What is a cancer-risk threshold—and who gets to set it?

Somewhere in the paperwork for the Esmeralda project there is a single number that decides how clean is clean enough before people live on the old mill site. It looks like a typo—one in a million versus one in a hundred thousand. It is not a typo. This page explains what the number means, who chooses it, and why the difference between those two versions is the whole argument.

First. What the number actually counts

A cancer-risk threshold is a ceiling on added lifetime risk. "One in a million" (written 10⁻⁶) means: if a million people each lived a full lifetime under the site's leftover contamination, the cleanup is built so that at most one extra cancer would be statistically expected on top of all the cancers that happen anyway. It is not a prediction of anyone's fate. It is a deliberately cautious budget.

The slider below turns that budget into people. Drag it, or tap the two markers, and watch the crowd change size. Each dot is a thousand people; the amber dot is the crowd that contains the one expected case.

Second. Who actually sets it

No one in the room invents the strict number. It arrives as a default—the starting point written into federal and state cleanup guidance. From there it passes through a short chain of hands: a consultant proposes, the public can object, the City adopts, the water board signs off on the technical study. The number that survives depends on which of those hands actually move.

Tap each actor below to open it. Then flip between the two real episodes—2009, when the strict number won, and the 2025 plan, which proposes the looser one. Watch what happens to step 3.

Third. Why "addendum" versus "new EIR" is the whole game

Step 3—the public comment period—only exists in a full environmental review. An addendum is the quiet path: not circulated, no comment period, no written replies required. A new EIR reopens that door. In 2009 a single comment moved the number from 1-in-100,000 to 1-in-1,000,000, on the record. On the addendum path, that comment never gets asked for.

So when the plan proposes the looser number through an addendum, it isn't sneaking past the science. It's routing around the one step where a neighbor's objection has to be answered in writing. Whether the City requires a new EIR is, in plain terms, the decision about whether you are in the chain at all.