Marine mining on the Outer Continental Shelf

[From the U.S. Government Printing Office, www.gpo.gov]

OCS Report
Environmental Effects 87-0035
Overview

Marine Mining
on the
Outer Continental Shelf

TN
291.5
.C78
1987 U.S. Department of the Interior
Minerals Management Service

OCS Report
Environmental Effects 87-0035
Overview

Marine Mining
on the
Outer Continental Shelf

By Michael Cruickshank, USGS, Mining Engineer, Oceanographer
Joseph P. Flanagan, NOAA, Environmental Protection Specialist
Buford Holt, MMS, Biologist
John W. Padan, NOAA, Mining Engineer

U.S. Department of the Interior LIBRARY
Minerals Management Service N0AA/C1-j,,-jq 1987
1990 )N, AVE.
ClqAS,, ,@C ')9-10@-2623

Acknowledgements

Special thanks are due to NOAA's Dr. Jeanne L. Snider who
searched the literature and drafted the initial version of
section 5. Her transfer prevented her from seeing this
document through to completion; any errors rest with the
other preparers. Teresa Wilson, MMS, assisted in the de-
sign of illustrations and drafted them.

Contents

Section 1. Introduction ....................... 1

Section 2. Diverse character of the Outer Continental Shelf ......... 2

Section 3. Mining methods .......................................... 10

Section 4. Normal operating environmental disturbances....,'......... 35

Section 5. Environmental impact concerns ............................ 37

Section 6. Conclusions ............................................. 53

Section 7. Minerals Management Service policy for environmental
protection .............................................. 54

Section 8. References .............................................. 56

Appendix 1. Table of conversion factors ............................. 65

Appendix 2. Area Comparison:
United States Outer Continental Shelf and
Exclusive Economic Zone ............. ........... 66

Illustrations

Figure 1 Exclusive Economic Zone of the United States, Commonwealth
of Puerto Rico, Commonwealth of the Northern Mariana
Islands, and U.S. territories and possessions ........... 5

Figure 2 Basic approaches to mining .............................. 11

Figure 3 Drag line dredge ........................................ 14

Figure 4 Trailing suction hopper dredge and representative drag
heads ................................................... 15

Figure 5 Crust miner ............................................. 18

Figure 6 Continuous line bucket dredge ........................... 19

Figure 7 Clamshell bucket dredge ................................. 21

Figure 8 Bucket ladder dredge used to mine gold in sheltered waters 22

Figure 9 Bucket wheel dredge for use in sheltered waters ......... 23

Figure-10 Anchored suction dredge (shallow waters) ................ 25

Figure 11 Anchored suction dredge (deep sea) ....................... 26

Figure 12 Cutterhead suction dredge .......................... 6600*0 28

Figure 13 Working a hard rock deposit from a floating platfo.rm .... 29

Figure 14 Fluidizing (slurrying) .................................. 31

Figure 15 Fluidizing (leaching) ................................... 32

Figure 16 Mining with the aid of an artificial island ............. 34

iii

Tables

Table 1 Classification of marine minerals resources .............. 3

Table 2 Mining methods applicable to OCS mineral deposits ........ 12

Table 3 Normal environmental disturbances of mining operations ... 38

Table 4 Key factors affecting degree of environmental impact ..... 40

Abbreviations

oc degree Celsius (centigrade)
cm 2 centimeter
cm square centimeter
ft foot
ft2 square foot
9 gram
in inch
kg kilogram
km kilometer
02 square kilometer
lb pound
m meter
M2 square meter
mg milligram
mi statute mile
mi2 square statute mile
mm millimeter
nm nautical mile

Acronyms

ATOS Anti-Turbidity Overflow System
DOI Department of the Interior
EEZ Exclusive Economic Zone
EIS Environmental Impact Statement
HI Hawaii, State of
MMS Minerals Management Service
NAS National Academy of Science
NEPA National Environmental Policy Act
NOAA National Oceanic and Atmospheric Administration
NOS National Ocean Service
OCS Outer Continental Shelf
OTA Office of Technology Assessment
SI International System of Units (metric)
U.S. United States
USGS U.S. Geological Survey

Introduction

This document is an overview of the ways in which mining may
be carried out under regulations being established by the
Minerals Management Service (MMS) of the Department of the
Interior (DOI). The objective is to provide the reader with
a sense of what is, and what is not, known about the envi
ronmental effects of mining on the Outer Continental Shelf
(OCS). As the difference between the Exclusive Economic
Zone (EEZ) and the OCS is strictly legal, similar environ-
mental effects would apply to marine mining on any parts of
the EEZ which may not be in the OCS.

Detailed analyses of specific areal environmental impacts
of OCS mining will be presented in Environmental Impact
Statements (EIS) as specific target areas and commodities
are considered for leasing, exploration, and development.
This document generally describes potential mining activities
on the OCS and their effects. Neither activities in waters
under State jurisdication nor-minor exploration activities
are specifically discussed.

Section 2 highlights the diverse mineral deposits and envi-
ronmental settings of the OCS. Section 3 describes the
mining methods that now appear most applicable to OCS mining
and gives references to supporting literature. Section 4
discusses how these mining methods would disturb the environ-
ment during the course of normal operation. Section 5 sum-
marizes the concerns raised by a literature search into the
known environmental impacts of OCS mining disturbances.
Conclusions based on current knowledge of the environmental
impacts that may follow the establishment of OCS mining regu-
lations are presented in Section 6. Section 7 describes
MMS's policy to comply with the National Environmental Policy
Act (NEPA) and provide for State, local, and public input, as
well as resource development.

Measurements in Section 3 are reported in U.S. customary
(English) units to conform to usual practice in the U.S.
mining industry. Other measurements throughout the report
are given in SI (International System of Units) metric units
in accordance with standard practice 'In geology and biology.
An English-metric conversion table is presented in Appen-
dix 1.

2. Diverse character of the Outer Continental Shelf

2.1. Mineral Mineral deposits on the OCS can be characterized either as
deposits unconsolidateds capable of being collected directly by
dredging; or consolidated, requiring additional energy to
fragment the deposit before collection (Cruickshank, 1962;
table 1). Either type may occur at or beneath the seafloor.

Unconsolidated deposits include construction materials such
as sand, gravel, and shells; heavy mineral placers, con-
taining materials such as titanium, tin, and gold; metallif-
erous muds such as those under development in the Red Sea;
and nodules and oozes of silica and calcium carbonate.

Consolidated deposits include bedded deposits, such as coal
and iron ore; crusts, such as the cobalt-rich manganese
oxides found on Pacific Ocean seamounts; massive sulfide
deposits in the form of mounds and stacks occurring at cer-
tain spreading centers; and essentially tabular veins or
mineralized channels in consolidated host rocks.

Fluids may be considered special cases. They are represented
by dissolved salts traditionally recovered by evaporation
ponds; slurries of fine-grained, loosely consolidated materi-
als; and hydrothermal solutions of materials.

Most of the known U.S. deposits that could be economically
mined are comprised of unconsolidated or weakly consolidated
materials. Possible exceptions are the consolidated, cobalt-
rich, ferromanganese crusts and polymetallic sulfides being
considered for leasing now. Consolidated deposits of phos-
phorite may also be of interest in the future, but potential
markets exist now for unconsolidated deposits of sand and
gravel and heavy mineral placers (Bureau of Mines, 1987a and
1987b).

It is assumed that most economically recoverable deposits are
found on the continental shelves at depths of 200 m or lesA.
Individual mine are expected to cover between 3 and 40 W
(about 8-100 M) or less than 0.01 percent of the roughly
400,OUO mi2 (about 1,000,000 km2) of c 'ontinental shelf.
Mines would last 20 years or more. The most extensive oper-
ations in U.S. waters probably would involve manganese crust
mining. Such a mine could require 500-600 km2 for a 20-year
operation. However, one such mine could provide half the
nation's demand for cobalt and substantial amounts of other
strategic metals.

Table 1 Classification Of marine mineral resources

Fluid Unconsolidated Consolidated

Seabed Subseabed Seabed Subseabed Seabed Subseabed

Seawater Hydrothermal Industrial Heayy Mineral Crusts Di ssemi nated,
fluids Materials Placers
Magnesium Phosphorite R-ratified. Vein, or
Sodium Sand & gravel Gold Cobalt Massive Deposits
Uranium Shells Platinum Manganese Coal
Bromine Aragonite Cassiterite Phosphates
& Gem stones Carbonates
Salts of Heavy Mineral Potash
26 other Placers Bedded Deposits Mounds and Stacks Ironstone
elements Magnetite osphorites Metallic sulfides Limestone
Ilmenite, Rutile Metallic sulfides
Chromite,Monazite Metallic salts

Nodules
Manganese
Phosphorite

Muds and oozes
Metal li ferous
Carbonaceous
Siliceous
Calcareous
Barite

2.2. Environ- The submerged lands of the U.S. EEZ@ established Iby President
mental settings Reagan's proclamation of March 10, 1983 (Procl. 5030, 3 CFR
22), are large and varied. They cover about 4.2 million mi2
(about 11 million km2), an area 30 percent larger than the
land area of the United States (figure 1). About 15 percent
of this area lies on the geologic continental shelf and is
shWower than 200 m. Another 10 to 15 percent consists of
the continental slope and rise, lying between 200 and 4000 m.
The remaining 70 to 75 percent are abyssal plains at depths
of 3,to 5 km.

The EEZ generally consists of those areas within 200 nm of
the coast of the United States and its territories and pos-
sessions, subject to adjustment with conflicting claims of
adjacent and opposite nations. Most of the EEZ is under
Federal jurisdictions, but the tidal and submerged lands
within 3 nm of shore are under State (and in some cases,
territorial) jurisdiction. In certain areas in the Gulf of
Mexico, State jurisdiction extends to 3 marine leagues
(9 nm).. The OCS includes those'portions of the EEZ subject
to Federal jurisdiction which are adjacent to the 50 States
and, in some regions, extends seaward beyond the EEZ. It
should be noted th'at the legal continental shelf includes
submerged lands which are not customarily considered part
of the geological continental shelf. When the term "con-
tinental shelf" is referred to in this overview, the geo-
logical continental shelf is meant.

The physical environments of the OCS are varied, with strong
regional variations in water depths, physiography, wind,
wave, tidal and current regimes, and biota. Detailed
descriptions of these variations on the continental shelf are
given in the EIS's prepared for offshore oil and gas lease
sales and some of the appendices of the DOI's program feasi-
bility document for OCS hard minerals leasing (DOI, 1979).
The EIS for the proposed lease sale of cobalt-rich manganese
crusts (DOI and HI, 1987) and the EIS for manganese nodule
mining (NOAA, 1981) describe two pertinent environments off
the continental shelf, although the latter involves an area
outside of the OCS and EEZ. Descriptions of a third will be
published in 1987 by the DOI and the State of Oregon as the
proceedings of the Gorda Ridge Symposium. Sections 2.2.1 and
2.2.2 outline variations in the bathymetry, physiography, and
biology of the OCS as background to discussions of the envi-
ronmental effects of OCS mining in Sections 4 and 5.

2.2.1 Regional Alaska
bathymetry and
physiography The continental shelves of northern and western Alaska are
notoriously hostile working environments. Ice cover is heavy
and mobile much of the year, resulting in deep gouging of the
shallower,portions of the seafloor, and the seafloor in
deeper waters is prone to slumping. The shelf is at least
100 km wide along the northern coast and is bounded to the
north by steep scarps that are scarred by slumps and leveed,
,channels. Seaward of the scarps lie abyssal plains at depths
of 2.5 to 3 km (Nikituk and Farris, 1986; Collins and.Lynch,
1985).

U.S. DEPARTMENT OF THE INTERIOR
MINERALS MANAGEMENT SERVICE ... .... I. U.S MAP NO. SM-

EXPLANATION

FANIMMA CONTINENTAL SHELF

OCS PLANNING AREAS
(1987-91 PROPOSED PROGRA1,0

PLANNING AREAS SEAWARD OF
FAN"N CONTINIENTAL SHELF

PANIMUM CONTINENTAL SHELF
REGIONS SEAWARD OF
PLANNING AREAS

+ + + +

+ A-
+ + + +
MERTO RICO-
VIRGIN ISLANDS
+ WAKE ISLAND +
MARIANA, ISI-ANDS + +

joHNSTON
GUAM ISLAND 16
+ + + + + + + + + + +
PA MIRA ATOLL-
KINGMAN REEF

HOWLA A D
No "
BAKER SLAM
&IRVIS ISLA

+ + + + + + + + +
do AMERICM SAMOA
1A

+ + + +

Figure I Exclusive Economic Zone of the United States Commonwealth of Puerto Rico, Commonwealth of the
Northern Mariana Islands, and U.S. territories and possessions.

West of the Alaskan mainland, the shelf is a shallow, gently
sloping extension of the coastal p1ain. Generally shallower
than 100 m, it ranges in width from over 830 km in the north
to 500 km in the south. With few exceptions the shelf floor
is nearly featureless and flat. The average slope is roughly
0.25 m/km (0.025 percent). To the south, this vast plain is
bounded by steeperi but still gentle, slopes that are scarred
by large canyons (Nikituk and Farris, 1986).

Southwest of the mainland, the Aleutian Islands, the adjacent
Aleutian trench, and a major chain of seamounts are the most
striking physiographic features. The seafloor in this area
is otherwise a sediment covered plain 3-5 km deep, with scat-
tered seamounts. The area is seismically and volcanically
active, with activity concentrated along the Aleutian Islands
(Nikituk and Farris, 1986).

Pacific Coast

Along the Alaskan panhandle and south along the Washington,
Oregon, and northern California coasts, the'shelves are very
narrow, generally about 25 km wide. The outer edges of these
shelves are generally at a water depth of 100-160 m. The
slopes bordering these shelves are characterized by exten-
sive slumping and massive canyons. The abyssal plains sea-
ward of these slopes are 2-3 km deep nort-h of the Mendocino
Ridge, and 3-4 km deep south of it. The ridge itself is a
500-meter high structure that lies along the seaward exten-
sion of the San@Andreas fault system. It is bordered to the
south by a major enscarpment that extends from Cape Mendocino,
California to the outer edge of the OCS (Nikituk and Farris,
1986; Shepherd, 1963).

Just north of the Mendocino ridge, and extending northward
along the southern third of the Oregoncoast, is the Gorda
Ridge, the only fragment of the global system of oceanic
spreading centers in the OCS. This ridge has an axial rift
valley whose floor lies 0.8-1.4 km below the adjacent ridge
crests and 3 km below the sea's surface. Many small sea-
mounts lie along the axial valley although these are often
buried by sediments of continental origin in the southern
part of the valley (Clague et al., 1984; DOI, 1983a).

Along the southern California coast, rugged, mountainous ter-
rain replaces the typical flat shelf. The crests of several
of these'mountains form the Channel Islands and shallow off-
shore banks. The basins between these islands and banks are
generally I to 2 km deep and are isolated from each other at
water depths greater than 500 m (NOS, 1975). The area, like
the rest of the Pacific coast, is seismically active.

Atlantic and Gulf Coast

The Atlantic and Gulf coasts show the zonation typical of the
Pacific coast; but the zones are broader. The continental
shelf in the North Atlantic is 40-330 km wide off the New
England coast with water depths of 200 m at the edge of the

shelf. The slope of the seafloor then steepens more than
tedfold in a zone, known as the continental slope, before
ending at depths of 2-3 km in the much gentler slopes known
as the continental rise. The continental rise then extends
seaward until it terminates in abyssal plains about 5 km
below the surface.

.The continental shelf of the Mid-Atlantic variesin width
from 25 km off Cape Hatteras to 200 km off New York. The
shelf slopes at I to 2 m/km (0.1 to 0.2 percent), reaching a
depth of about 200 m at its seaward,edge. The Mid-Atlantic
continental slope is steep and narrow, from 20 to 40 km wide,
and is cut by many large canyons (Nikituk and Farris, 1986).

The South Atlantic continental margin continues the simple
combination of shelf, slope, and rise, except for a'broad
plateau 6.6 to 1.2 km deep known as the Blake Plateau. This
plateau is about 280 km wide offshore northern Florida and
tapers gradually both northward and southward. The plateau
merges with the continental slope offshore North Carolina to
the north, and the Bahamas to the south * The shelf in the
South Atlantic is generally 30 to 140 km wide, exclusive of
the Blake Plateau (Charles River Associates, 1979; Nikituk
and Farris, 1985). The average slope of the continental
shelf is less than 3 m/km (0.3 percent) in the South Atlan-
tic. Water depths at the edge of the shelf generally average
50-90 m (Nikituk and Farris, 1986).

The geologic shelves of the Central and Western Gulf are
generally 100-200 km wide, The continental slope then ex-
tends another 250 km into the Gulf and lies between 100 and
3000 m deep. Geohazards include mass slumping, sediment
creep,, and landslides on the slope, particularly near the
mouths of the Mississippi River (Nikituk and Farris, 1986).

Carribean and Pacific Basins

The Caribbean and the Central and Western Pacific portions
of the OCS and EEZ consist primarily of abyssal plains with
scattered, steep-sided, submarine volcanoes or chains of
volcanic isl.ands such as the Hawaiian Archipelago. The
.principal exceptions are the island arcs of the Antilles in
the Caribbean and the Mariannas in the Western Pacific.
These areas are adjacent to deep, narrow, oceanic trenches.
.The oceanic islands, whether scattered or in chains, have
narrow, shallow shelvis comprised of liv *ing and dead corals
and steep, submerged slopes. For example, water depths
north of Puerto Rico are less than 20 m within 1 kilometer of
shore shore, but 200 m deep within the next kilometer. The
platform is about 5 km wide to the south, and 10-20 km wide
to the northeast and southwest. Ocean depths reach 7.5 km
north of the island, and over 5 km to the south (NOS, 1984).
The nearshore bathymetry around other oceanic islands in the
OCS and EEZ is similar (Shepherd, 1963).

2.2.2 Biology For the purposes of this overview, the most important bio-
logical variations in the OCS are associated with feeding
habits, life cycles, mobility, and adaptation to physical

disturbances. Biological impacts are summarized below;
further details are provided in Section 5.

Typically, species that inhabit areas subject to frequent
physical disturbance tolerate heavy sedimentation. Gener-
ally, these environments have few species, but many individu-
als of each of those species. In contrast, species living in
environments with low sedimentation rates often are quite
sensitive to turbidity and moderate to heavy sedimentation.
These environments frequently have many species, but most are
represented by only a few individuals at any'given site.
.However, these species may be widely dispersed geographically.

The fishes of coastal and upper oceanic waters should be able
to readily avoid mining disturbances as adults, but'may be
unable to do so during the egg and larval stages, when they
are attached to the bottom or passively floating. If so,
their highest exposure to injury from mi'ning would occur at
ages when the natural death rates are highest. Injuries to
these species caused by mining would be hard to detect, ex-
cept in laboratory tests. This would be especially true of
effects which are not themselves lethal, even though they may
make the animal more susceptible to other hazards, such as
predators. These so-called sublethal effects need continued
study, since end points other than death and disappearance
are not well understood (OTA, 1987). Species that are ter-
ritorial as adults, or that occupy rare habitats are effec-
tively immobile even if they are physiologically capable of
avoiding disturbances. Such species would besubject to ad-,
verse impacts as both juveniles and adults.

These generalizations concerning the life histories and be-
haviors of fish are also true of invertebrates, but there may
be*major differences in scale and sensitivity to mining. Many
invertebrates are smaller, more numerous, shorter lived, and
reproduce more rapidly than fish living in the same habitat.
These attributes facilitate rapid population growth and rapid
recovery of the impacted populations. However, many inverte-
brates are attached to the seafloor for parts of. their life
cycle; are slow-moving, burrowing, or floating species; or
are highly territorial; and hence unlikely to evade mining
activities. The result of these opposing sets.of attributes
probably will be a higher death rate, but more rapid repro-
ductive replacement in invertebrate than in vertebrate popu-
lations on a mine site. Both groups, however, will likely
recolonize abandoned mines relatively quickly by migration
from undisturbed areas.

Lists of the more important species in the various environ-
ments of the OCS, and pertinent details of their life cycles
and traits, can be found in standard biology texts and in the
EIS's prepared by the MMS for oil and gas lease sales in the
OCS. Similar accounts of species in the Central Pacific are
given in the EIS for the MMS's proposed lease sale for
cobalt-rich manganese crusts (DOI and HI, 1987). Accounts of
one portion of the deep sea that are typical of what is known
are given by the EIS prepared for manganese nodule mining
of the deep seabed (NOAA, 1981).

Previously unknown species are regularly encountered in
bottom samples from the deep sea, and up to 80 percent of
the animals obtained from the deep sea have never been seen
before (OTA, 1987). However, while we understand shallow
water communities and their responses to disturbances better
than deep water communities because we have studied the
shallow water organisms longer, the benthic fauna becomes
increasingly more uniform horizontally as water depth in-
creases. That is, the composition of the benthic community
changes more rapidly with small changes in depth than with
large horizontal changes as water depth increases. As a re-
sult, shallow or estuarine communities can be quite different
from shelf communities, and shelf com'munities from slope com-
munities (Sanders and Hessler, 1969; Boesch, 1972). However,
what we learn at one area in the deep sea will give us more
predictive power than would one area in shallow water
(Sanders and Hessler, 1969; OTA, 1987).

In general, the biomass of bottom dwelling organisms de-
creases,with depth, but there are local exceptions, such as
the great masses of giant worms and clams found near hydro-
thermal vents and some deep water hydrocarbon seeps (Paull
et. al., 1984; Grassle, 1985; Southward, 1985). These com-
munities are thought to develop far more rapidly than-the
typical deep sea assemblages which receive much lower quanti-
ties of food (Grassle, 1985).

The two deep sea areas proposed thus far for leasing in the
EEZ fit the general pattern of low biomass. Extensive photo
and video coverage of the cobalt-rich manganese crusts show
an extremely sparse fauna. Preliminary analysis of photo-
graphs seem to indicate a somewhat more abundant than normal
biota on or near the sulfide-mineral deposits on the Gorda
Ridge but the abundance is far short of that typical of vent
communities and the species present seem to be those found
throughout the region.

3. Mining Methods

There are four basic methods of mining solid minerals:
scraping the surface, excavating a pit or trench, removal
through a borehole in the form of a slurry or fluid, and
tunneling into the deposit (figure 2). All deposits on
land are mined by one or more adaptations of these methods
and OCS mining is amenable to the same basic approaches ,
(table 2). Each mining method has variations that may be
tailored to a specific situation, and most of the deposit
types can be mined by more than one method. Similarly any
one method can be applied to more than one deposit type
(Cruickshank, 1978).

OCS mineral deposits, whether consolidated or unconsolidated,
may occur at or beneath the seabed. Deposits at or near the
surface of the seabed can be gathered by mechanical devices
that scrape the seabed and gather the ore for lifting to the
surface or for other treatment. In its simplest form, the
action is like raking or shoveling or, in some cases, vacuum
cleaning. Where a thick layer of hard material is present,
the scraping action may be preceded by ripping or cutting.
Mineral deposits lying wholly or partially beneath the sea-
floor may be removed by excavation. The applicable mining
methods range from those designed to recover free-flowing
materials to those for excavating solid rock. Certain types
of deposits of solid rock may be mined by borehole methods,
whereby fluid is added and ore is transformed into a fluid or
slurry and removed by pumping. In some cases, a mineral may
be selectively leached and recovered in solution. In other
'cases, the ore body may be fragmented in such a manner that
a slurry of ore is recovered from beneath the seabed. De-
posits buried too deeply to mine from the seabed may also be
mined by conventional underground mining methods using shafts
and adits (tunnels that lead into mines) for access and vent-
ilation, either from shore or from natural or artifical
islands. The seabed location of the mines only slightly adds
to the conventional problems of access, safe overhead cover,
and ventilation. The effect on the environment is much the
same as with an onshore mine.

This section further explains each of the mining systems.
listed on table 2, describes the manner in which each may
disturb the marine environment, and notes types of deposits
with which it is normally used. For further reading refer-
ences are provided to literature describing commercial opera-
tions using these mining systems (Cruikshank et al., 1968;
Cruickshank and Marsden, 1973 and Cruickshank, 1973). To
'conform to conventi-onal usage in the U.S. mining industry,.
this section uses U. S. customary (English) units rather
than the SI (metric) units used in the rest of the document.

.10

SCRAPING EXCAVATING FLUIDIZING TUNNELING

GRAVEL
ISLAND

SEA
LEVEL

GRAVEL,
NODULES
SEA
FLOOR

ORE

. . . ... .. . . . . . ..
.. . ... . . . . . . .. .
. . . . . . . . . .

Figure 2 Basic approaches to mining

Table 2 Mining methods applicable to OCS mineral deposits

Mining Methods EEZ mineral deposit types
(with selected examples)
Unconsolid ted Deposits Consolidated Deposi s
Mining Mining Con-!@t-- Heavy Metal- Nodules Oozes Bedded Crusts Massive Mounds Veins
Approaches Systems ruction Mineral lifer- and and
Aggre- Placers ous Slabs Stacks
gates Muds

Drag line dredge A A
Trailing suction
Scraping dredge P, A A P F

Crust-miner F

Continuous line bucket F F F A F F

Clam shell bucket A A F F P

Bucket ladder dredge A P

Excavating Bucket wheel dred e A A

Anchored suction dredge A A A F F F
Cutterhead suction
dredge P A
Fluidizing Drilling and blasting F F P
(Sub- Slurnzing A A P F
Seafloor) Leaching F F
Tunneling
Shore entry P A
Beneath Artificial island-
Seafloor entry A A

P= Primary method applicable A= Also applicable F= Future use possible

3.1 Scraping Although there are many variations, there are basically four
mining systems that may be used to scrape the surface of the
seafloor. Two are wholly mechanical and two involve hydrau-
lic action to lift the mined rock..

3.1.1 Dragline This system is used in offshore mining and deep seabed sam-
dredge pling, as well as in construction. Its use has been ad-
vocated for the recovery of seafloor nodules and slabs of
phosphorites (Mero, 1965). The material would be recovered
by large dredge buckets that scrape slabs and nodules from
the surface of the depos'it and feed them into barges for
transportation,to shore (figure 3). Annual production at
such an OCS mine for phosphorite could be on the order of
400,000 tons (roughly 180,000 j(d of ore). This rate of
production could involve 50 yd-1 buckets scraping an average
of 20 tons of phosphorite from the seafloor every 20 minutes
in a water depth of about 600 feet.
At an average abundance of 20 lb/ft, nearly 2 mi2 of seafloor
would be mined annually. At a mine life of 20 years, a total
of 40 mi2 would be affected if the deposits were confined to
the surface of the seabed. Thicker deposits would allow
smaller areas of disturbance.

Assuming the presence of some fine-grained sediment on the
seafloor, as well as some breaking up of the phosphorite, a
benthic turbidity plume would be created by the scraping
action. Some fine material would inadvertently be introduced
into the dredge buckets and washed out either in route to the
surface or at the surface as a result of washing of the phos-
phorite in the barge. The fine sediments would eventually
rain to the seafloor, creating a blanket of fines.

3.1.2 Trailing A suction hopper dredge uses a pump to draw a slurry of
suction dredge bottom water and seafloor sediment into a riser or pipe
leading to the mining vessel. As the sediment accumulates
in the hopper, the water weirs overboard. This-system is
used primarily for maintaining harbor channels. However,
it is also used extensively for mining sand and gravel in
water depths up to 120 ft in the North and Baltic Seas
(Padan, 1983). New vessels, such as the ARCO Avon, launch-
ed in 1986, are designed to extend mining capability to
depths of 150 ft (Drinnan and Bliss, 1986). As its name
implies, this type of dredge mines while in motion, creat-
ing numerous shallow trenches in the seafloor commonly
about 3 ft wide and 1 ft deep (figure 4).

The suction dredge uses one of several types of drag head
with a coarse-grid steel framework across the opening of
the suction head to prevent large rocks from entering the
suction pipe. Coarser particle sizes are screened out and
rejected after passing through the pump. Fine materials
are washed overboard with the slurry overflow. In some
cases, vibrating screens allow part of the sand fraction to
be dumped back into the ocean since the ratio of sand to
gravel mined may differ from the desired marketable mix.

Ops

0.6

Figure 3 Drag Line Dredge

(A.) TYPICAL TRAILING DRAG ARM
(B.) CONFIGURATION OFSEASED
AFTER DREDGING
(C.) DIFFERENT DRAG HEADS

(C.) DRAG HEADS FOR DRAG HEADS FOR SAND AND GRAVEL DRAG HEADS FOR CLAY AND
SILT AND MUD COMPACTED SAND
Silt Head Typos OChesso Shave' Type

Visor Typo California Typo

Active Drag Head Type

A
1,11 Pro-Fluidizing
Venturi Type Water Jet Type

Figure 4 @_ Trailing suction hopper dredge and representative drag heads

Environmental disturbances that may result from this system
include the excavation of trenches in the seafloor, creation
of a turbidity plume by washing overboard clay particles
taken up in the dredge pipe, and production of a blanket of
fines covering the seafloor down current from the dredge.
However, measures have been developed in Japan and Great
Britain to either avoid or mitigate these problems. The
use of sand and gravel as construction material, for example,
requires that stringent measures be taken to avoid mining
any clay layers since the entire shipload would be considered
contaminated and unmarketable. Regulatory options include
mandating bottom discharge of overflow waters to reduce the
size of surface plumes, and in some cases, bottom discharge
of rejected sand to reduce the size of trenches or other
excavations. Further details on environmental effects and
the technical and administrative means the British have
used to control them are given by Drinnan and Bliss (1986)
and Pasho (1986). Additional detail on the equipment used
and extensive photographic documentation are given by Hess
(1971).

The volume of material that may be mined includes the sum of
the marketable material, the fraction to be rejected, and the
overburden initially stripped away. For example, in moving 1
million tons of product to shore annually, an equal amount of
sand might be rejected to reduce the sand/gravel ratio from
70:30 to a more marketable 40:60 (NAS, 1975). The 2 million
tons of annual excavation would result in a gradual 1 wering
of the ocean floor by about 2 ft over an area of 1 MO (about
2.1 million yd-3). As mining proceeds, the rejected sand re-
leased above the mined out area would partially smooth the
bottom contours.

Some silt and clay will typically be mixed in the mined
material despite avoidance of distinct clay layers. Dis-
charge of these fine materials, suspended in t.he seawater
overflowing from the hopper would cause turbidity plumes at
the depth of discharge. The daily increment of new plume in
this example would consist of 60,000 tons of water and about
200 tons of material finer than 200 mesh. Because the fines
will stay suspended for days, the impact of daily activity
of surface discharges could be considered cumulative. The
blanket of fines would settle gradually to the seafloor as
it travels with the currents, building up a very thin veneer
over a large area. Discharge near the seafloor would result
in a thicker layer over a smaller area.

Various methods exist to control turbidity and others are
being developed. Existing methods usually rely on control-
ling the depth and direction of discharge, but the Marine
Mining Panel of the U.S.-Japan Cooperative Program in Natural
Resources recently tested a technique to control the for-
mation of bubbles in the discharge streams to reduce the
settling time for particulates (Marine Mining Panel, 1984).
This Japanese-developed Anti-Turbidity Overflow System (ATOS)
was tested at a typical dredge site off the coast of Japan
to determine its potential for control of both surface
turbidity and sediment dispersion. The system appears to

work well in course-grained sediment. Data from tests in
finegrained sediments are still being evaluated.

Trailing suction dredges, if modified for great depths, can
also be used to mine,deep sea manganese nodules. Operating
ch-aracteristics and environmental data for this application
are well documented (NOAA, 1981).

3.1.3 Crust miner Recent interest in manganese oxide crusts containing rela-
tively high values of cobalt, and in some cases platinum,
has led to proposals to develop the deposits. The manganese
crusts vary in thickness from mere. stains up to about 15 in
thick and cover a variety of substrate rocks ranging from
hard basalt to weak hyaloclastite. The physical properties
of the crusts are similar to a hard coal. The crusts occur
extensively on the Pacific seamounts and submarine ridges at
depths between 2,600 and 7,800 ft. The mining system pri-
marily proposed for this work is a vessel equipped with a
hydraulic lift system with an active bottom miner (Halkyard
and Felix, 1987). The miner would be a self-propelled
tractor, controlled from the surface vessel. The miner would
be capable of breaking and removing the thin crust from the
underlying rock and feeding it to the hydraulic lift system
through a hydrocyclone to separate entrapped substrate (fig-
ure 5). The roughly cleaned ore would be pumped to the sur-
face vessel for further cleaning and transport to shore.

Potential environmental effects, as discussed in the EIS for
the proposed Hawaii-Johnston Island OCS/EEZ lease sale (DOI
and HI, 1987), are expected to be much the same as the
effects of the dragline dredge.

3.1.4 Continuous This system (figure 6) has been tested for possible future
line bucket dredge use in recovering manganese nodules (Masuda et al, 1972) and
is described in NOAA's EIS for deep seabed mining (NOAA,
1981). The continuous line bucket (CLB) may also be used for
mining phosphorite nodules and slabs, and its use has also
been proposed for cobalt crust mining.

The CLBs environmental disturbances would be similar to
those of'the dragline dredge, except that the latter would
involve discrete episodes of bottom disturbance and ihe CLB
system would be continuous.

3.2 Excavating Mineral deposits that are located mostly within the seabed
may be removed by excavation. These deposits include' thick
deposits of sands; metalliferous muds; layered or dissemi-
nated deposits of unconsolidated placer minerals or overlying
bedrock; and deposits of consolidated minerals in vein, tabu-
lar, or massive form, which may extend for considerable dis-
tances into the bedrock. The mining system used will depend
largely on the ease with which the material may be excavated
and removed from its surrounding environment, on the water
depth, and on the climate in the area of operations
(Cruickshank et al., 1969; Cruickshank, 1987). Six examples
of seabed mining operations arepresented here that range

Overflow
00

Feed LIOUID-SOLID CYCLONE
(HYDROCYCLONE)

'-Vortex
-W: Action

U nderflow

Figure 5 Crust miner

. .......... ...........

BUCKET
REMOVAL::.

...... .... ...

....................

.................

CON TROL BUCKET
THRUSTERS REPLACEMENT

BUCKET

POLYPROPYLENE
ROPES

TOP VIEW

UNLOADED
BUCKETS

DIGGING
CONTROL BUCKETS BUCKET
THRUSTERS SWATH

LOADED BUCKETS

CURRENT
DUIG
B C

Figure 6 Continuous line bucket dredge
19

from the excavation of free-flowing materials to the excava-
tion of hard rock.

3.2.1 Clamshell Clamshell buckets have been-used to mine sand and gravel in
bucket Japan and tin in Thailand, and to sample phosphorite off New
Zealand. The buckets are mechanically actuated to bite into
the seabed and remove material (figure 7). The need for
multiple cables to actuate the grabs can cause complications,
particularly in heavy seas where wave compensating devices may
also be needed. Moreover, the clamshell is inefficient in
clearing bedrock of fine materials. It is best suited for
excavation of large-size granular material where accuracy of
positioning is not important. The size of 3buckets may range
from a few cubic feet to as much as 10 yd .

The action of the grab on the bottom stirs up any fine
materials present and these also tend to wash out during the
lift to the surface. Where washout is of major significance,
it may be prevented or reduced by placing a canvas or plastic
hood over the bucket.

3.2.2 Bucket The bucket ladder dredge is most efficient for excavation of
ladder dredge deposits containing boulders, clay,.and/or tree stumps and
weathered bedrock (figure 8). Dredges of this type have been
used successfully all over the world for mining gold, tin,
and platinum placers, and diamonds, although their use off-
shore has been limited to gold and tin. They are frequently
used for clearing harbors because of'their capability for dig-
ging into broken rock and coral. The bucket ladder delivers
a virtually water-free product to the mineral dressing plant
on board the dredge. Discharge of water from the shipboard
operations is limited to that needed to concentrate the valu-
able constituents by techniques based on the use of flowing
water to remove the less dense materials. In the case of
gold, the bulk of concentrate recovered is only a few parts
per million so that virtually all the material removed from
the deposit is returned to the seabed.

Considerable turbulence accompan .es these operations, which
may involve up to 6.4 million ydi of material per year.
Bucket ladder dredges are limited to depths of about 150 ft
and rarely operate at depths over 65 ft. Few of these
dredges have been built for offshore mining in the last 30
years, and it is likely that they will be superseded by the
bucket wheel suction dredge.

3.2.3 Bucket Bucket wheel dredges use a small diameter bucket wheel
wheel suction mounted on the suction ladder to excavate material. This
dredge combines the best aspects of the bucket ladder and suction
dredges (figure 9). Very high torque or digging power can
be applied to the wheel, which can deliver the excavated
material directly into the mouth of the suction pipe for
transport to the sea surface. Digging capability is equal
to the bucket ladder with respect to ease of digging and
bucket capacity, while the depth capability is greatly
increased (Anonymous, 1984).

rl rl rl rl

fin tr mr] rin GRATE

IOD m
_o/
............

...........
I. . . ....... ...... ......

XIX@11--,-11-111-,@M-'@`, IN, -

........ .. - -..

Figure 7 Clamshell bucket dredge

BUCKET

SPUD

....................

...................
.............

...........
. ..........................
.......... .....

Figure 8 Bucket ladder dredge used to mine gold in sheltered waters

- - - - - - - - - - -

on oil m

_PI

- - - - - - - - - - - -

K. K

.................

............

Ax@.' xx@

.:.:.: ..........
C

Figure 9 Bucket wheel dredge for use in sheltered waters

The combination of simultaneous digging and suction at the
seafloor reduces bottom turbulence, and provides the option
to either treat the ore on the vessel or pipe it to shore.
Other disturbances would be similar to those from other
suction dredges.

3.2.4 Anchored Anchored suction dredges (figure 10) are widely used in
suction dredge Japan for mining sand and gravel at depths less than 100 ft.
These dredges have been used in Britain as well, although the
vessels built since 1980 are virtually all trailing suction
dredges (Drinnan and Bliss, 1986).

In contrast to the trenches left-bytrailing suction dredges,
anchored suction dredges leave pits in the ocean floor.
These tend to fill much more slowly than the trenches, and
are a greater source of problems for bottom trawlers. How-
ever, since fish often aggregate at scarps and other irreg-
ularities on otherwise flat bottoms, isolated pits may be
considered assets by recreational fishermen. The rate at
which the pits fill is a function of the size of the hole,
the type of material remaining, and the currents. Holes in
gravel, for example, are estimated to take 25 years to fill,
while trenches in sand may fill in a matter of hours or
months (Drinnan,and Bliss, 1986).

An anchored suction dredge has also been tested for mining
metalliferous muds at a depth of 6500 feet in the Red Sea
(figure 11). This deposit consists of about 700 million
tons of zinc, copper, and silver-rich muds in a small, en-
closed basin. The mud has the consistency of shoe polish
and is about 35 ft thick at the mine site. Mining involved
the conversion of a deep drilling oil exploration vessel
(the SEDCO 445) to carry a specially designed mud pump and
delivery pipe that was lowered to the seabed in a manner
similar to the lowering of a drill pipe. The pump was
vibrated.into the mud, with a water jet to fluidize the
material, and the ore pNmped to the ship for treatment.
Approximately 20,000 yd of muds were retrieved from 4 sites
over a period of about 6 weeks. The muds were dewatered
and subjected to froth flotation on board the vessel. The
effluent from both operations was discharged through a pipe
at a water depth of 1300 feet. All operations were fully
monitored to observe effects on the water column and the
biota.

In their report of the experiments, Mustafa and Amman (1981)
observed build-up of a highly diluted diffusion cloud at
about 3000 ft. They concluded dilution would be so extensive
that a concentrated pile of tailings on the deposit would not
occur, especially if a disposal depth of 1800-2400 feet were
chosen. Commercial mining operations in the Red Sea using
the anchored suction dredge may involve the removal of as
much as 3.5 million tons of material per year of which over
90 percent would be returned to the sea. Environmental
effects are further discussed in Thiel et al. (1986).

r] r] ri

r1r] rlrj

HOPPER
COMPARTMEN
T/

OVERFLOW
SYSTEM

..................
.. . . ... .....
vi-i ......
...........
......... ..........

............. i:i
............ .....
. . .............. . . . . . . . .........

....... . ...

..... . ..... ....
Kx
............ ...... .............. ..

i@ij

Fi gure 10 Anchored suction dredge (shallow waters)
Na

SEAWATER

PUMP

2000m

CONVEYER PIPE

METALLIFEROUS
BRINE

VIBRATOR

SHAFT

2200m
-------- --------------------------

DRIVING
POINT
SUCTION .... ....... ............
.....................
SIEVE ERO
.........................
M
m
UD

.. ............. .
--- ------------ -
i: j: i::ii i: @: xi: @4- i@i @ @ Wi @i% .....

........ .

BASALT BED

Figure 11 Anchored suction dredge (deep sea)

3.2.5 Cutterhead Typically cutterhead suction dredges are used to excavate
suction dredge fairly compacted, granular materials in water less than 100
ft deep. The rotating cutterhead is usually an open basket
with hardened teeth or cutting edges somewhat like an over-
sized dentist's drill (figure 12). The end of the suction
pipe is normally located within the basket. In standard
practice, the dredge is swung back and forth in an arc
pivoted from a large post or spud attached to the stern. The
dredge cutterhead cuts downward a short distance with each
swing. Because the cutter rotates in one direction only, the
bite is much stronger on one swing than the other. In mining
for heavy minerals, the action of the cutter tends to disin-
tegrate the material, allowing heavy minerals to separate,
fall below the cut, and be left on the seafloor. Cutter
suction dredges have never been used successfully for mining
gold, although they have been widely used for mining cassit-
erite (tin placers) in west Thailand, where the deposits are
rich enough to economically sustain the inefficient cleanup.

Suction dredges circulate large quantities of slurry that
must be decanted on board the dredge or pumped ashore by
pipeline. In either case, there is a significant discharge
of water containing fine particulate materials. Treat-
ment of the decanted solids may be unnecessary for construc-
tion sands and gravel, but may be required for heavy min-
erals. The valuable constituent or concentrate from these
ores will rarely amount to more than a few percent of the
materials mined. Therefore, as much as 95 percent of the
material dredged from such placers must be disposed of at
either the mine or the shoreside treatment site.

The cutterhead suction dredge may also be equipped with a
multiblade ripper to cut into moderately consolidated rock.
Present use is limited to the excavation of soft rock, such
as coal and shale. However, advances in rapid tunneling
technology suggest that rock cutterheads could be designed
for medium strength rocks, such as sandstone and limestone
(Hignett and Banks, 1984).

3.2.6 Drilling Deposits that are too hard to excavate by dredging must be
and blasting broken by other means. The normal system for excavating
hard deposits is to drill.into the deposit and blast with
explosives. Fracturing using highly pressurized fluids is
also possible, but would represent very special and rare
cases, and are not considered here. Blasting of the material
is only an intermediate step, and would be followed by the
gathering and lifting of the ore by one of the methods
previously described. Blasting operations are designed to
expend as much force as possible on fragmenting the ore so
the water column effects are much lower than those from
equivalent, unconfined explosions.

Drilling and blasting for offshore mining is rare, but may be
exemplified by the Castle Island Mine operations in the Gas-
tineaux Channel in southeast Alaska (figure 13). That de-
posit was a massive vein structure of barite which outcropped
on the island. Mining involved deepening the.mine pit to as

-------------

AA---^.--A@@

SPUD

CUTT
DREDGED BOTTOM

Figure 12 - Cutterhead suction dredge

DRILLING BARGE CLAMSHELL DRED

...........

............
.............. :************
. ........ . ....

... ... .
..... ..................
BARITE VEIN
.... -----

..... . ....
...........
..............
. .. ..... ...... . .......
BROKEN ORE
..... .....
.............
.......... ............

--- ---------------
. ..............

Figure 1,3 Working a hard rock deposit from a floating platform

much as 100 ft under water using conventional drilling and
blasting, followed by excavation of the broken ore with a
barge-mounted clamshell dredge. Blasting took place every
few weeks at the most. Localized fish kills were reported.
Traces of fine barite were noted in the bottom sediments as
much as 0.6 mi down current from the operations, but no indi-
cation of any effect on the biota was apparent (Thompson and
Smith, 1970).

With respect to the possibility of mining deep seabed de-
posits that require fragmentation, many more aspects need to
be examined. Technically acceptable means of drilling and
fragmenting hard rock in deep water have not yet been de-
veloped. However, methods of gathering and lifting the frag-
mented material may be assumed to be similar to the methods
developed for deep seabed nodule mining.

3.3 Fluidizing Under proper conditions, certain types of unconsolidated or
(slurries) marginally consolidated mineral deposits may be mined as a
fluid slurry through a drill hole penetrating the seafloor.
Subseabed sand was mined in this way in shallow waters off-
shore Japan in 1974 (Padan, 1983), and recent onshore experi-
ments in Florida proved the capability of this approach in
recovering phosphate from beneath thick overburden (Savanick,
1985). In this instance, a borehole was drilled from the land
surface to the base of the ore body, then a water-jet cutting
system was inserted through the borehole and used to fragment
the loosely consolidated phosphate (figure 14). At the same
time, a downhole slurry pumping system recovered the phos-
phate through the borehole, thereby creating a waterfilled
cavity about 18 ft in radius. After mining was completed, the
cavities were backfilled with sand to prevent ground subsi-
dence. A U.S. Bureau of Mines study found this system to be
cheaper than conventional land mining systems if the over-
burden is at least 150 ft. thick (Hrabik and Godesky, 1985).
In the recovery of sulphur, super-heated water is pumped into
,the deposit to melt the sulphur so that it may be pumped out
of the ground.

Environmental effects are primarily associated with the in-
stallation and movement of mobile drilling platforms, dis-
posal of drill cuttings and any waste rock that can not be
returned to subsurface, and release of any slurry or proces-
sing waters that are not recycled. (Recycling of slurry
waters is anticipated to occur to a substantial degree).

3.4 Fluidizing Hard rock deposits that are amenable to hydrometallurgical
(solutions) treatment of their ores are potentially extractable by
fluidizing methods (figure 15). The valuable constituent
is dissolved in place and the pregnant solution is removed
through a borehole. There are major problems in dealing
with toxic or corrosive solvents used to enlarge fractures
to provide a flow path for the solvent through.the,deposit
and to selectively extract the desired metals in complex
ores,

JACK-UP
RIG

ll@ IF.A 0 pr, hh"q PW P@ b',@'
Sea Level

MINING TOOL

ea Floor

B 0 R E H 0 L E
CAVITY

Figure 14 Fluidizing (slurrying)
S

b4*

h rx

Sea Level

WELLHEAD

PIPELINE

Sea Flo or

EDIME.

000,
NN
ROCK

PREGNANT
SOLUTION SOLVENT

AREA SHATTERED
ORE BODY BY
EXPLOSIVE CHARGE

32 Figure 15 Fluidizing (leaching)

These problems are being overcome on land, however, and the
methods developed there should be applicable in more sophis-
ticated.form to seabed deposits. Environmental effects
during normal operations should resemble those of slurry
mining.

Effects of accidental spills of solvents would depend on
the nature of the solvents and the sites impacted, but
should be localized so long as the solvent is water soluble,
due to the rapid dilution prevailing in the oceans and the
buffering capacity of seawater.

3.5 Tunneling Underground min.ing by tunneling is commonly practiced in sub-
beneath sea- surface hard rock. In certain cases, subseabed deposits of
floor bedded coal, potash, and ironstone, as well as veins of lead,
copper, and tin have been mined by conventional underground
methods. Entry to these mines is either from the shore or
from natural or artificial islands in shallow waters (figure
16). The location of.the mines in the seabed only slightly
adds to conventional problems of access, safe overhead cover,
and ventilation. The effect on the environment is similar to
that for any shoreside mine. The possibilityof developing
underground access through seabed airlocks has been con-
sidered for special cases but is not considered further here.

ARTIFICIAL SHAFT
CAUSEWAY GRAVEL ISLAND

-Z@ A
A A.,-,.#.-A@

0.-
SED

....... . . ... .
Xii;i i.!:@

..........................
xxiii ... ....
........ ..... .........
.... ........ . . . . . .
........ . . . .

............ . . .
............ ......... . . ....
Kiii:@iiii .................... . .. . . . . . .

...................

. . ..................
xxxxj
............ ............. i$

...... . . . . . . ....... ... ..... .
-------------- -
FAULT
. .......................... :::::::i
.. .......... ........
...................

XXXI

%. ........ ..................
X% XX

Figure 16 Mining with the aid of an artificial island

4. Normal operating environmental disturbances

Although there are many types of OCS mineral deposits,
mining methods, and environments in which mining may occur,
mining operations will affect the OCS environment in only a
few ways. The principal effects are those shown in table 3.
These forms of disturbance are not new. They individually
or in combination result from trawling operations, harbor
dredging, military manuevers, construction at sea, and in
some cases, natural causes. However, mining will create new
sources and new combinations of these disturbances, and
the locations, durations, and intensities of these effects
may be new.

On the seabed, one can routinely expect disturbance from
ore collection. The seafloor in the path of the collection
machinery will be raked, fragmented, suctioned up, or com-
pacted as the ore is gathered. Should fragmentation by
explosives be required, additional disturbances would be
introduced into the marine environment by shock waves.
Noise can be assumed to be a by-product of mining operations.
The attenuation of the noise will depend on its frequency
spectrum as well as the properties of the water masses
through which it moves. In some forms of mining, the area
near the mining machinery will be illuminated.

Movement of overburden or excavation of ore may create
trenches or pits in, or mounds on, the seafloor. These
mounds and depressions have implications for potential use
conflicts and other environmental impact concerns that may
persist after mining ceases.

Subsurface mines and slurry mining cavities have the poten-
tial of causing seafloor subsidence or collapse, but these
phenomena should be avoidable by proper mine design. In the
case of borehole mining, involving the removal of ore in a
slurry, the the resulting cavity can be backfilled with waste
rock as in subsurface mines before the site is abandoned.

Seabed mining will create a turbidity plume at the seafloor
to the extent that fine material is present on the seafloor,
in the deposit, or is created by fragmenting or grinding
rock as part of mining. The largest seafloor turbidity plumes
plumes may be created by mining systems designed to reject
fine material during pickup of the ore.

Surface turbidity plumes will be created by those systems
designed to pump orein a slurry to a surface vessel and
then allow the excess%water to overflow to the sea. The
size of the plume will vary in proportion to the amount of
fine material unavoidably recovered with ore. The fines
will tend to remain in suspension in the mining vessel

35,

and be discharged with the slurry water. Water column
environmental concerns generally focus on either these
suspended particulates or dissolved substances. Turbidity
plumes move away horizontally,from their sources with the
current and are rapidly diluted, but the existence of plumes
often can be detected far from the mine site.

The fine particulate material suspended in plumes eventually
rains to the seafloor, resulting in a thin layer of fine
material over a large area. The area affected can be minimized
by subsurface discharge or other techniques that force the
particulate material to settle closer to its source, resulting
in a heavier accumulation over that smaller area.

5. Environmental--impact concerns

The environmental impacts of mining in the OCS encompass both
the effects of mining itself, as depicted in table 3, and the
effects of transport, beneficiation and refining of the ore
mined. These'latter, nearshore and onshore sources of impact
will often be the more significant sources of impact, but
they are beyond the scope of this document with its focus on
impacts in the OCS. However, onshore sources of impact will
be considered in the lease sale EIS's the Department of
Interior will prepare as well as any environmental documenta-
tion required by the affected States and localities.

The effects on organisms of fragmentation/collection, excava-
tion., and subsidence can be characteri.zed as near-field, that
is, they are essentially restricted to the mine site,
although exceptions are possible. For example, species
extinctions and even regional impacts for example, seem
unlikely, but significant impacts on regional populations of
some species could result if breeding grounds were mined.
The potential for events of these magnitudes, however, is
carefully considered during-the preparation of EIS's or other
environmental' reviews for leasing and mining proposals, and
should be avoidable.

Effects of plumes and sedimentation--unlike the effects of
fragmentation/collection, excavation, and subsidence--can
be characterized as far-field since they may be felt well
beyond the mine site. The probability and severity of
resultant biological consequences depends on the character-
istics of the specific mining operation, the geologic
setting, and the geographical location of the mining activ-
ity. It is possible, however, in spite of such uncertainty,
to use the data base created by several past projects to
identify those far-field effects that are more likely to be
of concern. These include NOAA's Deep Ocean Mining Environ-
mental Study (DOMES), NOAA's New England Offshore Environ-
mental Study (NOMES), the Army Corps of Engineers' 5-year
Dredge Material Research Program, studies of offshore sand
and gravel mining operations in the United Kingdom, and basic
research studies of factors affecting impact,and recovery
from specific disturbances. These studies, which encompass a
variety of offshore environments suggest that effects on
organisms living in the water column are likely to be minor
in most areas of the OCS.

Effects at the seafloor--particularly those resulting from
the resedimentation of the benthic-turbidity plume, the
actual destruction of the biota, and the change in seafloor
topography--will generally be more important than effects of
changes in the water column. This conclusion is founded
upon both observations of dredging operations and laboratory

Table 3 Normal environmental disturbances

OD Mining ethods Seabed Water Column
Mining Mining Fragmentation/ Excavation SuSsidence Turbidity Resedimen- Suspended Dissolved
pproaches systems Collection Plume tation Particulates Substance

Dragline dredge X X X X X
Trailing suction
dredge X X X X X
Scraping
Crust-miner X X X X X
7-ontinuous line
bucket X X X X X

Clam shell bucket X X X X X

Bucket ladder dredge X X X X X
Excavating
Bucket wheel dredge X X X X X
Anchored suction
dredge X X X X X
Cutterhead suction
dredge X X X X X

Drilling and blasting X
Fluidizing
Slurrying X
(Sub-
Seafloor) Leaching

Tunneling Shore entry X
Beneath Artificial island
Seafloor entry X
1 X= Disturbance expected. Magnitudes of the disturbances are also dependent on the nature of the mineral'deposit
and the amounts of fine particles present on the seabed. Closed circulation systems are assumed for slurrying
and leaching. Open circuluaion would result in plumes and resedimentation.

studies of the effects of suspended materials concentra-
tions. Given the relatively rapid dilution of suspended
sediments and dissolved substances, their concentrations
should fall within acceptable ranges near the point of dis-
charge. Factors, both biological and nonbiological, that
may affect the validity of this conclusion are listed in
table 4, and each of these factors should be considered in
the determination of potential environmental effects.

The sensitivity and natural resiliency of the benthic com-
munity is important in determining the recovery of the
affected biota as a whole (ICES, 1975). Some species of
organisms will likely be more affected than others because
of feeding mode (e.g., filter feeders), life habit (e.g.,
surface dwellers), degree of mobility (e.g.,tube dwellers),
or sensitivity of life stage (e.g., larvae). Those organisms
living in an environment with episodes of high turbidity
and sedimentation can likely withstand some disturbance.
For example, oysters, which are filter feeders, are able to
jendure some increases in sedimentation (Macklin, 1961;
Dunnington, 1968; Loosanoff, 1962), and benthic deposit
feeders can burrow out from some increase in deposition
(Nichols et al., 1978; Hirsch et al., 1978; Maurer et al.,
1978). However, for both deposit and filter feeders, there
are redeposition thicknesses and rates beyond which the
animals cannot survive.

Several general, and numerous specific, factors have been
found to be critical in determining the rate at which a dis-
turbed area is recolonized by species that were previous
residents. A mobile adult stage allows faster recolonization
of large disturbed areas, especially if the larval stage is
nonmobile (Levin, 1984; Dauer and Simon, 1976). The season,
duration, and areal extent of the disturbance can be critical,
if the disturbance occurs during a period when stability of
the seafloor is important to the survival of certain life
stages of a species. For example, some fish lay eggs on the
seafloor and would be very sensitive to mining before the
eggs hatch. Hence, changes in the shape of the seafloor
could affect the survival of members of even those species
that spend most of their life in the water column. These
examples illustrate the multiplicity of factors that may
influence the degree of impact from OCS mining. Early identi-
fication of those factors are important in determining the
degree of impact and recovery rates and allows mining pro-
posals to be developed that consider potential impacts and
possible mitigating measures. However, until the areas of
mining are known, it is of limited value to try to predict
further the severity of impact from a particular mining
activity.

5.1 Physical Physical impacts of concern in the OCS will gene rally be
impact concerns those that impact marine organisms, fisheries,, other com-
mercial uses, or military operations. Nearer shore, in
State waters, potential impacts on coastal erosion will
require careful appraisal. The major concerns regarding
purely physical impacts will be space use conflicts and
poor housekeeping. Fouling of nets on discarded mining

Table 4 Key Factors Affecting Degree of Environmental Impact

Plume Effects (swimming or floating species)

Nonbiological

1 - areal extent
2 - season
3 - duration
4 - concentration
5 - currents
6 - water depth

Biological

1 - stage of development when impacted
2 - physiological sensitivity of species
3 - dispersal ability of species
4 - feeding mode
5 - dependency on light
6 - geographic range

Resedimentation Effects (benthic species)

Nonbiological

I - degree of alteration of substrate type
2 - depth of redeposition
3 - duration
4 - season
5 - areal extent
6 - currents
7 - water depth

Biological (primary effects)

1 - stage of development
2 - physiological sensitivity of species
3 - dispersal ability
4 - feeding mode
5 - life habit (e.g., burrowers)
6 - geographic range

gear, displacement of individual fishermen, unannounced
activity by miners, and fouling of gear in holes left by
mining have generally been the major concerns in Britain
(Drinnan and Bliss, 1986). However, these concerns have
administrative and technological solutions.

Ore collection will invariably be a source of physical
impact. The seabed in the path of the collection mechanism
will be raked, broken, and/or compacted as the ore is
gathered. If the ore needs to be fragmented by explosives,
shock waves will create additional disturbances. In some
forms of mining, the area near the mining machinery will be
illuminated. Usually the effects of fragmentation and col-
lection will be essentially limited to the mine site and the
period of mining. Other effects such as the creation of
trenches, pits or mounds on the seafloor may affect the biota
and fishery operations for years.

Alternatively, boulders may be uncovered, forming permanent
obstructions that snag fishing trawls. In this respect the
French have experimented with abutting dredging tracks to
obtain a flat seabed. Also, in some cases, rejected materials
can be guided back into the collector tracks immediately be-
hind the mining machines. Similarly, use of trailing suction
dredges, which interfere much less with bottom fisheries than
do anchored suction dredges, reduces conflicts with commer-
cial fisheries (Drinnan and Bliss, 1986).

Large excavations can also lead to coastal erosion if the
wave patterns and sediment movements near'shore are changed
sufficiently. These effects are being studied by 'the Army
Corps of Engineers, but an interim guide to safe practices
can be obtained from British experience. In their coastal
zones, dredging seemingly causes no problems in water,depths
greater than half the normal wave length, or more than one
fifth the length of extreme waves. Dredging in-waters over
20 m (abou't 60 ft) deep is usually approved with only a desk
review. Proposals for dredging in 10-20 m get more detailed
review and may require site specific information. Proposals
for dredging in waters shallower than 10 m may require
substantial study (Drinnan and Bliss, 1986).

Both the scraping and excavating approaches to mining can
also change the character of the substrate by exposing mate-
rials with different properties. For example, if exposure
of silts and clays is a concern, it may be necessary to
require that the bottom portion of the layer being mined be
left in place to minimize such change. However, for sand and
gravel mining and for some other minerals, the economics of
mining may provide strong incentives not to expose silts or
clays. If so, such regu'lations may be unnecessary.

Subsurface mines and slurry mining cavities may cause local
seafloor collapse or subsidence, possibly leading to coastal
erosion or changes in sediment patterns,, but this phenomenon
can be avoided by proper mine design. In the case of bore-
hole mining, cavities are likely to be water-filled during
the mining, and waste can be injected into the cavity before
the site is abandoned. Both practices reduce the potential

for collapse of the rock overlying the cavity and waste
injection reduces the volume of waste discharged at the
surface.

Seabed mining will create turbidity plumes at the seafloor
as fine materials are resuspended or created during mining.
The properties of the plume, particularly settling times of
the particles, will depend on their size distributions,
specific gravities and concentrations; which are also the
properties of greatest biological significance. Size and
specific gravity of the particles determine residence time
in the water column and influence the potential for resus-
pension. The largest of these plumes may be created by
mining systems designed to reject fine material during pick-
up of the ore. The chemical characteristics of the smaller,
slower settling particles in these plumes generally will be
similar to existing suspended sediment. However, they may
differ if mining exposes an anoxic layer, because the solu-
bility of adsorbed metals can differ greatly between re-
ducing and oxidizing environments. The effects of such
differences are likely to be local and brief due to rapid
dilution by oxygenated waters. Rock fragments created by
mining are likely to consist of relatively inert material
and are less likely to be a source of dissolved metals than
are resuspended sediments.

Surface turbidity plumes are created as wastes are dis-
charged and will vary in proportion to the amount of fine
material discharged and the disposal technique. The fines
will tend to remain in suspensi.on on board the mining vessel
and be discharged with the slurry water, and, in a contin-
uous mining operation, a continually renewed plume is
present. Sediment concentrations in any one parcel of water
decrease as the water mass moves away from the point of dis-
charge, but each such parcel is replaced by another. A
steady state then evolves in which high concentrations are
always found near the discharge point even though the concen-
trations in each parcel are continually decreasing.

The fine particulate material suspended in plumes eventually
falls to the seafloor, forming a thin layer over a large
area. The area affected can be reduced by subsurface dis-
charge or other techniques that force the particulate mate-
rial to settle close to its source, but this creates a
heavier accumulation in that smaller area. The appropriate
sedimentation pattern, and thus the appropriate disposal
methods, will depend upon the characteristics of the site,
including the biota.

Field studies and modeling results indicate that plumes,
both surface and benthic can be detected over distances on
the order of kilometers, and, in certain cases,'tens of
kilometers. Plumes from coastal dredging typically are
visible for only 1-5 km but may be visible up to 20 km
(DOI, 1974). In the clearer oceanic waters beyond the
continental shelf, reductions oflight levels sufficient to
measurably reduce rates of photosynthesis may be present
for 30 to 50 km downcurrent (Chan and Anderson, 1981), and
plumes can be measured up to 120 km from the point of

discharge (Lavalle et al, 1981). However, detection of
plumes at these distances requires the measurement of mate-
rials that are prominent in the discharge from the mining
vessel, but are rare in natural waters. Manganese in the
discharges of manganese nodule miners is an example (Lavelle,
et al, 1981).

Measurable effects of sedimentation will be much more local-
ized than those of plumes. Lavelle et al. (1981), for
example, found that 90 percent of the sediments suspended
by manganese nodule mining were redeposited-within 70 m,
even though the mine site was covered with clays that would
be expected to form a plume of small sized, slowly setting
particles, Thicknesses of the sediment layers resulting
from mining were less than 1-5 mm at 200 m from the dis-
turbed area, about 2-4 mm at 50 m, and 8 mm at 25 m.
Thicknesses of resedimentation may be considerably higher
in some mining operations, but the pattern of rapid de-
cline in sedimentation as distance increases can still be
expected.

In addition to the disturbances shown in table 3, mining
will also be a source of light and noise. Since light is
absorbed rapidly in water, and particularly so in turbid
waters such as may occur near the mining equipment, the
radius of the area affected will generally be a matter of
meters or tens of meters. Noise will affect a larger area
since sound propagates through water much mor 'e readily than
does light and may carry well beyond the mine site. How-
ever, noise is generally not expected to be a significant
problem.

5.2 Biological Biological impacts will occur on the areas actually mined,
impact concerns as immobile-and slowly moving organisms are destroyed by
the mining machinery. However, the areas mined are ex-
pected to be small relative to the total area occupied by
the affected species. The areas affected by the turbidity
plume and resultant sedimentation are considerably larger
but still small relative to the total area of the affected
habitat. The small scale of mining operations means that
the offshore impacts generally will be limited in areal
extent. However, since exceptions can be expected, assess-
ments of the potential impacts of individual projects will
be required to ensure minimal adverse impacts.

The most certain impacts will be the unavoidable impacts at
the mine site as machinery moves across the seafloor to
fragment, collect, or otherwise process ore or move over-
burden. Many organisms that cannot avoid the mining equip-
ment will be destroyed. The significance of that destruc-
tion will be addressed in the site specific environmental
analyses for proposed operations. However, because of the
limited areal extent of near-field impacts, the less certain
far-field impacts could be vastly more significant and so
are stressed in this document. Section 5.2.1 discusses
turbidity, 5.2.2 discusses sedimentation, 5.2.3 discusses
explosives, and 5.2.4 discusses light and noise.

Additional, independent assessments of expected'effects of
OCS mining will be available in an analysis to be published
in summer 1987 by the Office of Technology Assessment (OTA).
A workshop associated with this OTA study concluded that sur-
face and midwater effects should be minimal if appropriate
precautions are taken. The workshop participants deemed the
effects on bottom organisms would be the most pronounced.
Extinctions, which are the severest form of impact; sublethal
effects; and recovery rates were deemed to.need continued
study. These needs were felt to be particularly strong in the
deep sea where the identities of the organisms and their life
histories are generally unknown.

5.2.1 Turbidity The principal biological effects of increased turbidity from
mining are the interference with filter feeding, clogging of
gills, and inhibition of photosynthesis. because of decreased
illumination. Enough variables are involved to give seem-
ingly contradictory results when individual phenomena or
laboratory data are discussed in isolation, but generali-
zations are feasible if one examines the impacts of actual
dredging operations.

The effects of turbidity caused by mining in oceanic waters
are localized and relatively mild because of rapid dispersal
of particles. Nonswimming organisms will drift with the
plume as it rapidly dilutes, but their exposure to high
turbidity will be brief. Swimming organisms probably will
avoid the areas of highest turbidity completely. If so,
these organisms would be excluded from small portions of
their geographic range for the duration of mining. For
example, midocean discharges. during tests of manganese nodule
mining equipment resulted in near-ambient concentrations
within 4 km of the discharge point (NOAA, 1981). Similar
results generally prevail in the shallower waters of the con-
tinental shelf, although higher concentrations may occur.

Measurements by the French (Cressard and Augris, 1982),
during an experimental dredging of sand and gravel in the
Bay of Seine (dept-h 20 m), showed concentrations of 5 to 25
g/l of unknown duration. However, concentrations such as
these tend to be highly localized and recolonization of such
disturbed areas may be rapid. In the shallow waters of the
Beaufort Sea, large dumping operations during construction of
gravel islands produced downstream concentrations only about
three times the ambient concentration of 8-12 milligrams per
.liter (mg/1) within 340 m of the site. Concentrations were
only twice ambient levels within 1730 m. Similarly, concen-
trations of 100-300 mg/l at 100 m downstream of barge dumps
were predicted for island construction in the Canadian Arctic
(DOI, 1983b). These concentrations harm the more sensitive
individuals of the more sensitive species, but not all indi-
viduals of even these species are likely to be affected.
Concentrations that led to the death of 10 percent of the
tested organisms in the Beaufort were 10 g/l or more for
tolerant species and less than 1 g/l for highly sensitive
species. Even this lower threshold is 3 to 10 times the
concentrations measured 100 m downstream of barge dumps. The
'predicted or measured sediment concentrations a few hundred

meters away from the dump site were generally 10 to 100 times
below the lethal levels for even the most sensitive 10 per-
cent of the tested populations (DOI, 1983b).

In addition to sediment concentrations, there are three other
potential sources of concern. First, the presence of toxins
in the sediments can greatly increase the adverse impacts of
turbidity. However, the data showing such effects are based
on studies of sediments from harbors and estuaries in which
toxins, such as pesticides and heavy metals, are introduced
to the marine environment and subsequently adsorbed to the
surfaces of sediment particles. Such contaminants are
rarely found in more than trace amounts In the OCS. More-
over, in natural mineral deposits exposed to seawater, the
biologically active metals are in essentially insoluble
forms and generally are biologically inert.

Second, fluid muds (fluff) may form near the water-sediment
boundary and persist for weeks if there is insufficient
circulation to disperse them. However, lack of circulation
is rare in OCS waters, although fluff may form in coastal
waters. Shell dredging operations in Galveston Bay, for
example, resulted in a nearbottom mud flow with particle
concentrations from 20 to 150 g/l that lasted throughout the
dredging operations (Masch and Espay, 1967, from Peddicord,
1976). Such a condition could be a problem for fauna that
are not equipped to move through this layer to reach the
less turbid environment (Hirsch et al., 1978). However,
the significance of this layer is partially a function of
its thickness, a parameter which can be affected by the
mining methods. The potential for fluid mud formation when
fine, noncohesive materials are resuspended or discharged,
along with the resulting hazards, will strongly depend on
the site and the operating conditions.

Third, in all cases where mining involves the mechanical
fracturing of the rocks, the particles produced are more
likely to have sharper, more angular edges than resuspended
bottom sediments. These sharp fragments may damage organisms
more than natural sediments can.

Both laboratory and field observations have been made of
various organisms under conditions of increased suspended
sediments for various durations. The results, when compared
with increased concentrations expected in the water column,
suggest that these effects may not be a concern if the
dilution factor is high and there are no exceptionally
sensitive bottom communities in the area. For instance, a
study of animals from San Francisco Bay found that at least
90 percent of the animals in most of the 18 species tested
were alive after 10 days exposure to concentrations of 100
g/l kaolin clay suspensions (Peddicord, 1976). Even the
more sensitive species were only adversely affected by tens
of grams per liter of processed bentonite clays over several
days time. However, these experiments did show that the
sensitivity of some species to bentonite increased with
higher temperatures (e.g., 180C) or lower oxygen concentra-
tions (Wakeham et al., 1975), suggesting that in the San
Francisco Bay, seasonal changes in these two parameters may

be important in determining the severity of impact from
dredging and disposal. However, Peddicord (1976) noted that
the laboratory experiments did not evaluate physiologically
sublethal effects, which may be more important ecologically
than direct mortality. Lunz et al. (1984) in a recent sum-
mary of data for eggs, larvae, and adults of fish and shell-
fish harvested in the coastal zone found several of the
molluscs and crustaceans tested were sensitive to 100 mg/l
or more of suspended sediments during multiday exposures,
although others were tolerant of higher levels of 100 g/l or
more for 1 to 3 day exposures, a thousand fold difference in
concentration.

The results of laboratory studies of marine fish vary. Moore
and Moore (1976) found that turbidities of 126 to 135 mg/l
increased the time for the European flounder to see its prey.
Although it is likely to be of minor importance if the plume
is short-lived, this nonlethal effect would surely reduce the
feeding rate and, hence, the vigor of the affected animals.
Effects of manganese nodule mining plumes on captive yellow-
fin tuna and kawakawa havebeen studied by exposing the fish
to deepsea clays and nodule fragments. No detectable effect
was found in adults at concentrations from 9 to 59 mg/l.
Feeding continued to occur in concentrations of 11 mg/l, and
no change in behavior was noted in the presence of a tur-
bidity cloud (Barry, 1978). However, preliminary results by
Barry suggested that turbidities greater than 4 mg/l some-
times caused feeding inhibition and coughing in tuna in the
laboratory (Matsumoto, 1984).
Some studies of 1@rval fish have also shown feeding be-
havioral modifications because of decreased illumination, a
possible consequence of increased turbidity (Blaxter, 1980;
Kawamura and Hara, 1980; Riley, 1966; Wyatt, 1972; Houde,
1975; Saksena and Houde, 1972; Houde, 1977). However,
Matsumoto (1984) concluded from a revi.ew of existing litera-
ture that the dilution of the plume from manganese nodule -
mineship discharges would be rapid enough to prevent any
significant adverse impact on tuna and billfish eggs, larvae,
and adults.

A limited number of field observations have been made on the
behavior of marine fish in areas of high turbidity. The
results suggest adults are less sensitive than the young and
that there are differences among species. Whitebait (imma-
ture herring) and sprats have been found to avoid areas where
china clay wastes are being discharged. Mackerel, however,
do not seem to avoid these areas and exhibited no problems in
feeding, despite being visual feeders (Wilson and Connor,
1976; Shelton and Rolfe, 1971; Shelton, 1973). Fish are
observed to be abundant off the mouth of the Columbia River
where sediment concentrations may reach 10 to 100 mg/I
(Pruter and Alverson, 1972). Ritchie (1970) noted no ad-
verse effects from overboard dredge spoil disposal on 44
species of fish from Chesapeake Bay. Observations off Hawaii
showed that densities of fish*larvae were found to be nega-
tively correlated with higher turbidities, whether natural or
man related, which Miller (1974) suggests may be caused by
avoidance of turbid areas. Lunz et al. (1-984) summarized

laboratory reports of significant mortality of white perch,
yellow perch, and striped bass larvae at suspended sediments
concentrations of 500-5400 mg/1 after 1-4 days of exposure.
Larvae in the open ocean would not be exposed to such con-
centrations for such long periods, as they would drift with
the diluting turbidity current, and the potential signifi-
cance of exposures in the field may be overstated by these
laboratory data.

An excellent review of potential adverse effects on zoo-
plankton from a deep seabed manganese nodule mining plume
was conducted by Hanson et al. (1982). Many of these
species are filter feeders which ingest particles on the
basis of size. Research has shown that zooplankton would
most likely ingest nonnutritive particles from a mining
plume (Hirota, 1981; Hu, 1981), effectively reducing their
food intake. Not surprisingly, large increases in the
ratio of nonnutritive to nutritive particles are harmful.
For example, concentrations of 0.6 to 6 mg/l of clay wastes
from aluminum extraction resulted in lower body weights of
copepods (Paffenhoffer, 1972). However, the effects of non-
nutritive ingestion caused by presence of mining may not be
readily distinguished from natural variability. Hanson et
al., (1982) concluded from their review of manganese nodule
mining wastes that the oceanic zooplankton community would
probably not be significantly.harmed. Even though these
wastes included trace metals released from the nodule frag-
ments and pelagic clays as well as suspended.load, they
noted the plumes would be rapidly diluted, exposures would
be brief, and the animals could tolerate slight increases
in trace metals concentrations.

-Effects on marine phytoplankton are observed in response to
decreased illumination in the laboratory, but these shading
effects are not expected to be a problem in open waters.
Again the high dilution that would immediately occur prevents
significant effects. Measurements of primary productivity
and light intensity in a mining plume from deep seabed test
mining showed a possible 50 percent reduction of productivity
in an area 18 km by 2 km over several hours (NOAA, 1981).
In a commercial mining operation, a 50 percent reduction in
primary production may occur over an area approximately 20
km by 20 km (Chan and Anderson, 1981). Plankton in the
mixed layer might be expected to encounter reduced light
over an 80-to 100-hour period. This effect is similar to
the effect of a cloudy day (NOAA, 1981).

In summary, while most of the studies of dredge spoil and
mine tailings disposal have limited relevance to the OCS
(Bigham et al.,,1982), they indicate adverse effects to the
biota from increased turbidity are likely to be insignificant,
as long as there is a high dilution of the material (Kaplan
et al., 1974). Most organisms of the OCS are adapted to
natural variations in turbidity and can tolerate the higher
turbidities that may result from mining unconsolidated
sediments if exposure is brief. (As noted above, swimming
organisms can avoid a plume, while nonswimming organisms
will drift with the plume as it rapidly dilutes). Mining
consolidated rock should be less of'a problem as a turbidity

source since the particles released into the water column
are expected to be larger and consequently settle more
rapidly.

5.2.2 Sedimen- Feeding mode, life habit, degree of mobility, or sensitivity
tation of life stage all affect the vulnerability of organisms to
sedimentation. Some organisms are able to burrow out from
tens of centimeters of sediment, although there seems to be
a maximum depth below which no escape response is initiated
(Nichols et al., 1978; Hirsch et al., 1978; Maurer et al.,
1978). Other species can tolerate a slight increase in
sediment deposition above natural loads. Oysters have been
found to be fairly tolerant of some increase in sedimen-
tation, although a large amount of deposited material causes
suffocation (Mackin, 1961; Dunnington, 1968). Adults react
to slight increases through increased pumping, or in some
cases, through closing their valves. However, Loosanoff
(1962) found some animals died when stress was prolonged
for more than 48 hours. Larvae and eggs were most sensitive,
with normal development being affected at 188 mg/l and
stopped at 2 g/l. Clam larvae and eggs in general exhibited
less sensitivity to increased concentrations of silt (Davis
and Hidu, 1969).

The resiliency of animals may be much less if their typical
natural environment has low turbidity, such as is found in
much of the tropics. Hermatypic corals are known to depend
on light for growth (Goreau, 1961), with growth being in-
versely related to the amount of resuspended sediment (Dodge
et al., 1974). Consequently, a substantial increase in
suspended sediment in areas of coral growth could be of con-
cern, even though many coral's can withstand some sedimen-
tation through active removal. Bak (1978) studied the growth
rates of fringing corals before and after dredging in the
Caribbean. Although light levels were reduced to approxi-
mately 1 percent of the surface illumination for only a few
days, growth of Madracis mirabilis and Agarlicia agaricites,
both efficient s nt rejectors, was reduced by one-third
for more than 1 month. Colonies of Porites astreoides, how-
ever, were killed as they were unable to remove the sediment,
became covered with sediment, lost their zooanthellae
(symbiotic algae), and died.

Other areas that may not be able to withstand slight in-
creases in sediment deposition are those used by bottom-
spawning fish. For example, in the North Sea where gravel
dredging resulted in large pits 3 to 5 m deep, water flow
over these areas was slowed, resulting in finer sediments
being deposited (Dickson and Lee, 1973a and 1973b). Many of
these pits fill in slowly, with measured rates suggesting
that decades may be required before they fill with silt.
They may never return to premining conditions. Similarly,
monitoring of dredge channels along the Atlantic coast of
the United States has likewise shown that silt-clay particles
fill in the channels, in contrast to the surrounding sand
environment, resulting in an altered substrate (Taylor and
Saloman, 1967). In Europe, recommendations have been made to
avoid those areas where herring attach their eggs to the

seafloor as well as those areas and times of sand eel spawn-
ing (ICES, 1975; De Groot, 1979a). Similar bottom spawning
species exist off both coasts of the United States (e.g.,
herring, winter flounder, sand eels, rock sole) and deserve
attention, as the spawning areas of these species may be
affected by increased sedimentation, especially if a fluid
mud layer is created (Hirsch et al., 1978). Also, there are
special environments, such as the Arctic (DOI, 1983b), where
recolonization may be extremely slow, but on which little
information is available. Wright (1977) observed that full
benthic recovery may take more than 12 years as a consequence
of gravel island building for oil and gas development in the
Canadian Beaufort Sea. -

I
Dunton et al. (1982) stripped the organisms from a small area
in a cobble-kelp community in the Arctic and found most of
the areas still bare after 3 years. Such slow recovery of a
community suggests that this environment may deserve special
attention. Deep-sea environments probably would be equally
slow to recover, since they are also very cold and food is
limited. Seafloor spreading areas with hydrothermal vents
are another unusual environment that would deserve attention
if any mining were anticipated near them.

In cases where most of the benthic community is adversely
affected, recolonization will have to occur from popula-
tions outside the disturbed area. The rapidity of this
process seems to be highly influenced by the similarity of
the new substrate to the premining condition (De Groot,
1979b). De Groot (1979a) established that recovery of the
benthic fauna would take 2 to 3 years following sand and
gravel mining. Recovery is aided if some of the sand and
gravel deposit is left so that the substrate remains similar.
Pfitzenmeyer (1970) found that the upper Chesapeake Bay re-
covered to its original condition 18 months after dredge-
spoil disposal when there was no major topographic or strati-
graphic change and the sediment was similar. Kaplan et al.,
(1974) found that the number of species in an enclosed bay in
Long Island before and after dredging differed as a function
of sediment type, with sediment changes being related to the
circulation changes that resulted from the dredging.

Other studies of dredged, inshore areas have found rapid
recovery (Cronin et al., 1971; Harrison, 1967; Connor and
Simon, 1979). However, in many cases, while the biomass may
reach predredging conditions, the diversity and distribution
of species do not always replicate the premining environment
(May 1973; De Groot, 1979b). Such a shift in community
structure has been reported in experiments with recolonization
boxes at depths greater than 1 km (Desbruyers et al., 1980;
Grassle, 1977; Levin and Smith, 1984). Opportunistic species
able to move rapidly into an unoccupied area were the first
organisms to settle in the boxes and had the largest popUla-
tions. The number of those species, however, was low in
comparison to adjacent areas. After 26 months, the species
composition of the boxes in the deep waters still differed
greatly from -adjacent areas.

Shallow water studies have shown that marine communities
must evolve through successional stages (Thistle, 1981;
Shelton and Rolfe, 1971; Gallagher et al., 1983; Kaplan,
et al., 1974) before the redevelopment of the predredging
community begins. Gallagher et al., (1983) identified
certain species that had to move into an area before other
species could recolonize. These results suggest that having
-a similar substrate increases recovery, but other steps must
occur before the premining condition is reached.

Species that produce a large number of pelagic larvae are
frequently the first species that move into an area that
has been defaunated. However, other qualities have also
been found in opportunistic species. In intertidal environ-
ments, the first polychaete recolonizers were frequently
species whose adult stages were mobile (Levin, 1984; Dauer
and Simon, 1976). Levin also found that the scale of dis-
turbance, the type of larval development (that is, pelagic
or nonpelagic), the settlement patterns, and mobility of the
species were important to the success of recolonization.
Brooding adults of species that had a nonpelagic larvae
rapidly recolonized small areas of disturbance.

Polychaetes that had pelagic larvae were more adept at moving
into large disturbed areas, especially when the disturbance
occurred during the peak of the larval-dispersal period.
Consequently, the recovery rate of a mined area that results
in small shallow pits may differ considerably from large
areas that have been scraped in a contiguous manner.

In summary, sedimentation may have a significant effect on
the life cyles of some bottom living organisims such as
oysters and clams, particularly during larval stages. Such
effects could be lethal or sublethal. Care should be taken
therefore in the timing of activities likely to cause sedi-
mentation.

Recolonization of dredged areas depends on a number of dif-
ferent factors, and in most cases a complete return to the
premining condition is likely to be slow. If there are no
commercial species involved, change may not in itself be
harmful, but the importance of any change in population would
need to be assessed for the specific operation.

5.2.3 Explosives, Explosives were widely used at one time for deep seismic
impacts exploration offshore but have now been superseded,by other
methods such as air guns and sparkers. The present limited
use of explosives underwater for mining is strongly regulated
by both State and Federal authorities to minimize environ-
mental damage, particularly in areas where commercial fishing
is practical or protected species are present. In all cases
of use in Federal waters, environmental analyses are required
and all operations are subject to immediate shutdown if un-
acceptable environmental effects on mari.ne communities are
detected.

The use of explosives to breakup overburden and fragment the
mineral deposit will generate shock waves, which generally

The rarefaction wave is produced when the compression wave is
reflected from the water-air boundary and is transformed with
a loss of energy into a negative pressure pulse. These sud-
denly applied negative pressures appear to kill fish by ex-
plosion of the swimbladder. As a result the rarefaction wave
causes more damage near the surface of the water than at
depth where ambient pressures are higher. Dynamite produces
much higher negative pressures than black powder and is again
more harmful to fish. Baldwin (1953), for example, during
his observations of the use of black powder in geophysical
surveys in salmon fishing areas off California found no dead
or injured salmon even though many were seen swimming in the
blasting area before detonation. Rapid compression followed
by the negative pressure pulse caused by rarefaction thus
seems to be most responsible for injury to fish.

Several studies of fish kills showed conflicting results for
the effects of detonation at different depths, but the con-
flicts seemed to result from the different environmental con-
texts. Kearns and Boyd (1965), studying explosions in the
upper water column, concluded that the areas within which
fish would be killed increased with increasing depth of deto-
nation. Goertner (1981), studying explosions at the seafloor,
found that the probability of death was reduced with in-
creasing depth of explosion, and, hence, higher ambient
pressures. The differences apparently relate to the location
of the explosions, and perhaps, the absolute depths involved.

Research conducted in Japan on the relationship between ex-
plosion size, fish type, and distance from the blast found
that damage always occurs to the fish's stomach when the
force is 5 Lg per square centimeter or greater. A force of
3 kg/cm2 is considered safe. This force is equivalent to a
distance of 200 to 500 m from a 1.5-ton explosion, the largest
permitted by Japanese law (Padan, personal communication).

Studies of both behavioral and physiological effects on fish
larvae and juvenile stages caused by pressure pulses from air
guns and explosive removal of structures were conducted in
the Santa Barbara Channel under joint energy company and com-
mercial fisheries oversight. The reports are in preparation,
and similar studies are in progress in the Gulf of Mexico
with MMS support. Results will be available prior to any
anticipated OCS mining.

5.5.4 Light and noise

Light and noise generated by mining equipment may disturb
nearby benthic organisms and possibly modify behavior. How-
ever, many, if not most, mobile, nonterritorial organisms
should be able to move away from the disturbance. Even
though there is little natural light below 1 km, deepsea
organisms have functional eyes and the light introduced
during mining will attract some organisms and cause others
to move away. Moreover, observations from submersibles indi-
cate that fish exposed to bright, artificial light may be at
least temporarily mesmerized, possibly blinded. The exact
impact has not been determined (NOAA, 1981).

51A

will cause some deaths in the benthic invertebrate and fish
populations. The extent of the effects depend on the velocity
of detonation. For example, research has shown that dynamite
and TNT produce far more deaths in fish than black powder
(Hubbs and Rechnitzer, 1952; Kearns and Boyd, 1965; Anonymous,
1947 and 1948). Thus, the effects cannot be predicted until
the explosive material proposed for use in any specific case
is determined. These explosives may be novel materials,
since conventional mining explosives, such as gelignite and
ammonium nitrate, may not be suitable in deep water where the
pressure might reduce the effectiveness of the explosion,
(DOI, 1983a).

Adverse effects from individual explosions should be brief
and confined to a small area since explosive forces rapidly
dissipate with distance from the source. Significant, per-
manent, adverse impacts on the biological community would be
unlikely unless either rare or unusual species occur near the
mining operation or the cumulative effects of repeated ex-
plosions differ greatly from the effects of single events.
However, the presence of the normally prevalent species in
areas subject to explosions during war, naval training, and
occasional public works activities evidence lack of irrepar-
able damage from repeated explosions. Rates of recovery
probably will be similar to the rates of recovery from other
forms of OCS mining.

The organisms most susceptible to the shock waves generated
by the detonation of explosives are those fish species that
possess a gas-filled swimbladder. The swimbladder is a
membranous sac of gases that serves a hydrostatic function in
most fish that possess it. In some fish it may even partici-
pate in the production of sounds (Gross, 1972). Fish without
swimbladders are mostly deep water species or predators, such
as sharks, which swim at various levels in pursuit of prey.
Young (1973) found that invertebrates living on or near the
seafloor are more tolerant of explosives than fish with swim-
bladders.

The individual components of an underwater explos ion impor-
tant to impacts on fish are thought to be the amplitude (peak
pressure), the type of compression wave, and the rarefaction
wave (Hubbs and Rechnitzer, 1952). In an explosion, two
types of positive pressure waves are produced, the initial
compression or shock wave and the following bubble-pulse wave
(Cole, 1948). The compression wave causes the primary dis-
turbance to the water. Dynamite detonates instantaneously
and produces a sharp shock wave with an abrupt front of in-
tense pressure, which can seriously injure fish with swim-
bladders. Black powder burns more slowly and produces a less
intense peak pressure that is less injurious.' The bubble-
pulse wave from both dynamite and black powder explosions is
of relatively long duration and low maximum pressure. No
major impact on fish was observed from this wave by Hubbs and
Rechnitzer (1952), although some difficulties have occurred
with shallow explosions in seismic surveys. These reported
problems, however, may have been caused by rarefaction waves.

5.2.4 Mining Not much is known about the intensity,.frequency, and dura-
noises tion of mining noises. The type of collector most likely to
be used for mining manganese nodules may attract scavengers,
especially species like the rat-tail fish, that communicate
by sound (NOAA, 1981). Noise also affects marine mammals,
but the signficance is not well known (DOI, 1983a; DOI,
1983b). Most research has been conducted on the effects on
endangered and/or threatened marine mammals from OCS oil and
gas activities. Some researchers (Geraci and St. Aubin,
1980) have suggested that most animals become habituated to
low-level background noise, such as ship traffic and onshore
offshore petroleum activities; however, some animals show
abrupt responses to sudden disturbances. Responses to con-
tinuing abrupt noise disturbance by California sea lions,
Stellar sea lions, and harbor seals are fairly well docu-
mented (DOI, 1983a). Gales (1982) found that, although
there were no significant physiological effects, possible
auditory effects from a sonic boom, a pulse somewhat similar
to explosive seismic pulses, include startle, flight, audi-
tory discomfort, and hearing loss. Stationary dredging
operations in the arctic did not seem to greatly disturb
beluga and bowhead whales, but their swimming patterns did
change within 2.4 km of dredging operations (DOI, 1983b).
MMS-sponsored studies of the effects of noise on grey whales
off the California coast also found that ship and air gun
noises affect behavior, but much less so than biologically
meaningful sounds, such as the sounds of killer whales. This
response seems likely to be true of other animals as well.
It is probable that the effects of mining noise will resemble
the effects of noises from harbors, mechanized fishing gear,
military maneuvers, and shipping.

6. Conclusions

The following conclusions can be drawn from the research and
operational experience cited in the preceding sections.

Mining in the OCS will produce effects from both the
mining itself and the transport, beneficiation, and
refining of the ore mined.

0 The nearshore and onshore effects associated with the
transport, beneficiation, and refining of the ore are
common in existing ports, and hence familiar.

0 Site-specific studies or monitoring of environmental
effects of OCS mineral mining will often be necessary
during at least pilot tests of new equipment and new
operations. Knowledge of the method of mining, the type
of ore, and the characteristics of the mine site.are
needed to be able to predict the effects at the level of
detail needed in EIS's.

0 The OCS will be mined by the four basic methods of mining
used for solid deposits on land: scraping the surface,
excavating a pit or trench, drilling a borehole and
removing the valuable constituent in a slurry or as a
solution, or tunneling. Any of these mining methods is
applicable.to more than one type of mineral deposit.

0 Near-field effects associ'ated with fragmentation/col-
lection on, or excavation of, the seafloor will be limited
to the periods of active mining and will be limited to the
mine site.

0 Far-field effects in deep, oceanic waters are the least
known, with resedimentation being the main concern. Of
particular concern is the effect on benthic organisms and
the repopulation of mined areas.

0 Because of the rapid dilution prevalent in the waters of
the OCS, organisms living in the water column are unlikely
to be exposed to adverse concentrations of suspended sedi-
ments. In the immediate vicinity of mining operations
exposure is expected to be brief due to the transient
nature of the plume.

Organisms living at the seafloor are the most likely to be
affected because of the resedimentation of the benthic
plume, the actual destruction of the biota, and the change
in the character of the seabed.

7. Minerals Management Service policy for.environmental protection

The MMS has prepared this document in recognition of the need
to provide the public with an early overview of possible OCS
mining activities and potential impacts on the environment.
The MMS intends to prepare additional documents to comply
with the National Environmental Policy Act (NEPA) as leasing
proposals develop and more is known about the nature, magni-
tude, location, and rate of future mining.

The MMS will provide a comprehensive framework for environ-
mental protection during prospecting for, and mining of,
minerals other than oil, gas, and sulfur through develop-
ment of regulations, lease sale EIS's, and lease stipulations.
Environmental impacts will be addressed through the environ-
mental review process specified under NEPA. An EIS will be
prepared before the first lease sale of any of these minerals
in any new area where leasable targets are identified. These
EIS's will include detailed coverage of the environmental
issues and will be similar in scope to the EIS's prepared for
onshore mining and the offshore oil and gas programs. The
NEPA process will provide significant opportunities for
public involvement and comment.

The MMS is providing and will continue to provi de opportun-
ities for early input from State.and local governments
and the public. The MMS is developing the leasing program
for minerals on the OCS with the aid of joint Federal/State
task forces, where the States are willing to participate in
these joint efforts. The task forces, through open meetings
and consultations, will assess the economic feasibility of
mining, the potential environmental problems, and measures
to mitigate environmental problems. A task force studying
a specific leasing proposal will reports its findings to
the Governor(s) and the Secretary of the Interior. However,
this program is an evolving process and there may be cases
where a task force would not be to the benefit of the State
or the Federal Government,* and other new, innovative, leasing
approaches may also be used.
At this time MMS is developing a case-.by-case leasing program
with State cooperation in the belief that both the recovery
o'f minerals and protection of the environment can be best
accomplished by such an approach. The case-by-case approach
allows analysis and regulatory control to match the varied
operational and environmental factors and issues as these
become better defined. After issuing a lease, the MMS will
require that detailed exploration plans and site-specific
mine plans be submitted. Before the MMS approves new mine
plans, or modifications of existing plans involving signifi-
cant changes in potential environmental impacts, environ-
mental documentation specific to those plans will be prepared

and considered, allowing additional input by the public and
adjacent States. Only then may mining be allowed to proceed.

0'1-

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Appendix 1

I. English to Metric

Customary (English) Units Metric Units

0 Linear Measures
foot 0.3048 meters
fathom (6 feet) 1.8288 meters
statute mile (5280 feet) 1.6093 kilometers
geographic (nautical) mile (6076,115 feet) 1,,8520 kilometers

0 Square Measures
acre 0.4047 hectares
square statute mile (640 acres) 259.0 hectares
square statute mile 2.590 square kilometers

0 Volume Measures
cubic foot 0.0283 cubic meters
cubic yard (27 cubic feet) 0.7646 cubic meters

0 Weight Measures
short ton (2,000 pounds) 0.9072 tonnes (metric tons)
short ton 907.Z kilograms
long ton (2,240 pounds) 1.016 tonnes (metric tons)
long ton 1016. kilograms

II. Metric to English

Metric Units Customary (English) Units

0 Linear Measures
meter 3.281 feet
meter 0.547 fathoms
kilometer 3281 feet
kilometer 0.6214 statute miles
kilometer 0.5400 nautical miles

0 Square Measures
hectare 2.471 acres
square kilometer 247.1 acres
square kilometer 0.3861 square statute miles

0 Volume Measures
cubic meter 35.31 cubic feet
cubic meter 1.308 cubic yards

0 Weight Measures
tonne (metric ton) 1.102 short tons
tonne (metric ton) 0.9842 long tons

Appendix 2

Areal Comparison:
United States Outer Continental Shelf and
ExclusiTe -Economic Zone

Acres
(1) Onshore Land Area2 0 2,355,000,000
(2) OCS Planning Ared . 1,438,000,000
(3) OCS Planning Area + Onshore Land Area . 3,793,000,000
(4) Minimum continental shelf EEEZI . . . . 2,848,000,000
(5) Minimum continental shelf outside
OCS Planning Area . 0 & 0 0 0 0 0 0 * 1,599,000,000
(6) OCS Planning Area outside minimum
continqntal shelf . . . . . . . . . . 215,000,000
(7) Declared* continental shelf. 3,063,000,0005

Footnotes:

1. Areas include the Commonwealth of Puerto Rico, the U.S.
Virgin Islands, Guam, American Samoa, the Commonwealth
of the Northern Mariana Islands and other U.S. terri-
tories and possessions.

2. Land Area from U.S. Bureau of Census.

3. The OCS Planning Area is for the proposed 1987-1991
5-year oil and gas leasing program; total area between
landward and seaward limits is given, without deletion
for deferrals or exclusions.

4. The declared continental shelf (i.e., combination of the
OCS Planning Area and the minimum continental shelf) does
not represent the total extent of the U.S. continental
shelf; the seaward limit of the U.S. continental shelf,
including the seaward limit of the OCS, is not yet estab-
lished, and in some regions the legal continental shelf
will extend beyond the 200-mile minimum continental shelf.
Further, some international boundaries with other coastal
nations affecting the U.S. continental shelf and EEZ have
not yet been agreed to with the respective nations.

5. The sum of the minimum continental shelf and the OCS
Planning Area outside the minimum continental shelf does
not exactly equal the sum of the OCS Planning Area and
the minmum continental shelf outside the OCS Planning
Area as the landward limit of the OCS does not coincide
with the landward limit of the minimum continental shelf
offshore Texas and Florida in the Gulf of Mexico.

As the Nation's principal conservation
agency, the Department of the Interior
has responsibility for most of our nation-
ally owned public lands and natural
resources. This includes fostering the
wisest use of our land and water re-
sources, protecting our fish and wildlife,
preserving the environmental and cul-
tural values of our national parks and
historical places, and providing for the
enjoyment of life through outdoor recrea-
tion. The Department assesses our en-
ergy and mineral resources and works
to assure that their development is in the
best interest of all our people. The De-
partment also has a major responsibility
for American Indian reservation com-
munities and for people who live in Island
Territories under U.S. Administration.

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