EPA
United States
Environmental Protection
Agency
Office of
Research and
Development
Office of Energy, Minerals and
Industry
Washington, D.C. 20460
EPA-6 00/9-77-010
May 1977
WESTERN ENERGY RESOURCES
AND THE ENVIRONMENT:
GEOTHERMAL ENERGY
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The Energy/Environment R&D Decision Series
This volume is a part of the Energy/Environment R&D Decision Series. The series presents
the key issues and findings of the 17-agency Federal Interagency Energy/Environment
Research and Development Program in a format conducive to efficient information transfer.
The volumes are of three types: Summaries — short synopses of larger research reports;
Issue Papers — concise discussions of major energy/environment technical issues; and
Executive Reports — in-depth discussions of an entire programmatic or technical area.
The Interagency Program was inaugurated in fiscal year 1975. Planned and coordinated by
the Environmental Protection Agency (EPA), research projects supported by the program
range from the analysis of health and environmental effects of energy systems to the develop-
ment of environmental control technologies. The works in this series will reflect the full
range of program concerns. The Decision Series is produced for both energy/environment
decision-makers and the interested public. If you have any suggestions, comments or
questions, please write to Series Editor Richard Laska, Office of Energy, Minerals and
Industry, RD-681, U.S. EPA, Washington, D.C. 20460 or call (202) 755-4857.
prepared by Resource Planning Associates, Inc.
Design: Carol Libby, Brian Wishne
Photographs: Carolyn Zatz (pp. vi, viii,- 37, 78, 89)
Illustrations: Derick Haupert (pp. 17, 28, 73)
Barbara Emmel (pp. 2, 10, 13, 22, 27, 35)
Bruce Sanders (pp. 6, 8, 9, 12, 2.5, 55, 70, 76)
Brian Wishne (p. 63)
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Western Energy Resources
and the Environment
Geothermal
Energy
prepared for
Environmental Protection Agency
Office of Research and Development
Office of Energy, Materials and Industry
Washington, D.C. 20460
April 1977
Contract No. 68-01-4100
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This document on geothermal energy is the first in a series of summary reports to be prepared by
the Office of Energy, Minerals and Industry (OEMI) of the Environmental Protection Agency
(EPA). The purpose of the series is to describe what environmental effects are known or expected
from new energy resource development in the western third of the United States. Throughout the
series, we will emphasize those environmental impacts tbat currently are of greatest concern. We
will indicate some of the research and development activities under way and review the nonen-
vironmental constraints to resource development, The series will serve as a reference for planners
and policymakers on the entire range of problems and prospects associated with the development of
new energy resources.
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Contents
Introduction
Section I.
Geothermal Resources: Their Energy
Fbtential and Development
Technology
Section II.
Environmental Problems of
Geothermal Resource Development
Section HI.
The Future of Geothermal
Development
Page
vii
3 Overview
11 Chapter 1; Hydrothermal Convection Systems
26 Chapter 2: Hot Igneous Systems
33 Chapter 3: Conduction-Dominated Systems
36 References
40 Overview
44 Chapter 4: Land Use
49 Chapter?: Geology and Soils
54 Chapter 6: Water Resources
62 Chapter?: Noise
67 ChapterS: Air Quality
81 Chapter 9: Thermal Pollution and Climate
84 Chapter 10: Natural Biological Systems—Fish, Vegetation, and Wildlife
90 References
94 Chapter 11: Federal Environmental R&D Activities Related to
Geothermal Development
97 Chapter 12: Legal, Institutional, and Economic Constraints
to Geothermal Resource Development
Special Inserts 7 How Geothermal Resources Are Created
19 The Geysers Dry-Steam Field
23 The Imperial Valley: The Next Generation of Development
29 How Geothermal Resources Are Developed
31 Some Problems Related to Development Technology
79 ControlofHydrogenSulfideatTheGeysers
Bibliography 100 NOTE: Text references, indicated by a bracketed number in italics, are cited at
the end of each of the three major sections of this document.
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Tables
Section I.
Geotherma] Resources:
Their Energy Potential and
Development Technology
Section II.
Environmental Problems of
Geothermal Resource Development
Section in.
The Future of Geothermal
Development
Pkge
4 Table 1: Varying Projections of Electrical Generating
Capacity from Geothermal Resources in the
United States, 1985-2000
5 Table 2: USGS Estimates of Potential Energy Recoverable from U.S. Geothermal
Resources with Current or Near-Current Technologies
14 Table 3: USGS Estimates of the Potential Energy Assumed Recoverable from
Hydrothermal Convection Systems with Current or Near-Current
Technologies
15 Table 4: World Geothermal Power-Generating Capacity, 1972
42 Table 5: Potential Environmental Impacts of Geothermal Power Production
45 Table 6: Land Use Requirements for a Typical Geothermal Development Site
58 Table 7 • Expected Water Polluting Emissions for Alternative Electrical Generating
Processes, 1,000 MWe Plant
65 Table 8: Noise Levels of Geothermal Operations During Development Phase at The
Geysers
69 Table 9: Comparison of Noncondensable Gases in Steam from Wells at Two
Geothermal Power Plants
71 Table 10: Sources of Steam and Noncondensable Gas Emissions During
Geothermal Development
72 Table 11: Expected Total Air Emissions at The Geysers Prior to Operation of
Geothermal Wells for 1,000 MW of Generating Capacity
75 Table 12: Air Emissions of Alternative Electrical Generating Processes, 1,000 MWe
Plant
82 Table 13: Expected Waste Heat Emissions During Power Plant Operation for
Alternative Electrical Generating Processes, 1,000 MWe Plant
95 Table 14: Federal Environmental R&D Budgets for Specially
Focused Geothermal-related Research
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Figures
Page
Section I. 2 Figure 1 :
Geothermal Resources: Their 6 Figure 2:
Energy Potential and 8 Figure 3:
Development 9 Figure 4:
10 Figure?:
12 Figure 6:
13 Figure?:
17 FigureS:
17 Figure 9:
17 Figure 10:
21 Figure 11:
22 Figure 12:
25 Figure 13:
27 Figure 14:
28 Figure 15:
35 Figure 16:
Location of Hot, Normal and Cold Crustal Regions of the United States
Cross Section of the Earth
Divergent Plate Boundary
Convergent Plate Boundary
Relationship of Major Geothermal Systems and Boundaries
of Continental Plates
Structure of a Typical Hydrothermal
Convection Reservoir
Locations of Known Major Hydrotnermal Convection Systems
Dry-steam System (The Geysers, USA)
Flashed-steam System
Binary-cycle System
The Geysers Dry-steam Field
Location of Geothermal Resources in the Imperial Valley
Estimated Generating Capacity of Significant
Geothermal Reserves in the West
Areas of Identified Volcanic Systems
Technique for Developing Hot Dry Rock
Locations of Known Geopressured Zones Having Geothermal Resources
Section II.
Environmental Problems of
Geothermal Resource Development
47 Figure 17: The Lardarello Dry-steam Field
55 Figure 18: Cross Section of a Typical Drilling Site at
The Geysers Geothermal Field
55 Figure 19: Plan View of a Typical Drilling Site at The
Geysers Geothermal Field
57 Figure 20: Composition and Yearly Quantities of Major Pollutants in Condensate Return
Water of a 1,000 MWe Plant (The Geysers)
62 Figure 21: Noise Levels of Geothermal Operations at The Geysers Compared with those
of Familiar Sources
70 Figure 22: Physiological Effects of Hydrogen Sulfide
73 Figure 23: Typical System Cycle of Units 5 to 10 at Pacific Gas and Electric Company's
Geysers Power Plant
76 Figure 24: Expected Annual Hydrogen Sulfide Emissions During Operation of a
Hypothetical 1,000 MWe Plant Located at Several Geothermal Sites
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Introduction
Supplying the United States with "clean," affordable energy in the next 25 years
has become a problem of considerable importance in the current climate of un-
stable petroleum imports, dwindling reserves of natural gas, higher energy
prices, and an increasingly polluted environment. Numerous programs have
recently been undertaken to conserve energy, substitute renewable resources for
nonrenewable ones, develop domestic alternatives to imported fuels, and focus
on resources that may present few environmental problems.
One of the resources receiving increased scientific and public attention in
the United States is geothermal energy—the heat of the earth. Subsurface reser-
voirs of dry steam and hot water, called hydrothermal convection systems, are
viewed as sources of low-cost steam for use in steam-electric plants. In other parts
of the world, these systems have a long history of direct use for space heating and
process steam.
The most commercially feasible type of geothermal resource is dry steam.
However, only four commercial dry-steam generating plants are presently in
operation throughout the world; and only one of these—The Geysers, in Sonoma
County, California—is located in the United States. Although other geothermal
resource types, primarily hot-water systems, are far more abundant, their com-
mercial development is only now beginning in earnest. Worldwide, about a
dozen hot-water systems are in some stage of commercial development or opera-
tion. In this country, however, no hot-water plants have yet been commercially
developed.
The cost competitiveness of the electricity provided by The Geysers system
is proven, and demand is growing. What is not known is whether the hot-water
systems now being developed experimentally will prove to be as inexpensive as
alternative fuel sources.
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Introduction
Other important questions pertaining to geothermal energy remain unan-
swered, including: What share of the nation's energy needs tan it realistically
supply? What are the development costs? Can the technological requirements be
met? Will legal and institutional factors retard development, and if so, how?
What are the environmental problems and can they be addressed satisfactorily?
In this atmosphere of uncertainty, the federal government, primarily
through the Energy Research and Development Administration (ERDA), has
initiated a major effort to stimulate commercial interest in geothermal energy.
ERDA has launched a program to identify and verify the potential of the geo-
thermal resource, develop and test needed technology, and provide economic
incentives to the private market. The thrust includes a research program to
explore the potential environmental threats posed by development. At this early
stage, a great many questions about possible adverse effects of geothermal
energy have yet to be answered; evidence to date indicates that the potential is of
sufficient magnitude to warrant further attention and implies the need for care-
ful management and strict control.
This publication summarizes the state of knowledge about these possible
environmental effects. It is not a technical document but a general reference in-
tended as a guide to policymakers and the public. This document defines the
extent and potential of geothermal resources, the technology available for
development, and the constraints to growth. It highlights major research and
development efforts being carried out by ERDA, EPA, and other federal
agencies. In summary, this document aims to provide the reader with a balanced
picture of the problems and prospects for the development of geothermal energy
in the United States.
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I.
Geothermal Resources:
Their Energy Potential
and Development Technology
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Overview
Figure 1
Location of Hot, Normal, and Cold Crustal Regions of the United States
• HOT
|8|l NORMAL
IcOLD
1 500
miles
SOURCE. Nathanson, M. and L.J.P. Muffler, 1975. pp. 98, 99.
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3
Overview
Geologists at the United States Geological Survey (USGS) recently completed an exten-
sive investigation of areas in the United States where drilling data indicated variations in
the temperature readings of different locations drilled to identical depths [1 ] (see Figure 1).
They found the western third of the United States to be significantly "hotter'' than the
rest of the continent. This finding, combined with the region's history of volcanic
activity, geologically recent mountain-building, and earthquakes provides the basis for
the growing belief that the West offers significant potential for the development of geo-
thermal resources.
Geothermal resources are generally defined as reserves of heat relatively near the
earth's surface, created by the underlying geologic structure of the earth. (For a more
detailed explanation, see the insert, "How Geothermal Resources are Created." The
geothermal resource base—that is, the total amount of heat stored in the outer 10
kilometers of the earth—is enormous (calculated to be 3 x 1026 calories). [2] However,
because the heat is diffuse, only a tiny fraction of that amount is recoverable.
The best known geothermal resources are the geysers and hot springs that dot the
western part of the United States, giving rise to dozens of communities with names like
Sulphur Springs, Thermal, and Devil's Kitchen. However, although these geothermal
resources are the most readily identifiable, they do not represent the only geothermal
resources, nor even those with the largest potential as sources of energy.
In addition to geysers and hot springs, which are the visible signs of hydrothermal
convection systems, geothermal resources also include hot igneous systems and conduc-
tion-dominated systems. These three types of resources are distinguished by their
geologic characteristics and the means by which their heat is transferred to near-surface
areas.
Estimates of the near-term development potential of geothermal resources vary
widely, depending on the assumptions used. The prevailing view is that geothermal
energy is of greatest importance as a source of electricity, but only in certain local areas or
more widely in underdeveloped countries seeking alternatives to even more expensive
energy sources. The counterview is that the potential for geothermal energy is greatest in
non-electrical applications—including desalination, agriculture, and space heating.
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Overview
Table 1
Varying Projections of Electrical Generating Capacity
from Geothermal Resources in the United States, 1985-2000
(in megawatts of electricity)
Source of Projections
Federal Power Commission, 1970 Power Survey
December 1971
R. Rex (Senate Hearings)
1972
Bureau of Mines
1972
Department of Interior
1972
National Petroleum Council-l
1972 (high assumption)
National Petroleum Council— IV
1972 (low assumption)
W. Hickle, Geothermal Energy Heport
1972
California Division of Gas
1972 (in Stanford Research Institute Report, 1973)
Stanford Research Institute
1973 (separate report)
D.L. Ray, Energy Policy Office
1973
Project Independence
1974 (high assumption)
Project Independence
1974 (low assumption)
ERDA 86, Geothermal Energy Definition Report
1975-1976
Electric Power Research Institute (EPRI)
1976
By 1985
0
—
4.0
, 19.0
19.0
3.5
132.0
—
11.8
20.0
34.0
4.0
6.0
3.5
By 2000
0
400.0
40.0
75.0
—
—
395.0
7.5'
4.4*
80.0
—
—
39.0
10.0
SOURCE: Federal Energy Administration, 1974, and The Mitre Corporation, 1976.
•Within California only
—No forecast
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Overview
The conclusions of several recent studies have varied widely about the potential of
geothermal energy as a source of electricity by the years 1985 and 2000 (see Table 1). The
disparities result from different expectations of future technological breakthroughs,
information on resource characteristics, and the future costs of alternative fuels. To
develop a realistic assessment of the potential of geothermal energy, USGS has calculated
the energy potential of geothermal resources based on the cost of extraction (see Table 2).
USGS estimates that, disregarding cost, the potential is roughly equivalent to "140
Hoover dams or 140 average modern nuclear power plants,'' [3 ]
This chapter describes the distinguishing geologic characteristics of the three major
types of geothermal resources, identifies their known or probable locations, projects their
usable heat content, and briefly describes the development technology that must be ap-
plied to extract and use their heat.
Table 2
USGS Estimates of Potential Energy Recoverable from
U.S. Geothermal Resources with Current or Near-Current Technologies
Development Category
Geothermal reserves
(developable at
competitive costs)
Type of Geothermal Resource
Hydrothermal
Convection
3,500 MW-c*
Hot
Igneous
recovery
technology
undeveloped
Conduction-
Dominated
Marginal resources
(developable at costs 1-2 times
that of current alternatives)
Submarginal resources
(developable at costs more
than twice that of current
alternatives)
TOTAL magnitude of
geothermal resources
recoverable with present
technology, disregarding cost
3,500 MW-c
>1,000 MW-c
wide range of
estimates; at least
25,000 MW-c
>42,000 MW-c-
SOURCE: White, D.E. and D.L. Williams, 1975, pp. 147-155.
* 1 MW century (MW-c) is equivalent to 1000 kW produced continuously for 100 years.
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Figure 2
Cross Section of the Earth
Mid-Atlantic Ridge
Trench
SOURCE: Burke, K.C. and J.T. Wilson. 1976, pp. 46-57.
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How
Geothermal
Resources
Are Created
Current geologic theory purports that a cross-sectional diagram of the earth
(Figure 2) would reveal a core of heavy metals such as nickel, iron, and cobalt, sur-
rounded by zones of molten material, cooler near the surface than near the core.
Between the outer core and the surface of the earth lies the mantle, a thick zone of
molten rock (called magma). Above this is a relatively thin, cool layer, which
extends to just below the earth's crust.
The areas of the earth close to the surface are believed to consist of two
layers: the "lithosphere,"or outer layer, which is relatively cold and rigid; and the
"asthenosphere," which is both very hot and capable of being deformed slowly.
The asthenosphere, hence, is not liquid, but a solid that flows under stress, like
the ice of a glacier. Temperatures in the astbenosphere range from 650°C
f!200°F), the melting point of rock, to 1200°C (2142°F). This heat is radiated, or
conducted, outward to the surf ace.
Under certain geologic conditions, deposits of magma from the asthen-
osphere are found quite close to the earth's crust. These conditions result from
actions within the earth's interior that are often attributed to "plate tectonics,"a
recently developed theory that provides a unifying framework to explain events
such as earthquakes, mountain-building, and volcanoes.
Briefly, the theory states that the lithosphere is broken into about a dozen
plates in which the continents are anchored. These plates separate from one
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8
another at the crests of mid-ocean ridges, where undersea volcanoes add new
material and push them apart (Figure 3). The opposite process—the convergence
and overlap of tithospheric plates—frequently occurs at the edges of continents
(Figure 4). In these regions, called subduction zones, one plate plunges under
another, and its leading edge is reabsorbed into the mantle. The fractional heat
and pressure created by this movement can cause earthquakes, volcanoes, and the
building of mountain ranges such as the Andes in South America. Although not
yet thoroughly understood, the movement of the plate is thought to be a result of
"convection currents" in the mantle—roughly circular movements of hot earth
materials that rise from the depths and thus bring their heat close to the surface.
Figure 3
Divergent Plate Boundary
Inactive volcano
Ocean trench
Active volcano
Ocaanic crust
Mid-Oceanic Rift
Direction of plate movement
SOURCE: Geothermai Magazine, February 1975
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The location of geothermal resources is clearly controlled by the mechanics
of beat transfer deep within the earth and by plate movement. As shown in
Figure 5, many geotbermal areas, including The Geysers, are located near the
margins of the major lithospheric plates, Hotter-then-normal areas andvolcanoes
located in the middle of the plates have recently been attributed to the presence at
depths of "plumes"—rising, columnar currents of hot material. The plumes heat
surrounding material and produce magma near the surface.
Improved knowledge of the history and mechanics of these processes could
eventually enable geologists to predict the locations of commercially viable geo-
tbermal resources.
Figure 4
Convergent Plate Boundary
Oceanic crust
Ocean trench
Volcanoes
Continental crust
Mid-Oceanic Ridge
SOURCE: Geothfrtral Magazine, February 1976.
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10
Figure 5
Relationship of Major Geothermal Systems and Boundaries of Continental Plates
HOT SPOTS
I ZONE
xljUU.MID-OCEANIC RIFT
TRANSFORM FAULTS
• Philippine Plate
- Indo-Australian Plate
- Eurasian Plate
- Arabian Plate
- Somali Plate
-African Plate
- Antarctic Plate
- American Plate
- Caribbean Plate
- Nazca Plate
- Cocos Plate
-Pacific Plate
1
4,000
SOURCE: Kruger, P. and C, Otte, 1973, p. 71.
miles
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1. Hydrothermal
Convection
Systems
Subsurface reservoirs of steam or hot
water, which may display such surface
characteristics as boiling springs,
sulfurous mud flats, and steam spouts,
are categorized as hydrothermal convec-
tion systems. These systems are created
by the concurrence of several natural
geologic configurations (see Figure 6).
The creation of a hydrothermal convec-
tion system begins with a source of heat,
usually molten rock or magma, that lies
relatively close to the earth's surface
(usually at depths of 2 to 8 km). Over-
lying this magmatic deposit is a per-
meable rock formation containing water,
which expands and rises upward as it is
heated by the molten rock below. Above
the permeable rock is a layer of
impermeable rock, which traps the
superheated water. If this layer contains
cracks or fissures through which fluid
can rise, the fluid will emerge on the
earth's surface either as steam (a vapor-
dominated system) or hot water (a
liquid-dominated system).*
Hydrothermal convection systems are
usually associated with tectonic plate
boundaries and volcanic activity. (The
locations, by state, of known
hydrothermal convection systems are
shown in Figure 7.)
* The structure of a hydrotfeermal convection reservoir varies
depending upon whether it is Ikruid-dorninjtedor vapor-dominated;
however, rtw dttiercnces between the two are not fully understood. It
appears that the porosity of the rocks, the We u which the reservoir
is "rechvged" by water or steam ccndrnsate, and the geophysical
fetnires of the reservoir (whether it u • "flat "horizontal area, on
deep "columnar'' area) influence whether the liquid vaporizes to dry
steam at remains in a super-heated liquid state as it rises.
11
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12
Hydrothermal Convection Systems
Figure 6
Structure of a Typical Hydrothermal Convection Reservoir
10°C at
surface
Based on 1975 USGS calculations and
their reasonably cautious assumptions
about the physical recoverability of known
—but not yet developed—resources,
hydrothermal convection systems are
expected to "have an estimated electrical
production potential of 8,000 megawatt
century (MW-c) or 26,000 MW for 30
years."* [4]
However, only about half of the
production from identified systems is
expected to be from reserves, recoverable
with present prices and technology; the
rest is calculated from marginal and
submarginal resources.' * [5] Of these,
95 percent are from liquid-dominated
and 5 percent from vapor-dominated
systems. The USGS estimates that five
times as much energy is available in
undiscovered systems, with "a
considerable fraction" recoverable at
present prices and technology. Resources
having intermediate temperatures which
may be used for nonelectric purposes are
estimated at 2.87 x 1031 calories. [6]
The calculations are given in Table 3.
Table 4 lists the power generating
capacities of the major hydrothermal
convection systems operating in the
world as of 1972.
SOURCE: Austin. A.L, 1974, p. 15,
* Approiimately 1,000 MW (the c«p«ri (wpulnjon of onr millim
•• Afar^M/is defined Ivy USCS Bbnwwn 2 ind} limn the cost
at ilunuiivn. SHbmergtiul i^ defined is greater th*A 3 rimes tht coat
ofitternttivn.
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Hydrothermal Convection Systems
13
Figure 7
Locations of Known Major Hydrothermal Convection Systems
VAPOR-DOMINATED
The Geysers
LIQUID-DOMINATED
Rafi River
Cove Fort-Sulphurdale
Roosevelt
Valles Caldera
Long Valley
Coso Hoi Springs
Salton Sea
Niland
Heber
Brawley
East Mesa
SOURCE: Smith, R.L. and H.R. Shaw, 1975. pp. 68-72.
i
3QO
=3
miles
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14
Hydrothermal Convection Systems
Table 3
USGS Estimates8 of the Potential Energy Assumed Recoverable
from Hydrothermal Convection Systems with Current and Near-Current Technologies
Heat in Heat at
Ground Wellhead
1018caloriesb 1018 calories6
High-temperature systems ( >1 50°
Identified resources
Reserves
Marginal resources
Submargina! resources'
Undiscovered resourcesa
Intermediate-temperature systems
Identified resources
Undiscovered resources
Total
Conversion Beneficial Electrical
Efficiency Heatd Energy
1018 calories MW-century
MWfor
30 Years8
C; for generation of electricity)
257
1,200
(90° -150° C;
345
1,035
2,837
64
300
mainly non-electrical
86
260
710
0.08-0.2
0.08-0.2
uses)
0.24 20.7
0.24 62.1
82.8
3,500
3,500
>1 ,000
38,000
46,000
1 1 ,700
1 1 ,700
>3,300
1 26,700
153,400
SOURCE: White, D.E. and D.L. Williams, 1975, p. 150.
a. Estimates exclude national parks.
b. 10,18 calories is equivalent to heat raised by the combustion of 690 million barrels of oil or 154 million short tons of coal.
c. Assumed recovery factor is 0.25 for all convective resources.
d. Beneficial heat is defined to be thermal energy applied directly to its intended thermal (non-electrical) use. 1CT° cal of beneficial
heat, if supplied by electrical energy, would require at least 4.400 MW for 30 years; however, a user of this geothermal energy
must be located or must relocate close to the potential supply. Insufficient data is available to predict demand or to subdivide
into reserves, paramarginal, and submarginal resources.
e. Assumes that each MW-c of electricity can be produced at a rate of 3.33 MW for 30 years.
f. Small because systems with temperatures below 150° C have been excluded.
g. Perhaps as much as 60 percent will be reserves and marginal resources; costs of discovery and development are more
speculative than for identified resources.
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Hydrothermal Convection Systems
15
Vapor-Dominated Systems
These geologically complex dry steam
systems are characterized by the high
temperatures of the steam (240°C or
464°F) and the high pressures and
volumes at which the steam is vented
(35 kg/cm1). [7] Since the steam is
usually of high quality—that is, it
contains few particulates or other
substances that must be extracted before
use—it can drive conventional steam
turbines to generate electricity.
To date, only three vapor-dominated
systems have been identified in the
United States: The Geysers in Sonoma
County, California; the Mud Volcano
system in Yellowstone National Park,
Wyoming (Old Faithful); and a likely,
although not yet confirmed, system in
Mt. Lassen National Park, California.
Only one of these systems, The
Geysers, has been developed
commercially* (See insert for description
of "The Geysers Dry-Steam Field.")
Pacific Gas & Electric Company (PG&E)
presently is generating about 502 MWe
from this system, which is capable of
supplying electricity to a city with a
population of 500,000—equivalent to 74
percent of the electricity currently
demanded by San Francisco.
Thus, prospects for additional
electricity generated from vapor-
dominated systems appear to be limited
to the expansion of presently known
steam fields. Neither the technology nor
the requisite geophysical information
exists to predict and locate new vapor-
Table 4
World Geothermal Power-Generating Capacity
1972
MWe
Country
Italy
United States
New Zealand
Japan
Mexico
Soviet Union
Iceland
Total
Field
Larderello
Monte Amiata
The Geysers
Wairakei
Kawerau
Matsukawa
Otake
Pathe
Cerro Prieto
Pauzhetsk
Paratunka
Namafjall
Under
Operating Construction
358.6
25.5
302.0 110.0
160,0
10,0
20.0
13.0
3.5
75.0
5.0
0.7
2.5
900.8 185.0
Vapor-
dominated
Systems
358.6
25.5
412.0
20.0
816.1
Hot-water
Systems
760.0
10.0
13.0
3.5
75.0
5.0
0.7
2.5
269.7
SOURCE: Kruger, p. and C. Otte, 1973, p. 71.
* Three other commercial plants ire operating in Lardarello, Italy,
and Onkaind Miuukiwi, Jipan.
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16
Hydrothermal Convection Systems
dominated fields that do not have surface
discharges. However, the potential for
expansion at known sites is good. Pacific
Gas & Electric expects to produce 1800
MWe from The Geysers by 1985,
nearly a fourfold increase over the 1976
capacity. [8]
Once located, a vapor-dominated field
is explored to determine its chemical and
thermal characteristics. The processes
used are based on oil and gas exploration
and development techniques (see insert,
"How Geothermal Resources Are
Developed"). Actual utilization of the
geothermal energy once the steam-
bearing formation is penetrated involves
the application of an existing
technology: the steam turbine. Lines are
attached at the well head to transport
the steam to a centrifugal separator,
where dust and corrosive particles are
removed. The treated steam is then used
to drive the turbine, which generates
electricity (see Figure 8). Each of the
generating units now being installed at
The Geysers requires a throughput of 1
million Ibs/hr. of superheated steam,
from which 55 MW of electricity is
produced. [9]
Liquid-Dominated Systems
The chemical and thermal characteristics
of liquid-dominated or "hot water"
systems, which are far more common
than vapor-dominated, vary greatly by
site. Temperatures range from 90°C to
250°C (194°F to 662°F), with an
average of 150°C (302°F)—almost
100°C less than the average temperature
of vapor-dominated systems. [70] The
amount of total dissolved solids also
varies considerably. Extremes of 26 to
35 percent dissolved salts have been
found in the geothermal wells drilled
near the Salton Sea in California.
Hot-water systems are usually grouped
into one of three categories, based on
the temperature of their natural working
fluid:
High-temperature systems: greater than 130°C (302°F)
Intermediate-temperature systems: 90°Cto 150°C
(19-ST to 302°F)
Low-temperature systems: less than 900C(194°F)
High-temperature systems may be
further divided by the characteristics that
affect their performance, such as the
level of salinity, dominant chemical con-
stituents, rate of rechargeability,
structural and stratigraphic
environments, and presence or absence
of permeable reservoirs and insulating
cap rocks. These characteristics are
important to determine the commercial
viability of a hot-water system, either for
electricity or for other purposes.
Hundreds of hot water wells have
been drilled throughout the world, and
nine electric generating plants have been
developed based on high-temperature
hot-water systems. Most of these plants
are located in New Zealand, Japan, and
Mexico.
In the United States, a total of 63
high- and medium-temperature hot-
water systems have been identified by
USGS. [11] Federal policy initiatives and
research funds are being focused on
developing these systems by 1985. Hot
water wells are attractive to the electric
utility industry because knowledge about
their development and use is relatively
advanced and because most of the re-
quired technology, described below, can
be provided in the near future.
Significant discoveries of high-
temperature systems have been made at
half a dozen sites in the western part of
the United States. Most attention has
been given to sites in the Imperial Valley
of California, where a very large
reservoir appears to be located. There
the U.S. Bureau of Reclamation and the
Office of Saline Water are conducting a
pilot project to test the feasibility of
producing both electricity and
desalinized water. Nearby, at Niland, an
experimental plant is being developed
and is testing waste reinjection
techniques. Closer to the Mexican
border, at Heber, California, is the likely
-------
Hydrothermal Convection Systems
17
Figure 8 Figure 9
Dry-steam System (The Geysers, U.S.A.) Flashed-steam System
Figure 10
Binary-cycle System
1. Turbine
2. Generator
3. Cooling tower
Non-condensables 1. Separator
to atmosphere 2. Turbine
3, Generator
4, Condenser
Steam to
atmosphere
:-1b
=-7
**
%M
.a'^-^ -. ^ - .^i. *Cl^J"JB*J^.'^*^^ ^^. KJ^J. ^ *-.-" eife
1. Heat Exchange
2. Turbine
3. Generator
4. Condenser
SOURCE: Comptroller General of the United
States, 1975, p. 22.
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18
Hydrotherrnal Convection Systems
site of the first commercial liquid-
dominated electric generating plant in
the United States. Although, currently,
the combined power of these
experimental systems is small, it is
expected to grow significantly in the
next decade.
Moderate and low-temperature
systems are also being used around the
world for nonelectric needs such as space
heating, air conditioning, and industrial
drying; particularly in Iceland, Japan,
the Soviet Union, Italy, and the United
States. In the United States, the best
known project is at Klamath Falls,
Oregon, where 350 wells supply heat for
space heating. Elsewhere in Oregon—as
well as at Calistoga and Desert Hot
Springs, California; Boise, Idaho; and
other localities in the West—geothermal
waters are used to heat greenhouses,
baths and resorts, farm buildings, and
schools. In addition, 19 research
institutions representing private
industry, universities, and state and
local governments recently were awarded
contracts by the Energy Research and
Development Administration (ERDA) to
conduct demonstrations of the feasibility
of using geothermal heat for nonelectric
purposes.
The same exploration and development
techniques used for vapor dominated
systems are applicable to liquid dominated
systems. However, the production
technology differs significantly. Because of
the temperature requirements for
generating electricity from convection
systems, only the high-temperature,
moderate- or high-salinity system is being
developed extensively. Two processes, the
flashed steam and the binary cycle (or
heat exchange), currently are used. A
third system, the total'flowprocess, is
still in the design and testing stage, but
holds promise for greater efficiency than
the other two.
FLASHED STEAM. This technology
(see Figure 9) takes advantage of a
process that occurs naturally in some
hot-water systems; that is, the hot fluid
in a reservoir is usually under much
higher pressure below the surface than
at ground level. As the water is
withdrawn and nears the surface, the
pressure decreases, causing a portion of
the fluid (approximately 20 percent in
high-temperature fields) to boil and
"flash" into steam upon reaching the
surface. The steam is captured, passed
through separators to remove certain
particulates, and then used to drive
turbines in an electric power plant. Any
remaining water and condensed steam
are disposed of through reinjection or
surface drainage; noncondensables are
vented to the air. The energy efficiency
of this system is low; only 2 to 5
percent of the original stored heat of the
hot-water system is actually converted to
usable energy. This conversion efficiency
drops to 1 percent if the steam must be
passed through a separator.
Flashed steam plants currently are
operating in eight different locations in
the world. However, uncertainties about
their efficiency and environmental safety
have kept the process from being
introduced commercially to the United
States. The current best estimate for the
utilization of flashed steam is the early
1980s. [12]
BINARY CYCLE (or heat exchange
process). In this process, the hot water
withdrawn from the reservoir is used to
heat a second fluid (freon or isobutane)
having a lower boiling point (see Figure
10). The vapor thus generated by boiling
the second fluid is used to drive the
turbine. Once used, the vapor is
condensed and recirculated through the
heat exchanger in a closed system,
where it may be heated and used again.
This system appears to be the preferred
method for developing high-temperature,
high-salinity reservoirs.
A 3.8 MWe binary plant currently is
in use in Japan, and the Soviet Union is
reported to be using a .75 MWe binary
plant. Pilot plants in Long Valley and
Imperial Valley, California are being
constructed to test the applicability of
this process to high-temperature systems
of both high and low salinity.
TOTAL FLOW. The least developed of
the three liquid-dominated systems, total
flow utilizes the heat and natural
pressure of both the steam and water in
one generating process that combines a
steam turbine and waterwheel. Two
types of generators are being developed
in the United States: the impulse
turbine and the helical rotary screw
expander.
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19
The Geysers
Dry-Steam
Field
The Geysers geotbermalfield lies 75 miles north of San Francisco in the hilly and
rugged Mayacmas Mountains (see Figure 11). In this sparsely populated area, the
land is used, where at all, for cattle-grazing or hunting. In the past, however,
Lake County had a more colorful atmosphere. Resort hotels were built in the late
19th century offering the attraction of "healthful and refreshing warm baths"
piped straight from the bubbling hot springs which fed Big Sulphur Creek. In
1880, mercury was discovered and mines opened. They continued to operate
until the 1950s. There never were any real geysers in the development area, cer-
tainly nothing as spectacular as "Old Faithful" in Yellowstone Park; however,
numerous steam vents and hot springs testified to the presence of heat reservoirs.
The odor of hydrogen sulfide inspired the early explorers to name the stream
which flowed through the area "Big Sulphur Creek."
In the 1920s, entrepreneurs drilled in these hot springs and tried, unsuccess-
fully, to find a market for the electricity they thought they could produce. Then,
in the middle 1950s, Magma Power Company and Thermal Power Company
began drilling and eventually interested Pacific Gas and Electric (PG&E) in the
project. In 1960, anil MWe power plant built by PG&E began operation. Today,
Union Oil is in partnership with the other developers and owns 50 percent of the
field; Magma and Thermal own 25percent each. Other companies are exploring
the surrounding land.
At present PG&E is the only utility generating electricity at The Geysers.
Recently, however, a group of eight northern California cities, members of the
Northern California Power Agency, announced plans to undertake a develop-
ment program to ultimately produce 130-170 MWe of generating capacity in the
Lake County portion of The Geysers.
The Geysers land is owned by federal, state, and local interests. Leaseholds
have been acquired by firms that wish to search for and develop geotbermal
steam. These firms generally own easements and limited surf ace rights sufficient
to developgeothermal resources.
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20 Introduction
Of The Geysers' total original 163,428 acres, 11,450 were federally owned.
The Known Geothcrmal Resource Area (KGRA) has been analyzed several
times. In January 1974, a competitive lease sale was held for 8,755 acres and bids
totalling $5,526,827 were offered. Leases on these lands were issued in July 1974.
Pursuant to the Stock Raising Homestead Act of 1916, the federal government
holds mineral rights on an additional 14,000 acres within The Geysers. However,
whether these mineral rights extend to geothermal steam is not legally clear. The
federal government also owns lands adjacent to The Geysers that may be
valuable for geothermal steam production.
To date, a total of more than 100 wells have been drilled at The Geysers and
all but about W have produced steam. While the steam originally was found at
depths of less than 1,000 feet, the increased need for steam to generate power has
necessitated drilling to greater depths. Maximum well depth is now over 9,000
feet; average production depth is 6,000-7,000feet,
Generating units in use at The Geysers are relatively small; an average site
provides 110 MWe. About 15 to 20 wells are required to support a 110 MWe
generating unit. As individual well pressure decreases, new wells must he drilled
to maintain an adequate steam supply to the turbines. The average lifetime of a
well is expected to be 15 years.
Seventy-five wells now produce steam for 11 turbines, producing more than
500 MWe. The wells average 150,000 Ibsper hour of 350°F steam at 100psi. The
field is believed to be as extensive as 386 square miles (1000 km3) and capable of
supplying as much as 10 times the current generating capacity. If this scale of
development comes about, approximately 45 generating units will be
functioning, supplied by 6 75 geothermal wells.
Figure 11 (opposite):
The Geysers Dry-steam Field
SOURCE Pacific Gas & Electric Co.
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-------
22
Figure 12
Location of Hydrothermal Convection Resources in the Imperial Valley
SOURCE: Dutcher, L.C..W.F. Hardt, and W.R. Movie, Jr.,
1972, p. 3.
Palm Springs
Salton Sea
Niland
Bfawley
El Centre
Yuma
Mexicali
Cerro Pneto
Colorado River
Gulf of California
IMPERIAL VALLEY
Geo thermal
Resource Area
i
50
miles
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23
The Imperial
Valley:
The Next
Generation
of Development
The Imperial Valley holds the most promise as the site of the next major
development of geothermal energy in the United States. It is part of a large
structural basin that extends from the Coachella Valley to the Gulf of
California, and south to the Mexicali basin in Mexico. The entire depression is
called the Salton Trough and is filled with clay, silt, and sand deposited by the
Colorado River as part of the delta created over many hundreds of thousands of
years (see Figure 12).
This trough contains a thick layer of water-saturated sediment (as much as
20,000 feet), which in turn overlies a heat flow anomaly. Here heat flows range
from 4 to 10 times the average gradient of the earth. The combination of the ex-
tensive body of porous, water-bearing rock and the high heat flows have created
a series of related hydrothermal convection reservoirs, causing the Imperial
Valley to be regarded as the first opportunity for the commercial development
of a hot-water system.
The potential of the geothermal resource has been estimated at 10 to 15
million acre-feet of geothermal brine per year, and 20,000 to 30,000 MW of
electric power (see Figure 13).
In addition, great interest has arisen in the large amount of underground
water in this otherwise arid region, estimated at LI billion acre-feet, with 100
million acre-feet at temperatures below 1QO°C. Studies are under way to deter-
mine the economic feasibility and environmental effects of removing some
water for irrigation.
-------
24
Deep wells have been drilled throughout the area and several have been
the focus of extensive testing and development. A major steam field at Cerro
Prieto, Mexico, has been tapped; a 75 MWe plant has been built and is now in
operation, Niland, Heber, and Brawley, California are prime sites for the
possible production of electricity. At Niland, near the Salton Sea, the
Geothermal Test Facility of the San Diego Gas and Electric Company and
ERDA is located. This facility, a 10 MWe binary fluid experimental power plant
using highly saline brines, is complete and undergoing prestart-up tests;
however, the high salinity of the geothermal fluid at this site may preclude its
commercial development. Such uncertainties make it difficult to predict the
rate of future development in the Imperial Valley. However, at Heber, the
Standard Oil Company plans to develop a 50 MWe plant that could be in
operation as early as 1978. It would be the first commercial hot-water plant in
the U.S.
A large project to establish environmental baseline information on the
entire Imperial Valley has also begun. The Lawrence Livermore Laboratory
has been appointed by ERDA to lead this long-term project, which includes
obtaining information on the impacts of water withdrawal on subsidence and
induced seismicity; effects on the water supply and quality of the area; air
quality problems from the highly-mineralized reservoirs; and effects on the
fragile desert ecosystem of extensive development. Information is being
obtained on virtually every aspect of geothermal energy through field
monitoring and model development—on the hydrology, geology, ambient air
conditions, vegetation and wildlife, seismicity, health effects, and possible
socioeconomic impacts,
In addition to ERDA, EPA, the U.S. Bureau of Reclamation, and the U.S.
Geological Survey are also conducting significant research in the Imperial
Valley. When completed, an "integrated assessment" will be made of these
studies and the relevant research of universities and other federal, state, and
county programs. The combined information will be used to develop a strategy
to protect the area environmentally before it is developed extensively.
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25
Figure 13
Estimated Generating Capacity of Significant Geothermal Reserves in the West
Water-Dominated
t
Raft River, ID
50-100 MWe
Cove Fort &
Sulpnurdale, UT
150-250 MWe
East Mesa, CA
TOO-150 MWe
] Heber, CA
| 150-250 MWe
I Roosevelt, UT
150-250 MWe
, Coso Hot Springs, CA
'50-100 MWe
| Long Valley, CA
J110-200 MWe
I Valles Caldera, NM
150-250 MWe
| Brawley, CA
| 150-200 MWe
iNilartd, CA
160-210 MWe
Vapor-Dominated
The Geysers, CA
1800-2130 MWe
SOURCE: LaMori, P.N.. 1976, p. 112.
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26
2. Hot
Igneous
Systems
The second major type of geothermal
resource is hot igneous, which includes
both magma (molten rock occurring
near the surface of the earth), and hot
dry rock (the solidified margins around
the deposits of magma and the overlying
roof rock). Although hydrothermal
convection systems are also heated by
magmatic deposits, the rock formations
in hot igneous systems are not
sufficiently permeable to trap water.
Thus, heat is transferred through a solid
body rather than through a liquid.
According to current geologic theory,
volcanic rock of near-surface origin is
silicic, rather than basaltic. Thus,
inactive volcanic sites containing silicic
rock are believed to signal the probable
location of magmatic deposits at depths
of 3 km to 10 km. On the basis of
existing geological and geophysical data,
USGS has listed 17 inferred molten
bodies of silicic and intermediate
composition in the coterminous United
States, 24 bodies of mainly intermediate
composition in Alaska, and 1 basaltic
body in Hawaii. The total estimated heat
energy in these systems is at least
25,000 x 10" calories, 30 or more
times the estimated heat content of all
hydrothermal systems in the United
States at depths less than 3 km. [13]
USGS has further estimated that about
half of this heat is in molten or partly
molten bodies at temperatures between
650°C and 1200°C. USGS concludes,
' 'the large inferred volumes and cross-
sectional areas of a number of these
bodies make them suitable targets for
geophysical exploration." [14] (Figure
14 shows the areas identified by the
USGS.)
-------
Hot Igneous Systems
27
Figure 14
Areas of Identified Volcanic Systems
WASHINGTON
Mt. Baker
Glacier Peak
Mt. Rainier
Ml. Adams
Ml St Helens
OREGON
Ml Hood
Mt Jefferson Domes
Black Butte
Melvin-Three—'
Creeks Buttes
South Sister
Newberry
Odell Butte
Cappy-Burn Butte Area
China Hat & East Butte
Rustler Peak
Mt. Mclaughlin
CALIFORNIA
Shasta
Medicine Lake
Clear Lake
Sutler Buttes
Lassen Peak
Morgan Mtn. Domes
Warner Mis.
Jackson Buttes
Bndgeport-Brodie
Volcanic Complex
Paoha Island.
Mono Lake
Mono Domes
Long Valley
Big Pine
Coso Mts
Olancha Domes
Lava Mts.
Salton Sea
SOURCE: Smith, R.L. and H.R, Shaw, 1975, pp. 68-72.
OREGON
Crater Lake
Quartz Mountain
Glass Buttes
Cougar Mtn.
Harney-lvtalheur
Cougar Peak Area
WYOMING
Yellowstone Caldera
System
IDAHO
Island Park •
Huckleberry Ridge
System
Big Southern Butte
Blackfoot Domes
UTAH
Topaz Mt.
Smelter Knoll
White Mt. Rhyolite
Cove Creek Domes
Mineral Mts.
Tushar Mts.
NEW MEXICO
o. Agua Domes
alles Caldera
t. Taylor
ARIZONA
•San Francisco Mts.
Kendrick Peak
Sitgreaves Peak
Bill Williams Mtn
NEVADA
Steamboat Springs
Silver Peak
miles
-------
28
Hot Igneous Systems
Figure 15
Technique for Developing Hot Dry Rock
SOURCE: Smith. M.C., 1974, p. 33.
Magma
The recovery of geothermal energy
directly from magma is not yet feasible.
Although some information has been
developed on the location, temperature
ranges and depths of magmatic deposits,
many characteristics of the resource
remain largely unknown and the
technology for converting its energy to
useful forms in commercial quantities is
yet undeveloped.
Work is under way to develop drilling
and extraction equipment and materials
capable of withstanding the very high
temperatures and corrosive properties
encountered in a magmatic system.
Preliminary research into efficient and
durable heat extraction mechanisms also
has begun. Sandia Laboratories is
working on such a process, which would
use a closed system heat-exchange
device. Other techniques under
consideration are aimed at improving the
efficiency ratio of heat extraction. Field
tests at the Hawaiian lava lakes or other
suitable locations are planned.
Hot Dry Rock
The technology required to utilize hot
dry rock is just beginning to be
developed, and until several important
technical problems are resolved,
extraction of the stored heat cannot be
considered feasible. The late 1980s is
thus the earliest date projected for the
utilization of hot dry rock as an energy
source. [15]
Preliminary engineering approaches to
tapping the energy potential are focusing
on the design of a circulatory fluid flow
loop through the rock (see Figure 15).
First, a well would be drilled into the
hot formation; then cold water would be
injected under high pressure to fracture
the formation, and a second well would
be drilled to intersect the fractured
zone.* Finally, cool surface water would
be injected to the first well, passed over
the hot dry rock, and withdrawn
through the second well in the form of
steam or hot water. The heated fluids
generated could then be processed using
either the flashed steam or binary cycle
process.
ERDA recently announced the
successful fracturing of hot dry rock
using this technique at the Jemez
Mountain site being developed by a Los
Alamos Scientific Laboratory team.
However, the commercial applicability of
the system has yet to be proven.
A more exotic method of fracturing
hot dry rock is under study by the
American Oil Shale Corporation and the
Nuclear Regulatory Commission as part
of the Plowshare program, This method
would employ multiple nuclear
explosions to fracture the rock. Some of
the energy from the explosions would be
trapped as heat, and thus be recoverable
for power generation.
No experiments of fracturing hot dry
rock by this method have been
conducted to date; where similar
techniques have been used to stimulate
natural gas wells, little success has been
reported.
• Thermal fracturing may also result from iKc ihemul stresses
induced by the temperature change.
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29
How
Geothermal
Resources
Are Developed
The beat content of the earth cannot be considered to be an exploitable resource
unless it is found in circumscribed areas large enough to justify the costs of ex-
ploration and drilling. Therefore, stored heat must be concentrated in a form
similar to an oil or gas reservoir or a mineral deposit.
Locating a "heat pocket" is the first step in the development of a
geothermal resource. Exporation begins with aerial surveys by small aircraft or
helicopters equipped with modern aerial photographic equipment and
sometimes aeromagnetic or infrared sensing devices useful for mapping surface
heat.
Field measurements are then performed, beginning with regional geologic
and hydro logic surveys, to search for evidence of tectonic activity and seismic
disturbance, determine the distribution and age of young volcanic rocks, and
locate any surface discharges of steam, water, or warm mud. Temperature and
discharge measurements are taken, and a chemical analysis of the fluids is
performed. The water table is measured and evaluated to determine the
presence of water and to locate sources of recharge water. The results of these
measurements are used to predict the geologic and bydrologic conditions likely
to be encountered during drilling. Even vegetation and soil characteristics may
provide an indication of the underlying type and character of a reservoir.
-------
30
Next, geochemical reconnaissance involving the sampling and analysis of
waters and gases from hot springs and fumaroles is conducted to determine
whether the geothermal resource is liquid- or vapor-dominated. Following geo-
chemical analysis, geophysical surveys are conducted to define specific target
areas for drilling. At this point, physical measurements such as temperature,
electrical conductivity, magnetism, and passive seismic recordings are taken.
Seismic-noise detection and microearthquake measurements are especially
useful in detecting reservoirs and developing a regional model of an identified
reservoir. Deep drilling to test the temperature gradient and heat-flow of the
rocks or fluids may also be conducted, usually by drilling to depths of15 to 100
meters.
The final phase ofgethermal exploration is the drilling of exploratory wells
to depths of up to 3 km. Only through such drilling is it possible to determine
the actual characteristics of the reservoir, including its salinity level and type of
fluid, and thereby evaluate its potential as an energy resource.
Exploratory drilling is accomplished through the use of a rotating bit
attached to the surface with a length of pipe called a "drill string." Either an air
compressor or water is used for drilling. A "reserve pit" approximately 1,000
feet square and 8 feet deep is dug to store waste fluids flushed up during
drilling. Cuttings from the drilling operations are removed from the well
through the use of a fluid called "drilling mud," which is pumped down through
the drill pipe and then circulated back to the surface in the space between the
pipe and the well wall. In addition to removing cuttings, the drilling mud
maintains the hydrostatic pressure in the hole, thereby preventing a "blow-
out"—the unconstrained flow of liquids or gases from formation zones
penetrated as the hole is drilled. Once the drilling reaches the resource, tests are
conducted to determine flow rate and reservoir size.
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31
Some Problems
Related to
Development
Technology
Much of the technology needed to determine the location, magnitude, and
geologic characteristics of geothermal resources is presently in some stage of
research, design, or development. Therefore, only limited information is avail-
able, and that information relates only to known geothermal resources, most of
which have visible surface discharges. Geologists currently are working to
design techniques for locating underground geothermal resources, predicting
their chemical characteristics, modeling their hydro logic and geophysical
structures, and estimating their magnitude. In addition to locating and
evaluating the resource, drilling and extracting steam or hot water pose
difficult technological problems.
Drilling
Drilling rigs and surface pumps common to the petroleum industry can be used
in geothermal drilling. However, much of the equipment borrowed from the oil
and gas industry is inadequate. A list of some of the inadequacies follows.
Drilling bits. The hard, abrasive rock surrounding geothermal resources is dif-
ficult to penetrate even with the best available bits, which are made of tungsten
carbide. The composition of the rock slows drilling and causes excessive wear to
bits, requiring their frequent replacement.
Drilling mud. Vital to the drilling process, this fluid lubricates and cools the
drill string and bits, and is also used to remove cuttings as the well is drilled.
However, drilling mud deteriorates rapidly at temperatures above 177°C
(351°FJ, slowing the circulation rate of the cuttings being removed. Drilling
fluids resistant to the high temperatures found in geothermal reservoirs have
not yet been perfected.
-------
32
Logging instruments. These monitoring instruments are used to record the
temperature, flow rate, pressure, and physical characteristics of the geothermal
resource during drilling. Currently available devices and instruments are
accurate only to temperatures near 180°C, Logging and sampling in these high
temperatures cause great problems. The requisite technology is lacking but is
being studied.
General drilling equipment. Many of the basic parts of the equipment used in
drilling (bits, casing, piping) are subject to breakdown, corrosion, and scaling
caused by the high temperatures, high pressures, and varying salinities found in
geothermal resources. Improved cementing compounds and elastomers (rubber-
based substances) are being developed to help alleviate this problem. The high
rate of precipitation of solids in drill pipes interferes with drilling and requires
the pipes to be cleaned and replaced frequently.
Research and development of improved materials and methods for addressing
these technology-related drilling problems is under way. Improved drilling bits
and fluids are expected to be available by the late 1970s, and most of the other
technological problems should be resolved by the early 1980s.
Extraction
Once the geothermal resource has been tapped through drilling, the stored heat
and energy can be extracted. However, much of the equipment necessary to
extract that energy is presently in the design and demonstration stage. The
equipment under development includes:
Downhole pumps. These pumps are placed within the well during the binary
cycle conversion process to increase the rate of fluid extraction and maintain the
geothermal fluid underpressure.
Heat exchangers. Heat devices are used with high- and medium-temperature
hot-water systems to transfer the heat in the geothermal fluid to a second fluid
having a lower boiling point, thereby producing steam.
Reinjection equipment. This equipment is used to reinject the used geothermal
fluid into the ground to prevent land subsidence and minimize the need for
waste disposal.
The essential features of all the equipment being developed are resistance to
corrosion and scaling, and the ability to function effectively under a wide range
of temperature and salinity.
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33
3. Conduction-
Dominated
Systems
In hydrothermal convection systems,
heat is transferred from the earth's
interior to its surface by a circulating
fluid; in hot igneous systems, heat is
transferred through the near-surface
intrusion of magma. However, most of
the earth's heat is transferred from the
interior towards the surface through
solid rock—a process called conduction.
Where conduction is dominant, a
temperature gradient exists within the
earth such that temperatures increase
proportionally with depth from the
surface at a constant rate. This
temperature gradient, or rate of heat
flow, may be increased or decreased by
the presence of fluids or low-conductivity
rocks. The heat content is unrelated to
plate tectonics. Both of the geothermal
resources in this category are
conduction-dominated systems, referred
to as the normal gradient and
geopressured geothermal reservoirs.
Normal Gradient
The rate at which heat is conducted
through rock to the surface of the earth
is expressed in beat flow units.
Worldwide, the average heat flow rate is
1.5 heat flow units. [16] A range of heat
flow between 0.8 and 2.0 heat flow units
is considered to be the normal* gradient.
At this rate, temperatures of 75°C exist
at a depth of 3 km. In some areas,
temperatures at 3 km have been above
75°C (at least one region, near Clear
* Normal is defined u th» orthogonal, at perpendicular, rate of
temperature change.
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34
Conduction-Dominated Systems
Lake, California, is believed to be as
high as 100°C/km), but these are
anomalies.
Areas of normal gradient are
postulated to be sources of usable energy
where only low-temperature heat is
required. However, the extraction of
energy from the normal gradient is not
expected to be technically feasible for
many decades. Rock that is permeable
and thus capable of ' 'holding'' water at
these depths must be located. Drilling
costs are high, and the technology for
drilling where temperatures are high is
far from perfected. In addition, some
type of heat exchange device that uses a
transfer medium such as water must be
employed. It is, therefore, highly
unlikely that the normal gradient will be
selected for development while more
commercially feasible alternatives exist.
Geopressured Geothermal
Reservoirs
Like the normal gradient, geopressured
geothermal reservoir is conduction-
dominated; that is, temperatures of the
resource increase with depth at a
constant, normal rate. However, a
geopressured reservoir differs
significantly from a normal gradient in
being a formation of methane-saturated
water trapped in layers of sand and shale
beneath impermeable rock. The weight
of the sediment creates extremely high
water temperatures and high pressures.
Geopressured zones are known to
exist beneath an area of more than
278,500 km2 extending from the Rio
Grande in Texas to the mouth of the
Peal River in Louisiana, into the Gulf
Coast and out to the Continental Shelf
(see Figure 16). An additional inland
area of 52,000 km2 has also been
identified. Based on oil drilling (more
than 300,000 wells have been drilled
along the Gulf Coast) and inland drilling
data, this area may offer significant
potential for three types of energy;
thermal—from the water, which has
temperatures from 160°C to 200°C;
mechanical or hydraulic—from the high
pressures present in the formation; and
fuel—from the water, which is believed
to contain a high amount of dissolved
natural gas (methane). The presence of
methane deposits makes the zone
especially promising.
Based on a cautious drilling program
and stringent environmental standards,
the USGS has estimated that the
combined thermal equivalent of the
energy present in the onshore areas is
30,900 MW produced continuously for
30 years. [18]
While there is evidence of a large
potential resource, a great many
questions remain unanswered. Estimates
of the porosity of the rock and the
extent of the methane deposits are only
preliminary and may be proved to be
grossly overstated. A reliable assessment
of the resource has yet to be developed.
ERDA recently initiated exploratory
assessments and is presently developing
baseline environmental information. If
the initial test results indicate that
development is feasible, a resource could
be developed during the 1980s and
1990s. However, drilling at the
necessary depths may be economically
infeasible. In addition, the possibility of
subsidence (collapse of the surface) and
the environmental effects of drilling pose
serious potential hazards.
-------
Conduction-Dominated Systems
35
Figure 16
Locations of Known Geopressured Zones Having Geothermal Resources
Landward Boundary
of Miocene Deposits
Edge of
Continental Shelf
Gulf of Mexico
Depth Below Sea Level in Feet
more than 5.000
more than 10,000
1
I—
more than
i i
15.000
4C
>0
miles
SOURCE: Comptroller General of the United States, 1975. p. 14.
-------
Section I
References
Re/erto bibliography at end of book for complete citation,
Chapter 1 1 Diment, W. H.,etal., 1976,p.84ff.
2 White, D. E. and D. L. Williams, 1975, p. 147.
3 Ibid., p. 155.
4 LaMori, PhillipN., 1976, p. 105.
5 White, D.E. and D.L.Williams, 1975, p. 153.
6 Ibid.,?. 153.
7 Kruger, Paul and CarelOtte, 1973, p. 83.
8 Budd,C.F.,l973,p. 130.
9 «*/.,p.l30.
10 Keener, J.L.,etaL, 1975, p. 52.
11 Budd,C.F.,1973,p. 130.
12 LaMori, Phillip N., 1976, p. 111.
Chapter2 13 Peck, D. L, 1975, p. 122.
14 7M/.,p.l22.
15 LaMori, Phillip N., 1976, p. 114.
Chapter 3 16 White, D.E., 1973, p. 73.
17 Ibid., p. 74.
18 White, D. E. and D. L. Williams, 1975, p. 154.
-------
-------
-------
n
ironment^iiroblems
ia%4-1** i^-f^t-yi ci I HT f^OiOn i iTf^f^^-
-------
40
Overview
The widespread belief that geothermal resources represent a relatively "clean,"
nonpolluting energy source recently has played an important role in
heightening public interest in geothermal development. Although knowledge
of the related environmental impacts is still incomplete, geothermal resources
do appear to offer several significant environmental advantages over alternative
energy sources.
Since geothermal energy must be utilized or converted in the immediate
vicinity of the resource to prevent excessive heat loss, the entire fuel cycle, from
resource extraction to transmission, is located at one site. Unlike fossil fuel or
nuclear power production, in which large land areas are required for processes
such as mining, refining, transportation, fuel processing, and waste disposal,
geothermal energy is not a technology that requires a massive infrastructure of
facilities and equipment and large amounts of input energy. Although
geothermal development necessarily involves some disturbance of the earth's
surface, the effects are not as severe as are those resulting from the surface
mining of coal or uranium. Furthermore, the controversial safety issues that
have been raised about underground coal mining and the consequences of a
major accident during nuclear power production do not arise in connection with
geothermal power production.
Another environmental benefit arises from the fact that those geothermal
power plants that use steam as a working fluid to drive a turbine do not need an
external source of water for cooling purposes, because the condensed steam is
recycled for that purpose. Thus, they do not place additional demands on scarce
water supplies.
-------
Overview 41
In addition to these environmental benefits, the development and applica-
tion of geothermal power would reduce the demand for alternative fuels cur-
rently in critically short supply (specifically, oil, natural gas, and uranium) and
help to reduce the nation's dependence on foreign supplies.
Unfortunately, however, not all the potential environmental effects of geo-
thermal energy are positive. Among the most significant adverse impacts of the
exploration, development, and production of geothermal energy (see Table 5)
are possible land subsidence, seismic activity, air pollution resulting from the
discharge of noncondensable gases such as hydrogen sulfide, high noise levels of
drilling and power plant operation, and mineral or thermal pollution of surface
and ground waters. Other concerns include increased erosion and sedimentation
resulting from site disturbance; possible climatic changes resulting from the
release of heat, water vapor, and carbon dioxide; and disturbance of soils, vege-
tation, and wildlife.
The actual impacts of geothermal development can vary widely—probably
more widely than the impacts associated with fossil or nuclear energy sources.
For example, the chemical constituents of geothermal steam or hot water can
differ significantly from site to site, causing markedly different air and water
pollution emissions from power plants having identical generating capacities.
The potential severity of the environmental impacts associated with geothermal
development depends on several factors:
-------
42
Overview
Table 5
Potential Environmental Impacts of Geothermal Power Production
Impact
Land subsidence
Induced seismic activity
(earthquakes)
Air pollution resulting from
discharge of noncondensable
gases (e.g., hydrogen sulfide,
carbon dioxide)
High noise levels of drilling
and plant operation
Chemical or thermal pollution
of surface and groundwaters
Well blowouts
Increased erosion and sedimen-
tation resulting from site
disturbance
Consumption of water for
cooling purposes
Consumption of land for wells,
power plants, transmission lines
Short-term climatic changes
resulting from release of heated
steam and carbon dioxide
Disturbance of habitat; altera-
tion of ecosystems
Estimate of
Probability
moderate
low
high
high
moderate
low
high
high
high
high
moderate
to high
Technology/
Resource Type
hot-water
all
all except hot-water
binary fluid and
other "closed-cycle"
use of geothermal
fluids
all; worst for
vapor-dominated
all; greatest proba-
bility with hot-water
hot-water; vapor-
dominated
all
hot-water binary
fluid; hot dry rock
all
hot-water; vapor-
dominated
all
Severity of
Consequences
variable— can
be high
high
variable-
depends on
emission
controls
moderate
high
moderate
moderate
high
moderate
low
moderate
to low
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Overview 43
— Type of geothetmal resource being developed
— Chemical constituents of the geothermal fluid (steam or hot water) and sub-
surface rock
— Overall characteristics (geology, hydrology, topography, vegetation) of the
development site, both above and below the ground surface
— Engineering design technologies used to produce energy and control pollu-
tion.
Depending on the site, geothermal power production could result in either
equivalent or substantially lower pollution levels than those produced by a coal-
or oil-fired plant of identical capacity. Thus, generalizations about the magni-
tude and significance of the likely environmental impacts resulting from geo-
thermal development must be based on careful, site-specific analysis that takes
each of these factors into account.
Both the likelihood and potential severity of the possible impacts of geo-
thermal development warrant careful consideration in determining the signif-
icance of any impact. Even if the likelihood that a certain impact will occur is
relatively small, it requires close attention if its consequences are potentially
serious. For example, although at present it is considered unlikely that geo-
thermal development would induce a major earthquake, the extensive damage
that could result from such an event justifies its further investigation.
Because geothermal development has not been widely pursued, both the
likelihood and severity of many impacts are still relatively unknown. Extensive
information is available for only a few sites, such as The Geysers and the
Wairakei plant in New Zealand. Projections of impacts at other locations where
development is planned are still preliminary and highly speculative. Since
intensive research on environmental impacts is only just being initiated, it will
be several years before a detailed understanding of actual impacts is developed.
This chapter describes the major impacts of geothermal resource develop-
ment on various aspects of the environment. In each section, the anticipated
impacts of developing the two most immediately promising types of
hydrothermal convection systems—vapor-dominated and hot-water—are
discussed in detail. Because available information on the other types of geo-
thermal resources is limited, the probable impacts associated with their develop-
ment are noted but not discussed extensively.
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44
4. Land
Use
The development of all types of energy
resources, including geothermal,
necessarily involves the use of land.
However, the nature of the geothermal
resource and the production methods
employed in its development result in far
less extensive land disruption than occurs
with resources that require mining (coal,
uranium), transportation over long
distances (coal, gas, uranium,
petroleum), extensive processing facilities
(coal, petroleum, uranium), fuel storage
areas, or aboveground waste disposal
(coal, gas, petroleum). Unlike these,
geothermal energy is not a technology
that requires a massive infrastructure and
large amounts of input energy. The entire
geothermal energy cycle, from extraction
to ^>e transmission of electricity, occurs
in one location,
The severity of the land disturbance
required for geothermal operations also is
far less than that of other alternatives, in
particular those that require mining.
Restoration of land used for geothermal
development appears to be less expensive
and more likely to succeed than
reclamation of mined areas, in part
because it is possible to drastically reduce
harmful effects through proper
management.
Although the extent and severity of
land disturbance is relatively less than for
other resources, geothermal resource
development does have several significant
land-use impacts. These impacts relate to:
(1) the total acreage requirements for
development of a geothermal field and the
extent to which the land is disrupted, (2)
the compatibility of geothermal
development with adjacent land uses, and
(3) protection of sensitive land areas.
(Chapter 5 discusses impacts of
geothermal development on the
subsurface geology and soil stability, and
Chapter 10 discusses the effects of land
disturbance on vegetation and wildlife.)
Acreage Requirements
The development of a geothermal field
requires the installation of drilling pads for
supply and reinjection wells, sumps, by-
product processing facilities, access roads,
pipelines, generating plants, cooling
towers, and transmission lines. (Table 6
offers figures for the average amounts of
land required for each of these uses.) The
total land area required to develop a
geothermal reservoir is primarily a
function of the electrical capacity of the
generating plants, the number and
density of supply wells (which are, in
turn, dependent on the inherent
characteristics of the reservoir), and the
topography of the site. Impacts resulting
from these requirements are inherent in
thp Hfvplnnmpnt nrnrpHiirp.
Factors Affecting Acreage
Requirements
The first factor, electrical capacity, is the
easiest to comprehend: the larger the
generating plant, the more steam is
required to attain a given level of output,
and the more wells must be drilled.
The second factor, well spacing, is
influenced by several considerations:
first, wells must be drilled into specific
target areas—zones of subsurface fracture
where the heat reservoir is located—with-
out consideration to topography, surface
condition, or watersheds. Second, the
initial rates of steam flow and the con-
stituents of the steam may influence how
many wells must be drilled and whether
auxiliary facilities, such as those required
for the reclamation of chemicals or con-
densation of steam for water supplies, are
built. Third, whether the field develop-
ment policy is rapid or slow has a marked
effect on well spacing. Rapid development
is achieved by drilling more wells per acre
in a ' 'cluster" arrangement, with
relatively short pipelines feeding steam to
generating units located at the center of
the wells. With a slower rate of
development, wells are more widely
spaced, and relatively long main supply
lines are fed by a more extensive network
of feeder systems. [19]
The third factor, topography, can also
influence acreage requirements. As the
slope of the land increases, the total
-------
Land Use
45
surface area required for development
increases, because slope support must be
provided and cut-and-fill banks stabilized.
[20] Heavily sloped areas, as at The
Geysers, often require double the acreage
for a given activity. (Erosion and landslide
effects relating to topography are
discussed in Chapter 5.)
The amount of surface land disturbed
in a geothermal development area ranges
from 10 to 50 percent, with 20 percent as
the average. [21 ] Scaling up from the
acreage presently used at The Geysers
(see insert description of The Geysers
Steam Field, Chapter 1), a 1000 MWe
facility consisting of ten 100 MWe units
with a well spacing density of 1 well per
58 acres* would cover 2025 to 3645
hectares (5000 to 9000 acres) or 21 to 40
square kilometers (8 to 14 square miles)
of land. Of this amount, an average of 20
percent, or 405 to 729 square kilometers
(1000 to 1800 acres) of surface area
would be disturbed physically through
clearance of vegetation, grading, and
paving.
Variability in Land Requirements
Figures on land requirements vary con-
siderably from those recorded for the
geothermal operations at Lardarello, Italy,
and Wairakei, New Zealand. Based on
1970 figures at the dry-steam field of
Lardarello, 13 generating units supplied a
total capacity of 360 MWe from 467
" This current spacing at Thf Geysers is tower than will occur if
aiStioiul wells are drilled to exploit marginal areas. In that case.
.rage requirements probably will I* greater, and pertupi they will
double.
Table 6
Land Use Requirements for a Typical Geothermal Development Site
Phase
Surface Area
Exploration and Testing Phase
Road construction
Drill pads
Mud sump
3 to 4 miles, graded and compacted
1 acre each, cleared and compacted
Each one requires an area 100' x 125' x 10'
deep to temporarily store up to 1,000,000
gallons of effluent and cuttings.
Full Field Development
Road construction
Pipelines
Power generation facilities
—turbine generators & condensers
—cooling towers
-transformer
Transmission lines
Acreage varies. Access roads may be built
to drilling pads, mud sumps, buildings for
housing equipment and storage. Estimate:
30 acres of land cleared for every 15 wells.
Each pipeline is 10" to 30" in diameter,
raised on supports rising no more than 12
feet. The area cleared for the pipeline is
from 10' to 300' wide, depending on
whether access roads are constructed.
Roughly 5 acres are required; most of the
land must be paved or otherwise made
impervious.
Each is 150' x 65' x 60' high.
Each is 360' x 65' x 60' high.
Each is 100' x 100' x 55' high.
Lines consist of towers or poles at a height
of 80 to 120 feet, with concrete bases
40 feet apart.
SOURCE: U.S. Fish and Wildlife Service, 1976, p. 144 ff.
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46
Land Use
wells distributed over 168 square
kilometers (65 square miles)—a ratio of
1 well to 36 hectares (89 acres). In
1971, at the Wairakei hot-water field,
61 wells supplying a 160 MWe power
plant were concentrated in a compact
well field of less than 2.59 square
kilometers (1 square mile)—a ratio of 1
well to 4 hectares (10 acres). Thus, a
complete 1,000 MWe facility based on
the much more densely developed
Wairakei site would require 16 square
kilometers (6.25 square miles) far 381
wells.
Wherever possible in this report,
impacts are compared on a quantitative
basis. However, a quantitative
comparison of the total land requirements
of geothermal energy and alternative
energy resources is difficult to make
because of the complexity of the fuel cycle
for the alternatives. The specific acreage
requirements for the equipment common
to all types (such as power plants, cooling
towers, and electrical transmission lines)
are roughly the same for any 1,000 MWe
facility. Moreover, specific geothermal
equipment, such as drilling pads, do not
usually take up more space than oil or
natural gas drilling equipment. However,
the difficulty in comparing alternatives
arises in attempting to determine whether
the total amount of land required for all
other fuel types (fuel pipelines or trans
portation lines, processing facilities,
storage and disposal facilities) can
reasonably be attributed solely to provid-
ing 1,000 MWe of electrical power.
Compatibility With Adjacent
Land Use
Another important land-use issue
associated with geothermal development
is the extent to which such development
is compatible with surrounding land uses.
Possible adverse effects to adjacent land
could result from the changes in the use
of the land at the site, human activity,
and noise and pollutant emissions; fur
thermore, such impacts are likely to be
long-term in relation to the life of a geo-
thermal field.
To date, the use of geothermal
resources for the generation of electricity
has occurred primarily on undeveloped
lands. Consequently, geothermal develop-
ment has radically altered passive
multipurpose land uses such as wildlife
reserves, cattle grazing, and watersheds.
(Some potentially harmful consequences
of this change, such as forage reduction,
are discussed in Chapter 10.) As a result,
whatever value these uses once gave to
the land is now diminished. To the extent
that the scenic and aesthetic characteris-
tics of undisturbed landscape are replaced
by noise, odor, built forms, or defoliation,
the changes are not especially pleasing.
Human activity in the area must some-
times be restricted, especially during
testing, when the dangers of well blow-
outs are greatest—restrictions that could
lead to the overuse of adjacent areas.
The impact of geothermal development
on the productivity of adjacent lands is
not yet fully known, but appears to be
minimal. One important exception is the
tically reduce the value of the land
affected if easily damaged facilities, such
as irrigation canals or buildings, are
present. Subsidence is not rare. It has
occurred at Wairakei, New Zealand, and
Cerro Prieto, Mexico; but so far the
economic effects have been limited by the
relative remoteness of these areas. Both
are hot-water fields, which are apparently
more vulnerable to subsidence. If sub-
sidence were to occur as extensively in the
agricultural Imperial Valley, there would
be major adverse economic impacts. To
the extent that reinjection of geothermal
fluids may prevent subsidence, the
impacts would, of course, be less (see
Chapter 5).
To date, the impacts of geothermal
development on land fertility appear to be
minimal. During most of the 60 years of
field development at Lardarello, Italy, for
example, the surrounding land has had
varied agricultural uses. Today, pipelines
traverse vineyards, orchards, and farm-
lands with no known detrimental effect
(see Figure 17). At The Geysers, wilder-
ness surrounding the development area
has remained largely unaffected. Exten-
sive studies are presently being conducted
to identify additional effects on the sur-
rounding ecosystems.
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48
Land Use
Some concern has been expressed at
The Geysers about the extent to which
improved access to the wilderness area
provided by new roads would increase
residential and industrial growth,
especially over the extended life of the
field. To date, development of The
Geysers has spurred neither residential
nor industrial development. However, the
question remains important because the
development of geothermal sites in
remote areas of the West is certain to con-
tribute to a change in the social and
economic character of these lands.
Federal leasing regulations [22] require
that developers identify adjacent land
uses, assess their productivity, and predict
the effects of geothermal development on
the value of the land. The regulations
stipulate that geothermal activities on
leased land must be conducted in a
manner that prevents "unreasonable
interference with the multiple uses of the
land." [23] Effective emission controls,
noise muffling, proper plant and
equipment design, and continual moni-
toring of adjacent areas—in other words,
comprehensive planning and conscien-
tious management—can contribute
significantly to the prevention of adverse
effects.
Protection of Sensitive Lands
The Geothermal Steam Act of 1970 pre
eludes the geothermal development of
certain environmentally fragile land areas
in order to protect their specia! land-use
values or unique characteristics. The
protected lands are generally public lands
acquired with federal funds, and include
lands reserved for Native American
Indians, lands administered by the
National Park Service (including Yellow-
stone National Park), lands within
national recreation areas, lands used for
fish hatcheries, wildlife refuges, wildlife
or game range lands, wildlife manage-
ment areas, waterfowl production areas,
lands registered in the national wild and
scenic rivers system, and lands reserved
to protect and conserve species threatened
with extinction. The possibility that
geothermal developoment will cause
damage to certain types of sensitive or
critical land areas—such as valuable farm
land, mature or near-mature forest, or
historical and archeological sites—has also
resulted in various leasing restrictions.
Certain lands administered by the Depart-
ment of Agriculture and lands withdrawn
under the Federal Power Act (16 USC
818) may be leased only with the consent
of, and under the conditions prescribed
by, the governing legislation. [24 ]
Research Needs
An implicit issue facing geothermal
developers is the trade-off between the use
of land for geothermal energy versus its
use for recreation, watersheds, or agricul-
ture. In some areas of the country, this
trade-off may be a central barrier to the
rapid development of geothermal
resources. There is a need to determine
more specifically, in terms of economic
and natural resources, what productivity
may be lost when lands are developed for
their energy potential. Disruption of
aquifers, emission of potentially toxic
substances, erosion, and
subsidence—each of these may pose a
threat to the long-term productivity of
adjacent lands. Learning to measure the
potential for harm, and adequately con-
sidering this through the instrument of
the environmental impact statement, is a
primary research need.
The potential also exists for geothermal
development to beneficially affect the
productivity of adjacent lands. For
example, geothermal development may
facilitate water reclamation in semi-arid
and arid regions. This and other possi-
bilities need to be identified.
Finally, a clearer statement of the
potential for social and economic change
resulting from successful, widespread
development of resources in the now
scarcely populated areas of the West
should be attempted. The Integrated As-
sessment activity now ongoing in EPA
should advance knowledge on these
matters. The synergistic effects of mul-
tiple resource development projects (for
coal, uranium mining, and oil shale, for
example) and the role of geothermal
development in this problem needs to be
more carefully examined.
-------
5. Geology
and Soils
The stability of surface soil and subsurface
geologic formations can be affected in a
number of ways by the activities related to
developing geothermal resources. Among
the most significant potential adverse
effects are: surface soil ero&ion, land sur-
face subsidence, and inducement of seis-
mic activity.
Erosion
The exploitation of any geothermal
resource necessarily involves site
clearing, which disturbs the land surface,
particularly during the initial stages of
development. On steeply sloping sites,
extensive earth-moving, or "cut-and-
fill,'' may also be required for the con-
struction of access roads, drilling sites,
steam pipelines, power plants, and elec-
trical transmission lines. Such activities
invariably remove protective vegetation
and thereby accelerate erosion of exposed
soil by storm water runoff if protective
measures are not taken. The eroded soil is
carried into streams and subsequently
deposited, raising suspended solids levels
and causing sediment buildup on stream
bottoms. Both increased levels of
suspended solids and sedimentation can be
harmful to fish and other aquatic species.
Although erosion is most severe when the
soil is exposed during construction,
significant erosion from cuts, fills,
roadsides, and culverts continues
throughout all development stages. Earth-
moving activities may also disturb
national drainageways and slopes.
While some increase in the rate of
erosion and sedimentation can be
expected with virtually all types of
eeothermal development, the extent of
49
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50
Geology & Soils
the increase varies widely, depending on
particular site conditions and development
practices. At The Geysers steam field in
Northern California, for example, the
combination of steep slopes, poor soil
structure, and high seasonal rainfall and
runoff rates renders the soils highly
erodible. Because a steep slope is also a
site condition that requires substantial
earth-moving, extensive erosion has
occurred in the past. Frequently, fill
material has slumped and soil and rock
slipped above cuts into hillsides following
the construction of drill pads and roads,
particularly when built on active landslide
areas. Degradation of nearby streams by
siltation has also occurred.
In contrast, at the development sites
having flatter terrain and less erodible
soils, die impacts of geothermal develop-
ment have been less severe. Moreover,
since the land disturbance associated with
geothermal development is not nearly as
severe as that caused by the surface
mining of coal or uranium, a smaller total
amount of erosion is likely to occur.
The impacts of soil erosion and earth
movement during geothermal
development can be mitigated signifi-
cantly by applying readily available
erosion control techniques. Drains,
mulch, and matting can be installed;
revegetation measures can be taken; and
the total land area disturbed can be
minimized. Such techniques are currently
being used on all federal lands, because
federal leasing regulations require that
disturbance to vegetation and natural
drainage be minimal.
At The Geysers, the state of California
has recently begun to carefully regulate
earth-moving activities on the lands it
owns, thus markedly reducing the
severity of erosion-related impacts and
highlighting the need for site planning
prior to development.
Subsidence
Land subsidence resulting from the with-
drawal of geothermal fluids from the earth
is among the most serious of the potential
impacts of geothermal development.
Vertical subsidence and associated
horizontal ground movement can occur
whenever support is removed from
beneath the ground; such movements
have occurred throughout the United
States as a result of the pumping of
groundwater in numerous locations, as
well as during the development of mines
and oil fields.
Whenever subsurface fluids, such as oil
or water, are withdrawn, the cause of the
resulting subsidence is the same: a
reduction in the fluid pressure that
supports the overlying rock causes a
marked increase in effective stress and
subsurface compaction, or the collapse of
pores in the rock structure. In petroleum
fields, which are areas of unconsolidated
or semi-consolidated sedimentary rock
containing pore spaces, subsidence has
occurred but has been successfully con-
trolled by injecting water around the
periphery of the field to maintain fluid
pressures.
Likelihood of Subsidence
Land subsidence has not occurred during
the development of the two existing
vapor-dominated geothermal fields at The
Geysers and in Lardarello, Italy. The lack
of subsidence has been attributed to the
geologic conditions under which such
systems form. One of the fundamental
conditions considered necessary to
formation of a vapor-dominated system is
a "competent" host rock; that is, rock
not subject to compaction and, therefore,
not subject to subsidence. [25]
In contrast, hot-water systems are
expected to behave more like petroleum
reservoirs and subsidence is more likely to
occur unless subsurface pressures are
maintained through fluid reinsertion. In
Wairakei, New Zealand, where
geothermal water is discharged to a river
rather than reinjected after being used to
generate power, total vertical movement
has exceeded 3.7 meters (12 feet) since
1956, affecting an area of over 25 square
miles (65 square kilometers). Horizontal
movement also has been recorded. [26]
Significantly, the area of maximum
subsidence occurs outside the production
field, which means that subsidence could
affect the property of adjacent landowners
more than the immediate development
area.
In Cerro Prieto, Mexico, a hot-water
field located near the Imperial Valley in
California, subsidence was recorded some
seven miles outside the well field even
before extensive production began. [27]
At this site, geothermal waters have been
discharged to an evaporation and
sedimentation pond rather than reinjected.
-------
Geology Si Soils
51
Land subsidence has serious implica-
tions for the future development of the
Imperial Valley's geothermal resources.
fbtentially one of the most promising
geothermal areas, the valley is tectonic-
ally active and may be subsiding naturally.
Since most of the valley is a flat, fertile
plain with extensive agricultural irrigation
systems, subsidence induced by
geothermal development could cause
serious damage.
Concern about this issue has led to
extensive studies by the U.S. Geological
Survey and the state of California's
Division of Oil and Gas. To monitor the
extent of subsidence caused by both
geothermal development and naturally
occurring processes, surface benchmarks
have been measured since 1971. Research
to develop a reliable computer simulation
model of the subsurface environmental
effects of geothermal development has
been funded by the National Science
Foundation and is currently nearing
completion.
Subsidence is also a concern in develop-
ing geopressured reservoirs such as those
located along the Gulf Coast. However,
two conditions are expected to reduce the
likelihood of subsidence there: the deep
location (frequently more than 10,000
feet or 3,000 meters) of the reservoir sug-
gested by preliminary engineering
proposals, and a seal of cap rock above the
reservoir. Furthermore, the previous
withdrawal of oil and gas from these zones
has not yet resulted in detectable
subsidence. [28]
Control of Subsidence
The primary technology available to pre-
vent subsidence is the reinjection of
geothermal fluids to deep wells following
power production. While highly promis-
ing, the application of this technique may
be limited by at least six unresolved
problems.
First, while some compaction is elastic
and reversible, the withdrawal of fluids
can cause the irreversible collapse of some
of the air spaces or pores,
Second, geothermal fluids sometimes
contain a large amount of dissolved solids,
such as silica or calcium. If the lower
temperatures of the reinjected fluid cause
these dissolved solids to solidify or
precipitate, the reinjection pipes could
become clogged; thus reducing the
permeability of the aquifer. Concern about
this problem has prevented the use of re-
injection at the Wairakei power plant,
where the geothermal water has a high
content of dissolved silica. Such problems
could be solved by placing chemical
additives in the hot water to keep
dissolved solids in solution; however,
their use may create another problem:
because additives increase the ability of
the hot waters to dissolve solids (i.e., the
"solubility coefficient"), they dissolve
more solids in the host rock once
reinjected. Subsequent use of the
geothermal hot water containing in-
creased dissolved solids would, in turn,
worsen pipe clogging. This type of
problem represents a major uncertainty in
the development of geothermal energy.
Third, reinjection could lower the
temperature and hence the energy
potential of subsurface geothermal waters.
Fourth, only part of the geothermal
fluid may be available for reinjection
because part of the fluid used in the
electrical generating process may be
discharged as water vapor from a cooling
tower.
Fifth, while reinjection, particularly of
the concentrated brines characteristic of
the Imperial Valley, may not always be
practical at the site where the fluids were
withdrawn, reinjection at too great a
distance may induce seismic activity and
consequent earth movement at the
surface.
Sixth, the cost of creating reinjection
wells for hot-water systems can be quite
high relative to other, less environ-
mentally desirable means of fluid disposal,
thus increasing the cost of geothermal
power. [29]
Further research will be necessary to
evaluate the likelihood of subsidence for
varying resource types and under different
geohydrologic conditions, as well as to
resolve the potential problems of
reinjection as a control technology.
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52
Geology & Soils
Seismic Activity
Seismic activity induced by the
withdrawal or reinjection of geothermal
fluids is a potential hazard of geothermal
development. A connection between sub-
surface fluid pressures and earthquakes
has been suggested recently. A series of
earthquakes recorded at the Rocky
Mountain Arsenal near Denver,
Colorado, for example, followed the injec-
tion of waste fluids to crystalline rocks at a
depth of three miles (5,000 meters). At
Rangely, Colorado, earthquakes have
been associated with the injection of fluids
to oil fields as a way to increase produc-
tion. It is hypothesized that similar events
could occur as a result of geothermal
development.
Natural Relationship
with Geothermal Resources
Geothermal resources and seismicity
occur naturally at the same locations; the
unstable conditions in the earth's crust
that create geothermal resources are the
same conditions that produce faults and
earthquakes. In fact, the presence of
seismic activity is commonly used as a
prospecting tool in the search for
geothermal resources. As noted
previously, most of the geothermal
resources currently being developed are
located in zones of recent volcanic or
tectonic activity, which are often located
along the margins of major crustal
' 'plates.'' Active faults in some
geothermal areas appear to create zones of
high permeability that permit conduction
of heat to the surface and keep open the
cavities in which geothermal steam forms.
Micro-earthquakes—that is, earth-
quakes with magnitudes of less than 4 on
the Richter scale—have been observed
near many major geothermal areas
around the world, including The Geysers
and the Imperial Valley. Available data sug-
gest that geothermal zones experience
more frequent micro-earthquakes than do
immediately adjacent areas. However,
earthquakes having magnitudes greater
than 4.5 and the potential to cause signifi-
cant surface damage have rarely been
observed in geothermal areas, although
they may occur nearby.
The apparent difference in seismic
activity within geothermal areas and
outside is exemplified by the Imperial
Valley earthquake of 1940, one of the
largest to occur near a geothermal area.
With a magnitude of 7.1, it caused
faulting, which extended most of the
distance between the geothermal fields
just south of the Salton Sea, California,
and those near Cerro Prieto, Mexico; but
never into the geothermal areas. [30]
One possible explanation of this
distinction is that the frequent micro-
earthquakes in geothermal areas act to
relieve regional tectonic stress, thus
reducing the possibility of a major
earthquake. In immediately adjacent
areas, where no continual stress
release occurs, major earthquakes appear
to be more common. [31]
To date, there is no evidence to indicate
that geothermal activity has increased the
seismicity of an area; both The Geysers
and the Wairakei sites have been
monitored and no effects reported.
However, because data are insufficient to
reach any reliable conclusions, detailed
seismic monitoring is being conducted at
The Geysers and the Imperial Valley.
Underground nuclear detonation,
which is currently under consideration as
a technology for fracturing hot dry rock
formations, has been related tentatively to
the inducement of seismic activity.
Underground experiments with nuclear
detonation at the Nevada test site of the
Plowshare Program have created small
aftershocks, which represent the release
of natural strain energy. Even at substan-
tial distances, damages have been
reported to buildings as a direct result of
the shocks caused by these underground
nuclear detonations. Based on these
reports, the use of nuclear fracturing near
populated areas is probably impractical
[32]
The rock formations of the Gulf Coast
geopressured reservoir, the third type of
geothermal resource, are highly porous
and permeable. The faults in this area are
not tectonic, but result from relatively
minor ground settling due to continuing
deposition of sediment. Under these
geologic conditions, fluid withdrawal or
reinjection at geopressured reservoirs is
not expected to induce seismic activity.
However, conclusive information for this
assumption is not yet available.
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Geology & Soils
53
Monitoring and Prevention
Operating procedures that would reduce
or eliminate the possibility that
geothermal development could induce
seismic activity are not well known and
will require careful investigation if further
research indicates a probable seismic
hazard. For the present, structures in
geothermal areas, particularly those
housing super-heated steam and water,
should be designed to withstand naturally
occurring, local earthquakes. Since this
type of design is often expensive, the
likelihood and potential magnitude of an
earthquake should be determined before
design criteria are established. If addi-
tional research shows that earthquakes of
magnitudes greater than 4 or 5 are highly
unlikely to occur in a geothermal develop-
ment area, only moderate attention would
need to be directed to structural precau-
tions, except where faulting may occur
near the surface. [33]
Research Needs
Although the erosion-related impacts of
geothermal development can be
significant, they are predictable for a
proposed site and can be controlled with
available technology. Consequently, little
additional research needs to be
undertaken. The possibility of land
subsidence or induced seismicity at a
particular site, however, is difficult to
predict; and the adequacy of available
control measures—such as reinjection of
geothermal fluids—is uncertain.
Extensive research is currently under way
to develop adequate control measures,
and actual effects are being monitored at
development sites leased by the federal
government to private operators.
Most programs to monitor subsidence
have established local and regional
networks of interconnected surveying
(leveling) stations. Elevation is measured
repeatedly at these stations to determine
the degree of subsidence over time. The
instruments used include tiltmeters,
which measure surface deformation, and
extensometers, which can be used to
differentiate deep subsidence resulting
from the withdrawal of geothermal fluids
and shallow subsidence resulting from
groundwater pumping.
The imeragency Imperial Valley Sub-
sidence Detection Committee is presently
monitoring subsidence in the Imperial
Valley. One monitoring technique not
being employed that could provide useful
data is a gravity reading. While not as
accurate as detailed, "first-order"
leveling, gravity measurements can be
performed rapidly and inexpensively.
Moreover, when taken in conjunction
with first-order leveling, gravity readings
permit estimation of the net losses of
geothermal fluids from a reservoir and the
surrounding area. Both are important
parameters in determining the ultimate
life of the field and the optimum level of
production.
A wide variety of techniques can also
be used to investigate seismic effects.
Prior to geothermal development,
portable, high-frequency seismographs
should be used to establish levels of back-
ground seismicity, locate areas unsuitable
for reinjection, and help locate the geo-
thermal resource. Remote sensing
techniques, such as SLAR (side-looking
radar), and false-color infrared and con-
ventional aerial photographs, can also be
employed to identify surface features that
indicate active faulting. During the actual
development of new geothermal fields, a
network of permanent seismographs can
be installed to identify any induced
seismicity. Such a network is presently
being installed in the Imperial Valley and
should be installed in other prospective
geothermal areas as well.
A variety of research is currently under
way to evaluate the feasibility of reinjec-
tion at geothermal sites. While these
studies appear fo address most of the
important questions, at least one
additional problem should be
investigated: how to prevent reinjection-
well plugging. To understand the
chemical reactions that occur between
geothermal fluids and the geologic forma-
tions into which they are injected, basic
research on the precipitation of silica,
calcium carbonate, and other dissolved
minerals is needed first. Applied research
should be conducted on the prevention of
well-plugging and the related problem of
mineral deposition on operating equip-
ment. Based on this research, the
potential for both stabilizing geothermal
fluids against the precipitation of minerals
and deliberately inducing precipitation
before the fluids are reinjected should be
assessed. Laboratory studies should be
conducted based on actual samples from
proposed development areas.
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54
6. Water
Resources
Geothermal development raises three
primary concerns related to water
resources: water pollution, effects on
hydrology, and impacts on local water
supplies. Water pollution may result from
the disposal of fluids withdrawn from sub-
surface geologic reservoirs following their
use for testing wells or generating power.
Large-scale withdrawal and disposal of
geothermal fluids may also alter both the
surface and subsurface hydrology of an
entire development area. Finally, geo-
thermal development may affect local
water supplies in the largely arid
American West.
Water Pollution
The pollution problems associated with
vapor-dominated systems are generally
more manageable than those associated
with hot-water systems, because the
water from the geothermal steam is often
relatively low in pollutants. However,
water pollution can occur during any
stage in geothermal development—well
drilling, construction, or power plant
operation.
Sources of Pollution
Muds used during the early stages of well
drilling may contain various substances
harmful to water quality. To prevent the
contamination of surface waters, these
substances, together with rock dust and
the wastewater used in the drilling
operation, must be isolated. At The
Geysers, sumps with an impervious lining
or steel tanks are currently used to store
drill cuttings and waste fluid during
drilling operations (see Figures 18 and
19). Nontoxic wastes may be permanently
disposed of in a sump if it is protected
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Water Resources
55
Figure 18
Cross Section of a Typical Drilling Site
at The Geysers Geothermal Field
1. Blow line
2. Muffler
3. Mud mixing tanki
4. Blowout prevention equipment
5. Clay liner
6. Mud
Figure 19
Plan View of a Typical Drilling Site
at The Geysers Geothermal field
1. Air compressors
2. Generator
3. Mud pumpt
4. Drilling rig
5. Mud mixing tanki
§. Tank
7. Muffler
8. Blow line
9. Off ice
10. Pipe rack
11, Blowout prevention
hydraulic tytterfl
12. Catwalk
13. Mud logger
14. Chang* room
15. Part*
Headwall inlet
lined with concrete
SOURCE: Reed.M.J. and G.E.Campbell, 1975,p. 1409.
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56
Water Resources
from erosion; however, toxic wastes must
be transported to an approved waste
disposal site.
Well blowouts could also create water
pollution. The California Division of Oil
and Gas requires that blowout prevention
equipment be used during the drilling of
all geothermal wells as a control if
pressure conditions become unfavorable.
Only one well has blown out during the
drilling phase at The Geysers. Well
"Thermal 4" blew out in September
1957; as of 1975, it was discharging
about 80,000 kg/hr (176,000 Ib/hr) of
steam and noncondensable gases to the
atmosphere. Since the discharge is steam,
air pollution is a greater concern than
water pollution. However, the harmful
substances being released to the
atmosphere, such as mercury vapor, may
contribute to local water pollution if
removed from the atmosphere by rainfall.
Erosion and sedimentation associated
with the construction of drilling pads,
roads, transmission lines, and power
plants can have a significant effect on the
quality of nearby surface waters unless
careful monitoring and preventive control
measures are implemented. Recently,
state and federal agencies have directed
that increased attention be accorded to
limiting erosion and sedimentation at The
Geysers. These efforts have proven
successful in reducing the pollution of
nearby surface waters.
The most serious water pollution
problems are likely to develop during
power plant operation. The Geysers uses
a production method in which relatively
pure steam passes through turbines, is
then condensed by contact with cooling
water, and is finally evaporated in a
cooling tower. However, the rate of
evaporation from the cooling towers is
slower than the rate at which the steam is
fed into the turbines. Some of the steam
condensate must consequently be
removed in another fashion. On the
large injection wells. Figure 20 shows the
expected water pollutants contained in the
condensate return water of 1,000 MWe
of generating capacity at The Geysers.
[36]
average, 80 percent of the steam is
evaporated through the cooling towers,
leaving 20 percent as "blowdown"
water. [34]
From 1960 to 1971, the blowdown
wastewater at The Geysers was
discharged directly into a stream. [35]
There, the ammonia and boron contained
in the condensate caused some surface
water pollution and harm to aquatic life.
Since 1971, the wastewater has been re-
injected to die steam reservoir rocks.
Of the various disposal methods, re-
injection is considered to be the most
advantageous because the pollutants in
the wastewater do not come into contact
with relatively pure surface waters and
groundwaters. To ensure safety, reinjec-
tion wells must be carefully encased to
prevent the leakage of geothermal brines
to shallow aquifers.
Once introduced to the subsurface
reservoir, the wastewater boils and
produces steam, in effect artificially
recharging the reservoir. Because it has
proven to be effective in preventing both
surface and groundwater pollution, it will
be used in future expansion at The
Geysers.
Each 100 MWe of generating capacity
at The Geysers produces a relatively small
wastewater flow of over one million
gallons (3,785 cubic meters) per day—
volume that can be handled adequately by
one large injection well. An expanded
1,000 MWe of generating capacity would
produce over 10 million gallons (37,850
cubic meters) per day, requiring 8 to 10
Power plant operation at The Geysers
produces wastewater containing a
moderate amount of total solids. The
quantity of total solids produced during
power generation is higher than that
produced by nuclear or fossil fuel plants.
However, these technologies also
generate large amounts of pollutants
during mining and processing, which are
not involved in geothermal energy pro-
duction (see Table 7). Moreover, the
technology of reinsertion to the
geothermal reservoir—now being applied
at The Geysers and planned for hot-water
development sites in the West—would, if
successful, almost eliminate the major
cause of water pollution.
Hot-water systems pose far more dif-
ficult water pollution problems because
wastewaters from testing and production
are more abundant, more water pollutants
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Water Resources
57
Figure 20
Composition and Yearly Quantities of Major Pollutants
in Condensate Return Water of a 1000 MWe Plant (The Geysers)
Nitrate
Magnesium
Sulfur dioxide
Chloride
Silica
Calcium
Free sulluv
Boron
Total solids by evaporation
Organic* and volatile solids
Total alkalinity as HCO3
0.1 mg/liter
1.5 metric tons/yr
i 1.0 mg/liter
115 metric tons/y r
= 2.0 mg/liter
I 31 metric tons/yr
! 3.5 mg/liter
! 53 metric tons/yr
I I I
j 3.8 mg/liter
Iji5 metric tons/yr
JJ5.3 mg/liter
IB 80 metric tons/yr
8.4 mg/liter
133 metric tons/yr
is/vr
mg/liter
metric tons/yr
mg/liter
metric tons/yr
50 100
200
300
400
500
600
SOURCE: Resource Planning Associates, Inc.
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58
Water Resources
Table 7
Expected Water Pollution Emissions for Alternative
Electrical Generating Processes, 1000 MWe Plant
{metric tons/year, rounded to nearest fifty!
Process
Suspended Solids
A B
Dissolved Solids
A B
Nudear (light-water reactor)
Coal
Residual fuel oil
Natural gas
Low Btu synthetic natural gas
0
500
500
500
500
0
4,000
n/a
n/a
n/a
0. •
500
550
550
550
0
2,600
100,000a
0
2,600
(from coal)
Geothermal (The Geysers)
n/a
n/a
2,800b n/a
NOTE: Column A under each process includes total pollutants generated during power plant
operations; Column B includes total pollutants during all other steps (mining, etc.).
SOURCE: Teknekron, Inc.. 1975. 1976.
n/a—not available
a. Produced by a hypothetical 500.000 bbl/day refinery of which 34.000 bbl/day are residual fuel
oil to supply a 1,000 MWe power plant.
b, Total solids by evaporation.
are contained in the geothermal fluid, and
large amounts of cooling water are used.
At Wairakei (a 143 MWe plant),
approximately 30 million gallons
(113,600 cubic meters) of wastewater are
disposed of each day from the condensed
effluent and the excess water not flashed
to steam. This is a far greater proportion
than is produced at The Geysers. Such
large amounts of wastewater must be
disposed of in an environmentally safe
manner.
Characteristics of Geothermal Fluids
The quality of geothermal hot water—its
physical and chemical characteristics,
including impurities such as total
suspended solids—varies widely. While
some geothermal hot waters contain
relatively few pollutants, most contain a
relatively large amount of dissolved solids
and heavy metals because the high
temperatures of the brines increase the
dissolution rate of solids and heavy metals
in the rock, [3 7] Radioactive elements
such as radium and radon also may be
present.
The geothermal hot waters at Cerro
Prieto, Mexico, contain 1.5 to 2 percent
total dissolved solids (15,000-20,000
mg/1, compared to a value of about
35,000 mg/1 for sea water). At the
Imperial Valley in California, about 75
miles north, geothermal waters are
substantially more saline at most loca-
tions; brines with dissolved solid concen-
trations (typically over 25,000 mg/1 and
sometimes reaching 260,000 mg/1, or
26 percent of the total) are found in many
wells. [38]
In sharp contrast, at certain other loca-
tions in the West geothermal hot waters
are sufficiently pure to be used for agricul-
ture and industry. For example,
geothermal waters are used for stock
watering in Klamath Falls, Oregon, and
for domestic hot water supplies in Boise,
Idaho. In Iceland, geothermal waters are
widely used for both municipal heating
and domestic purposes. [39]
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Water Resources
59
The Special Problem of
Waste Disposal
Based on the variability in the amount
and type of dissolved solids in geothermal
fluids, a number of different methods for
disposing of wastewater from drilling and
power plant operation have been tested
and used. These include direct release to
surface water bodies, evaporation, surface
spreading to shallow aquifers, desalination
with subsequent water reuse, and reinjec-
t'on to the producing reservoir by use of
deep wells. The selection of a disposal
method has depended on local hydrologic
conditions, the quality of the wastewater,
and environmental regulations.
The only extensive commercial experi
ence with hot-water system waste disposal
has been outside the United States, and
some of the methods used in other
countries are not acceptable here because
of their harmful environmental effects.
For instance, at Wairakei, New Zealand,
wastewaters are discharged into a river
near the plant, substantially increasing
the arsenic, sulfur, and mercury levels of
the river. At Cerro Prieto, Mexico,
Production wastewaters are separated
from the geothermal fluid and then stored
m a large evaporation and sedimentation
Pond (8 sq. km. or 3 sq. miles in si/e for
'he existing 74 MWe plant). As the
waters in the evaporation pond become
njghly saline, developers plan to discharge
them into nearby waterways having high
natural salinity.
A major concern in the Imperial Valley
of California is the salinity level of the
Salton Sea and various shallow aquifers.
Local water supplies are limited and in
great demand for agriculture. Because
water supplies already contain large
amounts of dissolved solids, additional
salinity must be prevented. The state of
California has prohibited the discharge of
waste fluids with high dissolved solids
content into either surface waters or
shallow aquifers.
In complying with this restriction,
wastewaters produced during test drilling
at the Imperial Valley are stored in plastic-
lined holding ponds from which the water
evaporates. This disposal method prevents
infiltration to groundwater and has thus
far proven effective. However, the very
large volume of wastewater generated
during actual power plant operation limits
its use; the rate of evaporation is not fast
enough for large volumes of wastewater.
As a rough indication of the magnitude of
the problem, a 1,000 MWe plant in the
Imperial Valley is estimated to require the
disposal of approximately 50 billion
gallons (18,900,000 cubic meters) of
brine per year containing 50 million tons
of solids. [40] Thus, the most probable
long-term disposal method for wastewater
from power plant operation seems to be
reinfection to deep wells. Initial tests of
reinjection have proven promising. In a
year-long experiment, 2,727 liters (600
gallons) per minute were successfully in-
jected into a single well without reducing
the ability of the formation to receive
water. [41] However, a number of
complex technical problems remain to be
solved (see Chapter 5).
Desalination, which has the additional
benefit of producing usable fresh water for
a locality, is another alternative for waste-
water disposal. Currently, desalination is
being tested by the Bureau of Reclamation
at its East Mesa test facility in the
Imperial Valley. However, because the
expense of desalination increases with the
salinity of the water, the technology is
probably limited to waters with dissolved-
solids concentrations below 35,000
mg/1. This excludes a large proportion of
the Imperial Valley brines. [42] The
economic feasibility of desalination in the
Imperial Valley has also been questioned
recently because the temperatures of
geothermal brine at East Mesa are lower
than originally anticipated. If less heat is
extracted from the brines, less electric
power can be produced. Hence, at
relatively low temperatures a tradeoff
exists between the production of power
and the availability of fresh water.
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60
Water Resources
Hydrology
Geothermal development at The Geysers
has not as yet altered the area's surface
hydrology significantly. However,
continued withdrawal of geothermal fluid
could reduce the amount of water in the
deep steam reservoir and in the rate of
water flow and possibly change the tem-
perature or chemical characteristics of
nearby thermal springs.
Pressure decline tests indicate that The
Geysers reservoir is almost a closed
system; that is, it is not being recharged
with water at a rate sufficient to prevent a
decline in steam pressure as energy is
produced. Although some of the fluid is
restored through reinjection, geothermal
steam at The Geysers should be viewed as
a depletable, rather than a renewable,
resource.
Large-scale extraction and reinjection
of hot-water geothermal fluids in the
Imperial Valley also may cause changes in
the subsurface hydrologic system. Effects
such as alterations in groundwater
recharge rates have been extremely
difficult to predict quantitatively for the
valley. To better understand the
mechanisms of groundwater recharge in
this highly complex hydrologic system,
local, state, and federal agencies are
closely monitoring the water quality and
quantity in the valley.
The lack of comprehensive, reliable
data on subsurface hydrology makes
impossible the determination of whether
long-term power production would
ultimately deplete the geothermal
resources of the Imperial Valley or other
hot-water systems in the United States.
Investigations at Wairakei, New Zealand,
suggest that geothermal energy could be
developed at a rate that permits
production for an indefinite period of
time. [43]
Reinjection could also help to maintain
the long-term productivity of the
geothermal resource. Research involving
computer simulation of resource behavior
is under way to identify the most effective
long-term production strategy (including
the rate and method of withdrawal and
reinjection) for both hot-water and
geopressured reservoirs.
Water Supply
Geothermal power production may also
require the use of water for cooling
purposes. At The Geysers and other
vapor-dominated systems, water can be
supplied by the geothermal resource in
the form of condensed steam, thereby
eliminating the need for an external
source of water. A similar cooling system
can be used in a flash turbine hot-water
plant. However, in a binary fluid system,
because the geothermal hot water is
reinjected directly to the geothermal
reservoir once it has passed through a
heat exchange device, it is not available
for use in cooling the freon or isobutane
used to drive the turbine, and an external
source of water is needed.
Current Alternatives for Cooling
The cooling water can be provided to a
geothermal site in one of three ways: with
a "once-through" cooling system, in
which external water, frequently from a
river or lake, is utilized once for cooling,
and then discharged to its source; with an
evaporative or "wet" cooling tower, in
which the external water is evaporated to
the atmosphere; or with a "dry" cooling
tower, in which the fluid is cooled by air
and continually circulated in a closed
system.
The water requirements of these
systems may vary widely. "Once-
through" systems and wet cooling towers
require substantial amounts of water; dry
cooling towers very little. Their environ-
mental impacts also vary substantially (see
Chapter 9).
A once-through cooling system is
currently used at Wairakei, New
Zealand; however, the potential for
thermal pollution of surface water limits
the applicability in the United States.
New Designs for
Still-Undeveloped Resources
Preliminary designs prepared by Bechtel
Corporation for a 10 MWe demonstration
binary power plant with an evaporative or
' 'wet*' cooling tower indicate that 830
gallons per minute of makeup water is
required, of which about 20 percent is
"blown down'' and reinjected to the
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Water Resources
61
reservoir. At this rate, for a 1,000 MWe
plant, 83,000 gallons per minute (almost
134,000 acre-feet, or 165 million cubic
meters per year) are required. This
amount is substantially greater than that
needed by alternative power generation
systems because the thermal efficiency of
a geothermal plant is low. Such large
quantities of water may not be available in
many locations in the predominantly arid
western states, or may preempt scarce
water resources needed for other
purposes. Alternatively, a dry (air-cooled)
cooling tower could be used. Based on
present prototype designs, dry cooling
towers are expected to be 30 to 40 percent
more costly than evaporative towers, [44]
and may reduce the already low thermal
efficiency of the power plant.
A moderate quantity of makeup water
is required to operate hot dry rock
systems. Requirements are estimated to
be about 26,500 gallons (100 cubic
meters) per day for wells supplying 100
MWe of thermal energy; at this rate,
1,325,000 gallons (5,015 cubic meters)
per day (1,484 acre-feet, or 1,830,000
cubic meters per year) would be needed to
supply a 1,000 MWe plant, assuming
that a binary power plant with 20 percent
efficiency is used. [45] Additional cooling
water would, however, be required to
cool the isobutane or other working fluid.
Research Needs
In any geothermal development area,
impacts on water quality, hydrology, and
local water supply can be predicted only
on the basis of comprehensive, site-
specific data. Baseline environmental data
on water quality and hydrology are
presently being collected as part of
ongoing research programs in potential
geothermal development areas, such as
ERDA's Imperial Valley Environmental
Project.
Geologic and hydrologic data are
usually obtained from deep test wells
drilled during exploration for geothermal
fluids. Insufficient data are often obtained
from such wells at shallow and
intermediate depths. Data on the vertical
variation of water level, depth,
temperature, and pressure; and on rock
permeability, porosity, and cementation,
should be collected in each zone to the
extent required by USGS for wells drilled
by leaseholders on federal lands. To
provide a thorough understanding of local
hydrology and determine whether reinjec-
tion is likely to be successful, test wells
should also be drilled on the periphery of
geothermal areas, where temperatures
decrease rapidly and rock cementation
occurs.
In many geothermal areas, data on rock
porosity and permeability are insufficient
to assess the hydrologic nature of the
reservoirs. Well-logging techniques using
radioactivity (including gamma-gamma
and neutron logs) provide the most
reliable means of estimating porosity and
permeability. Where appropriate, such
techniques should be applied to new wells
(both deep and shallow) in geothermal
areas.
To assess impacts on water quality, data
should be collected not only on the
standard water quality parameters (e.g.,
dissolved solids) but also on the local
hydrologic systems and the characteristics
of geothermal waters that would disclose
their presence in surface and
groundwaters. Data would be particularly
useful on hydrogen and oxygen isotopes
present in water samples from surface
waters, shallow groundwaters, and
geothermal reservoirs. Detailed laboratory
analysis of the chemistry of geothermal
fluids, similar to that performed to
determine potential reinjection problems,
would also be helpful in determining
potential water quality problems.
The liquid wastewater disposed of
during geothermal operations often
contains a variety of chemical compounds.
Because wastewater is a potential source
not only of water pollution, but also of
water supply and commercially valuable
chemical by-products, high priority
should be assigned to developing
economical methods of producing fresh
water (desalination) and extracting
valuable chemicals such as boric acid and
sulfur compounds.
-------
62
7. Noise
Perhaps the most ubiquitous
environmental disturbance associated
with geothermal development is noise.
Loud, continuous noise occurs during
both the drilling and production testing of
geothermal wells and the operation of the
plant. Nevertheless, noise does not
represent as immediate a concern as do
some of the other environmental impacts
of geothermal development because its
effects are limited to the immediate area
under development. And because the
health and welfare effects of noise are well
documented, this section reviews those
effects only briefly and then focuses on the
sources of noise at a site.
Effects of Noise
The harmful health and welfare effects of
exposure to excessive noise levels or
vibration over a prolonged period of time
range from the relatively minor, such as
temporary task interference and irritation,
to the severe and permanent, such as
sleep loss, physiological stress, speech
impairment, and hearing loss (see Figure
21). Since the extent of harm is related
directly to the frequency and duration of
exposure to high noise levels, workers at
a geothermal site experience the highest
risk. Noise standards established by the
Occupational Safety and Health Adminis-
tration (OSHA) require that exposure of
workers to unmuffled noise at levels above
95 dB(A) be limited. [46] Several geo-
thermal development activities produce
noise at levels close to, or substantially
higher than, this level. Persons in the
vicinity of a geothermal site may be
exposed to continuous noise at levels
varying from 60 to 120 decibels, depend-
ing upon the ongoing development and
distance from the noise source.
-------
Noise
63
Figure 21
Noise Levels of Geothermal Operations at The Geysers Compared with Those of Familiar Sources
audible
loud
very loud
uncomfortably loud
pain threshold
Geothermal
Noise Sources
steam
line
separator
(at 25
ft)
muffled
testing
well
(at 5
•'••••'••:.:
Oft)
muffled
air
drilling
(at
••'••'•• ':'•::
25ft)
sisa.n
line
break
unmuffled
air
drilling
(at 50 ft)
Relative
Loudness
(human
judgement
of different
sound levels)
Measured
Noise
Levels
[dB(A>]
Familiar
Noise Sources
very soft conversation garbage motorcycle
whisper disposal (at 25 ft)
Boeing 707
before landing
(at 6000 ft)
turbofan
aircraft
at takeoff
(at 2000 ft)
military jet
with afterburner,
at takeoff
(at 50 ft)
SOURCE: Reed, M.J. and G.E. Campbell, 1975; U.S. Department of the Interior, 1972; Ecoview, Inc., 1974.
-------
64
Noise
In addition to direct health and welfare
effects, the noise generated by geothermal
development may have other adverse
impacts. In communities with little indus-
trial development, residents may regard
the continuous noise associated with
geothermal development—even at a rela-
tively low level—as an intrusion into their
previously quiet environment.
Until recently, for example, noise
related to activity at The Geysers had not
led to strong efforts by nearby residents to
limit noise. However, a new power plant
(unit No. 13) is currently planned for con-
struction close to a residential community
(1.7 miles), the village of Anderson
Springs. In response to concern expressed
by residents, Lake County, California, is
considering enacting noise control
standards.
Animal behavior also is affected by
excessive noise, which has been shown to
cause changes in the size, weight, repro-
ductive activity, and behavior of farm
animals. In some wildlife species, changes
in mating behavior, predator-prey rela-
tionships, and territorial behavior have
been observed (see Chapter 10).
Sources of Noise in
Geothermal Development
High noise levels are produced during
each of the major phases of geothermal
development: well drilling and production
testing, construction, and plant
operation. Table 8 lists typical noise levels
occurring at The Geysers for these
activities, which are summarized below.
Well Drilling and
Production Testing
The process of drilling and testing geo-
thermal wells is comprised of a number of
separate operations of varying duration in
which steam under high pressure escapes
to the atmosphere, generating high noise
levels. Some of these operations can be
effectively muffled, others emit essentially
unavoidable noise.
At vapor-dominated sites like The
Geysers, only the shallow portion of a
well can be drilled by using mud as the
circulating fluid. For much of the
procedure, compressed air must be used
as the circulating fluid when penetrating
the probable steam zone to avoid clogging
or damaging the steam-producing rock
fractures. Air drilling is much louder
[120 dB(A)] than mud drilling [75-80
dB(A)], primarily from the horizontal
pipe ("blow line" or "Hooieline"). The
engines operating the air compressor also
produce a deep resonant sound that
carries for considerable distances. Of the
total drilling period of two to three
months (during which drilling is
conducted 24 hours a day), about one-
third of the time is spent drilling with
compressed air.
Drilling companies have experimented
with a wide variety of methods for con-
trolling air drilling noise at The Geysers
and have tested several types of mufflers.
Recently, significant reductions in noise
have been achieved by directing the
discharge of the blow line into a large ' 'air
sampler," a large chamber designed to
capture loose rock cuttings. Injection of
water into the air sampler, a method
originally developed to increase the
amount of rock captured, also reduced
noise. [47] These techniques have been
employed extensively in recent well
drilling at The Geysers.
Once drilling is completed, the noise
levels associated with extraction do not
drop significantly. A well must first be
allowed to "blow" freely for three to six
days until the accumulated dust and rocks
are removed. Noise levels during the
procedure approach 118 dB(A). It is
generally considered infeasible to muffle
this operation, because only large rocks
blown up under pressure would damage
currently available muffling equipment.
Following the clean-out, the well is
tested to evaluate the steam reservoir and
production rate by releasing steam from
the well to the atmosphere. The accom-
panying noise level is high [approximately
118 dB(A)]. Several types of mufflers
have been used in an attempt to control
testing-related noise. One of the most
effective, a "rock muffler," significantly
reduced the noise level by 29 dB(A), from
118 to 89 dB(A), according to tests by
Union Oil Company. [48]
-------
Noise
65
A completed test or production well is
discharged or "bled"' continuously into
the atmosphere through a small diameter
pipe (bleed line), which permits releases
of 5 to 10 percent of the total potential
steam flow. The noise associated with
bleed line discharges is relatively
jow—about 86 dB(A}—and can be
lowered to 65 dB(A) by venting the line
into a rock-filled ditch. While this
discharge continues until the power plant
is operational (possibly more than a year if
delays are encountered), an attempt is
usually made to limit this source of air
and noise pollution by timing the com-
pletion of production testing to coincide
with the completion of the power plant.
Occasionally, wells are allowed to vent
at full pressure for several hours to
prevent the buildup of condensate
Because this operation is not usually
muffled, h produces about the same noise
levels [1 IB dB(A)] as do unmuffled test
wells.
Well blowouts, or unanticipated
venting, rarely occur during the drilling
phase of geothermal development. The
noise emitted when they do occur,
however, is extremely loud, probably as
loud as an unmuffled test well. If not
controlled, blowouts can continue to be
sources of air and noise pollution for
extended periods of time. At The
Geysers, "thermal" well No. 4 "blew
out" in September 1957 and is still
discharging some steam into the
atmosphere; however, this blowout has
been partially controlled and is no longer
a significant noise source.
Table s
Noise Levels of Geothermal Operations During Development Phase at The Geysers
Operation
Duration
Noise Level
[dB(A>]
Distance
[ft]
Well Drilling
Mud drilling
Air drilling, including
blow line
blow line with air sampler
blow line with air sampler
& water injection
Well cleaning; open well
Well testing; open well
Rock muffler
Well bleeding before connection
to generator
open hole
rock-filled ditch
blowouts
60 days/well
30 days/well
3-6 days
1 4 days
variable
variable (infrequent)
75-80
120*
95*
85
118*
118*
89
86
65
118*
50
25
25
25
50
50
50
5
5
50
Construction
Operation of construction
machinery (trucks, bulldozers, etc.
1 -2 years
70-90
50
Plant Operation
Steam line vent (muffled)
Jet gas ejector
unattenuated (old design)
with acoustical insulation
Steam line separator
Steam line breaks
Cooling tower
Turbine-generator building
20-30 years
intermittent
continuous
continuous
brief, infrequent
continuous
continuous
90
117*
84
80
100*
80-90
70
100
5-10
5-10
25
50
5-10
outside
SOURCES: Reed, M.J. and G. Campbell, 1975; U.S. Department of the Interior, 1972,
Ecoview, Inc., 1974.
* Noise level is at or above OSHA standard of 95 dB(AI
-------
66
Noise
Drilling noise levels pose less of a
problem in hot-water than in vapor-
dominated systems. Well drilling and
production testing for hot-water systems
is a far less noisy operation than for vapor-
dominated systems because mud, rather
than air, is used as the circulating fluid.
Also, the period of time required for
drilling in hot-water systems is somewhat
shorter—30 to 45 days rather than 2 to 3
months.
The most significant noise associated
with hot-water wells is that emitted
during production testing for power
generation, when 20 to 25 percent of the
hot water is flashed to steam. If
unmuffled, the noise of the expanding
steam could reach a level as high as 100
dB(A) at 50 feet. [49] Well blowouts
could also produce high noise levels.
Following the testing period, the wells are
completely capped and thus cease to be a
source of noise.
Construction Activities
Full development of a geothermal field
involves construction of access roads,
steam pipelines, generating plants, and
electrical transmission lines. Construction
of generating plants requires the longest
period of time—up to two years at The
Geysers. During this period, the
operation of earth-moving and construc-
tion equipment—such as large trucks,
bulldozers, tractors, cranes, and cement
mixers—generates noise levels familiar to
anyone who has experienced a city build-
ing-construction site. Noise associated
with construction activities can often be
controlled through the use of engine
mufflers and other abatement techniques.
However, construction equipment is
generally operated at the same time that
production wells are being drilled and
tested; the simultaneous field
development and plan construction phases
cause high noise levels.
Plant Operation
Operation of a geothermal power plant
also creates high noise levels. At The
Geysers, the most significant continuous
noise sources are the cooling towers and
jet gas ejectors, which release noncon-
densable gases from the condenser. The
noise created by the fans in the cooling
towers is continuous, but is confined by
the structure to the immediate vicinity of
the plant. [50] While the jet gas ejectors
on older units at The Geysers emit con-
siderable noise, newer units are
acoustically insulated and are therefore
considerably quieter. Installation during
late 1976 of improved air pollution
control equipment designed to transfer
gases from the jet gas ejectors to other
locations in the plant for the removal of
hydrogen sulfide may also reduce the
noise currently emitted from the ejectors.
The particle separators and the movement
of steam through the steam lines also
represent significant sources of noise.
Another loud but intermittent noise
source is the venting of steam lines during
plant shutdowns and accidental steam line
breaks.
Research Needs
The noise levels produced by any type of
geothermal development are largely
determined by the actual equipment used
and the operating procedures followed.
While the geothermal industry has
conducted extensive research and experi-
mentation on noise control, much of this
research has taken the form of ' "trouble-
shooting" aimed at controlling individual
operations such as well drilling at a
specific site. A need clearly exists for
comprehensive research on noise control
and the development of appropriate
equipment and operating procedures.
Ambient noise levels at new
geothermal sites should be monitored to
determine noise intensity, frequency, and
duration before and during development.
In addition to site-specific data collection,
a more general, comprehensive
engineering study should be undertaken
to analyze in detail each geothermal
operation that produces noise in the
development of both vapor-dominated and
hot-water fields. Existing equipment and
procedures used to reduce noise levels
during each operation should be
compared in terms of effectiveness,
reliability, cost, and environmental
impact, and specific procedures and
equipment recommended for use. Such a
study could also explore the need for
federal R&D to control the noise of opera-
tions that cannot be muffled with existing
technology, such as noise produced
development and plant construction
phases cause high noise levels.
-------
8. Air
Quality
67
Noncondensable gases and particulates
accompany the geothermal steam released
to the atmosphere during well drilling,
production testing, and plant operation.
At sufficiently high concentrations,
several of these substances—particularly
hydrogen sulfide—can have harmful
effects on human health. The odor of
hydrogen sulfide can also be regarded as
aesthetically objectionable.
To date, no significant health effects
resulting from emissions of hydrogen
sulfide or other air pollutants during
geothermal power production have been
documented, either at The Geysers or at
geothermat power plants in foreign
countries. However, relatively high
emission levels of various air pollutants
have been recorded at geothermal power
plants in other countries, and moderate
emission levels of hydrogen sulfide have
been documented at The Geysers.
Since data on health effects, air
pollutant emission levels, and ambient air
quality at geothermal development areas
are still incomplete, the air quality
impacts that will result from full-scale
geothermal development at sites currently
in the early stages of exploration and
development cannot be predicted accu-
rately. However, because the concentra-
tion of air pollutants in geothermal fluids
(and hence, of the steam released to the
atmosphere) varies widely from site to
site, the development of better methods to
evaluate and control emissions is
generally considered to be one of the most
important environmental issues associated
with geothermal development.
The following sections identify the
types of pollutants emitted during geo-
thermal power generation, describe their
potential health hazards, and discuss the
-------
68
Air Quality
major sources of emissions at existing
geothermal power plants.
Types of Pollutants
The types of pollutants likely to result
from geothermal development are
primarily determined by the chemical
composition of the geothermal fluid at a
site. Both the total quantity of gases in the
fluid and the relative concentration of
their constituents depend on the geo-
chemistry of the underground reservoir.
The chemical composition of the geo-
thermal fluid can vary substantially in
different reservoirs, at different wells
within the same reservoir, and even
during the lifetime of a single well. Thus,
the levels of pollutants emitted during
geothermal operations can also vary
widely overall. Table 9 compares the com-
position of geothermal steam at The
Geysers and Wairakei.
The gaseous emissions associated with
the geothermal production of electricity
differ considerably from those associated
with nuclear and fossil-fuel production.
Since geothermal processes operate
without combustion, the resulting
gaseous emissions are the reduced com-
pounds (primarily hydrogen sulfide,
ammonia, and hydrocarbons such as
ethane and methane) of elements
contained in the geothermal fluid. In the
burning of fossil fuels, these elements are
found in oxidized form as sulfur oxides,
nitrogen oxides, and carbon dioxides.
In vapor-dominated systems and in the
' 'flash'' steam process used with hot-
water systems, the geothermal steam
contains an assortment of noncondensable
gases. Carbon dioxide represents the main
component (75-95 percent); ammonia,
methane, hydrogen sulfide, and nitrogen
typically are present in smaller quantities;
and gases such as radon, mercury vapor,
and argon are present in trace amounts.
[51 ] Small quantities of minute
paniculate matter (including rock dust,
heavy metals such as lead and silver, and
boron) are also likely to be in suspension
in the steam. Measurements at sites
throughout the world indicate that
because the chemistry of geothermal
fluids in both vapor-dominated and hot-
water systems can vary so widely, neither
type of system inherently results in more
air pollution than the other.
Potential Health Hazards
Several of the noncondensable gases
emitted during geothermal power
generation pose potential health hazards.
To date, the emission levels associated
with existing geothermal power plants
have generally not been high enough to
cause most of the effects; however,
because the nature of the geothermal fluid
varies considerably from site to site,
serious effects could occur at new develoo-
ment sites. ^~
Hydrogen sulfide and ammonia present
the greatest potential hazards; carbon
dioxide, although usually present in
higher concentrations, is somewhat less
significant. Mercury and radon are of
concern because they are toxic even at
low concentrations.
Hydrogen Sulfide
Hydrogen sulfide (H,S) is a highly toxic
gas. Its direct effects on humans range
from a noxious, '' rotten-egg'' odor and
eye irritation at low concentrations to
respiratory damage and even death at high
concentrations. [52] Although atmos-
pheric dilution of geothermal steam
generally prevents ambient hydrogen
sulfide from reaching dangerously high
levels in the immediate vicinity of steam
releases, concentrations may be sufficient
to create an occupational health hazard
for workers. The potential hazard of this
gas is increased by the fact that it cannot
be detected by smell at the high
concentrations which are most dangerous
-------
Air Quality
69
Hydrogen sulfide is chemically
reactive, and readily converts to other
compounds of sulfur, such as sulfur
dioxide, sulfur trioxide, sulfuric acid, and
particulates (metal sulfides and sulfates).
Conversion is particularly likely to occur
in urban areas where ambient oxidant
levels are high. [53] Recent research
shows that this conversion frequently
occurs within hours or at most several
days following introduction of the gas to
the atmosphere. Figure 22 presents data
on the physiological effects of hydrogen
sulfide. The other sulfur compounds into
which hydrogen sulfide is converted also
have significant negative health effects on
humans, including increases in irritation
to the respiratory system.
Although the odor of these compounds
does not constitute a nuisance as does
hydrogen sulfide at similar concentra-
tions, they are of greater national
significance overall as air pollutants
because they are emitted in large
quantities by "stationary sources" such
as fossil-fuel-burning power plants.
Hence, geothermal emissions of hydrogen
sulfide contribute to raising ambient levels
of sulfur oxides regionally. This is par-
ticularly important because sulfur dioxide
(SOj) is one of the " criteria pollutants''
for which EPA sets and enforces national
ambient air quality standards under the
authority of the Clean Air Act and its
1970 amendments. Geothermal
emissions of hydrogen sulfide may also
contribute to regional climatic problems,
such as increases in the acidity of rainfall.
Table 9
Comparison of Noncondensable Gases in Steam
from Wells at Two Geothermal Power Plants
Gas
Range of Concentrations Measured (ppm)
Hydrogen sulfide
Carbon dioxide
Methane
Ethane
Ammonia
Nitrogen
Hydrogen
Geysers
Low
5
290
^3
3
9
6
11
High
1,600
30,600
1,447
19
1,060
638
213
Average
222
3,260
194
—
104
52
56
Wairakei
Average
40
600
5
1
8
3
10
SOURCES: Reed, M.J., and G. Campbell, 1975; Axtmann, R.C., 1976.
Ammonia
Most geothermal steam contains
ammonia at levels too low to pose a direct
health hazard. Moreover, as with
hydrogen sulfide, atmospheric diffusion
rapidly lowers ammonia levels to
acceptable values. Inhalation of high
concentrations (1000 ppm) of ammonia,
which can cause extensive irritation of the
eyes and upper respiratory tract, cough-
ing, and vomiting, is thus a rare occur-
rence. However, if ammonia reacts with
other chemicals to form more toxic
compounds (such as with hydrogen
sulfide to form ammonium sulfate),
harmful environmental impacts on
human health and certain plant and
animal species may result. [54]
Carbon Dioxide
Carbon dioxide is present in undiluted
geothermal steam in quantities more than
twice its toxic level. Because it is a normal
component of the atmosphere, it tends to
diffuse rapidly and therefore does not
usually pose a major danger. However,
the accumulation of carbon dioxide in
terrain depressions (which can occur as a
result of its greater density than air), may
result in high concentrations in the
ambient air.
-------
Figure 22
Physiological Effects of Hydrogen Sulfide
odor
nuisance
loss of
sense
of
smell
eye
irritation,
fatigue
eye
irritation,
photophobia
after
several
hours
eye and
respiratory
irritation
within
1 hour,
possible
death
within
43 hours
eye and
respiratory
irritation
within
30 min.;
slight
systemic
effects
within
4-8 hours;
dyspnea,
hemorrhage,
and death
within
48 hours
slight
systemic
effects
within
4 hours,
hemorrhage
and death
within
8 hours
slight
systemic
symptoms
within
1 hour,
death
within
4-8 hours
death
within
1 hour
Ppm
0.067
0.067-0.67
0.67-6.7
mg/md 0.1 0.1-1 1-10 10-150
SOURCE: Sheiler, L, Woodward-Clyde Consultants, 1975.
6.7-100
100-200
150-300
200-334
300-500
-------
Air Quality
71
Mercury
Mercury, which can be toxic to living
tissue, is a known constituent of some
geothermal fluids in trace amounts.
Because of its natural tendency to
vaporize, mercury can be emitted to the .
atmosphere through natural releases of
steam as well as those caused by
geothermal development, and can be
washed from the atmosphere by rainfall.
Mercuric compounds are soluble in water
and thus can be absorbed by living organ-
isms directly from water or indirectly
through the food chain. Because of its
recorded toxicity in living tissue
(inhabitants of the Minamata Bay area of
Japan have suffered nerve diseases and
death as a result of eating fish and
shellfish highly contaminated with methyl
mercury released from a plastics factory),
standards have been set by the U.S. Public
Health Service for mercury concentration
in air, water, and foods such as fish and
shellfish.
Radon
Radon-222, the only radioactive gas, is
found in trace amounts in the
noncondensable gas portion of geothermal
steam. It is produced by the decay of
uranium in the rocks of the geothermal
reservoir.
Although only a minute amount of
radon is present in geothermal effluents,
its very presence has caused considerable
concern. Once introduced to the atmos-
phere, radon acts as a source of highly
toxic decay products. While radon itself
does not accumulate in human beings, it
has a relatively short half-life of 3-82
days, and breaks down into "daughter
products" that readily attach to other
particles in the atmosphere. These
particles can, in turn, attach to human
tissue. Increases in lung cancer at
industrial sites have been associated with
exposure to radon and its daughter
products; A concentration standard of
three picocuries per liter has been set by
the state of California for the radon-222
concentration in the air.
Sources of Air Pollutants
The major sources of air pollutants
emitted during geothermal power
production are (1) direct releases of
geothermal steam during all stages of
development and (2) releases of noncon-
densable gases during plant operation (see
Table 10).
Vapor-dominated Systems
In vapor-dominated fields such as The
Geysers, dry steam is released to the
atmosphere when the steam-producing
zone is penetrated, during subsequent
well cleanout, and again during
production testing. Results of extensive
tests at The Geysers indicate that the
average initial steam flow of a well is
68,000 kg/hour (150,000 Ib/hour), al-
though initial steam flow rates as high as
172,000 kg/hour (378,000 Ib/hour)
have been recorded. [55] An average well
producing 68,000 kg/hour of steam with
an average hydrogen sulfide content of
222 parts per million (as shown in Table
11) would result in the emission of 15
kg/hour (33 Ib/hour) of hydrogen sulfide
during well testing. A successful
Table 10
Sources of Steam and Noncondensable
Gas Emissions During Geothermal Development
Relative Importance
as Pollution Source
Steam discharge during well drilling and clean-out Moderate
Production testing of wells Moderate
Well blow-outs Low
Venting or "bleeding" of test wells prior to power generation Low
Steam line vents during power plant operation Moderate
Accidental steam line breaks Low
Venting of wells during plant shutdown Low-Moderate
Power plant operation High
-------
72
Air Quality
exploratory well at The Geysers will be
cleaned and tested for approximately 20
days; during this time an average of
7,200 kg (15,800 Ib) of hydrogen sulfide
is emitted per well.
Following production testing, the well
is discharged continuously through a
bleed line until it is connected to the
power plant. The average steam and
hydrogen sulfide flows through a bleed
line are small-450 kg/hour (990
Ib/hour) and 0.1 kg/hour (0.221
Ib/hour), respectively; however, the time
period of discharge is variable, and can be
Table 11
Expected Total Air Emissions
at The Geyiers Prior to Operation
of Geothermal Wells for 1000 MW
of Generating Capacity
Constituent
Total,
Metric Tons"
Steam
Carbon dioxide
Ammonia
Methane
Hydrogen sulfide
Nitrogen and argon
Hydrogen
12.09 x 106
9.55 x 104
8.46 x 103
6.04 x103
6.04 x 103
3.63 x 103
1.21 x 103
SOURCE: Teknekron, Inc., 1975.
• Calculation assumes that well testing
continues for approximately 2 months
per well.
as long as several years. The total
estimated quantities of air pollutants
released to the atmosphere prior to power
plant operation for 1,000 MWe of gen-
erating capacity located at The Geysers
are shown in Table 11. These quantities
represent combined total emissions from
well drilling, clean-out and production
testing, and not rates of emissions per
unit oi time. Noncondensable gases
currently are not controlled at The
Geysers during these stages, although
emissions of particulate matter are con-
trolled through the injection of water into
the "blowline*' and the use of mufflers
(see Chapter 7).
Uncontrolled blowouts, which have
occurred infrequently during well drilling
and production testing, also represent a
source of air pollution. One such
uncontrolled blowout at The Geysers
(well "Thermal1' 4) has resulted in total
releases to the atmosphere of 4,000 tons
(3630 metric tons) of hydrogen sulfide,
5,000 tons (4535 metric tons) of
ammonia, and 6,000 tons (5440 metric
tons) of methane between 1957 and
1975. This is about one-eighth the total
that would have been emitted by a 100
MWe generating unit operating at The
Geysers over the same period without
special emission controls.
Rawer plant operation represents the
most significant source of air pollution
associated with geothermal power produc-
tion. The solids and particulates are
removed in a ' 'centrifugal separator''
built into each steam line. In existing
units, the steam is cooled in direct contact
with circulating cooling water. About
one-third of the total hydrogen sulfide,
and most of the other noncondensable
gases in the steam, are continuously
emitted to the atmosphere.
A portion of the gas, including about
two-thirds of the total hydrogen sulfide, is
dissolved in the condensed geothermal'
fluid, circulated to the cooling tower, and
then released to the atmosphere, along
with the evaporated water. [56] A small
amount of the hydrogen sulfide (less than
10 percent of the total) is naturally
oxidized to elemental sulfur and suUates
in the cooling tower and is reinjected to
the subsurface reservoir along with the
excess condensed water (Figure 23). [57]
Concentrations of hydrogen sulfide as
high as 0.87 ppm have been recorded in
the ambient air at a sampling station
located dose to a cooling tower near The
Geysers; the average of 44 measurements
taken was 0.126 ppm. Of 1,218 measure-
ments taken at 37 sampling stations in
the area, 84 percent recorded hydrogen
sulfide levels lower than the California
standard of 0.03 ppm. [58] However,
residents in the area have complained
about the noxious odor produced by the
emissions. Systematic air quality sampling
and statistical analysis to determine
average ambient levels of hydrogen sulfide
are currently being conducted, and
PG&E is currently undertaking an
extensive program which should
significantly reduce emissions of this gas
within the near future.
At The Geysers, emissions of gases
other than hydrogen sulfide are generally
low enough so that they neither
constitute a significant problem nor
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Air Quality
73
Figure 23
Typical System Cycle of Units 5 to 10 at Pacific Gas and Electric Company's Geysers Power Plant
Air ind evaporated water
Geothermal steam from wells
Cooling
8% of cteam water
on-
condensable
gases
at inl»t:
7.9 bar
180« r
Auxiliary
cooling
water pumps
Cooling water 27° C
Direct contact
condenser
Condensed steam
and cooling water
£XCM* steam
coiHJaniafe to
reinsertion wells
Condansate pumps
Electrical
power
Condensed steam
and cooling water
SOURCE: Pacific Gas and Electric Company
-------
74
Air Quality
violate state and federal standards. For
example, California Department of Health
standards require that radon concentra-
tions in uncontrolled areas be less than 3
picocuries [a quantity equivalent to
2.04 x 10-*° kilograms per liter (1.273 x
10"1* Ib/cubic foot)]; measurements show
that the standards are not exceeded in
areas of normal human access. [59]
Sampling to determine emission levels in
mercury and other heavy metals, and
their concentrations in air, water, soils,
and vegetation, is also currently being
conducted at The Geysers, Cerro Prieto,
and the Imperial Valley.
Table 12 compares the total air pollu-
tion emissions that would be generated by
a 1,000 MWe geothermal plant located at
The Geysers with air pollution emissions
from fossil-fuel and nuclear power plants.*
The comparison shows that geothermal
power plants are not necessarily
' 'cleaner'' than fossil fuel plants.
Furthermore, the odor of hydrogen sulfide
emitted by geothermal power plants
creates a nuisance that does not occur
with the sulfur dioxides and sulfates
emitted by fossil fuel plants. Experience at
The Geysers indicates that it is
technically feasible to reduce hydrogen
sulfide emissions during power plant
operation by as much as 90 percent. The
use of such controls is assumed in Figure
24.
• The relative significance of rich of these sources can be assessed
in terms of the total weight of polluting substances released.
Calculations of this weight are based on the average steam flow for
each source, size of the power plant, period of operation, and
concentration of noncondeiuable gases in the steam.
Hot-Water Systems
As previously noted, geothermal steam
derived from hot-water systems may
contain either more or fewer air pollutants
than does steam from vapor-dominated
systems. The likely emissions resulting
from development of a new hot-water
system can only be estimated based on (1)
detailed, site-specific analyses of the
chemistry of its geothermal fluid, (2)
monitoring of emissions and ambient air
quality.
During well drilling and production
testing, steam flashed from geothermal
hot waters may represent 20-25 percent
of the total fluid, depending on its tem-
perature. For comparable levels of
electricity generated, the total quantity of
steam released to the atmosphere during
these phases is probably comparable to
that emitted at The Geysers. The
resulting air pollution is strictly a function
of the amount of noncondensable gases in
the steam. Since the hot-water wells can
in some fields be "capped" or completely
shut off after production testing, well
'' bleeding'' prior to power plant
operation may not represent a source of
air pollution. [60]
During operation of a flash-turbine
power plant—the system currently used
at both Cerro Prieto, Mexico, and
Wairakei, New Zealand—noncondensable
gases are vented to the atmosphere; thus,
air pollution control techniques similar to
those at The Geysers should be
applicable. In the binary-fluid type of
generating unit, the geothermal hot
waters would be reinjected directly to the
production reservoir following use and no
air pollution emissions would occur.
However, binary-fluid systems are still
experimental.
At Wairakei, New Zealand,
geothermal steam is relatively ' 'clean";
it contains only about one-fifth as much
hydrogen sulfide as steam at The Geysers.
This 145 MWe plant discharges about 14
kg/hr (30.8 Ib/hr) of hydrogen sulfide to
the atmosphere at concentrations of about
5,000 ppm in the stack gas. About five
times this amount is transferred to the
plant's cooling water and discharged into
a nearby river. [61] In contrast, geo-
thermal steam at Cerro Prieto, Mexico,
contains substantially more hydrogen
sulfide; emissions of this gas from a 37.5
MWe unit have been measured at 355
kg/hr (780 Ib/hr). [62] Figure 24 shows
the expected annual hydrogen sulfide
emissions from a hypothetical 1,000
MWe power plant at both those locations
and at The Geysers.
Preliminary estimates indicate that
steam from the geothermal fluids of the
Imperial Valley will also contain large
amounts of hydrogen sulfide. [63] At the
experimental 10 MWe generating unit at
Niland, flashed steam will be "scrubbed"
to remove the polluting gas. However,
available data are insufficient to assess
accurately the total quantities of hydrogen
sulfide and other air pollutants that would
be emitted from a geothermal power plant
in this area. Current research and
monitoring at this and other potential
geothermal development sites should soon
provide better answers to this important
question.
-------
Air Quality 75
Table 12
Air Emissions of Alternative Electrical Generating Processes, 1000 MWe Plant
(metric tons/year)
Process
Nuclear (light-water reactor)
Coal
Residual fuel oil
la]
Natural gas
Low Btu synthetic natural gas
(from coal)
Geothermal (The Geysers)
[c]
sox
50
54,000
37,000
20,000
20
900
5,600
1,600
0
0
NOX
42
38,000
25,000
18,000
20,000
267
13,000
0
0
C02
0
n/a
n/a
n/a
n/a
n/a
n/a
n/a
250,000
CO
2,000
700
4,300
neg.
20
neg.
550
0
0
Hydro-
carbons
600
470
20,000
34
11
neg.
5
1 5,000
NH3 H2S Participates
8
23.000
150
2,000
5
n/a
12 5,000
15,000 1,700!bl 0
0
NOTE: The first row under each process defines emissions during power plant operation; second rows define emissions during other steps
(mining, transportation, etc.).
SOURCE: Teknekron, Inc., 1975.
neg.—negligible
n/a—not available
[a] Emissions from a hypothetical 500,000 bbl/day refinery which produces 34.000 bbl/day residual fuel oil to supply a 1000 MW power plant.
[b] Assuming 90 percent reduction of uncontrolled hydrogen sulfide emissions due to use of hydrogen sulf ide abatement equipment
(uncontrolled emissions are 17,000 metric tons/year!.
lc] See Table 11 for total pollutant emissions from wells prior to power plant operation.
-------
Figure 24
Expected Annual Hydrogen Sulfide Emissions
During Operation of a Hypothetical 1000 MWe Plant
Located at Several Geothermal Sites
82,900 metric tons/year
1,700 matric tons/year
controlled
857 metric tons/yMr
17,000 metric tons/year
uncontrolled
SOURCES: Calculated from data in Teknekron, 1976;
Axtmann, 1975; Mercado, 1975.
-------
Air Quality
77
Research Needs
The air pollution problems currently
receiving the greatest attention are those
related to hydrogen sulfide emissions.
ERDA, the Pacific Gas and Electric
Company, and other public and private
organizations are examining various ways
to control hydrogen sulfide during power
plant operation. Most of these approaches
focus on treating hydrogen sulfide after it
reaches the turbine in the power plant and
do not provide for pollution abatement
during periods when the plant is shut
down for maintenance or repairs.
Increased emphasis should be placed on
controlling hydrogen sulfide before it
reaches the turbine; not only would this
control pollution at ah1 times, but it could
improve the operating efficiency of the
plant as rock, dust, and other foreign
particles are removed from the
geothermal steam.
While hydrogen sulfide is known to be
harmful at high concentrations, little is
known about the possible health effects of
long-term exposure to low concentrations.
As these effects could include irritation of
the respiratory system and interference
with the transport of oxygen in the
human body, they should be thoroughly
investigated. Research should also be
conducted into me time required for
hydrogen sulfide to oxidize to sulfates and
sulfuric acid under varying topographic
and climatic conditions.
The development of control
technologies for other air pollutants, such
as arsenic, ammonia, mercury, and
radon, will be important if the modeling
and monitoring efforts currently under
way show that these compounds would be
geothermal development sites. For
example, researchers in New Zealand are
currently experimenting with removing
silica and arsenic from geothermal waste-
waters by adding slaked lime to precipitate
calcium silicate. The applicability of such
techniques in the United States should be
investigated.
Increasingly precise and systematic
techniques must be developed to monitor
air pollution in geothermal development
areas. Sophisticated chemical and radio-
chemical sampling methods must be
developed, for example, to determine the
concentrations of all harmful substances
at a site and to distinguish between the
effects of naturally-occurring and develop-
ment-related pollutant discharges. EPA
recently sponsored technical conferences
to evaluate ongoing research on
geothermal sampling techniques.
Removal of harmful air pollutants from
the gases discharged at a geothermal
facility may create solid waste disposal
problems. The ideal solution is the
development of an economically feasible
technology to recover waste materials in
usable form. To encourage this solution,
high priority should be assigned to the
development of hybrid geothermal
facilities that combine chemical
production and power generation.
-------
-------
79
Control
Of Hydrogen
Sulfide At
The Geysers
In recent yearn, concern about the effects of hydrogen sulfide emissions at The
Geysers has increased, based on its toxicity, noxious odor, and relatively high con-
centrations; and air pollution control technology has been directed primarily at
lowering these emissions.
The California Air Resources Board standard for hydrogen sulfide is its odor
threshold—0,03 ppm for ambient air. Since the "rotten egg" odor of hydrogen
sulfide is noticeable in the vicinity of The Geysers, the State Air Resources Board
and the Northern Sonoma County Air Pollution Control District have been is-
suing temporary variances for the hydrogen sulfide emissions from the power
plants.
PG&H has conducted extensive research and testing to develop an effective
program to control hydrogen sulfide emissions at The Geysers. A variety of
methods for control have been tested. The current abatement program planned
for the 1} existing generating units will install a ducting system on all existing
units that transfers the gases emitted from the jet gas ejectors to the cooling
tower. An iron catalyst will he added to the cooling waters to promote oxidation
of the hydrogen sulfide to elemental sulfur. The solid elemental sulfur thus
remains in the cooling water, and is ultimately removed from the excess conden-
sate reinjccted through the use of sand filters. However, in tests the iron catalyst
has caused corrosion; and while this method is capable of reducing hydrogen sul-
fide emissions to 10 percent of their original levels, it does not reduce other gase-
ous emissions.
-------
80
Netu units built at The Geysers will use an improved system. Noncondens-
able gases from the jet gas ejector will be transferred directly to a sulfur removal
unit ("Stetford plant"), which will reduce hydrogen sulfide emissions slightly
more (up to 98 percent). Both processes planned for use at The Geysers generate
large quantities of elemental sulfur, which must be disposed of at an approved
solid waste disposal site.
These control systems treat gases after they reach the turbine. If the turbine
is shut down, the hydrogen sulfide-laden steam is vented directly to the atmos-
phere. Because 24 hours are required to shut down a well and additional time re-
quired to reopen and clear out pebbles and rocks that can be picked up by the
steam and damage the turbine, it is impractical to shut down the well when the
turbine is shut off.
Treating steam before it reaches the turbine may prove feasible, and would
permit control during shutdown. ERDA-sponsored laboratory studies are pres-
ently exploring the possibility of using regenerate copper sulf ate to convert the
hydrogen sulfide in geothermal steam to copper sulfide and sulf uric acid.
-------
9. Thermal
Pollution
and Climate
Geothermal development can also have a
variety of thermal and climatic effects.
The most serious are caused by the
release to the atmosphere of waste heat,
water vapor, and carbon dioxide from
geothermal welk, steam lines, and power
plants.
Geothermal power plants emit larger
amounts of waste heat than do fossil fuel
or nuclear power plants because of their
lower "thermal efficiency1'; that is, less
of the total heat energy contained in the
geothermal fluid is converted to electrical
energy. For example, a typical generating
unit at The Geysers utilizes about 785
MWe of input energy to produce 110
MWe of electrical output, for a "primary
efficiency'' of 14 percent. At the
Wairakei plant in New Zealand, the
primary efficiency is approximately 8
percent. In comparison, fossil fuel and
nuclear power plants have primary
efficiencies ranging from 32 to 42
percent, thereby producing markedly less
waste heat (see Table 13).
Waste heat and water can be discharged
either to the atmosphere or to water. In
terms of environmental impacts, an
important tradeoff is involved: while the
discharge of waste heat and water vapor to
the atmosphere can have negative climatic
effects, discharge to bodies of water can
have harmful biological effects. Since
water quality effects are commonly con-
sidered the more harmful, the trend in
power plant construction has been toward
atmospheric discharge with the use of
cooling towers.
Cooling tower designs for any type of
power plant, including a geothermal, are
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82
Thermal Pollution & Climate
Table 13
Expected Waste Heat Emissions During
Power Plant Operation for Alternative
Electrical Generating Processes,
1000 MWe Plant (kilowatt-hours/year)
Total
Process Waste Heat
(x 1Q1Q)
Nuclear (light-water 1.86
reactor)
Coal 1.2
Residual fuel oil 1.2
Natural gas 1.2
Low Btu synthetic natural 1.2
gas (from coal)
Geothermaf: The Geysers 4.5a
Wairakei 9.7b
SOURCES: Teknekron, Inc.. 1975;
Axtmann, R.C., 1975.
a. Discharged to air.
b. 4.3 x 1010 is discharged to air.
5.4 x 10^0 is discharged to water.
of two basic types: the conventional
"wet" or evaporative cooling tower, and
the dry cooling tower. In the former, the
steam from the turbine enters a
condenser, where it is re-converted to
water. The steam heat is transferred to
circulating water, and the warm water
then transferred to the wet cooling tower,
where it is brought into contact with a
flow of air, which causes evaporation.
Since the cooling water is lost through
evaporation, the supply must be
replenished continuously.
In a dry cooling tower, the water
circulates in a closed system. It is cooled
by a flow of air created by either
mechanical or natural draft, as in an auto-
mobile radiator. Only the heat is
transferred to the atmosphere. Since water
is not lost through evaporation, a dry
cooling tower does not require a
continuous source of cooling water; con-
sequently it may be more desirable
environmentally than a wet cooling tower
in localities having limited water supplies
(see Chapter 6).
Dry cooling towers are significantly
more expensive than wet, and may reduce
the operating efficiency of the power plant
as well. This is why only wet cooling
towers have been constructed for large
power plants to date. Their effects at
fossil-fueled power plants have included a
slight heating of the atmosphere in the
vicinity, increased humidity, and
occasional fogging. These impacts are
generally considered to be minor and local
in scope.
At The Geysers, about 80 percent of
the geothermal steam is discharged from
wet cooling towers as water vapor con-
taining waste heat; the remainder is rein-
jected to the steam reservoir. The result is
a slight heating of the atmosphere in the
vicinity, increased humidity, and occa-
sional fogging. A greater incidence of
plant disease resulting from higher
humidity has been noted in some nearby
areas. Some vegetation has also been
"scalded" by direct releases of steam
from wells and steam lines.
At Wairakei, a liquid-dominated field,
the water of a nearby river is used for
cooling the geothermal hot waters (a
once-through cooling system). The
wastewaters remaining after steam
separation are also discharged to the river.
About half of the total waste heat remains
in the river; the other half enters the
atmosphere along with the water vapor.
This method has resulted in a heating of
the river and extensive ground level
fogging near the plant. [64] It is thus
unlikely that this system would be used at
new geothermal power plants.
-------
Thermal Pollution & Climate
83
In general, the climatic effects
associated with existing geothermal and
conventional power plants using cooling
towers are considered to be relatively
insignificant in comparison with other
environmental impacts. However, their
significance will increase as larger plants
are built. Moreover, if a geothermal
resource is located in an area whose
topography and local meteorological
conditions limit adequate atmospheric
dispersal of heat and moisture, lie
problem of local weather modification
could be significant. Preliminary analyses
of the potential for weather modification
resulting from geothermal development in
Lake County, California (adjacent to The
Geysers) indicate that ten 55-MWe gen-
erating units utilizing wet cooling towers
could increase the moisture content in a
small closed basin by almost 50 percent,
probably leading to some increase in fog
and icing. [65]
Larger-scale climatic effects are also
thought to be possible from geothermal
development. The emission of large
quantities of hydrogen sulfide might
increase the acidity of rainfall in a region
which would lead to corrosion and
harmful effects on vegetation and wildlife;
and the emission of carbon dioxide could
trap heat in the lower atmosphere,
thereby raising the earth's temperature
(the so-called "greenhouse effect").
While the scale of geothermal develop-
ment worldwide is unlikely to be large
enough to cause such significant effects,
the advantages of monitoring the
climatic effects of geothermal develop-
ment are clear.
Research Needs
Research into the thermal and climatic
effects of geothermal development has to
date been assigned relatively low priority
because these effects appear to be less
significant than other environmental
effects. However, certain potential
impacts are serious enough to warrant
further investigation. In particular,
changes in the acidity of rainfall should be
carefully monitored throughout the
regions surrounding geothermal develop-
ment, and any resulting damage to
aquatic species and terrestrial vegetation
and wildlife assessed. The pH and sulfate
levels of rainfall should be analyzed, not
only near geothermal development areas
but also in the surrounding region, both
prior to and during geothermal
development.
If extensive geothermal development is
planned in areas where topography and
local weather conditions limit atmos-
pheric diffusion of the heat and moisture
released from cooling towers—as it does
in narrow, closed valleys—extensive,
local climatic data should be collected. A
data base for predicting the likely extent
of weather modification should include
ambient wind speed and direction, rainfall
frequency, humidity, and temperature.
Similarly, if the development of a
particular geothermal site involves
significant thermal discharges to lakes or
streams, monitoring data on ambient
water temperatures, flow rate, and
currents should be collected.
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84
10. Natural
Biological
Systems:
Fish,
Vegetation
and
Wildlife
The development of geothermal resources
inevitably causes some disturbance to
natural biological systems in the vicinity
of a development site; primarily, land
disruptions, air and water polluting emis-
sions during well testing and power plant
operation, and increased levels of noise
and human activity. The extent, severity,
and long-term consequences of the dis-
turbance vary considerably from site to
site, depending upon the geochemistry of
the geothermal resource and the develop-
ment technology employed. Conscientious
application of sound management tech-
niques and pollution controls can reduce,
but not eliminate, the disturbance. None-
theless, the disturbances to biological
systems caused by geothermal develop-
ment are less severe than is the develop-
ment of alternative fuels that require large
land areas for mining, transportation, and
processing.
Types of Impact
Geothermal development may affect
natural biological systems by reducing the
diversity (the kinds of species in the eco-
system) or the total number of plants and
-------
Natural Biological'Systems
85
animals in an area. These impacts may be
of concern if the species endangered are
rare or if the disturbed habitat is
important to a large population. For
example, extinction of the Devil's Hole
Pupfish (a species believed to have existed
in the West for several million years)
would be regrettable because of its rarity,
antiquity, and unique characteristics; but
the loss would not affect any other
species. On the other hand, destruction of
an estuary would have far-reaching con-
sequences for numerous species.
In addition, certain species may be
valued for their beauty, for the recrea-
tional opportunity they provide, for their
economic value, or for all these reasons.
Snow geese, deer, and redwood trees are
examples of species which may be valued
for any or all of the reasons cited.
An extensive body of legislation
protects certain categories of wildlife from
disturbance. The most far-reaching, the
Rare and Endangered Species Act of
1973, grants the Department of the
Interior authority to prevent development
in areas where threatened species of plants
and animals will be adversely affected.
Little information presently is available
on species existing in the areas of the
West where geothermal development is
likely to occur. Without adequate baseline
information, maps of critical areas, and
knowledge of the interrelationships of the
plants and animals in the area—especially
in a desert ecosystem—substantial harm
can occur inadvertently. During the past
fiscal year, the Fish and Wildlife Service
of the Department of the Interior and the
Environmental Protection Agency have
embarked on several studies aimed at
filling the information void. For example,
FWS is working closely with the Bureau
of Land Management to develop baseline
information for use in government man-
agement programs. This information will
also be used by the U. S. Geological
Survey to conduct the federal geothermal
leasing program.
Sources of Adverse Impacts
The causes of adverse biological impacts
associated with geothermal development
that could lead to a reduction in the
diversity or population levels of species
are: land disruption, erosion and
sedimentation, water effluents, air
pollutant emissions, noise, and human
activity.
Land Disruption
The removal of earth and vegetation from
an area to accommodate geothermal
development can reduce habitat; kill
small rodents, reptiles, or birds living on
the land surface; and cause erosion. An
average of 20 percent of the total land
leased for geothermal activities is cleared
[66] and is changed sufficiently in
character to affect habitat (see Chapter 4).
Of this 20 percent, approximately half is
needed for permanent buildings and
facilities, such as roads and power plants,
which require original vegetation to be
replaced with impervious surfaces. In
addition, land along steam lines and
immediately surrounding drilling pads,
permanent buildings, and facilities may be
temporarily cleared of vegetation. [67]
The clearing of a site for geothermal
development usually has the following
adverse effects on an area's natural bio-
logical systems: [68]
— The nutritional support for the area is
altered as the physical aspects of the
habitat are altered.
— Specific types of habitat (such as an
' 'edge'' *), dependent upon complex
interrelationships, are severely affected.
— Lower population levels may result
until die site revegetates.
— Surface soil temperature and moisture
are altered.
— Erosion may be accelerated.
The recoverability of vegetation varies by
species, soils, climatic conditions, and
severity of disturbance. [69] In cool,
* An "edge" erfectoccurc when two levels of vegetation adjoin one
another, as when a shrub layer abuts a grassland. An "edge" makes
the environment doubly valuable, for instance, many small game
species can browse on grasses and find protection in the shrubs.
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86
Natural Biological Systems
moist, mountainous regions, areas
dominated by grasses and shrubs recover
relatively quickly; forested areas,
however, require a much longer recovery
time. In dry regions, where the
ecosystems are fragile, the amount of time
needed to restore a site is far longer.
During the recovery period, however, the
land is not totally sterile; some animal
species can forage on germinating
seedlings.
Careful plant design and road
placement can avoid excessive disruption
of the land surface during geothermal
development. Avoidance of the "edge''
and critical areas such as breeding
grounds, salt licks, wetlands, and surface
water bodies can help keep the immediate
environment biologically productive.
Erosion and Sedimentation
Disturbance of the surface soil of an area
through erosion interferes with the
fertility of the soil and its ability to retain
moisture. Topsoil, the most fertile part of
the soil structure, is often covered over or
dumped. Small root systems are turned
over and soil structure is altered, causing
additional erosion as the soil is loosened.
Erosion lowers soil fertility and thus
reduces the food available to support the
surrounding environment. Soil erosion
also increases sediment loads in surface
waters, which, in turn, reduces the
quality of streams and their capacity to
support aquatic organisms. Nutrients in
the soil are leached away to the stream-
beds, accelerating stream eutrophication.*
Sedimentation in critical parts of
streams, such as spawning areas, can
increase turbidity, which reduces the
penetration of light in the water. This
makes it difficult for fish to find food and
for aquatic vegetation to grow. In
addition, concentrations of mercury and
other trace metals frequently found in
sediments have been related to concentra-
tions found in fish and aquatic vegetation
living nearby.
The problems of erosion and the
resulting sedimentation of waterways
have proven to be particularly
troublesome at The Geysers, because the
drilling sites are located on steeply sloping
hillsides which receive high rainfall. But
even in this setting, the adverse effects
can be greatly reduced through measures
designed to control erosion, preserve the
topsoil, channel any runoff into an
appropriate treatment system, and
quickly restore the vegetation of
temporarily cleared sites.
Water Effluents
Water pollutants resulting from
geothermal activity—drilling muds, geo-
thermal fluids, and heat from condensed
steam—can have severe effects on aquatic
animal life and vegetation if runoff or
discharges enter streams. Numerous
elements and compounds, particularly
hydrogen sulfide, chlorine, ammonia,
boron, arsenic, mercury, and such heavy
metals as lead and silver, are toxic to
aquatic vegetation and fish at varying con-
centrations. Each of these may be present
in geothermal fluids or drilling muds.
Most freshwater fish are also sensitive to
rapid changes in pH or temperature.
Drilling muds and cuttings normally
are disposed of in a sump during test
drilling and production. Accidental
discharges may, however, occur, and
reach bodies of water. The severity of
their effects depends largely upon their
chemical constituency and the duration of
the discharge. [71]
* Eutrophication is the process by which nutrients build up quickly
in i waterway, nourishing the growth of vegetitkm rod depleting the
oxygen supply needed Co support fish life.
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Natural Biological Systems
87
Geothermal fluids, particularly in hot-
water fields, are often highly saline,
contain heavy metals, and have very high
temperatures (see Water Quality), In
Wairakei, New Zealand, a hot-water field
where reinjection techniques are not
practiced, the composition of disposal in
the nearby river and lake was recently
analyzed. [72] High levels of arsenic,
mercury, sulfur dioxide and hydrogen
sulfide were found in the water, the
aquatic vegetation, and the fish (e.g.,
mercury compounds at levels toxic to
humans, 0.5 mg/kg or 0.5 ppm, were
found in trout weighing more than 1.25
kg). Two large fish kills have been noted
in the nearby lake and the number of
trout in the immediate area of the plant
has been reduced, although they have
become more abundant just upstream and
downstream. Lake Aratiatia, below the
Wairakei plant, has fewer phytoplankton
and tooplankton species—the first links in
the food chain for fish in the lake.
The development of adequate reinjec-
tion techniques for hot-water systems will
help protect the environment from the
adverse effects of geothermal fluids. The
development of an adequate reinjection
technology will be particularly significant
in areas where economically valuable or
sensitive fish, wildlife, or vegetation exist,
such as in the tidal basins along the coast
of Texas and areas of the West where
fragile desert ecosystems can be disrupted
easily and restored only after long periods
of time, if ever.
Air Pollutant Emissions
Gaseous emissions from dry-steam fields
contain a number of potentially dangerous
products—including hydrogen sulfide,
carbon dioxide, and trace amounts of
radioactive gases (see Air Quality).
Studies to measure the buildup of these
emissions in vegetation, aquatic
organisms, and animals are just being
initiated. Recent studies of the egg and fry
of rainbow trout, for example, indicate
that this species is vulnerable even to very
low concentrations of hydrogen sulfide
(above 0.006 ppm). [73] In-stream
concentrations of hydrogen sulfide at
Wairakei have probably exceeded these
limits; botanists have reported
filamentous sulfur bacteria, which thrive
only in the presence of sulfide growing in
nearby Jakes. Recently completed studies
supported by the National Science
Foundation and the Fish and Wildlife
Service report previously unsuspected
damage by hydrogen sulfide to coniferous
trees and some types of shrubs and plants.
They also report highly variable
sensitivity in vegetation; the most
sensitive appear to be immature plants
and plants under stress from aridity.
[74, 75]
Sulfur dioxide, in particular, could have
especially adverse effects in humid areas,
where it oxidizes to sulfur trioxide and
sulfuric acid. Millions of research dollars
have been spent to determine the
detrimental effects of sulfur compounds in
the atmosphere. Compounds have been
shown to "acid rain" or "arid snow" (a
reduction in the pH of precipitation),
which can burn the leaves of trees and
shrubs, as well as heighten the acidifica-
tion of water bodies. The acidification of
lakes has, in turn, been related to the
widespread destruction of fish habitats,
[76]
Another possible hazard results from
trace amounts of radioactive elements
present in geothermal emissions. While
radon and other radioactive elements have
been studied to determine their effects on
humans and animals, the possibility of
radioactive substances becoming con-
centrated in the fatty tissues of organisms
and transmitted through the food chain as
a result of geothermal development has
not been investigated. The probability of
such an occurrence is, however, judged to
be moderate or slight. [77]
Steam emissions can also have more
direct and immediate effects. Trees in The
Geysers area have been scalded; birds and
other wildlife that come in contact with
the steam are also in danger of being
burned.
The outlook for the improved control
of sulfur emissions is promising. The
recently developed "Stretford" process,
which is to be installed at new generating
units at The Geysers, is expected to
remove 85 to 90 percent of the sulfur
prior to release (see Air Quality). This
process is expected to work on the
' "flashed-steam" hot-water system as
well. (The binary system involves no
release of pollutants.) Research projects
are ongoing to determine the threshold
levels of various species of fish, wildlife,
and vegetation to toxic gases, acid rain,
heavy metals, and steam; and to gauge
the effects of long-term exposure at sub-
lethal levels.
-------
H8
Natural Biological Systems
Noise and Human Activity
The impacts of noise on natural biological
systems have not yet been researched
extensively. Some studies have uncovered
no evidence of effects on animals in their
natural habitats at a reasonably short
distance from the site. [7ft] However,
other studies are being conducted to
measure subtler changes, including those
of behavior and physiology. [79] Of
particular importance is the possibility
that noise in frequency ranges inaudible
to the human ear may affect animals
adversely. Loud, continuous noise may
also affect animals who depend on acute
hearing for protection, hunting, or
mating. Particularly sensitive species need
to be identified. If animals were to
permanently abandon their habitat as a
result of noise, the ecosystem would
probably be affected adversely as well.
The impacts of human activities on
natural biological systems are even more
difficult to measure. Intrusion may pose a
severe threat to some species, but
relatively little to others. Associated
dangers such as fire, titter, and garbage
may pose threats to foraging animals. Yet,
at The Geysers, deer and other animals
have been reported to graze near the
drilling site and steam pipelines, where
they find warmth and forage in the winter.
Desert ecosystems may be threatened
more severely by human intrusion than
upland forests and grasslands. That
possibility is one of many under study by
the Fish and Wildlife Service.
Research Needs
To maintain the diversity, productivity,
and stability of an ecosystem subject to
intrusion from geothermal development,
extensive, site-specific examinations of
existing ecosystems must be conducted in
potential geothermal areas prior to
development. Such investigations are vital
to the development of management plans
for those activities that can reduce
harmful effects to the biota. Among the
baseline environmental information
which must be collected are: [80]
— Identification of plant and animal
species present, their distribution, and
population sizes
— Determination of critical ecological
characteristics, that is, characteristics
of the environment diat play a unique
or particularly important role to a
species and thus are critical to their
survival
— Identification of any species present
classified as "endangered" or
"threatened" by the U.S. Department
of the Interior or state agencies
— Life cycle characteristics
— Nutritional requirements and
susceptibility to disturbances of any
critical, threatened, or endangered
species present.
Examination of the environment prior to
development must be followed by
monitoring to detect possible changes
during development and subsequent
operations. The early identification of
impacts can prevent unnecessary and
extreme harm, and the information
gathered can be of potential use in other
research areas.
This type of environmental information
is beginning to be gathered in many areas
of the West by the U. S. Fish and Wildlife
Service. More widespread understanding
of the importance of early study and more
diligence in applying sound management
practices appear to be the greatest needs
in protecting natural biological systems.
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-------
90
Section II
References
'Refer to bibliography at end of book for complete citation,
Chapter 4 19 Ecoview Environmental Consultants, 1974, p. 95.
20 Ibid., p. 95.
21 #fc/.,p.94.
22 United States Department of the Interior, Bureau of Land Management, 1973,
43 CFR Part 3000,3200, Section 3200.0-6(b).
23 Ibid.
24 United States Department of the Interior, 1973, p. ffl-50.
Chapter 5 25 Bowen, Richard G., 1973, p. 202.
26 Axtmann,RobertC.,1975a,p.801.
27 Dutcher,LC.,etal.,1972,p.51.
28 Wilson, JohnS., etal., 1975, p. 49.
29 United States Geological Survey, 1972 , p. 49.
30 Ward, P. L, p. 3-
31 Ibid.,vA.
32 Sanquist, G. M. and G. A. Whan, 1973, p. 298.
33 Ward, P. L, p. 6.
Chapter 6 34 Reed, Marshall J. and Glen E. Campbell, 1975, p. 1409.
35 Ibid., p. 1409.
36 Teknekron, Inc., 1974, p. 186.
37 Bowen, R., 1974, p. 199.
38 Dutcher, L. C. , et al., 1972, p. 29-
39 Bowen, R., 1973, p. 199.
40 University of Oklahoma, 1975, pp. 8-15.
41 United States Department of the Interior, 1973 .
42 United States Geological Survey, 1972, p. 37.
43 Axtmann,RobertC.,1975a,p.801.
44 Teknekron, Inc., 1976, p. 52.
45 Ibid., p. 52.
Chapter? 46 Occupational Health and Safety Act, PL 91-596, Regulation 1910.95,
' ' Occupational Noise Exposure. ' '
47 Reed, Marshall], and Glen E. Campbell, 1975, p. 1405.
48 Ibid., p. 1405.
49 United States Department of the Interior, 1 972 .
50 Ibid.
-------
91
Chapters 51 Axtmann, Robert C, 1975a,p, 1324.
52 Shetler,Leroy,1975,p.3.
53 Ibid.,?A.
54 Ibid, p.4.
55 United States Department of the Interior, 1972, p. 163.
56 Reed, Marshall;, and Glen E. Campbell, 1975, p. 1409.
57 Weinberg, Dr. Carl, personal communication, 1976.
58 McCluer.H.K., Pacific Gas and Electric Company, personal communication, 1977.
59 Reed, Marshall;, and Glen E. Campbell, 1975, p. 1409.
60 United States Department of the Interior, 1972, p. 175.
61 Axtmann, Robert C.,1975b, p. 798.
62 Mercado, Sergio, 1975, p. 1397.
63 Goldsmith, M., pp. 29-34.
Chapter9 64 Axtmann,RobertC.,1975b,p.799.
65 Ibid., p.m.
Chapter 10 66 United States Department of thelnterior, 1973, H, V-80.
67 Ibid.
68 United States Fish and Wildlife Service, 1976, p. 163.
69 United States Department of the Interior, n,V-80.
70 Ibid., p. 131.173.
71 Ibid., p. 139-
72 Axtmann, RobertC., 1975b, p. 799.
73 M/.,p.798.
74 Thompson, Professor Ray, personal communication, 1976.
75 Spaulding, William, personal communication, 1976.
76 State of California, Division of Oil and Gas, 1974, p. 55.
77 Ibid., p. 53.
78 Thompson, Professor Ray, personal communication, 1976.
79 Spaulding, William, personal communication, 1976.
80 United States Fish and Wildlife Service, 1976, p. 63.
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• .-' -. „ fVTSJfea,
»—s • ' -*Lr'• -^S
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m.
The Future
of Geothermal
Resources
••..••:••:.. •-•. .^i. •. ..»•/-.
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94
11. Federal
Environmental
R&D Activities
Related
To Geothermal
Resource
Development
Over the past two years, funding for
environmental R&D related to
geothermal resources has doubled, as has
funding for the development of
geothermal technology. Much of this
increase has been directed to research
programs that address the environmental
effects of hydrothermal convection
systems, which are believed to offer the
most rapid development potential. Table
14 offers current estimates of federal
expenditures for environmental R&D.
Research on geothermal technology and
resource assessment, although not
specifically performed with "environ-
mental" R&D funds, also generates
significant information about environ-
mental effects. Unfortunately, the data
needed to calculate a dollar amount that
accurately reflects this "hidden" subsidy
are not available.
In 1974, Congress designated the
Energy Research and Development
Administration as the lead agency in the
development of geothermal resources.
Under ERDA's coordination, the federal
geothermal development program has
been organized into seven areas: environ-
mental control and institutional studies,
resource assessment and exploration,
hydrothermal technology, demonstration
-------
Federal Environmental R&D Activities
95
projects, advanced technology applica-
tions, engineering research and develop-
ment, and resource development funding.
R&D specifically focused on environ-
mental activities related to geothermal
development is now being undertaken by
ERDA and the Environmental Protection
Agency (EPA), the National Science
Foundation (NSF),* and several divisions
of the Department of the Interior,
particularly the Fish and Wildlife Service
(FWS). In addition, a Federal Interagency
Energy/Environment R&D Program that
coordinates large-scale R&D activities
contributes to geothermal research. The
following sections describe the activities
of these agencies.
Energy Research and
Development Administration
The bulk of ERDA's environmental-
related geothermal R&D is being funded
by its Division of Biomedical and
Environmental Research. The largest
single current program is being conducted
in the Imperial Valley of California by
ERDA's Lawrence Livermore Laboratory.
Valley-wide assessments are being made
of potential subsidence and seismic
problems associated with the development
of large-scale hot-water systems.
ERDA is testing the air, water,
vegetation, and wildlife impacts of
emissions and effluents from geothermal
conversion plants at San Diego Gas and
Electric Company's experimental facility.
ERDA is also studying the environmental
Table U
Federal Environmental R&D Budgets
for Specially Focused Geothermal-related Research
($000)
1975
1976"
1977b
National Science Foundation
Environmental Protection Agencyd
Energy Research & Development Administration
Fish and Wildlife Service
Total
1,500
340
Oe
300
2,140
600
365
2,000
300
3,265
Oc
636
2.300
1,500
4,436
SOURCE: Information for the budget figures was obtained through personal communication
with senior officials in the agencies listed.
a. Includes Transitional Quarter funds.
b. Budget requested for 1977 fiscal year.
c. NSF is phasing out all focused geothermal environmental R&D, as ERDA takes on full
responsibility.
d. The annual budgets for the Interagency Energy/Environment R&D Program for 1975 and
1976 were $134 and $100 million, respectively. However, since an insignificant fraction of
these amounts was specificially directed to geothermal R&D, it has not been included in these
calculations. The numbers for the other agencies include any funds from the EPA "pass-
through" that are being used for geothermal research,
e. ERDA did not begin funding this activity until its first full year in operation.
' In January 1975, NSF tniufenvd nearly i]] its soUrind
geothcnnil energy rtwtrch to ERDA; only somt NSF-RANN
projects remain in specuHud ireu.
-------
96
Federal Environmental R&D Activities
and socioeconomic impacts of The
Geysers plants in California. Preliminary
studies on the effects of developing hot
dry rock formations in the Jemez
Mountains of New Mexico are being
conducted at the Los Alamos Scientific
Laboratory.
Through its work on new energy
technologies, ERDA's Division of Geo-
thermal Energy is also involved in en-
vironmental research. It has defined two
specific goals for fiscal years 1976 and
1977: (1) development of baseline infor-
mation to determine the need for environ
mental impact assessments, and (2)
development of effective controls for
hydrogen sulfide emissions. Monitoring
guidelines and facility siting
methodologies are planned for develop-
ment in fiscal year 1978.
Environmental Protection Agency
To date, EPA's role in the federal geo-
thermal R&D program has involved
research on the air, water, noise, and
health effects of geothermal development.
Several major research projects currently
are under way.
EPA's Las Vegas Laboratory is
monitoring heavy metals and other air
emissions and water quality effects
resulting from the operation of
experimental facilities at five sites in the
west: The Geysers and Imperial Valley,
California; Klamath Falls, Oregon; Rio
Grande Rift, New Mexico; and Roosevelt
Hot Springs, Utah. Plant and soil uptake
of emissions from geothermal power
plants is being analyzed by fixed and
mobile stations. The effects on ground-
water of accidental or planned disposal
methods are also being studied.
EPA's Industrial Environmental
Research Laboratory (IERL) is surveying
the environmental regulations pertaining
to geothermal development, analyzing the
pollution hazards associated with geo-
thermal power, and investigating the need
for better control technologies.
National Science Foundation
The NSF's program focuses on a few
specific problems. Several projects
presently are being conducted on the
environmental effects of the extraction
and disposal of geothermal fluids,
including the potential for subsidence. In
this connection, NSF is experimenting
with a technique to trace geothermal
effluents in surface bodies by developing a
"fingerprint" of the geothermal fluid.
In another study, NSF has been
investigating the effects on birds and
animals of the noise generated by geo-
thermal power plants and interference
with flight caused by transmission lines.
The overall environmental effects of
geothermal energy production are being
examined in an effort to identify other
research needs.
Fish and Wildlife Service
As part of its work to establish a five-year
R&D priority plan, the Fish and Wildlife
Service of the Department of the Interior
is currently compiling information on the
potential effects of geothermal
development on natural biological
systems, FWS is also working at the five
western sites where groundwater is being
monitored by EPA to determine its effect
on the fish and wildlife in those areas.
Their study aims to develop techniques
for predicting the probable effects of
geothermal energy development on fish
and wildlife.
In response to increasing interest in
developing the geopressured reservoirs of
the Texas Gulf Coast, FWS has under-
taken a research project to identify the
possible environmental consequences to
the area. As part of this work, the FWS is
compiling an inventory of the area's
ecological system.
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12. Legal,
Institutional
and Economic
Constraints
To Geothermal
Resource
Development
Despite the existence of several promising
hydrothermal systems with temperatures
in the range practical for electrical genera-
tion, their commercial utilization has
been slow to develop. In addition to the
lack of resource information, unsophis-
ticated technologies, and environmental
difficulties, several legal, institutional,
and economic constraints seem to be
impeding more rapid growth.
Legal Constraints
The lack of a consistent, generally
accepted definition of geothermal energy
has led to widely varied interpretations of
laws governing ownership, regulation,
and taxation. Examples of some
significant complications include:
Ownership. A recent California Superior
Court decision (Geothermal Kinetics, Inc.
v. Union Oil of California, et al} defined
geothermal resources as "minerals,"
rather than "water,1' based on the fact
that the superheated steam withdrawn
was not used as water has traditionally
been used (that is, for agricultural
purposes and as a water supply), but as an
97
-------
98
Legal, Institutional & Economic Constraints
energy source. The court found that
Geothermal Kinetics, which had
purchased the mineral rights of 408 acres
known as The Geysers,' 'owned and was
entitled to the possession and control of
all the geothermal steam and power and
geothermal resources in and under the
subject property.'' The owner of the
surface rights, and also the water rights
(Union Oil of California), thus had no
claim to the steam from the geothermal
reservoir underlying the land.
Regulation. Depending on the accepted
definition of geothermal energy, the
owner of a geothermal field may be
subject to a variety of regulations that
affect development decisions. If
geothermal energy is classified as a
"mineral," the owner must comply with
a complex set of mining regulations; if it
is classified as ' 'water,'' the owner must
comply with complicated local, state, and
federal water control and use laws.
In response to water supply problems,
many western states have enacted legisla-
tion that prohibits the diversion of water
for uses outside the state without the state
legislature's authorization. Whether or
not these statutes are applicable to
developers of electricity produced from
geothermal resources defined as ' 'water''
is an issue yet to be resolved.
Taxation. In a 1972 case, Reich v. Com-
missioner of Internal Revenue, the court
held that a geothermal resource that was
primarily steam was classified as a "gas"
within the meaning of the IRS code.
Developers of the resource were therefore
eligible to take depletion allowances and
write off intangible drilling costs on their
tax returns. Such tax benefits do not
accrue to the developers of water
resources.
Institutional Constraints
The current overlap in administrative and
regulatory procedures among local, state,
and federal agencies significantly impedes
geothermal development. The problem of
overlapping authority is greatest in
issuing licenses and permits and
approving environmental impact
assessments.
The administrative problems associated
with geothermal development begin with
the leasing conducted under the
Geothermal Leasing Program. The
procedure by which lands are designated
as Known Geothermal Resource Areas
(KGRA) is impeded by inconsistent
criteria and inadequate resource informa-
tion. And while competitive bids are not
required to lease lands not designated as
KGRAs, the Federal Geothermal Leasing
Act permits the reclassification of land as
a KGRA if two or more lease applications
in a locality overlap by 50 percent or
more. The reclassified lands must thence
reopened to the public on a "lease sale"
or competitive bid basis. This procedure
often delays the exploration and develop-
ment of geothermal resources.
Once a tract of land has been leased, a
lengthy and complicated procedure is
required to obtain the necessary licenses
and permits to initiate and conduct
geothermal exploration, field
development, and construction. While
most of this procedure occurs locally,
state and federal land use commissions,
environmental agencies, and other
regulatory bodies are involved to some
extent. In Imperial County, California, for
example, more than 40 steps extending
over a long time period must be taken to
obtain the needed permits and approvals
for the commercial development of
geothermal resources.
Once the geothermal field is developed
sufficiently to produce electricity, other
regulatory agencies become involved.
Permits must be granted by the Federal
Power Commission and comparable state
and local agencies, and proposed rate
structures reviewed by public utility
commissions:
Economic Constraints
Substantial costs are involved in the
development and production of
geothermal resources, primarily (1) the
high capital costs per installed power unit,
and (2) operational costs per unit of
energy produced. Capital costs include
investments for exploration, drilling, and
-------
Legal, Institutional & Economic Constraints
99
completion of wells; steam gathering
lines; waste disposal systems; power
plants and transmission lines (electric
applications); distribution systems
(nonelectric applications); and environ-
mental control equipment. Operational
costs include operating and maintaining
the facilities. Actual costs usually depend
on the specific characteristics of the
reservoir, the size of the installed power
plants, and the applicable taxes.
Given the limited information about
the basic characteristics of geothermal
resources—including their location,
magnitude, lifetimes, distribution,
geochemical characteristics, and energy
potential—their development is regarded
to be a high-risk, long-term investment.
A geothermal reservoir capable of
supporting 200 MW of electrical
generating capacity is considered to be the
smallest development economically viable.
Uncertainty about the costs involved in
the discovery of a reservoir of even this
minimal capacity is reflected in the
developers' widely varying estimates,
which range from $3 million to $13.5
million. Once a site of sufficient potential
has been located, expenditures of $11 to
$15 million are required for drilling
(roughly two to three times the cost per
well of drilling for petroleum). Southern
California Edison estimates a total
development cost of $700 to $800 per
kilowatt of capacity, bringing the total
cost for a 200 MW plant to between $140
and $160 million.
This large investment may be increased
by economic constraints external to
geothermal development and by
production factors, the most serious of
which are generally believed to be:
— The uncertain exploration costs
involved in the replacement of wells
— The time lag between investment in
geothermal energy development and
the realization of a return
— Uncertainty about cost-competitive-
ness of hot-water versus fossil-fuel
systems.
Furthermore, developers believe the
incentives offered for development of
geothermal energy are fewer than those
offered for the development of other
energy resources. Taxation policies and
depletion allowances are most often cited.
Several federal programs have been
established to stimulate private
investment in geothermal development.
Perhaps the most significant is the
Geothermal Loan Guaranty Program,*
which provides guarantees against loss of
principal and accrued interest on loans
made for the following purposes:
— Determination and evaluation of the
commercial potential of geothermal
resources
— Research and development relating to
extraction and utilization technologies
— Acquisition of rights in geothermal
resources
— Development, construction, and
operation of equipment or facilities for
the demonstration or commercial
production of energy for electricity or
space heating, for example.
The limit on guarantees is $25 million for
single projects and $50 million for single
borrowers, subject to certain performance
and environmental criteria.
Investment in geothermal energy
development could be encouraged further
through a number of financial
mechanisms, including tax incentives,
depletion allowances, favorable rent and
royalty provisions for the leasing of land,
write-offs of intangible drilling costs or
dry holes, and cost-sharing for pilot and
demonstration programs. The feasibility
of these alternatives is presently being
investigated by the federal government.
• Authorized under Title n o< the Gwheraul Energy Raetrcli,
Development and Drmwvmlion Act of 1974 (PL 93-410).
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100
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White and D. L. Williams. Arlington, Va.: U. S. Geological Survey, 1975.
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Renner, J. L., etal. "Hydrothermal Convection Systems." In Assessment of Geothermal Resources of the
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Smith, M. C. "The Los Alamos Dry Geothermal Source Demonstration Project." In Proceedings of
the Geothermal Power Development Conference. Berkeley: University of California,
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Teknekron, Inc. ' 'Fuel Cycles for Electric Power Generation.'' In Comprehensive Standards: The
Power Generation Case (EPA No. 68-01-0561). Washington, D.C.: U. S. Environ-
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States of California and Oregon California Department of Conservation, Division of Oil and Gas, and Oregon Depart-
ment of Geology and Mineral Industries. Workshop on Environmental Aspects of
Geothermal ResourcesDevelopment; Proceedings, Sacramento: California Depart-
ment of Conservation, 1974.
U. S. Department of the Interior Draft Environmental Impact Statement on the Federal Geothermal Development
Program. VolumesI-HL Washington, D.C.: Government Printing Office, 1973.
U. S. Energy Research and A National Plan for Energy Research, Development and Demonstration: Creating
Development Administration Energy Choices for the Future. (ERDA 76-1). Washington, D.C.: ERDA, Preliminary
Draft, 1976.
Geothermal Energy Research, Development and Demonstration Program: Definition
Report. Washington, D.C.: ERDA (ERDA 86), 1975.
U. S. Fish and Wildlife Service Environmental Effects of Geothermal Energy. Washington, D.C.: U. S. Fish and
Wildlife Service, 1976. preliminary draft, unpublished.
U. S. Geological Survey Assessment of Geothermal Resources—1975. Arlington, Va.: U. S. Geological Survey
(USGS Circular 726), 1975-
Classification of Public lands Valuable for Geothermal Steam and Associated
Geothermal Resources. Arlington, Va.: U. S. Geological Survey (USGS Circular 647)
1971.
University of Oklahoma, Science and Energy Alternatives: A Comparative Analysis. Prepared for the Council on Environ-
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University of California, Geothermal Energy Resource Assessment. (UCID-3762). Berkeley: Lawrence
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Ward, P. L. ' 'Microearthquakes: Prospecting Tool and Possible Hazard in the Development of
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Wapora, Inc. Survey of Environmental Regulation Applying to Geothermal Exploration, Develop-
ment and Use, Draft Interim Report. Prepared for U, S. Environmental Protection
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Western Interstate Nuclear Board Energy Resource Development for the West. 1974.
White, D. E. ' 'Characteristics of Geothermal Resources.1' In Geothermal Energy, edited by P. F.
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Regulations
U. S. Department of the Interior, Bureau of Land Management. "Geothermal
Resources: Leasing on Public, Acquired and Withdrawn Lands; Revision of Proposed
Rule." 43 CFR Parts 3000, 3200, Section 3200.0-6(b), 1973.
Occupational Health and Safety Act, PL 91-596, Regulation 1910.95,
"Occupational Noise Exposure."
Communications __
Personal communication, Dr. Carl Weinberg, Pacific Gas and Electric Company, San
Ramon, California, 1976.
Personal communication, Professor Ray Thompson, University of California,
Riverside, California, 1976.
Personal communication, William Spaulding, Geothermal Environment Advisor
Fish and Wildlife Service ,1976.
Personal communication, H. K. McCluer, Pacific Gas and Electric Company, San
Ramon, California, 1977.
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