U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Preliminary Report on Aggregate Use and Permitting

Along the Colorado Front Range

(On-line version) (On-line version)

Open File Report 00-258

By David R. Wilburn1

 and William H. Langer1

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey

editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or

firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

1

U.S. Geological Survey, Denver, Colorado, 80225-0046
CONTENTS

FIGURES

Abstract 1

Introduction 1

Acknowledgements 2

Types of aggregate resources in the Colorado Front Range 2

Sand and gravel 2

Crushed stone 2

Resource availability 3

Producing aggregates for use 4

History of Colorado aggregate production 5

History of Colorado Front Range aggregate resource accessibility 7

Future production of aggregates 9

Future supply of aggregates in the Colorado Front Range 14

Sand and gravel 14

Crushed stone 16

Recycling 17

Discussion 18

Summary 20

Conclusions 20

References 21

Figure 1. - Index map showing two segments of study area. 2

Figure 2. - Block diagram showing landforms of alluvial deposits in the Colorado Front Range

study area. 3

Figure 3. - Significant events affecting Colorado aggregates use, 1951 - 1997. 5

Figure 4. - Colorado sand and gravel production by region and years. 7

Figure 5. - Colorado crushed stone production by region and years. 7

Figure 6. - Per capita production of aggregates, Denver metroploitan area, 1988 - 1997. 11

Figure 7. - Cumulative production of aggregates, 1998 - 2010, assuming regional use rates

projected for 2000. 12

Figure 8. - Projected annual aggregates use, Colorado Front Range, 1998 - 2010. 13

Figure 9. - Projected cumulative aggregates production, 8-county northern Colorado Front

Range. 13

Figure 10. - Flow diagram showing method to determine permitted aggregate resources. 15

Figure 11. - Cumulative aggregate permitted. 17

Figure 12. - Aggregate permitted each 7-year period, by region. 18

Figure 13. - Aggregate permitted in each region, by year. 18

Figure 14. - Relative amount of aggregate permitted in 2 regions, by 7-year period. 19

Figure 15. - Graph showing per capita aggregate permitted minus per capita aggregate

produced. 19

TABLE

Table 1. - Population data for the northern Colorado Front Range. 10
ABSTRACT

Regional growth, transportation, and land use planning all will be affected by the ability of

the aggregates industry to meet future demand for high quality aggregate resources. Increased

environmental awareness, public opposition, and stricter zoning regulations have made it more

difficult to obtain permits to develop new aggregate mines or expand existing operations in urban

areas such as the Colorado Front Range. Local demand for aggregates in the short term is expected to continue at reasonably high levels due to the projected population growth and associated demand for infrastructure improvements to accommodate such growth.

Although the Colorado Front Range has an abundance of potential aggregate resources,

recoverable resources are coming from greater distances as local resources are becoming inaccessible for extraction. Available resources are becoming more difficult to recover and more expensive to produce due to longer transportation distances, poorer quality of locally available sources,

more involved permitting requirements, and the encroachment of other land uses on undeveloped

potential resource.

The study indicates that the amount of aggregates being permitted has steadily decreased

over time. The Denver metropolitan area has been producing more aggregates than it is permitting since 1991, and the Fort Collins-Greeley area is currently permitting about what it is producing. If this trend continues, aggregate operators may be forced to move to resource areas even

farther away from local markets, resulting in even higher transportation costs. Increased costs

for these aggregates would be passed along to the State or counties as higher construction bids, to

the contractor as higher supply costs, and ultimately to the consumer in the form of higher taxes

or user fees.

INTRODUCTION

Meeting 21st century aggregate demands

on the Colorado Front Range (CFR) will be a

challenge to local suppliers. Regional growth,

transportation, and land use planning all will

affect the ability of the industry to meet future

demand for aggregate resources — high

quality rock and sand and gravel. Where are

our aggregate resources, how much is there,

and how good are they?

Previous studies have addressed these

questions, and have found that the CFR, in

general, is blessed with an abundance of

suitable quality aggregate resources. However, the aggregate resources in the CFR can

only be extracted if the land where the resources exist has been permitted for mining.

In the CFR, permitted resources make up only

a small fraction of the total resource base.

Increased environmental awareness, public

opposition, and stricter zoning regulations

make it difficult to obtain permits to develop

new mines or expand existing operations.

This study, therefore, addresses the question:

“Are aggregate resources being permitted fast

enough to meet the short and long term demand?”

This study investigates the supply and use

of aggregates along the northern portion of the

CFR, extending south from the ColoradoWyoming border to just south of the Denver

metropolitan area, a distance of about 180

kilometers. The area includes the counties of

Adams, Arapahoe, Boulder, Denver, Douglas,

Jefferson, Larimer, and Weld (fig. 1). Because

truck transportation of aggregates over long

distances is expensive, aggregate use is typically local, as long as local sources are available. Ideally, truck haulage of aggregates (the

1
most common mode of transportation) from

source to market seldom exceeds 56 kilometers (Socolow, 1995). Consequently, this

portion of the CFR has been subdivided into

two segments for this study: the Fort CollinsGreeley area and Denver metropolitan area.

Each area is a population center and market

area with a radius of about 56-kilometers.

TYPES OF AGGREGATE RESOURCES

IN THE COLORADO FRONT RANGE

Sand and gravel Sand and gravel

Lindsey (1997) described four general

types of sand and gravel deposits in the Colorado Front Range (fig. 2). These four deposit

types are: alluvial fans, high dissected terraces, terraces, and floodplains and low

terraces. Floodplains and low terraces are the

principal sources of aggregates that are recovered along the CFR. Sand and gravel deposits

underlying the alluvial fans and high dissected

terraces commonly are not used as specification aggregates because of inferior quality.

The surficial geologic units of the study

area are mostly Quaternary in age (up to 2

million years old). During the Quaternary,

some of the mountainous part of the study

area was exposed to repeated glaciations.

Glacial activity provided large amounts of

sediment, as well as meltwater to transport the

sediment to the streams along the CFR.

Consequently, gravel in the CFR area is

largely restricted to major streams with headwaters in the mountains. These streams

include the South Platte River, Clear Creek,

Boulder Creek, St. Vrain Creek, Big Thompson River, and the Cache la Poudre River.

Much of the coarse sediment load was deposited near the mountain front. The amount and

maximum size of coarse material decreases in

a downstream direction. However, along the

South Platte River this trend may be changed

where high energy tributary streams provide

an influx of coarse material to the deposits

downstream from their confluence with the

South Platte River. Streams that have their

headwaters on the plains commonly lack

coarse aggregates.

Crushed stone

Ideal quarry aggregates should be strong

and resistant to rough handling and use under

both wet and dry conditions or freeze/thaw

Acknowledgments Acknowledgments

The authors wish to thank Valentin V.

Tepordei from the USGS for his assistance in

collecting production data used in the preparation of this report, John Hickman, from

Lafarge, Inc. for sharing his insights of reserve

calculations and the permitting process, and

Kenneth Beckman from the USGS for suggestions regarding the use of proprietary data.

Figure 1. - Index map showing two segments

of study area.

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cycles, and not chemically reactive with

cement. Most crushed stone is quarried in the

mountains in Jefferson, Boulder, and Larimer

Counties, although a small amount is quarried

from rock capping buttes in Douglas County.

The rocks in the mountains are mostly of

metamorphic and igneous origin. Banded

rocks called gneiss and micaceous rocks

called schist originally were sedimentary or

volcanic rocks that have been recrystallized by

the heat and pressure of metamorphism.

Ribbons of light colored, coarse crystalline

rocks called pegmatite were injected as molten

rock into cracks in the metamorphic rocks.

Great masses of granite also intrude the

metamorphic rocks. The physical properties

and mineralogy of these rocks determine their

suitability for use as aggregates. Many, but

not all, of the gneisses, pegmatites, and granites make good crushed stone.

The rocks on the plains are mostly relatively soft shales, sandstones, and limestones

of sedimentary origin. In places near Castle

Rock, a volcanic rock called rhyolite overlies

the sedimentary rocks and forms a capstone on

the buttes. Of the rocks in the plains, rhyolite

may be used as aggregates, although it may

contain minerals that chemically react with

cement. Some of the harder sandstone or

limestone may also be used in some lowerspecification applications.

RESOURCE RESOURCE AVAILABILITY

A number of studies have been undertaken to determine the location and distribution of aggregate resources in the CFR.

Colton and Fitch (1974), Trimble and Fitch

(1974), and Schwochow and others, (1974a

and 1974b), all prepared maps delineating

aggregate resources in the CFR, and it is,

therefore, unlikely that a significant amount of

new resources will be discovered in the CFR.

Aggregate resources have a very low unit

value. Much of their value comes from their

location, thus they have a high place value. A

sand and gravel deposit located many miles

Figure 2. - Block diagram showing landforms of alluvial deposits in the Colorado Front Range

study area.

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from the market commonly has little or no

economic value for use as aggregate. The

place value of such a deposit may change over

time, however. As local reserves are depleted

or as a city (market area) grows outward, the

once-distant resource may become the closest

resource to the market area. Its place value

may increase to the point where the resource

becomes economic to mine.

Increased demand and technological

advances both can upgrade resources into

economic reserves. For example, as long as

sand and gravel was being mined along Clear

Creek, the sand and gravel resources along the

South Platte River between Commerce City

and Brighton were not developed. Now that

sand and gravel mining along Clear Creek is

limited, the resources along the South Platte

River between Commerce City and Brighton

are being mined. Similarly, the cost of preparing crushed stone limited its past production.

Technological advances have now made

crushed stone competitive with sand and

gravel for use as aggregate.

Land use issues can decrease the availability of resources. Even where aggregate

resources of suitable quality exist, competing

land uses can make extraction of the resources

uneconomical. For example, it is not presently cost effective to raze buildings in order

to mine aggregate from under them. Reports

by the Colorado Sand and Gravel Producers

Association (1957), the U.S. Geological

Survey (Soule and Fitch, 1974), and the U.S.

Bureau of Mines (Sheridan, 1967), demonstrate that preemptive land use has eliminated

more resources in the CFR than has depletion

by mining.

PRODUCING PRODUCING AGGREGATES FOR USE

Aggregate producers have limited facilities for storing product, so stockpile changes

are insignificant compared to annual production. Therefore, use of aggregate in the CFR is

considered to be equal to production. Production figures reflecting mine shipments, sales,

or marketable production (including use by

producers) were reported by the U.S. Bureau

of Mines (1951-1995) until 1996, by both the

U.S. Bureau of Mines and U.S. Geological

Survey (1996), and by the U.S. Geological

Survey (1997) since then.

Aggregates are generally high density,

low value materials, and long distance transportation costs can be prohibitive. Industry

data suggest that, with noted exceptions (such

as the importation of aggregates from Wyoming for Denver International Airport), most

aggregates produced in Colorado are used

locally, generally within a 56-kilometer radius

of the source of production. Discussion with

CFR producers has led the authors to conclude

that, although much of the material is used

within a localized area, some aggregate materials are transferred from county to county.

For example, sand and gravel is shipped from

Weld and Larimer counties to the Denver

metro area, and crushed stone is shipped from

Jefferson County to counties to the east that

have no exposed bedrock that is suitable for

crushing. This study assumes, therefore, that

reported production figures provide a reasonable approximation of use for the entire study

area, but that production in each of the two

market areas does not necessarily equal use in

that same area. It should also be noted that

this study uses the term “use” rather than

“consumption” to avoid the inference that

aggregates are being destroyed when consumed.

Historical production data used in this

report were compiled from the Mineral Industry of Colorado reports published annually by

the U.S. Bureau of Mines and the U.S. Geological Survey in their Minerals Yearbook

series (Bolen, 1998; Tepordei, 1998). Major

operators are the primary source for these

figures, and data are occasionally withheld to

prevent release of company proprietary information. These figures also do not reflect the

4
production from many smaller operators.

Therefore, the use figures are conservative

production values and are used only to monitor trends of general production cycles and

provide an approximation of aggregates

production activity.

HISTORY OF COLORADO

AGGREGATE PRODUCTION

Aggregates production data from sand

and gravel and crushed stone sources in

Colorado are shown in figure 3. Data for

crushed stone are shown in blue and sand and

gravel are shown in yellow. Population data

are shown by the red line. Figure 3 also

shows time frames for major Colorado construction projects that used significant quantities of aggregates. CFR projects are in bold

type. Construction project data were compiled

from U.S. Bureau of Mines publications and

Rocky Mountain Construction, a regional

trade publication. Correlation of production

and population with major construction

activities can provide information useful in

estimating future demand projections for

aggregates.

The 1950s and 1960s reflected a period of

increasing production for construction aggregates, primarily for large Federal Government

projects. The Federal Aid Highway Act of

1953 and Highway Revenue Act of 1956

provided funding for accelerated highway

construction in the United States. Much of the

Interstate Highway System in Colorado was

built over a 20-year period from 1953 to 1974,

although the Glen Canyon segment of I-70

through the Rocky Mountains wasn’t completed until 1990. The U.S. Bureau of Reclamation constructed several major water

Figure 3. - Significant events affecting Colorado aggregates use, 1951 - 1997.

5
storage and flood control projects during this

period, including the Dillon Reservoir and

Cherry Creek Dam projects, which provide

water for the Denver metropolitan area.

Cold war concerns led to increased

military construction along the CFR. During

the late 1950s and 1960s, construction of Fort

Carson and Peterson Air Force Base (Colorado

Springs), the NORAD facility (Colorado

Springs), Lowry Air Force Base (Denver), and

the Air Force Academy (Colorado Springs) all

used large amounts of construction aggregates.

Much of the infrastructure (roads, bridges,

airports, and dams) in use today were conceived or constructed during this period.

Infrastructure built during the 1950s and

1960s supported population growth that

occurred during the early 1970s. This growth

stimulated non-Government construction, both

residential and commercial. Large Government-mandated projects were less frequent,

and reflected expansions (NORAD), completions of technically challenging projects

(Eisenhower Tunnel, I-70 corridor), or selected high-priority projects (Chatfield and

Bear Creek dams, and the Frying Pan-Arkansas water collection system, including the

Turquoise and Pueblo Reservoirs). Major

flooding occurred in the Denver area in 1965

resulting in the need for additional flood

control, and subsequent urban growth along

the Front Range produced a need for additional water storage capabilities.

The building boom in the late 1970s was

followed by an economic recession period that

began in the early 1980s and was marked by a

decline in commercial construction in Colorado. Construction increased again during the

mid-1980s, primarily as a result of Federal

construction projects (I-70 Glenwood Canyon

segment, defense-related military construction

in Colorado Springs area), which proceeded in

spite of the economic downturn during this

period. In spite of this construction downturn,

aggregates use remained strong as continued

population growth sustained the need for

housing and related infrastructure. Both sand

and gravel and crushed stone production

showed gradual growth during this period.

Commercial development projects during

the early 1990s stimulated the construction

industry as well as the growth of CFR communities. The largest construction project

during this period was the Denver International Airport, where an estimated 6 million

tons of concrete were required for the runways

and aprons and an estimated 500,000 tons of

concrete for associated buildings. Local

aggregates production was not adequate to

meet the entire local aggregates demand

(Colorado use exceeded Colorado production),

so aggregates were imported by rail approximately 180 kilometers from Wyoming. It

should be noted that aggregates production

from Wyoming has not been included in figure

2.

Other large commercial development

projects that occurred in the early 1990s

included redevelopment of the Lower Downtown (Lodo) area of Denver, the construction

of Coors Field baseball stadium, a new Denver library, and expansion of the Colorado

Springs airport.

Commercial construction in the Denver

metropolitan area continued into the late

1990s, with development of the Pepsi Center

sports complex, a new aquarium, improvements of I-25 through Denver, continued

construction of E-470, and the commencement

of construction on a new football stadium.

Population growth in the Denver metropolitan

area continued to foster residential construction. Housing permits for this region in 1998

were the highest since 1983. Douglas County,

Colorado, was reported to be the fastest

growing county in the United States in 1997

and number 2 in 1998, in terms of population

growth.

Figures 4 and 5 suggest that the structure

of aggregates production from both sand and

6
gravel and crushed stone sources along the

CFR has changed dramatically since the

1950s. In the 1950s and 1960s, approximately

38 percent of Colorado sand and gravel

production and 30 percent of Colorado

crushed stone producThe Fort Collins-Greeley area currently

accounts for about 22

tion came from the 8-

county CFR area. By

the 1990s, the percentage of the Colorado

aggregates produced

along the Colorado

Front Range had

increased to approximately 54 percent of

sand and gravel and 70

percent of crushed

stone (excluding the

Colorado Springs/

Pueblo area).

During the 1990s,

the 6-county Denver

metropolitan area

produced about the

same share of total

Colorado sand and

gravel as it did in the

1950s, but significantly

less than in the 1970s.

The Denver metropolitan area has increased

its share of Colorado

crushed stone production from just 3 percent in the 1960s to 56

percent in the 1990s as a result of the opening

of several large quarries in the foothills west

of Denver during the 1970s.

In 1997, aggregates produced in the

Denver area were derived from sand and

gravel sources (55 percent), crushed stone (31

percent) and recycled aggregates (14 percent).

In contrast, aggregates in 1960 were derived

principally from sand and gravel sources (99

percent).

Figure 4. - Colorado

sand and gravel

production by region

and years.

percent of all of

Colorado’s sand and

gravel production,

reflecting a shift in

CFR sand and gravel

production further north

away from the Denver

metropolitan area.

Overall, crushed stone

production in the Fort

Collins-Greeley area

has increased since the

1960’s. However, as

stone production from

the Denver area quarries increased, the Fort

Collins-Greeley area

percentage of total State

crushed stone production

dropped from 27 percent

during the 1960s to 14

percent during the 1990s.

Figure 5. - Colorado crushed stone

production by

region and years.

HISTORY OF COLORADO FRONT

RANGE AGGREGATE RESOURCE

ACCESSIBILITY

Although the CFR has an abundance of

aggregate resources, many of those resources

are not accessible for extraction. Despite the

dependency of growth on aggregates, urban

expansion has worked to the detriment of its

production. Sand and gravel operations

commonly began from suitable deposits as

close as possible to the consuming areas - the

population centers – to minimize hauling

costs. The population centers have built out

and gradually encroached upon existing

deposits, thus rendering some nearby resources inaccessible.

In 1957, the Colorado Sand and Gravel

Producers Association produced an air photo

map to call attention to the diminishing avail7
able sand and gravel resources in the Denver

area. Ten years later, Sheridan (1967) of the

U.S. Bureau of Mines predicted that restrictive

zoning, lack of general public understanding

of sand and gravel occurrence and mining

operations, and conflicting land uses would

cause a shortage of near-by, low-cost aggregates in Denver. James Cooley (1971) restated the problem at the 74th National Western

Mining Conference.

During 1973, the Colorado legislature

officially recognized the problem and passed

House Bill 1529. That act declared that: 1) the

State’s commercial mineral deposits were

essential to the State’s economy, 2) the populous counties of the State faced a critical

shortage of such deposits, and 3) such deposits

should be extracted according to a rational

plan, calculated to avoid waste and cause the

least practical disruption to the ecology and

quality of life of the citizens.

H.B. 1529 did not succeed at protecting

existing aggregate resources in the Denver

area. County action taken to protect citizens

from mining worked against the need for

mineral resources. The U.S. Department of

Labor (1981) pointed out that the availability

of aggregate resources in the Front Range

continued to decline. They blamed the decline

on zoning regulations driven by environmental

and visual concerns, noncompliance with H.B.

1529, increased production, and reduced

resource quality (i.e., inadequate grain size to

meet specifications).

While encroachment continues to remove

large amounts of aggregate resources from

possible extraction, citizen opposition, zoning,

and other land use restrictions may exact an

even bigger toll on the availability of aggregate resources. Poulin and others (1994)

concluded that permits and regulations restrict

development or expansion of aggregate

deposits in established areas more than actual

resource availability.

Producers responded to the increasingly

limited access to aggregate resources near

Denver in a variety of ways (Schwochow,

1980). They developed lower-grade deposits

farther away from the market area, they used

rail to haul sand and gravel great distances to

the market area, and they developed crushed

stone quarries near the market.

During the 1980s, sand and gravel operators opened new facilities downstream (north)

of Denver along the South Platte River. The

sand and gravel deposits that had previously

been mining farther upstream were about 50

percent gravel and 50 percent sand. The

deposits mined north of Denver were about 20

percent gravel and 80 percent sand. Developing these deposits required more land area and

more processing, generated more waste

material, required a longer transport to the

market, and resulted in a more costly product.

During 1975, Western Paving Construction Company began using unit trains to haul

gravel over 70 km from its loading site at

Lyons, Colorado, to its asphalt plant on Clear

Creek at Pecos Street in Westminster, Colorado. Gravel currently is transported over 100

km to Denver by rail from a site near Carr,

Colorado.

Operators also began replacing sand and

gravel aggregates with quarried crushed stone.

Actually, crushed stone has been produced in

the CFR since the start of the 20th century

(Schowchow, 1980). Four quarries mined

crushed stone at South Table Mountain, with

the first operation starting as early as 1905.

These operations worked intermittently until

the 1950s, and provided concrete and asphalt

aggregates. One of these four quarries, the

Wunderlich quarry, provided rip-rap for

Cherry Creek Dam. The Rogers Brothers

quarry, started in 1925, mined crushed stone

from North Table Mountain and provided

concrete aggregates for Harlan County dam

near McCook, Nebraska (Argall, 1949). Two

8
crushed stone quarries operated north of

Golden at Ralston Reservoir. The Bertrand

quarry, operating at mouth of Clear Creek

Canyon in Golden, started in 1926, but closed

in 1975 because of a threatening landslide.

Six crushed stone quarries operate in the

CFR area today. Three quarries provide

metamorphic gneiss. The Holloway quarry on

Jackson Gulch south of Golden started in

1965, and produced rip-rap for Chatfield Dam.

Lafarge Corporation now owns that quarry,

which is referred to as the Specifications

Aggregate Quarry. Two other quarries, now

operated by Aggregate Industries, are the Deer

Creek Canyon Quarry, started in 1970 in Deer

Creek Canyon west of Chatfield Reservoir,

and the Strain Gulch Quarry, started in 1971

and located south of Morrison. The Asphalt

Paving Company mines latite from a quarry

located north of Golden at Ralston Reservoir

that was first permitted in 1975. The Andesite

Rock Company mines andesite from a quarry

located southwest of Lyons. Colorado Lien

Inc. mines limestone from a quarry located in

northern Larimer County that was permitted in

1978. Unit trains also haul crushed stone to

the Denver market area. Meridian Aggregates

Co. transports granite from a quarry located

west of Cheyenne, Wyoming, to two distribution yards in the Denver area. Other quarries

in the area mine limestone for use in the

manufacture of cement or dimension stone for

building and decorative use. Their production

is not considered in the analysis of aggregate

resources.

Today, crushed stone serves an important

function beyond replacement for sand and

gravel. Some specific applications require the

use of crushed stone. Specifications for

runway aggregates at Denver International

Airport required crushed stone. Similarly,

asphalt highways typically require crushed

stone aggregates in order to achieve required

strength parameters. Highways being constructed with money from the Federal government commonly must meet SUPERPAVE

specifications, which in effect require the use

of sand manufactured from the crushing of

rock, and prohibit the use of natural sand.

FUTURE PRODUCTION OF

AGGREGATES

There has been a steady increase in

production of aggregates from both sand and

gravel and crushed stone sources in Colorado

since the 1950s. Figure 2 suggests that even if

large construction projects were to cease,

production of aggregates in the short term

would continue at reasonably high levels due

to population growth and the associated

demand for infrastructure improvements to

accommodate such growth. It is reasonable to

expect that the Colorado portion of the Interstate Highway System (some portions are over

40 years old and designed for 1960s road use

patterns) will require increased maintenance

or replacement. Many of the early interstate

highways are insufficient to meet the anticipated traffic volume projected for the new

millennium. Road repair is a continual process Statewide.

The Transportation Equity Act for the

21st Century (TEA-21), which was signed into

law in 1998, will govern Federal highway

spending until 2003. Federal funding for

Colorado transportation projects (including

highway and mass transit projects) will gradually increase from about $260 million in 1998

to about $325 million in 2003. Under this 6-

year reauthorization law, Federal funding for

Colorado increased about 44 percent from the

previous 6-year reauthorization law. As a

result, Colorado and many other States have

proposed numerous highway construction

projects to make infrastructure improvements

and accommodate regional growth. Major

proposals include widening of I-25 from six to

up to ten lanes and expansion of light rail

service in portions of the Denver metropolitan

area. Such projects would require significant

9
amounts of construction aggregates from both

new and recycled sources.

One method of forecasting aggregate

production is to use sophisticated computer

models that analyze such factors as the overall

health of the local economy, proposed highway construction, housing development, and

the commercial construction outlook. These

models are difficult to construct and require

input data that is not always readily available.

A simpler approach was used, in which production of aggregates was estimated by reviewing historical production and use patterns,

relating aggregates use to population growth

trends, and then using these observations

toselect reasonable production scenarios based

upon per capita production. Per capita production rates estimated from historical data

were compared to industry estimates reported

in previous aggregates use studies.

Projections were made based upon population growth estimates for the counties under

consideration provided by the Denver Regional Council of Governments (DRCOG,

1999a,b) and the State of Colorado. It is not

the purpose of this study to provide precise

forecasts of aggregate production, but rather to

suggest a range of possibilities that accurately

reflect past historical trends and current data.

Production projections have been developed

for each of the two regional population centers. In some cases, data for a particular area

were not available, so were estimated. Where

data includes proprietary information, plots

are shown without units or proprietary data are

combined with other data to avoid disclosure.

Historical production patterns for aggregates can provide an indication of future

trends. Based upon historical data, there

appears to be a high degree of correlation

between population and aggregates production

(fig. 3). Historical production figures were

correlated with population projections for the

CFR on a yearly basis to estimate the region’s

total aggregates production for the year 2000.

Population projections were derived from

estimates of the DRCOG and the State of

Colorado. Population data (actual and projected) for the period 1990 to 2010 are shown

in table 1.

Source: State of Colorado Division of Local Governments (1998), and Colorado General

Assembly, Legislative Council, (1997) (p) - projected population estimate

County 1990 1995 2000(p) 2005(p) 2010(p)

Adams 265,038 299,755 337,694 379,470 426,034

Arapahoe 391,511 446,200 486,389 514,537 536,620

Boulder 225,339 256,737 281,428 303,331 324,662

Denver 467,610 496,171 511,487 522,127 535,291

Douglas 60,391 104,623 160,072 206,457 246,068

Jefferson 438,430 491,089 520,712 542,666 561,772

Denver Metro Total 1,850,309 2,096,590 2,299,782 2,470,593 2,632,457

Larimer 186,136 217,127 243,411 269,905 294,750

Weld 131,821 148,417 168,234 187,976 208,415

Larimer-Weld Total 317,957 365,544 411,645 457,881 503,165

8-County Total 2,166,276 2,460,139 2,709,427 2,926,469 3,133,612

Table 1. Population Data for the northern Colorado Front Range

10
Per capita (per person) production estimates were used in this study to provide an

indication of present and future aggregates

production. The weighted average per capita

production of aggregates along the northern 8-

county CFR has remained steady for the past

10 years at about 8.8 tons per capita for the

period. Actual production was lowest during

the recession year of 1990, and highest in

1995 as Denver International Airport was

completed and associated developments were

finalized. The weighted-average per capita

aggregates production rate in the 6-county

Denver area since 1960 was estimated to be

8.3 tons based on historical production data.

A linear regression analysis of the historical data, however, indicated that production of

aggregates in the Denver area has increased

over time. Aggregates production per capita

reported for the 6-county Denver metropolitan

area during the past 10 years is shown in

figure 6. The data suggest that per capita

production in the Denver area has increased

from more than 5 tons per person in 1988 to

over 7 tons per person in 1997. Since 1994,

per capita production appears to have leveled

off, or may have declined slightly as the

second order polynomial equation suggests

(fig. 6).

Regression analyses for the period 1988

to 1997 were performed in a similar manner

for the Fort Collins area. When projected to

the year 2000, a production figure of about 22

tons per capita was estimated for the Fort

Collins area. This per capita figure reflects the

high level of production (approximately 22

percent of all Colorado aggregates derived

from sand and gravel were produced in the

Fort Collins area) from a region with relatively low population density. Historical data

suggest that this region is supplying an increased percentage of aggregates from sand

and gravel sources to the Denver metropolitan

area, as local supplies are restricted from

development or as quality of the material in

the Denver area diminishes.

One method for estimating aggregates

production for the period 1998 through 2010

would be to assume that the projected regional

per capita use rates for 2000 would reflect an

approximation for regional production rates

over the entire 13-year period. Figure 7

illustrates the cumulative aggregates production for each of the two reported CFR population centers using such an approach. Based

upon these data, aggregates production for the

period 1998 to 2000 would amount to over 80

million tons for the 1998 through 2000 period.

CFR production could be distributed as 68

percent for the Denver area, and 32 percent for

the Fort Collins area. Similarly, over 401

million tons of aggregates would be produced

from the 8-county CFR region over the 1998

through 2010 period.

Aggregates production rates change with

time, however, and the construction industry

tends to be cyclical. Consequently, models

that provide a range of aggregates production

(8, 9.5, and 11 tons per capita of use) were

developed. These values generally correspond

with values used in unpublished proprietary

industry studies, as well as historical data

reported previously in this study. The lowest

production level would most closely reflect

Figure 6. - Per capita production of aggregates, Denver metropolitan area, 1988 - 1997.

11
recent historical production in the Denver

metropolitan area when no large construction

projects are considered (“low-growth scenario”). The mid-range production level

might represent an “average” construction

year (average-growth scenario). The Colorado

Geological Survey has been using a use value

of 10 tons/capita as a method of predicting

aggregates production in their long-range

analyses of aggregates needs (Nasser, 1987).

Some local producers have used the 11 tons

per capita level in their demand projections.

This corresponds to the “high-growth scenario”, reflecting continued construction and

population growth or where multiple large

projects are being constructed concurrently.

Figure 8 plots the projected annual production for the three rates assumed. For the

“low-growth scenario”, annual aggregates

production is projected to vary from 21 million tons per year to 25 million tons per year.

An average of approximately 23 million tons

per year would be required based on this

production scenario. Extrapolation to 2000 of

previously reported production data for the 8

northern CFR counties over the past 37 years

generates an aggregates production level that

would fall within the range of this scenario.

The “average scenario” of 9.5 tons per

capita production rate indicates a range of

aggregates production from about 25 million

tons per year to 30 million tons per year. An

average of approximately 28 million tons

would be produced based on this scenario.

Linear extrapolation to 2000 of aggregates

production data for the 8 northern CFR counties over the past 12 years generates an aggregates production level that would fall within

the range of this scenario.

The “high-growth scenario” reflects

annual aggregates production ranging from

about 29 million tons to 35 million tons per

year. An average of approximately 32 million

tons would be produced based on this sceFigure 7. - Cumulative production of aggregates, 1998 - 2010, assuming regional use rates

projected for 2000.

12
nario. Estimates derived by combining projected production from the two population

centers along the northern CFR generate an

aggregates production level that would fall

within the range of this scenario. This is to be

expected, as recent production figures reflect

the growth and high level of construction that

has occurred along the CFR region.

Figure 9 plots the cumulative production

for CFR aggregates indicated by the three

scenarios. Based upon the “low-growth

scenario” of 8 tons per capita, about 64 million tons of aggregates would be produced

during the 1998 through 2000 period, slightly

lower than the actual production from this 8-

county area for the 1995 through 1997 period.

Figure 9 suggests that 178 million tons would

be produced through 2005, and about 300

million tons would be produced through 2010.

Figure 8. - Projected annual aggregates use,

Colorado Front Range, 1998 - 2010.

Figure 9. - Projected cumulative aggregates production, 8-county northern Colorado Front

Range.

13
The “average scenario” of 9.5 tons per

capita suggests that a cumulative 76 million

tons of aggregates would be produced for the

period 1998 through 2000, about 211 million

tons would be produced through 2005, and

about 356 million tons through 2010. Values

generated from this scenario are comparable to

those estimated using the regional production

projections (figure 8) for the 2-year period

1998 to 2000, but become much lower as the

time interval increases.

The “high-growth scenario” of 11 tons per

capita suggests that a cumulative 88 million

tons of aggregates would be produced for the

period 1998 through 2000, approximately 244

million tons for the period 1998 through 2005,

and about 412 million tons for the period 1998

through 2010. This scenario most closely

corresponds to the production projections

shown in figure 7, when the full time interval

is considered.

FUTURE SUPPLY OF AGGREGATES IN

THE COLORADO FRONT RANGE

The Colorado Division of Mines and

Geology (CDM&G) maintains a database on

information related to mining permits in

Colorado including permits for sand and

gravel and crushed stone mining. Among

other things, the database includes information

on type of commodity mined, location of the

permitted property, total acres permitted, and

the year the permit was issued.

The area permitted for aggregate extraction alone does not indicate the actual amount

of permitted resources contained in the area,

and many aggregate companies are reluctant

or unwilling to discuss the particulars of their

operations. However, methods were developed to estimate permitted sand and gravel

and crushed stone by combining the permitting data with geologic information on potential aggregate resources compiled by the

Colorado Geological Survey and the U.S.

Geological Survey.

Sand and gravel Sand and gravel

A two-step process was used to calculate

permitted sand and gravel resources (fig. 10).

The first step determined the tons of permitted

sand and gravel by multiplying area permitted

times deposit thickness, then multiplying that

value by a constant to convert from volume to

tons. The second step diminished those

resources to account for permitted land that

will be set aside due to setbacks, operational

requirements, and environmental restrictions,

and to account for loss of resources due to

inadequate aggregates quality.

Tonnage calculations onnage calculations – CDM&G data

were used to estimate the amount of area of

sand and gravel resources that are being

permitted over time. Information regarding

sand and gravel thickness and quality was then

used to calculate volumes of sand and gravel

permitted. Thickness was estimated from

existing maps and reports (Schwochow and

others, 1974b; Trimble and Fitch, 1974,

Colton and Fitch, 1974). The resulting volume (acre feet of sand and gravel) was converted to a unit of weight (metric tons) by

multiplying by a constant (2,134) that takes

into account the density of sand and gravel.

Adjustments for areas set aside –

Commonly not all the land permitted will be

mined for aggregates. Most permits or regulations require setbacks from certain other land

uses such as residential developments, neighboring buildings, and setbacks from property

lines, pipelines, transmission lines, roads, and

streams. A requirement for a 100 ft. setback

from property lines would eliminate about 20

percent of a 100-acre site. Today, in order to

isolate operations from neighboring areas,

some sites have buffer areas in excess of one

half the permitted area.

The operation itself requires land for the

construction of buffers, access roads, scale

house, processing facilities, equipment stor14
age, settling ponds, and stockpiles, which can

occupy a significant part of the permitted mine

site. Processing and load-out areas, for example, may be very small or may occupy

more than 20 acres. Areas set aside for storing

unused equipment may also require extensive

space.

New more stringent environmental

requirements further reduce the amount of

permitted land that actually can be mined.

Regulations may prohibit mining from areas

of wetlands, floodplains, large stands of trees,

and specific wildlife habitat such as those that

contain rare or endangered species. During

the 1970s, many companies avoided excess

fees by permitting only the land to be used for

the mining process. Today, some companies

permit extensive areas to avoid having to

repeat the permit process. For example, a

company may own or lease an entire section

(640 acres) of land, only some of which is

underlain with aggregate. Nevertheless, they

may permit the entire section for mining.

Adjustments for material of unusable

quality– In those permitted areas where

aggregates can be mined, some of the underlying deposits will not meet the quality requirements for use as aggregates. Sand and gravel

deposits along the Front Range commonly are

overlaid by a layer of silt and clay (overburFigure 10. - Flow diagram showing method to determine permitted aggregate resources.

15
den). Although the stripping ratio of overburden to gravel may be as low as 1:9, (the

overburden may comprise 10 percent of a

deposit), the Colorado Geological Survey

(Schowchow and others, 1974a) considered

deposits under floodplains and low terraces to

be of commercial grade if the maximum

stripping ratio of overburden to gravel is 1:3

(the overburden may comprise up to 25

percent of a deposit). They considered deposits under high terraces and upland deposits to

be of commercial grade if the maximum

stripping ratio of overburden to gravel is 1:1

(the overburden may comprise up to 50

percent of a deposit). In addition, sand and

gravel may contain layers of silt and clay

within the deposit (interburden), and undesirable fine material or other deleterious (poor

quality) materials may be dispersed throughout the deposit.

In summary, it is reasonable to expect

from 20 percent (i.e. 100 foot setbacks in a

100 acre site is about 20 percent of the area) to

50 percent (estimated as a reasonable maximum by authors) of the permitted area to be

unavailable for aggregate extraction. It also is

reasonable to expect from 10 (minimum

stripping ratio) to 40 percent (estimated as a

reasonable maximum by authors) of the

permitted sand and gravel resources to be

unsuitable for use as aggregates.

The total permitted sand and gravel

resources can be estimated as follows:

a) total permitted area - % area set aside =

% available

b) % available – (% available X % unusable)

= % total permitted area available and

useable

The total permitted area of available and

useable sand and gravel will range from a best

case of about 70 percent to a worst case of

about 30 percent of the volume within the

permitted area. The best case scenario (20 %

set aside, 10 % unusable) is:

a) 100 –20 = 80 %

b) 80 % - (.1 X 80) = 72 % total permitted

area available and useable

The worst case scenario ( 50% set aside,

40 % unusable) is:

a) 100 –50 = 50 %

b) 50 % - (.4 X 50%) = 30 % total permitted

area available and useable

The authors believe that 30% useable

sand and gravel tends to reflect current conditions in the study area, and that 70% useable

sand and gravel tends to reflect conditions in

the study area during the 1970s. A 50%

useable sand and gravel level represents an

average or intermediate level.

Crushed stone

Estimating resources of crushed stone is

problematic and requires a different approach

(fig. 10) than that used for estimating sand and

gravel. Only seven quarries are currently

producing crushed stone in the CFR study

area. The quarries were permitted in such a

manner that disclosing the crushed stone

resources and the years that those resources

were permitted would make it possible to

calculate resources for individual operations.

To avoid disclosing proprietary data, generalized resource data from several sources

[Nasser (1987), proprietary data on resource

estimates from a number of aggregates companies’ unpublished reports, and proprietary

production rates] were used. Back calculating

allowed the estimation of original resources at

the time of permitting. It was not necessary to

diminish the tonnage of crushed stone to

16
account for unmined land or poor quality

because the data already accounted for those

factors.

Recycling

Even as production of aggregates from

natural sources (sand and gravel, crushed

stone) has increased, production of aggregates

from recycled sources has also increased,

particularly in large urban areas such as

Denver. Estimated production of recycled

aggregates in the 6-county Denver metropolitan area grew from about 1.2 million tons in

1997 to 2.5 million tons in 1998, with a

projected 1999 production of about 4 million

tons. Increasingly, large construction projects

include the recycling of cement and asphaltic

concrete in redevelopment plans. Consequently, redevelopment of Lowry Air Force

Base, Stapleton Airport, Cinderella City Mall,

Northglenn Mall, and road construction all

around the Denver area increased both demand and supply of aggregates since 1996.

Redevelopment of the former Stapleton

Airport in Denver will generate a total of 6

million tons of recycled concrete (Carder,

1999), from demolition of runways and

terminal buildings. Recycled material could

supply over 15 percent of projected demand

for aggregates by 2000, if historical production trends above hold true. Not all construction materials suitable for recycling as aggregates, however, meet the quality specifications

for construction aggregates. Consequently,

there is not a total substitution between natural

aggregates and recycled aggregates in all

applications.

Figure 11. - Cumulative aggregate permitted. Vertical scale is relative.

17
DISCUSSION

Three scenarios for sand and gravel in the

CFR area establish a range that brackets the

estimated rate that aggregate resources are

being permitted. The scenarios are based on

70 percent, 50 percent, or 30 percent recovery

of the sand and gravel resources, and 100

percent recovery of the crushed stone resources. Discussions in this report refer to the

50 percent scenario, except as noted.

Figures showing permitting of aggregate

resources (figs. 11 and 14) are based in large

part on proprietary data. Therefore, although

the graphs were created using calculated

values, the graphs are dimensionless and show

only relative values.

Figure 11 plots the cumulative aggregate

resources permitted by year at the 70 percent

and 30 percent rates, for the 8-county study

area. The curves were smoothed using a 2nd

order polynomial trend analysis. By using

cumulative figures, the slope of the line

directly reflects the rate of permitting; the

steeper the slope, the faster the rate of permitin the total study area was in the Denver

metro area. The percentage of aggregates

permitted in the Denver metro area decreased to about 57 percent and 29 percent

during the periods 1984-90 and 1991-97,

respectively (fig. 12).

In both the Denver metropolitan area

and the Fort Collins-Greeley area the

amount of aggregates permitted has steadily

decreased over time. In the Denver metropolitan area, about 65 percent of the aggregates permitted during the entire 21-year

study period was permitted during the

period 1977-83 (fig. 13). About 29 percent

was permitted during the period 1984-90,

and only 6 percent during the period 1991-

97. A similar trend occurred in the Fort

Collins-Greeley area, with values of about

42 percent, 36 percent, and 22 percent for

the three time periods.

Figure 14 shows the relative percentages of all aggregates permitted in the study

area by time period. The Fort CollinsFigure 12. - Aggregate

permitted each 7-year

period, by region.

ting. A horizontal

line would mean no

new material is

being permitted.

The line can never

have a negative

slope because the

line portrays

cumulative values.

The actual rate

of permitting

resources probably

lies somewhere

between the 70

percent and 30

percent curves, and

probably is moving

away from the 70

percent value

towards the 30

percent value due

Figure 13. - Aggregate permitted in each

region, by 7-year

period.

to environmental,

regulation, and

quality issues. Under

either scenario,

figure 11 demonstrates that the rate

that aggregates have

been permitted in the

CFR has been

steadily decreasing

since 1974.

To identify

permitting trends

over time, the permitting of aggregate

resources was divided into three 7-

year time periods.

During the period

from 1977-83, about

72 percent of the

aggregates permitted

18
Greeley area permitted about the same amount

of aggregates as the Denver metro area during

1984-1990 period, and permitted most of the

aggregates for the 1991-97 period.

To continuously meet projected production, the amount of aggregates permitted must,

on the average, equal or exceed the amount

produced. Furthermore, because aggregates

production generally relates to population, the

per capita amount of aggregates permitted

must equal or exceed the per capita amount of

aggregates produced. Figure 15 plots:

(aggregates permitted / population) – (aggregates produced / population)

From one year to the next, the amount of

aggregates permitted can vary greatly. To

account for these irregularities, the curves

showing aggregate permitted have been

smoothed by using a five-year moving average.

Aggregate producers started to move

away from the Denver metro area during the

Figure 14. - Relative amount of aggregate

permitted in 2 regions, by 7-year period.

Figure 15. - Graph showing per capita aggregate permited minus per capita aggregate produced.

Plots are smoothed using a 5-year moving average.

19
late 1970s to mine sand and gravel from the

St. Vrain River valley to the north. Starting in

1979, the per capita permitting rate for the

Fort Collins-Greeley area grew dramatically in

comparison with the Denver metro area.

Figure 15 illustrates that the Denver metro

area has produced more aggregates than it

permitted since 1992. The Fort CollinsGreeley area currently is permitting about

what it is producing. The entire study area has

been permitting less than it produces since

1994. In general, when the lines on fig. 15

cross the zero line (horizontal axis), more

aggregate is being produced than permitted.

This may signal potential problems regarding

future aggregates availability.

SUMMARY

There has been a steady increase in

production of aggregates from both sand and

gravel and crushed stone in Colorado since the

1950s. In the 1950s and 1960s, approximately

38 percent of Colorado sand and gravel

production and 30 percent of Colorado

crushed stone production came from the 8-

county CFR area. By the 1990s, the percentage of the aggregates produced along the

northern Colorado Front Range had increased

to approximately 54 percent of sand and

gravel and 70 percent of crushed stone.

The structure of aggregates production

from both sand and gravel and crushed stone

sources along the CFR has changed dramatically since the 1950s. In 1960, production of

aggregates in the Denver area was principally

from sand and gravel sources (99 percent). In

1997, estimated aggregate production of sand

and gravel sources was 55 percent, crushed

stone was 31 percent, and recycled aggregates

was 14 percent.

There has been a shift in CFR sand and

gravel production further north away from the

Denver metropolitan area. The Fort Collins

area currently accounts for about 22 percent of

all of Colorado’s sand and gravel production.

This overshadows a drop in crushed stone

production from the Fort Collins area because

about 75 percent of aggregates produced in

Colorado is from sand and gravel deposits.

The rate of permitting of aggregate

resources has dropped dramatically since it

peaked during the late 1970s and early 1980s,

when the granting of permits for several large

crushed stone operations introduced a large

amount of newly permitted resources into the

CFR area. Existing resources are currently

being used faster than new resources are being

permitted.

CONCLUSIONS

The steady increase in aggregates production and use that has occurred since the 1950s

is expected to continue. The data suggest that

even if large construction projects were to

cease, demand for aggregates in the short term

would continue at reasonably high levels due

to projected population growth and associated

demand for infrastructure improvements to

accommodate such growth.

Although the CFR has an abundance of

aggregate resources, recoverable resources are

coming from greater distances as local resources are becoming inaccessible for extraction. Available resources are becoming more

difficult to recover and more expensive to

produce, due to longer transportation distances, poorer quality of locally available

sources, more involved permitting requirements, and the encroachment of other land

uses on the potential resource.

Up until the mid-1970s, the majority of

the aggregate within the Denver metropolitan

area was produced from sand and gravel.

During the mid-1970s, several crushed stone

quarries began operating in the Denver metropolitan area. The increase in demand for

aggregate in the Denver metropolitan area

during this period was met largely from these

new stone quarries. During the 1980s changing conditions caused the aggregate industry

20
to start import sand and gravel to the Denver

metropolitan area from the Fort Collins –

Greeley area to meet aggregate needs of the

Denver metropolitan area. Many of the remaining sand and gravel deposits in the

Denver metropolitan area were excluded from

development because of conflicting land use,

poor quality, and citizen opposition. No new

crushed stone operations had been permitted,

and existing operations are operating at or

near capacity.

The study indicates that the amount of

aggregates being permitted has steadily

decreased over time. The Denver metropolitan area has been producing more aggregates

than it is permitting since 1992, and the Fort

Collins-Greeley area is currently permitting

about what it is producing. If this trend

continues, aggregates operators may be forced

to move to resource areas even farther away

from local markets, resulting in even higher

transportation costs. Increased costs for these

aggregates would be passed along to the State

or counties as higher construction bids, to the

contractor as higher supply costs, and ultimately to the consumer in the form of higher

taxes or user fees.

Today the Denver metropolitan area and

the Fort Collins-Greeley are becoming one

integrated production – use area for aggregates. Average transportation distances tend to

exceed the 56-kilometer rule-of thumb because of the large size of this 8-county area.

This has led to increased costs for aggregate,

at the point of use.

As growth continues and more road and

building construction projects are proposed, it

is essential that developers, contractors, and

governmental officials consider where future

aggregates supply will come from to support

such projects. This study suggests that while

permitted resources are sufficient for the short

term, the rate of permitting may not be sufficient in the future if strong demand for aggregates continue. Longer haul distances and

higher costs could occur unless policy makers

choose to enforce H.B. 1529, producers apply

for increased permit areas, planners approve

such permits, or alternatives such as recycling

increase.

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Quarterly, v. 44, n. 2, 477p.

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22