By decade reported
A reporting date is the date a leak was found, not the date it began. Everything about the shape of this file follows from that.
| Reported in | LPST cases | Share |
|---|---|---|
| 1970s | 3 | 0.0% |
| 1980s | 3,615 | 12.1% |
| 1990s | 17,926 | 60.1% |
| 2000s | 3,061 | 10.3% |
| 2010s | 2,603 | 8.7% |
| 2020s | 1,266 | 4.2% |
Why the 1990s
Leaks are found when tanks are dug up, tested or replaced. The federal deadline to remove or upgrade underground tanks fell in the 1990s, which meant hundreds of thousands of them came out of the ground across the country in a few years — and each excavation was an opportunity to discover a leak that had been there for a decade.
So the peak measures detection, not deterioration. Reading it as « the 1990s were bad » gets the causation exactly backwards: the 1990s were when we looked.
The same logic explains the tail. Fewer cases now does not mean fewer tanks — 43,173 are in use today — it means modern tanks are double-walled and monitored, so failures are caught before they become reportable releases.