California's State Water Resources Control Board has followed
the EPA's lead in deeming underground Diesel Exhaust Fluid tanks as
non-hazardous.
A statement from the body said: "The State Water Body has
determined that DEF, with an approximate urea solution of 30
percent, is not a hazardous substance as defined in Section 25281
of the Health and Safety Code and, accordingly, USTs [underground
storage tanks] storing DEF are not regulated under Chapter 6.7 of
the Health and Safety Code."