Underground Space. VoL 3, No.4. pp. 175-186. Pergamon Press 1979. Printed in Great Britain.

Classification and

of Subsurface

Valuation

Space

ALAN H. COOGAN

Department of Geology, Kent State University, Kent, Ohio 44242, U.S.A.

Increased interest in the utilization of subsurface space raises social and legal questions that should be addressed early in the planning stages. Successful planning for the development of subsurface space depends on a system for the classification and valuation of that space. A system is proposed here that classifies the different types of subsurface space, considers the actual and potential uses of subsurface space, and evaluates the relative importance of those uses. The three major uses are mineral extraction, access and transportation, and storage. These uses and their subclasses are valued according to nine criteria concerned with the extent of need, extent of primary impact, extent of secondary impact, and extent of need for major decision analysis. According to this valuation system, subsurface space is most needed for radioactive waste storage and the extraction of metallic and valuable ores. Radioactive waste storage, liquid pollutant storage, and mineral extraction are the uses with the greatest primary impact. The extraction of rare and metallic ores and the storage of radioactive waste also have the greatest secondary impact, and thus are the uses that demand further attention in the formulation of social policy.

INTRODUCTION

ALTHOUGH subsurface space has been used by man

for millenia, recent social concerns and new

engineering technologies have greatly increased

interest in the further development of this valuable

resource. The development of subsurfa_ce space, as

that of any national resource, raises social and legal

questions that should be addressed now, while

development is still in the planning stage and change

is possible [1) .

Planning for the development of subsurface space

hinges on a system for the classification and valuation

of that space. The central issues are: What kind of

subsurface space exists, how is it used, and how does

oqe value different subsurface space uses relative to

one another? For example, the three major uses of

subsurface space are for mineral extraction, access

and transportation, and storage. As the number of

suitable sites are limited, the possibility of conflict

between these uses exists - which use should assume

priority?

In an attempt to address these issues this paper

will: (1) develop a general classification system of

175

subsurface space for most discernible types of uses;

(2) consider the various actual and potential uses of

subsurface space; and (3) evaluate the relative

importance of the various uses. Such a classification

system will aid in the planning of subsurface space

use and in the formulation of social policy by

providing a basis for recognizing the most valuable

uses, and those uses that will require government

regulation or ownership.

CLASSIFICATION OF SUBSURFACE SPACE

Physical aspects

From a geologic standpoint, there are two major

and several subsidiary types of subsurface space (Fig.

1): particle dependent space, space that occurs

between or within particles of sediment or rock [2],

d transparticulate space, openings in the rock that

cut across the rock grains. The distinction between

particle dependent and transparticulate pores affects

the manner of extraction, exploitation, and storage of

liquids and related minerals [3] . Transparticulate

pore space may be further divided on a geometric

Alan H. Coogan 176

SUBSURFACE SPACE

PARTICLE DEPENDENT

I

INTERPARTICULATE INTRAPARTICULATE

(Between Grains) (Within Grains)

PARTICLE INDEPENDENT

TRANSPARTICULATE

(Across Grains)

NONLINEAR LINEAR

(Caves) (Joints, Fractures)

FIG. 1. Classification of subsurface space.

basis into linear and nonlinear space (a fracture is an

example of linear space, and a cave is an example of

nonlinear space).

Artificial subsurface space

Artificial subsurface space is·created by man to fill

a perceived need. All artificial subsurface space is a

form of transparticulate space, and is classified by its

mode of development into linear space (consisting of

joints, fractures and faults), and into nonlinear space

(consisting of cavities formed by physical excavation

or by solution [4]). Artificial subsurface space is

generally larger in volume than natural space,

although caverns in limestone terrain often exceed in

volume any man-made subsurface space.

Use classification

Although many authors speak of planning uses of

subsurface space [5], no systematic use classification

exists in the literature - therefore, a classification

system is constructed here to serve as the basis for an

evaluation of subsurface uses (Table 1). The system is

based on the three major uses of subsurface space -

mineral extraction, access and transportation, and

storage - and several subclasses. While not exhaus­

tive, the list appears to be comprehensive for our

purposes.

Table 1. Uses of subsurface space

I. Extraction of minerals A. Solids B. Liquids and gases

II. Access, transmission and transportation A. Access B. Transmission and transportation

III. Storage A. Permanent

1. Solids 2. Liquids and gases

B. Reuseable 1. Solids 2. Liquids and gases

Natural subsurface space uses

A preliminary evaluation of the uses of natural

subsurface space is made by combining the

classification of space with the classification of uses,

and by adding a numerical score to reflect the

perceived degree of use (Table 2). For each of the

uses listed (mineral extraction, access and transporta­

tion, and storage) points are assigned to indicate

whether the use is common (2 points), rare (1 point),

or very rare (0 points). Unknown uses are not valued.

As can be seen from Table 2, the use of particle

dependent subsurface space is common for the

extraction of fugaceous minerals such as petroleum,

potable and connate water and other minor minerals.

Natural space is also commonly used for permanent

or reusable storage of septic and other liquid wastes.

For example, depleted gas fields·can be used for gas

storage, depleted or low-yield water fields can be

recharged and used for storage of potable water, and

so forth.

Natural transparticulate linear pores commonly are

used for the same purposes as particle dependent

pores. (Efficient uses - e.g. mineral fluid and gas

extraction - usually involve additional enhancement

of the space network and therefore are valued in the

section on artificial space.) Caves and grottoes

(transparticulate nonlinear space) have had a shifting

history of use through the ages. At one time it was

essentially the only subsurface space accessible to

man and other animals. Consequently it was used for

storage, shelter, deposit of garbage, religious cere-·

monies, burial, recreation and occasionally for the

extraction of mineral deposits such as potable water

and bat guano. Today in industrial societies caves are

used principally for recreation.

Artificial subsurface space uses

Types of artificial space can be compared with the

classification of uses (Table 3) in a manner similar to

that used for natural space uses. Here an additional

Pores Nonlinear

(Caves and

Linear

(Fractures, grottoes) joints and

faults)

Uses I. Mineral extraction

A. Solids B. Liquids and gases

1 2 1

1) Oil 2 0 2

2) Gases 3) Water

2 0 2

a) Fresh 2 1 2

b) Salt 2 1 2

II. Access and transport A. Access 0 0 1

B. Transport 0 0 0

III. Storage A. Permanent 1) Septic wastes 2 1-2 1

2) Radioactive wastes 1 1 3) Liquids

4) Burial 1 1

1-2 1

1) Materials 1 2) Shelter 1 3) Petroleum 2 0 1

4) Gases 5) Water

a) Potable

2

2

1

2

2

b) Other 2 1 2

6) Experimental use 7) Historic or

1 1 1

natural wonder 2

Classification and Valuation of Subsurface Space 177

Table 2. Classification of natural subsurface space by type and use

Inter/ Intra- Transparticulate Particulate pores

B. Reuseable

distinction is made according to whether nonlinear

space is developed physically or by solution. Linear

transparticulate space is almost always physically

developed, though development may be chemically

assisted.

As in the case of natural subsurface space, points

were assigned for each of the uses listed according to

whether the use was perceived as common (2), rare

(1), or very rare (0). In addition, use subclasses were

expanded to include descriptive categories. The

reader may disagree with the numerical value assigned

and is free to change it.

A few observations are warranted . Compared to

natural subsurface space, artificially created space is

used more extensively for access, transmission and

transportation. In addition, the various uses for

storage are more common and diverse because more

suitable (size and location) sites are available. Finally,

linear transparticulate space includes faults which

really are more enhanced by man's activity than

created by it.

VALUATION OF SUBSURFACE SPACE

The third question to be addressed in this paper is

how to assign values to the uses of subsurface space.

As Tarlock noted, this is a problem of resource

allocation [6]. This approach will emphasize the

values assignable to artificial space for several reasons.

First, natural subsurface space is comparable in use,

and the same principles that apply to the valuation of

artificial space may be applied to natural space.

Second, the natural space that is accessible is, in a

sense, already in use and already valued. Third, with

the exception of particle dependent space (to which

one has little access without the additional

development of artificial space) natural space is

localized and is thus of less concern in the

development of social policy.

The valuation method considers aspects of

resource allocation and the impact of a particular use.

Nine categories of valuation are selected that provide

a rational approach to judging the importance of

subsurface space uses, and that provide a definite, if

not definitive, evaluation scheme. The nine categories

are: (1) need, (2) scarcity, (3) substitutability,

(4) duration of change resulting from the use,

(5) rate of change once the use has begun,

(6) primary impact on the surrounding area,

(7) secondary impact on the surrounding area,

(8) revocability of the decision for a particular use

once the commitment is made, and (9) need for an

orderly decision on the use before the commitment.

Alan H. Coogan 178

(1) Adits 2 2 (2)Tunnels 2 2 (3) Boreholes 2 2 2 Transmission (l) Pipes 2 1 1 (2) Cables/Wires 2 0

Physical Solution Joints/ fractures

Faults

Uses

.1. Extraction of minerals

(l) Coal 2 0 (2) Evaporites (Salt/KCL) 2 2 2 (3) Limestone/Dolomite 2 1 2 (4) Sandstone and

Table 3. Classification of artificial space

Mode of Development Transparticulate

Nonlinear (cavities) Linear

a. Solids

other aggregate 2 (5) Metallic ores 2 (6)0ther ores 2

b. Liquids/gases (1) Petroleum liquids 2 0 (2) Gases (3) Water

2 1

a) Potable 2 0 2 2 b) Salt /connate 2 2 2 1 c) Geothermal 2 2 2

2. Access/transport a. Access

b.

3. Storage a. Permanent /semi-permanent

(1) Wastes a) Radioactive l l 0 b) Pollutant solids 2 2 0 0 c) Pollutant liquids 2 2 2 2 d) Burial 2

b. Materials (l) Records 2 2 (2) Gases (3) Water

2 2

a) Potable 0 0 2 0 b) Salt /connate 0 2 2 0

(4) Other liquids 0 0 0 0 (5) Electricity by pumped storage 0 1 0 0

Three degrees of value {0, 1 and 2) are assigned to

each of the nine categories for each of the uses listed

in the modified use classification (Tabie 4). A fmer

scale, for example, using values from one to ten or

using exponents of ten could also be used, but as will

be explained later, it is felt to be simply inappropriate

at this preliminary stage.

Parameters of the nine categories

Each of the nine categories is reviewed below to

indicate the method of assigning particular values

{Table 4).

1. Need. Need is valued as low {0), medium {1)

and high {2). For example, the need for burial space

is high and has been so historically for reasons of

health and religion. On the other hand, need for

parking garages generally is perceived to be low

{although locally it could be high). The need for

transmission lines and space for tunnels depends on

extrinsic factors related to the need for the material

being transported or the material to which access is

sought. Accordingly, cemeteries are rated as 2, pipes

and tunnels as 1 and parking garages as 0.

2. Scarcity. The availability of land for a specific

subsurface space use is classified as widespread {0),

localized {1) or rare {2). For example, metaTI!c ores

are scarce and consequently space used for removal is

valued high {2). On the other hand, space for

cemeteries is widespread and hence valued as 0.

3. Substitutability. This category provides an.

extrinsic measure of space use compared to other

subsurface and surface uses. In addition, it considers,

in the case of development of subsurface space for

the extraction of minerals, the availability of

alternate materials. High substitutability is valued low

Classification and Valuation of Subsurface Space 179

(zero) and low substitutability is rated high (2).

Accordingly, space used for storage of highly

radioactive wastes is rated 2, since there are few

alternatives available, but space for cemeteries is rated

zero since cremation is an easy alternative.

4. Duration of change. Values for this category

reflect the length of time (years) of the changed use.

A low duration use (0) is for several months to one

year or so. A medium rating CD covers uses for tens of years. A high rating (2) represents very long or

essentially permanent use. Where the use is

irreversible over geologic time, for example the

storage of radioactive wastes, it is still valued at 2.

Water extraction is usually a use of medium duration

(1) but could last for hundreds of years (2). On the

other hand, use of space for the extraction of gaseous

hydrocarbons can be of short to moderate duration

(1).

5. Rate of change. The category evaluates the rate

of development of the artificial use in the same terms

as used for duration of change. For example, once a

commitment is made to use space for a cemetery, the

rate of development might be over tens of years (1).

On the other hand, the development of a small gas

field could be completed within one year (2). Fast

rates are valued high (2), slow rates are valued low

(0). Most rates are moderate (1).

6. Primary impact. Using the type of data

considered in the construction of environmental

impact statements (EIS) (under the requirements of

the National Environmental Policy Act), the impact of

a subsurface space use on the immediate surrounding

human and natural environment is evaluated. The

checklist of factors to be considered is gleaned from

several guidelines for the preparation of EIS [8] . The

checklist includes adverse environmental factors that

cannot be avoided (increased water and air pollution),

damage to life systems, any effect on property listed

in the National Register of Historic Places, increased

urban congestion, any irreversible and irretrievable

commitments of resources, impact on soils, fauna,

flora, aesthetics, water resources, human activity, the

economy, impact from noise, electromagnetic radia­

tion, radioactive radiation, the alteration of major

land uses and so forth. These checkpoints were

developed by federal agencies pursuant to the act,

which called for an analysis of impact for "major

federal actions significantly affecting the quality of

the human environment" [9] .

Weighting such complex factors in abstract is

tenuous, nevertheless, the category and tentative

evaluations of impact are shown in Table 4, at least

for illustrative purposes. Impact is valued in terms of

local (0), regional, i.e. between cities or over distances

of miles (1), and interregional, i.e. to hundreds of

miles (2). Most uses are rated low (0) for primary

impact.

7. Secondary impact. The same rationale and

criteria are used for evaluation of secondary impact,

with the emphasis on the secondary consequences of

the use. An illustration may assist in clarifying the

difference. The establishment of a recreational use for

a natural wonder in the form of a cave or the

excavation of a substantial hole for a football stadium

may have little direct or primary impact on the

surrounding area in terms of destruction of the

terrain or interference with the water table. The

secondary impact may be high, however, as the result

of the necessity to build access roads, parking

facilities, sanitary facilities, and other surface satellite

uses. In other words, the distinction between primary

and secondary impact is the difference between the

direct consequence of the development and use of

subsurface space in and of itself and the secondary

consequences of related activities. High impacts are

rated high (2).

8. Revocability. Revocability is one of the items

listed in the regulations for the development of EIS

[10] and is listed separately here because of its

perceived importance as a separate basis of

evaluation. In EIS terms, the question raised is

whether the commitment of the space to the use is

irreversible once the use has begun. In view of the

subsurface space use classification (for example,

permanent storage of wastes or extraction of ores) it

seems to be an especially pertinent aspect to value. As

an illustration, use of space for human burial is highly

revocable (0). On the other hand, commitment of

subsurface space in a salt mine to plutonium wastes

storage [11], with half-lives of geologically significant

periods of time, is an irrevocable commitment to that

use for a long time. Such use is valued here only as 2,

although the reader may wish to value it higher.

9. Need for an orderly decision. The last of the

nine categories calls for a judgment of the combined

effects of many factors, but relates most directly to

economic requirements. For example, the question

might be whether the use requires large-scale and

essentially front-end financing, or whether it is a use

that pays for itself once or many times over? The

higher the need for an orderly decision, the higher

the value assigned on the 0 to 2 scale.

Analysis of the valuation

Two approaches are used to evaluate the result of

assigning numerical values to the uses of subsurface

space in the nine categories. The first method is to

consider uses that are interrelated. To do this, one

compares several of the nine categories with one

another in a three-dimensional matrix. The second

0

g

Table 4. Classification and valuation of subsurface space

00

Categories of evaluation

Uses Need Scarcity Substitut- Change Impact Revoca- Ordered Total % Fig. ability Duration Rate 1st 2nd bility Decision Score Letter

I. Extraction of

minerals

A. Solids 1. Coal 2 1 1 1.5 1 1 2 2 1.5 13.0 72 A 2. Evaporites 1 0.5 1 1.5 1 0 1 1 0.5 7.5 41 B

3. Limestone 0.5 0 0 1.5 1 0 1 1 0.5 5.5 30 c 4. Sandstone 0.5 0 0 1.5 1 0 0 1 0.5 4.5 25 D 5. Metallic ores 2 2 2 2 1 0 2 2 2 15.0 83 E 6. Rare ores 2 2 2 1.5 1 0 1.5 2 2 14.0 77 F

B. Liquids & gases 1. Oil 2 1.5 1 2 1 0 2 2 2 13.5 75 G 2. Gas 2 1.5 1 2 1 0 2 2 2 13.5 75 H 3. Potable water 1 0.5 1 1 1 0 1 1 1 7.5 41 I 4. Connate water 0 0.5 0 1 0 0 1 1 1 4.5 25 J :to. 5. Geothermal 1 2 1 1 2 0 1 2 2 12.0 66 K IS"

II. Access and transmission :::s tJ::

1. Adits 2 2 0 1 2 0 0 0 1 8.0 44 L 2. Tunnels 2 2 0 1 2 0 0.5 1 2 10.5 58 M 3. Boreholes 2 2 0 1 2 0 0 2 1 10.0 55 N

<::>

4. Pipelines 0 1 0 -2 1-2 2 1-2 2 1 2 14.0 77 0 :::s 5. Cables 1 1 0-2 1-2 2 1-2 2 1 2 12.0 66 p

III.Storage

A. Wastes 1. Radioactive 2 2 2 2 2 1 2 2 2 17.0 94 Q 2. Pollutant solids 0.5 1 0 1-2 0 1 0 1 1 6.5 36 R 3. Pollutant liquids 0.5 0.5 0 2 2 0 1 2 1 9.0 50 s 4. Cemeteries 2 0 0 2 1 0 0 0 0 5.0 27 T

B. Materials

1. Records 0 0 0 1 1 0 0 0 1 3.0 16 u 2. Parking 0 0 0 1 1 0 0 0 1 4.0 22 v 3. Housing 0 0 0 1 2 0 0 0 1 4.0 22 w 4. Experimentation 0.5 2 1 1 1 0 0 1 2 8.5 47 X

C. Reusable 1. Petroleum liquids 1 1 0 1 2 0 1 2 1 9.0 50 y

2. Gases 1 1 0 1 2 0 1 2 1 9.0 50 z 3. Water Potable 0.5 1 0 0-1 1 0 1 0 1 5.0 27 I:

4. Connate 0 1 0 1 1 0 0 1 1 5.0 27 \ll

5. Liquids other 0.5 1.5 1.5 1 1 0 0 1 1 7.5 41 6. Pumped storage 0.5 1.5 1.5 0-1 2 0 1 1 1 9.5 52 ct>

1. Radioactive wastes (Q) 5.0

2. Liquid pollutants (S) 4.0

3. Mineral extraction (E) 3.0

4. Liquid/Gas extraction (G,H) 3.0

5. Tunnels (M) 3.0 6. Pipes and cables (O,P) 3.0 7. Burial (T) 3.0

..

Classification and Valuation of Subsurface Space 181

method is to sum the values assigned for each use to

determine the percentage for that use of the

maximum possible percent. This method leads to a

grouping of types of subsurface space by categories of

importance, in serial order, and is discussed after the

results of the first method are examined.

Four interrelated groups of the nine categories

were chosen to evaluate subsurface space. These are:

the Extent of Need, Extent of Primary hnpact,

Extent of Secondary Impact and Uses Needing

Further Decision Analysis. Since there are numerous

other possible combinations of the nine categories,

the four groupings (Figs. 2 -5) clearly are illustrative.

The reader is invited to construct his own diagrams

from Table 4. Note that in Figs. 2-5, the various

letters A to Z and the Greek alphabet letters' t/1, ..:l,

rp, are keyed to Table 4. For example, "T'' is used

throughout for human burial, "Q" is used for

permanent storage of radioactive wastes, and cp, is

used for pumped storage of electricity.

2

II> 0:

.cD:: u

0 <z

!>

0: g I

· l! Cl

Degree Of Need 0

ili 0

L OC A L REGIONAL

2

INTERREGIONAL

FIG. 2. Extent of need .

I. Most valued space

1. Radioactive waste disposal (Q)

2. Extraction of metallic and valuable ores (E)

3. Extraction of petroleum liquids and gases (G, H)

4. Extraction of coal (A) 5. Location of pipes and cables (0, P) 6. Pumped Electric storage (cp)

II. Intermediate valued space

1. Access to Subsurface space (Tunnels and adits) (L-M)

2. Space for experimentation (X) 3. Extraction of potable water (I)

4. Burial space (T)

III. Least valued space 1. Extraction of evaporites (B) 2. Location of pipes and cables (0, P) 3. Pollutant solid and liquid storage (R, S) 4. Liquid storage (e.g. petroleum)( ) 5. Extraction of potable water (I)

6. Extraction of aggregate (C, D) 7. Materials storage (U -W)

Value 6.0

6.0

4.5 4.0 4.0 3.5

4.0 3.5 2.5 2.0

2.5

2.0 1.5

2.0

1.0 0.5

0.0

Primary Impact

FIG. 3. Extent of primary impact. I. Uses with most effect

II. Uses with lesser impact

1. Watet extraction (I) 2. Solid pollutant disposal (R) 3. Pumped storage (cp)

4. Water (connate) storage (t/1) 5. Records storage (U) 6. Water (potable) storage( )

III Most regional impact

1. Coal extraction (A) 2. Pipelines and cables (O,P)

Value 2.0

2.5 2.5 2.0 2.0

1.5 3.5 5.0

Alan H. Coogan 182

(G,H) 4. Extraction of geothermal heat (K)

5 5

5. Storage of liquids (H) 3 6. Pumped storage (r/>) 3.5

7. Extraction of coal (A) 4.5 8. Tunnels and transmission lines

Secondary Impact

LOW HIGH

Need for Orderly Decision

FIG. 4. Extent of secondary impact.

I. Most scarce, unique and

greatest impact A. Extraction of rare and metallic

ores (E) B. Disposal of radioactive wastes (Q)

II. Most scarce, greatest impact but substitute available

A. Extraction of petroleum liquids and gases (G,H)

B. Extraction of coal (A) C. Pumped storage (r/>)

III. Scarcity moderate, impact moderate, alternatives available

A. Pipelines and cables (O,P) B. Extraction of potable water (I)

C. Tunnels (M) D. Storage of potable water( ) E. Storage of liquid pollutants (S) F. Storage of salt or connate water(\}!)

IV. Little scarcity, impact local, alternatives available

A. Tunnels (M) B. Solid waste disposal (R) C. Cemeteries (T) D. Storage of records (U)

Value

4.0 6.0

4.5 4.0 4.0

4.0 2.5 2.5 2.0 1.5 1.0

2.5 1.0 0.0 0.0

FIG. 5. Uses needing further decision analysis.

I. Uses needing most decision

analysis and action 1. Radioactive waste disposal (Q) 2. Extraction of metallic and rare

ores (E,F) 3. Extraction of petroleum and gas

and pipes (M,O,P)

II. Uses needing intermediate analysis action

1. Salt or connate water storage (1/1) 2. Extraction of potable water

(Large scale) (I)

3. Tunnels and transmission lines and pipes (M,O,P)

4. Storage of liquid pollutants (S) 5. Storage of solid wastes (R)

III. Uses needing least decision , analysis action

1. Burial plots (T) 2. Space for experimentation (X) 3. Material storage (M -W) 4. Extraction of aggregates (C,D) 5. Storage of liquid petroleum and gas

(Y,Z)

6. Tunnels and adits (L,M) 7. Extraction of potable water (I)

(small scale)

Value

6

6

3-5

2

3 3-5

3 2

0 4

1.0 1.5

3

1 -3 3.0

Classification and Valuation of Subsurface Space 183

The plotted value (Figs. 2 -5) is the combined

estimate from Table 4, the maximum value on the

block is 6. If one used a 10 digit scale in Table 4, the

illustration (Fig. 3) of "Most Valued Space" and

"Least Valued Space" would remain similar, but the

distance between plotted values would increase and

the blocks would be compressed. Similarly, if one

used a log scale in Table 4 so that the Table 4 value of

1 read 101 (=10), the value of 2 red 10 2 (=100) and

so forth, the "Most Valued" and "Least Valued" space

blocks would be similarly situated but very greatly

compressed. At first a log scale seems attractive.

Using a log scale the "Extent of Need" analysis

below, the use of subsurface space for the disposal of

radioactive wastes would be rated as 1,000,000

rather than 6 times more valuable than space for

underground parking. While this seems reasonable and

intrinsically coherent, on the same basis, a burial plot

(T) would be rated as one hundred times more

valuable than a parking garage and ten times more

valuable than space for extraction of potable water -

contrasts that are incompatible with experience.

Extent of need

The need for subsurface space for a particular use

is presented in terms of the three categories - degree

of need, scarcity and substitutability (Fig. 2). The

internal block of "Most Valued Space" is bounded by

the numerical values of 3 to 6. The internal block of

"Least Valued Space" is circumscribed by the

numerical values of 0 to 3. The remaining

three-fourths of the cube contains areas of inter­

mediately valued space. Of these, three uses deserve

mention.

Access to subsurface space by tunnels and adits

(0, P) is directly related to the specific use for which

access is required and consequently has a transversely

variable location in the diagram. Use of space for

experimentation (X) is valued at 3. Like the use of

caves for their natural beauty, experimental space use

is related to socially perceived uniqueness. The

amount of space required for scientific experimenta­

tion is minute, however its location may be critical

and consequently its substitutability ranges from high

to low. Space for human burial (T), valued at 2, may

be seen as having high need, low scarcity and high

substitutability.

Extent of primary impact

The analysis (Fig. 3) uses the categories of primary

impact, duration of use and rate of change from

Table 4. The results of the plot show that there is

little widespread impact, with the exception of

regional and interregional transmission lines. Of

course, an interregional subway might be built, but

probably not in the immediate future for economic

reasons. The closest equivalents to an interregional

subway are the intercity and hence regional BART

system in the San Francisco Bay Area, and the New

York City subway system. Most subsurface space use

has a primary impact at the local level. The

arrangement of the illustration allows the reader to

visualize the use of other space with other impact

values as these are developed.

Extent of secondary impact

Values are plotted (Fig. 4) in terms of the Table 4

categories of secondary impact, scarcity and substi­

tutability. Even a cursory consideration brings one to

the conclusion that whatever the secondary impact of a

subsurface use might be, it will probably not be

substantially different from a similar surface use,

similarly situated. For example, the secondary

economic effects of a city cemetery are likely to be

little different from those of a crematorium; the

effects of a subsurface gas storage reservoir are likely

to be similar to those of a tank farm, and a buried gas

transmission line the same as those of a surface

pipeline.

Adverse conditions resulting from the establish­

ment of a subsurface use such as a heightened air

pollution, increased water pollution, destruction of

historic, scenic, or recreational areas, impact on a

formally designated wildlife refuge, and destruction

of fisheries or major wetlands in the coastal zone may

constitute an interregional impact. In a like manner,

significant changes in land-use patterns, urban

congestion, distribution and use of regional waste­

water systems, significant changes in use of

commercial or prime agricultural land, destruction of

substantial established residential areas, adverse

changes in groundwater reservoirs, establishment or

abandonment of access roads, railways or airports, and

the alteration of major natural habitats can be

considered criteria for the recognition of a regional

impact.

The evaluation of these consequences is extremely

complex. With this caveat, the data are offered as an

approximation of the extent of secondary impact in

terms of scarcity and substitutability (Table 4). As

the data show, there are a large number of items that

have a moderate to high secondary impact and vary in

degrees of scarcity and substitutability.

Uses needing major decision analysis

Subsurface uses can be separated into those that

most require decision analysis and those that least

require it. This is done by comparing the categories of

need for an orderly decision with revocability and

substitutability. The result is that uses such as

cemeteries, adits, record storage, parking, and

extraction of low-grade aggregate (Table 4) are

deemed to be those needing least analysis (Fig. 5). On

the other hand, extraction of metallic ores,

petroleum, coal, the use of geothermal resources,

storage of radioactive wastes, and installation of

Least Cemeteries 4 22

Materials storage (parking, etc.) 3 16

184 Alan R Coogan

underground cables and pipelines are deemed to be

most in need of analysis. Clearly, many regulatory

requirements are in effect already. For example, the

development of a parking garage beneath a restaurant

owned by the same party is adequately covered by

extant property laws, local building codes and zoning

restrictions. On the other hand, private industry's

placement of radioactive wastes or other toxic wastes

into the deep subsurface through wells may indeed

require extensive governmental analysis [12] , may

have an impact on adjacent surface owners by a

permanent private inverse condemnation, may restrict

the use of superadjacent or subjacent subsurface

space for mineral extraction, and may be inherently

dangerous.

Important subsurface space

The second method of analysis of the valuation of

subsurface space uses {Table 4) is to add the values

assigned to each use for each of the nine categories

and to determine how close the sum is to the

maximum possible value {Table 5). Three categories

of relative importance of subsurface space use are

distinguishable {Table 5). The most important uses

(values 17 to 12, or 94% to 66% of the possible

maximum value) relate either to storage of

radioactive wastes or the extraction and transporta­

tion of rare materials, including resources for the

production of energy. The intermediate level uses

involve the storage of these same resources and

disposal of less toxic wastes {values 11 to 6, or 61%

to 33% of the maximum). The least important

subsurface uses involve extraction of common rock

aggregates, storage of various materials equally well

stored aboveground, and burial sites. All of these are

valued between 5 and 3 {27% to 16% of the

maximum).

Summary of valuation

The preceding discussion shows that by using the

physical and use classifications of subsurface space

{Tables 1-3) as a starting point and applying to them a

value scheme based on categories grounded in the

perception of social values {Table 4), subsurface space

uses can be ordered according to value priorities. A

few observations are worth noting:

{1) It is difficult to place numerical values on uses

in the abstract. Nevertheless, the author has presented

the opportunity to value these categories to several

audiences and with a little coaching, the values they

assigned are very similar to those shown in Table 4.

{2) It seems likely that the same values would

apply if the space were on the surface or a

combination of surface and subsurface space.

{3) If the classification and valuation are useful it

is because either the method itself is helpful or the

results appear intrinsically true. In either case, the

analysis points to uses of subsurface space that

require further attention, and provides a method of

evaluating new uses or combinations of uses.

Uses requiring further policy analysis

Based on the relative importance of subsurface

space uses, it is possible to suggest what categories of

uses are adequately covered within a

private-property-rights regime, unless there is a

compelling need for governmental regulation of

ownership. Clearly, ownership in fee, fee purchase,

and lease are adequate legal means to secure shallow

subsurface property for all uses except the storage of

radioactive wastes {Table 6). There may be uses that

require governmental action to guarantee the public

interest, but the irrevocability of commitment,

duration of change, rate of change, scarcity, and lack

Table 5. Important subsurface space*

Type of space uses Value Percent of maximum

Radioactive waste disposal 17 94 Extraction of metallic and

rare ores 15 83 Most

Inter­ mediate

Extraction of petroleum, coal and some use of tunnels and pipes 13 72

Geothermal energy production 12 66

Liquid storage 11 61 Pumped storage, boreholes,

experimentation 10 55 Extraction of water 9 50 Waste liquid disposal 8 44 Connate water storage 7 38 Solid waste disposal 6 33

Extraction of aggregates 5 27

*Serially ordered and classified based on 9 criteria.

Classification and Valuation of Subsurface Space 185

of substitutability of sites for storage of radioactive

wastes clearly puts this solely in the area of

governmental action. Governmental regulation may

be required for protection of water or geothermal

resources in the first group of uses (Table 6) needing

strong policy action. In the category of uses needing

intermediate policy action there is possible need for

governmental action for potable water protection

(13] and less often for pipes, cables and disposal of

other wastes [14] . In the third category, there may

be need for governmental ownership of tunnels,

experimentation sites and for state-owned projects.

located so deep that it would not interfere with

normal surface or subsurface uses or would not for

any practical purpose be accessible or needed by the

surface owner, how would one estimate its value in

money? Some questions are: does deep subsurface

space indeed have any intrinsic economic worth? Is it

possible to "own" deep subsurface space? How deep

is deep?

These questions raise the spectre that the

long-honored common law of property may not be

sufficient to provide the answer. The ancient rule was

that one owns the land from the heights of the sky to

Table 6. Subsurface uses needing fur(her policy analysis

Fee Purchase

Lease National Government

Expropriation

Not needed Not needed Rarely needed Not needed Possibly needed Governmental

activity solely

I.

Uses needing strong policy action

1. Metallic ore extraction X X

2. Coal extraction* X X

3. Water extraction* X X

4. Oil & gas extraction X X

5. Geothermal uses X X

6. Radioactive wastes X

II. Uses needing intermediate policy action

1. Pipes X X Rarely needed 2. Cables X X Rarely needed 3. Disposal & storage liquid wastes* X X Possibly needed 4. Water extraction* X X Rarely needed 5. Liquid storage X X Not needed 6. Pumped storage X X Not needed

III. Uses needing little policy action

1. Aggregate extraction X X Not needed 2. Tunnels and adits X X Possibly needed 3. Solid pollutants X X Not needed 4. Cemeteries X X Not needed 5. Materials storage X X Not needed 6. Experimentation X X Rarely needed

*Inadequately protected by state laws.

OTHER CONSIDERATIONS

The economic value of undeveloped subsurface space

If the amount of subsurface space to be acquired

for governmental use (because of inadequate

protection by private ownership) is small , the cost to

the taxpayer for condemnation is not burdensome

and there is little grumbling with the imperatives of

the Fifth Amendment guarantee against a taking of

property without just compensation. The difficult

question arises where the proposed use is regionally

extensive - for example, a subsurface transit system

hundreds of miles in length. If a transit system were

the depths of the earth [15] , but the rule has been

modified for air travel (16]. Assuming ownership of

deep space is possible, and knowing that the

subsurface space is valuable, the question of its value

remains. For an interesting, but not prevailing, view

the dissent in Edwards v. Sims (17] claims that the

space developer creates the value and, if he produces

no harm to the surface owner, has created essentially

an injury without fault and a liability of no monetary

value. Another possibility is that the sovereign may

own deep subsurface space (18], but federal

legislation probably would be required to implement

this suggestion.

REFERENCES

1. These issues were addressed at a 1973 workshop organized by the U.S. National Committee on Tunneling Technology (National Research Council) in cooperation with the Engineering Foundation Conference, and sponsored by the Science and Technology Program of the National Science Foundation. Questions discussed at the

186 Alan H. Coogan

workshop were: Can subsurface space be owned in and of itself as an enrity separate from the enclosing rock? What is the general status of the law that regulates ownership and use of subsurface space? What kinds of conflicts occur and how can they be classified to provide a framework for the application of legal concepts? The workshop also pointed to the need for a classification system for subsurface space. See Legal, Economic, and Energy Considerations in the Use of Underground Space, Proceedings of the Workshop of Standing Committee No. 3. National Academy of Sciences (1974), 121 pp. (hereinafter Workshop Proc.).

2. Coogan, A. and Manus, R. "Compaction and Diagenesis of Carbonate Sands", in Chilingarian and Wolf (eds.) Compaction of Coarse Grained Sediments , I. Elsevier, Amsterdam, p. 81 (1975).

3. Morrow, N. "Small-scale Packing Heterogeneities in Porous Sedimentary Rocks", Bull. Am. Assoc. Petrol. Geol. 55, 514 (1971).

4. Linear subsurface space may be created by stressing rock formations - for example, by overloading, releasing load, or by direct injection, pumping and lifting (See Haimson, B. "Well Communication in Salt Formations", in Fourth Symposium on Salt, North Ohio Geol. Soc. (1974) at 203). Where the rock is soluble, the stress is usually applied in conjunction with a solvent. Nonlinear space (such as quarries) is commonly created by physical excavation, although a solution cavity may also be formed by the solution of soluble rock material - for example, rock salt dissolved by fresh water, or limestone dissolved by acid.

5. See Hagman, D. "Planning the Underground Uses", in Workshop Proc., at 52; Newcomb, R. "Dynamic Analyses of Demands for Underground Construction", in Workshop Pro c., at 87; and any issue of Underground Space.

6. Tarlock, D. "Legal Aspects of Use of the Underground", in Workshop Proc. , at 41. "By definition, the optimum utilization of underground space is a problem in resource allocation. Underground space . . . can now be properly regarded as a potentially scarce resource as competing claims for the space intensify. It does not follow, however, that this competition is a critical problem requiring comprehensive federal or state allocation."

7. National Environmental Policy Act of 1969,42 U.S.C. Sec 4321 et seq. 8. Preparation of Environmental Impact Statements, Guidelines , Council on

Environmental Quality, 38 Fed. Reg. No. 147, Part II, Aug. 1, 1973, and Preparation of Environmental Impact Statememts, Final Regulations, Enviro:1mental Protection Agency, 40 Fed. Reg. No. 72, Part III, April l 4 (1975).

9. op. cit., supra, n. 7. 10. Preparation of Environmental Impact Statements, Guidelines, Council in

Environmental Quality, 38 Fed. Reg. No. 147. Part II. Aug. 1, 1973, and Preparation of Environmental Impact Statements, 40 Fed. Reg. No. 72. Part III, April 14 (1975).

11. McClain, W. "Status of AEC Project to Establish a Salt Mine Radioactive Waste Repository", in Fourth Salt S y mposium, p. 337.

12. State Underground Injection Control Program, Proposed Regulations, Environmental Protection Agency, 41 Fed. Reg. No. 170, Part II, Aug. 31 (1976).

13. National Water Commission, Water Policies for the Future (1973). 14. Op. cit., supra n. 12 and see 1509.081, 611 1 .01 et seq. Ohio Revised Code.

15. "Cujus est solum ·ejus est usque ad coelum et ad infernos" ("His is his alone from the heights of the sky to the depths of the earth"), Lord Coke, Batens' Case, 9 Coke 53.

16. Restatement of Torts, Chapt. 7, Sec. 159; "A trespass, actionable under the rule may be committed on, beneat h or above the surface of the earth", and Restatement (Second) of Torts, Chapt. 7, Sec. 159. (I) Except as stated in subsection (2), a trespass may be committed on, beneath or above the surface of the earth. (2) Flight by aircraft in the air space above the land of another is a trespass, if, but only if, (a) it enters into the immediate reaches of the air space next to the land, and (b) it interferes unreasonably with the other's use and enjoyment of his land".

17. Edwards v. Sims, 24. S.W. 2d 619(1929),Dissent : "Thevalue(ofthecave)isnotin the black vacuum . .. it is in his vision translated into reality. Those who visit it are they that give it value."

18. Thomas, W. "Ownership of Subterranean Space". Underground Space 3, No. 4, 155-163 (1978).