For example, a power plant that needs to build a new intake structure would need a Virginia Water Protection permit because of the discharge of fill material that is used to build the intake. The federal permit that is also a prerequisite is the Section 404 permit from the Army Corps of Engineers for the discharge of fill material. Power plants need varying amounts of water, depending on the size of the plant and the thermo-mechanical processes used to generate electricity and cool the equipment. The power plant may use cooling towers, in which waste heat is dissipated by converting liquid water into water vapor. Power plants that use cooling towers usually have high rates of consumptive use, about 80 percent of the amount of water that is withdrawn.
Water is taken though the power plant one time and is used to take away waste heat.
This process warms up the water but returns almost the same amount to the stream as was withdrawn. With this process, consumptive use rates are low. However, there are two main concerns with once-through cooling. It can heat up the stream that receives the discharge and harm the aquatic life - this would be a violation of the water quality standards for temperature. The second concern is that the fish eggs, fish larvae and small aquatic organisms can be damaged or destroyed if they are caught on the intake screen or drawn into the cooling system.