U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICALU.S. GEOLOGICALU.S. GEOLOGICALU.S. GEOLOGICALU.S. GEOLOGICAL SUR SUR SUR SUR SURVEYVEYVEYVEYVEY

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

Open File Report 00-258Open File Report 00-258Open File Report 00-258Open File Report 00-258Open 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 Surveyeditorial standards or with the North American Stratigraphic Code. Any use of trade, product, orfirm names is for descriptive purposes only and does not imply endorsement by the U.S. Govern-ment.

1U.S. Geological Survey, Denver, Colorado, 80225-0046

CONTENTSCONTENTSCONTENTSCONTENTSCONTENTS

FIGURESFIGURESFIGURESFIGURESFIGURES

Abstract 1Introduction 1

Acknowledgements 2Types of aggregate resources in the Colorado Front Range 2

Sand and gravel 2Crushed stone 2

Resource availability 3Producing aggregates for use 4History of Colorado aggregate production 5History of Colorado Front Range aggregate resource accessibility 7Future production of aggregates 9Future supply of aggregates in the Colorado Front Range 14

Sand and gravel 14Crushed stone 16Recycling 17

Discussion 18Summary 20Conclusions 20References 21

Figure 1. - Index map showing two segments of study area. 2Figure 2. - Block diagram showing landforms of alluvial deposits in the Colorado Front Rangestudy area. 3Figure 3. - Significant events affecting Colorado aggregates use, 1951 - 1997. 5Figure 4. - Colorado sand and gravel production by region and years. 7Figure 5. - Colorado crushed stone production by region and years. 7Figure 6. - Per capita production of aggregates, Denver metroploitan area, 1988 - 1997. 11Figure 7. - Cumulative production of aggregates, 1998 - 2010, assuming regional use ratesprojected for 2000. 12Figure 8. - Projected annual aggregates use, Colorado Front Range, 1998 - 2010. 13Figure 9. - Projected cumulative aggregates production, 8-county northern Colorado FrontRange. 13Figure 10. - Flow diagram showing method to determine permitted aggregate resources. 15Figure 11. - Cumulative aggregate permitted. 17Figure 12. - Aggregate permitted each 7-year period, by region. 18Figure 13. - Aggregate permitted in each region, by year. 18Figure 14. - Relative amount of aggregate permitted in 2 regions, by 7-year period. 19Figure 15. - Graph showing per capita aggregate permitted minus per capita aggregateproduced. 19

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

ABSTRACTABSTRACTABSTRACTABSTRACTABSTRACTRegional 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. Increasedenvironmental awareness, public opposition, and stricter zoning regulations have made it moredifficult to obtain permits to develop new aggregate mines or expand existing operations in urbanareas such as the Colorado Front Range. Local demand for aggregates in the short term is ex-pected to continue at reasonably high levels due to the projected population growth and associ-ated 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 inacces-sible for extraction. Available resources are becoming more difficult to recover and more expen-sive 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 undevelopedpotential resource.

The study indicates that the amount of aggregates being permitted has steadily decreasedover time. The Denver metropolitan area has been producing more aggregates than it is permit-ting since 1991, and the Fort Collins-Greeley area is currently permitting about what it is produc-ing. If this trend continues, aggregate operators may be forced to move to resource areas evenfarther away from local markets, resulting in even higher transportation costs. Increased costsfor these aggregates would be passed along to the State or counties as higher construction bids, tothe contractor as higher supply costs, and ultimately to the consumer in the form of higher taxesor user fees.

INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTIONMeeting 21st century aggregate demands

on the Colorado Front Range (CFR) will be achallenge to local suppliers. Regional growth,transportation, and land use planning all willaffect the ability of the industry to meet futuredemand for aggregate resources — highquality rock and sand and gravel. Where areour aggregate resources, how much is there,and how good are they?

Previous studies have addressed thesequestions, and have found that the CFR, ingeneral, is blessed with an abundance ofsuitable quality aggregate resources. How-ever, the aggregate resources in the CFR canonly be extracted if the land where the re-sources exist has been permitted for mining.In the CFR, permitted resources make up onlya small fraction of the total resource base.Increased environmental awareness, public

opposition, and stricter zoning regulationsmake it difficult to obtain permits to developnew mines or expand existing operations.This study, therefore, addresses the question:“Are aggregate resources being permitted fastenough to meet the short and long term de-mand?”

This study investigates the supply and useof aggregates along the northern portion of theCFR, extending south from the Colorado-Wyoming border to just south of the Denvermetropolitan area, a distance of about 180kilometers. The area includes the counties ofAdams, Arapahoe, Boulder, Denver, Douglas,Jefferson, Larimer, and Weld (fig. 1). Becausetruck transportation of aggregates over longdistances is expensive, aggregate use is typi-cally local, as long as local sources are avail-able. Ideally, truck haulage of aggregates (the

1

most common mode of transportation) fromsource to market seldom exceeds 56 kilome-ters (Socolow, 1995). Consequently, thisportion of the CFR has been subdivided intotwo segments for this study: the Fort Collins-Greeley area and Denver metropolitan area.Each area is a population center and marketarea with a radius of about 56-kilometers.

TYPES OFTYPES OFTYPES OFTYPES OFTYPES OF AGGREGAAGGREGAAGGREGAAGGREGAAGGREGATE RESOURCESTE RESOURCESTE RESOURCESTE RESOURCESTE RESOURCESIN IN IN IN IN THE COLORADO FRONTTHE COLORADO FRONTTHE COLORADO FRONTTHE COLORADO FRONTTHE COLORADO FRONT RANGE RANGE RANGE RANGE RANGE

Sand and gravelSand and gravelSand and gravelSand and gravelSand and gravelLindsey (1997) described four general

types of sand and gravel deposits in the Colo-rado Front Range (fig. 2). These four deposittypes are: alluvial fans, high dissected ter-races, terraces, and floodplains and lowterraces. Floodplains and low terraces are theprincipal sources of aggregates that are recov-ered along the CFR. Sand and gravel depositsunderlying the alluvial fans and high dissectedterraces commonly are not used as specifica-tion aggregates because of inferior quality.

The surficial geologic units of the studyarea are mostly Quaternary in age (up to 2million years old). During the Quaternary,some of the mountainous part of the studyarea was exposed to repeated glaciations.Glacial activity provided large amounts ofsediment, as well as meltwater to transport thesediment to the streams along the CFR.Consequently, gravel in the CFR area islargely restricted to major streams with head-waters in the mountains. These streamsinclude the South Platte River, Clear Creek,Boulder Creek, St. Vrain Creek, Big Thomp-son River, and the Cache la Poudre River.Much of the coarse sediment load was depos-ited near the mountain front. The amount andmaximum size of coarse material decreases ina downstream direction. However, along theSouth Platte River this trend may be changedwhere high energy tributary streams providean influx of coarse material to the depositsdownstream from their confluence with theSouth Platte River. Streams that have theirheadwaters on the plains commonly lackcoarse aggregates.

Crushed stoneCrushed stoneCrushed stoneCrushed stoneCrushed stoneIdeal quarry aggregates should be strong

and resistant to rough handling and use underboth wet and dry conditions or freeze/thaw

AcknowledgmentsAcknowledgmentsAcknowledgmentsAcknowledgmentsAcknowledgmentsThe authors wish to thank Valentin V.

Tepordei from the USGS for his assistance incollecting production data used in the prepara-tion of this report, John Hickman, fromLafarge, Inc. for sharing his insights of reservecalculations and the permitting process, andKenneth Beckman from the USGS for sugges-tions regarding the use of proprietary data.

FigurFigurFigurFigurFigure e e e e 1. - Index map showing two segmentsof study area.

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cycles, and not chemically reactive withcement. Most crushed stone is quarried in themountains in Jefferson, Boulder, and LarimerCounties, although a small amount is quarriedfrom rock capping buttes in Douglas County.

The rocks in the mountains are mostly ofmetamorphic and igneous origin. Bandedrocks called gneiss and micaceous rockscalled schist originally were sedimentary orvolcanic rocks that have been recrystallized bythe heat and pressure of metamorphism.Ribbons of light colored, coarse crystallinerocks called pegmatite were injected as moltenrock into cracks in the metamorphic rocks.Great masses of granite also intrude themetamorphic rocks. The physical propertiesand mineralogy of these rocks determine theirsuitability for use as aggregates. Many, butnot all, of the gneisses, pegmatites, and gran-ites make good crushed stone.

The rocks on the plains are mostly rela-tively soft shales, sandstones, and limestonesof sedimentary origin. In places near Castle

Rock, a volcanic rock called rhyolite overliesthe sedimentary rocks and forms a capstone onthe buttes. Of the rocks in the plains, rhyolitemay be used as aggregates, although it maycontain minerals that chemically react withcement. Some of the harder sandstone orlimestone may also be used in some lower-specification applications.

RESOURCE RESOURCE RESOURCE RESOURCE RESOURCE AAAAAVVVVVAILABILITYAILABILITYAILABILITYAILABILITYAILABILITYA number of studies have been under-

taken to determine the location and distribu-tion of aggregate resources in the CFR.Colton and Fitch (1974), Trimble and Fitch(1974), and Schwochow and others, (1974aand 1974b), all prepared maps delineatingaggregate resources in the CFR, and it is,therefore, unlikely that a significant amount ofnew resources will be discovered in the CFR.

Aggregate resources have a very low unit unit unit unit unitvaluevaluevaluevaluevalue. Much of their value comes from theirlocation, thus they have a high place valueplace valueplace valueplace valueplace value. Asand and gravel deposit located many miles

FigurFigurFigurFigurFigure 2.e 2.e 2.e 2.e 2. - Block diagram showing landforms of alluvial deposits in the Colorado Front Rangestudy area.

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from the market commonly has little or noeconomic value for use as aggregate. Theplace value of such a deposit may change overtime, however. As local reserves are depletedor as a city (market area) grows outward, theonce-distant resource may become the closestresource to the market area. Its place valuemay increase to the point where the resourcebecomes economic to mine.

Increased demand and technologicaladvances both can upgrade resources intoeconomic reserves. For example, as long assand and gravel was being mined along ClearCreek, the sand and gravel resources along theSouth Platte River between Commerce Cityand Brighton were not developed. Now thatsand and gravel mining along Clear Creek islimited, the resources along the South PlatteRiver between Commerce City and Brightonare being mined. Similarly, the cost of prepar-ing crushed stone limited its past production.Technological advances have now madecrushed stone competitive with sand andgravel for use as aggregate.

Land use issues can decrease the avail-ability of resources. Even where aggregateresources of suitable quality exist, competingland uses can make extraction of the resourcesuneconomical. For example, it is not pres-ently cost effective to raze buildings in orderto mine aggregate from under them. Reportsby the Colorado Sand and Gravel ProducersAssociation (1957), the U.S. GeologicalSurvey (Soule and Fitch, 1974), and the U.S.Bureau of Mines (Sheridan, 1967), demon-strate that preemptive land use has eliminatedmore resources in the CFR than has depletionby mining.

PRODUCING PRODUCING PRODUCING PRODUCING PRODUCING AGGREGAAGGREGAAGGREGAAGGREGAAGGREGATES FOR USETES FOR USETES FOR USETES FOR USETES FOR USEAggregate producers have limited facili-

ties for storing product, so stockpile changesare insignificant compared to annual produc-tion. Therefore, use of aggregate in the CFR isconsidered to be equal to production. Produc-

tion figures reflecting mine shipments, sales,or marketable production (including use byproducers) were reported by the U.S. Bureauof Mines (1951-1995) until 1996, by both theU.S. Bureau of Mines and U.S. GeologicalSurvey (1996), and by the U.S. GeologicalSurvey (1997) since then.

Aggregates are generally high density,low value materials, and long distance trans-portation costs can be prohibitive. Industrydata suggest that, with noted exceptions (suchas the importation of aggregates from Wyo-ming for Denver International Airport), mostaggregates produced in Colorado are usedlocally, generally within a 56-kilometer radiusof the source of production. Discussion withCFR producers has led the authors to concludethat, although much of the material is usedwithin a localized area, some aggregate mate-rials are transferred from county to county.For example, sand and gravel is shipped fromWeld and Larimer counties to the Denvermetro area, and crushed stone is shipped fromJefferson County to counties to the east thathave no exposed bedrock that is suitable forcrushing. This study assumes, therefore, thatreported production figures provide a reason-able approximation of use for the entire studyarea, but that production in each of the twomarket areas does not necessarily equal use inthat same area. It should also be noted thatthis study uses the term “useuseuseuseuse” rather than“consumptionconsumptionconsumptionconsumptionconsumption” to avoid the inference thataggregates are being destroyed when con-sumed.

Historical production data used in thisreport were compiled from the Mineral Indus-try of Colorado reports published annually bythe U.S. Bureau of Mines and the U.S. Geo-logical Survey in their Minerals Yearbookseries (Bolen, 1998; Tepordei, 1998). Majoroperators are the primary source for thesefigures, and data are occasionally withheld toprevent release of company proprietary infor-mation. These figures also do not reflect the

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production from many smaller operators.Therefore, the use figures are conservativeproduction values and are used only to moni-tor trends of general production cycles andprovide an approximation of aggregatesproduction activity.

HISTHISTHISTHISTHISTORORORORORYYYYY OF OF OF OF OF COLORADO COLORADO COLORADO COLORADO COLORADOAGGREGAAGGREGAAGGREGAAGGREGAAGGREGATE PRODUCTIONTE PRODUCTIONTE PRODUCTIONTE PRODUCTIONTE PRODUCTION

Aggregates production data from sandand gravel and crushed stone sources inColorado are shown in figure 3. Data forcrushed stone are shown in blue and sand andgravel are shown in yellow. Population dataare shown by the red line. Figure 3 alsoshows time frames for major Colorado con-struction projects that used significant quanti-ties of aggregates. CFR projects are in boldtype. Construction project data were compiledfrom U.S. Bureau of Mines publications andRocky Mountain Construction, a regional

trade publication. Correlation of productionand population with major constructionactivities can provide information useful inestimating future demand projections foraggregates.

The 1950s and 1960s reflected a period ofincreasing production for construction aggre-gates, primarily for large Federal Governmentprojects. The Federal Aid Highway Act of1953 and Highway Revenue Act of 1956provided funding for accelerated highwayconstruction in the United States. Much of theInterstate Highway System in Colorado wasbuilt over a 20-year period from 1953 to 1974,although the Glen Canyon segment of I-70through the Rocky Mountains wasn’t com-pleted until 1990. The U.S. Bureau of Recla-mation constructed several major water

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

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storage and flood control projects during thisperiod, including the Dillon Reservoir andCherry Creek Dam projects, which providewater for the Denver metropolitan area.

Cold war concerns led to increasedmilitary construction along the CFR. Duringthe late 1950s and 1960s, construction of FortCarson and Peterson Air Force Base (ColoradoSprings), the NORAD facility (ColoradoSprings), Lowry Air Force Base (Denver), andthe Air Force Academy (Colorado Springs) allused large amounts of construction aggregates.Much of the infrastructure (roads, bridges,airports, and dams) in use today were con-ceived or constructed during this period.

Infrastructure built during the 1950s and1960s supported population growth thatoccurred during the early 1970s. This growthstimulated non-Government construction, bothresidential and commercial. Large Govern-ment-mandated projects were less frequent,and reflected expansions (NORAD), comple-tions of technically challenging projects(Eisenhower Tunnel, I-70 corridor), or se-lected high-priority projects (Chatfield andBear Creek dams, and the Frying Pan-Arkan-sas water collection system, including theTurquoise and Pueblo Reservoirs). Majorflooding occurred in the Denver area in 1965resulting in the need for additional floodcontrol, and subsequent urban growth alongthe Front Range produced a need for addi-tional water storage capabilities.

The building boom in the late 1970s wasfollowed by an economic recession period thatbegan in the early 1980s and was marked by adecline in commercial construction in Colo-rado. Construction increased again during themid-1980s, primarily as a result of Federalconstruction projects (I-70 Glenwood Canyonsegment, defense-related military constructionin Colorado Springs area), which proceeded inspite of the economic downturn during thisperiod. In spite of this construction downturn,aggregates use remained strong as continued

population growth sustained the need forhousing and related infrastructure. Both sandand gravel and crushed stone productionshowed gradual growth during this period.

Commercial development projects duringthe early 1990s stimulated the constructionindustry as well as the growth of CFR com-munities. The largest construction projectduring this period was the Denver Interna-tional Airport, where an estimated 6 milliontons of concrete were required for the runwaysand aprons and an estimated 500,000 tons ofconcrete for associated buildings. Localaggregates production was not adequate tomeet the entire local aggregates demand(Colorado use exceeded Colorado production),so aggregates were imported by rail approxi-mately 180 kilometers from Wyoming. Itshould be noted that aggregates productionfrom Wyoming has not been included in figure2.

Other large commercial developmentprojects that occurred in the early 1990sincluded redevelopment of the Lower Down-town (Lodo) area of Denver, the constructionof Coors Field baseball stadium, a new Den-ver library, and expansion of the ColoradoSprings airport.

Commercial construction in the Denvermetropolitan area continued into the late1990s, with development of the Pepsi Centersports complex, a new aquarium, improve-ments of I-25 through Denver, continuedconstruction of E-470, and the commencementof construction on a new football stadium.Population growth in the Denver metropolitanarea continued to foster residential construc-tion. Housing permits for this region in 1998were the highest since 1983. Douglas County,Colorado, was reported to be the fastestgrowing county in the United States in 1997and number 2 in 1998, in terms of populationgrowth.

Figures 4 and 5 suggest that the structureof aggregates production from both sand and

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gravel and crushed stone sources along theCFR has changed dramatically since the1950s. In the 1950s and 1960s, approximately38 percent of Colorado sand and gravelproduction and 30 percent of Colorado

crushed stone produc-

The Fort Collins-Greeley area currentlyaccounts for about 22

tion came from the 8-county CFR area. Bythe 1990s, the percent-age of the Coloradoaggregates producedalong the ColoradoFront Range hadincreased to approxi-mately 54 percent ofsand and gravel and 70percent of crushedstone (excluding theColorado Springs/Pueblo area).

During the 1990s,the 6-county Denvermetropolitan areaproduced about thesame share of totalColorado sand andgravel as it did in the1950s, but significantlyless than in the 1970s.The Denver metropoli-tan area has increasedits share of Coloradocrushed stone produc-

tion from just 3 percent in the 1960s to 56percent in the 1990s as a result of the openingof several large quarries in the foothills westof Denver during the 1970s.

In 1997, aggregates produced in theDenver area were derived from sand andgravel sources (55 percent), crushed stone (31percent) and recycled aggregates (14 percent).In contrast, aggregates in 1960 were derivedprincipally from sand and gravel sources (99percent).

FigurFigurFigurFigurFigure 4.e 4.e 4.e 4.e 4. - Coloradosand and gravelproduction by regionand years.

percent of all ofColorado’s sand andgravel production,reflecting a shift inCFR sand and gravelproduction further northaway from the Denvermetropolitan area.Overall, crushed stoneproduction in the FortCollins-Greeley areahas increased since the1960’s. However, asstone production fromthe Denver area quar-ries increased, the FortCollins-Greeley areapercentage of total Statecrushed stone productiondropped from 27 percentduring the 1960s to 14percent during the 1990s.

FigurFigurFigurFigurFigure 5.e 5.e 5.e 5.e 5. - Colo-rado crushed stoneproduction byregion and years.

HISTHISTHISTHISTHISTORORORORORYYYYY OF OF OF OF OF COLORADO FRONT COLORADO FRONT COLORADO FRONT COLORADO FRONT COLORADO FRONTRANGE RANGE RANGE RANGE RANGE AGGREGAAGGREGAAGGREGAAGGREGAAGGREGATE RESOURCETE RESOURCETE RESOURCETE RESOURCETE RESOURCE

ACCESSIBILITYACCESSIBILITYACCESSIBILITYACCESSIBILITYACCESSIBILITYAlthough the CFR has an abundance of

aggregate resources, many of those resourcesare not accessible for extraction. Despite thedependency of growth on aggregates, urbanexpansion has worked to the detriment of itsproduction. Sand and gravel operationscommonly began from suitable deposits asclose as possible to the consuming areas - thepopulation centers – to minimize haulingcosts. The population centers have built outand gradually encroached upon existingdeposits, thus rendering some nearby re-sources inaccessible.

In 1957, the Colorado Sand and GravelProducers Association produced an air photomap to call attention to the diminishing avail-

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able sand and gravel resources in the Denverarea. Ten years later, Sheridan (1967) of theU.S. Bureau of Mines predicted that restrictivezoning, lack of general public understandingof sand and gravel occurrence and miningoperations, and conflicting land uses wouldcause a shortage of near-by, low-cost aggre-gates in Denver. James Cooley (1971) re-stated the problem at the 74th National WesternMining Conference.

During 1973, the Colorado legislatureofficially recognized the problem and passedHouse Bill 1529. That act declared that: 1) theState’s commercial mineral deposits wereessential to the State’s economy, 2) the popu-lous counties of the State faced a criticalshortage of such deposits, and 3) such depositsshould be extracted according to a rationalplan, calculated to avoid waste and cause theleast practical disruption to the ecology andquality of life of the citizens.

H.B. 1529 did not succeed at protectingexisting aggregate resources in the Denverarea. County action taken to protect citizensfrom mining worked against the need formineral resources. The U.S. Department ofLabor (1981) pointed out that the availabilityof aggregate resources in the Front Rangecontinued to decline. They blamed the declineon zoning regulations driven by environmentaland visual concerns, noncompliance with H.B.1529, increased production, and reducedresource quality (i.e., inadequate grain size tomeet specifications).

While encroachment continues to removelarge amounts of aggregate resources frompossible extraction, citizen opposition, zoning,and other land use restrictions may exact aneven bigger toll on the availability of aggre-gate resources. Poulin and others (1994)concluded that permits and regulations restrictdevelopment or expansion of aggregatedeposits in established areas more than actualresource availability.

Producers responded to the increasinglylimited access to aggregate resources nearDenver in a variety of ways (Schwochow,1980). They developed lower-grade depositsfarther away from the market area, they usedrail to haul sand and gravel great distances tothe market area, and they developed crushedstone quarries near the market.

During the 1980s, sand and gravel opera-tors opened new facilities downstream (north)of Denver along the South Platte River. Thesand and gravel deposits that had previouslybeen mining farther upstream were about 50percent gravel and 50 percent sand. Thedeposits mined north of Denver were about 20percent gravel and 80 percent sand. Develop-ing these deposits required more land area andmore processing, generated more wastematerial, required a longer transport to themarket, and resulted in a more costly product.

During 1975, Western Paving Construc-tion Company began using unit trains to haulgravel over 70 km from its loading site atLyons, Colorado, to its asphalt plant on ClearCreek at Pecos Street in Westminster, Colo-rado. Gravel currently is transported over 100km to Denver by rail from a site near Carr,Colorado.

Operators also began replacing sand andgravel aggregates with quarried crushed stone.Actually, crushed stone has been produced inthe CFR since the start of the 20th century(Schowchow, 1980). Four quarries minedcrushed stone at South Table Mountain, withthe first operation starting as early as 1905.These operations worked intermittently untilthe 1950s, and provided concrete and asphaltaggregates. One of these four quarries, theWunderlich quarry, provided rip-rap forCherry Creek Dam. The Rogers Brothersquarry, started in 1925, mined crushed stonefrom North Table Mountain and providedconcrete aggregates for Harlan County damnear McCook, Nebraska (Argall, 1949). Two

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crushed stone quarries operated north ofGolden at Ralston Reservoir. The Bertrandquarry, operating at mouth of Clear CreekCanyon in Golden, started in 1926, but closedin 1975 because of a threatening landslide.

Six crushed stone quarries operate in theCFR area today. Three quarries providemetamorphic gneiss. The Holloway quarry onJackson Gulch south of Golden started in1965, and produced rip-rap for Chatfield Dam.Lafarge Corporation now owns that quarry,which is referred to as the SpecificationsAggregate Quarry. Two other quarries, nowoperated by Aggregate Industries, are the DeerCreek Canyon Quarry, started in 1970 in DeerCreek Canyon west of Chatfield Reservoir,and the Strain Gulch Quarry, started in 1971and located south of Morrison. The AsphaltPaving Company mines latite from a quarrylocated north of Golden at Ralston Reservoirthat was first permitted in 1975. The AndesiteRock Company mines andesite from a quarrylocated southwest of Lyons. Colorado LienInc. mines limestone from a quarry located innorthern Larimer County that was permitted in1978. Unit trains also haul crushed stone tothe Denver market area. Meridian AggregatesCo. transports granite from a quarry locatedwest of Cheyenne, Wyoming, to two distribu-tion yards in the Denver area. Other quarriesin the area mine limestone for use in themanufacture of cement or dimension stone forbuilding and decorative use. Their productionis not considered in the analysis of aggregateresources.

Today, crushed stone serves an importantfunction beyond replacement for sand andgravel. Some specific applications require theuse of crushed stone. Specifications forrunway aggregates at Denver InternationalAirport required crushed stone. Similarly,asphalt highways typically require crushedstone aggregates in order to achieve requiredstrength parameters. Highways being con-structed with money from the Federal govern-

ment commonly must meet SUPERPAVEspecifications, which in effect require the useof sand manufactured from the crushing ofrock, and prohibit the use of natural sand.

FUTURE PRODUCTION OFFUTURE PRODUCTION OFFUTURE PRODUCTION OFFUTURE PRODUCTION OFFUTURE PRODUCTION OFAGGREGAAGGREGAAGGREGAAGGREGAAGGREGATESTESTESTESTES

There has been a steady increase inproduction of aggregates from both sand andgravel and crushed stone sources in Coloradosince the 1950s. Figure 2 suggests that even iflarge construction projects were to cease,production of aggregates in the short termwould continue at reasonably high levels dueto population growth and the associateddemand for infrastructure improvements toaccommodate such growth. It is reasonable toexpect that the Colorado portion of the Inter-state Highway System (some portions are over40 years old and designed for 1960s road usepatterns) will require increased maintenanceor replacement. Many of the early interstatehighways are insufficient to meet the antici-pated traffic volume projected for the newmillennium. Road repair is a continual pro-cess Statewide.

The Transportation Equity Act for the21st Century (TEA-21), which was signed intolaw in 1998, will govern Federal highwayspending until 2003. Federal funding forColorado transportation projects (includinghighway and mass transit projects) will gradu-ally increase from about $260 million in 1998to about $325 million in 2003. Under this 6-year reauthorization law, Federal funding forColorado increased about 44 percent from theprevious 6-year reauthorization law. As aresult, Colorado and many other States haveproposed numerous highway constructionprojects to make infrastructure improvementsand accommodate regional growth. Majorproposals include widening of I-25 from six toup to ten lanes and expansion of light railservice in portions of the Denver metropolitanarea. Such projects would require significant

9

amounts of construction aggregates from bothnew and recycled sources.

One method of forecasting aggregateproduction is to use sophisticated computermodels that analyze such factors as the overallhealth of the local economy, proposed high-way construction, housing development, andthe commercial construction outlook. Thesemodels are difficult to construct and requireinput data that is not always readily available.A simpler approach was used, in which pro-duction of aggregates was estimated by re-viewing historical production and use patterns,relating aggregates use to population growthtrends, and then using these observationstoselect reasonable production scenarios basedupon per capita production. Per capita pro-duction rates estimated from historical datawere compared to industry estimates reportedin previous aggregates use studies.

Projections were made based upon popu-lation growth estimates for the counties underconsideration provided by the Denver Re-gional Council of Governments (DRCOG,1999a,b) and the State of Colorado. It is not

the purpose of this study to provide preciseforecasts of aggregate production, but rather tosuggest a range of possibilities that accuratelyreflect past historical trends and current data.Production projections have been developedfor each of the two regional population cen-ters. In some cases, data for a particular areawere not available, so were estimated. Wheredata includes proprietary information, plotsare shown without units or proprietary data arecombined with other data to avoid disclosure.

Historical production patterns for aggre-gates can provide an indication of futuretrends. Based upon historical data, thereappears to be a high degree of correlationbetween population and aggregates production(fig. 3). Historical production figures werecorrelated with population projections for theCFR on a yearly basis to estimate the region’stotal aggregates production for the year 2000.Population projections were derived fromestimates of the DRCOG and the State ofColorado. Population data (actual and pro-jected) for the period 1990 to 2010 are shownin table 1.

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

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Per capita (per person) production esti-mates were used in this study to provide anindication of present and future aggregatesproduction. The weighted average per capitaproduction of aggregates along the northern 8-county CFR has remained steady for the past10 years at about 8.8 tons per capita for theperiod. Actual production was lowest duringthe recession year of 1990, and highest in1995 as Denver International Airport wascompleted and associated developments werefinalized. The weighted-average per capitaaggregates production rate in the 6-countyDenver area since 1960 was estimated to be8.3 tons based on historical production data.

A linear regression analysis of the histori-cal data, however, indicated that production ofaggregates in the Denver area has increasedover time. Aggregates production per capitareported for the 6-county Denver metropolitanarea during the past 10 years is shown infigure 6. The data suggest that per capitaproduction in the Denver area has increasedfrom more than 5 tons per person in 1988 toover 7 tons per person in 1997. Since 1994,per capita production appears to have leveledoff, or may have declined slightly as thesecond order polynomial equation suggests(fig. 6).

Regression analyses for the period 1988to 1997 were performed in a similar mannerfor the Fort Collins area. When projected tothe year 2000, a production figure of about 22tons per capita was estimated for the FortCollins area. This per capita figure reflects thehigh level of production (approximately 22percent of all Colorado aggregates derivedfrom sand and gravel were produced in theFort Collins area) from a region with rela-tively low population density. Historical datasuggest that this region is supplying an in-creased percentage of aggregates from sandand gravel sources to the Denver metropolitanarea, as local supplies are restricted fromdevelopment or as quality of the material inthe Denver area diminishes.

One method for estimating aggregatesproduction for the period 1998 through 2010would be to assume that the projected regionalper capita use rates for 2000 would reflect anapproximation for regional production ratesover the entire 13-year period. Figure 7illustrates the cumulative aggregates produc-tion for each of the two reported CFR popula-tion centers using such an approach. Basedupon these data, aggregates production for theperiod 1998 to 2000 would amount to over 80million tons for the 1998 through 2000 period.CFR production could be distributed as 68percent for the Denver area, and 32 percent forthe Fort Collins area. Similarly, over 401million tons of aggregates would be producedfrom the 8-county CFR region over the 1998through 2010 period.

Aggregates production rates change withtime, however, and the construction industrytends to be cyclical. Consequently, modelsthat provide a range of aggregates production(8, 9.5, and 11 tons per capita of use) weredeveloped. These values generally correspondwith values used in unpublished proprietaryindustry studies, as well as historical datareported previously in this study. The lowestproduction level would most closely reflect

FigurFigurFigurFigurFigure 6.e 6.e 6.e 6.e 6. - Per capita production of aggre-gates, Denver metropolitan area, 1988 - 1997.

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recent historical production in the Denvermetropolitan area when no large constructionprojects are considered (“low-growth sce-nario”). The mid-range production levelmight represent an “average” constructionyear (average-growth scenario). The ColoradoGeological Survey has been using a use valueof 10 tons/capita as a method of predictingaggregates production in their long-rangeanalyses of aggregates needs (Nasser, 1987).Some local producers have used the 11 tonsper capita level in their demand projections.This corresponds to the “high-growth sce-nario”, reflecting continued construction andpopulation growth or where multiple largeprojects are being constructed concurrently.

Figure 8 plots the projected annual pro-duction for the three rates assumed. For the“low-growth scenario”, annual aggregatesproduction is projected to vary from 21 mil-lion tons per year to 25 million tons per year.An average of approximately 23 million tons

per year would be required based on thisproduction scenario. Extrapolation to 2000 ofpreviously reported production data for the 8northern CFR counties over the past 37 yearsgenerates an aggregates production level thatwould fall within the range of this scenario.

The “average scenario” of 9.5 tons percapita production rate indicates a range ofaggregates production from about 25 milliontons per year to 30 million tons per year. Anaverage of approximately 28 million tonswould be produced based on this scenario.Linear extrapolation to 2000 of aggregatesproduction data for the 8 northern CFR coun-ties over the past 12 years generates an aggre-gates production level that would fall withinthe range of this scenario.

The “high-growth scenario” reflectsannual aggregates production ranging fromabout 29 million tons to 35 million tons peryear. An average of approximately 32 milliontons would be produced based on this sce-

FigurFigurFigurFigurFigure 7.e 7.e 7.e 7.e 7. - Cumulative production of aggregates, 1998 - 2010, assuming regional use ratesprojected for 2000.

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nario. Estimates derived by combining pro-jected production from the two populationcenters along the northern CFR generate anaggregates production level that would fallwithin the range of this scenario. This is to beexpected, as recent production figures reflectthe growth and high level of construction thathas occurred along the CFR region.

Figure 9 plots the cumulative productionfor CFR aggregates indicated by the threescenarios. Based upon the “low-growthscenario” of 8 tons per capita, about 64 mil-lion tons of aggregates would be producedduring the 1998 through 2000 period, slightlylower than the actual production from this 8-county area for the 1995 through 1997 period.Figure 9 suggests that 178 million tons wouldbe produced through 2005, and about 300million tons would be produced through 2010.

FigurFigurFigurFigurFigure 8.e 8.e 8.e 8.e 8. - Projected annual aggregates use,Colorado Front Range, 1998 - 2010.

FigurFigurFigurFigurFigure 9.e 9.e 9.e 9.e 9. - Projected cumulative aggregates production, 8-county northern Colorado FrontRange.

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The “average scenario” of 9.5 tons percapita suggests that a cumulative 76 milliontons of aggregates would be produced for theperiod 1998 through 2000, about 211 milliontons would be produced through 2005, andabout 356 million tons through 2010. Valuesgenerated from this scenario are comparable tothose estimated using the regional productionprojections (figure 8) for the 2-year period1998 to 2000, but become much lower as thetime interval increases.

The “high-growth scenario” of 11 tons percapita suggests that a cumulative 88 milliontons of aggregates would be produced for theperiod 1998 through 2000, approximately 244million tons for the period 1998 through 2005,and about 412 million tons for the period 1998through 2010. This scenario most closelycorresponds to the production projectionsshown in figure 7, when the full time intervalis considered.

FUTURE SUPPLFUTURE SUPPLFUTURE SUPPLFUTURE SUPPLFUTURE SUPPLYYYYY OF OF OF OF OF AGGREGAAGGREGAAGGREGAAGGREGAAGGREGATES INTES INTES INTES INTES INTHE COLORADO FRONT RANGETHE COLORADO FRONT RANGETHE COLORADO FRONT RANGETHE COLORADO FRONT RANGETHE COLORADO FRONT RANGEThe Colorado Division of Mines and

Geology (CDM&G) maintains a database oninformation related to mining permits inColorado including permits for sand andgravel and crushed stone mining. Amongother things, the database includes informationon type of commodity mined, location of thepermitted property, total acres permitted, andthe year the permit was issued.

The area permitted for aggregate extrac-tion alone does not indicate the actual amountof permitted resources contained in the area,and many aggregate companies are reluctantor unwilling to discuss the particulars of theiroperations. However, methods were devel-oped to estimate permitted sand and graveland crushed stone by combining the permit-ting data with geologic information on poten-tial aggregate resources compiled by theColorado Geological Survey and the U.S.Geological Survey.

Sand and gravelSand and gravelSand and gravelSand and gravelSand and gravel

A two-step process was used to calculatepermitted sand and gravel resources (fig. 10).The first step determined the tons of permittedsand and gravel by multiplying area permittedtimes deposit thickness, then multiplying thatvalue by a constant to convert from volume totons. The second step diminished thoseresources to account for permitted land thatwill be set aside due to setbacks, operationalrequirements, and environmental restrictions,and to account for loss of resources due toinadequate aggregates quality.

TTTTTonnage calculationsonnage calculationsonnage calculationsonnage calculationsonnage calculations – CDM&G datawere used to estimate the amount of area ofsand and gravel resources that are beingpermitted over time. Information regardingsand and gravel thickness and quality was thenused to calculate volumes of sand and gravelpermitted. Thickness was estimated fromexisting maps and reports (Schwochow andothers, 1974b; Trimble and Fitch, 1974,Colton and Fitch, 1974). The resulting vol-ume (acre feet of sand and gravel) was con-verted to a unit of weight (metric tons) bymultiplying by a constant (2,134) that takesinto account the density of sand and gravel.

Adjustments forAdjustments forAdjustments forAdjustments forAdjustments for ar ar ar ar areas set asideeas set asideeas set asideeas set asideeas set aside –Commonly not all the land permitted will bemined for aggregates. Most permits or regula-tions require setbacks from certain other landuses such as residential developments, neigh-boring buildings, and setbacks from propertylines, pipelines, transmission lines, roads, andstreams. A requirement for a 100 ft. setbackfrom property lines would eliminate about 20percent of a 100-acre site. Today, in order toisolate operations from neighboring areas,some sites have buffer areas in excess of onehalf the permitted area.

The operation itself requires land for theconstruction of buffers, access roads, scalehouse, processing facilities, equipment stor-

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age, settling ponds, and stockpiles, which canoccupy a significant part of the permitted minesite. Processing and load-out areas, for ex-ample, may be very small or may occupymore than 20 acres. Areas set aside for storingunused equipment may also require extensivespace.

New more stringent environmentalrequirements further reduce the amount ofpermitted land that actually can be mined.Regulations may prohibit mining from areasof wetlands, floodplains, large stands of trees,and specific wildlife habitat such as those thatcontain rare or endangered species. Duringthe 1970s, many companies avoided excess

fees by permitting only the land to be used forthe mining process. Today, some companiespermit extensive areas to avoid having torepeat the permit process. For example, acompany may own or lease an entire section(640 acres) of land, only some of which isunderlain with aggregate. Nevertheless, theymay permit the entire section for mining.

Adjustments for material of unusableAdjustments for material of unusableAdjustments for material of unusableAdjustments for material of unusableAdjustments for material of unusablequalityqualityqualityqualityquality– In those permitted areas whereaggregates can be mined, some of the underly-ing deposits will not meet the quality require-ments for use as aggregates. Sand and graveldeposits along the Front Range commonly areoverlaid by a layer of silt and clay (overbur-

FigurFigurFigurFigurFigure 10.e 10.e 10.e 10.e 10. - Flow diagram showing method to determine permitted aggregate resources.

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den). Although the stripping ratio of overbur-den to gravel may be as low as 1:9, (theoverburden may comprise 10 percent of adeposit), the Colorado Geological Survey(Schowchow and others, 1974a) considereddeposits under floodplains and low terraces tobe of commercial grade if the maximumstripping ratio of overburden to gravel is 1:3(the overburden may comprise up to 25percent of a deposit). They considered depos-its under high terraces and upland deposits tobe of commercial grade if the maximumstripping ratio of overburden to gravel is 1:1(the overburden may comprise up to 50percent of a deposit). In addition, sand andgravel may contain layers of silt and claywithin the deposit (interburden), and undesir-able fine material or other deleterious (poorquality) materials may be dispersed through-out the deposit.

In summary, it is reasonable to expectfrom 20 percent (i.e. 100 foot setbacks in a100 acre site is about 20 percent of the area) to50 percent (estimated as a reasonable maxi-mum by authors) of the permitted area to beunavailable for aggregate extraction. It also isreasonable to expect from 10 (minimumstripping ratio) to 40 percent (estimated as areasonable maximum by authors) of thepermitted sand and gravel resources to beunsuitable for use as aggregates.

The total permitted sand and gravelresources can be estimated as follows:

a) total permitted area - % area set aside =% available

b) % available – (% available X % unusable)= % total permitted area available anduseable

The total permitted area of available anduseable sand and gravel will range from a bestcase of about 70 percent to a worst case of

about 30 percent of the volume within thepermitted area. The best case scenario (20 %set aside, 10 % unusable) is:

a) 100 –20 = 80 %

b) 80 % - (.1 X 80) = 72 % total permittedarea available and useable

The worst case scenario ( 50% set aside,40 % unusable) is:

a) 100 –50 = 50 %

b) 50 % - (.4 X 50%) = 30 % total permittedarea available and useable

The authors believe that 30% useablesand and gravel tends to reflect current condi-tions in the study area, and that 70% useablesand and gravel tends to reflect conditions inthe study area during the 1970s. A 50%useable sand and gravel level represents anaverage or intermediate level.

Crushed stoneCrushed stoneCrushed stoneCrushed stoneCrushed stoneEstimating resources of crushed stone is

problematic and requires a different approach(fig. 10) than that used for estimating sand andgravel. Only seven quarries are currentlyproducing crushed stone in the CFR studyarea. The quarries were permitted in such amanner that disclosing the crushed stoneresources and the years that those resourceswere permitted would make it possible tocalculate resources for individual operations.To avoid disclosing proprietary data, general-ized resource data from several sources[Nasser (1987), proprietary data on resourceestimates from a number of aggregates compa-nies’ unpublished reports, and proprietaryproduction rates] were used. Back calculatingallowed the estimation of original resources atthe time of permitting. It was not necessary todiminish the tonnage of crushed stone to

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account for unmined land or poor qualitybecause the data already accounted for thosefactors.

RecyclingRecyclingRecyclingRecyclingRecyclingEven as production of aggregates from

natural sources (sand and gravel, crushedstone) has increased, production of aggregatesfrom recycled sources has also increased,particularly in large urban areas such asDenver. Estimated production of recycledaggregates in the 6-county Denver metropoli-tan area grew from about 1.2 million tons in1997 to 2.5 million tons in 1998, with aprojected 1999 production of about 4 milliontons. Increasingly, large construction projectsinclude the recycling of cement and asphalticconcrete in redevelopment plans. Conse-quently, redevelopment of Lowry Air Force

Base, Stapleton Airport, Cinderella City Mall,Northglenn Mall, and road construction allaround the Denver area increased both de-mand and supply of aggregates since 1996.Redevelopment of the former StapletonAirport in Denver will generate a total of 6million tons of recycled concrete (Carder,1999), from demolition of runways andterminal buildings. Recycled material couldsupply over 15 percent of projected demandfor aggregates by 2000, if historical produc-tion trends above hold true. Not all construc-tion materials suitable for recycling as aggre-gates, however, meet the quality specificationsfor construction aggregates. Consequently,there is not a total substitution between naturalaggregates and recycled aggregates in allapplications.

FigurFigurFigurFigurFigure 1e 1e 1e 1e 11.1.1.1.1. - Cumulative aggregate permitted. Vertical scale is relative.

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DISCUSSIONDISCUSSIONDISCUSSIONDISCUSSIONDISCUSSIONThree scenarios for sand and gravel in the

CFR area establish a range that brackets theestimated rate that aggregate resources arebeing permitted. The scenarios are based on70 percent, 50 percent, or 30 percent recoveryof the sand and gravel resources, and 100percent recovery of the crushed stone re-sources. Discussions in this report refer to the50 percent scenario, except as noted.

Figures showing permitting of aggregateresources (figs. 11 and 14) are based in largepart on proprietary data. Therefore, althoughthe graphs were created using calculatedvalues, the graphs are dimensionless and showonly relative values.

Figure 11 plots the cumulative aggregateresources permitted by year at the 70 percentand 30 percent rates, for the 8-county studyarea. The curves were smoothed using a 2nd

order polynomial trend analysis. By usingcumulative figures, the slope of the linedirectly reflects the rate of permitting; thesteeper the slope, the faster the rate of permit-

in the total study area was in the Denvermetro area. The percentage of aggregatespermitted in the Denver metro area de-creased to about 57 percent and 29 percentduring the periods 1984-90 and 1991-97,respectively (fig. 12).

In both the Denver metropolitan areaand the Fort Collins-Greeley area theamount of aggregates permitted has steadilydecreased over time. In the Denver metro-politan area, about 65 percent of the aggre-gates permitted during the entire 21-yearstudy period was permitted during theperiod 1977-83 (fig. 13). About 29 percentwas permitted during the period 1984-90,and only 6 percent during the period 1991-97. A similar trend occurred in the FortCollins-Greeley area, with values of about42 percent, 36 percent, and 22 percent forthe three time periods.

Figure 14 shows the relative percent-ages of all aggregates permitted in the studyarea by time period. The Fort Collins-

FigurFigurFigurFigurFigure 12.e 12.e 12.e 12.e 12. - Aggregatepermitted each 7-yearperiod, by region.

ting. A horizontalline would mean nonew material isbeing permitted.The line can neverhave a negativeslope because theline portrayscumulative values.

The actual rateof permittingresources probablylies somewherebetween the 70percent and 30percent curves, andprobably is movingaway from the 70percent valuetowards the 30percent value due

FigurFigurFigurFigurFigure 13.e 13.e 13.e 13.e 13. - Aggre-gate permitted in eachregion, by 7-yearperiod.

to environmental,regulation, andquality issues. Undereither scenario,figure 11 demon-strates that the ratethat aggregates havebeen permitted in theCFR has beensteadily decreasingsince 1974.

To identifypermitting trendsover time, the permit-ting of aggregateresources was di-vided into three 7-year time periods.During the periodfrom 1977-83, about72 percent of theaggregates permitted

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Greeley area permitted about the same amountof aggregates as the Denver metro area during1984-1990 period, and permitted most of theaggregates for the 1991-97 period.

To continuously meet projected produc-tion, the amount of aggregates permitted must,on the average, equal or exceed the amountproduced. Furthermore, because aggregatesproduction generally relates to population, theper capita amount of aggregates permittedmust equal or exceed the per capita amount ofaggregates produced. Figure 15 plots:

(aggregates permitted / population) – (aggre-gates produced / population)

From one year to the next, the amount ofaggregates permitted can vary greatly. Toaccount for these irregularities, the curvesshowing aggregate permitted have beensmoothed by using a five-year moving aver-age.

Aggregate producers started to moveaway from the Denver metro area during the

FigurFigurFigurFigurFigure 14.e 14.e 14.e 14.e 14. - Relative amount of aggregatepermitted in 2 regions, by 7-year period.

FigurFigurFigurFigurFigure 15.e 15.e 15.e 15.e 15. - Graph showing per capita aggregate permited minus per capita aggregate produced.Plots are smoothed using a 5-year moving average.

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late 1970s to mine sand and gravel from theSt. Vrain River valley to the north. Starting in1979, the per capita permitting rate for theFort Collins-Greeley area grew dramatically incomparison with the Denver metro area.Figure 15 illustrates that the Denver metroarea has produced more aggregates than itpermitted since 1992. The Fort Collins-Greeley area currently is permitting aboutwhat it is producing. The entire study area hasbeen permitting less than it produces since1994. In general, when the lines on fig. 15cross the zero line (horizontal axis), moreaggregate is being produced than permitted.This may signal potential problems regardingfuture aggregates availability.

SUMMARSUMMARSUMMARSUMMARSUMMARYYYYYThere has been a steady increase in

production of aggregates from both sand andgravel and crushed stone in Colorado since the1950s. In the 1950s and 1960s, approximately38 percent of Colorado sand and gravelproduction and 30 percent of Coloradocrushed stone production came from the 8-county CFR area. By the 1990s, the percent-age of the aggregates produced along thenorthern Colorado Front Range had increasedto approximately 54 percent of sand andgravel and 70 percent of crushed stone.

The structure of aggregates productionfrom both sand and gravel and crushed stonesources along the CFR has changed dramati-cally since the 1950s. In 1960, production ofaggregates in the Denver area was principallyfrom sand and gravel sources (99 percent). In1997, estimated aggregate production of sandand gravel sources was 55 percent, crushedstone was 31 percent, and recycled aggregateswas 14 percent.

There has been a shift in CFR sand andgravel production further north away from theDenver metropolitan area. The Fort Collinsarea currently accounts for about 22 percent ofall of Colorado’s sand and gravel production.

This overshadows a drop in crushed stoneproduction from the Fort Collins area becauseabout 75 percent of aggregates produced inColorado is from sand and gravel deposits.

The rate of permitting of aggregateresources has dropped dramatically since itpeaked during the late 1970s and early 1980s,when the granting of permits for several largecrushed stone operations introduced a largeamount of newly permitted resources into theCFR area. Existing resources are currentlybeing used faster than new resources are beingpermitted.

CONCLUSIONSCONCLUSIONSCONCLUSIONSCONCLUSIONSCONCLUSIONSThe steady increase in aggregates produc-

tion and use that has occurred since the 1950sis expected to continue. The data suggest thateven if large construction projects were tocease, demand for aggregates in the short termwould continue at reasonably high levels dueto projected population growth and associateddemand for infrastructure improvements toaccommodate such growth.

Although the CFR has an abundance ofaggregate resources, recoverable resources arecoming from greater distances as local re-sources are becoming inaccessible for extrac-tion. Available resources are becoming moredifficult to recover and more expensive toproduce, due to longer transportation dis-tances, poorer quality of locally availablesources, more involved permitting require-ments, and the encroachment of other landuses on the potential resource.

Up until the mid-1970s, the majority ofthe aggregate within the Denver metropolitanarea was produced from sand and gravel.During the mid-1970s, several crushed stonequarries began operating in the Denver metro-politan area. The increase in demand foraggregate in the Denver metropolitan areaduring this period was met largely from thesenew stone quarries. During the 1980s chang-ing conditions caused the aggregate industry

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to start import sand and gravel to the Denvermetropolitan area from the Fort Collins –Greeley area to meet aggregate needs of theDenver metropolitan area. Many of the re-maining sand and gravel deposits in theDenver metropolitan area were excluded fromdevelopment because of conflicting land use,poor quality, and citizen opposition. No newcrushed stone operations had been permitted,and existing operations are operating at ornear capacity.

The study indicates that the amount ofaggregates being permitted has steadilydecreased over time. The Denver metropoli-tan area has been producing more aggregatesthan it is permitting since 1992, and the FortCollins-Greeley area is currently permittingabout what it is producing. If this trendcontinues, aggregates operators may be forcedto move to resource areas even farther awayfrom local markets, resulting in even highertransportation costs. Increased costs for theseaggregates would be passed along to the Stateor counties as higher construction bids, to thecontractor as higher supply costs, and ulti-mately to the consumer in the form of highertaxes or user fees.

Today the Denver metropolitan area andthe Fort Collins-Greeley are becoming oneintegrated production – use area for aggre-gates. Average transportation distances tend toexceed the 56-kilometer rule-of thumb be-cause 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 andbuilding construction projects are proposed, itis essential that developers, contractors, andgovernmental officials consider where futureaggregates supply will come from to supportsuch projects. This study suggests that whilepermitted resources are sufficient for the shortterm, the rate of permitting may not be suffi-cient in the future if strong demand for aggre-gates continue. Longer haul distances and

higher costs could occur unless policy makerschoose to enforce H.B. 1529, producers applyfor increased permit areas, planners approvesuch permits, or alternatives such as recyclingincrease.

REFERENCESREFERENCESREFERENCESREFERENCESREFERENCESArgall, G.O., 1949, Industrial minerals of

Colorado: Colorado School of MinesQuarterly, v. 44, n. 2, 477p.

Bolen, W.P., 1998, Sand and gravel, construc-tion: Chapter in U.S. Geological Survey1997 Minerals Yearbook, 4 p., accessedMarch 23, 1999, at URL www.usgs.gov.

Carder, Carol, 1999, Demolition progressingat Denver’s old Stapleton Airport: RockyMountain Construction, January 11, 1999,p. 82.

Colorado Division of Local Government,1998, Colorado components of change, 4p.: accessed June 24, 1999, at URLwww.dlg.oem2.state.co.us.

Colorado General Assembly, LegislativeCouncil, 1997, Focus Colorado: economicand revenue forecast, September 1997,132 p.: accessed June 21, 1999, at URLwww.state.co.us.

Colorado Sand and Gravel Producers Associa-tion, 1957, The first complete aerial photomap of Denver metropolitan area with anoutline of our diminishing gravel re-sources: Denver, Colorado Sand andGravel Producers Association.

Colton, R.B., and Fitch, H.R., 1974, Map show-ing potential sources of gravel and crushed-rock aggregate in the Boulder-Fort Collins-Greeley Area, Front Range Urban Corridor,Colorado: U.S. Geological Survey Miscel-laneous Investigations Map I-856-A, scale1:100,000.

Cooley, J.B., 1971, Our rapidly disappearingsand and gravel deposits: 74th NationalWestern Mining Conference and Exhibi-tion, Mining Yearbook 1971, ColoradoMining Association, p. 17-20.

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Denver Regional Council of Governments,1999a, Regional population and house-hold estimates, Regional Report, June1999, 4 p.: accessed June 26, 1999, atURL www.drcog.org.

Denver Regional Council of Governments,1999b, Metro Vision 2020 ExecutiveSummary, 6 p., accessed March 29, 1999,at URL www.drcog.org.

Lindsey, D.A., 1997, An introduction to sand andgravel deposit models, Front Range UrbanCorridor: U.S. Geological Survey OpenFile Report 97-81, 6 p.

Nasser, Khalil, 1987, Supply/demand analysisof aggregates in the Denver metro area,Jefferson County Planning Department,20 p.

Poulin, R., Pakalnis, R.C., and Sinding, K.,1994, Aggregate resources - Productionand environmental constraints: Environ-mental Geology, v. 23, pp. 221-227.

Schwochow, S.D.,1980, The effects of mineralconservation legislation on Colorado’saggregate industry, in Proceedings of theFifteenth Forum on Geology of IndustrialMinerals: Colorado Geological SurveyResource Series no. 8, pp. 30-39.

Schwochow, S.D., Shroba, R.R., and Wicklein,P.C., 1974a, Sand, gravel, and quarry ag-gregate resources – Colorado Front Rangecounties: Colorado Geological Survey Spe-cial Publication 5-A, 43 p.

Schwochow, S.D., Shroba, R.R., and Wicklein,P.C., 1974b Atlas of sand, gravel, and quarryaggregate resources – Colorado FrontRange counties: Colorado Geological Sur-vey Special Publication 5-B, not paginated.

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resources, urbanization and future landuse, Front Range Urban Corridor, Colo-rado: U.S. Geological Survey Open FileReport OFR-74-178, 29 p., 5 map sheets.

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Trimble, D.E., and Fitch, H.R., 1974, Mapshowing potential sources of gravel andcrushed-rock aggregate in the ColoradoSprings-Castle Rock Area, Front RangeUrban Corridor, Colorado: U.S. Geologi-cal Survey Miscellaneous InvestigationsMap I-857-A, scale 1:100,000.

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