NATURAL AGGREGATE 

BUILDING AMERICA'S FUTURE 

By WILLIAM H. LANGER 

andY. M. GLANZMAN 

PUBLIC ISSUES IN EARTH SCIENCE 

U.S. GEOLOGICAL SURVEY CIRCULAR 1110 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

First printing, 1993 

Second printing, 1993 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1993 

Free on application to 

USGS Map Distribution 

Box 25286, Building 810 

Denver Federal Center 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Langer, William H. 

Nahual aggregate: building America's future I 

by William H. Langer and V.M. Glanzman. 

p. em.- (U.S. Geological Survey circular; 1110. 

Public issues in earth science) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.4/3: 

1. Aggregates (Building materials)-United States. I. Glanzman, V.M. 

II. Title. III. Series: U.S. Geological Survey circular; 1110. 

IV. Series: U.S. Geological Survey circular. Public issues in earth science. 

TN939.L36 1993 

338.2'762'0973-dcZO 93-13473 

CIP 
FOREWORD 

The United States produces nearly 2 billion tons of aggregate per 

year, which represents approximately one half of the non-energy mining 

volume in the country. Yet natural aggregate is one of the Nation's 

poorly understood resources. In this book, the authors discuss issues 

related to the geologic distribution and characteristics of aggregate and 

some implications of those factors for our Nation's economy. The two 

primary sources of aggregate are crushed stone and sand and gravel. 

Although potential aggregate is widely distributed throughout the 

United States in a variety of geologic environments, it is not evenly distributed geographically. Some areas are devoid of sand and gravel; 

potential sources of crushed stone may be lacking or covered by an overburden so thick that surface mining is uneconomical. In other areas, 

aggregate does not meet the physical or chemical property requirements 

for specialized uses. Furthermore, zoning, government regulations, or 

competing land uses may restrict or preclude the production of aggregate. Transportation to the user is an important factor in providing 

lower costs in construction projects. 

In the next decade, the restoration and rehabilitation of an aging 

infrastructure will require the mining of enormous amounts of aggregate. Earth scientists provide input critical to the identification, protection, and extraction of suitable aggregate and equally important to 

reclamation efforts that return the land to beneficial uses. This information will be used into the next century to provide economical supplies of 

aggregate while providing protection from the impacts of mining to both 

citizens and environment alike. 

Dallas L. Peck 

Director 

CONTENTS 

1 INTRODUCTION 

9 GEOLOGY 

21 SUPPLY AND DEMAND 

25 THE AGGREGATE INDUSTRY 

31 PLANNING AND REGULATION 

37 SUMMARY 

INTRODUCTION 

Crushed stone and sand and gravel are the main types of natural 

aggregate used in the United States. Aggregate is used in nearly all 

residential, commercial, and industrial building construction and in 

most public-works projects such as roads and highways, bridges, 

railroad beds, dams, airports, water and sewer systems, and tunnels. 

The widespread use of aggregate results not only from its general 

availability but also from economic considerations. Aggregate of good 

quality commonly is available near the site of use at relatively low cost. 

This aggregate can essentially be obtained and used with a minimum of 

processing. However, even though crushable stone and sand and gravel 

resources are widely distributed throughout the United States, 

availability is not universal. Some areas are devoid of sand and gravel, 

and some potential sources of crushed stone may be lacking or covered 

by overburden that is too thick to allow economical surface mining. In 

some areas, moreover, aggregate does not meet the physical-property 

requirements for certain uses, or it contains mineral constituents that 

react adversely when used in cement concrete. Furthermore, citizens 

commonly prefer that stone and sand and gravel not be mined nearby. 

Many citizens do not support mining, in part because they do not 

recognize the dependence of society on aggregate. Personal use is very 

little, if any, and individuals may not recognize aggregate mining as a 

necessary land use, even though the need for the commodity is constant. 

Thus, zoning, regulations, and competing land uses may restrict or 

preclude aggregate mining. 

Aggregate production accounts for 

about half of the 

nonfuel-mining volume in the 

United States. 

Between 1970 and 1990, aggregate use averaged 1.84 billion short 

tons per year, reaching a maximum of 2.17 billion tons during 1988. In 

the future, the rebuilding of deteriorated roads, highways, bridges, 

airports, seaports, waste disposal and treatment facilities, water and 

sewer systems, and private and public buildings will require that 

enormous quantities of aggregate be mined or quarried. Long-range 

planning is necessary to help ensure adequate economical supplies of 

high-quality aggregate in the future, while simultaneously protecting the 

public from unwanted effects of mining. This report provides an 

overview of the aggregate industry and of the availability of natural 

aggregate as an aid to those involved in protecting, conserving, and 

developing the Nation's resources. 
PRODUCTION AND USES OF AGGREGATE 

Sand and gravel are produced 

commercially in every State in the United 

States, and crushed stone is produced in 

every State except Delaware. Aggregate 

production accounts for about half of the 

nonfuel-mining volume in the United States; 

during 1990, production yielded a gross 

value of about $9.1 billion. The 1990 gross 

value far exceeded that of iron ($1.8 billion), 

copper ($4.2 billion), or the combined value 

of precious metals including gold, silver, and 

the platinum-group metals ($4.7 billion). 

In 1989 (the last year for which a 

complete survey of crushed-stone production 

was taken), 1,716 companies produced 1.2 

billion short tons of crushed stone from 3,416 

active quarries. Individual crushed-stone 

quarries range in size from small operations 

reporting production of less than 50,000 short 

tons annually to those with production of 

more than 10 million tons. For a variety of 

reasons, including the large investment in 

capital equipment, crushed-stone operations 

tend to be very large. For example, in 1989, 

10 companies operating 477 quarries 

produced 27.8 percent of the total output of 

crushed stone in the United States. 

AGGREGATE PRODUCED IN THE 

UNITED STATES IN 1990 

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NATURAL AGGREGATE 

Sand and gravel D Crushed stone 
In 1990, about 4,200 

companies produced 911 million 

short tons of sand and gravel 

from about 5,700 operations. 

Individual sand and gravel 

operations range in size from 

those reporting production of less 

than 25,000 short tons annually to 

those with production of more 

than 2.5 million tons. In contrast 

to crushed-stone operations, 

many sand and gravel operations 

are relatively small. In 1990, 

3,564 operations, representing 63 

percent of the total, each 

produced less than 100,000 short 

tons of sand and gravel. 

Production of crushed stone 

and sand and gravel is necessary 

to many industries in the United 

States. Sand and gravel (or sand 

alone) is used for sand casting in 

foundry operations, glass 

Other 

USES OF SAND AND GRAVEL 

Road base, 

unpaved roads 

USES OF CRUSHED STONE 

Other 

Concrete 

aggregate 

Concrete 

Bituminous 

aggregate 

manufacturing, abrasives, and 

filtration beds of water-treatment 

facilities. Crushed stone is used 

as a source of calcium for 

fertilizers, in metallurgy, and as 

the major component in the 

manufacture of cement and lime. 

Crushed stone may also be used 

in filtration systems and in the 

manufacture of glass. metallurgical Road base, Crushed stone and sand and unpaved roads 

gravel are primarily used for 

aggregate in the construction 

industry, especially in cement 

concrete for residential and 

commercial buildings, bridges, and airports, 

and as cement concrete or bituminous mixes 

(asphalt) for highway construction. A large 

percentage of aggregate is used without a 

binder as road base, for road surfacing, and 

as railroad ballast. Aggregate is also used to 

provide drainage around house foundations, 

for septic-system leach fields, for snow and 

ice control, and as fill in wet or swampy 

land. 

The view of any four-lane interstate 

highway with interchanges and bridges, 

international airports, or a great dam such as 

the Grand Coulee instantly conjures a picture 

BUILDING AMERICA'S FUTURE ~ 
of huge volumes of aggregate 

or concrete. Indeed, 

construction of 1 mile of fourlane interstate highway 

requires 85,000 tons of 

aggregate; the Denver 

International Airport, Colorado 

(pictured below), required 5 

million tons; and the Grand 

Coulee Dam required 17 

million tons. However, few 

homeowners realize that 

construction of an average sixroom house requires 90 tons of 

aggregate or that construction 

of one average-size hospital or 

school requires 15,000 tons. 

NATURAL AGGREGATE 
BASIC CONCEPTS AND TERMINOLOGY 

Natural aggregate consists of rock 

fragments that are used in their natural state 

or are used after mechanical processing such 

as crushing, washing, and sizing. Quarry 

stone is crushed and processed to produce 

aggregate. In this report, the term natural 

aggregate (or aggregate) includes mined or 

quarried stone that has been crushed, 

washed, and sized, as well as sand and 

gravel. 

Gravel generally is considered to be 

material whose particles are 3/ 16 inch to 3 

inches in diameter and tend to be rounded 

with smooth edges. Sand and gravel 

aggregate is a mixture (aggregation) of sand 

and gravel in which gravel constitutes about 

25 percent or more of the mixture. Gravel 

may be the predominant material in a 

natural deposit, but typically it occurs in 

layers or lenses with sand. 

BUILDING AMERICA'S FUTURE ~ 
Crushed stone, as its name 

implies, is artificially crushed 

rock, boulders, or large 

cobbles. Crushed stone tends 

to be angular with sharp 

edges. Most or all of the 

surfaces on the clasts or 

particles are produced by the 

crushing operation. Most 

crushed stone is quarried from 

bedrock that is blasted, mined, 

crushed, and processed into 

aggregate. Selection of the 

bedrock to be used for crushed 

stone depends primarily on the 

physical and chemical 

properties of the rock. 

PHYSICAL AND CHEMICAL 

REQUIREMENTS OF 

NATURAL AGGREGATE 

Most people probably assume that 

natural aggregate is used chiefly in cement 

concrete. Much natural aggregate, however, 

is unsuited for such use. We all have seen 

crumbling driveways and bridges or cracks 

in sidewalks and patios. Concrete 

deterioration has many causes, but 

unsuitable aggregate, containing deleterious 

ingredients, can be a primary or secondary 

cause of the problem. 

Natural aggregate varies widely in 

quality, depending on the source. To ensure 

that aggregate is suited for particular uses, 

testing laboratories compare aggregate 

properties with predetermined standards. 

The most generally used national guidelines 

for specifications and testing procedures are 

those of the American Society for Testing 

and Materials (ASTM). National 

specifications must be broad, and at best they 

serve as general guidelines. Local 

specifications need to reflect specific uses, 

NATURAL AGGREGATE 

availability and quality of local aggregates, 

and local climatic conditions. 

Suitable aggregate consists of clean, 

uncoated particles of proper size and 

gradation, shape, physical soundness, 

hardness and strength, and chemical 

properties. The final use of the aggregate 

determines the specific properties sought. 

Generally, specifications for aggregate used 

in cement concrete or bituminous mixes are 

more stringent than are those for other 

construction-related uses. 

Mechanical sieving or screening is used 

to grade, or sort to size, aggregate. In 

general, aggregate for cement concrete 

should be well graded throughout the sand 

and gravel range of particle sizes, although 

gap grading (aggregate with specific particle 

sizes missing) may be used and may be 

necessary for some products. Specifications 

for bituminous mixes are dependent on the 

pavement design, and therefore no general 

statement can be made regarding the sizes of 

aggregate used. 
Particle shape affects both the grading 

limits of aggregate used in cement concrete 

and the workability of the concrete. The 

presence of excessive amounts of angular 

particles can require addition of a greater 

percentage of sand to the mixture, which in 

turn requires more water and cement. In 

contrast, because intergranular contact 

provides strength in bituminous mixes, 

angular particles generally are desirable. 

Smooth particle surfaces offer little assistance 

in holding the aggregate in place in 

bituminous mixes. In both cement concrete 

and bituminous mixes, too many flat or long 

particles may be harmful. 

Physical soundness is the ability of 

aggregate to resist weathering, particularly 

freezing-thawing and wetting-drying cycles. 

Generally, aggregate that contains weak, 

easily broken, absorptive, or swelling 

particles is not suitable. Specifications for 

physical soundness are similar for use in 

cement concrete and bituminous mixes. 

Hardness and strength of aggregate 

affect the ability of the final product to resist 

mechanical breakdown. The breakdown of 

soft or weak particles during handling or 

mixing is deleterious in both cement concrete 

and bituminous mixes. Such breakdown 

affects the grading of the aggregate, and it 

can be aggravated by weathering or traffic. 

Specifications for hardness and strength of 

aggregate are similar for use in cement 

concrete and bituminous mixes. 

Ideally the aggregate is an inert filler, 

and it should not change chemically once in 

place. However, some aggregate contains 

minerals that chemically react with or 

otherwise adversely affect the concrete or 

bituminous mixes. In cement concrete, these 

chemical processes are reactions between the 

aggregate and the cement, solution of soluble 

materials, or oxidation of 

constituents. In bituminous 

mixes, chemical factors may 

influence oxidation of the 

asphalt or strip the bituminous 

film from the aggregate. 

When aggregate does not 

meet the required 

specifications, a number of 

corrective alternatives exist. 

These include (1) blending 

high-quality aggregate with 

the unsuitable aggregate to 

achieve an acceptable overall 

quality; (2) removing 

deleterious materials from the 

aggregate by processing 

techniques; (3) making 

adjustments during 

processing, such as recrushing 

to change particle shape; or (4) 

adding chemicals or making 

other adjustments to cement 

mixtures or bituminous mixes. 

BUILDING AMERICA'S FUTURE ~ 

GEOLOGY 

Sources of aggregate, such as sand and gravel and rock for crushed stone, were 

formed by geologic processes. Volcanoes, glaciers, wind, rivers, and seas formed the 

shape and character of rock materials over millions of years. The gravel used today 

may have been deposited thousands of years ago-just yesterday geologically. Hard, 

dense limestone may have been deposited as a limy ooze hundreds of millions of 

years ago. When an aggregate supply is required, geological investigations can 

determine the location, distribution, and nature of potential aggregate in an area. 

SAND AND GRAVEL 

Sand and gravel deposits are products of erosion of bedrock and surficial 

materials and the subsequent transport, abrasion, and deposition of the particles. 

The principal geologic agent that affects the distribution of deposits of sand and 

gravel is water. Consequently, gravel is widely distributed and abundant in 

glaciated areas, in alluvial basins, and in, adjacent to, or near rivers and streams. 

Windblown deposits generally are fine grained and rarely are used for aggregate. 

STREAM-CHANNEL AND TERRACE DEPOSITS 

Sand and gravel deposited by rivers or streams is widely distributed throughout 

the United States as stream-channel or terrace deposits. In hilly or mountainous 

areas, bedrock is chemically and physically weathered and is progressively broken 

into smaller and smaller particles. Chemically less resistant minerals are dissolved or 

altered into clay minerals; the more resistant minerals remain as rock fragments. 

Depending on the composition and structure of the bedrock and on the climate, land 

cover, and topography, the remaining soils may range in thickness from almost 

nothing to many tens of feet, and may range in composition from nearly all clay, 

through mixtures of clay, silt, sand, and gravel, to nearly all sand and gravel, to 

rubble. Gravity and sheetwash move some of this material downslope, where it 

forms a deposit called colluvium. Eventually the colluvium is moved into valleys of 

relatively high gradient streams. In the stream channels, rock fragments are 

subjected to abrasion, rounding, and sorting. The stream-transported material is 

deposited in channels and on floodplains and consists of sand and gravel in some 

areas and silt and clay in others. 

Aggregate occurs where nature 

placed it, not where 

people need it. 

Erosion can alter an already-established floodplain. If the river or stream incises 

its channel, the older channel and floodplain deposits are preserved as terraces. 

Repeated downcutting can result in the formation of a series of terraces or terrace 

remnants. 
GLACIAL DEPOSITS 

Many of the extensive sand and gravel 

deposits in the northern parts and higher 

elevations of the United States are products 

of either continental or alpine glaciation. As a 

glacier advances over the land surface, it 

erodes the surficial materials and underlying 

bedrock, depositing till, which is a nonsorted 

or poorly sorted mixture of clay-size to 

boulder-size particles. As the ice melts, rock 

particles that had been crushed and abraded 

by the ice are transported by meltwater. As 

these particles are carried along, they are 

further abraded and sorted. Angular 

NATURAL AGGREGATE 

fragments are rounded, and weak particles 

are broken into smaller pieces. Finer 

materials are carried away and deposited in 

lakes and ponds (glaciolacustrine deposits), 

while the coarser sand and gravel is 

deposited in and along the stream channels 

(glaciofluvial deposits). Glacial erosion and 

deposition are complex dynamic processes. 

Hourly, daily, and seasonal temperature 

changes and longer term climatic changes 

affect the rate of melting and the volume of 

meltwater. The particle size of glaciofluvial 

deposits, therefore, varies greatly, both 

areally and with depth, and the deposits 

accumulate in diverse topographic settings. 
ALLUVIAL-FAN DEPOSITS 

In the arid and semiarid Western United 

States, many valley basins contain thick 

deposits of unconsolidated alluvium. 

Alluvium (detrital material consisting of clay, 

silt, sand, or gravel) is eroded in the adjacent 

mountains and is transported to the basins 

during infrequent but torrential floods 

(typical of desert environments) down steepgradient streams. On reaching the basins, 

the water spreads out of the channel and 

infiltrates into the ground. The sudden 

change in gradient and reduced transporting 

capacity causes deposition of sediment, 

producing alluvial fans. Generally, the 

coarsest detrital material is deposited 

adjacent to the mountains. Deposition 

becomes progressively finer in the alluvial 

valleys toward the center of the basins. In 

time, the fans formed in adjacent valleys 

coalesce to form continuous thick deposits of 

alluvium. 

BUILDING AMERICA'S FUTURE ~ 
CRUSHED STONE 

Bedrock is classified in three main 

groups, based on its origin: sedimentary, 

igneous, and metamorphic. The sedimentary 

rocks limestone and dolomite make up about 

71 percent of current crushed-stone 

production. Igneous rocks, generally 

referred to in the aggregate industry as 

"granite" or "traprock" (basalt or diabase), 

compose 14 percent and 8 percent of crushed 

stone, respectively. Metamorphic rocks, such 

as gneiss, marble, or quartzite also are used 

and, together with other miscellaneous stone, 

account for the remaining 7 percent. 

Sedimentary rocks were formed by 

consolidation of loose sediment by chemical, 

biochemical, or mechanical processes or by 

direct chemical precipitation. Chemically or 

biochemically deposited sedimentary rocks, 

such as, hard, dense limestones and 

dolomites (calcium or calcium-magnesium 

carbonates), generally are good sources of 

crushed stone. Some limestone and 

dolomite, however, is too soft, absorptive, or 

friable to yield high-quality aggregate. 

NATURAL AGGREGATE 

Chert and flint are silicate rocks that 

were precipitated in water by organisms 

such as sponges. These rocks may be 

crushed for aggregate, but they may cause 

adverse reactions, such as cracking and 

scaling, in cement concrete. 

Clastic (mechanically deposited) 

sedimentary rocks are classified according to 

the sizes of individual particles. Rock that 

consists mostly of pebbles and larger size 

fragments is conglomerate; rock that consists 

mostly of sand-sized particles is sandstone; 

and rock that consists primarily of silt- or 

clay-sized particles is siltstone or shale, 

respectively. Of these rocks, hard, dense 

sandstone is the only type that generally is a 

source of crushed stone. In areas where no 

other material is available, it is a major 

source of aggregate, but it constitutes less 

than 3 percent of the total U.S. aggregate 

production. 

Igneous rocks solidify from a molten or 

partly molten state and are classified further 

by their origin. Intrusive igneous rocks 

solidify at depth within the earth and have 

coarse mineral crystals, owing to the slow 

cooling associated with 

deep burial. Light-colored 

intrusive igneous rocks 

commonly are referred to 

as "granite" in the 

aggregate industry. 

Extrusive igneous rocks 

solidify at or near the 

earth's surface and 

generally are composed of 

small or microscopic 

crystals that were formed 

by rapid cooling. Such 

rocks frequently are 

referred to as "traprock" in 

the aggregate industry. 

Igneous rocks that are 

hard, tough, and dense 

commonly are excellent 

sources of crushed stone. 

However, some are very 

friable and others are very 
porous. Some siliceous igneous rocks react 

deleteriously when used as aggregate in 

cement concrete. 

Metamorphic rocks form when existing 

rocks are subjected to heat and pressure 

within the earth. Common metamorphic 

rocks are slate, schist, gneiss, marble, and 

quartzite. Of these, only gneiss, marble, and 

quartzite commonly are used as aggregate. 

ALTERNATE SOURCES 

OF AGGREGATE 

In areas where natural 

aggregate is not economically 

available, does not meet physical 

or chemical specifications, or is 

preempted by land use or 

regulations, various other 

materials may be used as 

aggregate to avoid excessive 

transportation costs. 

Natural materials such as 

shells (as shown at the upper 

right), "clinker" (bedrock that was 

baked or melted by underground 

coal fires), and caliche (calcium 

salts) have all been substituted 

for crushed stone or sand and 

gravel. Aggregate can be 

manufactured from clay and 

shale expanded by firing. In 

addition, certain types of waste 

have even been used, including 

blast furnace slag, steel slag, ash, 

coal refuse, mine tailings, waste glass, and 

shredded rubber tires. 

Recycling cement concrete (shown in 

photograph and inset below) and asphalt 

(bituminous mix) currently is a viable 

alternative for natural aggregate, and can be 

both economically and environmentally 

beneficial. In some States, recycling is either 

encouraged or required. 

--

BUILDING AMERICA'S FUTURE ~ 
AGGREGATE REGIONS OF THE UNITED STATES 

Natural aggregate occurs where nature placed it, not where people need it. To concisely describe aggregate 

availability and quality in the United States, this report divides the country into 12 regions. In general, each 

region has similar occurrences of aggregate within its boundaries but is fairly distinct from other regions. 

Those regions where natural aggregate is abundant are shown in green. Regions shown in blue are where 

NATURAL AGGREGATE 

TOPOGRAPHY 

II WesternjMountain Ranges 

Tall, massive mountains alternating with relatively narrow, steepsided valleys. Larger valleys may have higher terraces. 

II Basin and Range 

Alternating basins or valleys and mountain ranges. 

II Columbta Plateau 

Gently sloping plateau underlain by a thick sequence of extensive 

lava flows separated by soil zones and interbedded sediments. 

II Colorado Plateau and Wyoming Basin 

High plateaus with deeply incised canyons, mountains, deserts, 

and badlands. Erosion has produced extensive, prominent cliffs. 

II 

II 

II 

II 
natural aggregate occurs in limited, but generally adequate, quantities; some areas may be devoid of aggregate. Regions shown in purple are where aggregate occurs in very limited quantities; large areas may be devoid of aggregate. In any region, quality problems can limit the use of aggregate, and conflicting land use, 

regulations, and other social and economic factors can restrict aggregate development. It should also be noted that these regional divisions are extremely simplified, and are intended only for general reference. 

CRUSHED STONE RESOURCES 

Mountains are underlain by igneous and metamorphic rocks, flanked by consolidated sedimentary rocks including some limestones. Potential 

sources of good-quality crushed stone are generally available 

The mountain ranges are commonly underlain 

by igneous, metamorphic, and consolidated sedimentary rocks. Potential sources of good quality 

crushed stone are generally available. 

The northern part of this region commonly is 

underlain by basalt that is generally a suitable 

potential sources of crushed stone. The southern 

part is underlain by basalt and other igneous 

rocks, some of which have physical or chemical 

properties that do not yield good aggregate. 

Generally underlain by poorly consolidated to 

consolidated sandstone, shale, and limestone, 

with the sandstone and shale being most prevalent and most extensive. In places the rock units 

contain significant amounts of gypsum or halite. 

The soft sandstone and shale tend to afford poorquality crushed stone. 

SAND AND GRAVEL RESOURCES 

Stream-channel or terrace deposits and limited 

glaciofluvial deposits are present. Quality problems tend to be localized. 

Large alluvial basins commonly contain extensive deposits of poorly sorted sand and gravel 

deposits. In addition, terraces and beaches found 

on mountainsides consist of well-sorted sand and 

gravel. Some areas are deficient in sand and 

gravel. Quality problems tend to be localized. 

Stream-channel, terrace, and glaciofluvial deposits are well distributed throughout the northern 

parts of the region. In the rest of the region, sand 

and gravel are rather limited, commonly being 

restricted to river and terrace deposits. Many 

gravel deposits have chemical and physical properties that do not yield good aggregate. 

Stream-channel, terrace, and glaciofluvial deposits occur along parts of the valleys of major 

streams, especially adjacent to the mountain 

ranges in the northern and eastern parts of the 

region. In the remainder of the region sand and 

gravel is generally limited to alluvium and terraces. Gravel commonly is derived from the erosion of soft sandstone or shale, and tends to be of 

poor quality. 

BUILDING AMERICA'S FUTURE ~ 
NATURAL AGGREGATE 

TOPOGRAPHY 

II High Plains 

Large, flat, gently eastward-sloping plain. Significant topographic 

features include sand dunes and wide valleys of braided streams 

that flow from the Rocky Mountains eastward across the plain. 

II N onglaciated Central Region 

Topographically complex region including lowlands and plains as 

well as hilly and mountainous areas. 

II Glaciated Central Region 

Flat plains, rolling hills and low rounded mountains. 

Glaciated Northeastern and Superior Uplands 

Rolling hills and low mountains. 

II 

II 

II 
CRUSHED STONE RESOURCES 

Bedrock consists of soft semiconsolidated sediments, almost all of which is unsuitable for use as 

crushed stone. 

Most of the northern part of the region and the 

part of the region flanking the Rocky Mountains 

is underlain by sedimentary rocks consisting 

mostly of sandstone, shale, and conglomerate. 

With the exception of scattered limestone, these 

rocks generally are poor sources of crushed 

stone. Most of the south-central region is underlain by limestone and dolomite. These rocks commonly yield suitable sources of crushed stone, 

although the presence of chert and other deleterious minerals may restrict certain uses. 

Bedrock consists of consolidated sedimentary 

rocks including sandstone, shale, limestone, and 

dolomite. These rocks are most prevalent in the 

central part of the area and are less prevalent in 

the east. The western parts of the region generally lack limestone or dolomite, and generally 

have inadequate sources of crushed stone. 

Throughout the region, even where suitable bedrock exists at depth, the thickness of overburden 

may be too great to extract the rock economically. 

Bedrock consists primarily of granite, syenite, 

anorthosite, and other intrusive igneous rocks 

and metamorphosed sedimentary rocks consisting of gneiss, schist, quartzite, slate, and marble. 

Most igneous rocks make suitable sources of 

crushed stone. The characteristics of metamorphic rocks vary widely, with the schists and slates 

commonly lacking the strength and shape characteristics for desirable crushed stone. 

SAND AND GRAVEL RESOURCES 

Stream-channel and terrace deposits of the major 

rivers and their tributaries. Deposits generally 

are progressively finer downstream from the 

mountains and commonly are deficient in coarse 

sizes. Gravels frequently have chemical or physical properties that do not yield good aggregate. 

The land surface in most of the region is overlain 

with a residual soil formed by the chemical and 

mechanical breakdown of the bedrock. The residual soils in the western part of the region are 

overlain with substantial thicknesses of windblown deposits. Stream-channel and terrace 

deposits are the source of sand and gravel 

throughout the region. The quality of sand and 

gravel is variable and depends on the type of parent material. 

The major sources of sand and gravel aggregate 

are glaciofluvial, stream-channel, and terrace 

deposits. Sand and gravel deposits are generally 

abundant throughout the region. In the northern 

part of the region, much of the aggregate is buried by fine-grained deposits. Aggregate is almost 

completely absent in the Illinois Coal Basin. 

Aggregate from the Missouri River tends to be 

contaminated with deleterious material from the 

underlying soft sandstone and shale bedrock. In 

the Great Lakes area and scattered throughout 

the region, aggregate may contain minerals with 

chemical properties undesirable for certain uses. 

Most of the valleys and other low areas commonly contain stream-channel, terrace, and glaciofluvial sand and gravel. In several areas, the 

unconsolidated deposits consist of clay and silt 

deposited in lakes that formed during the melting of the ice sheets. The major sources of goodquality sand and gravel aggregate are glaciofluvial, stream-channel, and terrace deposits. 

BUILDING AMERICA'S FUTURE ~ 
I 

NATURAL AGGREGATE 

TOPOGRAPHY 

II Piedmont Blue Ridge Region 

The topography of this region is varied and consists of low, 

rounded hills, long rolling ridges, and mountains, and contains the 

highest peaks east of the Mississippi River. 

II Atlantic and Gulf Coastal Plain 

The topography ranges from extensive, flat, coastal swamps and 

marshes occurring near sea level, to rolling uplands occurring near 

the inner margin of the region. 

II Alaska 

A complex area consisting of coastal plains, mountain ranges, and 

intermontane plateaus. 

II Hawaiian Islands 

Islands formed by lava that issued from one or more volcanic eruption centers. The islands have a hilly appearance resulting from 

erosion that has carved valleys into the volcanoes and built relatively narrow plains along parts of the coastal areas. 

II 

II 

II 

II 
CRUSHED STONE RESOURCES 

Bedrock consists of igneous and metamorphosed sedimentary and igneous 

rocks including granite, gneiss, schist, 

quartzite, slate, marble, and phyllite. 

Granite and gneiss are commonly used as 

crushed stone, whereas schist, slate, and 

phyllite are commonly avoided. Potential 

sources of good-quality crushed stone are 

generally available. 

Consolidated bedrock generally is inaccessible in the Coastal Plain region, except 

near the inner margin, and in southeastern Florida, which is underlain by semiconsolidated limestones that are of 

marginal use as aggregate. 

Underlain by a diverse assemblage of 

rocks. The principal mountain ranges 

have cores of igneous and metamorphic 

rocks. These are overlain and flanked by 

sedimentary and igneous rocks. The sedimentary rocks include carbonate rocks, 

sandstone, and shale. 

Each of the Hawaiian Islands is underlain 

by lava flows. Andesite and basalt flows 

are commonly used as a source of crushed 

stone. In addition, clinker from the tops of 

lava flows and cinders from cinder cones 

are also used as stone aggregate. 

SAND AND GRAVEL RESOURCES 

The mountains are bordered by low-gradient streams flowing in relatively narrow valleys. The land surface is underlain by saprolite, which is clay-rich, unconsolidated 

material developed in place primarily from the chemical 

weathering of the underlying bedrock. The valleys are 

underlain by relatively thin, moderately sorted alluvium. 

Stream-channel and terrace deposits are the source of sand 

and gravel throughout the region. Quality problems tend 

to be localized. 

The region is underlain with extensive deposits of semiconsolidated sand, silt, clay, and gravel, with sand being 

the predominant surficial material. Most gravel deposits 

occur near the inner edge of the Coastal Plain and occur as 

stream-channel and terrace deposits. These deposits are 

limited in occurrence and are the primary source of natural 

aggregate in the region. Isolated deposits of beach and terrace gravels are scattered throughout the area. The quality 

of the gravels depends on the parent material. The gravels 

in the Atlantic coastal area tend to be high in quartz and 

other silica minerals, whereas those in the Gulf coastal area 

are calcareous. Coarse materials are so limited in this 

region that shells are commonly substituted for gravel. 

Sand and gravel occur in parts of the Mississippi embayment as isolated terraces. Sand and gravel also occurs at 

depth under the alluvial clays of the Mississippi River 

floodplain. 

Approximately half of the region, including the mountain 

ranges and adjacent parts of the lowlands, was covered by 

glaciers. Glaciofluvial deposits in these areas commonly 

contain sand and gravel. In the intermontane plateaus, 

sand and gravel commonly is mined from stream channels, 

terrace deposits, and placer-mine tailings. The Arctic 

Coastal Plain consists of silt, sand, and gravel, with the 

northeastern part having moderate to high potential for 

sand and gravel. Much of the aggregate is frozen to some 

degree, and excavation requires drilling and blasting. 

In some areas alluvium of older and modern terraces and 

alluvial fans contain poorly sorted sand and gravel of variable quality. In coastal areas a thin layer of coral and shell 

fragments, volcanic debris, and clay form discontinuous 

beach deposits, which may be used as aggregate if they 

meet the required specifications. 

BUILDING AMERICA'S FUTURE ~ 

SUPPLY AND DEMAND 

Each region has a baseline demand for aggregate that responds to a 

continuing need for highway, road, and street maintenance and construction. 

Superposed on this need are requirements of the cities and 

towns-requirements that are proportional to urban size and growth rates. 

Transecting all these requirements are special demands of major construction 

projects such as interstate highways and airports. Such projects often require 

large quantities of aggregate in relatively short periods of time. 

The supply area is controlled by the 

geology of the area, ownership of the land, 

zoning, land use, and transportation. 

Because aggregate is a high-bulk, low-cost commodity, the transportation 

cost to the site of use is a significant part of the total cost. Therefore, natural 

aggregate commonly is used within 30 to 50 miles of the place of extraction. 

Ultimately the supply area is controlled by the geology of the area, ownership 

of the land, zoning or other land-use restrictions, and transportation routes. 

Rural counties and their communities commonly attempt to obtain aggregates 

within their boundaries. In contrast, urban areas generally meet their needs 

from surrounding areas. These urban areas act as distinct markets, and the 

demand for aggregate may greatly exceed the availability of material in the 

surrounding areas. Major construction projects generally need aggregate for 

only certain phases of construction and therefore it may be necessary to 

transport aggregate great distances to guarantee its supply. All of the users of 

aggregate may compete for a supply from the same sources, and major 

construction projects may significantly disrupt an otherwise predictable 

market. 

ESTIMATING SUPPLY 

Potential sources of crushed stone and sand and gravel may be extremely 

large, but specific land-use considerations, socioeconomic considerations, or 

the physical or chemical properties of the materials may limit the utility of 

these sources. Unless the distribution, availability, and quality of aggregate 

are known, it is difficult to formulate a reasonable plan to set aside or develop 

aggregate. Therefore, in planning for future aggregate needs it is necessary to 

determine the reserves for the planning area. 

Even before field investigations begin, a geologist or an engineer with 

geologic experience commonly conducts a preliminary evaluation. In an 

urban area, the maximum economically feasible shipping distance from the 

market area commonly defines a crude target area. In areas where aggregate 

is in short supply, the target area obviously must be much larger. Geologic 

and topographic maps and geologic and engineering reports aid in targeting 

promising areas or, conversely, aid in ruling out areas for further study. State 

geological surveys and highway departments and the U.S. Geological Survey 

can provide much of this information. 
Preliminary investigations may be 

followed by detailed studies involving 

aerial photography, geophysical 

studies, and field reconnaissance 

studies (as shown in the photographs 

at right) of the target areas to more 

accurately define the limits of the 

potential sources of aggregate. These 

field studies focus on natural 

exposures such as stream cuts, cliffs, 

and other natural outcrops, and on 

artificial exposures such as highway 

and railroad cuts and abandoned or 

active pits and quarries. These studies 

commonly are augmented by the use 

of hand-sampling techniques and 

portable power-auger or coring 

equipment. Also important are rough 

estimates of the areal extent and 

volumes of the deposits, as well as 

specific physical or chemical 

properties of the materials. 

Laboratory analyses provide 

additional information about the 

physical and chemical properties of 

specific samples. Field observations 

should include information related to 

mineralogy and texture of the 

materials, thickness of overburden, 

water availability, and road access to 

the area. 

Detailed exploration of an 

identified source of aggregate may 

vary depending on the nature of and 

intended uses of the aggregate. 

Bulldozers, loaders, or backhoes are 

used to collect bulk samples; bulk 

sampling of bedrock may require 

drilling or blasting. Truck-mounted 

power augers or drill rigs can be used 

to collect deeper underground 

samples. In addition, seismic 

refraction may be used to determine 

the thickness of overburden and 

thickness of desired material, and 

electrical resistivity may be used to 

determine gross textural changes 

within the deposit, such as changes 

from gravel to sand or shale to 

sandstone. 

NATURAL AGGREGATE 

ESTIMATING DEMAND 

The U.S. Bureau of Mines and State and 

local agencies monitor the production of 

natural aggregate. One purpose of this 

monitoring is to provide data that can be 

used to project future needs. The production 

of aggregate, by itself, is relatively 

meaningless as a predictive tool. To improve 

forecasting techniques, a contingency 

analysis of the factors that could cause the 
demand to deviate from its current trend 

commonly is performed. Because crushed 

stone and sand and gravel are used mostly in 

the construction industry, reasonable 

estimates of the future demand for natural 

aggregate are based on predictions of future 

construction, such as the number of 

residential and nonresidential buildings, 

highway award contracts, and public 

construction products. Other factors 

commonly used to predict future aggregate 

production include population, employment, 

personal income, mortgage rates, and State 

or National gross domestic product. These 

factors can be compared, singly or in 

combination, to past and present aggregate 

production to determine if correlations exist. 

The objective is to find a socioeconomic 

factor that is predictable, and then to use it 

as a surrogate for predicting future aggregate 

production. 

(j) 

z 

0 

II-

([ 

0 

I 

(j) 

LL 

0 

(j) 

z 

0 

:J 

_J 

:::2: 

2000 

1500 

1000 

500 

PRODUCTION OF CRUSHED STONE 

AND SAND AND GRAVEL 

(f) 5000 a: 

::5 

-' 0 

~ 4000 C1) 

Q) 

fz 

~ 3000 

(f) 

z 

0 

u 

~ 2000 

(f) 

z 

0 

:::; 

a5 1000 

REAL GROSS 

DOMESTIC PRODUCT 

~~--~--~--~ 

1975 1980 1985 1990 

YEAR 

EXPLANATION 

(f) 

a: 

::5 

-' 

0 

0 

1'-

400 

~ 300 

fz 

<( 

f-

(fJ 

z 

0 

~ 200 

0 

(f) 

z 

0 

:::; 

-' 

ii'i 

100 

CONSTRUCTION 

1975 1980 1985 1990 

YEAR 

----- Crushed stone --+- Sand and gravel ____...._ Total 

YEAR 

BUILDING AMERICA'S FUTURE ~ 

THE AGGREGATE INDUSTRY 

Aggregate is produced from open pits in four major steps: site 

preparation, mining, processing, and reclamation. Site preparation 

consists of (1) clearing trees and vegetation; (2) stripping, transporting, 

and storing topsoil and overburden; (3) constructing fences, berms, 

buffer zones, roadways, and sediment traps; and (4) constructing or 

installing permanent or portable processing equipment. 

MINING AND PROCESSING 

Mining of crushed stone or sand and gravel is dependent on the 

geologic characteristics and the areal extent and thickness of the deposit. 

Open-pit mining and quarrying commonly are used, although some 

stone is mined underground (as shown in the photograph on the 

following page). Sand and gravel deposits above the water table may be 

excavated with conventional earth-moving equipment such as 

bulldozers, front-end loaders, tractor scrapers, and draglines. Deposits 

below the water table, including stream and lakebed deposits, may be 

The most acceptable method for 

the community and the producer is 

to plan mining and reclamation 

before the aggregate is extracted. 
excavated with draglines or from 

barges using hydraulic or ladder 

dredges. Mining and quarrying stone 

generally requires drilling and blasting, 

after which the rock is extracted with 

power shovels, bulldozers, and 

draglines. The broken rock or the sand 

and gravel is then transported to a 

processing facility on trucks or 

conveyors. 

Processing plants are generally 

constructed on the site of extraction, 

but for some short-term projects the 

operator may utilize portable 

processing equipment. Processing of 

mined or quarried rock requires 

primary and possibly secondary 

crushing, depending on the sizes of 

aggregate needed. After crushing, 

crushed stone and sand and gravel 

usually are sorted to size. Silt and clay 

are removed by washing. At this stage, 

the coarser aggregate commonly is 

moved by conveyors (as shown at 

lower left) to bins or is stockpiled by 

size. Finally, aggregate is blended to 

the proportions of each particle size 

specified by the user (as shown at 

lower right). In some areas where the 

demand for aggregate is significant but 

production is impractical or 

uneconomical, producers set up 

distribution yards. Aggregate is moved to these yards by bulk transportation methods and 

subsequently is blended for final use and distribution . 

NATURAL AGGREGATE 

. ... . . . • • u4: • r 

. ~ 

..... 'I' ... •"n 

' 

. 
TRANSPORTATION 

The three principal types of 

transportation are road, rail, or water. 

Aggregate is either used at the site of 

extraction (such as in cement concrete or 

bituminous mixes) or is transported to the 

point of use. The preferred mode of 

transportation depends on a variety of 

factors, including delivery-schedule 

requirements, the distance to be hauled, the 

volume of material, loading and unloading 

facilities, and the availability of 

transportation methods. 

Transport by truck is by far the most 

common method. Trucks can quickly and 

simply be loaded at points of origin and can 

dump or drop their loads unassisted at the 

destination. They are not restricted to 

railways or waterways and can deliver 

practically anywhere there is a road. Trucks 

from small pickups to rigs that carry 28 tons 

can be matched to requirements and thus can 

make deliveries without great economic 

consequences. 

If pits or quarries have access to 

railroads, rail delivery may be more 

economical than truck delivery. The choice 

depends on two principal variables-the 

tonnage of aggregate to be moved and the 

distance it must be hauled. Other factors to 

be considered are loading and unloading 

facilities and schedule requirements. If the 

aggregate shipped annually exceeds 20,000 

short tons, or if the aggregate is to be hauled 

more than 45 miles, rail shipping may be 

more economical than truck transport. With 

greater tonnages and distances, the 

advantages of rail shipment are even greater. 

Aggregate can be loaded on either 100-ton 

bottom-dump hopper cars or gondolas and 

moved in single cars (the most expensive 

way to ship by rail), or can be joined and 

moved as multiple cars, by trainloads, or by 

unit trains (the least expensive way). 

The midcontinent of the United States 

has many navigable rivers that have been 

modified to permit movement of freight by 

water. Moving aggregate by hopper or flat 

deck barges may be economical. Because the 

movement of aggregate by water is not 

regulated by government agencies, the rates 

are established by agreements between the 

user and the barge line. As with rail 

transport, economic advantages of shipping 

by barge increase as the tonnages and 

BUILDING AMERICA'S FUTURE ~ 
distances of transport increase. Hopper 

barges commonly hold 1,500 tons of 

aggregate and can be grouped into tows of 

30 to 40 barges, depending on the width and 

depth of the river to be traveled and the size 

and horsepower of the tow boat. 

Lake or ocean freighters only recently 

have become an efficient means to transport 

aggregate. Along the Atlantic and Gulf 

Coasts of the United States, where local 

supplies of good quality aggregate are in 

short supply, aggregates are imported from 

Mexico, Scotland, Canada, and other foreign 

countries. Transportation by ship is possible 

in part because of back-haul pricing. A 

commodity other than aggregate moves one 

way, and pays most of the cost of round-trip 

shipping. After unloading the initial 

commodity, the ship is loaded with 

aggregate for the return voyage. 

Transporting the aggregate on the return 

voyage at a low price prevents the vessel 

from returning to the point of origin with an 

empty hold. 

NATURAL AGGREGATE 

RECLAMATION 

Reclamation of a mined-out area is 

highly important to communities near 

aggregate operations because residents do 

not want a scarred landscape near their 

property. The most acceptable method for 

the community, and commonly the most 

economical for the producer, is to plan 

reclamation before the aggregate is extracted. 

Aggregate can be mined with the final landsurface contours in mind, equipment can be 

used for both mining and reclamation, and 

mined-out areas can be reclaimed concurrent 

with extraction in other parts of the 

operation. 

The primary goal of reclamation is to 

return the land to a beneficial use. 

Residential developments are a popular use 

for reclaimed sites. The natural setting 

provided by rock outcrops and water fulfill a 

demand for scenic, lake-front property. 

Reclaimed pits or quarries have also been 

converted to industrial and commercial 

properties or to office parks, golf courses, 

parks and recreation areas, storm-water 

management, farmland, and landfills. 
Reclamation procedures depend on 

the configuration and character of the 

mined-out area. Progressive reclamation 

typically involves the following steps: (1) 

terracing the pit or face walls during or 

after extraction, (2) final shaping of the 

worked out area by replacing and 

recontouring the overburden, and (3) 

landscaping. Reclamation plans are most 

effective if operators and planners select 

a strategy that satisfies the land use 

needs of the community and at the same 

time provides an economic incentive for 

the operator. 

BUILDING AMERICA'S FUTURE ~ 

PLANNING AND REGULATION 

D EVELOPMENT 

Although nature dictates the location of natural aggregates, other factors 

influence the development of the resource. Prime aggregate sources are lost if 

parking lots, houses, or other buildings are constructed over the resources. 

Aggregate operations that were initially established in rural areas commonly 

are terminated when residential land use encroaches on the operations. 

Valuable lessons can be learned from areas in which development has engulfed 

aggregate sources that originally were distant from communities. 

Citizens frequently consider aggregate operations to be a nuisance, and 

they wish to be protected from aggregate development near their communities. 

Aggregate development may create temporary environmental impacts such as 

increased airborne particulates, increased sediment yield to streams, and 

increased noise levels. Permanent impacts may result from major changes to 

the landscape. Increased truck traffic is both an environmental concern (dust 

and noise) and a safety concern (traffic congestion and hazards). For these and 

other reasons, many levels of government may impose regulations that must be 

accommodated before development can begin. 

Cooperative planning by developers, 

government, and citizens is the key 

to successful protection and 

utilization of aggregate resources. 

However, a continuing and uninterrupted supply of aggregate is an 

indisputable need. In meeting that need, aggregate operators must address 

other factors in addition to the societal and regulatory factors. For economic 

reasons, aggregate operations must be within reasonable distances of the 

market area. Zoning that permits extraction of the aggregate is necessary. 

Other land uses that preclude extraction of aggregate must be evaluated, and 

in some cases revision of zoning may be necessary. 

When natural aggregates are mined, they probably will not be used 

exclusively in the community that produces them. The benefits of 

development are likely to be dispersed throughout a market area of many 

hundreds of square miles, but most, if not all, of the problems associated with 

extraction will be concentrated within a few miles of the aggregate operation. 

The local community may enjoy few of the benefits while enduring most, if not 

all, of the undesirable side effects. On the other side of the issue, however, if 

extraction is denied in favor of local interests, the consumers within the market 

area may be denied the resource at a reasonable cost, and the region may 

sustain greater, more widely dispersed environmental and economic costs. For 

example, the denial of a local operation on the basis of truck traffic may 

actually increase truck traffic because of longer haul routes from distant 

aggregate sources. Furthermore, increased traffic consumes more energy, 
increases emissions, increases wear-and-tear 

on equipment and highways, and increases 

exposure to the risk of traffic accidents. 

Planning for and developing adequate 

supplies of aggregate thus is a complicated 

process, balancing the needs of a region for 

aggregate resources with the needs of the 

local community, and requires enlightened 

planning, resource protection, and 

regulation. Basic data related to aggregate 

resources provide a basis for decisions 

related to the locations, volume, and quality 

of potential aggregate in the planning area, 

and possibly an estimate of future needs. 

Plans then can contain provisions that 

balance the regional needs for aggregate with 

the protection of the environment and the 

right of the public to minimize operational 

nuisances. 

RESOURCE PROTECTION 

One step to ensure a continuing and 

uninterrupted supply of aggregate is to 

identify and protect existing aggregate 

resources. This is particularly important not 

only where supply is limited but also in 

high-demand areas, even where sources of 

aggregate are abundant. Some short-term 

and long-term techniques can be used to 

preserve aggregates. 

All sites of potential aggregates cannot 

be protected. Protection of several separate 

sites 10 miles or so apart, instead of one very 

large site, minimizes future hauling costs, 

stimulates competition among industry 

operators, and hedges against the possibility 

of successful local resistance to development 

of any specific site. 

Aggregate resources commonly are 

protected by zoning regulations. Potential 

areas of aggregate development are included 

in existing use districts that are compatible 

with mining, such as agricultural, industrial, 

or open space. However, zoning commonly 

permits a variety of land uses and can be 

changed at any time in the future. Other 

permitted uses that exclude aggregate 

development can be implemented in a 

NATURAL AGGREGATE 

specific zone and can exclude an area from 

further consideration for mining. Therefore, 

zoning tends to be effective only for sites that 

are likely to be developed in the near future. 

Longer term techniques to protect 

aggregate resources involve actions that 

clearly identify the land for aggregate 

extraction. 

• Operators can purchase or lease the land 

and a surrounding buffer area. 

• Local governments can directly reimburse 

land owners or offer tax incentives in 

return for an agreement to delay 

development for other purposes until 

after aggregate is removed. 

• Local governments can buy resources for 

later resale to operators, a plan called 

"land banking." 

• Local governments can regulate land use 

by designating "resource conservation 

areas" or "extractive-use districts" 

whereby only aggregate extraction is 

permitted and all other uses are 

controlled through conditional use or 

special exception. 

• When aggregate sources to be protected 

are identified, they are placed in an 

overlay zone. The land is then subject 

to both the original zoning 

requirements and regulations that 

protect the extractive overlay zone. 

Planning can include efforts to make 

aggregate extraction more beneficial to the 

local residents. A sequential-use process can 

dedicate mined-out land to the community 

after extraction and reclamation have been 

completed. Extraction can be made more 

beneficial to the local area if a severance tax 

is returned to the local area or if 

development of recreational or other public 

facilities follow extraction. Other means are 

available to protect local communities from 

nuisance of extraction. Development rights 

can be transferred to permit higher density 

development in residential areas away from 

aggregate extraction in exchange for forgoing 

residential development near extraction sites. 

In essence, this expands the buffer zone with 

no net loss in residential development. 
D 

Extraction precluded by development 

D 

Site of previous extraction 

D 

Current extraction pe rmit 

D 

Owned open space 

D 

Designated open space 

D 

Potentially first-class sand and gravel deposit 

D 

Potentially extractable lowe r class sand and 

gravel deposit 

A'·" -- \,..\ - - I 

--. 

l 

L I 

""' - : ....... 

iu. 

~'-'~ 

'!' ll "' 

5)19 

Huz~ L 1 ,_, 

F rom J. A . Pend leton, city geologist, Boulder, Colorado (mapping scala 1 · 12.000) 

Sand and gravel planning map for part of the Boulder, Colorado, urban area 

BUILDING AMERICA'S FUTURE ~ 
LIVING WITH 

AGGREGATE OPERATIONS 

To design guidelines or regulations for 

crushed stone or sand and gravel operations, 

it is necessary to predict what effects such 

operations may have on the surrounding 

communities and environment. Regulations 

should set minimum operational standards 

to control impacts such as noise, traffic, dust, 

pollution of streams and water supplies, and 

erosion. The task for planners is to balance 

the needs of the operators with the public's 

right to minimum nuisance resulting from 

the extraction. Aggregate operators 

generally wish to be good neighbors and are 

willing to cooperate if cooperative efforts 

lead to a more smoothly operating facility. 

In fact, many innovative actions taken to 

decrease environmental impacts have been 

conceived and voluntarily implemented by 

aggregate operators. 

Planning efforts such as those described 

above help to limit public exposure to the 

NATURAL AGGREGATE 

impacts of aggregate mining and processing. 

Buffer zones, in particular, help mitigate 

impacts. Regulations or permits should set 

minimum standards for buffer-zone widths. 

Buffer zones shield adjacent residents and 

land owners from mining operations and at 

the same time protect mining operations 

from intrusion or adjacent land-use conflicts. 

Berms, fences, screens, dense tree plantings, 

or other barriers contribute to public safety 

and provide aesthetic controls that help to 

screen objectionable views. Newly exposed 

rock faces can be treated to match adjoining 

naturally weathered surfaces. 

Excavation of sand and gravel below the 

water table can affect aquifers. Regulations 

may prohibit penetration of the aquifer or 

may allow penetration of the aquifer only if 

operations will not adversely affect water 

supplies. If such excavations are to be 

refilled, the filling should meet waterpollution-control standards. 

The impact of noise depends on adjacent 

land use; noise can be mitigated through the 

use of buffer zones, berms, and muffling 
equipment. Noise-generating equipment 

(such as the primary crusher shown in the 

photograph to the right) can be placed near 

the middle of the site, in pits below grade, in 

sound-insulated buildings, or away from 

residential areas. Haul roads can be kept 

away from property lines, and the use of 

conveyor belts can minimize traffic within 

the site. 

Truck traffic is one of the most serious 

problems associated with aggregate 

development. Some traffic can be mitigated 

at the site. Operators can be required to 

provide acceleration and deceleration strips 

on both sides of all entrances and exits to the 

operations. Paving and limiting the number 

of entrances and exits and wheel washing 

procedures can minimize the amount of dirt 

deposited by trucks on adjacent highways. 

The most serious problems associated with 

truck traffic-noise and safety problems-are 

on public rights-of-way. Conveyors 

constructed to carry aggregate under 

highways, reduced speed limits, restriction of 

routes for truck traffic, and restriction of 

hours of operation all can help minimize 

traffic problems. 

Dust can be reduced by minimizing the 

amount of area mined at any time, by 

planting vegetation or constructing other 

wind breaks, by using wet or chemical dust 

suppression systems, and by enclosing dustgenerating equipment in vacuum-equipped 

buildings (such as those shown in the 

photograph below). Erosion can be 

controlled through techniques such as 

settling ponds and revegetation. 

Reclamation plans can require the land 

to be left as originally contoured, or they can 

provide for acceptable final uses of the land. 

Performance bonds can be required to ensure 

that reclamation takes place according to 

plan. Contemporaneous mining and 

reclamation can reduce the impact of mining, 

accelerate revegetation, and allow 

incremental bond release to the operator. 

Cooperative planning by developers, 

government, and citizens is the key to 

successful protection and utilization of 

aggregate resources. 

BUILDING AMERICA'S FUTURE ~ 

SUMMARY 

Present annual aggregate use in the United States is about 9 short tons for every 

person. This tonnage will increase as the aging infrastructure requires repair or 

replacement. Coupled with the demand for the resource, there also is an increasing 

demand for increased economy in large construction projects and for decreased cost in 

housing development. 

Provisions for uninterrupted future supplies of aggregate should be made. Even 

though potential aggregate sources are widely distributed throughout the United States, 

some areas lack quality aggregate, or potential aggregate may be covered by overburden 

so thick that surface mining is impractical. Economic factors require that pits and 

quarries be near population centers. However, citizens and regulatory agencies in 

residential communities commonly desire that mining operations be conducted far from 

their boundaries. Furthermore, citizens commonly do not support mining because they 

do not recognize the community dependence on natural aggregate. They purchase 

little, if any, aggregate and do not recognize that aggregate mining is a necessary land 

use. 

Proper long-range planning can help assure adequate supplies of aggregate, while 

simultaneously protecting the public from the unwanted effects of mining. Long-range 

plans should incorporate a multiple land-use program that includes identification and 

protection of natural resources, strategies that will permit development of resources in 

relation to future market needs and environmental considerations, and a beneficial use 

of mined-out areas. 

Geologic maps and surveys provide useful information about potential aggregate 

sources. Judicious use of these sources is critical in areas where reserves are small or 

where urban pressures preempt their use. By using geologic information to identify 

resources near the sites of use, operators can provide the most economical resource for 

the consumer. Advance planning of haulage routes and conveyor distribution can 

minimize undesired impacts of transportation of aggregate, and application of advanced 

technology can alleviate many other inconveniences of aggregate mining. 

A projected mine plan can diagram stages of an operation over a period of time. 

Adequately planned reclamation can be accomplished concurrent with mining. 

Predetermined uses for the reclaimed land can be mandated so that the final use will be 

beneficial to the community. As land is backfilled and recontoured, it can be converted 

to office parks, public parks, or wildlife habitats for the benefit of people living in the 

area. If land for housing is scarce or expensive, reclamation can provide additional 

home sites, some with lakefront access. 

Mining operators, public officials, consumers, and community residents no longer 

can remain independent of one another. All groups and individuals must work 

together to ensure adequate community and environmental protection from the 

nuisances of mining, while at the same time ensuring low-cost construction and 

maintenance of the infrastructure. 

As we progress into the 21st century, the view of aggregate production must be 

changed from one of a scarred landscape to one of protection of a valuable resource. 

Although natural processes move gravel from one section of a river to another, new 

detrital material is added at an imperceptible rate. Bedrock being formed by geologic 

processes today will not be available for use as aggregate for thousands of years. 

Aggregate mining must be seen as an interim use of the land, not the final use. 
FURTHER READING 

American Society for Testing and Materials, 1980, Annual book of ASTM standards, pt. 

14, Concrete and mineral aggregates: Philadelphia, Pa., 878 p. 

Barksdale, R.D., ed., 1991, The aggregate handbook: National Stone Association, 16 chapters numbered separately. 

Bauer, A.M., 1991, Mineral resources management programs and the construction aggregate industry: Planning and Zoning News (April), p. 5-7. 

Buttleman, C.G., 1992, A handbook for reclaiming sand and gravel pits in Minnesota: 

Minnesota Department of Natural Resources, 65 p. 

Carter, R.A., 1989, Reclamation: A growing concern: Rock Products, v. 92, no. 9, p. 34-40. 

---1989, Reclamation: A regulatory view: Rock Products, v. 92, no. 10, p. 58-74. 

---1989, Landfills can be profitable: Rock Products, v. 92, no. 12, p. 58-62. 

---1990, Planning for second uses: Rock Products, v. 93, no. 1, p. 66-71. 

Cook, C.W., Hyde, R.M., and Sims, P.L., 1974, Guidelines for revegetation and stabilization of surface mined areas in the western states: Colorado State University, Range 

Science Series No. 16, 73 p. 

Crosby, E.J., Hansen, W.R., and Pendleton, J.A., 1978, Applications in a mountain front 

environment, Front Range Urban Corridor, Colorado; guiding development of 

gravel deposits and of unstable ground, in Robinson, G.D., and Spieker, A.M., eds., 

Nature to be commanded: U.S. Geological Survey Professional Paper 950, p. 30-41. 

Dolar-Mantuani, Ludmila, 1983, Handbook of concrete aggregates, a petrographic and 

technological evaluation: Park Ridge, N.J., Noyes Publications, 345 p. 

Kusler, J.A., 1980, Regulating sensitive lands: Cambridge, Ballinger Publishing Co., 248 p. 

Langer, W.H., 1988, Natural aggregates of the conterminous United States: U.S. Geological Survey Bulletin 1594, 33 p. 

Laurence, R.A., 1973, Construction stone, in Brobst, D.A., and Pratt, W.P., eds., United 

States mineral resources: U.S. Geological Survey Professional Paper 820, p. 157-162. 

Law, D.L., 1984, Mined-land rehabilitation: New York, Van Nostrand Reinhold Co., 184 p. 

Mather, K., and Mather, B., 1991, Aggregates, in Kiersch, G.A., ed., The heritage of engineering geology; the first hundred years; Geological Society of America, Centennial 

Volume 3, p. 323-332. 

Mencacci, M.C., and Carter, R.A., 1989, Mine it-reclaim it-bank it: Rock Products, v. 92, 

no. 11, p. 47-57. 

Moore, B.M., 1991, Extraction operations and the comprehensive plan: Planning and Zoning News (April), p. 7-10. 

Pugliese, J.M., Swanson, D.E., Engelmann, W.H., and Bur, T.R., 1979, Quarrying near 

urban areas: An aid to premine planning: U.S. Bureau of Mines Information Circular 

8804,50 p. 

Robnett, Q.L., 1983, Use of marginal waste materials in highway construction-An overview, in Ault, C.H., and Woodard, G.S., eds., Proceedings of 18th Forum on Geology 

of Industrial Minerals sponsored by Indiana Geological Survey and Indiana University, April14-16, 1982, p. 199-211. 

Rock Products, 1989, Reclamation: Planning for success: Rock Products, v. 92, no. 9, p. 

41-47. 

Tepordei, V.V., 1992, Construction sand and gravel: U.S. Bureau of Mines Annual Report 

1990,34 p. 

---1992, Crushed stone: U.S. Bureau of Mines Annual Report 1990,32 p. 

Toy, T.J., and Hadley, R.F., 1987, Geomorphology and reclamation of disturbed lands: 

Orlando, Academic Press, Inc., 480 p. 

U.S. Bureau of Mines, 1991, Mineral commodity summaries: U.S. Bureau of Mines, 196 p. 

Water and Power Resources Service, 1981, Concrete manual: 627 p. 

Werth, J.T., 1980, Sand and gravel resources-Protection, regulation, and reclamation: 

American Planning Association Report 347,33 p. 

NATURAL AGGREGATE 
PHOTO CREDITS 

The authors gratefully acknowledge the following individuals or organizations who 

have contributed photographs or who have helped to obtain photographs for 

this circular. 

Cooley Gravel Company, Denver, Colorado- p. 28 (left), 34 

Jonathan Eady, Littleton, Colorado- p. 20, 25, 36 

Michael J. Hart, Hart & Associates, Boulder, Colorado- p. 4 (center), 13 (lower left, 

lower right), 27 (upper right), 28 (right) 

Luck Stone, Richmond, Virginia- p. 6, 12, 24,35 (top, bottom) 

National Aggregates Association, Silver Spring, Maryland- p. 4 (lower left), 26 (center, lower left, lower right), 27 (lower right), 29 (top), 35 (middle) 

Oklahoma Geological Survey, Norman, Oklahoma- p. 26 (top) 

South Suburban Park and Recreation District, Theo L. Carson Nature Center, Littleton, Colorado- cover, p. 29 (bottom left, bottom right) 

U.S. Bureau of Mines, Washington, D.C.- inside front cover 

U.S. Geological Survey, Photographic Archives Library, Lakewood, Colorado -p. vi, 

4 (top, bottom right), 5 (top, bottom), 7, 8, 10 (top, bottom), 11, 13 (top), 22 (top, 

bottom), 27 (left), 30 

In addition to the photo credits given above, the authors wish to acknowledge the 

following people for their assistance in obtaining photographs for this 

publication: Joseph Andrews, Jr., Luck Stone Corporation, Richmond, Virginia; 

Cheryl Barker, President, The Communicators, Denver, Colorado; Rob Laird, 

Cooley Gravel Company, Denver, Colorado; Richard C. Meininger, National 

Aggregates Association, Silver Spring, Maryland; and Raymond Sperger, South 

Suburban Park and Recreation District, Littleton, Colorado. The authors 

especially wish to acknowledge Albert J. Froelich for the inspiration provided 

by his career-long efforts to apply geology to real-life situations. 

Published in the Central Region, Denver, Colorado 

Manuscript approved for publication March 1993 

Graphics by Ramon E. Sabala and Roger D. Highland 

Editing and design by Robert K. Wells 

Photocomposition by Joan G. Nadeau 

BUILDING AMERICA'S FUTURE ~ 

*U.S. ~ PRIN'l'll[; OFFICE: 1993-0-573-038/86006