HI SB446

Prohibits construction, modification, or expansion of landfill units mauka (inland) of the underground injection control line without establishing a buffer zone of at least one-quarter mile around the landfill, effective July 1, 2025

Bans the use of fly ash, bottom ash, or combined ash from municipal waste combustors for road building, construction, or as alternative daily cover material on landfills

Requires fly ash and bottom ash from municipal waste combustors to be disposed of only in double-lined, licensed municipal solid waste or hazardous waste landfills

Exempts existing properly permitted landfills from the new buffer zone requirements, provided they do not require physical expansion (vertical above ground surface or horizontal) that would need additional permitting

References the November 2021 Red Hill fuel storage facility spill as justification for protecting Hawaii's aquifers, which provide approximately 99% of the state's domestic water supply