Sources
Where the numbers come from.
The report rests on two public, authoritative sources. You can look up either one yourself, and every risk and limit in the report traces back to them.
What's found in private wells
USGS domestic-wells program
The US Geological Survey has sampled private (domestic) wells across the country and published which contaminants exceed human-health benchmarks, organized by principal aquifer and region. It's the best public evidence of what actually turns up in wells like yours, and the basis for which contaminants the report ranks for your area.
usgs.gov · groundwater and domestic well quality
The limits each risk is measured against
EPA National Primary Drinking Water Regulations
The EPA's legally enforceable Maximum Contaminant Levels (MCLs) for contaminants like nitrate, arsenic, lead, and coliform bacteria. These are the thresholds a public water system must meet, and the ones the report holds each contaminant against.
epa.gov/ground-water-and-drinking-water · national primary drinking water regulations
EPA Secondary Standards & health advisories
For contaminants without an enforceable MCL, or aesthetic concerns like hardness and pH, the report uses EPA Secondary Maximum Contaminant Levels and published health advisory levels, clearly labeled as such so you know which kind of limit you're looking at.
epa.gov · secondary drinking water standards and health advisories
Guidance for well owners
EPA and CDC private-well guidance
The EPA and CDC both publish guidance on testing private wells, including recommended baseline tests and how often to retest. The report's "how to get tested" and retesting notes follow this guidance.
epa.gov/privatewells · cdc.gov · private wells
A note on honesty
These sources describe risk across populations of wells, not your individual well. The report is upfront that it is a regional model built from this public data, and that a certified laboratory test is the only way to measure your own water. That's covered in full in the methodology.
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