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The Environmental Imperative for Renewable Energy: An Update Land, Water, and Wildlife Impacts |
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A. LAND USE While power plants themselves take up relatively little space, provisioning the plants can require extensive land use. Table 6 estimates the land required by some energy technologies. Not only the quantity but the nature of energy-related land use can vary widely. For example, some forms of biomass cultivation can promote more biodiversity of birds than row crops do, although not as much as forests. 81 Similarly, while a 25-MW wind farm may occupy between 475 and 1,150 hectares, depending on the arrangement of the turbines, the machines themselves only require 5-10% of that area, leaving the remainder for customary agricultural or range use. 82 Wind turbines can coexist with traditional land uses such as farming and ranching. Coal mining imposes some of the most severe energyrelated environmental costs on American land. Historically, mining operations harvested the timber over coal beds to furnish burgeoning railroads with ties, and the mines themselves with props. Timber cutting left remaining land cover vulnerable to forest fires and subsequent pest infestations, and facilitated flooding and erosion, thereby clogging steams. 83 Since 1930, coal mining has disturbed about 2.4 million hectares of American land, the vast majority of which once held forests. 84 In addition to old, abandoned mines, coal mines supplying electric power plants currently disturb about 680,000 hectares. 85 The Surface Mining and Control and Reclamation Act of 1977 (SMCRA) requires mine owners to post bonds for land rehabilitation, although land is rarely if ever restored to original conditions. Partly as a result of SMCRA's requirements, mining firms increasingly resort to "mountaintop removal," explicitly exempted from the 1977 law. This technique employs heavy equipment to lop several hundred feet off the peak of a mountain, and cache the resultant debris in hollows and valleys. In West Virginia, surface mines produced only 10% of the state's coal in the 1960s; the figure now stands at about one third, and each site can occupy 10,000 hectares. 86 As a result of the Clean Air Act, which in recent years has helped drive many utilities toward lowsulfur Western coal, the Powder River Basin of Wyoming and Montana hosts comparable mining activity on, in some cases, an even larger scale. 87 In addition to conventional mining-related land disruptions, uranium mining presents special hazards. These include the release of radon gas and airborne radioactive dust from uranium mines and mills, as well as radioactive seepage from waste rock piles and contaminated groundwater pumped out of mines. 88 The United States now imports about three-quarters of its uranium, mostly from Canada. The remainder comes from processing waste rock and "in situ leaching" rather than conventional mines; these techniques use ammonium carbonate or sulfuric acid to remove the uranium from mine walls. (While leaching avoids accumulation of radioactive and potentially toxic tailings, the leaching liquid represents a hazard, especially to groundwater, if not contained.) But tailings from historic mining operations, unregulated until 1980, represent the huge bulk of lowlevel radioactive waste in the United States. The principal radioactive components of mill tailings, thorium230 and radium226, have halflives of about 75,000 and 1,600 years, respectively. Toxic heavy metals contained in the tailings, such as molybdenum and manganese, pose a threat to groundwater as well. Nearly onethird of uranium milling waste is found on Navajo lands. 89
B. ACID MINE DRAINAGE As coal and uranium mining expose rock rich in iron sulfide (pyrite) to oxygen and water, the resulting acid drainage endangers aquatic ecosystems, in some cases for centuries. Acid drainage harms 12,000 miles of American rivers, damaging and in some cases eliminating aquatic life. 90 Mitigation options include neutralizing acid runoff with limestone, impounding pyrite-bearing waste rock, and other techniques. Unfortunately, such solutions can be impermanent. Where owners abandon the mine or declare bankruptcy, acid drainage can constitute an environmental threat long afterward. Because most acid-producing metal mining takes place in the drier West, coal mining - historically concentrated in the wetter Northeast - gives rise to 75% of acid mine drainage sites and perhaps 95% of total acidic gallons. 91
C. WATER USE In 1995, U. S. fossil-fueled power stations required about 135 billion gallons of water per day (Bgal/ d). Nuclear plants used 55 Bgal/ d, and geothermal less than 2 Bgal/ d. These "thermoelectric" facilities use water mostly for cooling condensers and reactors. Surface fresh water supplied some 69% of the total, and surface saline water the rest. As a group, thermoelectric plants represent the largest single category of U. S. water use (fresh and saline), and the largest by far in the East. 92 The "once-through" cooling systems in place at most power plants return water heated to approximately 40° C to its source, where it can disrupt marine life (see the next section). Plants using closed cooling systems require only enough water to replace that lost to evaporation during passage through cooling towers and ponds. Overall, the power sector returns about 98% of the water it uses back to the source. Hydroelectric plants require 3,160 Bgal/ d, virtually all of it fresh. While hydroelectric generation itself consumes little or none of this water, a certain amount evaporates from reservoirs and during repeated reuse at pumped-storage hydropower facilities. 93 Energy-related activities also contribute to water use. Mining accounts for 3,770 Bgal/ day, of which 40% is fresh surface water, 28% is fresh groundwater, and the rest is saline. 94 Consumptive use accounts for 27% of the total. It is not clear, however, what fraction of that total is used in coal mines. Petroleum refining requires a large amount of water as well. On a longer time frame, global climate change would certainly alter the distribution of water in the global ecosystem, and the quantity available for human use. 95 Plant operators at the Geysers geothermal facility have successfully injected reclaimed sewer water into the geothermal field. In addition to disposing of an environmental liability, this process raises pressure in the affected portion of the field, and, in this case, increased electricity production by 10%. While other fields may respond similarly to the same process, reinjection of reclaimed water remains so far an experimental technique. 96
D. WILDLIFE IMPACTS Most human health risks due to energy production potentially threaten wildlife as well. For example, the nesting habits of insectivorous birds change in areas with high levels of sulfur dioxide. 97 A literature review in 1988 indicated that biological effects in animals occur at or below the levels set by regulatory standards for SO2 , ozone, and particulates. 98 Hazardous air pollutants also have an impact - for instance, high levels of cadmium can cause death, reduced blood enzyme levels, and joint lesions in songbirds, shrews, and badgers. However, normal energy-related emissions by themselves would presumably not produce such effects. In many cases, air pollution harms wildlife by depleting forage and prey, such as aquatic invertebrates vulnerable to acidification of lakes and streams. Acid deposition can also trigger the ionic release of aluminum, which kills fish, and the depletion on land of calcium, resulting in weaker eggshells for calcium-deprived birds. 99 Coal mining endangers local waterfowl, primarily through acid mine drainage, but also through altering water availability, leaks of chemicals, and runoff from coal storage piles and tailings, among other factors. 100 In many cases, careful management and judicious siting can mitigate the impact of energy projects on local wildlife. For example, it became apparent in the late 1980s that endangered (and federally protected) golden eagles and red-tailed hawks were dying among the 7,000-odd wind turbines of California's Altamont Pass. One two-year study of the area counted 182 dead birds, including 119 raptors; researchers attributed 55% of raptor deaths to collisions with turbines, 11% to collisions with wires, 8% to electrocutions, and 26% to unknown causes. 101 A few other locations, such as Tarifa, Spain, have experienced similar problems. Yet the Altamont Pass, Tarifa, and a few other highmortality wind farms appear to represent anomalies, whose danger to birds reflects comparatively rare combinations of such risk factors as proximity to migration routes, nearby development encroaching on habitat, the presence of prey, and the absence of alternative perches. Most locations have not experienced such problems, indicating the value of careful siting, installing noperch tubular towers, burying transmission lines, and other techniques. 102 It is worth comparing the wildlife impact of wind power to that of conventional energy use. In addition to the endemic effects of air pollution and acid mine drainage noted earlier, a single catastrophic event can have far greater impacts. For instance, 3,000 birds died in two successive nights in 1982 from collisions with four chimneys at the Florida Power Corporation's Crystal River Generating Facility. 103 Or, to take a notable example not centrally associated with electric power, the oil spill occasioned by the grounding of the Exxon Valdez tanker killed between 90,000 and 270,000 seabirds. 104 Large environmental shifts such as global warming will certainly have large effects on wildlife as well. For example, 50-80% of the nation's duck population breeds in the prairie potholes of the northern Great Plains. Research suggests that warming of 1°C would cull duck populations by about 25% if rainfall remains constant. The same degree of warming plus a 15% increase in precipitation could boost duck populations by 25%, however. 105 The operation of hydroelectric dams can have especially severe consequences for wildlife, in particular fish. Dams hamper ocean-going species such as salmon as they attempt to spawn in the rivers of their birth. They also hinder young fish seeking passage back to the ocean. Notwithstanding the installation of mitigation measures such as fish ladders and altered operating practices to facilitate fish migration (e. g., maintaining minimum water flows even during times of low electricity demand), many fish species have declined. In the 1960s, for instance, even after construction of dams on the Columbia River, some 100,000 steelhead and salmon per year migrated up the Columbia's tributary, the Snake River. In 1998, several years after the construction of four dams on the Snake, biologists counted only 9,300 steelhead, 8,426 spring-summer Chinook salmon, 927 fall Chinook, and 2 Sockeye salmon. 106 The federal government now classifies all these species as threatened or endangered, and in the 1980s declared the Snake River coho salmon extinct. Scientists at Oak Ridge National Laboratory hold federal dams primarily responsible for reducing the Pacific Northwest salmon population from 16 million to 300,000 wild fish per year. 107 In addition to the physical barriers represented by dams, hydroelectric power can alter the aquatic environment in other ways. On the Columbia River, for instance, enough pressure builds on water pouring from high spillways to supersaturate it with airborne gases that, when absorbed by fish, can injure or kill them. In the Tennessee Valley, system operators allow only limited flow in the summer. As a result, cooler water - which holds less oxygen than warm - collects at the bottom, suffocating striped bass and other fish. Low-oxygen water can absorb toxic metals from surrounding rocks, as well. In many hydroelectric systems, rapid fluctuations in response to changing demand for power disturbs habitat and strands fish in shallow water. 108 The use of water in nuclear and fossil power plants harms marine life too. Many plants discharge heated water from their once-through cooling systems, introducing substantial thermal pollution to rivers and coastal waters. In addition, fish and other animals can be sucked into and crushed against filters in water intake pipes, or swept into the plant itself. Over 40 million fish per year die in the inlets of 90 Great Lakes power plants using once-through systems; the annual toll at New York's Indian Point Two and Three nuclear reactors exceeds 1.5 million fish. 109 Since 1983, some 187 federally protected harbor seals and California sea lions have died in the ocean intake structures of the San Onofre nuclear plant. Other coastal plants cause similar fatalities. 110
E. SOLID WASTE: Coal-fired facilities produce ash equivalent to 10% of fuel input, compared with biomass plants at under 2%, oil plants at about 0.1%, and gas plants at close to zero. Bottom ash, or slag, collects at the bottom of the boiler, while particulate collectors and other elements trap the finer fly ash borne up on the flue gas. According to EPA, about a third of the ash generated by U. S. coal plants finds its way to some sort of productive use, for example in cement production; electricity producers manage most of the rest in onsite impoundments and landfills. In addition, many facilities must condition flue gases to remove sulfur, giving rise to a separate variety of waste, known as fluegas desulfurization sludge, most of which ends up in onsite landfills and impoundments. 111 Sludge can also be used in asphalt production and wallboard fabrication. While most of the volatile selenium and mercury contained in coal leaves power plants in the flue gas, other toxic metals collect in the ash and sludge. For instance, solid waste from average current coal plants contains over twice the arsenic, cadmium, and nickel as the stack effluent; triple the lead; and four times the chromium. 112 By contrast, biomass ash, which is not toxic, generally represents a management issue rather than a hazard. While solid wastes can be managed more easily than airborne pollutants, the Resource Conservation and Recovery Act of 1980 exempts most coal and oil waste from hazardous waste rules, pending a decision by EPA to regulate. 113
F. LAND IMPACTS OF BIOPOWER: Among energy technologies, biopower presents perhaps the widest swing between potential environmental benefits and possible environmental damage. Part of the range reflects the variety of technologies and practices included under the rubric of biopower. As Box 3 illustrates, the term encompasses a wide variety of fuels, conversion technologies, and production strategies. Biopower is appealing precisely because it can bring nonenergy benefits. Currently, most if not all biomass used for power production in the United States comes from wastes rather than purposegrown crops. For instance, California's biopower industry relies on residues from mills, agriculture, forests, and urban uses. In the absence of a biopower sector in that state, landfills would receive 62% of waste biomass used as fuel, with attendant land use and water quality issues. Some 10% of the rest would accumulate in forests, increasing the risk of catastrophic fires, reducing water yield, and impairing forest health. 114 In the case of energy crops, specific areas of environmental uncertainty in which energy crop cultivation can help or harm the environment include: 115
As this list illustrates, the environmental consequences of energy crop production will depend heavily on the practices at individual plantations; it should be possible to manage bioenergy so as to maximize its advantages and minimize its environmental costs.
G. PHOTOVOLTAICS AND HEAVY METAL A final environmental consideration concerns the composition of photovoltaic modules. Two advanced PV technologies rely on semiconductor materials that incorporate heavy metals rather than silicon: cadmium telluride (CdTe) cells and copper indium diselenide (CIS) cells accounted for 0.8% and 0.1% of the global market in 1998, respectively. 116 While these metals are toxic, the quantities involved are small; a CdTe module of one square meter may contain 6 grams of cadmium, compared with 2.5 grams in a nickel cadmium penlight battery. Release of cadmium and selenium to the environment through their use in PV technology usually occurs through resource mining, refining, module use, and module decommissioning, and can be minimized through appropriate module fabrication procedures, construction techniques, and recycling programs. One source estimates base-case emissions of cadmium from the total life cycle of CdTe modules at 0.5 g/ GWh, and of selenium from CIS modules at 8.9 g/ GWh. 117 By comparison, another source estimates emissions of cadmium in the flue gas and solid waste (and not including mining and refining) from average current coal plants at 13.9 g/ kWh, and emissions of selenium at 420 g/ GWh. 118
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The Environmental Imperative for |
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