Environmental Engineers and Chemical Engineers Take a Narrow View of Thermal Pollution

Coastal Thermal Pollution and Related Policy Issues in the United States: An Overview. ©

By Brock McCracken

Coastal Policy Class

Dr Steffen Schmidt

Nova Oceanographic Center

© Copyright, Brock McCracken. Any citation must attribute this research to the author.

INTRODUCTION

Thermal Pollution

Pollution is the contamination of Earth’s environment with materials that interfere with human health, the quality of life, or the natural functioning of ecosystems (living organisms and their physical surroundings). Although some environmental pollution is a result of natural causes such as volcanic eruptions, most is caused by human activities.

Water Pollution is the contamination of streams, lakes, underground water, bays, or oceans by substances harmful to living things. Water is necessary to life on earth. All organisms contain it and some live in it and most drink it. Plants and animals require water that is moderately pure, and they cannot survive if their water is loaded with toxic chemicals or harmful microorganisms. If severe, water pollution can kill large numbers of fish, birds, and other animals, in some cases killing all members of a species in an affected area. Pollution makes streams, lakes, and coastal waters unpleasant to look at, to smell, and to swim in. Fish and shellfish harvested from polluted waters may be unsafe to eat. People who ingest polluted water can become ill, and, with prolonged exposure, may develop cancers or bare children with birth defects.

The major water pollutants are chemical, biological, or physical materials that degrade water quality.

Water is often drawn from rivers, lakes, or the ocean for use as a coolant in factories and power plants. Almost half of all water withdrawn in the United States each year is for cooling electric power plants. The cheapest and easiest method is to withdraw water from a nearby body of surface water, pass it through the plant and return the heated water to the same body of water. The water is usually returned to the source warmer than when it was taken. This process is called once through cooling or wet cooling as opposed to dry cooling. The water absorbs the excess heat of nuclear rods or other machinery and then returned to the environment. See Figure 1.

Large inputs of heated water from a single plant or a number of plants using the same lake, ocean or bay region, or slow-moving stream can have harmful effects on aquatic life. This is called thermal pollution. Even small temperature changes in a body of water can drive away the fish and other species that were originally present, and attract other species in place of them. Thermal pollution can accelerate biological processes in plants and animals or deplete oxygen levels in water. The result may be fish and other wildlife deaths near the discharge source.

Thermal pollution can also be caused by the removal of trees and vegetation that shade and cool streams. The deforestation of shoreline aggravates soil erosion and increases the amount of light that strikes the water. Soil erosion leads to muddy water, which lowers the clarity of water, with the introduction of impurities in water, containing microbes and dissolved minerals, which increase the light absorption from the atmosphere. The waters increased light absorption will see a rise in the temperature of water from the heat energy of light.

Figure 1. The figure depicts wet cooling or once through cooling tower versus dry cooling tower. Dry cooling is the newer technology. Dry cooling is more efficient, reduces air emissions, uses less water, and lowers the temperature of water discharges more effectively. Many existing facilities are replacing wet cooling towers with dry cooling towers. Dry cooling towers are also smaller in size and do not produce as much noise as wet cooling towers. Although, once through cooling towers is the preferred technology in coastal areas.

Source: U.S. Department of Energy.

Effects Of Thermal Pollution

Warmer temperatures lower dissolved oxygen content by decreasing the solubility of oxygen in water. Temperature often determines the kind of microorganism that exists in an aquatic environment. Warmer water also causes aquatic organisms to increase their respiration rates and consume oxygen faster, and it increases their susceptibility to disease, parasites, and toxic chemicals. Discharge of heated water into shallow water near the shore of a lake also may disrupt spawning and kill young fish. This will upset balance in the whole system.

Because of complexity of natural systems, it is misleading to generalize on temperature effects on aquatic biota. More proper is to study locally important species. Temperature is important to maintenance of optimum characteristics in water based ecological systems. Fish and other organisms adapted to a particular temperature range can also be killed from thermal shock, which is the effect of sharp changes in water temperature when new power plants open up or when plants shut down for repair. One example is temperatures, which do not kill fish, or shellfish may produce effects in metabolism, reproduction and growth as well as reducing certain food organisms.

Many fish also die on intake screens used to prevent fish from clogging the heat exchanger-pipes. This issue is rapidly becoming a hotly contested debate and has led to new legislation that will be explored in another section of the paper.

Many reactions effecting water quality are biochemical and center around microbial activity. Most reactions occur at low temperatures in presence of enzymes, which in turn are temperature sensitive. Most are in the mesophylic classification and thrive on temperature range of 10 to 40ºC.Maximum activity occurs between 30 and 37ºC and then falls off.

Environmental engineers and chemical engineers take a narrow view of thermal pollution, unfortunately. Their jobs are to remove heat from waste streams so that discharge regulations are satisfied. The regulation may be stated as the volumes and temperatures that are permissible for discharge or as the thermal rise that is that is tolerable for the receiving water. In a broader sense, and with the concern about global warming, engineers do little to mitigate the effects on earth because they take air or cool water from the environment to exchange heat with their waste streams.

REGULATIONS AND POLICY ISSUES

Summary

As the nations population increases, so does the need for increased electricity and drinking water supplies from surface waters and groundwater. Coastal populations are overwhelmingly increasing as more and more people seek the comforts coastal communities bring to everyday life. Electricity producing power plant sites are a priority in meeting the nations needs for these resources. More and more states are looking at coastal sites for power plants as the search for diminishing water supplies intensifies. Proposed and existing facilities must meet and be in compliance with federal, state, and local siting criteria. The best technologies available must be used when planning such facilities. Thermal discharges must be at a level that would assure protection and propagation of a balanced indigenous population of fish, shellfish and wildlife.

For instance, in California and most other states, new facilities must apply for a National Pollution Discharge Elimination System (NPDES) permit through the State Water Resources Control Board (SWRCB), which applies to water discharge requirements. A proposed facility must also meet state coastal zone management thermal plan legislation as set forth by such state programs (i.e. California Coastal Commission), which deal with biological and human health issues that are scientifically based in the Coastal Act. The regulations at this level are usually different interpretations relating to water quality issues. Approval must be obtained from these kinds of authorities. Coastal zone management programs are federally approved. Finally, the facility must be in compliance to the federal Clean Water Act and its guidelines addressing thermal discharges into a body of water section 301(a) and 310(b). The effluent discharged must be within 20 degrees F of the existing water body temperature (receiving water) and use the best available technology for minimizing adverse environmental impacts.

Individual states do have the authority to implement even more stringent regulations but cannot approve a project that does not meet federal requirements. This section will focus on some of the existing policies.

Background

In the United States, the serious campaign against water pollution began in 1972, when Congress passed the Clean Water Act. The Clean Water Act defines pollutant very broadly encompassing ant type of industrial, municipal, and agricultural waste discharged into U.S. waters, including heat. This law initiated a national goal to end all pollution discharges into surface waters, such as lakes, rivers, streams, wetlands, and coastal waters.

The law required those who discharge pollutants into waterways to apply for federal permits and to be responsible for reducing the amount of pollution over time. The law also authorized generous federal grants to help states build water treatment plants that remove pollutants, principally sewage, from wastewater before it is discharged. The EPA sets standards, approves state control plans, and steps in when necessary if state programs are failing to enforce its own rules.

The EPA has equivalents in many countries, although details of responsibilities vary. For instance, the federal governments may have a larger role in pollution control, as in France, or more of this responsibility may be shifted to the state and provincial governments, as in Canada. Because many rivers, lakes, and ocean shorelines are shared by several nations, many international treaties also address water pollution. For example, the governments of Canada and the United States have negotiated at least nine treaties or agreements, starting with the Canada-U.S. Boundary Waters Treaty of 1909, governing water pollution of the many rivers and lakes that flow along or across their common border.

The oceans, as vast as they are, are not invulnerable to pollution. Several major treaties deal with oceanic pollution, including the 1972 Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter and the 1973 International Convention for the Prevention of Pollution from Ships (known as MARPOL). International controls and enforcement, however, are generally weak.

NPDES Permitting

Pollution may reach natural waters at spots we can easily identify, known as point sources, such as waste pipes, ditch, channel, or mine shafts. The Clean Water Act prohibits the discharge of pollutants through a known point source into existing U.S. waters unless they have an NPDES permit (US EPA, 1999). The permit will contain limits on what can be discharged, monitoring and reporting requirements, and other provisions to ensure that the discharge does not seriously degrade water quality or people’s health. The permit translates general requirements of the Clean Water Act into specific provisions designed to meet the operations of each discharged pollutant (US EPA, 1999).

NPDES permits are issued by states that have obtained EPA approval to issue such permits or by EPA Regions in states without such approval (US EPA, 1999). The permit requires the facility to sample its discharges and notify EPA and the state regulatory agency when the facility determines it is not in compliance with the requirements of the permit. EPA and state regulatory agencies also periodically send inspectors to ensure compliance with permits. Injunctions or penalties, such as fines, can be administered if a facility is deemed in violation of the issued permit requirements. The Clean Water Act limits the length of NPDES permits to five years but they can be renewed at any time (US EPA, 1999).

On a side note, non-point sources are more difficult to recognize. Pollutants from these sources may appear a little at a time from large areas, carried along by rainfall or snowmelt. For instance, the small oil leaks from automobiles that produce discolored spots on the asphalt of parking lots become non-point sources of water pollution when rain carries the oil into local waters. Most agricultural pollution is non-point since it typically originates from many fields.

Coastal Power

Coastal power plants use ocean water in once through cooling system designs. The plants intake ocean water through cooling water intake structures and use this water for heat exchanges between the water and their equipment and then discharge this water directly along the shore. Most current regulations require discharges to be a significant distance from the shore depending on the biological aspects of the immediate aquatic species in the coastal zone. The discharge pipes lie on the seafloor and can extend 1000 feet or more. The use of ocean water for cooling such structures is given a high priority by regulatory agencies as opposed to fresh water sources. In other words, it is the preferred method and strongly encouraged when new sites for facilities are being proposed even though the dry cooling and hybrids between the wet cooling and dry cooling methods are more efficient and use smaller amounts of sea water.

The modernization or re-powering of existing power supply plants is gaining widespread acceptance in the industry. This involves the reuse of existing discharge and intake facilities at an existing power plant site while replacing the power generating facility. Re-powering of these projects may result in the regional water quality control board treating the thermal discharge as a new discharge, and usually require the reevaluation of federal and state permit conditions. Typically, establishment of a comprehensive database on the existing biological resources potentially being impacted is required for any proposal to re-power or modernize. For example, in California, the California Coastal Commission in its Coastal Act and the SWRCB policies give preference to and top priority in using existing plants to increase energy output. By retrofitting the plant and by not increasing the intake and discharge flow a generator is able to use existing grand fathered NPDES discharge permits. The procedure is subject to review by the proper authority on a case-by-case analysis of course. Generators are accelerating this procedure with the apprehensive and almost reluctant support from regulatory agencies. In addition in California, the SWRCB has adopted an Ocean Plan and a Thermal Plan, with which such projects must comply.