Geothermal energy and the environment the global experience (3)

This means that the turbine floor level for 50-100 MW units can be reduced to 5 m, 5 m lower than that required for the usual steel shell condensers.” Conflicting land use has affected g

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GEOTHERMAL ENERGY AND THE ENVIRONMENT:

THE GLOBAL EXPERIENCE

Department of Geography, Arizona State University, Tempe, AZ 85281 U.S.A zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

(Receked 29 M ay 1979)

A bstract-The conflict between energy supply and the environment is one of the critical issues of our time

and geothermal energy, often touted as plentiful and environmentally benign, has received a measure of

attention as one possible answer to the problem Some environmental issues, however, have been

encountered during the development of the world’s geothermal resources and these have had an impact on

the speed of development The environmental problems at each of the world’s geothermal generating stations

are discussed in this paper

The significant environmental impacts include conflicts in land use, air pollution, subsidence water

pollution, induced seismicity, blowouts, and noise, and every country has encountered some difficulty with one

or more of these problems Development plans have been slowed by environmental concerns in tome

countries In the U.S.A., this problem has been the emission of hydrogen sulfide: in Japan, land use in national

parks plus waste-water disposal; in El Salvador, waste-water disposal Other environmental impacts which

have not had an appreciable effect on development plans include: waste-water disposal and subsidence in New

Zealand, land use and air pollution in Mexico Italy has encountered no particular environmental barriers yet

but this may be a function of minimal monitoring

Collectively, the environmental difficulties at the operating power stations around the world have been

minor compared to the actual disasters that have befallen other processes of generating electricity Even the

polenlial environmental hazard of geothermal energy development is much less It cannot be compared to a

massive oil spill, a strip mine, or a radiation leak Nevertheless, geothermal development faces an array of rules

and regulations which, in view of world-wide environmental experience, need not be so strict Regulation i\

particularly tight in the United States, a country which would, with appropriately relaxed controls, stimulate a

global acceleration in development Instead, the U.S lies smothered in rules, and electrical geothermal

development everywhere remains mired in a role of insignificant contribution

INTRODUCTION

Within the past ten years we have become most clearly aware of the finite nature of two

commodities, energy resources and environmental quality During that time it has become

increasingly apparent that not only is there an “energy crisis” but there is also an “energy and

environment crises” No step in the development of energy zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA resources is free of

environmental impact, and no action on behalf of the environment is without energy im-

plications Individually each topic touches our daily lives Collectively there may be no more

central theme in the broad spectrum of relationships between man and his world One hope for

the future is an energy source which is at once plentiful and environmentally benign, one which

removes us from the painful position of choosing in favor of one need at the expense of the

other In the search for such a source of power geothermal energy has received a share of

attention

Although geothermal resources have been known and utilized in various forms for

thousands of years, their use for the generation of electricity or even for large-scale direct

applications such as space conditioning has been small and little noted Rising costs of fossil fuels

and the claim of a relatively small environmental impact from geothermal development have lately

stimulated interest in reversing this situation Ironically, environmental regulations have often

played an important part in slowing the development and use of the resource, especially in the

United States

With new developments being proposed, the need for a global sharing of environmental

experience and solutions becomes apparent and meaningful Such exchange can allay ap-

prehensions while sensitizing responses in areas of appropriate concern In theory, at least, this

should render the decision-making process everywhere speedier and more commensurate with

the facts

Applicable data have been accumulating rapidly and we are now at a point where the

worldwide body of experience is large enough to allow beneficial analysis but not quite too

compendious for brief summary and study In such light the aim of this paper is to summarize

III

112 M zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA PASQUALETTI

and evaluate the actual operational environmental experience of the world’s geothermal power

plants (Table 1) (Fig 1) This will be done in terms of what the problems have been and what is

being done about them

Environmental impacts may vary with differences in local environmental sensitivities,

reservoir characteristics, bureaucratic procedures, and long-term cultural heritage, but it

appears that most countries face similar environmental problems in developing their geothermal

resources Clearly, these problems are not mutually exclusive, but ‘for purposes of presentation

they have been categorized as follows: land use, air pollution, subsidence, water pollution,

induced seismicity, blowouts, and noise

The order of presentation of course has been largely subjective The topic of land use is

placed first because, in one way or another, most of the problems can be reduced to the

considerations of land use An early discussion of land use is also a convenient way to

introduce each geothermal area The subsequent placement of air pollution is a function of the

emphasis it has received Subsidence, water pollution, and induced seismicity are tied together

by considerations of reinjection Blowouts and noise are generally lesser problems One will

note that issues of societal impact are not mentioned This should not be construed as a deletion

for lack of significance but rather a reflection of sparse data Partially filling this void a new bookt

on geothermal development in California considers many socio-economic issues

Table 1 Summary of operating geothermal power plant installed capacity Source: Ronald DiPippo, “A summary

of the technical specifications of the geothermal power plants in the world” U.S Dept of Energy Contract

EY-76-S-02-4051.AOO1, Report No CATMEC/ZI, Brown University, Draft, Revision 1

Iceland

Namafjall

Waciferous region)

Larderello 2 (5 units) Larderello 3 (6 units) Gabbro

Castelnuovo V.C (4 units) Serrazzano (5 units) Lag0 2 (3 units) Sass0 Pisano (2 units) Monterotondo

Sant'Ippolito-Vallonsordo Lagoni Rossi 1

Lagoni Rossi 2 Sass0 1 Capriola Molinetto Travale (Monte Pmiata region) Bagnore 1

Bagnore 2 Piancastagnaio

Matsukawa Otake Onuna Onikobe Hatchobaru Takinoue (Kakkonda) Binary (pilot)

Mexico

Cerro Prieto I, Unit 1 Cerro Prieto I, Unit 2 Cerro Prieto I, Unit 3*

Cerro Prieto I Unit 4*

-_

lG3

69.0 120.0 15.0 50.0 47.0 33.5 15.7

0.9 3.5 3.0 7.0 3.0

1:::

1959

25.0 50.0 50.0 1.0

60 Mw

3.0 Mw

Wahrl Fdmunds and Adam Rose (Fds.), Geothermal Energy and Regional Development: The Case of Imperial County

Praeger, New

Table zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA I (C’ontd)

Country/Plant Site zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAYear Start-up zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA of

Unit 1 JMP) Unit 2 (MP) Unit 3 IMP)

Kizildere, Wellhead Unit

Union of Soviet Socialist Republics

The Geysers, Unit 13*

53.0 53.0 53.0 53.0 53.0

110.0 55.0

World total instal?ed capacity _ 1680.15 Mw

*Units added too late for complete reworking of the text Unless specifically noted, all calculations and comments

refer to the situation prior to the commercialization of the new units

The present paper should not be considered as a guide to everything which may happen or

even a methodology for policy makers; other problems may still arise Events suspected but not

evidenced have received little attention I am not deliberately trying to predict future events

The parameters for the study have been as follows: (1) Those aspects which have effects on

environmental quality In other words, little notice has been paid to problems which generally

do not threaten the environment directly, e.g scaling, corrosion, and cavitation; (2) topics

dealing with normal construction and operations, as well as accidental occurrences; (3) those

operations which have had an appreciable effect or at least have been studied

The topics discussed are not unique to geothermal sites but usually may be found in some

phase of conventional energy development Nevertheless, no concerted effort is being made

here for a point by point comparison between geothermal operations and more conventional

power plants The approach taken has been to present the geothermal data and to allow the

reader the opportunity to compare it with any specific conventional power plant

It should be mentioned that it has not been possible to visit each site personally, but

available public and in-house material has been complemented by correspondence with experts

within each country, conversations with persons in the U.S who have had recent first-hand field

experience, and discussions with foreign experts who have visited the U.S I would welcome

additional data on any site

114 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA M J PASQUALETTI

Geothermal energy and the environment: the global experience II5

LAND USE Two inherent characteristics of geothermal energy are fundamental to all considerations of land use: (I) site specificity, and (2) the lack of many aspects of conventional fuel extraction, processing, and transportation The site specific nature of the resource is directly related to the desire to maintain heat quality: the greater the distance the steam or hot water is piped the more the original temperature will drop Such decreased heat content affects plant efficiency and ultimately energy price

With the power plant effectively constrained to the site of the reservoir, field development must give close consideration to the nature of the land surface and its present use, whether it be wasteland or scenic wonder, flat or mountainous agricultural field or metropolis Competitive land use, actual or foreseen, can slow and even halt development unless all parties are satisfied Even if the area is unpopulated and scenically commonplace, a hilly, inaccessible location will present problems of extra expense and slope stability which would be absent in a flat area well serviced by a preexisting road network

Potential effects on land use reach beyond the actual site of the power plant Noise, roadway construction and use, odors, climatic effects, and alteration of wildlife habits and habitats may all be noticeable some distance from the center of activities and influence land use there

The absence of several traditional steps in the generation of electricity from geothermal resources has been offered as an environmental argument in favor of its development.’ It is contended, correctly, that this absence reduces the collective negative impact on land use By the same token, however, impacts from the remaining steps are unalterably found in a single area and can influence substantial land locally Significantly, the degree of disturbance, though over a wide area, is comparatively light, and farming, for example, can continue between pipelines and power plants This is not possible within the perimeter fence of other types of generating stations Two criteria are primarily responsible for the scattered location of facilities at geothermal generating sites First, geothermal developments require extra spacing between individual turbine houses This is a direct function of the short distance the steam/water can be piped and the need to maintain reservoir temperature and pressure: if the entire well field were in one area, the resource would be depleted more rapidly Second, extra area is needed for injection wells These must be positioned at a distance close enough to recharge the production zone but far enough away to avoid quenching

A generalized scheme of land needs has been worked out The drill site commonly occupies

an area of approx 250 km2 The entire pad generally involves an area of less than half a hectare which must be cleared and graded Adjacent to the actual drill rig are the mud pumps, mud tanks, generators, drill pipe rack, tool house, etc., normal to many types of drilling Other facilities not usually on the drill pad include storage tanks for water and fuel A sump sometimes lies adjacent to the drill pad and may be a pit about 95 m* and 1.8 to 2.4 m deep into which waste fluids and cuttings are dumped during drilling operations In addition to all these land requirements drilling presupposes access, and often geothermal fields are quite isolated and road construction is required

It is during construction of the power plant and the transmission pipes and lines that land disruption is more noticeable and probably most significant The pipes themselves are, at present always on the surface although there has been some consideration of underground pipes in the Imperial Valley of California

In a discussion of land area and impacts definitions are important If we define the entire geothermal development in terms of the outermost wells, then geothermal developments affect

a substantial amount of land, in some cases more than other forms of generation A distinction must be made, however, between land removed from current or potential use and land which lies within the perimeter marked by such wells The land actually removed from other use includes that needed for wells (production and injection), piping, the turbine house, cooling apparatus, transmission facilities and perhaps access roads All this equipment might be spotted within an area substantially larger than that needed for a more conventional develop- ment but, in terms of land actually displaced, the area is smaller The existence of transmission pipes at geothermal sites need not constrain land use appreciably If the site was previously gridded with a network of roadways along which pipes may be placed (e.g in a flat agricultural area), indeed there may be virtually no change due to piping requirements Thus, the land actually within a

116 M J

perimeter delimited by the farthest wells could make geothermal development appear land-

consumptive In actuality much of the land within geothermal field development remains useable

even after full operational status is achieved.*

Once the wells have been drilled and the construction phase completed, the effects on the land

begin to diminish Of course there may be changes brought about by faulty practices or faulty

construction which are greater than immediately realized but it is unlikely that they would present

disruption to the land at a level comparable to the construction phase The environmental effects

decline as the field comes into full-scale production There is, for example, no continuing mining,

fuel processing or transportation or ash disposal as there is at a coal-burning power plant It is at

this point that active multiple land use may be started In terms of the overall change, assuming the

power generation capacity is large enough, the area may change from essentially one land use to an

industrial one.’

Directional drilling is a common method of reducing the impact on the land The additional

cost which results from this type of drilling is partially offset by the consolidation of wellhead

equipment Up to six wellheads can be accommodated in an area only slightly larger than that

previously needed for one wellhead

In order to limit heat degradation in the steam the pipelines are never very long Usually

they do not exceed 2 km This also serves to reduce the effects of construction and the

rights-of-way needed to move the steam from the wellheads to the units

U.S.A

The hilly Geysers Known Geothermal Resource Area (KGRA) was discovered

by the white man in the mid-1800s After that time the area zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA wa s use d for watershed, hunting, balneology, and the extraction of mercury The mercury mines remained in

production until the mid-l%Os, and many of the shafts are still visible High mercury

concentration is still common in surface waters

As the field has been developed, odor and noise have increased They have attracted

serious attention by those who live immediately downwind, over Cobb Mountain to the east

(Fig 2) Much of the income in this part of Lake County is derived from the tourist industry,

and the expressed concern regarding the impact of odors and noise on tourists has been added

to complaints by local residents These complaints have occurred even though natural emis-

sions must have periodically exceeded the current allowable concentration Such competition in

land use continues to plague geothermal development at The Geysers, and prodigious amounts

of money are being expended to reduce emissions

Fig 2 Geysers geothermal field

Fig 3 Typical drilling site for multiple wells at The Geysers

In addition to problems of noise and odor, several detailed surveys have been made to gather data on habitat disturbance Each 110 MW(e) power plant at The Geysers requires from

14 to 20 wells to provide the approx 909,000 kg/hr of required steam supply Each well typically requires from 8-16 ha,4 but this is bottom-hole spacing Most wells are now directionally drilled, meaning that a site of less than one hectare can accommodate 5 wells (Fig 3) In the earlier days of development at The Geysers about half a hectare was required for each well Of course, there are other land use requirements such as the power plant itself, pipes, and roads (Fig 4; Table 2)

Conservatively estimated, the amount of land actually disturbed per magawatt at The Geysers ranges from 0.19 to 0.32 ha.’ This contrasts to about 4 ha/MW for the Navajo coal-fired power plant

at Page, Arizona (including 30 years of strip mining at Black Mesa) The land use impacts at a geothermal development located on flat land (e.g the Imperial Valley) would be even less than at The Geysers6

The most visible biological change at The Geysers is the removal of vegetation, and the most serious consequence of such removal is the loss of animal habitat In speaking of biological impact, Suter cautions that the “Appearance of minimal habitat loss is only real if critical habitat components are preserved”.’ Site preparation in this hilly area has required the removal of more vegetation than would be removed in a flatter landscape A recent wildlife study showed that, in one area, the Big Sulphur Creek watershed, only 410 ha of the total of 10,364 ha has been developed for roads, well pads, pipeline easements and power plants as of February 1976 This amounted to less than 4% of the entire watershed study area The habitat loss within the Kelsey and Putah Creek watersheds was 3.7 and 2.4%, respectively This factors to a bit more than 0.8 ha/MW, or more than twice the figure for the development as a whole.” This figure was revised downward to the 0.19-0.32 ha/MW after more detained photogrammetric analysis

The concern that the removal of habitat will have deleterious

i

effects on native fauna has

118 M J zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA PASQUALE~I

Table 2 Habitat loss at The Geysers Source: Weinberg, Ref 5

3.4

received more support than claims that the animals are affected by the increased commotion within

the KGRA.9 Regardless, both domestic and wild animals have been seen feeding immediately

adjacent to geothermal equipment

In addition to the impact that habitat removal has on animals, it has been considered a cause

for observed changes in vegetation surrounding the cleared area Species usually associated

with early successional plant communities appear to increase in density near developed areas

However, species more dependent upon a climax or stable plant community decrease in density

in developed areas In general, “the areas adjacent to geothermal development show a series of

shifts in individual species abundance rather than a uniform increase or decrease of all wildlife

species”.” The cause for this is considered to be only partly a response to geothermal

development Weinberg indicates that “it appears that several habitat parameters other than the

extent of geothermal development may be more significant in explaining the differences

observed in population density”,” although he does not mention what those other factors might be

Removal of vegetation increases slope instability at The Geysers The entire area is prone to

mass wasting, and the development activities have periodically resulted in some movement

Sensitivity of the land in this regard is responsible for an isolation of construction activities to

the dry summer months On a related matter, the trouble which has been experienced with wild

wells has been largely a result of unknowing placement of the well sites atop old, camouflaged

landslips zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

New Zealand

Wairakei is located on New Zealand’s North Island within an extensive thermal area about

50 km wide and 250 km long The land devoted to the Wairakei operations was formerly scrub

and pine lands, much as the surrounding land is today It was occupied by Maori and other

settlers The burough of Taupo catered to tourists visiting the site of the famous natural vents

Except for the natural geothermal activity, these lands are not unique in their timber resources

and the loss of some area of them has not affected the economy Bolton” has called the region “a

small area of wasteland of little aesthetic value”, and Axtmann13 has indicated that the present

existence of the geothermal facilities has actually improved the aesthetic value of the area

Natural emissions have been reduced by the development of the field, but the greater

Geothermal energy and the environment: the global experience II9

publicity the generation facility has produced is largely responsible for the 100,000 visitors who

visit Wairakei yearly Aside from changes in roadways and facilities which have been neces-

sitated by construction and the additional influx of tourists and scientists, the field development

has required some very noticeable changes in the use of the land

The most noticeable change in land use is in the bore field where all the vegetation has been

removed The wells are up to 1.6 km away from the power station, and vegetation has also been

removed in corridors along which the pipes pass Land was also required for the construction

of the power houses and electrical transmission facilities

Had the site not been developed for geothermal energy, it would now probably be in use for

pastoral farming.14 Many of the present farmers have found it necessary to travel longer routes

during their activities because of the addition of obstacles associated with geothermal develop-

ment

Mexico

Cerro Prieto lies a few meters above sea level on the delta sediments of the Colorado River It is

possible to farm this land with excellent yields all year when good water is available Originally, the

site was primarily barren, clayey, and saline, partly devoted to therapeutic hot baths Some

agricultural fields were nearby Since geothermal development began, both farming and spa

activities have halted, and the land now within the well field is barren and devoted only to

generating electricity Eighteen wells atop this land are needed to generate the first 75 MW 9

connected to each 37.5 MW unit; the remainder of the 41 wells drilled through 1974 (Figs 5 and 6)

were on standby and are now used in Units 3 and 4 There are 4 main steam gathering lines which

run to the first power house The total length of gathering pipelines of diameter greater than 406 mm

is over 12 km (for 4 units).”

The vacant land in between pipes in the well field goes unused at Cerro Prieto Although

agriculture is practiced within other geothermal well zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA fields (e.g in Italy), it would be very difficult and inefficient at Cerro Prieto because of the need for careful cultivation and irrigation in its arid

environment and because the pipe network has been layed out without agriculture in mind In its

present condition the land at Cerro Prieto is also unable to support lifestock

El Salvador

The Ahuachapan power plant lies at an elevation of about 800 m on gently sloping,

agricultural land along a small tributary of the Rio Paz The Rio Paz in turn is part of the

TO SAN LUIS-

L

Evaporation Pond

120 M J PASQUALETTI zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Ml1

(A fte r Re f 15)

Fig 6 Well location and steam pipeline gathering system for units No I and 2 at Cerro Prieto

international border with Guatemala The Ahuachapan thermal area is situated on the western

(nonactive) margin of a volcanic complex which includes Santa Ana and Izelco volcanoes In

their arrangements of facilities and their care during construction and operation the developers

have been notably successful in minimizing the impact on the land

Twenty-eight wells have been completed, 10 of which operate the turbines (5 to each) (Fig

7) The separation between the wells is not less than about 150 m The average spacing over the

entire field is roughly 23 ha per well, although near the central portion of the field the wells are

spaced at 11 ha per we11.‘6

The natural vegetation reflects seasonal stress brought about by a distinct dry season which

ends about May of each year The volcanic soil provides the basis for surrounding plantations

(notably coffee), parts of which have been removed during development of the field Besides

agriculture, cattle grazing is common around the geothermal development, even within the bore

field zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Ztaly

The Boraciferous Region includes power plants at 12 locations and covers a surface of

approx 170 km2 This region is found within a basin known as Larderello, an area believed to

cover about 25,000 ha (250 km*).” In addition, the Travale region, about 13 km to the southeast of

the Larderello basin, is sometimes included in the Boraciferous Region The Travale field is very

small, and it has been impossible to maintain fluid output at 1960 levels.‘*

Through March 1975, 511 wells had been drilled in the Boraciferous Region (excluding

Travale), at an average density of drilling of 2.7 wells per km* One hundred and ninety of these

were productive and 181 were branched onto the pipeline network Nine were under obser-

vation for reservoir engineering study I9 The well pipelines in the Boraciferous Region totaled

94 km in length and extended over the 170 km* with a density of 533 m/km2

The Mt Amiata Region, located about 70 km southeast of Iarderello, is characterized by

productive features which individually never exceed a surface area of more than 10 km2

Drilling has been concentrated on small separated plots which cover an aggregate area of

40 km2 By March 1975, 60 wells had been drilled, with a density of 1.5 wells per km2.20 At that

\ ( J A 11.1 CY.II,r lSl8 m R., II

Fig 7 Well arrangement at Ahuachapan geothermal

time there were 11 producing wells with a mean specific output of 39 t/hrt, approximately twice

that of the Boraciferous Region, and reflected in the lower well density

The generating units at Mt Amiata were installed close to the productive wells, and the

length of the pipeline totals only a few thousand meters, with a density of 215 m/km’ The

bellow-joint or sliding-joint systems for compensating thermal expansion have been replaced by

the “zigzag” or “lyre” system.2’ zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Japan

All six operating geothermal power plants in Japan are located in national parks, and their

development and operation falls under the National Park Law 22 One of the results of national

park regulations has been a marked irregularity and sometime segmentation of parcels available

for geothermal development This compounds a problem of small total area allowed for each

development, a problem which effectively limits the generation usefulness of the land that is

available, and actually leads to an overstated impression of the parcel size

The Japanese are committed to developing their geothermal resources and doing so in an

environmentally acceptable manner,23 but conflicting land use has slowed development at

individual sites In March 1972, in an agreement between the Environmental Agency and the

Ministry of International Trade and Industry, geothermal power generation was restricted to six

areas in the whole country in order to protect the environment and to prevent pollution.” This

agreement has been eased since, partly in response to experience gained during the operation of

the existing power plants These new data will aid in the development of another 100 known

geothermal fields which also lie within national parks

Much like the requisite protection of national parks, hot springs have garnered considerable

protective consideration This is apparently a consequence of a certain sense of national and

historical preservation, but it also results from political pressure to maintain the commercial

value of the spas This competition between resource use, of course, has land use implications

as well and these considerations have limited the number of areas planned for development

Five wells from a vapor-dominated reservoir supply geothermal steam to the Matsukawa power

plant The plant is located in the Matsukawa Valley, 50 km from the City of Morioka on the

southern flank of Mt Iwate, an active volcano in the Hachimantai volcanic region (Fig 8) Owing to

the existence of Matsukawa andesite, natural geothermal activity is rare The rugged terrain of the

122 M J PASQUALEIT

Fig 8 Matsukawa power plant

site has been largely responsible for the higher building and operating costs, and higher costs and a larger commitment of land have resulted also from the widely separated wells

The Onuma power plant, north of Matsukawa, was constructed by the Mitsubishi Metal Corporation to supply electricity to one of its metal processing mills Its location in the Towada-Hachimantai National Park has required some impact mitigation Directional drilling has been used to reduce land needed for well pads In addition, the turbine itself was placed

at ground level and auxiliaries beneath the floor to maintain a low roof elevation

The most recently commissioned commercial-size power plant in the Kakkonda liquid- dominated field located between Matsukawa and Onuma at Takinoue All the wells are directionaily drilled, again partly as a method to reduce the amount of lands disturbed in the national park” (Fig 9)

The Onikobe power plant is supplied from a vapor-dominated reservoirt in the Kurkoma National Park about 120 km south of Matsukawa The field is within the so-called Onikobe basin, extending 9 km north-south and 7 km east-west and was once covered with lake deposits Hot springs and fumaroles are common in the lake deposits and around the basin Twelve production wells currently supply the power plant which has been designed to blend into the surroundings in terms of color and low profile of buildings.26

The Otake generating station, on Kyushu, is supplied from a liquid-dominated reservoir An initial unfamiliarity with hot water systems delayed early development, but after the successful operation of a liquid-dominated power plant in New Zealand, interest in Otake was renewed The plant was located because of the clear manifestation of geothermal activity, low population density and the cooperation of the local residents.”

Otake is located in a rugged area of the Aso National Park at an elevation of 900- 1100 m near Mt Aso and four other peaks ranging 1300- 1600 m in elevation (Fig 10) Plant surround- ings have a basin topography with arcs of dome-shaped volcanoes The plant was designed to blend into the scenic surroundings of the national park.28

Forty hectares are available to the power company for the entire operation at Otake Currently the power plant occupies 8600 m2, which includes 4800 m2 for the power station, and

3800 m2 for the steam wells and gathering system The power house takes up 393 m2.29 All five exploratory wells were successful, but there have been subsequent problems and currently only

tWith substantial liquid

I!3

Fig 9 Steam gathering system for Kakkonda power plant

two wells (O-9 and O-IO) are still producing This has resulted in over a 40% drop in plant capacity from I I MW to a current value of about 6.4 MW.m In view of the small area available for expansion, it will be difficult to drill new production wells

The Hatchobaru generating plant is located about 2 km from Otake in the same mountainous area of the Aso National Park (Fig I I) Most of the seven production and four injection wells are directionally drilled

The capacity of the field has been calculated by dividing the amount of land needed per well (22,500 m*) into the amount of area available to development (36 x lo4 m*) About 10 production wells could be drilled on this land and this means a maximum power potential of about 50 MW The Kyushu Electric Power Co., Inc intends to mask the power plant to conform

to the scenic qualities of the area The plant itself is smaller than normal because for the first time in a Japanese geothermal power plant, a low-level, jet condenser was used Unlike the Otake configuration with the condenser outdoors, the space is formed inside the concrete foundation of the turbine-generator unit at Hatchobaru and is lined with polyester resin to be used as a jet condenser chamber This means that the turbine floor level for 50-100 MW units can be reduced to 5 m, 5 m lower than that required for the usual steel shell condensers.” Conflicting land use has affected geothermal development in Japan, and even in those areas where a proven reserve lies, restriction on expansion, size of the power plant facilities, and overall aesthetic impact of the facilities can completely limit further capacity development The juxtaposition of these land uses is an interesting problem because only 0.1% of the total

124 M J PASQUALETTI

Fig 10 Location of production and injection wells at Otake

national park area would be needed to support 20,000 MW of geothermal power (8% of the

country is in national parks) The government zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA is thus faced with a policy decision with environmental quality on one side and the electrical needs of the country on the other So far,

they have chosen to minimize the impact as much as possible by absolutely restricting available

land and by encouraging the development of more compact units They will also soon initiate

r-f zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

I ’

i

0 Prod”crion we,, Rel”,eelio” we,,

- 2 Phase Pipehe

-waste Liquid

Fig 11 Gathering and reinjection system for Hatchobaru

environmental impact assessments in six geothermal resource areas, and part of that impact

evaluation will deal with conflicting land usage Such studies will represent the first attempt in

Japan at full environmental assessment in advance of development.32

AIR POLLUTION

The potential for and the effects of air pollution have frequently garnered the largest portion

of the environmental interest at geothermal power plants Constituents released often include

Geothermal energy and the environment: the global experience zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA I?5

arsenic, mercury, and even boric acid, but the focus of attention has been the emission of noncondensible gases such as carbon dioxide, hydrogen sulfide, and radon Carbon dioxide is generally released in greater volume from fossil fuel plants, and this fact, coupled with its nontoxic nature, accounts for the relatively limited attention it has received as a pollutant This attitude may be changing, however, as data accumulate with regard to the effects of carbon dioxide on global climate

The two gases generally given most attention are hydrogen sulfide and radon Hydrogen sulfide (HS) is the air emission which has received the greatest environmental attention Partly this is because of its low odor threshold (detectable at 0.03 ppm), and partly because it can produce serious health consequences (Table 3) As a contributing hazard the gas is 17.5% heavier than air and can accumulate in low places if ventiliation is inadequate, during stagnant and air inversion conditions Out of doors it can reach toxic levels Hydrogen sulfide may also harm vegetation and produce accelerated corrosion of exposed metals, paints, and other surface coatings, communication equipment and wire insulation

Armstead has identified eight “escape paths” for air pol1utants:33 (1) condenser gas ejection discharge, (2) with warm vapor and air rising from cooling towers, (3) wells discharging to waste when undergoing test or when a plant is unable to absorb all the steam from the bores connected thereto, (4) wild bores, (5) traps and drains, (6) in solution in the surplus condensate where cooling towers are used, (7) in solution in the main body of cooling water-where river cooling is adopted for the turbine condenser, (8) in solution in the water phase in wet fields, when the water is discharged into rivers or streams (relatively small) The most intensive studies of H2S have been at The Geysers, U.S.A and at Wairakei, New Zealand

U.S.A

Over 99% of the natural steam at The Geysers is water vapor, with the noncondensible percentage ranging from 0.1 to 1.0% by weight34 (Table 4) A drop in the percentages of noncondensibles has occurred over time, presumably because the gases have tended to accumulate in the upper part of the reservoir Concentrations have also varied with well depth; shallower wells commonly have less steam and more of the other gases.35 Expectedly, constituent percentages differ with well location

Emission of noncondensibles at The Geysers are from power and nonpower plant sources, most of which were in Armstead’s list above The nonpower plant sources include well venting

to clear out the accumulation of rock particles, a process which usually takes 3-5 days at The Geysers, and well venting during clearing and testing of a successful exploratory well, a process taking 3 weeks Well bleeds and fugitive dust produced during construction are sources of emissions as are particulates produced when cuttings and dust are blown to a sump during drilling In the latter case, 20% go to the atmosphere The major concern, however, is emissions from the power plant, particularly in the form of H2S

Table 3 Effect of hydrogen sulfide on humans Source: Hartley see Ref 41

distinct odor; can cause nausea, headaches

odor offensive and moderately intense

odor strong but not intolerable

can cause loss of sense of smell in few minutes

olfactory paralysis

paralysis

occur rapidly, upon very short exposure

Hydrogen sulfide emissions H2S emissions continue to be the major environmental problem

at The Geysers The rate of H2S emission into the atmosphere from the geothermal operations rose from 13.6 kg/hr in l%O to 759 kglhr in 1975.% In 1970 it was noticed that the air quality standard for H2S was being exceeded in Sonoma County Publicity was focused on these emissions by citizens complaining of unpleasant odors wafting over Cobb Mountain to the east

of The Geysers field These complaints along with related, increasingly stringent emission regulations by local Air Pollution Control Districts (APCDs), the California Air Resources Board (ARB) and the California Energy Conservation and Development Commission (CECDC), resulted in substantial testimony, slowed expansion somewhat, and resulted in the promulgation of new standards of compliance

As part of the power cycle, noncondensibles used to be removed by the two-stage gas ejector system which vented the gases to the atmosphere through 18-26m stacks Concen- trations of lO,OOOppm, H2S have been measured at these ejectors.37By December 1976, however, the gas-ejector effluents from all operating units had been ducted into the base of the cooling towers This procedure was required in order to implement the iron catalyst abatement process described below It also happens to carry the gas-ejector effluent to high altitudes with the buoyant air leaving the cooling tower, and this reduces the amount of H2S reaching the ground The first 502 MW is supplied by 1 I turbines powered by steam from 75 wells Concentrations of H2S in the geothermal steam range from 150 to 300ppm by weight Thus, for a well producing 100,000 kglhr of steam, the H2S emission rate would be 15-30 kg/hr Using a median concentration

of 200 ppm and an average discharge from the 75 wells of 68,000 kglhr, unabated emissions would total 27,173 kglday for the entire field (1132 kgfhr; 362 kg/day/well) Based on a steam input of 821,000 kglhr into a 110 MW plant, the unabated H2S emission rate would be about 182 kglhr The actual emissions are much lower, but they have downwind impact which often do not meet state and regional ambient air quality standard of 0.03 ppm H$ During a 23-month period between

1976 and 1978 hourly average H2S levels equal to or in excess of 0.03 ppm were measured 279 times out of 75,350 readings (0.4%) at five sampling stations maintained in the area by Stanford Research InstituteT9

In September 1977, the North Sonoma County Air Pollution Control District (NSCAPCD) reported that a total of 534 kglhr of hydrogen sulfide was emitted by The Geysers power plants (for

502 MW) Nonpower plant sources were estimated at about 29 kg/hr.@ Thus a total of about

563 kg/hr HzS was emitted from the entire 502 MW Geysers operation-94.9% from the power plant (Table 5) Included in this total is “Thermal 4”, the so-called “wild well” which blew out in

1958 It currently emits over 19 kgfh H& an emission rate about equal to the expected emissions from Unit 13, which will produce 135 MW of electricity

Geothermal energy and the environment: the global experience Table 5 Hydrogen sulfide emissions at The Geysers for operating (1-l I) and planned (12, 14, 15, 17) units (a) As

measured by District personnel (b) Assumes 4.5% natural abatement (c) Assumes 90% abatement Case I-All

power plants 90% abated except Units I & 2 Case 2-All power plants 90% abated with no more than

22.7 kg/hr/plant uncontrolled well abated and controlled emissions Source: Northern Sonoma County Air Pol

Con District, see Ref 40 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

KG/HRb

JAN-SEPT CASE CASE

101.8 15.9

104.1 18.6

104 18.6

2a.6c 8.2C

110.9 116.8 178.6

13.2 13.2 1.4

10.4 10.5 18.6

6.2 1.8

4.09 1.36

1.36 1.36

1.36 1.36

Impacts of HZS emissions Citizen complaints were responsible for slowing expansion

of The Geysers’ capacity for over four years These complaints were almost always a

response to offensive odors, and the present limit of 0.03 ppm is designed to eliminate such

odors The limit is based on odor and not any demonstrable physiological effect, and of course

it is aimed more at nearby inhabitants than power plant workers The Occupational Safety and

Health Administration (OSHA) regulations list an acceptable continuous ceiling concentration

in the work place of 20 ppm.4’

In addition to the perception of H2S odor there have been a few cases of floral damage The

effects of air pollution on local vegetation were first noticed in early summer 1973.42 Color

changes were observed in the leaves of the big leaf maple (Acer macrophy lhm), and obser-

vations during the next four summers revealed the same overall effects Although field checks

showed some signs of damage in other trees (oaks and conifers), the big leaf maple showed the

symptoms most clearly This accounted for 15% (506) of the trees field checked but 80% (272)

of the trees affected The damage is believed to have been caused by the boron which is emitted

in the cooling tower drift 43 Damage should be reduced in coming years “due to improvements

in drift abatement and cooling tower technology”.”

Thompson and Kats4’ conducted experiments on the effects of H2S on several crops and

trees; one of the trees, California buckeye (Aescufus califomica), is common within The

Geysers Known Geothermal Resource Area (KGRA) Plants were fumigated with the following

levels of H2S: 0 ppb, 30 ppb, 300 ppb and 3000 ppb, all in carbon filtered air The buckeye was

quite resistant to H2S, but “at the 3000ppb level, a bronzing of the leaves occurred after four

weeks exposure with less at 300 ppb and none at the lowest level Some defoliation occurred at

zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

128 M J PASQUALEW

the highest level after eight weeks exposure Total sulfur analysis of leaves showed 1.02, 2.49,

4.40, and 5.5% sulfate on a dry weight basis in plants receiving 0, 30, 300, and 3OOOppb,

respectively”.46 Of all the plants tested, the slower growing ones such as the Buckeye had a

slower accumulation of sulfur

It is possible for effluents from power plants to contribute to an increased acidity in

rainwater, either from the oxidation of hydrogen sulfide to sulfur dioxide and then to sulfuric

acid or from the conversion of ammonia to nitric acid Such acids can be brought to the plants

and soil with rainfall Such occurrences are a demonstrated consequence of some conventional

power plants and they could theoretically occur from the operation of geothermal power plants

too Farmers near The Geysers and even some 160 km downwind have expressed a concern

that “acid-rains” produced because of operations at The Geysers will harm their crops It has

not been linked to The Geysers operation, however, and it is considered highly unlikely

The weak sulfuric acid attacks electrical circuitry and corrodes such materials

as carbon steel, cast iron, copper-based alloys, zinc, cadmium, silver, wood, and concrete

Reactions of this type have led to careful design and materials consideration Some of these

adjustments have included the use of stainless steel, aluminum, aluminum alloys, cement-

asbestos, epoxy-lined pipe, and polyvinyl chloride (PVC) as tower fill material

Other pollutants Atmospheric release of the radioactive noble gas radon (‘“Rn), its daugh-

ters and precursors, has also prompted interest and study Radon mixes with steam, flows to the

surface and may escape through any natural or artificial opening Maximum measurements of

radon from the steam at a well geyser in this “controlled area” is 8.3 picocuries/liter4’ (pCi/l)(Table

6) The state health standard for radon in an uncontrolled area is 3 pCi/l (One picocurie of radon is

about 6.8 x 10m2’ kg.)

The particular hazard from radon involves the inhalation and deposition of the short-lived

daughters The 222Rn does not deposit on lung tissues when inhaled, but is merely exhaled The

short-lived daughters, however, are usually deposited, and these can cause cancer

The incidence and significance of radon emission at The Geysers has been the subject of a

long-term study by Lawrence Livermore Laboratory In the final report of that study,

Anspaugh& indicated the maximum rate of release of radon for the entire field is 1.43 Ci/day, but its

effect is “not discernible because of the naturally occurring levels of “‘Rn and its daughters in the

environment” (from the soil).49 The amount released from the soil approximately equals that from

the steam This corroborates Stoker and Kruger in a 1975 article which dealth withgeothermal sites

in general?’

Measurements of other potlutants have shown generally tolerable levels A high volume air

sample study conducted between December 1976 and August 1977 (spanning an abnormally dry

winter season) revealed particulates in the ambient air through The Geysers “to be less than

allowed by the State Standard (mean annual particulates 60pg/m3, 24-hour episode

100 pglm’)“.” Robertson et ~1.‘~ reported that the mercury levels in the area of the geothermal

development are equivalent to general ambient levels zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Hy drogen sulfide zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAcontrol In view of currently favorable returns on investment from

geothermal power plants, plus public resistance to the construction of fossil and nuclear power

plants, and California’s avowed preference for geothermal power,‘3 substantial emphasis has

been placed on solving the problem of hydrogen sulfide emissions at The Geysers When the

first units were constructed in the early l%Os, control standards did not exist Even the most

recently completed units emit hydrogen sulfide which contribute to exceeding ambient standards

Attention has been focused on this problem by downwind Lake County residents even through

predevelopment natural emissions may have exceeded 30 ppb occasionally

Table 6 Maximum measurements of radon emissions at The Geysers Measurements by PG&E Note: California

Dept of Health requires radon cow be less than 3 picocurielliter in uncontrolled areas Source: Reed and

Campbell, see Ref 35

Geothermal energy and the environment: the global experience

In working toward statutory and technical emission control, developers and regulatory agencies have had to answer two key questions: What degree of abatement is necessary? What degree of abatement is technically feasible? Answers to such questions in turn rest largely on area1 and generating expansion; the greater the generating capacity and the nearer the plants are

to local residents, the more stringent the guidelines are likely to be

The California Air Resources Board (ARB) has drafted applicable regulations and has requir-

ed all APCD’s in California to follow suit These regulations are designed to ensure that no new stationary sources for which an air quality permit is issued shall prevent or interfere with the attainment or maintenance of any applicable air quality standards.54 Such limits are designed to maintain H2S emissions below the odor thresho1d.5s

In large measure the H2S emissions at The Geysers have resulted from the use of direct- contact condensers This type of condenser has been installed on the first 11 units and thus the technical reduction of emissions must address two problems: (1) how to retrofit the existing units, and (2) what equipment to install on future units Any possible control technique must meet at least three criteria: (1) it should not degrade steam quality, (2) it should be inexpensive and simple to operate, and (3) it should produce useful or environmentally benign byproducts

Li et ~1.‘~ include a fourth stipulation: that it be applicable upstream of power generation equipment in order to reduce H2S corrosion problems

A recent publication of the Environmental Protection Agency” discussed eleven processes

of HH,S removal, four in terms of chemistry and costs These processes are under serious consideration and test at The Geysers Each has peculiar benefits and drawbacks One is the Stretford Process

The Stretford process was developed in the early 1950s by the United Kingdom Gas Board for use as a cleanup technique for the gas industry ‘* As used at geothermal plants it scrubs noncondensible gases from the condenser ejector with a removal efficiency of 99% and yields high quality sulfur.” The process does not have any detrimental effects on the power cycle, but its use requires a surface (tube and shell) condenser rather than the direct contact type installed

at The Geysers

Use of surface condensers leaves lo-20% of the hydrogen sulfide in solution with the condensate The hydrogen sulfide dissolved in the condensate is stripped out of solution in the cooling tower and emitted to the atmosphere Therefore, if the Stretford system is used 8090%

of the hydrogen sulfide existing in the turbine discharge can be removed Pacific Gas and Electric is planning to use surface condensers (the first dry steam geothermal plant in the world to be so equipped) and the Stretford process in Units 13-15 At Unit 13 emissions have been estimated to be 0.08-o 19 kg/MWh or 11.25-24.75 kg/hr.@’

If the rate of removal characteristic of the Stretford process is to be improved “the condensate must be treated before it enters the cooling water circuit, perhaps by chemical oxidation of the hydrogen sulfide to a nonvolatile form”.6’ A system which does this is the iron catalyst (or Ferrifloc) system, one which has been developed by PG&E and is presently installed in three units at The Geysers Ferric sulfate is added in solution to the cooling water,

“thus oxidizing the hydrogen sulfide contained in the aqueous phase The noncondensible condenser ejector gases are ducted to the cooling tower and hydrogen sulfide is scrubbed by the falling water containing the ferric sulfate catalyst”.62 The catalyst must be added upstream of the cooling tower The process yields elemental sulfur, water, and ferrous ions

The major advantage of this system is its applicability to units already equipped with direct contact condensers From an environmental point of view, however, the system “has proven undependab1e”;63 reduction of hydrogen sulfide has been only 40-70% effective at full scale operation However, preliminary tests have indicated that addition of hydrogen peroxide may improve removal efficiency to 90% Operationally, filtration removal of elemental sulfur from the cooling water generates large amounts of toxic sludge which requires an industrial waste disposal site or landfill disposal site In addition, the iron increases corrosion potential

The third technique, the EIC upstream process, removes hydrogen sulfide from raw geothermal steam by scrubbing it with an aqueous solution of copper sulfate Because removal

is effected prior to the steam entering the powerhouse, corrosion of turbine and condens- ing/cooling cycle equipment is minimized In addition, the process can also remove the H$ from the plant input steam even during down time The EIC process is still in the early stages of

130 M J zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA PASQUALETTf

development but so far results are promising At Unit 7 in December 1976 a 30 hr test of

200 ppm hydrogen sulfide at 450 kg/hr of steam yielded efficiencies generally over 97% Eighty

per cent of the ammonia and boric acid was also removed

At this point in time it is not clear if any of these systems will reduce hydrogen sulfide

emissions to required discharge levels Ultimate emission standards have not yet been

established “Even 95% control of hydrogen sulfide may not be sufficient if a reduction down to

one third of current emission levels is required Control efficiencies of %-99% appear to be

required if ultimate compliance with standards and full field development is desired”.& If 99%

abatement of H2S becomes necessary, it will be necessary to install a condensate treatment system,

in addition to the facilities to treat the noncondensable gases.6’

In addition to interest in controlling emissions from the power cycle, attention has also been

given to steam vent and drilling phase emissions 66 The use of a bed of iron oxide absorbant to

desulfurize the steam directly without condensation appears to be the more favorable approach

to steam vent emissions,6’ while tests have indicated sulfide abatements of up to %% have been

achieved during the drilling phase by continuous injection of aqueous hydrogen peroxide and

sodium hydroxide solutions into the geothermal steam upstream from the muffler.68 By injecting

hydrogen peroxide during well drilling, Union Oil has been meeting the 2.7 kg/hr emission limit

on drilling wells set by the Northern Sonoma County APCD.69

Special abatement requirements and research are required under conditions set in authori-

ties to construct steam transmission lines for Units 12, 14, and 15 The companies are exploring

upstream H2S abatement, mechanical curtailment, steam transfer and chemical abatement One

company has proposed a completely automated steam transmission line This system would be

capable of curtailing the amount of steam normally supplied to the power plant by 60% within two

hours.”

Union Oil Company currently uses the steam transfer technique to reduce H2S emissions to

the atmosphere, but it is limited to 113,636 kg steam/hr and it takes many hours to accomplish

They are expected to test some chemical treatment techniques in the future They have also

installed 60 special valves which give them the capability of automated curtailment.”

A plan is under study by PG&E to build a small power plant, perhaps binary, to utilize the

energy of the wild well At the same time H2S from the well would be reduced 90%.” zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Proposed strategy If emission standards are not tightened with further field development,

total emission amounts will increase after 1980 and equal 1976 levels by 1990 However, they

will be spread over an area about 50 times larger than the 5000 ha covered by the current held.73

Each new power plant permit application will therefore be examined in terms of whether or not

the addition will result in the violation of ambient air quality standards If required levels of

control prove technically or economically infeasible, field expansion may again be delayed

sometime in the future

Both the California Energy Commission and the state Air Resources Board (ARB) have

expressed their support for the future development of geothermal resources.74 A workshop,

organized by the ARB, was held on 17 February 1978, and various members of the industry,

principal state and local agencies, and the public concerned with geothermal energy parti-

cipated Information generated at the workshop has been incorporated into an analysis of the

possible growth of electric power at The Geysers and the H2S control strategy necessary “to

attain and maintain the state ambient air quality standard under the projected development”.”

The proposed strategy was determined by: “(a) relating current H2S emissions to recently

monitored atmospheric HZS concentrations; (b) estimating the rate of development of electric

power at The Geysers; (c) using the range of measured concentrations of H2S in the steam to

forecast future H2S emissions at The Geysers; (d) assessing the future technological capability

to reduce H2S emissions and the expected availability of the control technologies; and (e)

estimating the degree of control which needs to be met by future developments”.76 The

outcome has been a set of performance standards which should allow field expansion to

4000 MW of electrical generating capacity by the year 2000 while attaining and maintaining the

H2S air quality standard

Based on an understanding of current abatement capabilities as well as on assumptions of

future abatement efficiencies the Air Resources Board staff recommended a model rule for the

performance of Geysers power plants.” It addressed, specifically, power plants with direct contact

condensers, emissions from steam supply operations (e.g well drilling, testing, bleeds), emissions during normal operations and during shutdowns or outages, and controlling the “wild well” Emission rate goals were stipulated for particular years (always with progressively smaller amounts allowable) on the basis of grams of H2S emitted per MWhr

The ARB believed implementation would maintain emissions at acceptable levels (Fig 12) Northern Sonoma County APCD adopted, on 27 June 1978, rules which substantially follow the ARB recommendations, although the dates for compliance are slightly different

These rules represent but a small part of the overall regulations which govern geothermal development at The Geysers, but because of the emphasis which har been placed on air emissions

they have become the most significant

In I%1 Armstead reported that the steam at Wairakei contained between 0.36 and 0.50% noncondensible gas by weight of the bore steam The majority of this gas component, carbon dioxide, is joined by lesser amount of hydrogen sulfide, hydrogen, nitrogen, methane, ammonia boric acid, silicon fluoride, and hydrogen fluoride.‘* Separated at the well-head, the steam contains all of the gases These gases pass through the turbines, are extracted from the condenser and are vented to the atmosphere through gas exhaust stacks at the power house Gas has decreased over the years By 1972 the amount of gas was less than 3 1 kg per minute or 0.18% by weight of the steam.79 In 1977 Bolton stated that total gas had decreased “by a factor of lO”.H” Even though total gas has dropped, the H2S component has remained essentially constantx’ and H?S emissions have continued to gain most of the air pollution attention Diluted by a 3 : 7 mixture of CO2 and air the concentration of H2S in the stack gases is about 5000 ppm.‘* Eighty per cent of the H$ is transferred to the cooling water of the river while the rest (approx 14 kg/hr) emerges from the 30 m ejector stacks 83 Both the CO2 and H2S tend to settle to the ground, and

on calm foggy days the odor of H2S around the power stations is “frequently strong”.x4 However, even when the plant is undergoing maintenance and all the steam from 60 wells discharges to the atmosphere, at an average concentration of 30ppm, in the steam, the H2S emissions are “well below the toxicity level”.85

Although there is concern about air pollution in New Zealand the New Zealand Clean Air Act of 1972 does not set standards Nevertheless, the Health Department must be consulted at the time of licensing, and their current limit for H2S is 5 ppm The limit is, of course, much

132 M J zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Table 7 Gaseous impurities entering turbine Source: S Mercado, “Cerro Prieto geothermal field Mexico-wells

and plant operation” zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Proc Int Gong on Thermal W ater, Geothermal Energy, Vulcanism of the M editerranean

area: Geothermal Energy, Vol I, pp 394-408 Athens, Greece, (as cited in DiPippo, Ref 15) (1976)

below the actual emissions from Wairakei, but the emissions are not in violation of the law

Even though the odor of sulfur is often strong, HS concentrations which exceed the

prescribed limit are investigated only when there exists proof of publich nuisance As one

example, the odor of H2S is not detectable at the Wairakei Village 2 km north of the plant,

although there have been reports of blackening of brass 86 As at The Geysers, hydrogen sulfide

emissions from the geothermal operations at Wairakei are well below those from fossil fuel

plants, and Axtmanns7 concluded that at Wairakei “atmospheric H2S emissions appear less an

environmental issue than one of industrial hygiene”

There are no specific plans for the implementation of abatement devices similar to those

under test at The Geysers The Ministry of Works and Development has had difficulty

formulating a policy for emissions because they find it hard to persuade the authorities to

specify requirements *’ This attitude has resulted largely as a response to sparse populations,

small industries, and large ocean areas generally available for dispersal At the Broadlands site,

however, the geothermal developers will install either a tall stack or an atmospheric cooling

tower in order to maintain low concentrations at ground leve1.89 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

M exico

The geothermal steam at Cerro Prieto contains about one per cent noncondensable gases, by

weight, mostly carbon dioxide and hydrogen sulfide The average concentrations of these two

constituents is about 15,000 and 1600 ppm, respectively.m Hydrogen sulfide concentration as the

steam enters the turbine is 1500 ppm (Table 7), and upon discharge (for 75 MW) 832 kg/h or

19.97 t/day (Table 8) The specific discharge of HzS is more than 11 kg/MWh a rate 55 times higher

than the rate being suggested by the U.S Environmental Protection Agency for operations in the

u.s.9’

The gas extraction system “consists of a t-stage steam ejector with an inter- and after-

condenser There are three first-stage steam ejector nozzles operating in parallel, presumably

for redundancy Each is connected to a separate inter-condenser: there are three second-stage

steam ejectors, also in parallel, and three after-condensers The gas extraction system requires

24.2 t/h of motive steam from the main steam line and 373 t/h of cooling water0.92

Forty-meter ejector stacks are used to increase dispersal, and low level extraction fans are

used, especially on calm days, to prevent the accumulation of harmful levels of H# Alarm

systems guard against the dangerous concentration of HzS.~~ In addition, a

58.42 cm diameter, 1250 m-long resin-lined, steel vent duct connects the base of the stacks with

the evaporation pond Large-diameter extractors drive the gases toward the pond This has

reduced substantially the hydrogen sulfide levels around the plant but some still remains

because it has been dissolved by the cooling water in the barometric condensers and ejector

coolers, and is later released at the (mechanical, induced draft) cooling tower The cooling

towers are the source of the largest amount of pollution; to mitigate the impact of the emissions

they are positioned 100 m down the prevailing wind direction from the plant.%

There has been no attempt at environmental air emission abatement, other than those measures

described The several measures implemented to protect electrical equipment have ranged from

gold plating high voltage contacts to isolating areas and providing them with air conditioning and

Geothermal energy and the environment: the global experience Table 8 Gaseous discharge at Cerro Prieto (No 2 unit at 32 MW, 9 July 1973) Source: Mercado, see Ref 93

special filters to avoid corrosive gases Although air emissions have “undoubtedly” affected the

local ecological equilibrium, 9s the vastness and barren nature of the area is considered to be a

buffer These impacts could be “reduced to insigiticance” if there was some compulsion to do so.% zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

El Salvador

Noncondensable gases at Ahuachapan are 0.05% (by weight) of the total well flow and 0.2%

(by weight) of the steam flow Hydrogen sulfide amounts to 12.1% by volume of the gases

(Table 9) The gas extraction system consists of a 2-stage, steam ejector connected to the gas

cooler section of the condenser There are two sets of extractors for each unit, arranged in

parallel, one of which serves as a stand-by system.98

Emission controls on H$ do not exist, and concentrations of l-4ppm are reached at the

boundary of the plant site 99 Personal observations by DiPippo’@’ indicate that the odor of

hydrogen sulfide “is noticeable but not objectionable downwind of the power house and cooling

towers” At full output about 1000 kg/hr of noncondensables are ejected, of which % kg/hr of

H2S is emitted: i.e 158OglMWh on a specific power basis.“’

Italy

At Larderello noncondensable gases constitute from 1 to 20% by weight of the total fluid

flow, on average The gas content has remained pretty constant during the period of exploita-

tion This is attributed to the fact that “the natural surface thermal manifestations which have

existed for centuries have prevented a buildup of large amounts of gas”.“* The reservoir is thus

believed to be in a steady-state as regards the evolution of such gases The weighted average

for noncondensables in the Larderello region is 5.9% (Table 10)

Ente Nazionale per I’Energia Electrica (ENEL) puts CO2 at about 4.8% (by weight), H2S at 0.5%

and all others at less than I% Specific data on gas constitutents have been published on some of the

power plants in the Bociferous Region (Table 1 l), and other units The Gabbro equipment can

accommodate steam with a gas content as high as 8% (by weight),‘03 though the most recent reports

chow a gas concentration of only 6.7% ‘04 The gas contant of Castelnuovo-Val Cecina is 10% by

weight, and the units are designed to handle up to 12% (by weight) of noncondensables.‘05

The lowest gas content report for any geothermal plant in Italy is at Monterotondo The

percentage of noncondensables has fallen from a value of 2.5% (by weight) in 1960’06 to 2.2% in

1%9, and to 1.7% in 1974.‘@’

At Sant’Ippolito-Vallonsordo the gas content ranges from 4 to 7% (by weight), whereas

the original steam flow contained about 20% noncondensables.‘m The most current reports for

Table 9 Noncondensable gases at Ahuachapan (by volume)

Carbon dioxide, CO2

Hydrogen sulfide, H2S

Hydrogen, H2 Nitrogen, N2

Amnia, NH3 Methane CH4

134 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA M zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA I PASQUALEITI Table 10 Total 8as content at Italy’s geothermal fields (by volume) Source: Ceron et al., see Ref 19

Gas content

in mass (I) Boraciferous Region

Total Power stations in the Boraciferuus Region and weighted averages

Mt Amiata Region

16 Bagnore 1

17 Bagnore 2

ia Piancastagnaio Total Mt Pmiata region power stations and weighted averages

Grand total and weighted averages

that location indicate a gas content of only 3.3% (by weight) ‘09 The two Lagoni Rossi units are

flexible enough to handle gas contents ranging from 4 to 20% (by weight) The Sasso I, Capriola

and Molinetto units deal with an average gas content of 3.3% (by weight)

Power at the Larderello power plants is produced either by noncondensing turbines (“Cycle

I”) or condensing turbines (“Cycle 3”) The units with the higher percentages of noncondensables

operate under Cycle 1: Sant’Ippoiito-Vallonsordo, Lagoni Rossi, Sasso, Capriola, and Molinetto

Travale is also operated as Cycle 1 All exhaust to the atmosphere The weighted average of

noncondensables at these plants is 16% higher (5.7 vs 6.8) than at the Cycle 3 plants

Table 11 Composition of noncondensable gases found in geofluid produced in the Boraciferous Region of Italy

Source: G Pollastri, “Design and construction of steam pipelines” In Piso 2,780-811 (1970)

La

1:::

23::

3.8 2.2 1.8

3 1.7

5.7

:::

3.8 2.7

Geothermal energy and the environment: the global experience

The Cycle 3 plants include Larderello, Gabbro, Castelnuovo, Serrazzano, Lago, Sasso Pisano, and Monterontondo These plants are all much larger than the Cycle 1 plants, and this total installed capacity is 362.7 MW All these plants use natural draft cooling towers

At Monte Amiata noncondensables constitute a substantially larger percentage of the steam than at the Boraciferous Region The noncondensable percentage has declined from a high of 90% (by weight) of the natural steam when the field was first developed to a present range of 7-20% On average, the noncondensable gas contains (by volume) 95% carbon dioxide, 0.4% hydrogen sulfide, 0.4% hydrogen, 3.5% methane, and 0.7% nitrogen.“’

Efforts to reduce geothermal air emissions have begun only recently in Italy and are still on a small scale Consequently, the odor of H2S is frequently quite noticeable, especially close to the power plants.“’ The hilly topography is often conducive to high concentrations of H2S in lower areas of the fields, but most of the habitations are located on the slopes and ridges The potential for high concentrations is greatest in the most northerly part of the Possera Valley, especially at night

in radiative situations when a katabatic flow moves down the valley Unlike the situation at The Geysers, complaints of odor have not been reported This may be a reflection of the local reliance

of much of the population on employment at the geothermal power plants

There are no applicable emission standards for hydrogen sulfide in Italy Even if there were, only the federal ones would apply because all the geothermal operations in Italy are federally owned and controlled In other words, the chance is slim at best of a repeat of the situation at The Geysers, where private developers and utility companies have been denied permits by local regulatory bodies

This is not to say there is not environmental interest in Italy but rather that official government involvement is just beginning.“’ One measure of this new level of interest is Project 5, a cooperative program of monitoring and analysis between ENEL and the U.S Department of Energy (DOE) started in 1976 Under this program and its successors, H$, radon and radon daughters, are being monitored at several sites Accumulated data are not yet sufficient for definitive evaluation, although so far radon does not seem excessive.“3 Actual radon measurements have recorded 0.6 Ci.‘14 Earlier monitoring of radon was related to its use

as a natural tracer in reservoir engineering’ls with follow-on implication for environmental study.“” zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Japan

In view of their concern for the aesthetics of geothermal power plants vis a vis their location

in natural parks, and considering there was some early evidence of vegetation damage from air emissions”’ it is somewhat surprising to find that H2S from the condenser gas ejectors is simply discharged to the atmosphere at all plants.“8 In large part this attitude stems from the relative isolation of all of the operating power plants Future developments, however, will be closer to habitations, and it appears that such plants will be subject to more demanding control.“’ To date, most of the concern regarding HIS control has stemmed from the damage it can cause to mechanical equipment At Matsukawa the substation has been positioned about 600 m from the turbine house because of the extremely corrosive atmosphere in the latter’s location.‘20 The tail pipes of the condenser for the gas extraction system are now made of stainless steel Moreover

“the main electrical equipment is sealed in oil-filled containers and terminals are coated with conductive grease; bare wires are made of aluminum and supporters are coated with anti-rust point”.“’

The main steam at Matsukawa contains between 0.03 and 0.11% of HIS by volume (Table 12) The 2-stage steam jet ejectors remove the H2S and the other noncondensables and discharge them through the cooling tower (45 m high) The specific emissions levels from the plant range from 5050 to 20,800gm/MWh.‘22 The concentration of HIS in the turbine room is between 0.06 and 0.40 ppm.‘23

The specific amount being discharged to the atmosphere at Otake is not large (Table 13): it amounts to about 542 gm/MWh, based on a concentration of 48 mglkg of main steam, 113 t/hr of turbine steam flow and MW output The overall noncondensable gas content is 0.8% by weight

of inlet steam.‘24 The plant operates with a cross-flow, mechanical-draft cooling tower, and motor-driven, reciprocating vacuum pumps on the ejection system The same type cooling and

136 M J PASQUALETTI

Table 12 Characteristics of geothermal steam and condensate at Matsukawa (by volume) Source: Kawasaki, see

Ref 126 (as cited in Ref 30)

Composition of Noncondensable gases

gas extraction equipment is used at the Onuma plant, where the noncondensable gas content is

0.1% by weight of inlet steam.“’

Onikobe has the highest concentration of H2S of any operating geothermal power plant in

Japan (Table 14) Even the natural concentration of H2S in the air is high, amounting to

0.2 ppm; thus the effects of corrosion place severe design constraints on the Onikobe plant.‘26

For example, extensive corrosion fatigue tests were conducted on the turbine rotor and blades

materials.12’

The noncondensable gas content at Onikobe is 0.5% by weight of the inlet steam-36% of

which is H2S Hydrogen sulfide is released to the atmosphere without control The concen-

Table 13 Characteristics of geothermal steam and condensate at Otake zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (by volume) Source: Kawasaki, see Ref

126 (as cited in Ref 30)

Composition of Noncondensable Gases

Geothermal energy and the environment: the global experience 137 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA

Table 14 Characteristics of geothermal zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBAsteam and condensate at Onikobe(by volume) Source: KawasakLsee Ref

126 (as cited in Ref 30)

Composition of Noncondensable Gases

tration in the turbine room is 0.40 ppm, in the control room 0.050 ppm “Since the main steam

contains about 3400 mg/kg, the specific emission level is approx 31,4OOgm/MWh, an

extremely high value”.‘** The gas extraction apparatus consists of one set of two steam jet

ejectors (in parallel) The cooling tower is counter-flow, mechanical-draft

At the Hatchobaru power plant 2 km south of Otake, the noncondensable gases are vented

to the atmosphere through the cooling tower to maximize dispersion.‘29 The hot steam contains

0.3% noncondensables by weight ‘30 The innovate ERR gas extraction system (for steam

Ejector-Radial blower-Radial blower), combines steam jet ejectors, which are very efficient for

high vacuum use, with radial blowers, which are better suited for low-vacuum.‘3’ About

1250 kg/hr of geothermal gas plus 260 kg/hr of air released from the cooling water must be

removed from the condenser.13* The ERR system has a capacity of 1970 kg/hr The cooling

tower is the same type as at Onikobe The specific level of H2S is likely to be about the same as

Otake; i.e rather low Ambient air quality measurements indicate the H2S concentrations are

generally less than 20 ppb; the lower limit of instrument sensitivity.‘33

At Kaddonda the natural steam contains about 0.3% noncondensables by volume, of which

nearly 17% is H2S and 71% is CO* The other gases include hydrogen, nitrogen and methane, in

small amounts.‘34 The condenser, cooling tower, etc are essentially the same as for Onikobe

SUBSIDENCE

Types of crustal deformation include compression, expansion, doming, and subsidence All

four types are potentially important to geothermal developments though subsidence, or down-

warping of the earth’s surface, has consistently received most of the attention In general,

subsidence is to be expected when fluid is removed from subsurface reservoirs and

the reservoir pressures are not maintained It can take place under varied circumstances of

geology, hydrology, and tectonics, but it occurs most often when fluid is withdrawn from an

aquifer which consists of a porous medium in compressible and/or fractured beds One of the

best known examples of such subsidence occurred at the Wilmington oil field of Southern

California where vertical and horizontal displacements reached 8.2 and 3.7 m respectively.‘35

Other examples are numerous.‘36

The relationships which produce subsidence in nongeothermal fields differ from those in

geothermal fields One cause for this contrast is the higher temperatures of the geothermal

reservoir: “Plastic deformation of grains and grain solution at contacts may be more important