Water Quality Issues of Electricity Production:
Pollution of Water Bodies

What do we mean by water quality impacts?

Water bodies come in many forms: huge oceans; large and small lakes; and a diversity of rivers and streams. Each of these ecosystems feature a tapestry of waterborne species that are all dependent upon a high degree of water quality. These bodies of water are also essential to human survival and public health. For example, underground aquifers often supply us with drinking water. Waterways are also not only key transportation routes for billions of dollars in global commerce, but they represent popular opportunities for recreation in the form of fishing, boating and water sports. Some particularly pristine spots in or near ocean, lakes and rivers may be candidate for long-term preservation because of their stunning aesthetic values.

The construction and continued operation of power plants, particularly those fueled by fossil or nuclear fuels, are among the human activities that can have the most profound and wide ranging negative impacts on water quality.

How can electricity production impair water quality?

The following procedures all can occur during routine operations and maintenance of power plants and each can significantly impact water quality:

Boiler blowdown: This waste stream results from periodic purging of the impurities that become concentrated in steam boiler systems. These pollutants include metals such as copper, iron and nickel, as well as chemicals added to prevent scaling and corrosion of steam generator components.

Coal pile run-off: This waste stream is created when water comes in contact with coal storage piles maintained on the power plant site. While most piles are kept covered, active piles used to meet the power plants immediate needs are often open to the elements. Metals and other naturally occurring contaminants contained in coal leach out with the rainfall and are deposited in nearby water bodies.

Cooling process wastes: Water used for power plant cooling is chemically altered for purposes of extending the useful life of equipment and to ensure efficient operation. Demineralized regenerants and rinses are chemicals employed to purify waters used as makeup water for the plant's cooling system. Cooling tower blowdown contains chemicals added to prevent biological growth in the towers and to prevent corrosion in condensors.

Boiler cleaning wastes: These wastes derive from the chemical additives intended to remove scale and other byproducts of combustion.

Thermal pollution: Thermal plants create or use steam in the process of creating electricity require water for cooling. This water typically comes from adjacent water bodies or groundwater sources and is discharged back into the water body at significantly higher temperatures. By altering the temperature in the "mixing zone," the discharge of thermal wastewater can both negative and positive effects on aquatic life. On the plus side, the warmer temperature water may create more favorable feeding and breeding conditions for certain species located near the power plant's water source. However, when the power plant is suddenly shut down for routine maintenance or unplanned outage, the resulting wide swing to colder temperatures can be lethal to sensitive fish populations. Hydropower dams can also alter the natural temperature of the water, as discussed above.

What are the impacts of power production on water quality?

Many large central station fossil and nuclear power plants rely upon water for cooling and are therefore located near bodies of water. In some instances, the diversion of rivers creates reservoirs adjacent to power plants for cooling, rinsing and the releases of effluents. A variety of processes associated with fuel handling and ongoing maintenance of large thermal power plants create or concentrate chemical pollutants that are then discharged into nearby water bodies. Even when releases are limited to what is allowed in water use permits, there is still the occasional but inevitable accidental release.

Both of these sources of pollution can be legal and alone can cause significant harm to streams, rivers, lakes, estuaries and groundwater. Water quality can degrade to the point where fish and other aquatic life populations decline - even when power plant operators abide by water permit restrictions. Often, the water used in the power plant is also being diverted from other "higher" uses such as recreation or tourism, drinking water supplies, and other less intrusive commercial opportunities.

In addition, the habitat of many animal and plant species can be destroyed during the construction of and continued operation of large fossil and nuclear power plants. These same facilities represent challenges to maintaining a sense of aesthetics in scenic environments.

Construction and operation of hydropower facilities can also have negative impacts on water quality. By slowing the river's flow, most dams increase water temperatures. Other dams decrease temperatures by releasing cooled water from the reservoir bottom. Fish and other species are sensitive to these temperature irregularities, which often destroy native populations. These temperature changes, when combined with water stagnation, may also lead to the accumulation of decaying materials in the reservoir and a corresponding loss of oxygen, which then increases substances toxic to aquatic wildlife in the reservoir. And when this oxygen-deprived water is released from behind the dam, it can kill fish and vegetation downstream. Alternatively, water falling over spillways to spin turbines to generate electricity can super-saturate the water with gases from the surrounding air. The gas bubbles, which are absorbed into fish tissue, may cause damage and ultimately kill the fish. Crystal-clear rivers can also degrade quickly when water is impounded behind a man-made dam, accumulating sediment and silt.

Hydropower dams also impact fish and wildlife habitat. Construction of a dam converts river habitat into a lake-like reservoir. This often eliminates native populations of fish and other wildlife. Warm, slow moving reservoirs also often favor predators of naturally occurring species. It has been argued that reservoirs can enhance waterfowl habitat, but such artificially created habitats may be of considerably lower quality than the naturally evolved and undisturbed river systems. Peaking power operations can also cause dramatic changes in reservoir water levels -- often up to 40 feet -- that degrade shorelines and disturb fisheries, waterfowl, and bottom-dwelling organisms.

(See also Hydropower Generation, Water Consumption and Land Impacts Issue Papers for more information on hydropower impacts.)

How can consumer electricity choice address water quality problems?

Water quality impacts vary - sometime significantly - from electricity generating technology to technology. Many renewable energy technologies such as wind and solar photovoltaic technology produce electricity without generating any waste effluent released into waterways or without relying upon any cooling water. By contrast, thermal power plants that run on coal and other fossil fuels introduce a myriad of chemicals for maintenance or operational purposes, and through combustion, liberate other chemicals from the fuel that wind up in the power plant's discharge. Nuclear power plants consume even more water than fossil fuel facilities because of the additional cooling requirements of reactor cores and can have major impacts on marine environments.

Consumers can help maintain the sustainability of rivers and streams, lakes and oceans, by ensuring that their power comes from low impact and renewable sources that do not rely upon water for cooling. Some renewable resources, such as solar thermal facilities or geothermal power plants may require cooling water and therefore may have more of an impact than those other renewable sources that lack any need for water cooling. Most renewable resources, however, are smaller than coal and nuclear power plants and therefore their negative impacts on water bodies are considerably less.

Additional Information:

American Rivers http://www.americanrivers.org

Low Impact Hydropower Institute http://www.lowimpacthydro.org