A comparative review of entrainment survival studies at power plants in estuarine environments

Steam-electric power plants drawing cooling water from surface waters entrain a variety of plankton and weak-swimming nekton. These small organisms pass through the intake screens and are carried along with the cooling water through the plant and are subjected to thermal, physical, and chemical (biocide) stresses. In once-through cooling systems, entrained organisms are returned to the source water body, where they are subjected to rapidly decreasing temperatures as cooling waters are mixed into receiving waters. With 4316(b) of the Clean Water Act as the impetus, studies were conducted at many power plants to quantify the number of entrained organisms. Early studies focused on simple abundance, and assumed total mortality. By the late 1970s and early 1980s, advances in sampling technology demonstrated that many entrained organisms survived. Continuing refinement of sampling techniques revealed impressive survival statistics for many species (>90% in some cases), with concomitant reductions in perceived impacts. This paper reviews state-of-the-art sampling methods and results of field entrainment studies at seven power plants. This review demonstrates that high entrainment survival of a variety of aquatic organisms does, in fact, occur and specifies the plant-operating and environmental conditions under which high survival occurs.