Sources

Every threshold on this site traces to a specific published federal source. Nothing here is estimated.

Thresholds

• Maximum Contaminant Levels (MCLs): EPA National Primary Drinking Water Regulations, 40 CFR Part 141.
• Lead and Copper Rule action levels: EPA National Primary Drinking Water Regulations, 40 CFR Part 141 Subpart I.
• Secondary Standards: EPA National Secondary Drinking Water Regulations, 40 CFR Part 143. Non-enforceable, taste and odor based.
• Health Advisories: published EPA Health Advisory and Reference levels, used where no enforceable MCL exists (manganese, radon).

Groundwater context

State-level notes on naturally occurring contaminants (arsenic, radon, uranium) reference public findings from the USGS National Water-Quality Assessment program and USGS national predictive-mapping research on private-well water quality. These stay deliberately qualitative. No specific percentage is published here for any state, because actual risk depends on the aquifer a well draws from, not just the state.

The matching engine

Browser-based PDF text extraction (pdf.js), with on-device OCR fallback (Tesseract.js) for scanned reports. Each line is matched against a maintained alias table of lab-report label variants, then compared numerically against the tables above. No large language model, embedding model, or third-party AI service touches the analysis.

Corrections

Found an outdated threshold, or a lab report format we don't recognize? Tell us. Corrections to published federal figures are the fastest thing we fix.