GroundTruth / methodology
Four EPA datasets, each downloaded in bulk, archived immutably (content-addressed, so every fact traces to the exact federal file), and refreshed on a schedule: Superfund/NPL site list (SEMS), Safe Drinking Water Act systems and violations (SDWA via ECHO), Toxics Release Inventory basic files (latest complete reporting year), and ECHO compliance data (from which we index ONLY facilities carrying a current significant-noncompliance flag).
Great-circle distance from the queried coordinates to each record's published coordinates, in km. Records without coordinates cannot appear in radius results (a stated coverage gap).
Systems are matched by the county/city they report serving. Service-area boundaries are not public data, so this is approximate by construction; the biggest matching system is listed first as the most likely server of an address, and your water bill is authoritative.
Composite scores, rankings, and "is it safe" verdicts. TRI pounds are not toxicity; an enforcement flag is not a conviction; an NPL listing is a cleanup-process fact.