The proposed changes to Chapter 62-780, F.A.C., clarify specific rules pertaining to derivation of alternative cleanup target levels and the use of probabilistic risk assessments. The first proposed revision to rule 62-780.650, F.A.C., is the addition of a list of sources of information that can be used as references for the latest science with regard to toxicity or exposure factors. This expanded list of references will enable the use of the most current information in calculating alternative cleanup target levels and in making risk management decisions. A second proposed revision to rule 62-780.650, F.A.C., provides clarification to an existing rule provision regarding the use of probabilistic risk assessments (PRAs). The proposed language clearly identifies the appropriate components of a PRA and the level and detail of supporting information. A third proposed revision is to rule 62-780.680, F.A.C., to provide for risk-based site closure without institutional or engineering controls upon demonstration that such controls are not necessary based upon scientific studies or reports relating to a contaminant’s toxicity or carcinogenicity or based upon non-site-specific exposure factors. Previously, the rule required institutional controls in all cases where contamination above the default cleanup target levels was being left on site. This revised provision provides regulatory relief from that requirement. A fourth, technical amendment to rule 62-780.100 clarifies that the Referenced Guidelines in the Chapter are for informational purposes only and are not enforceable. One of the referenced guidelines, the Institutional Controls Procedures Guidance, has been updated. OTHER RULES INCORPORATING THIS RULE: 62-730.210, 62-730.225, 62-701.510, 62-777.150, 62-777.170, 62-780.150, 62-780.200, 62-780.210, 62-780.220, 62-780.450, 62-780.500, 62-780.550, 62-780.560, 62-780.610, 62-780.690, 62-780.700, 62-780.750 and 62-780.900, F.A.C. EFFECT ON THOSE OTHER RULES: The amendments to 62-780.100, .600, .650 and .680, F.A.C., will not have any effect on those rules cited above.