FL S1302

Defines "background concentration" as naturally occurring contaminants or those from anthropogenic impacts unrelated to site discharge, and "long-term natural attenuation" as natural attenuation approved by the Department of Environmental Protection for more than 5 years.

Requires DEP to include protocols for long-term natural attenuation in cleanup rules where site conditions warrant, and expands consideration of contaminant effects to include interactive, synergistic, and antagonistic effects rather than just additive effects.

Modifies surface water exposure standards to allow cleanup target levels based on groundwater standards if demonstrated that contaminants do not cause or contribute to surface water quality exceedances, with compliance measured in groundwater immediately adjacent to surface water.

Permits alternative cleanup target levels without requiring institutional controls if specific conditions are met, including nuisance-only exceedances, state water quality standard compliance, property boundary compliance, demonstrated non-migration, offsite water supply access, and property owner acceptance.

Authorizes use of relevant data and probabilistic risk assessment modeling when assessing cleanup target levels, and encourages use of natural attenuation monitoring including long-term natural attenuation after source removal completion.