This environmental assessment consists of an evaluation of the ecological and indirect human health impacts for the discharge of cuttings contaminated with synthetic-based drilling fluids (SBFs) with respect to discharges of water. In addition, this document describes the environmental characteristics of SBF drilling wastes (e.g., toxicity, bioaccumulation, biodegradation), the types of anticipated impacts, and the pollutant modeling results for water column concentrations, pore water concentrations, and human health effects via consumption of affected seafood. The geographic areas considered under this analysis are those where EPA knows SBFs are currently used and those where EPA projects SBFs will be used as a result of the SBF Effluent Guidelines. This includes the Gulf of Mexico and Cook Inlet, Alaska. EPA considered Offshore California but industry currently projects that even if SBF controlled discharges are allowed under effluent guidelines, operators would not discharge SBF-cuttings. Thus, EPA projects that pollutant loadings will change in the Gulf of Mexico and may change in Cook Inlet, Alaska as a result of the final rule. It is only these two regions that are included in the various environmental impact analysis of this environmental assessment.