps

Well-sampled analytes (15+ samples)

  • Iron 125 samples
  • Manganese 143 samples
  • Chloride 330 samples
  • Lead 457 samples
  • Nitrate 445 samples
  • Uranium 339 samples
  • Fluoride 377 samples
  • Arsenic 349 samples
  • Nitrite 443 samples
  • Sodium 133 samples
  • pH 145 samples
  • Hardness 84 samples

No private-well PFAS data for Grand Isle County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Grand Isle 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 Grand Isle County

27 Active public water systems
11,967 Residents on public water
34% Households on private wells

Public water systems in Grand Isle 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 Grand Isle 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.

Contaminant Associated Condition Grand Isle County Prevalence VT Average Source Year
Nitrate Cancer prevalence 8.1% 7.0% 2020
Lead Heart disease rate 6.9% 6.3% 2020
Uranium Kidney disease rate 2.9% 2.8% 2020

Source: CDC PLACES county-level estimates. Raw data: Download Grand Isle County CDC PLACES data →

Data Sources

This report aggregates data from the following public databases:

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 VT with at least one sample for that analyte.

Last updated: 2026-07-31

Full methodology →