Almost all older power plants use once-through systems which take water from a river, lake, ocean, etc., for cooling and then discharge the heated fluids back into the same body of water. Such once-through systems have significant impacts on the local aquatic environments through the entrainment and entrapment of many millions of fish and fish larvae and through the heated water discharged at the end of the cooling cycle.

Closed-cycle cooling systems use much less water than once-through systems. In such closed-cycle systems, the cooling water is pumped through the plant’s condenser and then through cooling towers. Closed-cycle systems used 95-98 percent less water than once-through systems.

New power plants generally are required to have closed-cycle cooling systems, but many older plants still used once-through systems. When these plants’ water permits are being renewed, however, the issue arises of whether the plant’s cooling system should be converted from a once-through to a closed system.

	Evaluation of the reasonableness of the estimated cost of making conversions to closed-cycle systems and the estimated performance and costs penalties associated with operating closed-cycle cooling systems.
	Quantification of the impact of converting to closed-cycle cooling systems on the expected profits of the plant’s owner
	Analysis of the impact of proposed cooling system conversions on electric system reliability