CHAPTER 14 AN ENVIRONMENTAL OVERVIEW OF GEOTHERMAL RESOURCES DEVELOPMENT

• Jurisdiction: United States

Geothermal Resources Development
(Jan 1977)
CHAPTER 14
AN ENVIRONMENTAL OVERVIEW OF GEOTHERMAL RESOURCES DEVELOPMENT
A. Dan Tarlock
Richard L. Waller
Indiana University
Bloomington, Indiana

INTRODUCTION

A large part of the case for the increased development of geothermal resources is that this energy source is environmentally superior to fossil fuel and nuclear produced electricity, and arguably even hydroelectric power.¹ Geothermal energy can be produced with less landscape disturbance and residual discharge than is required for fossil fuel, nuclear and hydroelectric power.² For example, at The Geysers in northern California about twelve square miles are necessary for the 150 wells required to support a 1000 M-2 plant. In 1972 the Atomic Energy Commission estimated that the nuclear industry held more than nineteen million acres of land for uranium mining and exploration. When the land use requirements of The Geysers' field are extrapolated to all geothermal sites that may be in production by 1986, the favorable comparison between geothermal and nuclear energy is evident, and similar comparisons can be made between geothermal and coal.³ Similar comparisons can be made for residual discharges. A 1000 M-w plant at The Geysers without pre-treatment discharges about one fourth the sulfur dioxide of a coal-fired plant.⁴

There are two major variables in the level of any potential adverse environmental impact from geothermal development. These are the character of the heat resource and the stage of development. The two most important hydrothermal geothermal reservoirs are liquid-dominated ones which produce hot liquids and vapor-dominated ones which produce steam.⁵ Geothermal exploration can be divided in the exploration, test drilling, production testing, field development, and power generation stages.⁶ This first section of the paper discusses the major expected physical adverse environmental impacts which can be expected during each of the five major stages.

I CLASSIFICATION OF ENVIRONMENTAL IMPACTS

Four categories of potential adverse environmental impacts have been identified: land use conflicts, air pollution, water pollution and noise. Land use conflicts and water pollution appear to be the most important problems.

A. Land Use Problems

During the exploration and drilling stages there will be various land use disturbances associated with road and well site preparation. These range from short lived nuisance conditions to the possible permanent displacement

[Page 14-2]

of wildlife habitats. If a field proves to be productive, a well will be drilled every 1/4 to 1/8 of a mile, pipelines laid, and a powerplant constructed. A geothermal field and associated power plant raise the same land use problems as any other industrial use: Is it or can it be made compatible with surrounding land uses? Since a power plant must be built at the field, geothermal development will generally convert undeveloped land or a more intense use, and the dedication of land to energy development may be opposed on the grounds that maintenance of a natural environment to enhance landscape aesthetics is the preferred use. Aesthetic conflicts are likely to be most intense if geothermal leasing⁷ is allowed in wilderness areas. However, since geothermal development will often occur in scenic areas, aesthetic objections to geothermal development are likely to be frequent. Leaving aside the value questions inherent in choosing between aesthetics and development, the Department of Interior's Final Impact Statement on the leasing program is optimistic that land use conflicts in connection with geothermal development will be limited,⁸ although other studies are somewhat more skeptical:⁹

The adverse environmental effects of geothermal development may decline as the field comes into full-scale production. If proper environmental measures have been fully implemented during the construction phase, vegetative cover will begin to cover exposed soils where conditions are conducive to plant growth, drainage and soil erosion measures will control run-off to minimize both on and off-site damage. The physical disturbances and activities associated with construction will have ended. During the production period, activities primarily will consist of the operation and maintenance of the power plant and related facilities and the drilling, redrilling, and workover of geothermal wells to maintain production capacity. Overall activity will be considerably reduced over that required during field development and the construction of power generation, power transmission and related facilities. A state of use equilibrium will be reached which will be conducive to broader multiple land uses of the leased area, particularly uses such as wildlife habitat, grazing and agriculture. For example, the Larderello field in Italy is in an area of intensive agricultural development. Within the confine of the field there are many farms, vineyards and orchards adjacent to producing wells, pipelines and power plants.

B. Water Pollution Problems

During the drilling phases the most serious water (and air) pollution

[Page 14-3]

problems will occur if there is a blow out. The danger is greatest during test drilling due to the limited available knowledge about subsurface geological and thermal conditions, although a blow out could occur at any subsequent stage. In addition to blow outs in the immediate vicinity of the well, other areas some distance away can be affected by a well experienceing difficulties; cratering and mud ejection could cause local property damage and water pollution. Considerable experience about blow outs has been gained in New Zealand, at the Geysers, and in the Imperial Valley so that more is now known about the proper technology to be applied during drilling.¹⁰

Water pollution problems during power generation may arise in connection with the disposal of cooling waters and the disposal of wastes from liquid dominated systems. The latter is by far the most serious problem, since although a geothermal plant is less efficient than a nuclear or coal-fired plant, it does not require a supplementary source of cooling water. Dry steam systems present almost no environmental hazard since the steam is either evaporated through a cooling tower or reinjected into the reservoir. Liquid-dominated systems can also be recycled but more risk of pollution is associated with the deep well reinjection of saline brines back into the reservoir. If these saline brines are allowed to mix with ground water acquifers tapped for municipal or irrigation users, serious water pollution would result. The problem is further complicated by the fact that reinjection may be necessary to prevent subsidence. "Hot water fields, by contrast" to dry steam fields "could behave like unconsolidated petroleum reservoirs, and unless pressures are maintained by fluid return there may be subsidence."¹¹ Some concern has also been expressed that reinjection will trigger seismic activity in the area.

C. Air Pollution Problems

A geothermal power plant discharges about 98-99.5 percent water vapor and operates without combustion. Of the small flow of non-condensate gases 1.4% of this is hydrogen and 4.5% is hydrogen sulfide. The latter presents the most important air pollution problem. As mentioned previously, a geothermal plant can discharge sulfur dioxide but the amount discharged is one-fourth that of a similar coal-fired plant, and technologies exist to further reduce the discharges. Hydrogen sulfide is discharged in amounts substantially above its toxic levels and it smells. However, the discharges are basically a localized nuisance problem¹² which is solvable by technology.¹³ Still the lack of scientific research about potential air pollution problems will cause concern in some areas when geothermal development is proposed. Napa County in northern California listed the "spectors of acid rain fall, smog, effects from the increased levels of non-condensate emissions and thunderstorm prevention" as reasons for its proposed Oil, Gas and Geothermal Resource Exploration and Development ordinance.¹⁴

D. Noise Pollution Problems

Well drilling is generally noisy as the testing and maintenance of

[Page 14-4]

geothermal wells presents special, if localized, noise pollution problems. Wells must be bled before they go into production and again during production so that they will remain operational. The venting of large amounts of steam can produce a high volume roaring for hours or days at a time. Mufflers are used at the Geysers with considerable success, but nuisance problems remain. Even with the use of mufflers, a geothermal field and associated power plants will change the noise level of an areas to that of an industrial area. Depending on the location of the field and the character and density of surrounding land uses, noise control will be a major factor in the application of land use regulations.¹⁵

Two common themes run through this brief description of the potential adverse environmental impacts of geothermal development. First, most of the impacts seem to be localized. Geothermal development is not without risks of environmental harm but it does not present the long term risks that nuclear energy or the use of chemical pesticides does. The second and related theme is that most environmental problems connected with geothermal use can be solved through the adoption of mitigation measures during the various stages of development. Geothermal development does not force a regulator to make the difficult decision of whether something should be allowed or prohibited entirely. Therefore because of its favorable environmental impacts compared to coal and nuclear energy, geothermal development ought to be presumed beneficial, and regulatory activities should focus on conditioning the development of the resource at each of the five stages.

The next section of the paper...